Archief

Datum: 29/6/2018
Tijd: 14:45 - 15:15

Sparse image representation using discrete moments

Sparse representations of images or signals by means of an overcomplete basis, usually called a dictionary, have seen successful application in image processing, denoising, compression, etc. An important aspect is the choice of the properties of the chosen dictionary, such as for instance the average coherence between its elements. In this talk we explore the idea of using moments based on discrete orthogonal polynomials to create suitable predesigned dictionaries. Unlike dictionaries trained on a set of representative examples, the predesigned dictionaries are generic and besides fast computation have supportive theoretical foundations.
Joint work with Srdan Lazendic.

Plaats: 40.08.130.065
Organisator: Hendrik De Bie
Datum: 28/6/2018
Tijd: 14:00

The Mathematical Structure of Tensor Networks

Verdediging van de masterproef

The Mathematical Structure of Tensor Networks

door Gert Vercleyen. Promotoren: Jutho Haegeman en Frank Verstraete.
Plaats: S9, lokaal 120.005
Organisator: Opleiding Wiskunde
Datum: 27/6/2018
Tijd: 11:00

Outranking relaties voor dominantiegebaseerde vaagruwverzamelingenleer met didactische component

Verdediging van de masterproef

Outranking relaties voor dominantiegebaseerde vaagruwverzamelingenleer met didactische component

door Hanne Van De Vijver. Promotoren: Chris Cornelis en Hendrik Van Maldeghem.
Plaats: S9, leslokaal 1.1
Organisator: Opleiding Wiskunde
Datum: 27/6/2018
Tijd: 10:00

Uitbreiding van het dominantiegebaseerde ruwverzamelingenmodel naar vaagverzamelingenleer

Verdediging van de masterproef

Uitbreiding van het dominantiegebaseerde ruwverzamelingenmodel naar vaagverzamelingenleer

door Karen Van Belle. Promotor: Chris Cornelis.
Plaats: S9, Leslokaal 1.1
Organisator: Opleiding Wiskunde
Datum: 26/6/2018
Tijd: 13:00

Polynomial Diffusions with applications in Financial Mathematics

Verdediging van de masterproef

Polynomial Diffusions with applications in Financial Mathematics

door Louis D'hiet. Promotor: Michèle Vanmaele.
Plaats: S9, leslokaal 1.1
Organisator: Opleiding Wiskunde
Datum: 26/6/2018
Tijd: 10:40

Verkeersmodellering en reistijdpredictie op Floating Car Data

Verdediging van de masterproef

Verkeersmodellering en reistijdpredictie op Floating Car Data

door Tom Van Herck. Promotor: Veerle Fack.
Plaats: S9, auditorium A3
Organisator: Opleiding Wiskunde
Datum: 22/6/2018
Tijd: 14:45 - 15:15

Special solutions for the parabolic Dirac operator

Abstract
During this talk, I will introduce the Fischer decomposition for the parabolic Dirac operator which factorizes the heat equation. We first establish and study the Fischer decomposition for the homogeneous part of the parabolic Dirac operator. Subsequently we construct null-solutions of the parabolic Dirac operator by means of series expansions in terms of cylindrical co-ordinates. At last, using the obtained recursive relations and through the use of the generalized hypergeometric functions we get a neat and simple form of the null-solutions of the parabolic Dirac operator

Plaats: 40.08.130.065
Organisator: Hendrik De Bie
Datum: 22/6/2018
Tijd: 10:00

Similariteitsleren voor classificatie gebaseerd op vaagruwverzamelingenleer door middel van heuristische zoekalgoritmen

Verdediging van de masterproef

Similariteitsleren voor classificatie gebaseerd op vaagruwverzamelingenleer door middel van heuristische zoekalgoritmen

door Bram Verbeke. Promotor: Chris Cornelis.
Plaats: S9, leslokaal 3.2
Organisator: Opleiding Wiskunde
Datum: 21/6/2018
Tijd: 11:00

Sets, Trees and Incompleteness

Verdediging van de masterproef

Sets, Trees and Incompleteness

door Ben De Bondt. Promotor: Andreas Weiermann.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 20/6/2018
Tijd: 15:00

Linear Codes Generated by Projective Spaces

Verdediging van de masterproef

Linear Codes Generated by Projective Spaces

door Sam Adriaensen. Promotor: Leo Storme.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 20/6/2018
Tijd: 14:00

Maximum Rank Distance Codes

Verdediging van de masterproef

Maximum Rank Distance Codes

door Lisa Commerman. Promotor: Leo Storme.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 20/6/2018
Tijd: 11:00

Het numeriek oplossen van de meerdimensionale (tijdsafhankelijke) schrödingervergelijking via matslise

Verdediging van de masterproef

Het numeriek oplossen van de meerdimensionale (tijdsafhankelijke) schrödingervergelijking via matslise

door Toon Baeyens. Promotor: Marnix Van Daele
Plaats: S9, leszaal 1.1
Organisator: Opleiding wiskunde
Datum: 20/6/2018
Tijd: 10:00

Evenaarsmeetkunden in eindige gebouwen

Verdediging van de masterproef

Evenaarsmeetkunden in eindige gebouwen

door Dago Van Poeck. Promotor: Hendrik Van Maldeghem.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 20/6/2018
Tijd: 9:00

Kegelsneden en ovalen: een vergelijkende studie van euclidische en projectieve definities

Verdediging van de masterproef

Kegelsneden en ovalen: een vergelijkende studie van euclidische en projectieve definities

door Nele Keppens. Promotor: Hendrik Van Maldeghem.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 18/6/2018
Tijd: 14:00

Exponential sums and applications in number theory and analysis

Verdediging van de masterproef

Exponential sums and applications in number theory and analysis

door Frederik Broucke. Promotor: Jasson Vindas.
Plaats: S4, lokaal 0.3
Organisator: Opleiding Wiskunde
Datum: 15/6/2018
Tijd: 14:45 - 15:15

Discrete orthogonal polynomials and superintegrability

Abstract: The spectral properties of the classical orthogonal
polynomials of one and several variables have deep connections with
the representation theory of Lie algebras and quantum superintegrable
systems. Over the years, these connections have played a crucial role
in the discovery of fundamental results with numerous applications in
mathematics and physics. I will discuss recent results in a joint work
with Yuan Xu relating spectral properties of discrete orthogonal
polynomials to superintegrability.

Plaats: 40.08.130.065
Organisator: Hendrik De Bie
Datum: 14/6/2018
Tijd: 9:30

Permanenten: een link tussen verleden, heden en toekomst door stellingen, vermoedens en secundair onderwijs

Verdediging van de masterproef

Permanenten: een link tussen verleden, heden en toekomst door stellingen, vermoedens en secundair onderwijs

door Kwinten Verbruggen. Promotoren: Tom De Medts en Hendrik Van Maldeghem.
Plaats: S23, lokaal Euclides
Organisator: Opleiding Wiskunde
Datum: 12/6/2018
Tijd: 14:00

De randlengte van patches met vlakken van grootte ten hoogste zes

Verdediging van de masterproef

De randlengte van patches met vlakken van grootte ten hoogste zes

door Simon Van den Eynde. Promotor: Gunnar Brinkmann.
Plaats: S9, leslokaal 1.1
Organisator: Opleiding Wiskunde
Datum: 8/6/2018
Tijd: 14:45 - 15:15

Szegö-Radon transform for biaxial monogenic functions

Abstract:
In this talk, I will introduce the Szegö-Radon transform for biaxially monogenic functions.
Using the biaxial decomposition of homogeneous polynomials, we get two types of biaxially monogenic
functions which satisfy a Vekua system, depending on the degree of homogeneity. Using
these expressions, we can calculate explicit formulas for the Szegö-Radon transforms for biaxially
monogenic functions according to their total degree of homogeneity. Furthermore, we simplify
these results making use of the Funk-Hecke theorem and orthogonality results of appearing
special functions.

Plaats: 40.08.130.065
Organisator: Hendrik De Bie
Datum: 1/6/2018
Tijd: 14:45 - 15:45

Recurrence Relations for Wronskian Hermite Polynomials

Abstract: We consider polynomials that are defined as Wronskians of certain sets of Hermite polynomials. Our main result is a recurrence relation for these polynomials in terms of those of one or two degrees smaller, which generalizes the well-known three term recurrence relation for Hermite polynomials. The polynomials are defined using partitions of natural numbers, and the coefficients in the recurrence relation can be expressed in terms of the number of standard Young tableaux of these partitions. Using the recurrence relation, we provide another recurrence relation and show that the average of the considered polynomials with respect to the Plancherel measure is very simple. Furthermore, we show that some existing results in the literature are easy corollaries of the recurrence relation
Spreker: Niels Bonneux

Plaats: 40.08.130.065
Organisator: Hendrik De Bie
Datum: 29/5/2018
Tijd: 13:20 - 17:35

Aspects of Quantum Integrability

13:30-14:30 - Richardson-Gaudin models and the Heine-Stieltjes connection (Pieter Claeys)
14:30-15:20 - Introduction to Bannai-Ito and Racah algebras (Hendrik De Bie)
15:45-16:45 - Two-point boundary correlation functions of dense loop models (Alexi Morin-Duchesne)
16:45-17:35 - State transfer in spin chains and relations with orthogonal polynomials (Joris Van der Jeugt)

Plaats: 40.08.130.065
Organisator: Hendrik De Bie
Datum: 25/5/2018
Tijd: 14:45 - 17:00

Third order chemical kinetics: an initial analysis

Talk given by Zoë Gromotka
Abstract: As a result of research into first and second order kinetics, our group (Denis Constales, Daniel Branco Pinto) has classified several invariants. These invariants are constant in time and are made up of functions of chemical concentrations where the concentrations are time dependent.
To determine whether the idea of invariants can be extended to the domain of third order kinetics an analysis has been done into these kinetics. This talk will cover the background of third order kinetics and discuss the initial findings

Plaats: 40.08.130.065
Organisator: Clifford Analyse
Datum: 25/5/2018
Tijd: 9:30 - 17:00

Belgian Mathematical Society: PhD-day

The Belgian Mathematical Society invites all PhD students linked to mathematic to present a poster or a talk at the PhD-Day. Grab the opportunity to show your research to your fellow PhD students, to meet each other, and exchange ideas.

Every PhD student in mathematics, presenting a poster gets one panel to present a poster in A0 format. At the end of the PhD-Day, there will be the best poster award. The best poster will be selected on the criteria of layout, contents, and clarity of the poster.

We also offer the possibility to present a contributed talk. The scientific committee will make a selection among the proposed abstracts.

After the posterpresentations there will be a job fair.


More information can be found at http://bms.ulb.ac.be/phdday

Plaats: Campus Sterre, S9
Organisator: Belgian Mathematical Society
Datum: 18/5/2018
Tijd: 18:00

Complex Tauberian theorems and applications to Beurling generalized primes

Openbare verdediging van het doctoraat

Complex Tauberian theorems and applications to Beurling generalized primes

door Gregory Debruyne. Promotor: Jasson Vindas.
Plaats: S25, Emmy Noether
Organisator: Vakgroep Wiskunde
Datum: 4/5/2018
Tijd: 17:00

Contributions to the linear and non-linear theory of ultradistributions

Openbare verdediging van het doctoraat

Contributions to the linear and non-linear theory of ultradistributions

door Andreas Debrouwere. Promotoren: Hans Vernaeve en Jasson Vindas.
Plaats: S25, Emmy Noether
Organisator: Vakgroep wiskunde
Datum: 4/5/2018
Tijd: 15:40

Spaces of Dirichlet series

Colloquium talk by José Bonet from the University of Valencia

Abstract:

In the first part of this lecture, which is of survey type, we recall several results about Bohr’s problem concerning the largest possible strip on which a Dirichlet series of complex numbers converges uniformly but not absolutely. We will explain classical work by Harald Bohr (1913), Bohnenblust and Hille (1931), and recent ones by Boas, Defant, Frerick, García, Khavinson, Maestre, Ortega-Cerdá, Ounaïes and Seip, among others.

In the second part we report on spaces of Dirichlet series. Defant, García, Maestre, Pérez-García investigated in 2008 Bohr’s problem concerning the largest possible strip on which a Dirichlet series converges uniformly but not absolutely for Banach valued Dirichlet series. They showed that the largest possible strip on which a Dirichlet series with coefficients in a Banach space converges uniformly but not absolutely depends on the geometry of the Banach space. We study and compare the abscissas of convergence, uniform convergence and absolute convergence of vector valued Dirichlet series with respect to the original topology and with respect to the weak topology of a Fréchet space X. The relation of their coincidence with geometric or topological properties of the underlying space X is investigated.

Plaats: S25, Emmy Noether
Organisator: Vakgroep wiskunde
Datum: 4/5/2018
Tijd: 14:30

Smooth functions on compact sets

Colloquium talk by Jochen Wengenroth from the University of Trier.

Abstract:

There are essentially two ways to define smooth functions on compact subsets K ⊆ Rd (which may be too small to determine enough directional derivatives): Either one considers the space of restrictions C(K) or the space of Whitney jets E(K). A celebrated theorem of Whitney characterizes when a family of continuous functions on K belongs to E(K) by approximation properties of the formal Taylor polynomials. The restriction spaces Cn(K) have been characterized by Fefferman but a characterization for C(K) is still not known.

In this talk we compare both spaces and discuss the problem whether there exist continuous linear extension operators E(K) → C(Rd) and/or C(K) → C(Rd) (where E(K) and C(K) are endowed with their natural Fréchet space topologies).

If the restriction space does not coincide with E(K) the question for C(K) is wide open. We discuss some sufficent conditions as well as necessary ones which, for one-dimensional sets, allow to improve relatively recent results of Fefferman and Ricci as well as Vogt.

The talk is based on joint work with Enrique Jordá (Alcoy) and Leonhard Frerick (Trier).

Plaats: S25, Emmy Noether
Organisator: Vakgroep wiskunde
Datum: 7/3/2018
Tijd: 12:00

voordracht Prof. Mikhail KLIBANOV ( University of North Carolina at Charlotte)

Phaseless inverse scattering and global convergence for inverse problems

Abstract:

Inverse coefficient problems without the phase information are very important in optical imaging of nanostructures and biological cells. We will present some uniqueness results and reconstruction techniques along with numerical results. The second topic is the topic of globally convergent numerical methods for coefficient inverse problems. We will present the so-called "convexification" method. Numerical results for experimental data will also be presented along with the theory.


Plaats: S8, lokaal 2.060
Organisator: Marian Slodicka
Datum: 6/3/2018
Tijd: 19:00

Gastlezing Esko: “The mathematics of color conversions”

Gastlezing Esko: “The mathematics of color conversions”.
Veel studenten vragen zich af wat voor job zij kunnen uitvoeren. Kristof Vanderhoydonck een wiskundige, oud Prime-bestuurslid en werknemer van Esko zal ons wat meer vertellen over zijn huidige job. Kristof zal eerst zichzelf voorstellen en vervolgens uitleggen aan welke projecten hij werkt. Tot slot zal hij nog enkele tips meegeven voor studenten die werk zoeken.

Esko is een bedrijf dat software levert om verpakkingen te ontwikkelen en te printen. Kristof werkt in een R&D team dat zich bezig houd met de kleuren van de verpakkingen. Daarvoor gebruikt hij computationele meetkunde, zoals triangulaties en zoek-algoritmes in grafen./

Plaats: A3
Organisator: Prime
Datum: 1/3/2018
Tijd: 17:30 - 18:45

Surfing with wavelets, lezing Ingrid Daubechies

Prof. Ingrid Daubechies, wereldautoriteit op het gebied van wavelets, brengt een unieke lezing over haar passie. Ze geeft een antwoord op de vragen: 

- Wat zijn wavelets?

- Hoe werken ze?

- Waarom zijn ze nuttig voor beeldverwerking en -compressie?

Klinkt dit allemaal behoorlijk abstract? Geen nood! Prof. Daubechies gaat daarna namelijk verder met het bespreken van hoe wavelets recentelijk zijn toegepast bij de studie van schilderijen van Van Gogh, Gauguin en Giotto.

Deze lezing is niet te missen aangezien prof. Daubechies niet vaak in ons land verblijft en ze één van onze meest vooraanstaande wiskundigen is.

 

Barones Ingrid Daubechies is professor aan de Duke universiteit en voormalig voorzitter van de International Mathematical Union. Ze behaalde haar doctoraat in de theoretische fysica aan de Vrije Universiteit Brussel. Haar bijdragen aan de theorie van wavelets liggen aan de basis van de jpeg-standaard.

De lezing gaat door op 1 maart om 17u30. Gelieve uw aanwezigheid hier aan te geven, zodat we het aantal aanwezigen kunnen schatten.

Plaats: Jozef Plateauzaal
Organisator: PRIME
Datum: 21/2/2018
Tijd: 17:30

Asymptotic distribution of Beurling’s generalized prime numbers - A survey

Inaugurele voordracht

Asymptotic distribution of Beurling’s generalized prime numbers - A survey

door Prof. Dr. Jasson Vindas.

Gelieve uw aanwezigheid op de aansluitende receptie te bevestigen aan secwis@cage.ugent.be

Plaats: S25, Emmy Noether
Organisator: Vakgroep Wiskunde
Datum: 7/2/2018
Tijd: 9:00 - 17:30

Unimath

Alle informatie is te vinden op

http://www.unimath.ugent.be/

Plaats: S9
Organisator: Opleiding Wiskunde
Datum: 2/2/2018
Tijd: 10:00

Numerieke methoden voor het bepalen van een plaatsafhankelijke warmtebron

Verdediging van de masterproef

Numerieke methoden voor het bepalen van een plaatsafhankelijke warmtebron

door Serge Vereecken. Promotoren: Marian Slodicka en Karel Van Bockstal.
Plaats: S8, Leslokaal 3.065
Organisator: Opleiding Wiskunde
Datum: 26/1/2018
Tijd: 10:00

Grafen met weinig hamiltoniaanse cykels

Verdediging van de masterproef

Grafen met weinig hamiltoniaanse cykels

door Barbara Meersman. Promotoren: Jan Goedgebeur en Carol Zamfirescu.
Plaats: S9, PC-klas Zuse
Organisator: Opleiding Wiskunde
Datum: 24/1/2018
Tijd: 14:30

Het verdubbelingsproces van enkele klassen van hypergeometrische orthogonale veeltermen

Verdediging van de masterproef

Het verdubbelingsproces van enkele klassen van hypergeometrische orthogonale veeltermen

door Lukas Boelens. Promotoren: Joris Van der Jeugt en Roy Oste.
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 16/1/2018
Tijd: 12:00 - 13:30

Broodje Martinnovatie: "Implementatie van een alternatief onderwijsmodel in de bacheloropleidingen wiskunde en fysica aan de KU

Dit seminarie focust op het OASE-project binnen de Faculteit Wetenschappen van de KU Leuven. Dit project past het flipped classroom model toe binnen BA1 van de opleidingen wiskunde en fysica.
De krachtlijnen van het OASE-project zijn:

Betere afstemming van het doceer- en leerproces (counteren van uitstelgedrag)
Een voorbereidings-feedback model in plaats van een klassiek presentatie-assimilatie model (flipped classroom, just-in-time-teaching)
Meer permanente evaluatie, geen nood meer aan een stresserende eindspurt door (deel)toetsen en huistaken.

Concreet zijn er minder contacturen, meer interactieve werkvormen en voldoende tijd en ruimte voor zelfstudie en begeleidingssessies. Meer info over het OASE-project van de KU Leuven kan u hier vinden.

Spreker: Iris Peeters - KU Leuven (Faculteit Wetenschappen)

Praktisch:
Dinsdag 16 januari 2018, 12u - 13u30
Campus Sterre, gebouw S2, vergaderzaal 3.1 (3-de verdieping), ingang aan de kant van S1

Inschrijven: via eventmanager

Plaats: S2, vergaderzaal 3.1 (3-de verdieping), ingang aan de kant van S
Organisator: Faculteit Wetenschappen
Datum: 10/10/2017
Tijd: 17:30

Presentaties van de stages

In het nieuwe masterprogramma wiskunde kan het vak stage gevolgd worden (hetzij als vak uit de minor onderzoek, hetzij als keuzevak).
Tijdens de voorbije zomermaanden hebben opnieuw vijf wiskunde-studenten hun stage afgelegd.
(Tom Van Herck en Wouter Van Steenberghe bij Be-Mobile , Toon Baeyens bij Yazzoom, Louis D'hiet bij KBC en Simon Van den Eynde bij het FOD Binnenlandse Zaken)

Op dinsdag 10 oktober zullen zij (vanaf 17u30 tot ongeveer 19u15) hun stagewerk presenteren. Onderaan deze email vinden jullie het uurschema terug.

Ze zullen het, naast de bespreking van de inhoud van de stage, ook hebben over hoe zij de stage hebben ervaren, in welke omgeving zij terechtkwamen, hoe ze werden begeleid, enz.
Op de presentaties zullen ook enkele begeleiders van de stages uit de bedrijven aanwezig zijn.

Graag nodig ik jullie, studenten (je denkt er misschien ook na om een stage te volgen en je vraagt je af wat stage precies inhoudt), uit op deze presentaties.

Met vriendelijke groeten,

prof. M. Van Daele
verantwoordelijk lesgever voor het vak stage
------------------------------------------------------------
Presentaties van de stages in de opleiding wiskunde 2017-2018
Dinsdag 10 oktober 2017 - auditorium A2 - gebouw S9, Campus Sterre

17u30 Louis D'hiet
bedrijf: KBC
onderwerp: Separatie van krediet- en liquiditeitscomponent in sovereign credit spreads en andere aanpassingen aan de huidige VaR-berekeningsmethode

17u50 Simon Van den Eynde
bedrijf: FOD Binnenlandse Zaken - Stafdienst ICT
onderwerp: Neurale netwerken: toepassen van deep learning op visumdata

18u10 Tom Van Herck
bedrijf: Be-mobile
onderwerp: Filedetectie en lanedetectie

18u30 Wouter Van Steenberghe
bedrijf: Be-mobile
onderwerp: Langetermijnspredictie in het verkeer

18u50 Toon Baeyens
bedrijf: Yazzoom
onderwerp: Automatische logparsing

Plaats: auditorium A2, gebouw S9
Organisator: Prof. Marnix Van Daele
Datum: 21/9/2017
Tijd: 16:00 - 18:00

OCW-café

De Opleidingscommissie wiskunde vindt het belangrijk dat alle lesgevers/assisten/begeleiders... zich betrokken voelen bij de opleiding wiskunde. Vandaar een uitnodiging voor een infosessie onder de vorm van een OCW-café.

Tijdens het OCW-café zullen op een losse/ongedwongen manier (bij een drankje en een knabbeltje) gedurende een uurtje enkele thema’s aangekaart worden die in de OC Wiskunde aan bod komen of gekomen zijn. Enkele mogelijke thema’s zijn:
- wat is het portfolio … stand van zaken
- peerleerbezoek … wat houdt dit in, wanneer komt het er aan
- enkele actuele aspecten zoals toetsing, evaluatievormen, werkvormen,competentiematrices, benchmarking, internationalisering, …
- de stand i.v.m. de lerarenopleiding
- ...

Het is tevens een moment om het oude academiejaar af te sluiten en het nieuwe academiejaar in te zetten.
Deze uitnodiging werd verspreid naar de lesgevers van de opleiding. Aan de lesgevers wordt gevraagd deze uitnodiging zeker ook door te sturen naar begeleiders/assistenten/... kortom iedereen die bij de opleiding wiskunde betrokken is.

Met vriendelijke groeten,
prof. M. Van Daele
OCW-voorzitter
 

Plaats: Gebouw S9, A3
Organisator: Opleidingscommissie Wiskunde
Datum: 8/9/2017
Tijd: 14:00

Computationele detectie van homoclinische en heteroclinische connecties voor geïtereerde afbeeldingen

Verdediging van de masterproef

Computationele detectie van homoclinische en heteroclinische connecties voor geïtereerde afbeeldingen

door Laura Vanhulle. Promotor: Willy Govaerts.
Plaats: S9, PC-zaal Zuse
Organisator: Opleiding Wiskunde
Datum: 1/9/2017
Tijd: 16:30

doctoraatsverdediging Ana Filipa Costa da Silva

titel Universal groups for right-angled buildings

Plaats: Emmy Noether
Organisator: Opleiding wiskunde
Datum: 11/8/2017
Tijd: 11:00 - 12:00

Computing Tutte Paths

It is my pleasure to announce the upcoming talk of Andreas Schmid (Max Planck Institute for Informatics, Saarbrücken, Germany). He will speak about Tutte paths, an essential tool for attacking problems revolving around hamiltonian cycles in planar graphs. Everyone is welcome!

Plaats: S9, V2
Organisator: Carol Zamfirescu
Datum: 30/6/2017
Tijd: 16:15

Doctoraatsverdediging Michal Galba

titel : Advanced numerical methods for inverse problems in evolutionary PDEs

promotor: prof. M. Slodicka

Plaats: Jozef Plateauzaal, Plateaustraat
Organisator: M. Van Daele
Datum: 30/6/2017
Tijd: 14:00

A study of mathematical and statistical models for tumor growth in colon cancer

Verdediging van de masterproef

A study of mathematical and statistical models for tumor growth in colon cancer

door Femke Van Zwynsvoorde. Promotor: Els Goetghebeur.
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 29/6/2017
Tijd: 16:15

Doctoraatsverdediging Joraslav Chovan

titel : Comprehensive Numerical Schemes for Computational Electromagnetism

promotor: prof. M. Slodicka

Plaats: Jozef Plateauzaal, Plateaustraat
Organisator: M. Van Daele
Datum: 29/6/2017
Tijd: 12:00

Statistische evaluatie van het Average Treatment effect in the Treated (ATT)

Verdediging van de masterproef

Statistische evaluatie van het Average Treatment effect in the Treated (ATT)

door Kasper De Blieck. Promotor: Stijn Van Steelandt.
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 28/6/2017
Tijd: 16:00

Constructie van alle verschillende nanotube caps uit een fullereen

Verdediging van de masterproef

Constructie van alle verschillende nanotube caps uit een fullereen

door Emiel Ergo. Promotor: Gunnar Brinkmann.
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 28/6/2017
Tijd: 10:30

Numerieke methoden voor tweede-orde differentiaalvergelijkingen

Verdediging van de masterproef

Numerieke methoden voor tweede-orde differentiaalvergelijkingen

door Evelien Vlyminck. Promotor: Marnix Van Daele.
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 28/6/2017
Tijd: 9:45

Symplectische methoden voor het numeriek oplossen van Hamiltoniaanse problemen

Verdediging van de masterproef

Symplectische methoden voor het numeriek oplossen van Hamiltoniaanse problemen

door Nico De Ridder. Promotor: Marnix Van Daele.
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 28/6/2017
Tijd: 9:00

Prijsbepaling van Hawaiiaanse opties met dynamisch programmeren

Verdediging van de masterproef

Prijsbepaling van Hawaiiaanse opties met dynamisch programmeren

door Tine De Plekker. Promotor: David Vyncke.
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 27/6/2017
Tijd: 16:15

Analytical study of the Nuker model

Verdediging van de masterproef

Analytical study of the Nuker model

door Jurjen de Jong. Promotor: Maarten Baes.
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 23/6/2017
Tijd: 10:00

Platypus grafen: structuur en generatie

Verdediging van de masterproef

Platypus grafen: structuur en generatie

door Addie Neyt. Promotoren: Jan Goedgebeur en Carol Zamfirescu.
Plaats: S9, PC-klas Zuse
Organisator: Opleiding Wiskunde
Datum: 22/6/2017
Tijd: 14:30

Constructions of incidence geometries using representations of linear algebraic groups

Verdediging van de masterproef

Constructions of incidence geometries using representations of linear algebraic groups

door Jeroen Meulewaeter. Promotoren: Tom De Medts en Hendrik Van Maldeghem.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 22/6/2017
Tijd: 13:30

De Dehnfunctie van SL(n,Z) en diens actie op de symmetrische ruimte SL(n,R)/SO(n,R)

Verdediging van de masterproef

De Dehnfunctie van SL(n,Z) en diens actie op de symmetrische ruimte SL(n,R)/SO(n,R)

door Jens Bossaert. Promotor: Tom De Medts.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 22/6/2017
Tijd: 11:00

Skew-symmetric distributions and associated inferential problems

Verdediging van de masterproef

Skew-symmetric distributions and associated inferential problems

door Elissa Burghgraeve. Promotor: Christophe Ley.
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 22/6/2017
Tijd: 10:00

Uncertainty theory and statistics

Verdediging van de masterproef

Uncertainty theory and statistics

door Els Molkens. Promotor: Christophe Ley.
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 20/6/2017
Tijd: 10:00

Digitale beeldverwerking met behulp van partiële differentiaalvergelijkingen

Verdediging van de masterproef

Digitale beeldverwerking met behulp van partiële differentiaalvergelijkingen

door Arnaud Devos. Promotoren: Marian Slodicka en Karel Van Bockstal.
Plaats: S8, 3e verdieping, Lokaal 3.065
Organisator: Opleiding Wiskunde
Datum: 19/6/2017
Tijd: 13:00

Een grondige statistische studie van het Belgische kustklimaat

Verdediging van de masterproef

Een grondige statistische studie van het Belgische kustklimaat

door Elke Debrie. Promotoren: Els Goetghebeur en David Dehenauw.
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 16/6/2017
Tijd: 16:00

Alternatieve strategieën voor genpredictie in de Unipept Metagenomics Analysis Pipeline

Verdediging van de masterproef

Alternatieve strategieën voor genpredictie in de Unipept Metagenomics Analysis Pipeline

door Aranka Steyaert. Promotor: Peter Dawyndt.
Plaats: S9, 1e verdieping, lokaal 030
Organisator: Opleiding Wiskunde
Datum: 15/6/2017
Tijd: 11:00

Computerzoektochten in de eindige meetkunde

Verdediging van de masterproef

Computerzoektochten in de eindige meetkunde

door Lins Denaux. Promotor: Peter Vandendriessche.
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 15/6/2017
Tijd: 10:00

Subspace codes en hun meetkundige achtergrond

Verdediging van de masterproef

Subspace codes en hun meetkundige achtergrond

door Jozefien D'haeseleer. Promotor: Leo Storme.
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 15/6/2017
Tijd: 9:00

Meetkundige verbanden met subspace codes en locally recoverable codes

Verdediging van de masterproef

Meetkundige verbanden met subspace codes en locally recoverable codes

door Lisa Hernandez Lucas. Promotor: Leo Storme.
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 14/6/2017
Tijd: 16:30

doctoraatsverdediging Eric Rijcken

Titel: Local Moufang Sets (promotor: Tom De Medts)

Plaats: multimediazaal, S9
Organisator: M. Van Daele
Datum: 14/6/2017
Tijd: 14:00

Genererende functies voor 2D partities

Verdediging van de masterproef

Genererende functies voor 2D partities

door Chiara De Vos. Promotor: Joris Van der Jeugt.
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 14/6/2017
Tijd: 14:00

Optimalisatiealgoritmen voor distributieproblemen

Verdediging van de masterproef

Optimalisatiealgoritmen voor distributieproblemen

door Nathan Sinnesael. Promotor: Veerle Fack.
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 14/6/2017
Tijd: 14:00

Benaderingsalgoritmen voor discrete optimalisatieproblemen

Verdediging van de masterproef

Benaderingsalgoritmen voor discrete optimalisatieproblemen

door Margot Vanhoubroeck. Promotor: Veerle Fack.
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 6/6/2017
Tijd: 16:00

Discreet analytische functies: van het complexe vlak naar hogere dimensies

Verdediging van de masterproef

Discreet analytische functies: van het complexe vlak naar hogere dimensies

door Stefano Dalbosco. Promotoren: Hendrik De Bie en Hilde De Ridder.
Plaats: S8, 3e verdieping, lokaal 3.065
Organisator: Opleiding Wiskunde
Datum: 19/5/2017
Tijd: 16:00

doctoraatsverdediging Manuel Mérida Angulo

Exploring $\mathbb{F}_{1}$-Geometry: Deitmar schemes, loose graphs and motives

Plaats: Emmy Noether
Organisator: M. Van Daele
Datum: 15/5/2017
Tijd: 14:00 - 17:00

PhD Seminar - Functional analysis

You are all kindly invited to the next seminar, having the following schedule.

14:00 Coffee

14:15 Andreas Debrouwere (UGent) - On the non-triviality of Gelfand-Shilov spaces.

15:15 Eduard Nigsch (Uni. Vienna) - Colombeau Algebras.

16:15 Loïc Demeulenaere (Uni. Liège) - Topological invariants, diametral dimension, and one related question.

17:00 Drinks


Abstracts can be found on http://cage.ugent.be/phdseminars/.

Plaats: S23, Euclides
Organisator: Manuel Mérida Angulo & Anneleen De Schepper
Datum: 3/5/2017
Tijd: 11:30

Logic & Analysis seminar: Talk by Ben De Bondt

On Wednesday, May 3, Ben De Bondt of UGent will give a presentation in the Logic & Analysis seminar. You are cordially invited! Everyone is welcome! Please notice that the location of the seminar is moved to Auditorium E in building S4, see the link below for directions

https://soleway.ugent.be/?to=40.04.100.058&language=nl&language=en&user_id=521&exact=true

Date: Wednesday, May 3
Time: 11:30am
Place: S4, Auditorium E


Speaker:
Ben De Bondt, UGent

Title:

Elementary substructure proofs in set theory.

Abstract:

We discuss a method for proving theorems in set theory and related
areas (topology, combinatorics, ...) by considering elementary
substructures of (fragments of) the universe of sets.
We illustrate this method with proofs selected from the literature.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 20/4/2017
Tijd: 19:00

Rekruteringsforum

Eén van de vragen die ieder van ons aspirant-wiskundigen al eens gesteld is geweest: wat kan je daarmee doen? Misschien heb je het jezelf al eens afgevraagd. Op dit rekruteringsevent stellen 6 bedrijven zich voor en, wat misschien belangrijker is, wat zij voor ons en wiskundigen voor hen kunnen betekenen. Een uniek inzicht in het bedrijfsleven dat velen onder ons nastreven en de ideale manier om verschillende sectoren te verkennen en wat te netwerken.

Wij stellen met trots de zes bedrijven voor die zichzelf zullen presenteren: ArcelorMittal, Amplidata, Deloitte, KBC, PwC en Yazzoom.

Na een korte presentatie van elk bedrijf is er ruim tijd voorzien om met de afgevaardigden in dialoog te gaan en alle vragen beantwoord te zien waarbij PRIME een hapje en een drankje voorziet.

Plaats: S9, A3
Organisator: PRIME
Datum: 5/4/2017
Tijd: 14:00 - 17:00

PhD Seminar: Differential Geometry

The next session of the PhD Seminar has the following schedule.

14:00 Coffee

14:15 Goedele Waeyaert (UGent) - Time-dependent Hamiltonian systems.

15:15 Alfonso Garmendia (KULeuven) - Foliations and Groupoids.

16:15 Jaume Alonso i Fernández (UAntwerpen) - Hocus Pocus Focus-Focus.

17:00 Drinks in Café De Pinte.


Abstracts can be found on http://cage.ugent.be/phdseminars/.

Everyone (including students) is welcome!

Plaats: S25, Emmy Noether
Organisator: Manuel Mérida Angulo & Anneleen De Schepper
Datum: 3/4/2017
Tijd: 14:00

Logic & Analysis seminar: Talk by Michael Ruzhansky

On Monday, April 3, Michael Ruzhansky of Imperial College London will give a presentation in the Logic & Analysis seminar. You are cordially invited! Everyone is welcome! Please notice that the location of the seminar is moved to Auditorium E in building S4, see the link below for directions

https://soleway.ugent.be/?to=40.04.100.058&language=nl&language=en&user_id=521&exact=true

Date: Monday, April 3
Time: 14:00
Place: S4, Auditorium E

Speaker:

Michael Ruzhansky, Imperial College London

Title:

Very weak solutions to wave equations

Abstract:

We will discuss a notion of very weak solution to hyperbolic PDEs with singular coefficients. We will demonstrate several applications of this notion to some physical models and to numerical simulations, as well as show links to function theory, analysis on Lie groups, and harmonic analysis.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 29/3/2017
Tijd: 11:30

Logic & Analysis seminar: Talk by Andreas Weiermann

On Wednesday, March 29, Andreas Weiermann of UGent will give a presentation in the Logic & Analysis seminar. You are cordially invited! Everyone is welcome! Please notice that the location of the seminar is moved to Auditorium E in building S4, see the link below for directions

https://soleway.ugent.be/?to=40.04.100.058&language=nl&language=en&user_id=521&exact=true

Date: Wednesday, March 29
Time: 11:30am
Place: S4, Auditorium E

Speaker:

Andreas Weiermann, UGent

Title:

The duality theorem of Sierpinski and Erdös


Abstract:

We prove a classical result about the duality between null sets and sets of first category. The result
will depend on the continuum hypothesis.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 22/3/2017
Tijd: 11:30

Logic & Analysis seminar: Talk by Hans Vernaeve

On Wednesday, March 22, Hans Vernaeve of UGent will give a presentation in the Logic & Analysis seminar. You are cordially invited! Everyone is welcome! Please notice that the location of the seminar is moved to Auditorium E in building S4, see the link below for directions

https://soleway.ugent.be/?to=40.04.100.058&language=nl&language=en&user_id=521&exact=true

Date: Wednesday, March 22
Time: 11:30am
Place: S4, Auditorium E


Speaker:
Hans Vernaeve, UGent

Title:

Different models for topology

Abstract:

Nonstandard models provide a way to add infinitesimal elements to topological spaces. They provide a way to streamline many topological arguments, especially when compactness is involved in the proof. The Baire category theorem and its consequences for functional analysis (especially the Banach-Steinhaus theorem) can sometimes be viewed as a substitute for compactness arguments. But here nonstandard models do not automatically provide a similar simplification. It was discovered around 1995 that a special type of models is able to treat these arguments properly with infinitesimals. Also the treatment of topology beyond first countable spaces requires a special type of models. Unfortunately, both types are incompatible. We survey these observations, and outline a possible remedy for this situation.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 15/3/2017
Tijd: 11:30

Logic & Analysis seminar: Talk by Lenny Neyt

On Wednesday, March 15, Lenny Neyt of UGent will give a presentation in the Logic & Analysis seminar. You are cordially invited! Everyone is welcome! Please notice that the location of the seminar is moved to Auditorium E in building S4, see the link below for directions


https://soleway.ugent.be/?to=40.04.100.058&language=nl&language=en&user_id=521&exact=true


Date: Wednesday, March 15
Time: 11:30am
Place: S4, Auditorium E


Speaker:
Lenny Neyt, UGent

Title:

On the asymptotic of partitions and the Matula numbers

Abstract:

In 1917, Hardy and Ramanujan made the first results towards solving the asymptotic of the unrestricted partitions of the natural numbers. The question on how many ways one can write a natural number as a sum of integral parts (independent of the order) is surprisingly deep, and has since served as the inspiration of many problems and techniques to come.

Basically, one searches for the asymptotic (strong or weak) of the counting function of the semigroup generated by a sequence of positive real numbers increasing towards infinity. In this talk, we will discuss how one may find such strong asymptotics by the use of Ingham's complex Tauberian theorem. Then, later, we illustrate these methods by example of the Matula numbers. These numbers arise from enumerating the rooted trees by prime factorization, and show themselves in plenty of interesting combinatorial counting problems. They may also be applied in ordinal counting functions.

The talk will be based on work in progress in collaboration with Jasson Vindas and Andreas Weiermann and is situated in the realms of number theory, functional analysis and logic.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 10/3/2017
Tijd: 11:30

Logic & Analysis seminar: Talk by Djordje Vuckovic

On Wednesday, May 10, Djordje Vuckovic of UGent will give a presentation in the Logic & Analysis seminar. You are cordially invited! Everyone is welcome! Please notice that the location of the seminar is moved to Auditorium E in building S4, see the link below for directions

https://soleway.ugent.be/?to=40.04.100.058&language=nl&language=en&user_id=521&exact=true

Date: Wednesday, May 10
Time: 11:30am
Place: S4, Auditorium E

Speaker:
Djordje Vuckovic, UGent

Title:

Global Wave Front Sets on Spaces of Ultradistributions

Abstract:

In this talk we will define a global wave front set on the spaces of ultradifferentiable functions and ultradistributions, both of Beurling and Roumieu type, and study its properties.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 8/3/2017
Tijd: 11:30

Logic & Analysis seminar: Talk by Jasson vindas

Speaker:
Jasson Vindas, UGent

Title:

New developments in the non-linear theory of generalized functions: optimal embeddings of ultradistributions and hyperfunctions

Abstract:

Generalized functions are very useful tools in mathematical analysis and its applications. Many important instances of generalized functions arise as sheaves of linear spaces that are closed under differentiation; the most well-known classes of such spaces are the distributions, the ultradistributions, and the hyperfunctions, whose constructions are intimately connected with the (topological) duals of the spaces of smooth functions, Denjoy-Carleman ultradifferentiable functions, and real analytic functions, respectively.

In general, multiplication is not a well-defined operation within the linear theory. The central goal of the non-linear theory of generalized functions is to construct differentiable algebras in order to remedy the lack of multiplication for the linear spaces of generalized functions. In the case of Schwartz distributions, this problem was first solved by Colombeau in the early 80's.

In this talk we give an overview of various recent developments concerning the possibility of constructing optimal embeddings of ultradistributions and (infra)hyperfunctions into algebras of generalized functions. Part of the exposition will be of introductory character, we will discuss in detail the main differences between non-quasianalytic and quasianalytic Denjoy-Carleman classes, and will sketch a construction of Hörmander's sheaf of infrahyperfunctions.

The talk is based on collaborative works with Andreas Debrouwere and Hans Vernaeve.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 8/3/2017
Tijd: 10:30

Similarity-based logics for approximate entailments

In this presentation we will deal with logics for similarity-based reasoning. In his seminal work on similarity-based reasoning, Ruspini builds up a framework for approximate inference that is based on the mutual similarity of the propositions involved. Following these lines, a number of approaches have dealt with fuzzy similarity-based reasoning from a logical perspective. In particular, the so-called logic of Approximate Entailment (LAE), and the logic of a dual notion of Strong Entailment (LSE) have been studied by Esteva et al. These logics formalise the effect on the validity of inferences due to small changes in their components using fuzzy similarity relations to model the notion of approximate inference. In this talk we will present the main notions and properties of LAE and some of its variants. LAE is a propositional graded modal logic where propositions are interpreted, as in classical logic, by subsets of worlds, but the set of worlds is assumed to be endowed with a fuzzy similarity relation, which associates with each pair of two worlds their degree of resemblance. The basic semantic structures are these fuzzy similarity spaces, and the core syntactic objects of LAE are implications between propositions endowed with a degree. The intended meaning of a statement of the form A >_c B is that B is an approximate consequence of A to the degree c, where c is a real number between 0 and 1. We will present complete axiomatizations for LAE and some its varients, and moreover we will show how the framework can be enhanced in case of dealing with similarities on linearly ordered spaces.

Main references:
- F. Esteva, L. Godo, R. O. Rodriguez, T. Vetterlein., Logics for approximate and strong entailments, Fuzzy Sets Syst. 197 (2012), 59 - 70.
- T. Vetterlein, Logic of approximate entailment in quasimetric spaces, Int. J. Approx. Reasoning, 64 (2015), 39-53
- T. Vetterlein, F. Esteva, L. Godo. Logics for Approximate Entailment in ordered universes of discourse. Int. J. Approx. Reasoning 71: 50-63 (2016)

Plaats: lecture room A.0 of building S12
Organisator: Chris Cornelis
Datum: 1/3/2017
Tijd: 11:30

Logic & Analysis seminar: lecture by Gregory Debruyne

Title:

General Tauberian remainder theorems

Abstract:

In Tauberian theory, one if often interested to deduce asymototic information for a function S, which satisfies a Tauberian condition, (such as monotonicity or boundedness), from information on a certain transform of the function. One could construct Tauberian theorems of this type for each transform separately, but it would be more time-efficient and insightful, to construct a Tauberian theory for a large class of transforms at once. This approach is called general Tauberian theory.

The first breakthrough came with Wiener in 1930s, when he developed his celebrated Wiener Tauberian theory, which provides a pretty much complete general Tauberian theory for the remainder o(1).

Since then, there were some attempts to find general Tauberian theorems for other remainders. Beurling was the first one to give a general Tauberian remainder theorem, but his class of transforms was rather restricted. Another breakthrough came with the work of Ganelius in the 1970s when he was able to obtain general Tauberian remainder theorems for a large class of transforms and also proved that his results were sharp in many cases.

The results of Ganelius didn't receive much attention in applications however. The main reason for this is that the remainders he obtained were rather weak, despite being optimal. In this talk we will provide the main ideas for our recently developed general Tauberian remainder theory. Our theory will be able to obtain much better remainders than the theory of Ganelius ever could, while still retaining a pretty broad class of transforms. The talk is based on work in progress in collaboration with Jasson Vindas.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 24/2/2017
Tijd: 14:00 - 17:00

PhD Seminar - Number Theory

The next session of the PhD Seminar has the following schedule.


14:00 Coffee

14:15 Gregory Debruyne (UGent) - The prime number theorem.

15:15 Saskia Chambille (KULeuven) - Integration over the p-adic numbers.

16:15 Harry Smit (Utrecht) - Global field isomorphisms.

17:00 Drinks in Café De Pinte.


Abstracts can be found on http://cage.ugent.be/phdseminars/.


You are all kindly invited!


(The PhD Seminar is a seminar intended for a general mathematical audience and can hence also be followed by (master) students interested in the topic of the seminar and/or research).

Plaats: S25, Emmy Noether
Organisator: Manuel Mérida Angulo & Anneleen De Schepper
Datum: 23/2/2017
Tijd: 15:00 - 18:00

Wiskunst 200

Tijdens deze namiddag wordt de faculteitsraadszaal voor het publiek geopend.
Getoond worden sommige schilderijen (landscapes en seascapes) van A.Weiermann.

Plaats: Faculteitsraadzaal S2 3rd verdiep
Organisator: Andreas Weiermann
Datum: 22/2/2017
Tijd: 11:30

Logic & Analysis seminar: lecture by Andreas Debrouwere

Speaker:

Andreas Debrouwere, UGent

Title:

The first Cousin problem for quasianalytic functions

Abstract:

The solution to the first, or additive, Cousin problem for Stein open sets is a classical result in the theory of functions of several complex variables.The aim of this talk is to explain this problem and show that it is in fact solvable for general classes of (vector-valued) quasianalytic functions.

Plaats: S4, Auditorium E
Organisator: Andreas Debrouwere
Datum: 17/2/2017
Tijd: 16:00

Doctoraatsverdediging Goedele Waeyaert

Doctoraatsverdediging Goedele Waeyaert
Promotoren: Frans Cantrijn en Willy Sarlet

Plaats: Emmy Noether
Organisator: Voorzitter examencommissie Marnix Van Daele
Datum: 8/2/2017
Tijd: 9:30 - 16:00

Unimath

Woensdag 8 februari staat in het teken van Unimath. Alle leslokalen in S9 staan die dag ter beschikking van leerlingen van middelbare scholen.

In de voormiddag volgen de leerlingen (net zoals de voorbije jaren) gedurende 2 x 75 minuten een van de aangeboden onderwerpen. In de namiddag nemen de klassen het tegen elkaar op met wiskundige spelletjes/raadsels ...

Plaats: S9
Organisator: Opleiding Wiskunde
Datum: 24/1/2017
Tijd: 14:00 - 17:00

PhD Seminar - Combinatorics

The next session of the PhD Seminar is on combinatorics and has the following schedule.

14:00 Coffee

14:15 Anurag Bishnoi (UGent) - An incidence bound an its applications.

15:15 Hao Chen (St. Andrews, UK) - Combinatorial problems from ball packings

16:15 Sam Mattheus (VUB) - TBA.

17:00 Drinks in Café De Pinte

Abstracts can be found on http://cage.ugent.be/phdseminars/.


You are all kindly invited!

Plaats: S22, C
Organisator: Anneleen De Schepper & Manuel Mérida Angulo
Datum: 13/1/2017
Tijd: 16:00

Integral transforms related to the slice Dirac operator

PhD defence Lander Cnudde

Plaats: Jozef Plateauzaal (campus Boekentoren)
Organisator: Lander Cnudde
Datum: 21/12/2016
Tijd: 11:30

Logic & Analysis seminar: lecture by Andreas Weiermann

Speaker:
Andreas Weiermann, UGent

Title:

Relating Hilbert's basis theorem and MacLagan's theorem to finite and infinite Young diagrams.

Abstract:

We present some recent results about the complexity of Hilbert's basis
theorem and MacLagan's theorem (from commutative algebra). The results
will be formulated in terms ofcombinatorial assertions about tuples of natural numbers. The talk is
low level and will be accessibleto students of Bachelor level.

Plaats: S22, Auditorium C
Organisator: Andreas Debrouwere
Datum: 20/12/2016
Tijd: 10:00

Some contributions to incidence geometry and the polynomial method

Anurag Bishnoi will defend his PhD thesis.

Plaats: Auditorium Emmy Noether
Organisator: Bart De Bruyn (Supervisor)
Datum: 19/12/2016
Tijd: 17:00

Reaching a Consensus under Multi-agent Preferences

PhD defense Sofie De Clercq

Plaats: S9 (Multimediazaal)
Organisator: Martine De Cock
Datum: 19/12/2016
Tijd: 15:00 - 16:00

Computational Social Choice meets Logic

Two major roles that logic can play in collective decision making are (a) expressing prefer-
ences and reasoning about them, and (b) expressing beliefs in reasoning about them. The
talk will cover both of them. For (a), we will discuss various issues such as preference logics
and their sublanguages, nonmonotonic reasoning about preferences, and preference repre-
sentation languages for individual, collective or strategic decision making. For (b), we will
discuss epistemic issues in strategic voting and fair division, as well as epistemic issues and
incomplete preferences in collective decision making. This will mainly be a position/survey
talk.

Plaats: S9, V2
Organisator: Martine De Cock
Datum: 14/12/2016
Tijd: 11:30

Logic & Analysis seminar: Lenny Neyt

Speaker:
Lenny Neyt, UGent

Title:
The Asymptotic Behavior of Generalized Functions

Abstract:
The theory of generalized functions provides an excellent framework for asymptotic analysis, where the asymptotic behavior of many analytic operations, such as the Laplace transform, is obtained from the asymptotic behavior of a single generalized function.

In this talk we will discuss the approach to generalized asymptotics developed by Kanwal and Estrada, and in particular the moment asymptotic expansion will be studied, which expresses the behavior of a generalized function at infinity by its evaluation on the Taylor series of the test function. Many examples will be given.

In the last part of the talk we investigate how the moment asymptotic expansion may be implemented into ultradistributional spaces and review some characterizations.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 13/12/2016
Tijd: 10:30

presentatie USolv-IT

Beste lesgever,

U bent van harte uitgenodigd voor een presentatie over het elektronisch oefenplatform USolv-IT. Deze presentatie gaat door op dinsdag 13 december om 10u30 in lokaal 0.A - S12 (Campus Sterre, gebouw 40.12 - S12). USolv-IT werd ontworpen door medewerkers aan de KULeuven en de UGent en heeft een groeiend aantal gebruikers in scholen en in het hoger onderwijs.

De presentatie wordt gebracht door collega prof. Paul Igodt (KULeuven-Kulak):

“USolv-IT: een oefen- en inspiratieplatform op basis van gedeelde inhouden wiskunde, fysica, chemie, statistiek en economie.”

We presenteren de genese en de filosofie van dit platform dat inmiddels bijna 14000 oefeningen telt, waaronder alle opgaven van ijkingstoetsen, de opgaven van het toelatingsexamen Arts, en duizenden andere oefeningen die horen bij zowel het secundair als het hoger en universitair onderwijs. USolv-IT is binnen de UGent geconnecteerd aan het leerplatform Minerva.

Deelname is gratis. Inschrijven kan via https://webapps.ugent.be/eventManager/events/usolvit.

Vriendelijke groet,
Mieke Adriaens

Plaats: lokaal 0.A - S12
Organisator: Dienst Onderwijsondersteuning van Faculteit Wetenschappen
Datum: 12/12/2016
Tijd: 14:45 - 17:30

PhD Seminar

The second session of the PhD Seminar is on Algebra. We have the following schedule.

14:30 Coffee

14:45 Ana Silva (UGent) - The universal groups for trees travelling to other geometrical universes.

15:45 Thierry Stulemeijer (KULeuven) - The prime power conjecture, quadratic forms and the field with one element.

16:45 Andreas Bächle (VUB) - TBA.

17:30 Drinks in Café De Pinte

More info (a.o. abstracts) can be found on http://cage.ugent.be/phdseminars/.

Everyone is welcome!

Plaats: S22, vergaderzaal
Organisator: Manuel Mérida Angulo & Anneleen De Schepper
Datum: 8/12/2016
Tijd: 14:00

Algebra seminarie: p-group actions on smooth projective varieties

Olivier Haution (LMU Munich): p-group actions on smooth projective varieties

Abstract: I will discuss how the geometry of an algebraic variety restricts the possible actions of p-groups on it, especially concerning fixed points.

Plaats: N1, campus Proeftuinstraat
Organisator: Tom De Medts
Datum: 7/12/2016
Tijd: 11:30

Logic & Analysis seminar: Hans Vernaeve

Speaker:
Hans Vernaeve, UGent

Title:
Nonstandard functional analysis

Abstract:
In the 1960s, Abraham Robinson developed Nonstandard Analysis, a way to add infinitely small (=infinitesimal) and infinitely large numbers to the real number system in such a way that many arguments by the pioneers of the calculus using infinitesimals become rigorous. This theory also yields a way to add infinitesimals to topological spaces. In particular, this gives an alternative way to describe the topological vector spaces that are used in analysis. In this talk, we will survey similarities and differences between the standard and the nonstandard approach.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 2/12/2016
Tijd: 14:30

Seminar talk by Tijl De Bie (ELIS)

Exploratory data mining: an information-theoretic perspective

As the abundance of data grows exponentially, so does the
challenge of extracting the full value data holds. Extracting such value
is often done by means of machine learning, building models to predict
expensive or hard-to-measure target variables. Often however, data
analysts have no specific target variables in mind, and only wish to
explore the data in order to learn something that is interesting to
them. The latter type of task is much less well-defined, as the degree
to which a relation found in data is interesting to somebody is
inherently subjective. This talk surveys a framework to put it onto a
more rigorous footing, and discusses instantiations of this framework to
a range of data mining problem types.

Plaats: Technicum, left entrance, first floor
Organisator: Hendrik De Bie
Datum: 30/11/2016
Tijd: 11:30

Logic & Analysis seminar: Djordje Vuckovic

Speaker:
Djordje Vuckovic, UGent

Title:
Toroidal pseudodifferential operators and spaces of ultradistributions on T^n

Abstract:
In this talk we will study a class of symbols and corresponding pseudodifferential operators of finite order on torus T^n that act continuously on a space of ultradistributions on torus, of Beurling and Roumieu type, and develop symbolic calculus for these classes.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 23/11/2016
Tijd: 11:30

Logic & Analysis seminar: Geert Vernaeve

Speaker:
Geert Vernaeve, UGent

Title:
Logic, the Universe, and Everything

Abstract:
It was long held impossible to do "real" mathematics in a fully formalized way. Since the arrival of the computer, this has become more and more feasible practically, and even industrial applications are becoming more and more important.

We sketch the history of the subject, show how a very short computer program yields a surprisingly efficient theorem prover; we indicate some of the different potential problems and the diverse methods of avoiding them and the different resulting logics.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 18/11/2016
Tijd: 16:00 - 17:00

Mathematics Colloquium: Vesselin Drensky

Speaker:
Vesselin Drensky
Institute of Mathematics and Informatics
Bulgarian Academy of Sciences
Sofia, Bulgaria

Title:
Games on Partitions: The Bulgarian Solitaire

Abstract:
The (quite amusing) story presented in the talk is an example of this how an elementary mathematical game can inspire serious mathematical investigations in combinatorics, graph theory, discrete dynamical systems, cellular automata, linear algebra, statistics, and economic models. The topic has the advantage that most of the problems can be stated in a form which attracts young people to mathematical research.

The main object of the talk is the Bulgarian solitaire. This is a mathematical card game played by one person. A pack of n cards is divided into several decks (or "piles"). Each move consists of removing of one card from each deck and collecting the removed cards to form a new deck. The game ends when the same position occurs twice. It has turned out that when n=k(k+1)/2 is a triangular number, the game reaches the same stable configuration with size of the piles 1,2,...,k. The problem was brought to Bulgaria from Russia in 1980 and then was spread to the world. The first solutions appeared in 1981 in Bulgarian and Russian. The name was given by Henrik Eriksson and then popularized by Martin Gardner.

In the language of partitions, each division of the pack of n cards into decks corresponds to a partition of n. The set P(n) of all partitions of n is considered as a discrete dynamical system. Starting with a partition, each move of the Bulgarian solitaire plays the role of the updating function of the system. The main problem is, starting with a partition (the initial state), to determine the state that the system reaches after some time interval t. The study of the system involves methods from combinatorics, graph theory, linear algebra, statistics, etc.

The Bulgarian solitaire has several "younger brothers," e.g., the Austrian, Carolina, and Montreal solitaires, the Red-green, Three-dimensional, Dual, and Multiplayer Bulgarian solitaires, Stochastic Bulgarian solitaires.

The talk is based on the recent paper

V. Drensky,
The Bulgarian solitaire and the mathematics around it,
Math. and Education in Math.,
Proc. of the 44-th Spring Conf. of the Union of Bulgar. Mathematicians,
SOK-Kamchia, April 2-6, 2015, 79-91.
http://www.math.bas.bg/smb/2015_PK/tom_2015/pdf/079-091.pdf,
arXiv:1503.00885v1 [math.CO],

with additional information collected after its publishing.

Plaats: S3, Leszaal Benoit Emile Clapeyron
Organisator: Andreas Weiermann
Datum: 18/11/2016
Tijd: 14:30

Logic & Analysis (and Algebra) seminar: Ivan Chipchakov

Speaker:
Ivan Chipchakov, Institute of Mathematics and Informatics, Bulgarian Academy of Sciences

Title:
Bounds and formulae for Brauer p-dimensions of Henselian fields

Abstract:
Let E be a field and A an associative central simple E-algebra of finite dimension. The degree deg(A), the Schur index ind(A)=deg(D_A) (where D_A is the Wedderburn -- underlying division algebra of A), and the exponent exp(A) (the order of the equivalence class [A] in the Brauer group Br(E)) are basic invariants of A; ind(A) and exp(A) are invariants of [A] as well. It is known that (ind(A),exp(A)) is a Brauer pair, i.e., exp(A) divides ind(A) and is divisible by the prime divisors of ind(A). The converse need not be true over global or local fields or other special fields.

The Brauer dimension Brd(E) and its p-analogues, the Brauer p-dimensions Brd_p(E), where p runs across the set P of prime numbers, contain essential information on index-exponent relations over E. Other invariants of E like the absolute Brauer dimension abrd(E) and the absolute Brauer p-dimensions abrd_p(E), p in P, have a strong influence on the behaviour of the noted relations over finitely-generated transcendental extensions F of E. For example, Brd(F)=∞, if abrd(E)=∞, and when abrd_p(E)=∞, for some p, all p-primary Brauer pairs are index-exponent F-pairs (sp., Manuscr. Math. 148 (2015), No. 3-4, 485-500). Similarly to other problems on central division algebras, the existence and known properties of valuations on F motivates the study of index-exponent relations by the methods of valuation theory; specifically, it attracts interest in Brd_p(E) in the special case where E has a Henselian valuation v.

The main results of this talk give lower and upper bounds on Brd_p(E) and abrd_p(E), under the hypothesis that abrd_p(Ê) is finite, which depend only on invariants of the residue field Ê and the value group v(E). Usually, we restrict to the following three cases: p≠char(Ê); char(E)=p and (E,v) is maximally complete; v is discrete. Formulae for Brd_p(E) are deduced, when Ê is of special type, like a global field or local field, or a perfect field whose absolute Galois group is a projective profinite group.

Plaats: S22 Meeting Room
Organisator: Paul Shafer
Datum: 18/11/2016
Tijd: 13:30

Logic & Analysis seminar: Paula Henk

Speaker:
Paula Henk, ILLC, University of Amsterdam

Title:
A Modal Perspective on Slow and Ordinary Provability

Abstract:
The notion of slow provability for Peano Arithmetic (PA) was introduced by Friedman, Rathjen, and Weiermann. While it is true (in the standard model) that slow provability is equivalent to ordinary provability, this fact is not provable in PA: PA considers it possible that slow provability is a weaker notion than ordinary provability, i.e. that not all ordinary proofs can be converted into slow proofs.

Given the above, it is interesting to ask how does the joint behaviour of slow and ordinary provability look like, as seen from the perspective of PA. We answer this question by using modal logic. The bimodal logic GLT is shown to be the joint provability logic of slow and ordinary provability: its theorems are exactly the principles of interaction between slow and ordinary provability that are provable in PA. Interestingly, GLT is also the joint provability logic of ordinary and Parikh provability, where the latter can be seen as a sped-up version of ordinary provability.

Plaats: S22 Meeting Room
Organisator: Paul Shafer
Datum: 16/11/2016
Tijd: 11:30

Logic & Analysis seminar: Gregory Debruyne

Speaker:
Gregory Debruyne, UGent

Title:
Remainders in the prime number theorem and the Wiener-Ikehara theorem

Abstract:
The Wiener-Ikehara theorem is one of the most famous theorems in Tauberian theory. It was originally designed to give a simple proof of the prime number theorem. Therefore remainder versions of it should give relatively simple proofs for remainders in the prime number theorem. Some recently discovered remainder versions will be discussed.

As an application, we will indicate in some detail how these remainder versions can be used to deduce remainders in the prime number theorem from the currently best known zero-free region of the zeta function.

The talk is based on collaborative work with Jasson Vindas.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 9/11/2016
Tijd: 14:00

PhD Seminars

Three young researchers will give a talk aiming for general mathematical audience in which they will discuss their research and interests. The topic of the day will be Algebraic Geometry.

You can find all the information in http://cage.ugent.be/phdseminars

Plaats: Meeting room, S22
Organisator: Vakgroep Wiskunde
Datum: 9/11/2016
Tijd: 11:30

Logic & Analysis seminar: Jasson Vindas

Speaker:
Jasson Vindas, UGent

Title:
On a prime number theorem equivalence for Beurling numbers

Abstract:
In classical prime number theory there are several asymptotic formulas said to be "equivalent" to the prime number theorem (PNT). One of them is the mean-value vanishing of the Moebius function, that is, the asymptotic bound

M(x)= o(x),

where M is the sum function of the Moebius function. For Beurling generalized numbers, this estimate is not an unconditional consequence of the PNT.

Generalized numbers are multiplicative semigroups generated by (rather general) unbounded sequences of real numbers, called "generalized primes" and introduced by Beurling in order to study how independent prime number theory is from the additive properties of the natural numbers.

In this talk we discuss PNT equivalences for generalized number systems, focusing on relations for the Moebius function. We give several conditions that yield the Beurling version of the bound for M and examples illustrating failures when these conditions are not satisfied.

The talk is based on recent collaborative work with Gregory Debruyne and Harold Diamond.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 27/10/2016
Tijd: 15:00

Seminar on graph colouring by Oliver Schaudt

Everybody is cordially invited!

Speaker:
Dr. Oliver Schaudt, University of Cologne and RWTH Aachen University, Germany

Title:
News on the list k-colorability problem in H-free graphs

Abstract:
In the list k-colorability problem, each vertex of the input graph is equipped with a list that is a subset of {1,...,k}, and the task is to decide whether there is a proper coloring that assigns to each vertex a color from its list. This generalizes the classical k-colorability problem and the precoloring extension problem.

I will explain our recent results on list 3-coloring in H-free graphs, and the methods used to prove these results.

A focus will be given to the problem of characterizing the minimal obstructions against list 3-colorability.

Based on joint work with Flavia Bonomo, Maria Chudnovsky, Jan Goedgebeur, Peter Maceli, Maya Stein, and Mingxian Zhong.

Plaats: S9, leszaal V3
Organisator: Jan Goedgebeur
Datum: 26/10/2016
Tijd: 19:30

PRIME Quiz

De ondertussen legendarische PRIME Quiz is dit jaar aan haar negende editie toe. Buig je in ploegen van vier over originele vragen, uitdagende breinbrekers en een praktische puzzelproef; doorzie de rode draden en beleef een avond vol amusement en aha-erlebnissen! De PRIME Quiz is speciaal toegankelijk voor wie er nog nooit een heeft meegemaakt, maar ook de ervarener ploegen kunnen hier hun hart ophalen. Er liggen prijzen klaar voor iedere individuele deelnemer, maar wie best scoorde, kiest eerst! We voorzien het einde van de quiz rond middernacht.

Plaats: S9, A3
Organisator: PRIME
Datum: 26/10/2016
Tijd: 11:30

Logic & Analysis seminar: Paul Shafer

Speaker:
Paul Shafer, Ghent University

Title:
Honest elementary degrees without the cupping property

Abstract:
An element a of a lattice cups to an element b > a if there is a c < b such that a join c is b. An element of a lattice has the cupping property if it cups to every element above it. We study cupping in the lattice of honest elementary degrees, in which functions with elementary recursive graphs are compared via the elementary-recursive-in relation. Kristiansen showed that every sufficiently large honest elementary degree has the cupping property. This result prompted Kristiansen, Schlage-Puchta, and Weiermann to ask if every non-zero honest elementary degree has the cupping property. We answer their question negatively by showing that if b is a sufficiently large honest elementary degree, then there is a non-zero honest elementary degree a < b that does not cup to b. Building on work of Cai, we also prove non-cupping results for the degrees of relative provability. Finally, we discuss the connections among the honest elementary degrees, the degrees of relative provability, and provability in Peano arithmetic and its fragments.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 19/10/2016
Tijd: 11:30

Logic & Analysis seminar: Andreas Weiermann

Speaker:
Andreas Weiermann, UGent

Title:
Natural Gödel incompleteness results and necessarily long proofs

Abstract:
We give a short survey about natural independence results and will indicate how they lead to necessarily long proofs. The point will be that there exist true, hence provable (in Peano arithmetic), existential statements about natural numbers for which there is no proof (in Peano arithmetic) that can be written down physically on a sheet of paper. This might lead to an alternative view on ultrafinitism.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 17/10/2016
Tijd: 19:00

Mathematical Imagery (Jos Leys)

Google de naam Jos Leys eens, en je ziet meteen dat we te maken hebben met een grootmeester in wiskundige visualisaties. Spectaculaire fractalen in 2D en 3D, hyperbolische betegelingen, topologische animaties, en de films Dimensions and Chaos zijn maar een greep uit de galerij van visualisaties die hij heeft ontwikkeld.

Tijdens deze lezing Mathematical Imagery vertelt Jos Leys over de gevarieerde wiskunde die er schuilt achter zijn creaties.

Plaats: Emmy Noether
Organisator: PRIME
Datum: 12/10/2016
Tijd: 11:30

Logic & Analysis seminar: Andreas Debrouwere

Speaker:
Andreas Debrouwere, UGent

Title:
Abstract Moment Problems and Their Applications

Abstract:
We shall discuss the following abstract moment problem: Let E and F be topological vector spaces and let (f_n)_n subset L(E,F) be a sequence of continuous linear functions. We seek conditions on (f_n)_n such that for each sequence (y_n)_n subset F the infinite system of equations

f_n(x) = y_n; n in N

admits a solution x in E. It turns out that this functional analytic framework is very convenient for solving multidimensional and vector-valued moment problems. We provide many examples.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 11/10/2016
Tijd: 17:00

Presentatie stages

Beste studenten,
beste lesgevers,

in het nieuwe masterprogramma wiskunde kan het vak stage gevolgd worden (hetzij als vak uit de minor onderzoek, hetzij als keuzevak).
Tijdens de voorbije zomermaanden hebben de eerste vijf wiskunde-studenten

(Aranka Steyaert bij INBO , Arnaud Devos bij KBC, Addie Neyt bij BNP Paribas Fortis, Femke Van Zwynsvoorde en Kelly Van Lancker bij Janssen Pharmaceutica) hun stage afgelegd.

Op dinsdag 11 oktober zullen zij (vanaf 17u00 tot ongeveer 19u00) hun stagewerk presenteren.
Ze zullen het, naast de bespreking van de inhoud van de stage, ook hebben over hoe zij de stage hebben ervaren, in welke omgeving zij terechtkwamen, hoe ze werden begeleid, enz.

Graag nodig ik jullie, studenten (je denkt er misschien ook na om een stage te volgen) of lesgevers, uit op deze presentaties.

Met vriendelijke groeten,

prof. M. Van Daele
verantwoordelijk lesgever voor het vak stage

Plaats: S9, aud. A0
Organisator: M. Van Daele
Datum: 24/8/2016
Tijd: 0:00

Vernieuwde website en kalender

Afgelopen week is de website geüpdatet. Er is gestreefd om hem overzichtelijker te maken en navigatie te vereenvoudigen.

Andere belangrijke aanpassingen zijn de toevoeging van een (beknopt) Engelstalig luik en een wekelijkse activiteitenupdate.
Deze activiteitenupdate hebben we in het leven geroepen om lezingen, workshops... die georganiseerd worden rond de ruime opleiding wiskunde, meer gehoor te geven.

Organiseert u zelf een activiteit dan kan u die simpelweg toevoegen door u aan te melden op www.wiskunde.ugent.be/kalender en bovenaan 'nieuwe activiteit' te klikken.

De bugs, onnauwkeurigheden, foutjes die de website hoogstwaarschijnlijk nog bevat, of gewoon opmerkingen die u heeft, kan u steeds mailen naar Marnix.VanDaele@UGent.be

Met de vriendelijkste groeten,
Toon Baeyens

Plaats: Opleiding wiskunde aan ugent
Organisator: Marnix Van Daele
Datum: 2/8/2016
Tijd: 10:00 - 17:00

Graph Theory Workshop on Longest Paths and Longest Cycles (Day 2)

All talks will be held in room V2 on the third floor of building S9 of the Department of Applied Mathematics, Computer Science and Statistics, Ghent University, Krijgslaan 281. We take the coffee breaks in room V3 on the third floor.

Programme of the second day:

10:00-10:25 Varga: On the minimum degree of minimally 1-tough graphs
10:30-10:55 Katona: Complexity questions for minimally t-tough graphs
10:55-11:15 Coffee Break
11:15-11:40 Kardos: Barnette was right: not only fullerene graphs are Hamiltonian
11:45-12:10 Van Cleemput: Connections between decomposition trees of 3-connected plane triangulations and Hamiltonian properties
12:10-15:00 Lunchtime
15:00-15:25 Surmacs: Pancyclic arcs in Hamiltonian cycles of tournaments
15:30-15:55 Kliemann: A streaming algorithm for the undirected longest path problem
16:00 Problem Session

Plaats: S9, Campus Sterre
Organisator: Carol Zamfirescu
Datum: 1/8/2016
Tijd: 9:50 - 17:10

Graph Theory Workshop on Longest Paths and Longest Cycles (Day 1)

All talks will be held in room V2 on the third floor of building S9 of the Department of Applied Mathematics, Computer Science and Statistics, Ghent University, Krijgslaan 281. We take the coffee breaks in room V3 on the third floor.

Programme of the first day:

9:50-10:00 Welcoming
10:00-10:25 Ozeki: Hamiltonicity of graphs on surfaces
10:30-10:55 Harant: On longest cycles in essentially 4-connected planar graphs
10:55-11:15 Coffee Break
11:15-11:40 Cameron: Degree-constrained spanning trees
11:45-12:10 Wiener: Finding spanning trees with few leaves using DFS
12:10-15:00 Lunchtime
15:00-15:25 Thomassen: Chords in longest cycles
15:30-15:55 Li: Long properly colored cycles in edge-colored graphs
15:55-16:15 Coffee Break
16:15-16:40 Steffen: Edge colorings and circular flow numbers of regular graphs
16:45-17:10 Goedgebeur: Finding minimal obstructions to graph coloring

Plaats: S9, Campus Sterre
Organisator: Carol Zamfirescu
Datum: 1/7/2016
Tijd: 15:00

A classification scheme for the inverse problem in arbitrary dimension

Two talks by Prof Geoff Prince and Dr Thoan Do (both La Trobe University, Melbourne) in the `Differential Geometry and Mechanics seminar'.

Abstract: We present a new classification scheme for the inverse problem in the calculus of variations in arbitrary dimension. This generalises the Douglas scheme for a pair of second order ODEs in a surprising way showing that Douglas “got it wrong” but in dimension 2 this is immaterial. We also give a comprehensive treatment of the hard case where some eigenspaces of the Jacobi endomorphism are integrable and some are not.

Plaats: room C, S22
Organisator: Tom Mestdag
Datum: 23/6/2016
Tijd: 10:30

On various aspects of Stein's method: quantitative approximation for stochastic limit theorems

Verdediging van de masterproef

On various aspects of Stein's method: quantitative approximation for stochastic limit theorems

door Arne Gouwy. Promotor: Christophe Ley.
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 20/6/2016
Tijd: 14:00

Surjecties in lokaal convexe ruimtes

Verdediging van de masterproef

Surjecties in lokaal convexe ruimtes

door Lenny Neyt. Promotor: Hans Vernaeve.
Plaats: S22, C
Organisator: Opleiding Wiskunde
Datum: 20/6/2016
Tijd: 11:00

Automatisch bepalen van de similariteitsrelatie in vaagruwverzamelingenleer

Verdediging van de masterproef

Automatisch bepalen van de similariteitsrelatie in vaagruwverzamelingenleer

door Elke Roelandts. Promotor: Chris Cornelis.
Plaats: S9, zaal Turing
Organisator: Opleiding Wiskunde
Datum: 20/6/2016
Tijd: 10:30

Representations of C*-algebras

Verdediging van de masterproef

Representations of C*-algebras

door Astrid Massé. Promotoren: Paolo Boggiatto en Hans Vernaeve.
Plaats: Universiteit van Turijn
Organisator: Opleiding Wiskunde
Datum: 16/6/2016
Tijd: 11:30

Reverse mathematics of the Browder-Göhde-Kirk fixed point theorem

Verdediging van de masterproef

Reverse mathematics of the Browder-Göhde-Kirk fixed point theorem

door Robin Vandaele. Promotoren: Paul Shafer en Andreas Weiermann.
Plaats: S22, C
Organisator: Opleiding Wiskunde
Datum: 14/6/2016
Tijd: 18:00

Hedging of swaptions in a Lévy-driven Heath-Jarrow-Morton model

Verdediging van de masterproef

Hedging of swaptions in a Lévy-driven Heath-Jarrow-Morton model

door Joni Goossens. Promotor: Michèle Vanmaele.
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 14/6/2016
Tijd: 17:00

Van copula tot risico

Verdediging van de masterproef

Van copula tot risico. Algoritmen voor het numeriek berekenen van de verdeling van een som van kansvariabelen met copulagemodelleerde afhankelijkheid.

door Hans Van Eetvelde. Promotor: David Vyncke.
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 14/6/2016
Tijd: 11:30

Implementation, validation and comparison of different algorithms to solve the Bateman equations for very large systems

Verdediging van de masterproef

Implementation, validation and comparison of different algorithms to solve the Bateman equations for very large systems

door Maren Vranckx. Promotor: Marnix Van Daele.
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 14/6/2016
Tijd: 10:45

Utility based risk measures

Verdediging van de masterproef

Utility based risk measures

door Jasmine Maes. Promotor: David Vyncke.
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 14/6/2016
Tijd: 10:00

Studie van CP-methoden voor Sturm-Liouville problemen

Verdediging van de masterproef

Studie van CP-methoden voor Sturm-Liouville problemen

door Rebekka Moyson. Promotor: Marnix Van Daele.
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 13/6/2016
Tijd: 14:00

Finite geometry and graph theory intertwine: Turán numbers

Verdediging van de masterproef

Finite geometry and graph theory intertwine: Turán numbers

door Sam Mattheus. Promotor: Leo Storme.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 13/6/2016
Tijd: 13:00

Codes from finite planes

Verdediging van de masterproef

Codes from finite planes

door Arne Botteldoorn. Promotor: Leo Storme.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 13/6/2016
Tijd: 11:00

Intuïtionistische representatie van toonhoogtes, met didactische component

Verdediging van de masterproef

Intuïtionistische representatie van toonhoogtes, met didactische component

door Hannah Peersman. Promotoren: Bart Van Gasse en Hendrik Van Maldeghem.
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 9/6/2016
Tijd: 11:00

Topologische eigenschappen in selectieve universa

Verdediging van de masterproef

Topologische eigenschappen in selectieve universa

door Charlotte Deconinck. Promotor: Hans Vernaeve.
Plaats: S22, C
Organisator: Opleiding Wiskunde
Datum: 7/6/2016
Tijd: 16:00

Een brug tussen incidentiemeetkunde, grafentheorie en onderwijs

Verdediging van de masterproef

Een brug tussen incidentiemeetkunde, grafentheorie en onderwijs

door Katrijn Vandewalle. Promotor: Hendrik Van Maldeghem.
Plaats: S25, Emmy Noether
Organisator: Opleiding Wiskunde
Datum: 3/6/2016
Tijd: 14:00

Tensor Representations of the Orthosymplectic Lie Superalgebra

Verdediging van de masterproef

Tensor Representations of the Orthosymplectic Lie Superalgebra

door Sam Claerebout. Promotor: Hendrik De Bie.
Plaats: Technicum, zaal Van Bladel
Organisator: Opleiding Wiskunde
Datum: 25/5/2016
Tijd: 11:30

Logic & Analysis seminar: Astrid Massé

Speaker:
Astrid Massé, UGent

Title:
Representations of C^*-algebras

Abstract:
The aim of this seminar is to develop the basic theory of Banach- and C^*-algebras and their representation as a subalgebra of L(H), the C^*-algebra of bounded operators on a Hilbert space H. We cover among other things the Gelfand representation of a commutative Banach algebra and the fact that this extends to an isometric isomorphism for commutative C^*-algebras. This implies the functional calculus and spectral theorem for self-adjoint operators on a Hilbert space. We further discuss operators on Banach and Hilbert spaces and pay special attention to compact and Fredholm operators. The representation of C^*-algebras as a subalgebra of the space of bounded operators on a Hilbert space is examined, including the Gelfand-Naimark-Segal construction. We conclude with a short notion of compactifications and non-commutative topology.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 18/5/2016
Tijd: 11:30

Logic & Analysis seminar: Djordje Vuckovic

Speaker:
Djordje Vuckovic, UGent

Title:
Rotation invariant ultradistributions

Abstract:
In this talk we will prove that an ultradistribution is rotation invariant if and only if it coincides with its spherical mean. For it, we study the problem of spherical representations of ultradistributions on R^n. Our results apply to both the quasianalytic and the non-quasianalytic case.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 11/5/2016
Tijd: 11:30

Logic & Analysis seminar: Ben De Bondt

Speaker:
Ben De Bondt, UGent

Title:
Exploring the higher infinite: the smaller large cardinals

Abstract:
The study of so-called large cardinal axioms lies close to the beating heart of modern set theory. In this humble introduction, we study cardinal numbers at the basis of the large cardinal hierarchy. As it turns out, a mutual comparison is possible. We discuss several principles that allow us to define such cardinals, their origins ranging over combinatorics, model theory and analysis.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 4/5/2016
Tijd: 11:30

Logic & Analysis seminar: Charlotte Deconinck

Speaker:
Charlotte Deconinck, UGent

Title:
Topological properties in selective universes and a nonstandard uniform boundedness principle

Abstract:
Most models for nonstandard analysis, introduced by A. Robinson, are constructed with ultrafilters. Some properties of these ultrafilter models depend on the specific kind of ultrafilter that is used to construct the model. Models of big cardinality have been thoroughly studied, but in this talk we will take a look at models of low cardinality, constructed by selective ultrafilters. We will show how an ultrafilter model for nonstandard analysis is constructed, give the definition and some properties of a selective ultrafilter and go through results of selective universes, leading to a nonstandard uniform boundedness principle.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 27/4/2016
Tijd: 11:30

Logic & Analysis seminar: Jasson Vindas

Speaker:
Jasson Vindas, UGent

Title:
Complex Tauberian theorems for Laplace transforms and power series

Abstract:
Complex Tauberian theorems for Laplace transforms and power series have shown to be strikingly useful tools in diverse areas of mathematics such as number theory and spectral theory for differential operators. Many developments in complex Tauberian theory from the last three decades have been motivated by applications in operator theory and semigroups.

In this talk we will give an overview of recent developments in the area. We will focus on two important groups of statements, usually labeled as Fatou-Riesz theorems and Wiener-Ikehara theorems. To motivate the study of these results, we present quick deductions (via Tauberian theorems) of the prime number theorem and the Katznelson-Tzafriri theorem for power-bounded operators.

An attractive feature of Tauberian theorems is that their statements can be understood and directly applied by non-specialists. So students and non-analysts are also welcome to this talk.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 20/4/2016
Tijd: 11:30

Logic & Analysis seminar: Arno Pauly

Speaker:
Arno Pauly, ULB

Title:
What does computing with analytic functions mean?

Abstract:
In a constructive setting, there is a difference between "an analytic function" and "a continuous function that is not not analytic." We will detail both notions within the framework of computable analysis and characterize precisely how much of a difference there is. The same treatment can be done with other function classes, e.g. bounded support and Schwartz functions. The abstract is based on joint work with Florian Steinberg (http://arxiv.org/abs/1512.03024).

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 13/4/2016
Tijd: 11:30

Logic & Analysis seminar: Paul Shafer

Speaker:
Paul Shafer, UGent

Title:
Reverse mathematics, well-quasi-orders, and Noetherian spaces

Abstract:
A quasi-order Q induces two natural quasi-orders on P(Q), but if Q is a well-quasi-order, then these quasi-orders need not necessarily be well-quasi-orders. Nevertheless, Goubault-Larrecq showed that moving from a well-quasi-order Q to the quasi-orders on P(Q) preserves well-quasi-orderedness in a topological sense. Specifically, the upper topologies of the induced quasi-orders on P(Q) are Noetherian, which means that they contain no infinite strictly descending sequences of closed sets. In this talk, we explain Goubault-Larrecq's results and analyze their logical strengths.

This is joint work with Emanuele Frittaion, Matt Hendtlass, Alberto Marcone, and Jeroen Van der Meeren.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 6/4/2016
Tijd: 11:30

Logic & Analysis seminar: Lenny Neyt

Speaker:
Lenny Neyt, UGent

Title:
Acyclic (LF)-spaces

Abstract:
The general solvability of partial differential or convolution equations over certain spaces depends on the surjectivity of the corresponding operator. In the case of (LF)-spaces, such as the space of test functions, the question of being surjective is closely related to the concept of acyclicness, a notion that stems from homology.

In the first part of this talk, I will discuss the foundations of the theory and its connections. In the second part, I will introduce several useful regularity properties and discuss how they are equivalent to acyclicness in the case of regular (LF)-spaces and the case of (LFM)-spaces.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 30/3/2016
Tijd: 11:30

Logic & Analysis seminar: Gregory Debruyne

Speaker:
Gregory Debruyne, UGent

Title:
Remainders in the prime number theorem for generalized primes

Abstract:
The analytic proofs of remainder versions of the prime number theorem can be split in two big parts. The first part consists of showing suitable information on the zeta function, typically the absence of zeroes in a certain region, while the second part consists of translating that information to get the desired conclusion. For the second part, one can use Tauberian theory, and some useful theorems in this context will be discussed. For the first part, we will discuss some classical methods showing that the Riemann zeta function has no zeroes in certain regions, and we will indicate how they can be applied in the context of generalized primes.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 23/3/2016
Tijd: 11:30

Logic & Analysis seminar: David Fernández-Duque

Speaker:
David Fernández-Duque, IRIT (Toulouse) and ITAM (Mexico City)

Title:
Transfinite reflection principles and subsystems of second-order arithmetic

Abstract:
If T is a formal theory, local reflection over T is the scheme that states that if A is a theorem of T, then A must be true. More generally, uniform reflection allows parameters in A and states that if T proves A(n*), where n* is the numeral of n, then A(n) must hold. A classic result of Kreisel and Lévy states that Peano arithmetic is equivalent to primitive recursive arithmetic (PRA) together with the uniform reflection scheme for PRA.

In this talk, we will discuss extensions of this result to some of the 'big five' theories of reverse mathematics. To be precise, we will define reflection principles for variants of omega-logic with oracles. Then, we show that both the theory ATR_0 of arithmetical transfinite recursion and Pi^1_1-CA_0 of comprehension for Pi^1_1 formulas are equivalent to versions of these reflection principles over a weak base theory.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 18/3/2016
Tijd: 10:00 - 12:00

Debate: Facing the facts for a better world

In a world eager for information, the public and hence the media cares more for anecdotes than for carefully gathered evidence it seems. One episode of violence towards women in Koln does more to change awareness than 50.000 cases of domestic violence reported in Belgium per year. Should it? How are the numbers in the wake of the refugee crisis presented and what are the consequences? Today, carefully gathered statistics fall additionally into the shadows of sexy `big data analytics’. Whilst leading companies invest in data and technology to improve the health of their business, we wonder whether the health of society and indeed our personal health is best served by slow and careful science or fast and broad but personalized big data. What can drive meaningful changes for a healthy, prosperous and caring society? Where should academia and governance invest?

Join the debate with two honorary doctors 2016 and experts:

Prof. Michael Marmot, epidemiologist
Prof. Louise Ryan, biostatistician
A corona of experts including Peter Diggle, president of the Royal Statistical Society (UK)
Admission is free of charge, but registration requested.

http://www.cvstat.ugent.be/index.php?page=honorarydoctor/home.php

Plaats: Auditorium Quetelet, Tweekerkenstraat
Organisator: Els Goetghebeur
Datum: 17/3/2016
Tijd: 18:30

Peter Diggle - a Data Science for the 21st Century

The rise of data science could be seen as a potential threat to the long-term status of the statistics discipline. I first argue that, although there is a threat, there is also a much greater opportunity to re-emphasize the universal relevance of statistical methods to the interpretation of data, and I give a short historical outline of the increasingly important links between statistics and information technology. The core of the paper is a summary of several recent research projects, through which I hope to demonstrate that statistics makes an essential, but incomplete, contribution to the emerging field of ‘electronic health’ research. Finally, I offer personal thoughts on how statistics might best be organized in a research-led university, on what we should teach our students and on some issues broadly related to data science where the Royal Statistical Society can take a lead.​

Plaats: Campus Ledeganck (Aud 5)
Organisator: Els Goetghebeur
Datum: 17/3/2016
Tijd: 17:00

Louise Ryan (Honorary Doctor) - Statistics and Big data

The advent of the big data era is bringing about massive changes in the way that analysts access data. In particular, researchers are increasingly reliant on the
use of administrative data, for example, disease registry data. In this talk, I will discuss some of the emerging new technologies for distributed data analysis,
including the so called "divide and recombine" strategy that can be implemented in systems such as Tessera. We will also
talk about implications for privacy preservation and confidentiality protection using data collected from the Australian census and also from the Department of Health.

Plaats: Campus Ledeganck, Aud 5
Organisator: Els Goetghebeur
Datum: 16/3/2016
Tijd: 11:30

Logic & Analysis seminar: Colin Rittberg

Speaker:
Colin Rittberg, VUB

Title:
A set-theoretic argument for a metaphysical debate

Abstract:
In recent years, some philosophers have understood that mathematics is a human activity. These philosophers have shifted their focus onto the philosophical investigation of mathematical practices. The mathematical practice investigated in this talk is set theory. I present some new set-theoretic results by Hugh Woodin and show how Peter Koellner connects these to a metaphysical debate some set theorists are currently having. This shows that mathematics can be set up to produce arguments in a metaphysical debate without overstepping its disciplinary boundaries, which reveals a connectedness between mathematics and philosophy.

The currently accepted axioms of set theory, ZFC, are formally incomplete; there are set-theoretic statements which can neither be proven nor disproven from ZFC. Some set theorists, the non-pluralists, hold that there is a unique background concept of set. For them, formal incompleteness shows a poverty of our current set-theoretic methods of discovery and they are looking to extend ZFC by new axioms which could resolve some of the incompleteness issues. The pluralists on the other hand argue that there is no such unique background concept of set; set-hood is relative to the set-theoretic model under consideration. The pluralism/non-pluralism debate is thus a debate about the metaphysical nature of sets.

Woodin has recently presented a family of axioms, each of which could, if accepted, resolve the incompleteness issue. This would be a victory for non-pluralism. Woodin has proposed a method to choose amongst these axioms. Koellner connects this method to the pluralism/non-pluralism debate in such a way that doing more mathematics generates an argument for this debate. Mathematics is set up to exert pull on the metaphysical debate.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 9/3/2016
Tijd: 11:30

Logic & Analysis seminar: Andreas Weiermann

Speaker:
Andreas Weiermann, UGent

Title:
Analytic combinatorics of the transfinite

Abstract:
I am going to survey how analytic methods can be used in studying interesting properties of ordinals. Possible applications concern logical limit laws and phase transitions for Gödel incompleteness. Since no proofs will be given the talk should be accessible to any student of mathematics.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 3/3/2016
Tijd: 13:00

Logic & Analysis seminar: André Nies

Speaker:
André Nies, University of Auckland

Title:
Analysis, reverse mathematics, and randomness

Abstract:
Recent research shows new connections between all three fields. We study the strength of Jordan's theorem that every bounded variation function is the difference of two non-decreasing functions. Depending on whether continuity is required for all functions or not, this is equivalent to arithmetic comprehension, or weak König's lemma. In the second part of the talk we look at the strength of randomness existence axioms (such as weak weak König's lemma) and their connections to differentiability of real functions.

This is joint with Keita Yokoyama (JAIST/Berkeley) and Marcus Triplett (Auckland).

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 2/3/2016
Tijd: 11:30

Logic & Analysis seminar: Andreas Debrouwere

Speaker:
Andreas Debrouwere, UGent

Title:
On the-non triviality of certain classes of Gelfand Shilov type. Fourier ultrahyperfunctions of fast growth.

Abstract:
The test function space of Fourier ultrahyperfunctions (in one dimension) consists of entire functions that decay faster than e^(-k|z|) on each strip |Im z| < k for each k > 0. We are interested in the following generalization: let M be a non-decreasing positive function defined on the positive half-axis, e.g. the associated function of a weight sequence Mp. Denote as U_M the space of of entire functions that decay faster than e^(-M(k|z|)) on each strip |Im z| < k for each k > 0. We obtain analytic representations of elements of the dual space U’_M and provide an edge of the wedge type theorem. By using these results we show that the space U_M is non-trivial if and only if the weight function M grows slower than e^(kt) on the positive half-axis for each k > 0.

In this talk we shall explain the general notion of analytic representations and edge of the wedge type theorems and comment on the aforementioned results.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 26/2/2016
Tijd: 16:00

Seminar by Jeffrey De Fauw - Research Engineer at Google DeepMind

When I was studying mathematics here at UGent less than two years ago, I was fascinated almost solely with the most abstract subjects within algebra. Now, I work as a research engineer at Google DeepMind where I focus mostly on applied mathematics. In this talk I hope to give you an honest insight into this apparent transition and talk about some problems I find interesting in machine learning / statistics. The talk should be accessible to most audiences.

Plaats: De Sterre, S9, A3
Organisator: Stijn Vansteelandt
Datum: 24/2/2016
Tijd: 11:30

Logic & Analysis seminar: Bruno Bauwens

Speaker:
Bruno Bauwens, Research University Higher School of Economics

Title:
Uniform van Lambalgen's theorem fails for computable randomness

Abstract:
Van Lambalgen's criterion for a notion of randomness states that the following should be equivalent:

- A sequence is random.
- The odd bits of the sequence are random and the even bits are random relative to the odd bits.

Martin-Lof randomness is perhaps the most popular notion of randomness used among researchers and satisfies this criterion. A few years ago, I gave a tutorial on Martin-Lof randomness where we proved this result.

In this talk I will consider a more intuitive notion of randomness, called computable randomness. A sequence is computably random if there exists no computable betting strategy for which the capital grows unbounded along the sequence.

It was believed for a long time that van Lambalgen's criterion was satisfied for computable randomness (with the uniform version of relative randomness). Some years ago, Jason Rute pointed out an error in the argument. In this talk I prove that van Lambalgen's criterion does not hold, and the argument turns out to be surprisingly simple!

Plaats: S22, Auditorium A
Organisator: Paul Shafer
Datum: 17/2/2016
Tijd: 11:30

Logic & Analysis seminar: Paul Shafer

Speaker:
Paul Shafer, UGent

Title:
Reverse mathematics and the strong Tietze extension theorem

Abstract:
We survey versions of the Tietze extension theorem formulated in second-order arithmetic and show that a certain uniformly continuous version is equivalent to WKL_0 over RCA_0, which confirms a conjecture of Giusto and Simpson.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 10/2/2016
Tijd: 11:30

Logic & Analysis seminar: Quentin Brouette

Speaker:
Quentin Brouette, UMons

Title:
Differential Galois theory, from Picard-Vessiot extensions to strongly normal extensions.

Abstract:
I will give an introduction to Picard-Vessiot theory and its generalization developed by Kolchin: the theory of strongly normal extensions. I will state a natural analog of Galois correspondence for strongly normal extensions whose constant field is algebraically closed. I will explain why this correspondence does not occur when the field of constants is not algebraically closed: a simple counterexample will be provided. This talk will be accessible to a large audience.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 28/1/2016
Tijd: 16:00

Algoritmen voor symbolische sommatie van reeksen met hypergeometrische termen

Verdediging van de masterproef

Algoritmen voor symbolische sommatie van reeksen met hypergeometrische termen

door Elias Theuwissen. Promotor: Joris Van der Jeugt.
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 13/1/2016
Tijd: 14:00 - 18:00

Workshop on Functional Analysis

We will have series of lectures on functional analysis:

Hans Vernaeve
Microlocal analysis in algebras of generalized functions using nonstandard principles

Jasson Vindas
Translation-invariant spaces of distributions

Bojan Prangoski
Pseudodifferential operators

Andreas Debrouwere
Sheaves of quasianalytic ultradistributions

Dorde Vuckovic
Ultradistributional boundary values of harmonic functions on the sphere

Gregory Debruyne
A distributional approach to the Wiener-Ikehara theorem with remainder

Plaats: Aud. C, S22
Organisator: Jasson Vindas
Datum: 13/1/2016
Tijd: 11:30

Logic & Analysis seminar: Bojan Prangoski

Speaker:
Bojan Prangoski, Ss. Cyril and Methodius University of Skopje

Title:
Parametrices and convolution in quasianalytic classes of Gelfand-Shilov type

Abstract:
We construct a special class of ultrapolynomials and use them to construct parametrices in generalized Gelfand-Shilov spaces that have as special cases the Fourier hyperfunctions and Fourier ultra-hyperfunctions. We apply them in the study of topological and structural properties of several quasianalytic spaces of functions and ultradistributions. As a consequence, we develop a convolution theory for quasianalytic ultradistributions of Gelfand-Shilov type.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 17/12/2015
Tijd: 10:00

Some stability results in Hamiltonian systems

Eduardo Garcia-Torano Andres (Universidad Nacional del Sur, Argentina) will give a talk in the 'Differential Geometry and Mechanics Seminar'. This talk will be accessible to non-specialists and students. Everyone is cordially invited!

Abstract: The main aim of this talk is to introduce the Energy-Casimir method in Hamiltonian mechanics. This is an extension of the classical Lagrange-Dirichlet stability criterion which finds its main application in the analysis of the "steady states" (the so-called relative equilibria) of the system. We will apply it to study the stability of the rigid body.

Plaats: leszaal C, S22
Organisator: Tom Mestdag
Datum: 16/12/2015
Tijd: 11:30

Logic & Analysis seminar: Dorde Vuckovic

Speaker:
Dorde Vuckovic, UGent

Title:
Eigenfunction expansions of ultradifferentiable functions and ultradistributions in R^n

Abstract:
We obtain a characterization of S^{M_p}_{M_p}(R^n) and S^(M_p)_(M_p)(R^n), the general Gelfand-Shilov spaces of ultradifferentiable functions of Roumieu and Beurling type, in terms of decay estimates for the Fourier coefficients of their elements with respect to eigenfunction expansions associated to normal globally elliptic differential operators of Shubin type. Moreover, we show that the eigenfunctions of such operators are absolute Schauder bases for these spaces of ultradifferentiable functions. Our characterization extends earlier results by Gramchev, Rodino and Pilipović for Gevrey weight sequences. It also generalizes to R^n recent results by Dasgupta and Ruzhansky which were obtained in the setting of compact manifolds.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 9/12/2015
Tijd: 11:30

Logic & Analysis seminar: Leo Storme

Speaker:
Leo Storme, UGent

Title:
The use of group theory to help break the Enigma machine

Abstract:
The Enigma machine was the encryption device used by the German army during the Second World War. In this talk, I will describe how some ideas and techniques arising from group theory were used to help break the code of the Enigma machine. I will also talk about some historic facts about the Enigma machine, and make some links to the movie The Imitation Game.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 8/12/2015
Tijd: 11:30

Logic & Analysis seminar: Robin Vandaele

Speaker:
Robin Vandaele, UGent

Title:
Reverse mathematics: Brouwer's fixed-point theorem on the unit square

Abstract:
Over RCA_0 it is possible to prove Brouwer's theorem that any continuous function from the unit interval [0,1] to itself has a fixed point. However, when we look at the same theorem where the domain is given by [0,1]^n (n > 1), this theorem becomes equivalent to WKL_0 over RCA_0. Brouwer's theorem can be further generalized to the convex hull of a nonempty finite set of points in R^n, which can also be proven to be equivalent to WKL_0 over RCA_0. We shall stick to the proof of the equivalence where the domain in Brouwer's theorem is given by the unit square [0,1]^2.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 26/11/2015
Tijd: 14:30

Voordracht Wil Schilders

Platform Wiskunde Nederland en PR voor wiskunde
Prof. dr. W.H.A. (Wil) Schilders, directeur PWN

Donderdag 26 november 2015 om 14u30 S9, lokaal V3

In 2010 werd het Platform Wiskunde Nederland opgericht teneinde de positie van de wiskunde in Nederland te verbeteren. De oprichting van PWN is ingegeven door het feit dat de zichtbaarheid van wiskunde als zelfstandige discipline verbetering behoeft, op allerlei terreinen. Daarnaast is er de duidelijke wens om te komen tot één enkel gezicht voor de wiskunde dat de gehele beroepsgroep in Nederland vertegenwoordigt. Het platform beoogt te komen tot de versterking van de financiële, bestuurlijke, wetenschappelijke en publicitaire positie van de wiskunde in Nederland, evenals de coherente en effectieve inzet van middelen ten behoeve van het wiskundeonderzoek en wiskundeonderwijs, zowel in wetenschappelijk als in maatschappelijk opzicht. Een en ander dient te worden bereikt door het bestuur, het bureau, en 5 commissies welke zich bezighouden met verschillende deelaspecten: onderzoek, onderwijs, innovatie, publiciteit en publicaties.
Inmiddels bestaat het platform 5 jaar, en is er veel bereikt. In het jaar 2014 werd de zogenaamde 3-trapsraket gelanceerd, bestaande uit een visiedocument (Formulas for Insight and Innovation, Mathematical Sciences in the Netherlands 2025), het Deloitte-rapport (Mathematical sciences and their value for Dutch economy) en het schitterende boek "Succesformules" waarvan bijna 10000 exemplaren zijn verspreid.
Een en ander heeft geleid tot de opdracht van het ministerie van Onderwijs, Cultuur en Wetenschappen om een commissie in te richten welke een plan zou maken om de in het visiedocument genoemde actielijnen uit te werken. Inmiddels is dit "Deltaplan voor de Nederlandse wiskunde" gereed, en zal binnenkort aangeboden worden bij het ministerie.
Een en ander leidt inmiddels ook tot een forse toename van het aantal eerstejaars wiskundestudenten, zowel binnen het wetenschappelijk als het hoger onderwijs (bedrijfswiskunde). Was er in 2003 nog een absoluut dieptepunt van 200 eerstejaars in het gehele land, recent hebben we een persbericht doen uitgaan waarin we melding maken van het feit dat de grens van meer dan 1000 eerstejaars is overschreden.
In de voordracht zal, nadat eerst kort is ingegaan op PWN als geheel, vooral ingegaan worden op de publicitaire acties welke zijn ondernomen om wiskunde als discipline een verbeterd imago te geven, zowel bij het grote publiek, leerlingen als binnen het bedrijfsleven.

Plaats: S9, lokaal V3
Organisator: OCW
Datum: 9/11/2015
Tijd: 10:00

Overbodige ongelijkheden, inbeddingen, en uiterste grafen

De voordracht wordt gegeven door Bart Demoen (KUL)

In een combinatorisch probleem komt het vaak voor dat een aantal beperkingen weggelaten of toegevoegd kunnen worden
zonder de oplossingsruimte te veranderen. Zulke beperkingen zijn bijgevolg overbodig. De aanwezigheid van overbodige
beperkingen heeft invloed op de performantie van oplossingsalgoritmen, mogelijk in beide richtingen. Dezelfde
problematiek bestaat ook bij het kleuren van grafen, en voor problemen met enkel onge\-lijkheden zijn die twee equivalent.

Resultaten i.v.m. overbodige ongelijkheden worden getoond in de context van Sudoku, het Latijnse
Vierkant en het Latijnse Bord: een volledige klassificatie van alle ongelijkheden voor de eerste twee werd bekomen. Er
wordt even ingegaan op het probleem van het inbedden van een Latijns Bord in een Latijns Vierkant. Daarna wordt het
probleem van het bestaan van een kleuring-overbodige boog in een graaf behandeld: de grootste en kleinste grafen met een
bepaald aantal knopen worden bepaald.

Plaats: leszaal 0.A gebouw S12
Organisator: WE02
Datum: 4/11/2015
Tijd: 11:30 - 12:30

Logic & Analysis seminar: Gregory Debruyne

Speaker:
Gregory Debruyne, UGent

Title:
A PNT equivalence for Beurling prime numbers

Abstract:
In classical prime number theory, several asymptotic relations are considered to be equivalent with the prime number theorem. However, for Beurling prime numbers, this is no longer the case and often extra conditions on the number system have to be imposed to show the equivalence between two of those asymptotic relations. In this talk, we will investigate conditions under which the so-called "sharp Mertens relation" is equivalent with the PNT. The proof that will be presented relies heavily on a Tauberian theorem and we will take the opportunity to explain why these kinds of theorems are of such importance in prime number theory.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 28/10/2015
Tijd: 11:30 - 12:30

Logic & Analysis seminar: Jasson Vindas

Speaker:
Jasson Vindas, UGent

Title:
Some points on the integration theory for functions of one real variable. A general integration theory.

Abstract:
The purpose of this talk is two-folded. On the one hand, we will make a historical tour on integration theory for functions of one real variable. We will discuss various weak points of the Lebesgue integral and how they motivated the construction of the so-called non-absolute integrals, namely, alternative (and more general) integration theories by, e.g., Denjoy, Perron, and Henstock-Kurzweil. We will also explain the main features of these classical integration theories. On the other hand, we will present the construction of a new integral in the second part of the talk, the distributional integral, that is more general than the Lebesgue and the Denjoy-Perron-Henstock-Kurzweil integrals, and which also allows the integration of functions with distributional values everywhere or nearly everywhere.

The distributional integral still has many of the useful properties of the standard integrals, including integration by parts formulas, substitution formulas, even for infinite intervals --in the Cesàro sense--, mean value theorems, and convergence theorems. The distributional integral satisfies a version of Hake's theorem.

The talk is based on collaborative work with R. Estrada.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 21/10/2015
Tijd: 11:30

Logic & Analysis seminar: Stéphane Le Roux

Speaker:
Stéphane Le Roux, ULB

Title:
Infinite subgame perfect equilibrium in the Hausdorff difference hierarchy

Abstract:
This talk is at the intersection of game theory and descriptive set theory, but most of it can be understood without prior knowledge in these fields. Subgame perfect equilibria are specific Nash equilibria in perfect information games in extensive form. They are important because they relate to the rationality of the players. They always exist in infinite games with continuous real-valued payoffs, but may fail to exist even in simple games with slightly discontinuous payoffs. This talk is considering only games whose outcome functions are measurable in the Hausdorff difference hierarchy of the open sets (i.e. Delta^0_2 when in the Baire space), and it characterizes the families of linear preferences such that every game using these preferences has a subgame perfect equilibrium: the preferences without infinite ascending chains (of course), and such that for all players a and b and outcomes x,y,z we have not z <_a y <_a x and x <_b z <_b y.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 19/10/2015
Tijd: 10:30 - 17:30

Getaltheorie in het Vlakke Land

Vijf voordrachten met een getaltheoretische inslag. Zie deze website voor abstracts en meer details. Iedereen is welkom (maar registratie via de website is gewenst)!

10u30 - 11u30: Linear algebra with errors, coding theory, cryptography and Fourier analysis on finite groups door Steven Galbraith (Auckland)

11u30 - 12u30: Variations on quadratic Chabauty door Jennifer Balakrishnan (Oxford)

(middageten)

14u00 - 15u00: Chebychev's bias for elliptic curves over function fields door Florent Jouve (Parijs)

15u00 - 16u00: Real points of small height and the André-Oort conjecture door Martin Orr (Londen)

(koffiepauze)

16u30 - 17u30: On the (linear) MDS conjecture door Jan De Beule (Gent)

(diner)

Plaats: Auditorium Emmy Noether (S25)
Organisator: Wouter Castryck, Leo Storme
Datum: 14/10/2015
Tijd: 11:30

Logic & Analysis seminar: Hans Vernaeve

Speaker:
Hans Vernaeve, UGent

Title:
Distribution theory for model theorists

Abstract:
The creation of a rigorous theory of mathematical analysis using infinitesimal quantities (Abraham Robinson, 1960) has given mathematicians the possibility to (re)develop parts of analysis in the spirit of the founders of analysis, but no longer on shaky foundations. In this talk, we show how in this framework theorems in analysis can be proved using functions with infinitesimal and infinitely large values, whereas classically more abstract constructs like Schwartz distributions are required.

Plaats: S22, Auditorium C
Organisator: Paul Shafer
Datum: 7/10/2015
Tijd: 11:30 - 12:30

Logic & Analysis seminar: Andreas Debrouwere

Speaker:
Andreas Debrouwere, UGent

Title:
On the non-triviality of test function spaces in the theory of ultradistributions

Abstract:
In this talk I address the problem of non-triviality of spaces consisting of ultradifferentiable functions which are the analogue of the test function spaces \mathcal{D} and \mathcal{S} in the theory of distributions as introduced by L. Schwartz.

Plaats: S22 Auditorium C
Organisator: Paul Shafer
Datum: 8/9/2015
Tijd: 12:00

Spectrum van een graaf

Verdediging van de masterproef

Spectrum van een graaf: Eigenschappen met behulp van de (Laplaciaanse) eigenwaarden van een graaf

door Matthias Peulders. Promotor: Hendrik Van Maldeghem.
Plaats: S22
Organisator: Opleiding Wiskunde
Datum: 3/9/2015
Tijd: 11:00

Een studie van reguliere schier veelhoeken met behulp van algebraïsche combinatoriek

Verdediging van de masterproef

Een studie van reguliere schier veelhoeken met behulp van algebraïsche combinatoriek

door Dries Hoste. Promotor: Bart De Bruyn.
Plaats: S22, A
Organisator: Opleiding wiskunde
Datum: 26/6/2015
Tijd: 15:00

Hedging and pricing of life insurance portfolios

Verdediging van de masterproef

Hedging and pricing of life insurance portfolios

door Hélène De Coninck. Promotor: Michèle Vanmaele.
Plaats: S9, V3
Organisator: Opleiding wiskunde
Datum: 26/6/2015
Tijd: 14:30

Optieprijzen en verzekeringspremies via Esschertransformaties

Verdediging van de masterproef

Optieprijzen en verzekeringspremies via Esschertransformaties

door Lieselot Vanslembrouck. Promotor: Michèle Vanmaele.
Plaats: S9, V3
Organisator: Opleiding wiskunde
Datum: 23/6/2015
Tijd: 14:00

Exponentieel gefitte methoden voor het oplossen van differentiaalvergelijkingen

Verdediging van de masterproef

Exponentieel gefitte methoden voor het oplossen van differentiaalvergelijkingen

door Arne Naert. Promotor: Marnix Van Daele.
Plaats: S9, V2
Organisator: Opleiding wiskunde
Datum: 22/6/2015
Tijd: 15:30

Groepen en meetkundes gerelateerd aan gebouwen

Verdediging van de masterproef

Groepen en meetkundes gerelateerd aan gebouwen

door Anneleen De Schepper. Promotor: Hendrik Van Maldeghem.
Plaats: S25, Emmy Noether
Organisator: Opleiding wiskunde
Datum: 22/6/2015
Tijd: 14:00

Eigenschappen en axioma's van de E6 meetkunde

Verdediging van de masterproef

Eigenschappen en axioma's van de E6 meetkunde

door Magali Victoor. Promotor: Hendrik Van Maldeghem.
Plaats: S25, Emmy Noether
Organisator: Opleiding wiskunde
Datum: 19/6/2015
Tijd: 14:30

On Fourier coefficients of certain mock-modular forms

Verdediging van de masterproef

On Fourier coefficients of certain mock-modular forms

door Wouter van de Vijver. Promotor: Pierre Charollois.
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 16/6/2015
Tijd: 15:00

Meetkundige constructies van twee-karakterverzamelingen

Verdediging van de masterproef

Meetkundige constructies van twee-karakterverzamelingen

door Lieve Vandewalle. Promotor: Jan De Beule.
Plaats: S22
Organisator: Opleiding wiskunde
Datum: 16/6/2015
Tijd: 11:00

Aspects of the Finslerian geometry behind Lagrangian systems

Talk by Tom Mestdag in the "Differential Geometry and Mechanics Seminar". Everyone is cordially invited!

Plaats: room A, S22
Organisator: Tom Mestdag
Datum: 15/6/2015
Tijd: 13:00

Afgeleide representatieschema's

Verdediging van de masterproef

Afgeleide representatieschema's

door Jens Hemelaer. Promotor: Koen Thas.
Plaats: nog te bepalen
Organisator: Opleiding wiskunde
Datum: 15/6/2015
Tijd: 11:00

De reconstructie van een tijdsafhankelijke convolutiekern in een semilineaire parabolische integraal-differentiaal vergelijking

Verdediging van de masterproef

De reconstructie van een tijdsafhankelijke convolutiekern in een semilineaire parabolische integraal-differentiaal vergelijking

door Fien Gistelinck. Promotor: Marian Slodicka.
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 12/6/2015
Tijd: 14:30

Vezelbundels en connecties: met didactische vertaling

Verdediging van de masterproef

Vezelbundels en connecties: met didactische vertaling

door Lisa Lampo. Promotor: Frans Cantrijn.
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 10/6/2015
Tijd: 11:00

Improving report retrieval through automatically generated keywords

Verdediging van de masterproef

Improving report retrieval through automatically generated keywords

door Silke Govaert. Promotor: Arnout Van Messem.
Plaats: S9, V2
Organisator: Opleiding wiskunde
Datum: 10/6/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Dorde Vuckovic

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!


Speaker:
Dorde Vuckovic

Title:
Ultradistributional boundary values of harmonic functions on the sphere

Abstract :
In this talk we will present a theory of ultradistributional boundary values of harmonic functions on the unit sphere $S^{n-1}$ of $\mathbb{R}^{n}$. In connection with this boundary value problem, we will also discuss a characterization of ultradifferentiable functions and ultradistributions on the unit sphere in terms of the growth of the norms of their projections onto spaces of spherical harmonics.These results are based on precise estimates for partial derivatives of spherical harmonics, which are of independent interest.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 9/6/2015
Tijd: 14:00

Een studie van reguliere schierveelhoeken met behulp van algebraïsche combinatoriek

Verdediging van de masterproef

Een studie van reguliere schierveelhoeken met behulp van algebraïsche combinatoriek

door Dries Hoste. Promotor: Bart De Bruyn.
Plaats: S22, A
Organisator: Opleiding wiskunde
Datum: 9/6/2015
Tijd: 12:00

Exponential-fitting-methoden

Verdediging van de masterproef

Exponential-fitting-methoden

door Elien Vandensteen. Promotor: Marnix Van Daele.
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 9/6/2015
Tijd: 11:20

Gestructureerde populatiemodellen

Verdediging van de masterproef

Gestructureerde populatiemodellen

door Nina Keersmaekers. Promotor: Willy Govaerts.
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 9/6/2015
Tijd: 10:40

Populatiedynamica van interagerende soorten

Verdediging van de masterproef

Populatiedynamica van interagerende soorten

door Sieglinde Callewaert. Promotor: Willy Govaerts.
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 9/6/2015
Tijd: 10:00

Numerieke methoden voor het oplossen van randwaardeproblemen

Verdediging van de masterproef

Numerieke methoden voor het oplossen van randwaardeproblemen

door Lien Gillis. Promotor: Marnix Van Daele.
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 9/6/2015
Tijd: 10:00

Van gesloten tot gelocaliseerde verzamelingen in rekenkunde van de tweede orde

Verdediging van de masterproef

Van gesloten tot gelocaliseerde verzamelingen in rekenkunde van de tweede orde

door Steven Van den Bulcke. Promotor: Hans Vernaeve.
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 4/6/2015
Tijd: 11:00

Torsion and the second fundamental form for distributions

Prof Geoff Prince (Australian Mathematical Sciences Institute) will give a talk in the 'Differential Geometry and Mechanics Seminar'. Everyone is cordially invited!

Abstract: The second fundamental form of Riemannian geometry is generalised to the case of a manifold with a linear connection and an integrable distribution. This bilinear form is generally not symmetric and its skew part is the torsion. The form itself is closely related to the shape map of the connection.

Plaats: zaal A, S22
Organisator: Tom Mestdag
Datum: 3/6/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Andreas Weiermann

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!


Speaker: Andreas Weiermann

Title: Goodstein sequences: How to fight against iterated exponentials

Abstract:
We discuss Abrusci style variants of the classical Goodstein sequences.
Given a natural number m we define by recursion on the natural
number k a natural number m_k which
incorporates two processes. One is based
on exponentiation (which makes m_{k+1} usually much bigger then m_k)
and the other consists in subtracting a one.

Computer simulation will indicate that the sequence m_k diverges
quickly to infinite. We will show that the sequence m_k
surprisingly converges to zero.

Our construction provides a further natural example for Gödel incompleteness
of Peano arithmetic.

Plaats: S22, aud C
Organisator: Seminarie Logica en Analyse
Datum: 29/5/2015
Tijd: 17:00

Doctoraatsverdediging Jeroen Van der Meeren - Connecting the Two Worlds: Well-partial-orders and Ordinal Notation Systems

Indien u de aansluitende receptie wenst bij te wonen, gelieve een mail te sturen naar jeroen.vandermeeren@ugent.be voor vrijdag 22 mei.


Samenvatting:
Goede partiële ordeningen worden gebruikt in informatica, bewijstheorie, algebra, combinatoriek, etc. Ordinaal notatiesystemen worden gebruikt in bewijstheorie om grote ordinaal getallen te beschrijven op een natuurlijke manier. Ordinaal notatiesystemen geven aanleiding tot het beschrijven van één van de belangrijkste karakteristieken van een formele theorie, het bewijstheoretisch ordinaalgetal.

In dit proefschrift bestuderen we het verband tussen de werelden van goede partiële ordeningen en ordinaal notatiesystemen. Meer specifiek karakteriseren we Friedman’s ordeningen van bomen met gap-conditie in termen van ordinaal notatiesystemen.

Promotor: Prof. Dr. Andreas Weiermann
Examencommissie: Prof. Dr. Marnix Van Daele (voorzitter), Prof. Dr. Lev Gordeev, Prof. Dr. Michael Rathjen, Prof. Dr. Monika Seisenberger, Dr. Paul Shafer, Prof. Dr. Leo Storme, Prof. Dr. Jasson Vindas.

Plaats: S25, Emmy Noether
Organisator: Jeroen Van der Meeren
Datum: 29/5/2015
Tijd: 10:00

New progress in the inverse problem of the calculus of variations

Thoan Do (La Trobe University, Melbourne) will give a talk in the 'Differential Geometry and Mechanics' seminar. Everyone is cordially invited!

Abstract: We present a new class of solutions for the inverse problem in the calculus of variations in arbitrary dimension n. This is the problem of determining the existence and uniqueness of Lagrangians for systems of n second order differential equations. We also provide a number of new theorems concerning the inverse problem using exterior differential systems theory. Our new techniques provide a significant advance in the understanding of the inverse problem in arbitrary dimension and, in particular, how to generalise Jesse Douglas's famous solution for n = 2. We give some non-trivial examples in dimensions 2,3 and 4. We give a new classification scheme for the inverse problem in arbitrary dimension.

Plaats: zaal A, S22
Organisator: Tom Mestdag
Datum: 29/5/2015
Tijd: 10:00 - 13:00

Mini-Workshop on Logic

You are all cordially invited!



10u00 - 11u00:
Speaker: Michael Rathjen (University of Leeds)
Title: Remarks on geometric theories.
Abstract:
A famous theorem of Barr's yields that geometric implications deduced in classical (infinitary) geometric theories also have intuitionistic proofs. Barr's theorem is of a category-theoretic (or topos-theoretic) nature. In the literature (e.g. in P. Johnstone's "Sketches of an elephant") one finds mysterious comments about the involvement of the axiom of choice. In the talk I'd like to speak about the proof-theoretic side of Barr's theorem and aim to shed some light on the AC part.

11u00 - 12u00:
Speaker: Monika Seisenberger (Swansea University)
Title: Programs from Proofs.
Abstract:
We give an overview on the current state of art in program extraction from proofs by means of examples from sat solving and ongoing work in monadic parsing and infinite combinatorics.

12u00 - 13u00:
Speaker: Lev Gordeev (guest-professor Ghent University)
Title: On Harvey Friedman's Finite Phase Transitions.
Abstract:
We give explicit and intriguing examples for finite phase transitions.

Plaats: Emmy Noether, S25
Organisator: Seminarie Logica en Analyse
Datum: 28/5/2015
Tijd: 17:00

Doctoraatsverdediging Korneel Debaene

Promovendus Korneel Debaene verdedigt zijn doctoraatsproefschrift getiteld "Analytic Estimates of Class Numbers and Relative Class Numbers".

Plaats: Emmy Noether, S25
Organisator: Korneel Debaene
Datum: 28/5/2015
Tijd: 14:00

Seminarie Algebra

Speaker: Douglas Peter Overholser (KU Leuven)

Title: Tropical geometry, enumeration, and mirror symmetry

Abstract: During the 1980's, physicists predicted the existence of pairs of Calabi-Yau manifolds related by a delicate duality. This relationship came to be known as mirror symmetry, and was used to give enumerative predictions (counts of curves) that stunned mathematicians. We will discuss this history in some detail and show how parts of mirror symmetry can be understood in terms of tropical geometry, the study of certain piecewise linear objects.
Plaats: S22 Aud. C
Organisator: Wouter Castryck
Datum: 27/5/2015
Tijd: 10:00

Extensions of the inverse problem of the calculus of variations

Marta Farre Puiggali (ICMAT, Madrid) will give a talk in the 'Differential Geometry and Mechanics' seminar. Everyone is cordially invited!

Abstract: The inverse problem of the calculus of variations consists in determining whether a system of second order differential equations is equivalent to the Euler-Lagrange equations for some regular Lagrangian. I will show a characterization of this problem which is easily extended to include constrained systems, in particular nonholonomic systems, discrete systems, that is, second order difference equations, and second order differential systems on Lie algebroids.

Plaats: zaal A, S22
Organisator: Tom Mestdag
Datum: 30/4/2015
Tijd: 14:00

Seminarie Algebra

Speaker: Lore Kesteloot (KU Leuven)

Title: Rational points and the specialization index

Abstract:

In this talk, we will study the existence of rational points on varieties. A rational point corresponds to a zero of a set of polynomials. We will give a historical introduction to a specific problem on rational points: the C1 conjecture.

Next, we will look at the index of a variety. This index is equal to one if the variety has a rational point, but the converse is not necessarily true. We introduce a new invariant, the specialization index, that will contain more useful information about rational points.
Plaats: S22 Aud. C
Organisator: Wouter Castryck
Datum: 29/4/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Jeroen Van der Meeren

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!


Speaker:
Jeroen Van der Meeren

Title:
Applications of well-quasi-order-theory in mathematics and proof theory

Abstract:
The talk consists of two parts.
In the first part, we survey some examples and applications of well-quasi-orders in mathematics. E.g. in algebra, graph theory, computer science,…
In the second part, we discuss how one can use well-quasi-orders to construct natural examples of statements unprovable in some well-known formal theories.

The talk is also open to students.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 20/4/2015
Tijd: 16:00

Coloring graphs without long induced paths

Everybody is cordially invited!

Speaker:
Dr. Oliver Schaudt, University of Cologne, Germany

Title:
Coloring graphs without long induced paths

Abstract:
The complexity of coloring graphs without long induced paths is a notorious problem in algorithmic graph theory. An especially intriguing case is that of 3-colorability. Here, the state of the art is our recent poly-time algorithm to solve the problem on graphs without induced paths on seven vertices, so-called P_7-free graphs.

So far, much less was known about certification in this context.
We prove that there are 24 minimally non-3-colorable graphs in the class of P_6-free graphs, and give the complete list. In particular, we obtain a certifying algorithm for 3-coloring graphs in this class.

We also show that our result is best possible, in the following sense. If H is a connected graph that is not an induced subgraph of P_6, then there are infinitely many minimally non-3-colorable H-free graphs.

This is joint work with:

Flavia Bonomo, Maria Chudnovsky, Peter Maceli, Maya Stein, and Mingxian Zhong

resp.

Maria Chudnovsky, Jan Goedgebeur, and Mingxian Zhong

Plaats: S9, leszaal V2
Organisator: Jan Goedgebeur
Datum: 1/4/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Andreas Debrouwere

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!


Speaker:
Andreas Debrouwere

Title:
VARIOUS WAYS OF DEFINING THE SPACE OF DISTRIBUTIONS

Abstract:
Schwartz introduced the space of distributions as the dual of some topological vector space. Although very powerful, the theory of topological vector spaces is not well known to non-analysists. In this talk we present two other ways of defining the space of distributions and hope to give a more intuitive picture of what these objects are. We first follow Silva's axiomatic approach and then express the space of distributions as a quotient space of certain classes of holomorphic functions. Finally, we discuss how one can define objects more general then distributions, so called ultradistributions.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 25/3/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Bruno Bauwens

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!


Speaker:
Bruno Bauwens

Title:
The computational difficulty of data compression and the power of a few random bits.
(Joint work with Marius Zimand.)

Abstract:
Let C(x) denote the Kolmogorov complexity, i.e. the optimal compression length of a bitstring x. It is shown that some natural data-compression task can not be solved by an algorithm whose running time is bounded by a computable function. At the same time, this task can be solved by a probabilistic polynomial time algorithm that uses a few random bits. (This result is unrelated to the BBP=P problem.) More precisely, we show that there exists a probabilistic algorithm that on input (x, C(x)) computes in polynomial time with probability 0.99 a program for x of length C(x) + O(log^2 x). However, any deterministic algorithm that on input (x, C(x)) computes a program p for x of length at most C(x) + o(l(x)), must have a computation time that exceeds any computable function. We will briefly present the proof of an easier and similar result by reducing it to a combinatorial problem (matching and online matching in bipartite graphs), which can be solved using techniques from the literature.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 18/3/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Andreas Weiermann

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!

Speaker:
Andreas Weiermann

Title:
Een ordinaalsystem voor $\epsilon_0$ steunend op oneindig veel kardinaalgetallen.

Abstract:
We bespreken een zeker ordinaal notatie systeem dat niet triviaal op oneinding veel kardinaalgetallen steunt.
We tonen aan dat het een verrassend kleine ordeningtype heeft als men de optellingsfunctie uit de constructie verwijdert.
(Open for students who know ordinals)

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 11/3/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Jasson Vindas

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!


Speaker: Jasson Vindas (Ghent University)

Title:
On the Stieltjes moment problem

Abstract:
In its basic form, the Stieltjes moment problem consists of finding solutions g to

a_n= \int_{0}^{\infty} g(x)x^n dx, n\in\mathbb{N},

where (a_n) is a given sequence of complex numbers.


In this talk we shall discuss an abstract approach to moment problems via functional analysis techniques. We will replace the sequence of monomials (x^n) involved in Stieltjes' classical problem by a rather arbitrary sequence of continuous linear functionals (f_n) in a Frechet space, and study conditions on the Frechet space that ensure the solvability of any general "Stieltjes moment problem" with respect to (f_n), that is, the infinite system of equations

\left\langle f_n,g \right\rangle= a_n, n\in\mathbb{N}.

We will illustrate our ideas with several examples and applications to classical moment problems.

Students welcome!

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 4/3/2015
Tijd: 19:00

Wiskundigen aan het werk

Vier alumni spreken over hun werkervaringen:

Céline Balliu: Head of Product Development Professionals and Small Enterprises Life Insurance, AG Insurance
Bart De Coninck: Afdelingshoofd Organisatiebeheer Eandis
Koen De Naeghel: Leerkracht Onze-Lieve-Vrouwecollege Assebroek
Filip Pynckels: Directeur-Generaal ICT, FOD Binnenlandse Zaken en President eu-LISA

Plaats: S25, Emmy Noether
Organisator: QED / PRIME
Datum: 4/3/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Paul Shafer

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!


Speaker: Paul Shafer (Ghent University)

Title:
Computability: from Turing to today

Abstract:
We survey Alan Turing's foundational work in computability theory and its development into a major branch of mathematical logic.
(Open for students!)

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 25/2/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Andreas Weiermann

Als je graag op de e-maillijst staat waardoor je automatisch uitnodigingen krijgt voor het Seminarie Logic en Analyse, gelieve een mail te sturen naar jvdm@cage.ugent.be


Everyone welcome!


Speaker: Andreas Weiermann

Title: Boolean basics

Abstract:
We bespreken een elementaire opgave over propositielogica uit het boek
The Art of Computer Programming deel 4 van Don Knuth.
Indien we niets over het hoofd zien is de opgave
fout voor n=1 maar wel correct voor n>1.
Deze voordracht vereist geen voorkennis.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 10/2/2015
Tijd: 10:00 - 11:00

Seminarie Logica en Analyse: Ivan Dimitrov Georgiev

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Everyone welcome!


Speaker:
Ivan Dimitrov Georgiev (Bulgaria)

Title:
Subrecursive computability in Analysis

Abstract:
The talk concerns computability of real numbers and functions from the point of view of complexity theory. We will compare the representations of real numbers by convergent sequences of rationals and by continued fractions. We will discuss the complexity of the elementary functions of calculus.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 19/12/2014
Tijd: 15:00

A refined boundedness theorem

Title: A refined boundedness theorem
Spreker: Robin Vandaele

It is shown that the order type of an arithmetically
definable well ordering
for which its well orderedness can be proven in an
infinitary system with height alpha does not exceed alpha.
This result (by Beckmann) can be used to classify
the provable well orderings of the fragments of PA.

Plaats: S25 Emmy Noether
Organisator: Andreas Weiermann
Datum: 19/12/2014
Tijd: 13:00

How to characterize provably total functions by local predicativity

Title: How to characterize provably total functions by local predicativity

Spreker: Steven Van den Bulcke

Abstract: It is shown that every provably total function of PA is eventually majorized
by a function of the Hardy hierarchy of level less than epsilon_0.

Plaats: S25 Emmy Noether
Organisator: Andreas Weiermann
Datum: 18/12/2014
Tijd: 11:15

Global convergence for inverse problems and phaseless inverse problems


Speaker

Michael V. Klibanov
Department of Mathematics and Statistics
University of North Carolina at Charlotte
U.S.A.


Abstract

In this talk three topics will be discussed. Corresponding papers were published in 2008-2014, also see www.arxiv.org. These topic are:
1. A globally convergent numerical method of the first type for coefficient inverse problems with single measurement data. Both the theory and numerical results will be presented. Numerical results will be focused on the most challenging case of blind backscattering experimental data for buried targets.
2. A globally convergent numerical method of the second type type for coefficient inverse problems will be presented. This method is based on the construction of a globally strictly convex cost functional. The key element of this functional is the Carleman Weight Function.
3. The first solution of a long standing problem (since 1977). This is uniqueness of the 3-d coefficient inverse scattering problem in the case when only the modulus of the complex valued scattering wave field is measured, whereas the phase is unknown. In quantum inverse scattering only the differential cross-section is measured, which means the modulus. On the other hand, the entire theory of quantum inverse scattering is constructed for the case when both the modulus and phase of the scattering wave field are measured.

Plaats: Galglaan 2, S22, Auditorium C
Organisator: Marian Slodicka
Datum: 18/12/2014
Tijd: 10:30

Numerical Method for solving an boundary value inverse heat conduction problem


Speaker:
Natalia Yaparova
Department of Applied Mathematics
South Ural State University (National Research University)
Russia

Abstract

In this talk two different approaches based on the Laplace and Fourier transforms will be discussed. Corresponding papers were published in 2013-2014.
Application of the Laplace transform makes it possible to obtain an integral equation describing the explicit dependence of the unknown boundary value function on the initial data at the other boundary. Regularization methods are then used to solve this equation. This eliminates the unstable procedure of numerical inversion of the Laplace transform in the computational process. The proposed method was used in a computational experiment to obtain a numerical solution of the inverse problem. Experimental error estimates of the obtained solutions show sufficient stability of these solutions.
The approach based on the projection regularization method for the direct and inverse Fourier transforms with respect to the time variable provides regularized solutions with guaranteed accuracy. The estimation of errors of these solutions are the exact with respect to the order. This property provided the basis for comparative analysis of the solutions obtained by the Laplace and Fourier transform methods.
The proposed methods were employed to carry out a computational experiment. The objectives of this experiment were to test effectiveness of the proposed approaches and to evaluate the errors of the regularized solutions provided by each approach. The computational results confirm the stability of the solutions obtained by these methods.

Plaats: Galglaan 2, S22, Auditorium C
Organisator: Marian Slodicka
Datum: 17/12/2014
Tijd: 11:30 - 12:30

Seminarie Logica en Analyse: Jeroen Van der Meeren

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Everyone welcome!


Speaker:
Jeroen Van der Meeren

Title:
Reverse mathematics of gap-sequences

Abstract:
If one goes from a normal embeddability relation to a gap-embeddability relation on a structure, one creates a stronger notion of well-partial-orderings. For example, the well-partial-orderedness of sequences with the normal (=Higman) embeddability relation is provable in PA (which is normal arithmetic), but the well-partial-orderedness of sequences with the gap-embeddability relation is not.
This is a known result from a proof-theoretical point of view.
In this talk, we will investigate the reverse mathematical approach: we study the reverse mathematical strength of a statement concerning sequences on natural numbers with this gap-embeddability relation.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 10/12/2014
Tijd: 11:30 - 12:30

Seminarie Logica en Analyse: Gregory Debruyne

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Everyone welcome!


Speaker:
Gregory Debruyne

Title:
Some examples in the theory of Beurling's generalized numbers

Abstract:
In the theory of Beurling primes several conditions on the counting function of the generalized integers have been shown to imply the prime number theorem. Generally an example of a Beurling prime number system is needed when one wants to show that the conditions are sharp or that one theorem does not imply the another.

Several examples will be presented and in a bit more detail a recently discovered example showing that the theorem of Schlage-Puchta and Vindas is not a special case of the theorem of Kahane, will be discussed.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 3/12/2014
Tijd: 11:30 - 12:30

Seminarie Logica en Analyse: Jasson Vindas

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Everyone welcome!


Speaker:
Jasson Vindas

Title:
Asymptotic distribution of Beurling's generalized prime numbers

Abstract:
This talk is a survey on classical and recent results concerning the asymptotic distribution of generalized prime numbers.

The goal of Beurling's generalized prime number theory is to replace the ordinary prime numbers by a rather arbitrary non-decreasing sequence of positive real numbers (generalized primes), consider then the multiplicative semigroup generated by it (generalized integers), and then establish relations between asymptotic properties of the counting functions of generalized primes and integers.

We will discuss various mild conditions that ensure the validity of the prime number theorem in this context. In particular, we shall present the solution of a problem that was recently posed by Gabor Halasz to the speaker.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 26/11/2014
Tijd: 11:30 - 12:30

Seminarie Logica en Analyse: Ludovic Patey (Université Paris Diderot)

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Everyone welcome!


Speaker:
Ludovic Patey (Université Paris Diderot)

Title:
On universal instances of theorems in reverse mathematics.

Abstract:
Many theorems of ordinary mathematics can be seen as problems, with a natural class of instances and, for each instance, a collection of solutions. For example, in König's lemma, which states that every infinite, finitely branching tree has an infinite path, an instance is an infinite, finitely branching tree T and a solution to T is an infinite path through T.

A theorem admits a universal instance U if for every instance X and every solution to U, U computes a solution to X. A few theorems are known to admit a universal instance (e.g., König's lemma and the rainbow Ramsey theorem). Many other theorems do not have universal instances. This is for example the case with the Ramsey theorem for pairs and the ascending descending sequence theorem. In this talk, we will present different proof techniques for proving the presence or absence of universal instances for ranges of theorems.

Plaats: S22, aud C
Organisator: Seminarie Logica en Analyse
Datum: 25/11/2014
Tijd: 15:00

Seminarie Algebra

Diophantine equations and local-global methods
by Arne Smeets (KU Leuven / Univ. Lille 1)

Plaats: UGent, S22, vergaderzaal
Organisator: Wouter Castryck
Datum: 21/11/2014
Tijd: 13:00

So what is a tangent vector?

Talk by Prof David Saunders (University of Ostrava, Czech Rep) in the 'Differential Geometry and Mechanics Seminar'. This talk does not require much background and is therefore accessible for non-specialists and students. Everyone is cordially invited!

Title: So what is a tangent vector?

Abstract: When we think of surfaces in Euclidean space, we imagine a tangent vector as an `arrow' in a plane touching the surface at some point. Although this picture gives us a good geometrical intuition, it cannot be used for a definition when we have a differentiable manifold given in abstract, as a topological space with a family of smoothly compatible charts.

Fortunately differential geometry is a generous subject, and offers us three completely different definitions of a tangent vector: the classical definition, the algebraic definition, and the geometrical definition. These definitions are (usually!) equivalent. In the same way there are three definitions of a cotangent vector, again (usually) equivalent. In this talk I shall examine the three approaches, and show how they are related.

Plaats: Zaal A, S22
Organisator: Tom Mestdag
Datum: 19/11/2014
Tijd: 11:30 - 12:30

Seminarie Logica en Analyse: Andreas Debrouwere

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Everyone welcome!



Speaker:
Andreas Debrouwere

Title: Wave Fronts via Fourier Series Coefficients

Abstract:
In this talk it will be explained how discretized characterizations of various types of wave fronts can be obtained. The idea is to study microlocal properties at x_0 of a distribution f through the Fourier series expansion of the periodization of some suitable localization of f around x_0.

Plaats: S22, aud C
Organisator: Seminarie Logica en Analyse
Datum: 12/11/2014
Tijd: 13:00

2014 Fields Medallists Symposium

Op 13 augustus 2014 werden de winnaars van de Fields Medaille bekend gemaakt op het International Congress of Mathematicians in Seoul, Zuid-Korea. Met dit symposium willen we alle wiskundigen en geinteresseerden in Belgie informeren over de wiskunde en de wiskundigen aan wie deze prestigieuze prijzen werden uitgereikt.
Er wordt verzocht op voorhand te registreren.
Plaats: Paleis der Academiën, Brussel
Organisator: Belgisch Wiskundig Genootschap & Nationaal Comite voor Wiskunde
Datum: 5/11/2014
Tijd: 11:30 - 12:30

Seminarie Logica en Analyse: Korneel Debaene

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Iedereen welkom!



Speaker:
Korneel Debaene

Title : Dimensions of the irreducible representations of $A_n$ and $S_n$

Abstract : In this talk the speaker will describe his proof of a conjecture concerning the irreducible representations of $A_n$ and $S_n$, namely the statement that their sets of dimensions are different for $A_n$ and $S_n$. Due to the celebrated correspondence between irreducible representations and integer partitions, the proof is fairly elementary. The main ingredient is a result on "large" prime factors in "short" intervals. One part of the proof is theoretical and another part relies on computer verification.

Plaats: S22, aud C
Organisator: Seminarie Logica en Analyse
Datum: 29/10/2014
Tijd: 11:30 - 12:30

Seminarie Logica en Analyse: Andreas Weiermann

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Everyone welcome!



Speaker:
Andreas Weiermann

Title: Binary trees and ordinals

Abstract: We prove in an elementary way a claim of Harvey M. Friedman
about the connection of binary trees and ordinals that are relevant for Peano Arithmetic (joint work with Floris Van Vugt)

Plaats: S22, aud C
Organisator: Seminarie Logica en Analyse
Datum: 22/10/2014
Tijd: 11:30 - 12:30

Seminarie Logica en Analyse: Paul Shafer

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Speaker:
Paul Shafer
Ghent University
Paul.Shafer@UGent.be
http://cage.ugent.be/~pshafer/

Title:
Exploring randomness, diagonally non-recursiveness, and Ramsey-type combinatorial principles in reverse mathematics

Abstract:
This is joint work with Laurent Bienvenu (LIAFA, Paris 7) and Ludovic Patey (PPS, Paris 7).

Stephen Flood introduced Ramsey-type weak König's lemma (RWKL), a simultaneous weakening of weak König's lemma (WKL) and Ramsey's theorem for pairs and two colors. An instance of RWKL is an infinite binary branching tree T, and a solution to this instance is not an infinite path through T as with WKL, but an infinite set consistent with being a path through T. Among several results, Flood proved that RWKL implies DNR, but he left open whether or not the reverse implication holds.

Motivated by Flood's question of whether or not DNR implies RWKL, we introduced Ramsey-type variations of other consequences of WKL and studied their relationships with DNR. Specifically, we studied RSAT, a Ramsey-type variant of the Boolean satisfiability problem (i.e., compactness in propositional logic); RWWKL, a Ramsey-type variant of weak weak König's lemma (WWKL); and RCOLOR(k), a Ramsey-type variant of the fact that every locally k-colorable graph is k-colorable. We found that RSAT is equivalent to RWKL and that RWWKL is equivalent to DNR (the latter equivalence reflecting results of Kjos-Hanssen and of Greenberg and Miller). We also proved that there is a recursive instance of RCOLOR(2) such that the measure of oracles that compute solutions to the instance is zero. It follows that WWKL does not imply RCOLOR(2). Combining this result with the well-known fact that WWKL implies DNR and the fact that RWKL implies RCOLOR(2) answers Flood's question: DNR does not imply RWKL.

Plaats: S22, aud C
Organisator: Seminarie Logica en Analyse
Datum: 30/9/2014
Tijd: 14:30 - 15:30

Polyhedra in biology

In biology, symmetric structures are common, as few instructions are sufficient for self-assembly.
In mathematics, examples of highly symmetric structures include some convex equilateral poly-
hedra Platonic, Archimedean and rhombic and helices. Many of these are found in biology,
including some viruses and protein complexes with icosahedral symmetry, the ferritin cage with
octahedral symmetry, and some viruses as well as DNA with helical symmetry. However, in
geometry, the word polyhedron requires planar faces. Thus, some structures in biology and
chemistry including large fullerenes, the clathrin cages responsible for endocytosis in cells,
and some viruses too have nonplanar faces and are simply cages. However, some cages with
nonplanar faces can be converted to polyhedra. The di fference, cage versus polyhedron, may
have functional consequences.

Plaats: Auditirium A0, S9
Organisator: Gunnar Brinkmann
Datum: 27/8/2014
Tijd: 11:00

The reverse mathematics of inductive inference

Speaker:
Rupert Hölzl
National University of Singapore

Title:
The reverse mathematics of inductive inference.

Abstract:
(Joint work with F. Stephan and S. Jain.)

It is a widespread intuition among mathematicians to think of certain theorems as stronger or
weaker versions of other theorems. Of course, strictly speaking, all true theorems are logically
equivalent, so at first sight it might not be obvious how one would go about formalizing this
intuition. In the 1970’s, Friedman proposed a way of making this formalization and thereby
inspired a new way to look at mathematics. He suggested to study classical mathematical
theorems and their relations by analysing how they mutually imply each other over
weak logical systems. Over such systems it then becomes meaningful to discuss whether
theorems are equivalent, imply each other, and so on. This approach has been used to study
and classify theorems from many areas of mathematics.

In this talk, we will discuss recent work that applies the reverse mathematics method to the
field of Inductive Inference. This field deals with the ability of machines or algorithms to learn
objects when provided with partial information about these objects. We will look at a number
of classical results in this area, in particular results by Angluin, and analyse them using the
methodology of reverse mathematics. In particular we will identify two different weak logical
systems and study in what situations, depending on the different learning environments, they
are sufficient to permit learning, and in what situations they are not.

Plaats: S25, Emmy Noether
Organisator: Seminarie Logica en Analyse
Datum: 22/8/2014
Tijd: 14:00

NUMERICAL SOLUTIONS OF THE INVERSE PROBLEM OF PHARMACOKINETICS

The talk will be delivered by
Voronov Dmitriy Andreevich
(Novosibirsk State University, Russia)

Abstract:

Pharmacokinetics deals with kinetics of absorption, distribution, metabolism and excretion of drugs and their corresponding pharmacologic, therapeutic or toxic responses in man and animals.
What happens to the drug in the body can be visualized by considering the body as being made up of a large number of compartments, each of which has a volume where the drug is well mixed. Drug is then transferred between these compartments, either transported by the blood from one to another, or by passing an interior membrane in some body organ.
We can visualize this whole process as a dynamic system described by a system of ordinary differential equations.
Parameter identifiability analysis for dynamic system ODE models addresses the question of which unknown parameters can be quantifies from given input-output data. The linear compartment models that we focus on in this report are never identifiable, except in the trivial case of a model with only one compartment. This forces us to look for identifiable reparametrization of our model. In this report we consider scaling reparametrization that is obtained by replacing an unobserved variable by a scaling version of itself, and updating coefficients accordingly.
In real life we determine a series of time points at which blood samples are taken and plasma concentrations are measured. Here inverse problem arises: it is required to find rate constants (entries of matrix) knowing concentration of a drug at the given moments of a time in one compartment. The quality of those data depends on our choice of time points. An inappropriate choice may make up miss the peak concentration or we may not have sampled long enough to obtain a good estimate of the rate constants. It is demonstrated that the resolving ability of the inverse problem can be improved by varying of the location of measurement data points. The Frechet derivative matrix was constructed.
Different types of three-compartment models with central elimination and two-compartment model with extravascular drug administration with absorption are covered in this report. Also an algorithm for solving inverse problem in case of n-compartment is covered in this report.
Inverse problem is solved by different algorithms: Landweber iterations method, Newton-Kantorovich method and Singular Value Decomposition. The question of choosing initial approximations is covered in this report. It is shown that physical properties of initial approximations strongly affect on obtained solutions. The results of numerical experiments are presented.

Plaats: Galglaan 2, S22, Auditorium C
Organisator: Marian Slodicka
Datum: 7/7/2014
Tijd: 14:00

Chromatic Number of Euclidean Spaces

In 1950, Edward Nelson posed the following problem:

How many colors are required to color the plane
so that no two points at unit distance have the same
color?

The problem was eventually discovered and popularized
by Paul Erdoes who offered $1000 for a solution.

The chromatic number of a metric space S (denoted chi(S))
is the minimum number of
colors needed to color the points of the space so that no two
points at unit distance are the same color.
So Nelson was asking for chi(R^2).
It is not difficult to show that 4 <= chi(R^2) <= 7.
However, beyond this, no progress has been made in more than 50 years.

More recently, generalizations of the problem have been extensively studied for
n-dimensional Euclidean, spherical, and hyperbolic spaces.
In this talk, we will survey the history of the general problem, report on
some new results for R^n and Q^n, and discuss a number of open
geometric, combinatorial, and computational problems.

Plaats: S9, V1
Organisator: Gunnar Brinkmann
Datum: 2/7/2014
Tijd: 10:30

Feedbackbeurs

Aansluitend op de proclamatie is er feedback voorzien op de examens van het tweede semester, in het bijzonder voor de eerste en tweede jaren uit de bacheloropleiding. Tijdens de feedbacksessie zijn de lesgevers en/of assistenten beschikbaar om verder uitleg te geven over uw scores.

Joris Van der Jeugt, de voorzitter van de examencommissie, zal ook aanwezig zijn voor bijkomend studieadvies, eventueel meer uitleg over het examenreglement, enz.

Plaats: A3, S9
Organisator: Opleiding wiskunde
Datum: 2/7/2014
Tijd: 10:00

Proclamatie

De geslaagde studenten per deliberatiepakket (1e, 2e of 3e bachelor; 1e of 2e master) worden in volgorde van resultaat openbaar afgeroepen. De studenten die slagen voor een opleiding (bachelor of master) wordt ook een graad van verdienste toegekend.

Onmiddellijk na de proclamatie kan elke student (geslaagd, niet-geslaagd, GIT-student,…) zijn/haar puntenbriefje krijgen. Studenten die niet aanwezig kunnen zijn op de proclamatie kunnen vanaf 18.00u (2 juli) zelf hun puntenbriefje downloaden via oasis (eerder zijn de punten niet zichtbaar).

Plaats: A2, S9
Organisator: Opleiding wiskunde
Datum: 30/6/2014
Tijd: 9:00

Statistische analyse van de impact van fluid overload op sterfte bij intensieve zorgen patienten

Masterproefverdediging Nele De Soete

Plaats: De Sterre, S9, V3
Organisator: Opleiding Wiskunde
Datum: 26/6/2014
Tijd: 17:00

Combinatorische grondslagen van de Gebouwentheorie

Verdediging van de masterproef Combinatorische grondslagen van de Gebouwentheorie door Nigel Vinckier (promotor: Hendrik Van Maldeghem).
Plaats: S22, A
Organisator: Opleiding wiskunde
Datum: 26/6/2014
Tijd: 16:00

The quantum mechanical Segal-Bargmann transform using Jordan algebras

Verdediging van de masterproef The quantum mechanical Segal-Bargmann transform using Jordan algebras door Sigiswald Barbier (promotor: Hendrik De Bie).
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 26/6/2014
Tijd: 14:00

Convolutions of hypercomplex Fourier transforms with applications in image processing

Verdediging van de masterproef Convolutions of hypercomplex Fourier transforms with applications in image processing door Klaus Rubrecht (promotor: Hendrik De Bie).
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 26/6/2014
Tijd: 10:00

Niet-lineaire fenomenen in de economie

Verdediging van de masterproef Niet-lineaire fenomenen in de economie door Jolien Vandenameele (promotor: Willy Govaerts).
Plaats: S9, V2
Organisator: Opleiding wiskunde
Datum: 24/6/2014
Tijd: 14:00

Optimalisatie-algoritmen voor het sorteren van permutaties door omkeringen

Verdediging van de masterproef Optimalisatie-algoritmen voor het sorteren van permutaties door omkeringen door Karel Vandenbroucke (promotor: Veerle Fack).
Plaats: Krijgslaan 281-S9, leszaal V1
Organisator: Opleiding wiskunde
Datum: 23/6/2014
Tijd: 11:30

Cameron-Liebler sets and related geometrical structures

Verdediging van de masterproef Cameron-Liebler sets and related geometrical structures door Andries Vansweevelt (promotor: Leo Storme).
Plaats: S22, A
Organisator: Opleiding wiskunde
Datum: 23/6/2014
Tijd: 10:30

Algebraïsche grafentheorie: van polaire ruimten tot onderzoekend leren

Verdediging van de masterproef Algebraïsche grafentheorie: van polaire ruimten tot onderzoekend leren door Linda Van Puyvelde (promotor: Jan De Beule).
Plaats: S22, A
Organisator: Opleiding wiskunde
Datum: 20/6/2014
Tijd: 12:45

Dynamische predictie van nosocomiale infecties via landmark analyse

masterproefverdediging Lisa Vanluchene

Plaats: De Sterre, S9, V2
Organisator: Opleiding Wiskunde
Datum: 20/6/2014
Tijd: 12:00

Detectie van risicofactoren en prognose van ziekenhuisinfecties bij intensieve zorgen patienten

Masterproefverdediging David Dooms

Plaats: De Sterre, S9, V2
Organisator: Opleiding Wiskunde
Datum: 20/6/2014
Tijd: 10:15

Vaagruwverzamelingenleer in datareductie

Verdediging van de masterproef Vaagruwverzamelingenleer in datareductie: theoretische en experimentele studie van benaderende gelijkheid en didactische uitwerking van een lessenreeks door Annelies Baeyens (promotor: Chris Cornelis).
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 20/6/2014
Tijd: 9:30

Coveringgebaseerde ruwverzamelingen en hun uitbreiding naar de vaagverzamelingenleer

Verdediging van de masterproef Coveringgebaseerde ruwverzamelingen en hun uitbreiding naar de vaagverzamelingenleer door Tara Vanhecke (promotor: Chris Cornelis).
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 18/6/2014
Tijd: 18:00

Moving from Value-at-Risk to Expected Shortfall under Basel III regulatory framework

Verdediging van de masterproef Moving from Value-at-Risk to Expected Shortfall under Basel III regulatory framework door Jody Verstraeten (promotor: David Vyncke).
Plaats: S9, V3
Organisator: Opleiding wiskunde
Datum: 18/6/2014
Tijd: 17:30

Temperatuurderivaten

Verdediging van de masterproef Temperatuurderivaten door Sarah Vanhuylenbroeck (promotor: Michèle Vanmaele).
Plaats: S9, V3
Organisator: Opleiding wiskunde
Datum: 18/6/2014
Tijd: 10:00 - 11:15

Mini-course 'Differential Geometry and Mechanics'

Prof Ioan Bucataru (A.I. Cuza University, Iasi, Romania) will give a series of lectures in the 'Differential Geometry and Mechanics Seminar'. The course will be accessible for Master and Phd students. Everyone is cordially invited!

The schedule for the rest of the mini-course will be fixed by the interested participants, after the first lecture.

Abstract: I will start with a short introduction of Frolicher-Nijenhuis formalism. This formalism is very useful to develop a geometric framework for studying systems of second order ordinary differential equations (SODE). Within this framework one can approach various problems associated to a SODE, such as: the equivalence problem, stability of solutions, inverse problem of Lagrangian mechanics. I will focus on the inverse problem of Lagrangian mechanics and two of its particular cases: Finsler metrizability and projective metrizability. More exactly, I will show how to use Frolicher-Nijenhuis formalism to reformulate the classic Helmholtz conditions and how one can study their integrability. This approach can be extended to provide generalized Helmholtz conditions for Lagrangian systems with non-conservative forces.

Plaats: room C, S22
Organisator: Tom Mestdag
Datum: 17/6/2014
Tijd: 12:00

Veralgemeende stellingen van Mertens als toepassing van Tauberse stellingen

Verdediging van de masterproef Veralgemeende stellingen van Mertens als toepassing van Tauberse stellingen door Giles Miclotte (promotor: Jasson Vindas).
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 17/6/2014
Tijd: 11:00

Topological properties of the spaces of ultradifferentiable functions

Verdediging van de masterproef Topological properties of the spaces of ultradifferentiable functions door Igor Voulis (promotor: Jasson Vindas).
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 17/6/2014
Tijd: 10:00

Distributionele randwaarden van analytische functies

Verdediging van de masterproef Distributionele randwaarden van analytische functies door Andreas Debrouwere (promotor: Jasson Vindas).
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 10/6/2014
Tijd: 10:00

Symplectische connecties

Verdediging van de masterproef Symplectische connecties door Mats Dedeyne (promotor: Frans Cantrijn).
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 5/6/2014
Tijd: 14:45

Implicatoren: theorie en praktijk, met didactische vertaling

Verdediging van de masterproef Implicatoren: theorie en praktijk, met didactische vertaling door Iris Van Melkebeke (promotor: Mike Nachtegael).
Plaats: S9, V2
Organisator: Opleiding wiskunde
Datum: 5/6/2014
Tijd: 14:00

Triangulaire normen: theorie en praktijk, met didactische vertaling

Verdediging van de masterproef Triangulaire normen: theorie en praktijk, met didactische vertaling door Hannelore Verkimpe (promotor: Mike Nachtegael).
Plaats: S9, V2
Organisator: Opleiding wiskunde
Datum: 5/6/2014
Tijd: 11:00

Tauberse stellingen toegepast op de theorie van veralgemeende priemgetallen

Verdediging van de masterproef Tauberse stellingen toegepast op de theorie van veralgemeende priemgetallen door Gregory Debruyne (promotor: Jasson Vindas).
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 5/6/2014
Tijd: 11:00

Aggregatieoperatoren op eindige kettingen

Verdediging van de masterproef Aggregatieoperatoren op eindige kettingen door Caro Lievens (promotor: Glad Deschrijver).
Plaats: S9, V2
Organisator: Opleiding wiskunde
Datum: 4/6/2014
Tijd: 10:00

A new formulation of the Bianchi identities

Prof Geoff Prince (Director, Australian Mathematical Sciences Institute) will give a talk in the 'Differential Geometry and Mechanics Seminar'. Everyone is cordially invited!

Abstract: This talk is about linear connections with torsion. Motivated by the relationship between the Cartan structure equations, the Bianchi identities and the Jacobi identity, a fresh, coordinate-free, approach to the structure equations appears. I will demonstrate some of its apparent virtues and some of its mysteries. A certain intrinsic shape map plays a key role.

Plaats: room C, S22
Organisator: Tom Mestdag
Datum: 22/5/2014
Tijd: 11:00 - 12:00

Associative algebras and Lie-algebras defined by Lindon words

Voordracht door Tatyana Ivanova.

Plaats: Emmy Noether S25
Organisator: Andreas Weiermann
Datum: 21/5/2014
Tijd: 11:00 - 12:00

On index-exponent relations and Brauer $p$-dimensions of finitely-generated field extensions

Voordracht van Ivan Chipchakov

Plaats: Emmy Noether S25
Organisator: Andreas Weiermann
Datum: 20/5/2014
Tijd: 14:00

Bachelorprojecten

14:00 Thomas De Praetere (Veerle Fack)
14:25 Emiel Ergo (Veerle Fack)
14:50 Elke Roelandts (Michele Vanmaele)
15:15 Jolien Roels (Willy Govaerts)
15:50 Koen Van de Velde (Marnix Van Daele)
16:05 Jorne Biccler (Stijn Vansteelandt)

Plaats: Krijgslaan 281-S9, leszaal V1
Organisator: Docenten Toegepaste Wiskunde
Datum: 20/5/2014
Tijd: 8:30

Bachelorprojectvoorstellingen

Voorstelling van 13 bachelorprojecten. Schema:

8u30: Arne Gouwy (analyse): Compacte afbeeldingen en compacte operatoren op Hilbertruimten, vervolgens
Robin Vandaele (logica): Intuitionistische propositielogica
Michiel Van Couwenberghe (algebra): Karaktertabellen en Random Walks
Domien Craens (grafentheorie): Algebraische grafentheorie
Lenny Neyt (analyse): De stelling over Jordan-krommen
Sam Mattheus (algebra): Arithmetiek van elliptische krommen
Serge Vereecken (discrete wiskunde): Voortbrengende functies
Jorgin Herremans (logica): Martins Axioma

PAUZE/LUNCH

Astrid Masse (analyse): De Stone-Cech compactificatie van de natuurlijke getallen
Katrijn Vandewalle (grafentheorie): Critical Graphs
Tim Seynaeve (algebra): Het woordprobleem voor groepen
Hans Van Eetvelde (logica): Volledigheid van de Modale Logica
Charlotte Deconinck (analyse): Poolse ruimten

Plaats: S25, Auditorium Emmy Noether
Organisator: Docenten Analyse/Logica/Algebra/Discrete Meetkunde
Datum: 15/5/2014
Tijd: 13:00 - 17:00

Projective constructions of half spin geometries and Cartan varieties

Het betreft een self-contained laatste les van de cursus "Capita Selecta in Geometry" waarin een nieuwe en geheel meetkundige constructie uitgelegd wordt van de standaardinbeddingen van de half spin meetkundes en van de exceptionele meetkunde van type E_{61,} (de zogenaamde Cartan variëteit), over een willekeurig veld.

It concerns a self contained final session of the course "Capita Selecta in Geometry" in which a new and entirely geometric construction of the standard embeddings of the half spin geometries and of the exceptional geometry of type E_{6,1} (the so-called cartan variety) over an arbitrary field is explained.

Plaats: S22, Audotorium B
Organisator: Hendrik Van Maldeghem
Datum: 12/5/2014
Tijd: 11:30 - 12:30

Tutorial on algorithmic randomness and Kolmogorov complexity

Speaker:
Bruno Bauwens

Title:
Tutorial on algorithmic randomness and Kolmogorov complexity

Abstract:
Many definitions exist for randomness of infinite bitsequences. We
focuss on the simplest and most popular one: Martin-Lof randomness (for
uniform measure). It is given in terms of betting schemes. To
illustrate the definition, we show Van Lambalgen's theorem: a sequence
is random if and only if its odd bits are random and its even bits are
random relative to its odd bits. (I recently showed that this theorem
fails for some non-uniform measure.)

Prefix Kolmogorov complexity of a string is the minimal length of a
program that computes the string. Intuitively, a sequence is random
if the initial segments can not be compressed. We prove the coding
theorem (a very central result) and use it to prove two connections
with algorithmic randomness:
-The Martin-Lof random sequences are exactly those sequences for
which all initial segments have prefix complexity at least their length
minus a constant.
-The Martin-Lof random sequences relative to the halting problem are
exactly those sequences who have infinitely many initial segments for
which prefix-complexity is maximal up to a constant (among strings of
the same length).

I will cover less or more, depending on reactions and questions of the
audience.

Plaats: S22, aud A
Organisator: Seminarie Logica en Analyse
Datum: 12/5/2014
Tijd: 10:00 - 11:15

Phase transitions for the Pigeonhole Principle

Speaker:
Steven Van Den Bulcke

He will give a presentation about a project he did for the course Phase Transitions in the seminar of Logic and Analysis.
It is about phase transitions for the Pigeonhole Principle.

Plaats: S22
Organisator: Seminarie Logica en Analyse
Datum: 8/5/2014
Tijd: 14:00 - 16:45

Weakly increasing subsequences and a related phase transition

Speaker:
Pieter De Smet

He will give a presentation about a project he did for the course Phase Transitions in the seminar of Logic and Analysis.
It is about weakly increasing subsequences and a related phase transition.

Plaats: S22
Organisator: Seminarie Logica en Analyse
Datum: 5/5/2014
Tijd: 11:30 - 12:30

Menger's theorem in Pi^1_1-CA_0

Speaker:
Paul Shafer

Title:
Menger's theorem in Pi^1_1-CA_0

Abstract:
Let A and B be disjoint sets of vertices in a graph G. Menger's theorem states that there is a collection of disjoint paths P, each starting in A and ending in B, with a selection C of one vertex from each path in P such that removing the vertices C from the graph G disconnects A from B. Menger's theorem is a classical result for finite graphs and was first proved for countable graphs by Aharoni. The special case of Menger's theorem restricted to bipartite graphs is called König's duality theorem which, in the countable case, is equivalent to ATR_0 over RCA_0. The reversal is due to Aharoni, Magidor, and Shore, and the proof in ATR_0, which came later, is due to Simpson. We provide a proof of Menger's theorem for countable graphs in Pi_1^1-CA_0. This proof uses several metamathematical techniques, most notably that of countable coded beta-models. By general considerations, Menger's theorem cannot be equivalent to Pi_1^1-CA_0 over RCA_0. Thus Menger's theorem is at least as strong as ATR_0 and is strictly weaker than Pi_1^1-CA_0.

Plaats: S22, Aud A
Organisator: Seminarie Logica en Analyse
Datum: 28/4/2014
Tijd: 10:00 - 11:00

Effective counting of certain Cebotarev subsets of the primes

Speaker: Korneel Debaene

Title: Effective counting of certain Cebotarev subsets of the primes.

Abstract : The Cebotarev density theorem gives the asymptotic density of many subsets of primes. The shortcoming is that it gives an asymptotic result only, which we try to supplement with effective inequalities in one specific concrete family. We will describe our effort using the Selberg Sieve which we will introduce. We will aim to give many examples, and broad sketches of methods, so as not to put off those unfamiliar with the topic.

Plaats: S22, Aud A
Organisator: Seminarie Logica en Analyse
Datum: 11/4/2014
Tijd: 10:00

Optimal Portfolio: Mathematics and Economics

door Prof.dr. Tahir CHOULLI
University of Alberta, Canada

Abstract:
The two pillars of portfolio analysis founded by Markowitz and Merton
respectively will be discussed. For both contexts, the connection between the
existence of these portfolios and some economics concepts will be explained.
The mathematical formulation of these economic conditions will be detailed,
and the mathematical/statistical structures that these economics notions
induce, will be given as well. These structures allow us to better control and
quantify the impact of any extra uncertainty on the market model.
Throughout the talk, it will be highlighted how some mathematical and
statistical tools are tailor-made for some economics conditions.

Plaats: Leszaal V2, S9
Organisator: M. Vanmaele
Datum: 31/3/2014
Tijd: 10:00 - 11:00

Analytic approximations related to unordered trees and corresponding phase transition problems

Speaker: Lev Gordeev

Title: Analytic approximations related to unordered trees and corresponding phase transition problems.

Abstract:
I consider a classical problem: How many unordered trees (in particular, binary ones) of the size n don't contain a homomorphic image of a given complete tree of the height d. In each case I define the corresponding power series OGF (ordinary generating functions) and investigate its speed of convergence relative to that of basic OGF counting all trees (resp. all binary trees) of the size n.

Plaats: S22, Aud C
Organisator: Seminarie Logica en Analyse
Datum: 25/2/2014
Tijd: 14:30 - 15:30

Calculus of Variations 250 years after Lagrange: a symbiosis of algebra, analysis, geometry and physics

Talk by Prof Olga Rossi (Stockholm University & University of Ostrava) in the Colloquium of the Department of Mathematics. Everyone is cordially invited!

Abstract: The idea of using differential geometry in the calculus of variations goes back to Élie Cartan who in 1921 introduced a differential form, now called the Cartan form, to study the variational integral. The work of Cartan and his successors opened new horizons for modern developments in the calculus of variations as a mathematical discipline, with close relationships to differential geometry, the topology of smooth manifolds, global analysis, the theory of exterior differential systems and PDEs, algebraic topology and algebraic geometry. It also extended the scope of classical variational calculus: its techniques now are used beyond analytical mechanics to investigate deep theoretical issues in physics, for instance in relativity, gauge theory, string theory and geometric quantization, as well as in engineering and control theory. In this talk I will discuss the current state of the field with its challenging applications.

Plaats: Emmy Noether, S25
Organisator: Vakgroep Wiskunde
Datum: 11/2/2014
Tijd: 17:30 - 18:45

Info-uurtje programmawijziging

Het nieuwe programma van de opleiding wiskunde zal worden voorgesteld aan alle studenten en bij de opleiding betrokkenen, met aandacht voor de motivaties en overgangsmaatregelen.

Meer info volgt later.

Plaats: S9, A3
Organisator: Opleiding wiskunde
Datum: 22/1/2014
Tijd: 13:45 - 14:30

Phase transitions for Gödel incompleteness

Speaker: Andreas Weiermann

We discuss basic examples for phase transitions related
to Gödel incompleteness and Kruskal's tree theorem.
Our result improves a previous result
by Harvey M. Friedman.

Plaats: Aud. 5, Ledeganck
Organisator: Faculteit Wetenschappen
Datum: 5/12/2013
Tijd: 11:30

Dirac reduction by Lie group actions

Talk by Eduardo Garcia-Torano in the 'Differential Geometry and Mechanics' seminar. Everyone is cordially invited!

Plaats: room C, S22
Organisator: Tom Mestdag
Datum: 2/12/2013
Tijd: 14:30

Dirac structures on vector spaces, part II

Talk by Eduardo Garcia-Torano in the 'Differential Geometry and Mechanics' seminar. Everyone is cordially invited!

Plaats: room C, S22
Organisator: Tom Mestdag
Datum: 29/11/2013
Tijd: 14:30 - 15:30

Colloquium Vakgroep Wiskunde

Cameron-Liebler line classes in finite 3-dimensional projective spaces, by Prof. Dr. Klaus Metsch (Giessen).

Abstract: A spread of the finite 3-dimensional projective space PG(3,q) of order q is a set S of lines that partition the point set of the projective space; it consists of q^2+1 lines. A Cameron-Liebler line class of the projective space is a set L of lines such that every spread has the same number x of lines in common with L, and x is called the parameter of L. Cameron-Liebler line classes with parameter 0 or q^2+1 correspond to the empty set and the set of lines. An example of a Cameron-Liebler line class with parameter x=1 is the set consisting of all lines through a given point of the space. A similar construction gives examples with parameters 2, q^2-1 and q^2. A more involved example was constructed by Bruen and Drudge and has parameter x=1/2.(q^2+1) for all projective spaces PG(3,q), q odd. Though there are examples with other parameters as the ones mentioned so far, these examples are all sporadic. Research is done on the one hand to find infinite series with new parameters and on the other hand to prove non-existence criteria. The talk gives an introduction to Cameron-Liebler line classes, their basic properties, and some new results.

Plaats: Auditorium Emmy Noether
Organisator: Vakgroep Wiskunde
Datum: 28/11/2013
Tijd: 10:00

Dirac structures on vector spaces

Talk by Eduardo Garcia-Torano in the 'Differential Geometry and Mechanics' seminar. Everyone is cordially invited!

Plaats: room A, S22
Organisator: Tom Mestdag
Datum: 19/11/2013
Tijd: 11:30

Feedback stabilization of impulsive underactuated mechanical systems using Lyapunov constraints

Talk given by Mohammed Chaalal in the 'Differential Geometry and Mechanics Seminar'. Everyone is cordially invited!

Abstract: In this talk I present a new theoretical control approach for the feedback stabilization of a class of underactuated mechanical systems with impulsive effects. The approach is based on using the Lyapunov conditions for asymptotic stability as kinematic affine constraints where the corresponding constraint force is the control force. We prove that the conditions for existence and uniqueness lead to a system of nonlinear partial differential equations whose solution is the required Lyapunov function.

Plaats: room A, S22
Organisator: Tom Mestdag
Datum: 18/11/2013
Tijd: 19:00

Lezing: Hoe leid je een halve keer af?

Deze lezing door David Eelbode behandelt een eenvoudige vraag, die in essentie werd beantwoord door P. A. M. Dirac in 1928: hoe kan je de wortel uit een differentiaaloperator nemen? Dit probleem, dat verband houdt met de bewegingsvergelijking van het electron, ligt in essentie aan de basis van een volledige tak uit de analyse die gekend staat als Cliffordanalyse (waarin de UGent, onder leiding van Prof. Em. R. Delanghe, steeds een pioniersrol heeft gespeeld). De bedoeling van deze lezing is om dit onderwerp te illustreren, en te verklaren wat het verband is met dat ene cruciale begrip uit de theoretische fysica: symmetrie.

Plaats: S25, Emmy Noether
Organisator: PRIME
Datum: 29/10/2013
Tijd: 11:15 - 12:00

Classical Invariant Theory - Old and Recent

Everyone knows at least one theorem in Invariant Theory:

Every symmetric polynomial can be expressed in a unique way
as a polynomial of the elementary symmetric polynomials.

Invariant theory studies the following generalization:
Let K[X] be the polynomial algebra in d variables x_1,...,x_d over a field K
of characteristic 0. The group GL(d,K) of d x d invertible matrices
acts canonically on the vector space with basis {x_1,...,x_d}.
Then this action is extended diagonally on K[X] by the rule
g(f(x_1,...,x_d))=f(g(x_1),...,g(x_d)), where g is in GL(d,K) and f is in K[X].

For a subgroup G of GL(d,K) the algebra of G-invariants K[X]^G consists of
all f in K[X] with the property g(f)=f for all g in G.

One of the main problems of Classical Invariant Theory is the study of the algebra
of invariants for the group SL(2,K) of 2 x 2 matrices with determinant 1
acting in different ways on the d-dimensional vector space.
More generally, one considers the invariants of any reductive subgroup of GL(d,K).

The purpose of the talk is to survey some results in Classical Invariant Theory
as the problem for the finite generation of the algebras of invariants, their
explicit generators and defining relations, their Hilbert (or Poincaré) series.
The survey includes both historical overview of old results, and very recent
results obtained in the latest decade.

Plaats: S25 Emmy Noether
Organisator: Andreas Weiermann
Datum: 28/10/2013
Tijd: 19:00

Workshop Grafen & Grinvin

Linda Van Puyvelde geeft in deze workshop eerst wat uitleg over grafen en Grinvin, waarna jullie zelf aan de slag gaan met oefeningen van verschillende moeilijkheidsgraden. Deze workshop is geschikt voor beginners die (nog) niet weten wat een graaf is, maar ook voor specialisten die mee aan dit programma geschreven hebben, en alle studenten die zich ergens tussen deze twee uitersten bevinden.

Grinvin is een zeer gebruiksvriendelijk softwarepakket waarmee je grafen kunt bestuderen, hun eigenschappen (invarianten) en de relaties tussen die eigenschappen. Bovendien beschikt Grinvin over de capaciteit om vermoedens te genereren over bepaalde eigenschappen van (een lijst van) grafen. De software werd aan de UGent ontwikkeld.

Grafen Grinvin logo

Plaats: S9, PC-zaal Turing
Organisator: PRIME
Datum: 11/10/2013
Tijd: 14:00

Lezing door Dimiter Skordev: on computability in topological spaces

Title: On computability in topological spaces
Abstract: The content of the talk concerns an analog of the considerations on computability in metric spaces presented in my paper "An epsilon-delta characterization of a certain TTE computability notion"

Plaats: S22
Organisator: Logic and Analysis
Datum: 9/10/2013
Tijd: 19:00

Lezing: De Grondslagencrisis

De grondslagencrisis: over de geschiedenis en de filosofie van de wiskunde aan het begin van de twintigste eeuw.

Vele gebeurtenissen rond de eeuwwissel rond 1900 hebben de wiskunde gevormd tot wat ze nu is, van de 23 problemen van Hilbert tot de axiomatisatie van de verzamelingenleer. Doctoraatsstudent Bert Seghers vertelt op anekdotische wijze over de meest markante feiten uit die periode, met een bijzondere aandacht voor de wiskundige David Hilbert.

Deze lezing is toegankelijk voor iedereen met interesse voor de wiskunde in het algemeen.

Plaats: S9, A1
Organisator: PRIME
Datum: 7/10/2013
Tijd: 10:30

Gastvoordracht: 3D-reconstructie EIT

Talk by Prof. Cristiana Sebu (Oxford Brookes University )

Title: Sparse 3D reconstructions in Electrical Impedance Tomography using real data

Abstract:
We present a 3D reconstruction algorithm with sparsity constraints for Electrical Impedance Tomography (EIT).
EIT is the inverse problem problem of determining the distribution of conductivity in the interior of an object from simultaneous measurements of currents and voltages on its boundary. The feasibility of the sparsity reconstruction approach is tested with real data obtained from a new planar EIT device developed at the Institut of Physics, Johannes Gutenberg University, Mainz, Germany. The complete electrode model is adapted for the given device to handle incomplete measurements and the inhomogeneities of the conductivity are a priori assumed to be sparse with respect to a certain basis. This prior information is incorporated into a Tikhonov-type functional by including a sparsity-promoting l1-regularization term. The functional is minimized with an iterative soft shrinkage-type algorithm.

Plaats: Galglaan 2, S22, Auditorium A
Organisator: Marian Slodicka
Datum: 4/9/2013
Tijd: 15:00

Eredoctoraat voor Prof. Dr. Harvey M. Friedman

Op dinsdag 4 september reikt de UGent een eredoctoraat uit aan Harvey M. Friedman.
Op woensdag 5 september vindt er naar aanleiding van dit evenement een workshop plaats.
Verdere details zijn te vinden op: http://cage.ugent.be/programFriedman


September 4th 2013
Venue: Het Pand: Refter
15:00–16:00 General audience talk
Logic: Interdisciplinary Adventures in Mathematics, Philosophy, Computer Science, and Theology by Harvey M. Friedman

16:00–17:00 Break and possibility for a press conference

17:00-17:05 Speech by Paul Van Cauwenberge, Rector of UGent

17:05-17:15 Laudatio by Andreas Weiermann, Head of Research Group Logic and Analysis

17:15-17:25 Ceremony

17:25-17:35 Speech by Harvey M. Friedman

17:35-18:00 General audience talk
A Foundationalist looks at the Piano by Harvey M. Friedman

18:00-19:00 Piano concert 1 by Harvey M. Friedman

September 5th 2013
Venue: Het Pand: Refter
10:00-10:45 Research Talk
Concept Calculus by Harvey M. Friedman

Friedman will start by describing the general program, then focus on nine consistency proofs, using objects and classes of objects (i.e., flat).
11:15–12:15 Research talk
Concrete Mathematical Incompleteness by Harvey M. Friedman
Friedman will begin with his general program, then focus on finite sequences of positive integers and rational vectors.
12:15–14:00 Lunch

14:00–14:40 Sort expository talks
Harvey M. Friedman’s research in the foundations of mathematics

Sam Sanders: Reverse mathematics
Florian Pelupessy: Adjacent Ramsey
Jeroen Van Der Meeren: Well partial orders
Andreas Weiermann: Finite forms

15:00--17:00 Invited talks

Albert Visser: Friedman on Interpretations
Ulrich Kohlenbach: On the computational content of proofs that use ideal elements
Matthias Baaz: Towards a Proof Theory of Analogical Reasoning
Ali Enayat (tba)

17:00–18:00 Break

18:00–19:00 Piano concert 2 by Harvey M. Friedman

19:00-20:00 reception

Plaats: Het Pand
Organisator: Andreas Weiermann
Datum: 10/7/2013
Tijd: 14:00

Dominating the directed cylinder

Simon Crevals (Helsinki) vertelt over zijn doctoraatsonderzoek in Helsinki dat vooral over de
de "domination number" gaat. Studenten die niet alleen over zijn onderzoek iets willen weten, maar ook
hoe het is in het buitenland een doctoraatsopleiding te volgen, zijn ook welkom.

Simon heeft een "master in de wiskundige informatica" van de UGent.

Plaats: S9 V1
Organisator: Gunnar Brinkmann
Datum: 5/7/2013
Tijd: 16:00

Doctoraatsverdediging Vladimir Vrabel

Titel: Advanced Numerical Techniques in Partial Differential Equations: Nonstandard Boundary Conditions and Regularization of Inverse Problems

Plaats: Jozef Plateauzaal, Jozef Plateaustraat 22
Organisator: Vladimir Vrabel
Datum: 4/7/2013
Tijd: 16:00

Clifford analysis seminar

16:00: Dr. Mario Kieburg (University of Bielefeld)

Abstract. Random Matrix Theory is a big branch of statistics and statistical physics with a broad range of applications ranging from physics over mathematics to engineering and social science. One particular mathematical technique in this field is the supersymmetry method. It was introduced in the early 80's and enjoys a wide popularity in Random Matrix Theory. Its big advantage is the impressive reduction of number of integrals to be performed by employing dualities between different matrix spaces. In my talk I will give an introduction to this map. In particular I will present two important mappings to superspace known as the generalized Hubbard-Stratonovich transformation and the superbosonization formula. Moreover I will sketch what the main problem with supermatrices are (namely the changes of coordinates like eigenvalue and singular value decomposition) and what the solution for particular cases are.

Plaats: S22, Aud C
Organisator: Hendrik De Bie
Datum: 1/7/2013
Tijd: 17:00

Doctoraatsverdediging Kim Bauters

Titel: Epistemic Extensions of Answer Set Programming

I investigate how Answer Set Programming (ASP) can be used for epistemic reasoning and which extensions can further increase the ability of ASP to model and reason about knowledge. Specifically, I look at Communicating ASP, where multiple context are able to communicate, and Possibilistic ASP, where we want to model and reason about uncertain information. In both cases, I am interested in the resulting complexity of these extensions.

Plaats: S9, A2
Organisator: Kim Bauters
Datum: 1/7/2013
Tijd: 16:00

Clifford analysis seminar

16:00: Prof. Joachim Hilgert (University of Paderborn)

Abstract. In this talk I will explain the category of supermanifolds as manifolds equipped with structure sheaves of superalgebras and the corresponding group objects: Lie supergroups. Moreover, we explain how to relate this to supergroup pairs consisting of a Lie group and a compatible Lie super algebra.

17:00: Dr. Kevin Coulembier (UGent)

Abstract. A classical result of Borel and Weil provides a unified method to construct all finite dimensional representations of semisimple Lie algebras as holomorphic sections on a line bundle of the flag manifold of a Lie group. Bott extended this result to identify the higher cohomology groups on such line bundles. For algebraic Lie groups this problem can be reformulated in terms of the Zuckerman functor and its derived functors. We take this approach for Lie supergroups. We review the results obtained on this subject by I. Penkov, V. Serganova and R.B. Zhang before proceeding to some new recently obtained progress on this subject.

Plaats: S22, Aud C
Organisator: Hendrik De Bie
Datum: 1/7/2013
Tijd: 14:30 - 16:15

Symposium logic engineering

UGent-VUB symposium on Logic Engineering

14:30 Welcome

14:45 Prof. Salem Benferhat (Universite d'Artois) about DL-Lite logics, which allow a fl exible representation of knowledge with a low computational complexity of the reasoning process. This talk investigates an extension of DL-Lite logics in a possibility theory framework.

15:30 Dr. Marina De Vos (University of Bath) about developing Answer Set Applications. Answer set programming (ASP) has become one of the state-of-the art formalisms in knowledge representation and reasoning. In this talk, new challenges for ASP, originating from ASP applications, will be addressed.

16:15 Coff ee break

17:00 Public PhD defense of Kim Bauters

Plaats: S9, A2
Organisator: Kim Bauters
Datum: 27/6/2013
Tijd: 15:30

Masterproef Lien Lambert

Verdediging van de masterproef Random network coding and designs over GF(q) (promotor: Prof. Leo Storme).
Plaats: S22, Vergaderzaal
Organisator: Leo Storme
Datum: 27/6/2013
Tijd: 15:00

Masterproef Roy Oste

Verdediging van de masterproef The Clifford-Helmholtz system and related Fourier transforms (promotor: Prof. Hendrik De Bie).
Plaats: S25, Emmy Noether
Organisator: Hendrik De Bie
Datum: 25/6/2013
Tijd: 12:00 - 13:00

Masterproef Jos Polfliet

Verdediging van de masterproef Structurele geneste modellen voor het effect van alcoholgebruik op mortaliteit (promotor: Prof. Stijn Vansteelandt).
Plaats: S9, V3
Organisator: Stijn Vansteelandt
Datum: 25/6/2013
Tijd: 11:00 - 12:00

Masterproeven Financiële Wiskunde II

Verdediging van de volgende masterproeven (promotor: Prof. David Vyncke):

11:00 Kevin Bockstael, Reguliere Vines
11:30 Jorrit Barbry, Modelleren van hoogdimensionele financiële data met afgeknotte reguliere vines.

Plaats: S9, V2
Organisator: David Vyncke
Datum: 24/6/2013
Tijd: 14:00 - 17:00

Masterproeven Financiële Wiskunde I

Verdediging van de volgende masterproeven:

14u:
Lieven De Norre, LIBOR-marktmodellen (promotor: Prof. Michèle Vanmaele)
Alicia Van den Bogaert, Lévyrentevoetmodellen (promotor: Prof. Michèle Vanmaele)
Sander Willems, Gevoeligheidsanalyses van opties aan de hand van de Malliavincalculus (promotor: Prof. Michèle Vanmaele)

15u30:
Dorien Haesen, Aziatische opties onder Lévymodellen (promotor: Prof. Michèle Vanmaele)
Joachim Hendrickx, De Fear Index (promotor: Prof. David Vyncke)
Scarlett Vanlerberghe, Niet-lineaire verwachtingswaarden en stochastische calculus onder onzekerheid (promotor: Prof. Michèle Vanmaele)

Plaats: S9, V3
Organisator: Michèle Vanmaele
Datum: 21/6/2013
Tijd: 13:30

Bachelorproeven Ian Beyst en Fien Gistelinck (Statistiek)

Verdediging van de volgende bachelorproeven:
- Ian Beyst: Empirische Processen
- Fien Gistelinck: Statistische Methoden voor de Analyse van het Microbioom van Mucoviscidose-patiënten aan de hand van Unipeptdata

Plaats: S9, V3
Organisator: Karel Vermeulen, Stijn Vansteelandt, Lieven Clement
Datum: 21/6/2013
Tijd: 10:00

Masterproeven Astrofysica

Verdediging van de volgende masterproeven:

10u00: Jasmijn De Clercq, Interstellar dust in edge-on spiral galaxies (promotor: Prof. Maarten Baes)
10u30: Robbert Verbeke, Starburst in blue compact dwarf galaxies triggered by gas inflow (promotor: Prof. Sven De Rijcke)
14u00: Thomas Boelens, Dynamica van algemeen-relativistische sterclusters (promotor: Prof. Sven De Rijcke)

Plaats: S9, V2
Organisator: Maarten Baes, Sven De Rijcke
Datum: 19/6/2013
Tijd: 10:00

Masterproef Frederik De Keersmaeker

Verdediging van de masterproef Symmetriereductie van Lagrangiaanse systemen op Lie-algebroïdes (promotor: Dr. Tom Mestdag).
Plaats: S22, A
Organisator: Tom Mestdag
Datum: 17/6/2013
Tijd: 10:00

Masterproef Erik Rijcken

Verdediging van de masterproef Congruentiedeelgroepen in SLn(Z) (promotor: Prof. Tom De Medts).
Plaats: S22, C
Organisator: Tom De Medts
Datum: 13/6/2013
Tijd: 13:00

Masterproef Rien Boete

Verdediging van de masterproef Vaagrelaties - Fundamenten en toepassingen (promotor: Prof. Mike Nachtegael).
Plaats: S9, A3
Organisator: Mike Nachtegael
Datum: 10/6/2013
Tijd: 15:00

Combinatorial Structures over Finite Chain Rings

Spreker: Prof. Ivan Landjev, Bulgarian Academy of Sciences, Sofia

Abstract. Let R be a finite chain ring with |R| = q^m, R/ RadR ∼= F_q. Every submodule M of R^n is isomorphic to a direct sum of cyclic modules:

M ∼= R/N^λ1 ⊕ R/N^λ2 ⊕ . . . ⊕ R/N^λn,

where λ1 ≥ λ2 ≥ . . . ≥ λn ≥ 0 are integers and N = Rad R. The n-tuple (λ1, λ2, ... , λn) is called the shape of M. Let τ ≺ κ ≺ (m, m, . . . , m), where ≺ is the lexicographic order. A τ-(n, κ, l) R-design is a collection D of submodules of shape κ such that each submodule of shape τ is contained in exactly l elements of D. In this talk we discuss some new and old results about R-designs in the Grasmannian of all submodules of R^n of given shape.

Plaats: S25, Emmy
Organisator: Leo Storme
Datum: 7/6/2013
Tijd: 17:00

Doctoraat Claudia Degroote

Titel: Undecidability problems and diophantine sets over polynomial rings and function fields

Plaats: S25, Emmy Noether
Organisator: Jan Van Geel
Datum: 6/6/2013
Tijd: 10:30

Classes of generalized functions with finite type regularities

Prof. Stevan Pilipovic (University of Novi Sad)

Generalized functions can be considered through the analysis of nets of smooth functions.
Our program involves the study of various classes of function spaces via the analysis of the corresponding nets.
Such an analysis is called regularity theory within the theory Colombeau generalized functions.
My talk is devoted to Zygmund and Besov type regularities.

The lecture will be preceded by a short introductory talk on Colombeau generalized functions and regularity of distributions by Hans Vernaeve.

Plaats: S22, C
Organisator: Andreas Weiermann
Datum: 31/5/2013
Tijd: 17:00

Doctoraat Sofie Beke

Titel: Generic isotropy for algebras with involution, specialisation of involutions and related isomorphism problems.

Plaats: S25, Emmy Noether
Organisator: Jan Van Geel
Datum: 31/5/2013
Tijd: 14:00

Dynamical systems of binary vectors

Spreker: Prof. Anastasiia Zharkova, Saratov State University, Russia

Abstract. We study nite dynamic systems, whose states are binary vectors, which are naturally repre- sented by graphs. The evolutionary function is de ned in such a way that on the language of graphs the next state obtained from the given state by reorientation of all sinks into the sources. We present some of the results obtained for these systems whose states are associated with certain types of graphs.

Plaats: S9, V1
Organisator: Gunnar Brinkmann
Datum: 30/5/2013
Tijd: 14:00

Graph models of fault tolerance

Spreker: Prof. Mikhail Abrosimov, Saratov State University, Russia

Abstract. Fault-tolerant multiprocessor systems are widely used in di fferent areas. Two types of failures in multiprocessor systems are interesting: processor failures and link failures. In 1976 John P. Hayes proposed a graph-based model for the study of fault tolerance. A technical system Σ is associated to a labeled graph G, whose vertices correspond to elements of the system Σ, edges to relations between the elements, and labels (or colours) indicate the type of elements. The fault of an element of the system Σ refers to removing the corresponding vertex of the graph G and all its edges. Later Frank Harary and John P. Hayes proposed the model to study the failures of links: edge fault tolerance. The system Σ* is called k-node(edge) fault-tolerant implementation of the system, if faults of any k elements (links) of Σ* lead to a graph, into which the graph of Σ with given labels (or colours) of vertices can be embedded. It is proved that these problems are computationally difficult. This talk is about some results about these models.

Plaats: S9, V1
Organisator: Gunnar Brinkmann
Datum: 24/5/2013
Tijd: 16:30

Doctoraat Jan Goedgebeur

Doctoraat in de grafentheorie.

Titel: Generation Algorithms for Mathematical and Chemical Problems
Promotor: Prof. Gunnar Brinkmann

Plaats: S9, A2
Organisator: Jan Goedgebeur
Datum: 24/5/2013
Tijd: 14:00 - 15:00

Ramsey numbers

Spreker: Prof. Stanislaw Radziszowski (Rochester Institute of Technology, USA).

Kader: Deze befaamde expert over eindige Ramseygetallen bezoekt de UGent naar aanleiding van de doctoraatsverdediging van Jan Goedgebeur en geeft een gastvoordracht. Voor de lezing is geen specifieke voorkennis over Ramseygetallen nodig. Allen zijn hartelijk welkom.

Abstract: In this talk we study Shannon capacity of channels in the context of classical Ramsey numbers. We overview some of the results on capacity of noisy channels modelled by graphs, and how some constructions may contribute to our knowledge of this capacity. We present an improvement to the constructions by Abbott and Song and thus establish new lower bounds for a special type of multicolor Ramsey numbers. We prove that our construction implies that the supremum of the Shannon capacity over all graphs with independence number 2 cannot be achieved by any finite graph power. This can be generalized to graphs with bounded independence number.

Plaats: S9, V3
Organisator: Jan Goedgebeur
Datum: 24/5/2013
Tijd: 12:00

Quadratic algebras, Yang-Baxter equation, and Artin-Schelter regularity

Spreker: Tatiana Gateva-Ivanova, Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, Sofia, Bulgaria and American University in Bulgaria

Abstract. We study two classes of n-generated quadratic algebras over a field K. The first is the class of all n-generated PBW algebras with polynomial growth and finite global dimension. We show that a PBW algebra A has polynomial growth and finite global dimension iff its Hilbert series is $H_A(z)= 1/(1-z)^n$. Furthermore the class contains a unique (up to isomorphism) monomial algebra. The second is the class of n-generated quantum binomial algebras A, where the defining relations R are nondegenerate square-free binomials $xy-c_{xy}zt$, with nonzero coefficients $c_{xy}$. Our main result shows that the following conditions are equivalent: (i) A is an Artin-Schelter regular PBW algebra. (ii) A is a Yang-Baxter algebra, that is the set of quadratic relations R defines canonically a solution of the Yang-Baxter equation. (iii) A is a binomial skew polynomial ring. (iv) The Koszul dual A! is a quantum Grassmann algebra.

This work is a continuation of our study of the cannonical algebraic objects associated with solutions to YBE a basic equation in the theory of Quantum groups . The study of Artin-Schelter regular algebras, their classification and finding new classes of such algebras is one of the main problems in noncommutative algebraic geometry.

Plaats: S25, Emmy Noether
Organisator: Andreas Weiermann
Datum: 24/5/2013
Tijd: 9:00

Bachelorprojecten DM en LHD

De verdedigingen van de bachelorprojecten die aansluiten bij de vakken `Differentiaalmeetkunde' en `Lagrange- en Hamiltondynamica' gaan door vanaf 9u, in de volgende volgorde:

9u: Lisa Lampo - Hamilton-Jacobitheorie

9u30: Bas Dielemans - De krommingstensor van varieteiten en toepassingen in de algemene relativiteit

10u: Silke Govaert - De stelling van Noether in de klassieke veldentheorie

10u30: Arne Naert - De Gauss-Bonnetstelling

11u: Helene De Coninck - Lagrangiaanse systemen met niet-holonome bindingen

Iedereen is van harte welkom!

Plaats: leszaal C, S22
Organisator: Tom Mestdag
Datum: 24/5/2013
Tijd: 8:30

Presentaties Bachelorprojecten Analyse en Logica

Presentaties van de bachelorprojecten met een onderwerp dat aansluit bij Analyse en/of Logica.
De volgorde van de studenten is als volgt:

- Sieglinde Callewaert
- Steven Van den Bulcke
- Lieselotte Deloddere
- Wouter van de Vijver
- Tine Baert
- Lieselot Vanslembrouck
- Jeroen Bruylandt

Elke presentatie duurt 15 à 20 minuten, vragen niet inbegrepen.

Plaats: S25, Emmy Noether
Organisator: Hendrik De Bie, Hans Vernaeve, Andreas Weiermann
Datum: 23/5/2013
Tijd: 13:00

Presentaties Bachelorproeven Algebra-Meetkunde-Grafentheorie

Presentaties van de bachelorproeven met een meetkundig, algebraïsch en/of grafentheoretisch onderwerp. De volgorde van de studenten is als volgt:

Annelies Cuvelier (grafentheorie)
Anneleen De Schepper (grafentheorie-meetkunde-algebra)
Jeffrey De Fauw (algebra)
Jens Hemelaer (algebra)
Dries Hoste (grafentheorie-meetkunde)
Hannah Peersman (meetkunde)
Lieve Vandewalle (grafentheorie)
Magali Victoor (grafentheorie-meetkunde)

Elke presentatie duurt tussen 20 en 25 minuten, vragen niet inbegrepen. We voorzien een korte pauze tussen Jens en Dries.

Plaats: Auditorium Emmy Noether
Organisator: Bart De Bruyn, Jan Van Geel, Hendrik Van Maldeghem
Datum: 22/5/2013
Tijd: 15:00

Proclamatie Vlaamse Wiskunde Olympiade

Meer informatie: officiële website.

Plaats: VUB, Elsene
Organisator: VWO
Datum: 21/5/2013
Tijd: 14:30 - 15:30

Pierre Deligne ontvangt Abelprijs

Prof. Koen Thas presenteert leven en werk van Pierre Deligne, laureaat van de Abelprijs 2013. Live streaming van de uitreikingsplechtigheid is dit jaar niet mogelijk.

Plaats: S25, Emmy Noether
Organisator: Vakgroep Wiskunde
Datum: 21/5/2013
Tijd: 14:00

Verdediging bachelorprojecten toegepaste wiskunde

14.00u Devooght, Bram (Numerieke analyse: Splines)
14.25u Gillis, Lien (Numerieke analyse: Splines)
14.50u Verdonck, Haike (Toegepaste wiskundige evolutiemodellen: Het basisreproductiegetal voor besmettelijke ziekten)
15.15u Vandensteen, Elien (Wiskundige optimalisatie: Clusteren van grafen in de celbiologie)
15.40u Van De Velde, Koen (Numerieke analyse: Interpolatie)

Plaats: S9, leszaal V1
Organisator: Vakgroep WE02
Datum: 2/5/2013
Tijd: 11:00 - 12:15

Group actions in design theory

Spreker: Reinhard Laue, University of Bayreuth, Germany

Abstract: Using groups of automorphisms allows to reduce the e ort needed to construct combinatorial objects. We consider t-designs on small point sets, since they present various challenges. Several t-designs for t  9 can be found and classi ed up to isomorphism, using group actions and their homomorphisms. Of course, then some symmetries are known in advance and can be shown, but also resolvability can often be visualized. Combining designs yields enormous numbers of isomorphism types already on rather small point sets.

Plaats: S9, V3
Organisator: Gunnar Brinkmann
Datum: 19/4/2013
Tijd: 11:30

Seminarie Logica en Analyse - Korneel Debaene

Class numbers of Cyclotomic Fields

When one considers finite extensions of the rational number field, one finds therein a 'ring of integers', which is the analogue of Z in Q. Curiously, the usual laws of integer arithmetic as we know them in Z do not necessarily hold in these rings of integers; e.g. in many cases we do not have unique decomposition of a number in prime factors. There is an invariant, the class number, which gives a quantative interpretation of exactly how miserable the state of affairs is in a given ring of integers. It is notably hard to compute. We will discuss the history of, and our recent result on the estimation of the class numbers of cyclotomic fields.

Plaats: Vergaderzaal S22
Organisator: Andreas Weiermann
Datum: 29/3/2013
Tijd: 10:00 - 11:00

Gap-sequences

by Jeroen Van der Meeren

In 1985, Schütte and Simpson defined on order relation with gap-condition on the set of finite sequences of natural numbers strictly less than n. Define this set with this ordering relation as S_n. They proved that the statement `\forall n (S_n is a well-partial-ordering)' is unprovable in the standard arithmetic PA. Furthermore, they translated this theorem in a miniaturized version, so that they obtain an unprovable statement which can be expressed with `normal' combinatorics.

In this talk, I will sketch their results and I will connect the gap-sequences with a class T(W) introduced by Weiermann. With this connection in mind, I will sketch some proofs about the maximal order type of some of these classes and I will connect this with the usefull collapsingfunction \theta.

The talk is accessible for students.

Plaats: Vergaderzaal
Organisator: Logica en Analyse
Datum: 15/3/2013
Tijd: 14:00 - 15:00

Reverse Mathematics and Nonstandard Proof Methods

Reverse mathematics is a research program in foundations of mathematics, initiated by H. Friedman in 1970's and most notably advanced by S. Simpson. Already in 70's, J. Steel proved the determinacy of open games by an ingenious method of psuedhierarchies in ATR. During these two decades, our group in Sendai have developed nonstandard analysis for weak subsystems of second order arithmetic. In this talk, the speaker will highlight the importance of nonstandard proof methods in reverse mathematics.

Plaats: S25 Emmy Noether
Organisator: Andreas Weiermann
Datum: 15/3/2013
Tijd: 11:30

General Stieltjes moment problems

by Jasson Vindas

The problem of moments, as its generalizations, is an important mathematical problem which has attracted much attention for more than a century. In its basic form, the Stieltjes moment problem consists of finding solutions f to

a_n= \int_{0}^{\infty} f(x)x^n dx,

where (a_n) is a given sequence of complex numbers. In 1939, Boas and Pólya, independenly, showed a surprising result: for any arbitrary sequence the Stieltjes moment problem admits a solution. A major improvement to this result was archieved by A. Durán, who was able to show that there is always a solution f which is smooth and rapidly decreasing at infinity.

In this talk we shall discuss some results concerning general Stieltjes moment problems, that is, the analogous problem obtained by replacing the sequence x^n by a suitable (but rather arbitrary) sequence of functions (or measures) g_n. In particular, we shall consider discrete moment problems, namely, we find conditions on an infinite matrix B=(B_{n,j}) of complex numbers so that the infinite system of equations

a_n= \sum_{n=0}^{\infty} f(j) B_{n,j}

has always a (smooth rapidly decreasing) solution f.

Plaats: vergaderzaal, S22
Organisator: Jasson Vindas
Datum: 8/3/2013
Tijd: 11:30 - 12:30

Oneindige spelen

De voordracht is bedoeld als smaakmaker voor
de theorie van oneindige spelen. We bespreken eerst de topologie
op de Baireruimte en dan
de gedetermineerdheid van gesloten spelen.
Spijtig
genoeg moeten we (steunend op het
keuzeaxioma) even vaststellen dat niet
alle spelen gedetermineerd zijn. (Een mooi
gevolg van het globale gedetermineerdheidsaxioma
zou geweest zijn dat alle deelverzamelingen
van reële getallen meetbaar zouden zijn.)

Plaats: vergaderzaal S22
Organisator: Andreas Weiermann
Datum: 5/3/2013
Tijd: 19:30

PUMA 2013

Op 5 maart organiseert PRIME haar eigen wiskundewedstrijd. Op deze avond lossen we met pen en papier allerlei leuke problemen op. Je kan de vragen een beetje vergelijken met de vragen van de 'Vlaamse Wiskunde Olympiade'. Deelnemen is gratis maar we vragen wel om op voorhand in te schrijven door hier je naam en e-mailadres in te vullen. Voor de winnaars voorzien we mooie geldprijzen. Geen reden om niet deel te nemen dus. De proclamatie van deze PUMA gebeurt op ons π-zzafestijn van 14 maart (π-dag).

Plaats: S9, A3
Organisator: PRIME
Datum: 22/2/2013
Tijd: 15:00

Independence Number of Graphs

Problems and Results Motivated by Efficient Computation of the Independence Number


By Craig Larson, Virginia Commonwealth University, VS

Abstract. The independence number of a graph is the size of a maximum number of pairwise non-adjacent vertices of a graph. This number is of practical and theoretical interest but NP-hard-to-compute. The independence number can be computed eciently for many graph classes. Certainly the class of graphs with this property can be extended. We discuss some new structural results as well as problems arising from a project to extend independence number theory.
Plaats: S9, A3
Organisator: CAAGT
Datum: 16/1/2013
Tijd: 10:00

IRSES Meeting on Differential Geometry and Mechanics

This is a workshop in the framework of the IRSES project Geometric Mechanics (EU-FP7). See this webpage for details about the schedule, titles of the talks, abstracts, etc. Everyone is cordially invited!
Plaats: Emmy Noether, S25
Organisator: Frans Cantrijn en Tom Mestdag
Datum: 15/1/2013
Tijd: 10:00

IRSES Meeting on Differential Geometry and Mechanics

This is a workshop in the framework of the IRSES project Geometric Mechanics (EU-FP7). See this webpage for details about the schedule, titles of the talks, abstracts, etc. Everyone is cordially invited!
Plaats: Emmy Noether, S25
Organisator: Frans Cantrijn en Tom Mestdag
Datum: 14/1/2013
Tijd: 10:00

IRSES Meeting on Differential Geometry and Mechanics

This is a workshop in the framework of the IRSES project Geometric Mechanics (EU-FP7). See this webpage for details about the schedule, titles of the talks, abstracts, etc. Everyone is cordially invited!
Plaats: Emmy Noether, S25
Organisator: Frans Cantrijn en Tom Mestdag
Datum: 17/12/2012
Tijd: 14:30

Inverse Problems with Experimental Data

Talk by: Michael V. Klibanov ( University of North Carolina at Charlotte)

Abstract

Traditionally numerical performance of algorithms for various inverse problems is verified on computationally simulated data. Basically this is because it is not easy to obtain experimental data. Recently our research group at University of North Carolina at Charlotte has built an experimental apparatus for collecting backscattering data of electromagnetic waves propagation. We have learned that there is a huge mismatch between thes data and the theory. In purely mathematical terms this means thousands percent of the noise. Therefore, to make mathematical theory working, it is necessary to pre-process the data. So that the preprocessed data would look somehow similar with computational simulations. Results of performance of the globally convergent inverse algorithm of [1] on these and other real data will be presented.

[1]. L. Beilina and M.V. Klibanov. Approximate Global Convergence and Adaptivity for Coefficient Inverse Problems, Springer, New York, 2012

Plaats: De Sterre, S22, Auditorium C
Organisator: Marian Slodicka
Datum: 7/12/2012
Tijd: 10:00 - 16:30

JSPS-FWO workshop on mathematical logic

See webpage: http://cage.ugent.be/~sasander/JFML/
But the correct timetable is:

10:00 - 11:00: Kojiro Higuchi
11:00 - 12:00: Richard Kaye
14:00 - 15:00: Keita Yokoyama
15:30 - 16:30: Jeroen Van der Meeren
16:30 - 17:30: Takeshi Yamazaki

Everything is in S25, Emmy Noether

Plaats: S25, Emmy Noether
Organisator: Andreas Weiermann
Datum: 6/12/2012
Tijd: 10:00 - 17:30

JSPS-FWO workshop on mathematical logic

See webpage: http://cage.ugent.be/~sasander/JFML/
But the correct timetable is:

10:00 - 11:00: Tin Lok Wong, S25 Emmy Noether
13:00 - 14:00: Naohi Eguchi, S22 aud c
14:00 - 15:00: Florian Pelupessy, S22 aud c
15:30 - 16:30: Makoto Fujiwara, S22 aud c
16:30 - 17:30: Sam Sanders, S22 aud c

Plaats: S25 en S22 aud c
Organisator: Andreas Weiermann
Datum: 5/12/2012
Tijd: 10:00

Geometric aspects of homogeneous spaces, part IV

Talk by Eduardo Garcia-Toranio in the `Differential Geometry and Mechanics' seminar. Everyone is cordially invited!

Plaats: S22, room A
Organisator: Tom Mestdag
Datum: 19/11/2012
Tijd: 17:30

Doctoraatsverdediging Stephanie Vanhove

Promovenda Stéphanie Vanhove verdedigt publiekelijk haar doctoraatsproefschrift in de informatica.

  • Titel: Alternative routing algorithms for road networks
  • Promotor: Prof. dr. Veerle Fack
  • Voorzitter examencommissie: Prof. dr. dr. Kris Coolsaet
Plaats: S9, A3
Organisator: WE02
Datum: 16/11/2012
Tijd: 17:00

Doctoraatsverdediging Florian Pelupessy

Florian Pelupessy verdedigt zijn doctoraat: Connecting the Provable with the Unprovable: Phase Transitions in Unprovability.

Plaats: Emmy Noether
Organisator: Andreas Weiermann
Datum: 16/11/2012
Tijd: 13:30 - 15:30

Workshop on Logic and Analysis

13:30-14:00 Jasson Vindas:

A multiplicative partition problem: Asymptotic distribution of a class of integers having certain prime factorizations

14:00-14:30 Tin Lok Wong:

Revisiting cuts and indicators.

14:30-15:00 Jeroen Vandermeeren:

Well-partial-orderings and recursively defined trees.

15:00-15:30 Konrad Zdanowksi:

On computational properties of notations for natural numbers.

Plaats: Auditorium C
Organisator: Andreas Weiermann
Datum: 9/11/2012
Tijd: 16:00 - 16:30

The future of mathematical textbooks

Guest: Bruce Cooperstein

Bruce Cooperstein is Professor in Mathematics at the University of California, Santa Cruz. He will present his own view on textbooks and course notes, used in universitary undergraduate mathematics education.

Talk/discussion/conversation/debate: the future of mathematical textbooks.

Plaats: S25, Emmy Noether
Organisator: Bruce Cooperstein
Datum: 9/11/2012
Tijd: 9:45 - 10:45

Solution to a question posed by J. Korevaar: A new proof of the Tauberian theorem for weighted algebras. Part II

Talk by Jasson Vindas

In a previous talk on the topic, I have discussed an open question posed by J. Korevaar concerning Tauberian theorems in the so-called Beurling algebras. In this talk I will present a solution to his question.

An important theorem of N. Wiener characterizes the dense translation invariant subspaces of the algebra of Lebesgue integrable functions in terms of non-vanishing properties of the Fourier transforms of their elements (Ann. of Math 33 (1932), 1-100).

Wiener used this result to give a unified treatment of Tauberian theory. Wiener's Tauberian theory has shown to be a powerful tool in various areas of mathematics. For instance, using his theory, Wiener was the first who showed that the prime number theorem directly follows from the nonvanishing of the Riemann zeta function on the line Re s=1. Wiener theory has been extended into several directions; particularly, A. Beurling showed an analog to Wiener theorem for weighted algebras, the so-called Beurling's approximation theorem.

In 1965, J. Korevaar gave a short and simple proof of Wiener's theorem. His treatment is based on the theory of Schwartz distributions. Moreover, Korevaar has posed the following open question: Can Beurling's approximation theorem be obtained by a suitable extension of the distributional proof of Wiener's theorem?

I shall give a positive answer to Korevaar's question. I will present a proof of Beurling's approximation theorem which is based on the theory of ultradistributions and supplementary (elementary) properties of subadditive functions.

Plaats: S22, A
Organisator: Logica en Analyse
Datum: 7/11/2012
Tijd: 19:00

Lezing: Priemgetallen in de Knoop

De priemgetallen zijn een perfect voorbeeld van hoe een elementair concept tot bijzonder lastige problemen kan leiden in de wiskunde. Hetzelfde zie je bij knopen: hoewel zelfs kleuters er regelmatig mee in aanraking komen, is de zogenaamde knopentheorie, die knopen wiskundig beschrijft, nog lang niet vrij van mysterie.

Lieven Le Bruyn is professor aan de universiteit van Antwerpen. Hij komt ons vertellen over priemen en knopen, maar vooral over de link tussen beide. Die link vormt de basis van de arithmetische topologie, een vrij recente tak in de wiskunde.

Iedereen is welkom! Na een eerder zachte inleiding in de wereld van priemen en knopen, kan je eens proeven van het recent onderzoek in deze branche. Na de lezing voorzien we brownies van Quetzal en een drankje.

Plaats: S25, Emmy Noether
Organisator: PRIME
Datum: 31/10/2012
Tijd: 10:00 - 11:15

Geometric Methods for the Integration of PDEs

Talk by Prof Geoff Prince (La Trobe University, Melbourne and the Australian Mathematical Sciences institute) in the `Differential Geometry and Mechanics' seminar. Everyone is cordially invited!

Abstract: Unlike ordinary differential equations the contact distribution associated to PDEs is not Frobenius integrable. So the first problem to be overcome in geometrically describing their solution is to find the smallest integrable distributions containing this contact distribution. In this talk I describe work done with Naghmana Tehseen on this problem and on the subsequent production of group invariant solutions. This talk assumes only basic exterior calculus.
Plaats: S22, room A
Organisator: Tom Mestdag
Datum: 24/10/2012
Tijd: 13:00 - 14:00

Logics and complexity in a calculus of problems

Spreker: Paul Shafer
Abstract:
The phrase "calculus of problems" in the title of this talk comes from Kolmogorov's informal notion of a calculus of problems that he hoped would lead to an interpretation of intuitionistic logic as a logic of problem solving. Medvedev and Muchnik both gave formalizations of Kolmogorov's notion, basing their calculi on the idea that problem A reduces to problem B (i.e., B is at least as hard as A) if every solution to B can be used to compute a solution to A. We discuss the logics that Medvedev's and Muchnik's calculi interpret. Medvedev's and Muchnik's calculi formalize the "difficulty" relation among mathematical problems, and we also use their calculi to argue that this relation is as complicated as possible, even when restricted to simple classes of problems.

Plaats: Auditorium B in S22
Organisator: Andreas Weiermann
Datum: 24/10/2012
Tijd: 10:00 - 11:15

Geometric aspects of homogeneous spaces, part III

Talk by Eduardo Garcia-Torano in the `Differential Geometry and Mechanics' seminar. Everyone is cordially invited.
Plaats: S22, room A
Organisator: Tom Mestdag
Datum: 19/10/2012
Tijd: 10:00 - 11:00

Solution to a question posed by J. Korevaar: A new proof of the Tauberian theorem for weighted algebras

Talk by Jasson Vindas

An important theorem of N. Wiener characterizes the dense translation invariant subspaces of the algebra of Lebesgue integrable functions in terms of non-vanishing properties of the Fourier transforms of their elements (Ann. of Math 33 (1932), 1-100).

Wiener used this result to give a unified treatment of Tauberian theory. Wiener's Tauberian theory has shown to be a powerful tool in various areas of mathematics. For instance, using his theory, Wiener was the first who showed that the prime number theorem directly follows from the nonvanishing of the Riemann zeta function on the line Re s=1. Wiener theory has been extended into several directions; particularly, A. Beurling showed an analog to Wiener theorem for weighted algebras, the so-called Beurling's approximation theorem.

In 1965, J. Korevaar gave a short and simple proof of Wiener's theorem. His treatment is based on the theory of Schwartz distributions. Moreover, Korevaar has posed the following open question: Can Beurling's approximation theorem be obtained by a suitable extension of the distributional proof of Wiener's theorem?

In this talk I shall give a positive answer to Korevaar's question. I will present a short proof of Beurling's approximation theorem which is based on the theory of ultradistributions. The talk will start with an expository review of applications of Wiener's Tauberian theorem; in particular, I will discuss a proof of the prime number theorem via Lambert summability.

Plaats: S22, Aud. A
Organisator: Logica en Analyse
Datum: 19/10/2012
Tijd: 9:30 - 16:45

The Freudenthal-Tits Magic Square

An international colloquium around the theme "Freudenthal-Tits Magic Square" will be held in Ghent (Belgium) on Friday October 19th, as part of the "DAG"-days (Discrete Algebra and Geometry).

09:30 - 10:30 Coffee and tea
10:30 - 11:30 Hendrik Van Maldeghem (U Ghent): "A (geometric) introduction to the Magic Square"
11:30 - 11:45 Coffee break
11:45 - 12:45 John Faulkner (U Virginia): "TBA"
12:45 - 14:30 Lunch break
14:30 - 15:30 Alberto Elduque (U Zaragossa): "A Freudenthal-Tits Supermagic Square"
15:30 - 15:45 Coffee break
15:45 - 16:45 Laurent Manivel (U Grenoble): "The Magic square in algebraic geometry"

Plaats: Emmy Noether, S25
Organisator: Tom De Medts, Hendrik Van Maldeghem
Datum: 17/10/2012
Tijd: 10:00 - 11:15

Geometric aspects of homogeneous spaces, part II

Talk by Eduardo Garcia-Torano in the `Differential Geometry and Mechanics' seminar. Everyone is cordially invited!
Plaats: S22, room A
Organisator: Tom Mestdag
Datum: 16/10/2012
Tijd: 11:00 - 12:00

New Methods in Projective Geometry, Algebra and Combinatorics

Spreker: dr. David Glynn

Plaats: S22, vergaderzaal
Organisator: Incidentiemeetkunde
Datum: 15/10/2012
Tijd: 14:30 - 15:45

Right triangle problems in ancient China

Douglas Rogers verzorgt een gastcollege, kaderend in Geschiedenis van de Wiskunde.

Abstract: The mathematical literature of ancient China is replete with problems that we recognize as being about right triangles or rectangles, especially what we call in the Euclidean tradition the Pythagorean Theorem. Generations of students focused on Chapter IX of Jiu Zhang Suan Shu and the commentary on it by Liu Hui. More elaborate problems appear in Ji Gu Suan Jing, by Wang Xiao-Tong, in early C7. By the mid-C13, the thrust of the problems in Ce Yuan Hai Jing and Shu Shu Zhu Zhang seems to have changed, with the emphasis placed on algebraic manipulation executed on the counting board, a process that reaches its high point with Si Yuan Yu Jian (1303).

Plaats: Emmy Noether
Organisator: Albrecht Heeffer
Datum: 15/10/2012
Tijd: 10:00 - 11:15

Mathematical Modelling and Data Analysis of TAP Experiments

Speaker: Denis Constales

Abstract: Temporal Analysis of Products (co-invented by J.T. Gleaves at the Monsanto Company in 1988) is a specially designed experimental procedure in heterogeneous catalysis research. It relies on a small reactor that incorporates many deliberate simplifications for its mathematical modelling, so that a general theoretical framework for it can be based on the Laplace transform. This will be presented during the present talk, along with its implications for the data analysis methods used in practice.

Plaats: S22, C
Organisator: Hendrik De Bie
Datum: 10/10/2012
Tijd: 10:00 - 11:15

Geometric aspects of homogeneous spaces

Talk by Eduardo Garcia-Torano in the `Differential Geometry and Mechanics Seminar' . This will be a gentle introduction. Everyone is cordially invited.

Plaats: Room A, S22
Organisator: Tom Mestdag
Datum: 4/10/2012
Tijd: 20:00

New avenues to old puzzles

Prof. Marcus Arndt (Universiteit Wenen) bezoekt de UGent voor o.a. een avondlezing. Dit ter gelegenheid van de Solvay tentoonstelling over de kwantummechanica, die heel de maand oktober in het UFO kan bezocht worden. (Meer uitleg vind je hier.) Prof. Arndt is vermaard om zijn baanbrekende experimenten met kwantuminterferentie van gigantische (tot zelfs semi-organische) moleculen.

U bent van harte uitgenodigd op de avondlezing New avenues to old puzzles: Testing the foundations of quantum mechanics with massive nanoparticles

Plaats: UFO
Organisator: Museum Wetenschappen
Datum: 21/9/2012
Tijd: 9:00 - 17:20

Buekenhout Geometry

9:00 Coffee and thee
9:30 Ernest Shult (Kansas): "On 'Tweaking' Classical Theorems"
10:25 Coffee break
10:45 Guglielmo Lunardon (Napels): "Linear sets: genealogy and applications"
11:45 Peter Cameron (London): "Geometries, chamber systems, and designs"

12:45 Lunch break

14:30 Jef Thas (Gent): "Non-linear embeddings of affine planes in projective spaces"
15:25 Coffee break
15:45 Hendrik Van Maldeghem (Gent): "Twisted A2 and E6"
16:30 James Hirschfeld (Sussex): "Curves over Finite Fields"

Plaats: Emmy Noether, S25
Organisator: Bernhard Mühlherr, Jef Thas, Hendrik Van Maldeghem
Datum: 20/9/2012
Tijd: 9:00 - 18:00

Buekenhout Geometry

9:00 Coffee and thee
9:50 Welcome
10:00 Arjeh Cohen (Eindhoven): "Riemann surface models and regular maps"
10:55 Coffee break
11:10 Antonio Pasini (Siena): "Non-projective embeddings of generalized quadrangles"
12:10 Bernhard Muehlherr (Giessen): "Tits-indices for affine buildings"

13:00 Lunch break

15:00 Dimitri Leemans (Auckland): "Geometries constructed from the Suzuki simple groups"
15:55 Coffee break
16:10 Koen Thas (Gent): "From buildings to hyperstructures, and back"
17:10 Pierre-Emmanuel Caprace (Louvain-la-Neuve): "Specimens from a zoology of simple groups"

Plaats: Emmy Noether, S25
Organisator: Bernhard Mühlherr, Jef Thas, Hendrik Van Maldeghem
Datum: 11/9/2012
Tijd: 11:00 - 11:30

Zwak compacte kardinaalgetallen en een compactheidsstelling

Bachelorproef
van Pieter De Smet

Plaats: Auditorium B
Organisator: Andreas Weiermann
Datum: 29/6/2012
Tijd: 15:00 - 16:30

Thesisverdedigingen wiskundige natuurkunde

Uur Naam Promotor Onderwerp
15:00 Karel Paternoster (Burg. Ingenieur) Henri Verschelde Variationele simulatiemodellen voor metalen met onzuiverheden
15:30 Laurens Vanderstraeten (Burg. Ingenieur) Henri Verschelde Continue matrix product toestanden voor de beschrijving van verstrengelde kwantumsystemen
16:00 Boye Buyens Karel Van Acoleyen UV-protected inflatie
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 29/6/2012
Tijd: 11:00

Thesisverdedigingen logica

Bachelorprojecten:
Uur Naam Promotor Onderwerp
11u00 Anke Bellens Andreas Weiermann Primitief recursieve graden
11u30 Klaas Walcarius Andreas Weiermann Herschrijfsysteem voor het hydragevecht en de uitgebreide Grzegorczyk hierarchie
Masterproef:
12u00 Gabriel Hollander Sam Sanders Reverse mathematics: over equivalenties in de wiskunde
Plaats: S22 auditorium B
Organisator: Opleiding Wiskunde
Datum: 28/6/2012
Tijd: 14:00

Thesisverdedigingen sterrenkunde

Uur Naam Promotor Onderwerp
16:00Elien Pacqué Maarten Baes Analytische eigenschappen van het Sérsic model
16:30Sebastiaan Vandewoude Maarten Baes en Karl Gordon Een efficiënte toepassing van octtree structuren in Monte Carlo stralingsoverdrachtssimulaties
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 28/6/2012
Tijd: 10:00 - 11:30

Thesisverdedigingen financiële wiskunde

Uur Naam Promotor Onderwerp
10:00 Dorien Roels Michèle Vanmaele Hedging van sterfte- en rentevoetrisico
Britt Grootaerd David Vyncke Staartafhankelijkheid in vine copula's en pair-copula constructies
Plaats: S9, V3
Organisator: Opleiding Wiskunde
Datum: 27/6/2012
Tijd: 13:30

Thesisverdediging Evelien Brisard

Naam Promotor Onderwerp
Evelien Brisard Hans Dierckx Dynamica van spiraalgolven op gekromde en anisotrope oppervlakken
Plaats: S9, V1
Organisator: Opleiding wiskunde
Datum: 27/6/2012
Tijd: 11:00

Thesisverdediging Yannick Neyt

Naam Promotor Onderwerp
Yannick Neyt Jeroen Demeyer Niet-commutatieve delingsalgebra's
Plaats: S22, C
Organisator: Opleiding Wiskunde
Datum: 26/6/2012
Tijd: 10:00

Thesisverdediging Jordy Vanpoucke

Naam Promotor Onderwerp
Jordy Vanpoucke Leo Storme Mutually orthogonal latin squares and their generalizations
Plaats: S22, A
Organisator: Opleiding Wiskunde
Datum: 21/6/2012
Tijd: 14:00

Data-Based Analysis of Winner-Loser Models of Hierarchy Formation in Animals

Professor Lindquist is currently in Gent to discuss the collaboration of his University and Ghent University on the Incheon campus in South Korea. At this occasion, he will give a talk with the title as above and abstract as below. The corresponding paper won the 2010 Lee Segal prize from the Society of Mathematical Biology. Everybody is cordially invited.

Abstract    We review winner-loser models, the currently popular explanation for the occurrence of linear dominance hierarchies, via a three-part approach. 1) We isolate the two most significant components of the mathematical formulation of three of the most widely-cited models and rigorously evaluate the components’ predictions against data collected on hierarchy formation in groups of hens. 2) We evaluate the experimental support in the literature for the basic assumptions contained in winner-loser models. 3) We apply new techniques to the hen data to uncover several behavioral dynamics of hierarchy formation not previously described. The mathematical formulations of these models do not show satisfactory agreement with the hen data, and key model assumptions have either little, or no conclusive, support from experimental findings in the literature. In agreement with the latest experimental results concerning social cognition, the new behavioral dynamics of hierarchy formation discovered in the hen data suggest that members of groups are intensely aware both of their own interactions as well as interactions occurring among other members of their group. We suggest that more adequate models of hierarchy formation should be based upon behavioral dynamics that reflect more sophisticated levels of social cognition.

Plaats: S9, V2
Organisator: Vakgroep TWI
Datum: 20/6/2012
Tijd: 16:00

Seminar Prof. K. Srinivasa Rao

Prof. K. Srinivasa Rao (Inst. of Math. Sciences, Chennai and Srinivasa Ramanujan Center Kumbakonam)
Title: “Gauss, Ramanujan and Hypergeometric series”

Abstract:
Carl Friedrich Gauss in Germany discovered the second order ordinary differential equation, named after him since, in 1812. Ramanujan discovered the Gauss summation theorem, for the hypergeometric series, as well as the most general summation theorem for generalized hypergeometric series, called the Dougall-Ramanujan summation theorem, independently, though Ramanujan had no formal education. In this lecture, the lives and works of Gauss and Ramanujan on hypergeometric series will be presented briefly and some of the applications of the series to quantum theory will be mentioned.

Plaats: S9, leszaal V1
Organisator: Joris Van der Jeugt
Datum: 20/6/2012
Tijd: 8:30

Thesisverdediging Hannah Fredrick

Naam Promotor Onderwerp
Hannah Fredrick Roger Van Keer Galerkinmethode met polynomiale chaos in de stochastische warmtevergelijking
Plaats: S22, C
Organisator: Opleiding wiskunde
Datum: 19/6/2012
Tijd: 15:00

Thesisverdediging Lotte Muylaert

Naam Promotor Onderwerp
Lotte Muylaert Glad Deschrijver Aggregatie-operatoren in besluitvorming
Plaats: S9, V2
Organisator: Opleiding wiskunde
Datum: 14/6/2012
Tijd: 10:30 - 15:30

Bachelorproeven analyse en differentiaalmeetkunde

Uur Naam Promotor Onderwerp
10:30 - 11:00 Iris Van Melkebeke Hendrik De Bie Unieke karakterisatie van de Legendre-transformatie
11:00 - 11:30 Sarah Vluymans Tom Mestdag Minimale oppervlakken
11:30 - 12:00 Michiel Elewaut Hans Vernaeve Convexiteit in Banachruimten
Middagpauze
13:30 - 14:00 Andreas Debrouwere Hans Vernaeve Tauberse theorie: een distributionele benadering van de priemgetallenstelling
14:00 - 14:30 Mats Dedeyne Tom Mestdag / Goedele Waeyaert Toepassingen van de variatierekening in de differentiaalmeetkunde
14:30 - 15:00 Igor Voulis Hans Vernaeve Meetkunde in metrische ruimten
15:00 - 15:30 Hannelore Verkimpe Nele De Schepper Semi-klassieke orthogonale polynomen
Plaats: S22, Aud. B
Organisator: Opleiding Wiskunde
Datum: 13/6/2012
Tijd: 11:00

Thesisverdediging Sofie De Clercq

Naam Promotor Onderwerp
Sofie De Clercq Martine De Cock Redeneren over kennis met vaagmodale epistemische logica
Plaats: S9, V2
Organisator: Opleiding wiskunde
Datum: 1/6/2012
Tijd: 17:00

Doctoraat Heide Sticker

Promotor: Prof. dr. dr. Kris Coolsaet

Proefschrift: Classification of arcs in small Desarguesian projective planes

Examencommissie:

  • Dr. Jan De Beule
  • Dr. Yves Edel
  • Prof dr. Veerle Fack
  • Prof dr. Alessandro Siciliano
  • Prof dr. Leo Storme
  • Prof dr. Andreas Weiermann (voorzitter)

Plaats: S9, A3
Organisator: Vakgroep TWI
Datum: 1/6/2012
Tijd: 12:00 - 12:30

Bachelorproef statistiek

Uur Naam Promotor Onderwerp
12:00 - 12:30 Jody Verstraeten Stijn Vansteelandt Het schatten van probabilistische indices in gerandomiseerde studies met baseline covariaten
Plaats: S9, V1
Organisator: Opleiding Wiskunde
Datum: 31/5/2012
Tijd: 15:30 - 17:30

Bachelorproeven financiële wiskunde

Uur Naam Promotor Onderwerp
15:30 - 16:00 Lisa Vanluchene Michèle Vanmaele Minimalisatie van VaR en CVaR voor optieportefeuilles
16:00 - 16:30 Barbry Jorrit Michèle Vanmaele Lineaire programmering en arbitrage
16:30 - 17:00 David Dooms Michèle Vanmaele Berekenen van een Spaar-Consumptieplan
17:00 - 17:30 Künegonde Cardoen Michèle Vanmaele Optimalisatie van de conditionele value-at-risk
Plaats: S9, V3
Organisator: Opleiding wiskunde
Datum: 30/5/2012
Tijd: 10:00 - 16:00

Mathematics in Chemical Kinetics and Engineering

After the successful international Mackie-conferences and seminars, the local organizers at Ghent University have again invited two world-class experts from the fields of mathematics and chemical engineering, Prof. B. Andresen (Copenhagen) and Prof. V.N. Parmon (Novosibirsk) to give seminar talks during a one-day mini-symposium.

Participation to the seminar is free, but registration is strongly recommended before May 16, 2012. Please e-mail to Denis.Constales@UGent.be to register. A complimentary lunch is offered to the participants at the venue.

Organizing Committee
  • Denis Constales (LCT and NaM2)
  • Geraldine J. Heynderickx (LCT)
  • Guy B. Marin (LCT)
  • Roger Van Keer (NaM2)
Program

10:00 Coffee and registration
10:45 Introduction
11:00 Bjarne Andresen on Finite-time optimization of chemical and unrelated reactions
12:00 Question time and discussion
12:30 Lunch
14:30 Vladimir N. Parmon on Thermodynamic form of kinetic equations and an experience of its use for analyzing complex reaction schemes
15:30 Question time and discussion
16:00 Concluding remarks and closing address

Abstracts and more information: www.mackie-workshops.com.

Plaats: Pand
Organisator: NaM²
Datum: 25/5/2012
Tijd: 14:00 - 15:00

On a Gap between Truth and Provability: Some of Total Functions Are Not `Provably' Total.

Speaker: Naohi Eguchi

Title: On a Gap between Truth and Provability: Some of Total Functions Are Not `Provably' Total.

Abstract:
As a consequence of famous Goedel's second incompleteness theorem, for any consistent axiomatic system of Mathematics there exists a statement that is true (if interpreted as the one about natural numbers) but not a theorem of the axiomatic system. This implies that for any consistent axiomatic system there exists a total function over naturals whose totality is not provable in the system - hence the title.

This talk is intended to be a brief introduction to describing total functions whose totality is provable in a given axiomatic system. We will discuss about the axiomatic system for ordered semi rings and its extensions. Familiarity with ordinal numbers is welcome but not assumed.

Plaats: Auditorium C
Organisator: Andreas Weiermann
Datum: 24/5/2012
Tijd: 15:30

Some related topics to Classical Field Theories

Talk by Elisa Guzman (Universidad de La Laguna) in the `Differential Geometry and Mechanics' seminar

Abstract: In this talk, the standard multisymplectic formulation for describing geometrically classical field theories (Lagrangian and Hamiltonian formalism) will be recalled. The aim of this talk is introduced a Tulczyjew's triple associated with a fibration and described the dynamical equations in terms of Lagrangian submanifolds of premultisymplectic manifolds. Moreover, we will discusse if this triple is also useful to deal with classical field theories subject to constraints.

Plaats: S22, Aud B
Organisator: Tom Mestdag
Datum: 24/5/2012
Tijd: 9:00 - 18:30

Math Art Summit

Tweedaagse lezingenreeks op donderdag 24 en vrijdag 25 mei 2012. Wiskundigen en kunstenaars spreken in 24 lezingen over hun visies en werk. Donderdag spreekt onder andere Octave Landuyt (°1922, bekend Vlaams kunstenaar die o.a. samenwerkte met Gaudí, Dalí, Picasso en Le Corbusier) en op vrijdag prof. Ingrid Daubechies (voorzitter International Mathematics Union).

Meer informatie hier. Inschrijven op deze pagina wordt op prijs gesteld.

Plaats: Academie, Rue Ducale 1, Brussel
Organisator: Wiskunst.be
Datum: 23/5/2012
Tijd: 15:00

VWO-proclamatielezing: Jan Vonk

Plaats: UFO, Sint-Pietersnieuwstraat, Gent
Organisator: VWO
Datum: 23/5/2012
Tijd: 9:00 - 12:00

Bachelorproeven toegepaste wiskunde

Uur Naam Promotor Onderwerp
9:00 - 9:30 Jolien Vandenameele Willy Govaerts Wiskundige modellering van competitie en mutualisme bij 2 diersoorten
9:30 - 10:00 Sarah Vanhuylenbroeck Willy Govaerts Wiskundige modellering van de celgrootte in een populatie
10:00 - 10:30 Annelies Baeyens Veerle Fack Wiskundige optimalisatiemethode voor marker-assisted gene pyramiding
10:30 - 11:00 Karel Vandenbroucke Willy Govaerts Normaalvormen van dynamische systemen
11:00 - 11:30 Ruben Van de Velde Joris Van der Jeugt Perron-Frobeniustheorie van niet-negatieve matrices
Plaats: S9, V2
Organisator: Opleiding Wiskunde
Datum: 22/5/2012
Tijd: 12:30 - 17:00

Bachelorproeven algebra & meetkunde

Uur Naam Promotor Onderwerp
12:30 - 12:55 Sigiswald Barbier Jan Van Geel Abelse velduitbreidingen
12:55 - 13:20 Giles Miclotte Jan Van Geel De verdeling van het lemniscaat met passer en liniaal
13:20 - 13:45 Joris Roels Jeroen Demeyer Elliptische krommen
14:00 - 14:25 Gregory Debruyne Tom De Medts Vrije groepen
14:25- 14:50 Andries Vansweevelt Hendrik Van Maldeghem Groepen en grafen
14:50 - 15:15 Nigel Vinckier Hendrik Van Maldeghem Ramsey-getallen
15:25 - 15:50 Nele De Soete Frank De Clerck Maximale bogen in Desarguesiaanse projectieve vlakken
15:50 - 16:15 Linda Van Puyvelde Frank De Clerck Unitalen in Desarguesiaanse projectieve vlakken
16:15 - 16:40 Tara Vanhecke Frank De Clerck Kwadrieken en quasi-kwadrieken
Plaats: S22, Aud. B
Organisator: Opleiding Wiskunde
Datum: 21/5/2012
Tijd: 11:00

Getaltheorie in het Vlakke land

Zie http://math.univ-lille1.fr/~bhowmik/seminaire/APP_mai_21_2012.html
Plaats: TBA
Organisator: Jan-Christoph Schlage-Puchta
Datum: 12/5/2012
Tijd: 16:00 - 17:00

Wiskunst in cartografie en landmeetkunde

In het kader van de Dagen van de Wiskunst gaan in Gent drie lezingen door, waarvan deze de derde is. Marijke Brondeel, auteur van Van lijn tot lay-out zal hier ingaan op de kunstzinnige aspecten van het wiskundige landmeten.

Om organisatorische redenen wordt gevraagd om zich voordien hier in te schrijven. Meer informatie over de Dagen van de Wiskunst, een evenementendriedaagse vol workshops, vindt u op www.wiskunst.be.

Plaats: Sint-Lucas, Hoogstraat 51, Gent
Organisator: Wiskunst.be
Datum: 10/5/2012
Tijd: 18:30 - 19:30

Wiskunst: op zoek naar de ideale bouwsteen

In het kader van de Dagen van de Wiskunst gaan in Gent drie lezingen door, waarvan deze de tweede is, die de evenementendriedaagse vol workshops opent. Deze lezing wordt verzorgd door Rinus Roelofs, de befaamde kunstenaar die mathematisch interessante beelden maakt, onder andere met zijn grote beton-3D-printer. Een impressie op Google Images.

Om organisatorische redenen wordt gevraagd om zich voordien hier in te schrijven. Meer informatie over de Dagen van de Wiskunst vindt u op www.wiskunst.be.

Plaats: Sint-Lucas, Hoogstraat 51, Gent
Organisator: Wiskunst.be
Datum: 4/5/2012
Tijd: 13:30 - 14:30

Computing with infinitesimals (Sam Sanders)

The WWII war hero Alan Turing laid the foundations for what we call "computers" today. His "Turing Machines" constitute the standard model of computation, based on natural numbers. In the past decades, new models of computation (e.g. Weihrauch's 'Computable Analysis') have been (are being) developed where the notion of *real number* is fundamental. This development is motivated by the observation that real numbers feature prominently in Physics and Engineering.

Arguably, infinitesimals feature (even more) prominently in the latter disciplines. Nonetheless, models of computation based on infinitesimals are almost inexistent. In this talk, we develop an intuitive/straightforward model of computation based on infinitesimals. Time permitting, we discuss foundational implications to be presented at www.phil.cam.ac.uk/foundations.

No particular knowledge of Nonstandard Analysis is required.

Plaats: S22, Aud. A
Organisator: Logica & Analyse
Datum: 4/5/2012
Tijd: 9:30 - 17:20

Colloquium on Galois Geometry

Zie http://cage.ugent.be/geometry/cgg/cgg3.html
Plaats: S25, Emmy Noether
Organisator: Jan De Beule, Leo Storme
Datum: 2/5/2012
Tijd: 13:30 - 16:00

Algebra special seminar: Chow groups of quadrics (part II: Sofie Beke)

As part of the course "Capita Selecta in Algebra", there is this seminar on "Chow groups of quadrics". The aim of the seminar is to show how recent techniques involving Chow groups have been used to prove results in quadratic form theory. The seminar consists of two parts and each part focuses on a specific result. For the first part, see the previous announcement.

PART II: The possible values of the first Witt index of an anisotropic quadratic form (Sofie Beke)

Let q be an anisotropic non-degenerate quadratic form of dimension at least 2 over a field F of characteristic not 2. The first Witt index i1(q) is the Witt-index of q over its function field F(q).

In 2003, N. Karpenko proved D. Hoffmann's conjecture on the possible values of i1(q). The theorem says that the 2-adic expansion of i1(q) - 1 is the 2-adic expansion of dim(q) - 1, truncated at some point. This can be restated as i1(q) ≤ 2^[v2(dim(q)-i1(q))]. We will explain the main ideas of this proof, leaving out a fair bit of the technical details.

Let now q be a non-degenerate quadratic form of dimension at least 2 over a field F, and X the associated projective quadric. I will first discuss the structure of the Chow group of a (split) quadric, and say a few words about Chow groups in general.

In order to obtain information on i1(q), we will study the Chow group modulo 2 of XL², Ch(XL²). A lot of the statements we will discuss can be nicely visualised by looking at certain "pictures" associated to cycles in Ch(XL²). Properties of Steenrod operations will eventually lead to the statement about i1(q).

Plaats: S25, Emmy Noether
Organisator: Algebra
Datum: 27/4/2012
Tijd: 13:30 - 14:30

Korneel Debaene: Artin's conjecture for primitive root

Artin's conjecture on primitive roots is a central open problem in Number Theory. I will
explain the heuristic argument that led Artin to the precise form of his conjecture. I
will sketch the proof by Hooley that assumes the Generalised Riemann Hypothesis (GRH),
and explain in what way other methods might be applied to allow for a proof with milder
assumpion then the GRH.

Plaats: S22, Aud. A
Organisator: Seminarie Logica & Analyse
Datum: 25/4/2012
Tijd: 13:30 - 16:00

Algebra special seminar: Chow groups on quadrics (part I: Jan Van Geel)

As part of the course "Capita Selecta in Algebra", there is this seminar on "Chow groups of quadrics". The aim of the seminar is to show how recent techniques involving Chow groups have been used to prove results in quadratic form theory. The seminar consists of two parts and each part focuses on a specific result. For the second part, see the next announcement.

PART I: Springers theorem and the Chow group of zero cycles of a quadric (Jan Van Geel)

The classical theorem of Springer in quadratic form theory states that an anisotropic quadratic form over a field of characteristic different from 2 remains anisotropic over a field extension of odd degree. We will give a short introduction to Chow groups and then explain an algebro-geometric proof of Springers theorem for a non-degenerate quadratic form. We will then zoom in on the Chow group of zero cycles of a quadric and show that it is generated by the class of a rational point if the quadric is isotropic, and by the class of a degree 2 point in the anisotropic case.

Plaats: S22, Aud. B
Organisator: Algebra
Datum: 20/4/2012
Tijd: 14:00 - 17:20

Joint UGent-ULB-VUB seminar

14:00h -- 14:50h: Elizabeth Callens (UGent): Classification of Moufang sets arising from polarities on octonion planes.

15:20h -- 16:10h: Thomas Connor (ULB): A rank 3 geometry for the O'Nan group related to the Livingstone graph.

16:30h -- 17:20h: Markus Stroppel (U Stuttgart): Finite unitals admitting all translations.

Plaats: S25, Emmy Noether
Organisator: Hendrik Van Maldegem
Datum: 20/4/2012
Tijd: 13:30 - 14:30

Model theory, arithmetic and cuts

Speaker: Tin Lok Wong (UGent)

Abstract:
The concept of "algebraic closure" for fields has several analogues in Robinson-style model theory. I will give a brief exposition of these analogues, with examples coming from the real numbers and the natural numbers. I will also present a few recent results on this line from my joint research with Richard Kaye (Birmingham, UK) on "generic cuts".

Most of this talk will be accessible to mathematicians and students with minimal knowledge in logic.

Plaats: Auditorium A
Organisator: Andreas Weiermann
Datum: 17/4/2012
Tijd: 19:00

Lezing: Muziek in de Riemannzetafunctie

Pieter Belmans is een masterstudent wiskunde aan de UGent maar is ook reeds lang bezeten door muziek en alle achterliggende theorie. In deze lezing zal hij zijn studie combineren met zijn hobby en ons uitleggen wat het verband is tussen het stemmen van een muziekinstrument en de Riemannzetafunctie (zegt dit je niks: dat is die van de Riemannhypothese en bijhorende prijs van 1 miljoen dollar). Gewapend met deze kennis zal hij ook uitleggen wat diophantische approximatie is en waarom muzikanten hier van heel dichtbij mee te maken hebben.

Als dit alles je afschrikt: het is ook de allereerste PRIME-lezing met live orkest(je), en aansluitend zijn er drankjes en brownies van Quetzal!

Plaats: S25, Emmy Noether
Organisator: PRIME
Datum: 23/3/2012
Tijd: 13:00 - 14:00

Construction of a Dirichlet series with prescribed domain of meromorphic continuation

The Riemann zeta function is an example of a Dirichlet series, which can
be meromorphically continued to the entire complex plane. This behaviour is
rather exceptional, in general one would expect that a function represented
by a Dirichlet series cannot be continued beyond some half-plane. However,
here we show that any open subset $\Omega\subseteq\C$ is the maximal domain
of meromorphic continuation of a Dirichlet series $D(s)$, provided only that
$\Omega$ is connected and contains some right half-plane. Under somewhat
stronger assumptions on $\Omega$ we can even construct $D$ in such a way that
it has an Euler product decomposition. This disproves a conjecture by du Sautoy.

Plaats: Auditorium A
Organisator: Jan-Christoph Schlage-Puchta
Datum: 21/3/2012
Tijd: 19:00

Lezing: Jongleren met Wiskunde

De patronen die een jongleur in de lucht tekent zijn vaak bijzonder fascinerend, zeker voor wiskundigen. Op deze avond nodigen we Karsten Naert uit om ons te vertellen over de wiskundige wereld van het jongleren. Het wordt een boeiende lezing die aan te raden is voor iedereen die de schoonheid van jongleerpatronen niet kan ontkennen.

Deze activiteit wordt georganiseerd in samenwerking met QED, de vereniging voor oud-studenten Wiskunde aan UGent. Zij zullen na de lezing een receptie voorzien. Ook zullen er brownies voorzien worden door Quetzal.

Plaats: S25, Emmy Noether
Organisator: PRIME
Datum: 16/3/2012
Tijd: 14:00 - 17:00

workshop on logic

Workshop on logic
14:00-14:30 Kazuyuki Tanaka (Tohoku University) Survey on reverse mathematics
14:00-14:30 Keisuke Yoshii (Tohoku University) Infinite games in reverse mathematics
15:00-15:30 Tin Lok Wong (Ghent University) Generic properties of cuts
15:30-16:00 Jan-Christoph Schlage-Puchta (Ghent University) Elementary degrees
16:00-16:15 break
16:15-17:00 Short Talks (<=15 minutes) by Claudia Degroote (variations on Hilbert ten), Florian Pelupessy (indpendence related to coloured Ramsey), Sam Sanders
(non standard reverse mathematics) and Andreas Weiermann (elementary functions and transfinite cardinals)
[all from Ghent University]

Plaats: S25 leszaal Emmy Noether
Organisator: Andreas Weiermann
Datum: 12/3/2012
Tijd: 14:30 - 15:30

Finite oscillator models and discrete orthogonal polynomials

Talk by Joris Van der Jeugt

Title: Finite oscillator models and discrete orthogonal polynomials

Abstract: The requirement to use a finite version of a quantum oscillator comes from quantum optics.
We shall introduce a well known model for a quantum oscillator in finite dimensions, which is based on the Lie algebra su(2). In that case, the discrete wave functions are in terms of Krawtchouk polynomials, so this model is often referred to as the Krawtchouk oscillator. It can be seen, in plots and by computing limits, that these discrete wave functions tend to the standard oscillator wave functions in terms of Hermite polynomials when the dimension (of the representation) tends to infinity.
Recently, we have investigated one-parameter deformations of su(2) and its representations. New finite oscillator models can be constructed based on these deformed algebras. The discrete spectrum of the position and momentum operators can be determined explicitly, and it is shown that the corresponding discrete wave functions are in terms of Hahn polynomials. We shall present some basic properties of these wave functions. Of interest is also the discrete Fourier transform that maps position wave functions into momentum wave functions.

Plaats: S22, Auditorium C
Organisator: Hendrik De Bie
Datum: 10/3/2012
Tijd: 7:00 - 0:30

Wiskunde in Parijs

Na de vele positieve reacties op onze uistap met de vakdidactiek wiskunde naar Den Haag, willen we dit semester heel graag zelf voor jullie een gelijkaardige activiteit organiseren. Deze keer gaan we richting Parijs waar momenteel de tentoonstelling "Mathematics: A Beautiful Elsewhere" loopt. Deze tentoonstelling schenkt aandacht aan de rijkheid van de wiskunde en is gemaakt in samenwerking met enkele grote wiskundigen. Daarom ook dat wij met PRIME daar graag eens een kijkje willen nemen!

We vertrekken 's morgens vroeg met de bus op de campus en komen pas laat in de avond terug naar Gent. Zo kunnen we een hele dag genieten van Parijs. Enkel de tentoonstelling zullen we in groep bezoeken, daarna kan iedereen Parijs bezoeken naar eigen smaak.

Meer info: http://prime.ugent.be/parijs

Plaats: Vertrek aan S9 richting Parijs
Organisator: PRIME
Datum: 9/3/2012
Tijd: 14:30

Blood flow modelling in microfluidic devices with biomedical applications

Talk by

Ivan CIMRAK
University of Zilina, Slovakia

Abstract:

In the treatment of cancer, for exact diagnosis it is crucial to know the amount of circulating tumor cells (CTC) in the peripheral blood of the patients. Due to their rare occurance, CTC need to be filterred in the blood sample.

We model the flow of blood inside microfluidic channels that will act as filtering devices. The modelling is done on the level of particular blood cells immersed in the blood plasma. We create a functional computational model including fluid-structure interactions, elastic properties of the blood cells and collisions between the immersed objects. The focus of the presentation will be put on the representation of the elastic properties. We raise several questions about the modelling of the cell adhesion to antibody-covered surfaces.

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 9/3/2012
Tijd: 13:00 - 14:00

Riemann's example of a continuous, "non-differentiable" function

Talk by Jasson Vindas

Abstract:

The trigonometric series $R(x)=\sum_{n=1}^{\infty}n^{-2}sin(n^{2}x)$ has attracted much attention over the past 150 year. It was first introduced by Riemman. According to the tradition, Riemann would have proposed this function as an example of a continuous nowhere differentiable function; however, historical research has revealed that Riemann anticipated much of the later work on this function.

In this expository talk we discuss the known properties of Riemann's "non-differentiable function".

The interest in this function lies in the fact that it displays a very irregular pointwise behavior, being perhaps the chief example of a multi-fractal function. Hardy showed in 1916 that it is non-differentiable at any irrational multiple of $\pi$. His result thus confirmed the belief that $R$ would be nowhere differentiable. The result of Gerver (1970) came then as a surprise: Riemann's function actually admits derivatives at certain rational multiples of $\pi$. The complete understanding of the pointwise properties of Riemann's function was only settled down until 1996 by Jaffard. The techniques involved in the analysis of this function are very rich, ranging from number theory to wavelet analysis.

Everyone is welcome! Notes of the talk will be available at http://cage.ugent.be/~jvindas/talks.html

Plaats: S22, A
Organisator: Logic and Analysis
Datum: 7/3/2012
Tijd: 13:30 - 15:30

Andrew Dolphin: refined Witt decomposition for hermitian forms in characteristic 2

Spreker: Andrew Dolphin (Universität Konstanz, Germany)

For quadratic forms over fields, Witt's decomposition theorem says that any quadratic form can be uniquely written as the sum of an anisotropic form and a hyperbolic form. In this talk, we will discuss a series of refinements that can be made to the analogous decomposition theorem for hermitian forms over a division algebra with involution when the base field is of characteristic 2. We will further discuss the applications of this refinement to the generic splitting of algebras with involution in characteristic 2.

Plaats: S25, Aud. Emmy Noether
Organisator: Algebra
Datum: 6/3/2012
Tijd: 19:30

PUMA (Pure Mathematics)

De vierde editie van onze wiskundeolympiade PUMA (Pure Mathematics) zal opnieuw een uitdaging zijn voor iedereen die houdt van wiskundige problemen, gaande van korte en elegante vraagjes tot ingewikkelde raadsels. Deze wedstrijd is een aanrader voor studenten wiskunde, fysica, informatica, burgerlijk ingenieur en iedereen die vroeger plezier beleefde aan de Vlaamse Wiskundeolympiade.

De proclamatie vindt een week later plaats op dezelfde locatie, gedurende de middagpauze van pi-dag (op het PRIME pi-zzafestijn). De beste drie deelnemers krijgen een certificaat en een geldprijs geschonken door Optiver.

Plaats: S9, A3
Organisator: PRIME
Datum: 6/3/2012
Tijd: 11:00

Approximate Global Convergence and Adaptivity for Hyperbolic Coefficient Inverse Problems

Talk by

Mikhail KLIBANOV
University of North Carolina at Charlotte

Abstract

The central question in the numerical solution of a Coefficient Inverse Problem is the question of obtaining a good approximation for the unknown coefficient without any advanced knowledge of any point in a small neighborhood of this coefficient. As soon as this approximation is obtained, Newton-like methods can refine it. This is an ENORMOUSLY challenging question. Especially under the condition that the corresponding numerical method should be numerically efficient: otherwise there is no point to work on.

Because of this challenge, it is inevitable that some reasonable approximations should be made. On the other hand, because of these approximations, it is crucial that the numerical method should be verified computationally. Roughly speaking, the above is what “approximate global convergence” is about.

In the past few years we have developed several versions of such a numerical methods. Their convergence to the exact solution is guaranteed within framework of a certain approximate mathematical model.

These algorithms were verified on both computationally simulated and experimental data. Especially on the most challenging case of blind experimental data. Computational results are accurate.

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 2/3/2012
Tijd: 14:00

Well partial orderings and recursively defined trees.

Talk by Jeroen Van der Meeren

Title: Well partial orderings and recursively defined trees.

Abstract:
First, we will give some basic properties of well partial orderings. Well partial orderings play an important role in for example logic, computer science and mathematics. They are the essential ingredient of famous theorems like Higman's lemma, Kruskal's theorem and the graph minor theorem.

Secondly, we will give an upper bound for the maximal order type of well partial orderings related to tree-embeddability relations. These well partial orderings are based on a Friedman-style gap-condition.

Plaats: S22, Auditorium A
Organisator: Andreas Weiermann
Datum: 29/2/2012
Tijd: 13:30 - 15:30

Raf Bocklandt: an introduction to mirror symmetry from a noncommutative point of view

Spreker: Raf Bocklandt (Newcastle University, UK)

The aim is to give a little historic overview of homological mirror symmetry and work out some basic examples, such as the projective line and other Riemann surfaces.

To do this we introduce some techniques from noncommutative algebraic geometry and category theory and apply these to these specific examples.

Plaats: S25, Aud. Emmy Noether
Organisator: Algebra
Datum: 27/2/2012
Tijd: 14:30 - 15:30

From approach theory to index calculus

Talk by Bob Lowen (University of Antwerp)

Abstract: In this talk we give an overview of approach theory, index
calculus and applications in topology, functional analysis and probability
theory.

Plaats: S22, Auditorium C
Organisator: Hendrik De Bie
Datum: 24/2/2012
Tijd: 17:15 - 17:45

Vacuum Spacetimes of Embedding Class 2

Alan Barnes (Aston University, Birmingham, UK)

Many years ago Yakupov stated, without proof, that the torsion vector in embedding class two vacuum spacetimes is necessarily a gradient vector and so can be scaled away. This result is equivalent to the fact that the two second fundamental forms associated with the embedding necessarily commute. Yakupov also claimed, again without proof, that the class 2 vacua of Petrov type III do not exist. His results are much quoted and the vanishing of the torsion has been assumed in later investigations of class 2 vacuum space-times; for example those by Hodgkinson and Van den Bergh.

I will report on the progress made to prove this result since my last talk in Ghent in 2010. In particular it is shown that that there are no type III embeddings with torsion of vacuum spacetimes (with Λ=0). This, together with Van den Bergh’s result that there are no such embeddings without torsion, proves Yakupov’s second result.

Furthermore it is shown that the only vacuum spacetimes (with Λ=0) that could possibly be embedded with torsion in a 6-D flat space are type N plane waves and Minkowski space. For both of these spacetimes there definitely exist embeddings without torsion, but embeddings with torsion may also exist. This latter question is currently being investigated. The case with non-zero Λ will also be discussed.

Plaats: S22, C
Organisator: N. Van den Bergh
Datum: 24/2/2012
Tijd: 16:00 - 17:00

Complex Windmill Transform Solution-Generating Technique

Con Lozanovski (ACU, Melbourne, Australia)

Complex transformations can be used to relate two known families of spaceitmes or generate new solutions from seed. For example, as demonstrated by the well known technique due to Newman and Janis. The Newman-Janis algorithm, commonly referred to a "trick", has been established as a viable solution generating technique when considering static spherically symmetric seed solutions. The algorithm has proved particularly useful in generating interior solutions of the Kerr spacetime. Not confined to classical general relativity the algorithm has extended applications, from higher dimensional relativity to aspects of string theory.

Motivated by recent developments with the Newman-Janis algorithm we consider a different type of complex transform to due McIntosh (1992) [and Harvey (1989, 1992)] where the Kasner spacetime is related to the Lewis vacuum spacetime, in the so-called windmill metric form discussed by MacCallum (1998) and McIntosh (1992). A careful analysis of their approach leads to a natural generalisation of the transformation. We then apply this generalised version of the transformation and find, given reasonable assumptions associated with the energy-momentum and Weyl tensors, together with other technical assumptions, that this leads to new purely magnetic fluid spacetimes in the class of Wainwright B(ii) and windmill spacetimes. We show that one of these solutions is a contributing member to the Wylleman-Van den Bergh classification of irrotational, type I, purely magnetic perfect fluid spacetimes. Finally, we speculate on some further results associated with vacuum spacetimes and briefly consider the McIntosh-Hickman complex NP formalism for future study.

Plaats: S22, C
Organisator: N. Van den Bergh
Datum: 24/2/2012
Tijd: 14:00 - 16:00

Internationalisation@home

You are cordially invited to the 1 rst Internationalisation@Home 2012 Activity of the Faculty of Sciences.

During an informal gathering, a professor from Mexico visiting Ghent University and a UGent professor will talk about their international experiences as a researcher. Participation is free of charge, but for practical reasons, we kindly ask everybody participating to this event to register by sending an e-mail to erasmus@cage.ugent.be.

Program:

  • 14u00-14u45: Prof. dr. Andres Cedillo (Mexico): Chemist from Mexico via the USA to Belgium.
  • 15u00-15u45: Prof. dr. Mohamed Lamkan (VIB/Ghent University): An international research career.

The organisers:

P. Bultinck and P. Van Der Voort
Department of Inorganic and Physical Chemistry
Ghent University

L. Storme
Department of Mathematics
Ghent University

Plaats: S3
Organisator: Leo Storme
Datum: 23/2/2012
Tijd: 16:30 - 17:30

Density growth in Kantowski-Sachs cosmologies with cosmological constant

Michael Bradley (Umea University, Sweden)

The growth of density perturbations in Kantowski-Sachs cosmologies with a positive cosmological constant is studied, using the 1+3 and 1+1+2 covariant formalisms. For each wave number we obtain a closed system for scalars formed from quantities that are zero on the background and hence are gauge-invariant. The solutions to this system are then analyzed both analytically and numerically. In particular the effects of anisotropy and the behaviour close to bounces in the cosmic scale factor is considered.

Plaats: S22, C
Organisator: N. Van den Bergh
Datum: 23/2/2012
Tijd: 15:00 - 16:00

The Opera Neutrino Velocity Measurement

Alan Barnes (Aston University, Birmingham, UK)

In September 2010 the Opera collaboration announced the results of a two year long experiment to measure neutrino velocities over a distance of about 730km between CERN and LNGS in central Italy. They reported early arrival times of neutrinos of about 60ns compared to the expected time assuming propagation at the speed of light (about 2.34ms) This corresponds to a superluminal velocity v: (v-c)/c = 2.37×10-5 with a high degree of statistical significance >6σ.

The experiment is described in some detail and a number of relativistic effects which might affect its conclusion are considered. Most are too small to be significant.; however, the Sagnac effect due Earth’s rotation was not considered in the original Opera analysis and amounts to 2.2ns. As LNGS is to the east of CERN this effect is a delay so its inclusion in the analysis strengthens the Opera result somewhat.

The Global Positioning System (GPS) is crucial to the Opera experiment as it is used both to determine the exact length of the baseline between CERN and LNGS and to synchronise clocks at the two sites. Thus the GPS system is described in some detail and relativistic effects which might affect these measurements are considered including some which are normally neglected in GPS. Again all these relativistic effects appear to be too small to be significant for the Opera result.

Plaats: S22, C
Organisator: N. Van den Bergh
Datum: 21/2/2012
Tijd: 16:30 - 17:30

On the splitting of spacetime tensors in electric/magnetic parts

Lode Wylleman (UGent & Stavanger University, Norway):

In this talk I shall present a simple procedure for obtaining a twofold splitting of any spacetime tensor relative to an observer, in arbitrary spacetime dimension. When applied to the four-dimensional Weyl tensor the procedure reproduces the usual definitions of purely electric and magnetic parts. Doing the same for the Riemann and Ricci tensors one arrives at the concepts of Weyl or Riemann purely electric/magnetic spacetimes. I shall make contact with the Penrose-Debever null alignment theory and its higher-dimensional generalization, and rederive/extend various results in a simplified way. This is work done in collaboration with Sigbjorn Hervik and Marcello Ortaggio.

Plaats: S22, C
Organisator: N.Van den Bergh
Datum: 21/2/2012
Tijd: 15:00 - 16:00

Spacetime dynamics of spinning particles --- exact gravito-electromagnetic analogies

Filipe Costa (University of Porto, Portugal):

We compare the rigorous equations describing the motion of spinning test particles in the gravitational and electromagnetic fields, and show that if Mathisson-Pirani spin condition holds, exact gravito-electromagnetic analogies emerge for both the force on the particle and its spin evolution. The former can be stated as follows: both the electromagnetic force on a magnetic dipole and the gravitational force on a gyroscope are given by a contraction of a Rank 2 magnetic type tidal tensor (B_ab, H_ab), with the dipole/spin 4-vector. B_ab is a covariant derivative of the magnetic field measured in the particle's MCRF; its gravitational counterpart H_ab is the magnetic part of the Riemann tensor, as measured by the particle. The tidal tensor analogy extends to Einstein and Maxwell field equations [PRD 78 024021, 2008]. It provides a familiar physical interpretation for H_ab, as well as means for a transparent comparison between the two interactions.
Exploring the differences in the tensorial structure proves especially enlightening. In contrast with B_ab, H_ab is symmetric (in vacuum) and spatial. That signals fundamental differences in the interactions, as the antisymmetric parts of the electromagnetic tidal tensors encode the laws of electromagnetic induction. They imply e.g. that observers moving in a non-homogeneous electromagnetic field always measure a non-vanishing B_ab (so that the magnetic dipoles they carry feel a force), an effect which has no counterpart in gravity.

Plaats: S22, C
Organisator: N.Van den Bergh
Datum: 7/2/2012
Tijd: 20:00

Escher en het Droste-effect

Toegankelijke lezing door Hendrik Lenstra, Universiteit Leiden

In 1956, the Dutch graphic artist M.C. Escher made an unusual lithograph with the title Print Gallery. It shows a young man viewing a print in an exhibition gallery. Amongst the buildings depicted on the print, he sees paradoxically the very same gallery that he is standing in. A lot is known about the way in which Escher made his lithograph. It is not nearly as well known that it contains a hidden Droste effect, or infinite repetition; but this is brought to light by a mathematical analysis of the studies used by Escher.

On the basis of this discovery, a team of mathematicians at Leiden produced a series of hallucinating computer animations. These show, among others, what happens inside the mysterious spot in the middle of the lithograph that Escher left blank.

Deze lezing vereist helemaal geen wiskundige voorkennis. Iedereen is welkom, ook familieleden en vrienden. Er wordt verzocht vooraf in te schrijven via deze link.

Plaats: S25, Aud. Emmy Noether
Organisator: Conferentie Incidence Geometry and Buildings
Datum: 23/1/2012
Tijd: 15:30

Using the Hopf fibration for fun and profit: a new formulation for point vortices on the sphere

Talk by dr Joris Vankerschaver (UGent and UC San Diego) in the Differential Geometry and Mechanics seminar.

Everyone is cordially invited!

Plaats: S22, Zaal A
Organisator: Tom Mestdag
Datum: 23/1/2012
Tijd: 14:30

On the Hamiltonization problem of nonholonomic systems

Talk by Prof Paula Balseiro (Universidade Federal Fluminense) in the Differential Geometry and Mechanics Seminar.

Abstract: In this seminar we will start by explaining the Hamiltonization problem of nonholonomic systems. We will present a geometric way to treat this problem based on a deformation of the classical nonholonomic bracket in order to generate a family of brackets describing the dynamics. Rigid bodies with constraints (such as the Chaplygin ball) are treated with these geometric tools to explain their hamiltonization.

Everyone is cordially invited!

Plaats: S22, Zaal A
Organisator: Tom Mestdag
Datum: 12/1/2012
Tijd: 11:00

Comparative analysis of typical approaches for inverse source problems

Talk by
Prof. Alemdar Hasanoglu (Hasanov),
Izmir University, Turkey

Title:

Comparative analysis of typical approaches for inverse source problems
with boundary and final time measured output data for parabolic
equations


Abstract:

This lecture presents a systematic study of typical approaches for inverse source
problems for a separated form F (x)H(t) source terms in the heat conduction (or linear parabolic)
equation u_t = (k(x)u_x )_x + F (x)H(t).

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 23/12/2011
Tijd: 10:30

SEMINAR: The wild bootstrap for nonparametric analysis of competing risks and multistate models

Jan Beyersmann, University of Freiburg

Title: The wild bootstrap for nonparametric analysis of competing
risks and multistate models

The motivating research question comes from studying
infectious complications after peripheral blood stem cell
transplantation. Allogeneic transplants are considered to lead to more
blood stream infections as compared to autologous
transplants. Bloodstream infections are a severe complication and
increase mortality. An initial analysis of 1616 patients found that
allogeneic transplants increased the infection proportion (number of
infections divided by number of patients), but decreased the infection
rate (number of infections divided by patient-days). A nonparametric
competing risks analysis provides for an interpretation of this
result: Allogeneic transplants do lead to more infections, but the
increase comes with a time delay. The question at hand is whether the
early difference between the infection probabilities is
significant. This question is relevant for investigating antibiotic
prophylaxis, which is not the same for both treatment groups. The
statistical problem is that nonparametric analysis of the cumulative
event probabilities over time regions and based on asymptotic theory
is hampered by the complicated structure of the limiting covariance
process. This is often attacked via a simple resampling technique
using conditional multiplier approximation. The idea is to keep the
data fixed and to introduce computer generated normal variates in
martingale representations of the statistics of interest. We extend
the resampling technique to non-normal multipliers (wild bootstrap),
left-truncated data, Greenwood-type variances and more complex
multistate models. Our approach relies on approximating the asymptotic
distribution corresponding to the multiple transitions hazards first
and on subsequently using product integration and the functional delta
method.

Plaats: S9, Room V2
Organisator: Stijn Vansteelandt
Datum: 22/12/2011
Tijd: 17:00 - 18:30

Maarten Bekaert: Do patients die from or with infection?

Finding the answer through causal analysis of longitudinal intensive care unit data.

Doctoraatsverdediging van Maarten Bekaert (Tielt, 16-6-1983).

Promotoren: Prof. dr. Stijn Vansteelandt, WE02 - Prof. dr. Dominique Benoit, GE01

Officiële aankondiging: hier.

Plaats: S9, A2
Organisator: Statistische Data-analyse
Datum: 22/12/2011
Tijd: 14:30 - 17:00

Samenkomst werkgroep instroom en PR

Het is drie jaar geleden dat verschillende wiskundigen de koppen bijeen staken om zich te beraden over de instroom wiskunde en de initiatieven die we zouden kunnen nemen. Op die vergadering werd UniMath ontwikkeld, dat in zijn pilootjaar 2009 enkel Projectieve vlakken en codes bevatte en toen nog door het leven ging als Project Vrije Ruimte. Toen was de term cursuscruisen nog niet bedacht.

Drie jaar later zouden we terug willen samenkomen hierrond. Zoals Hendrik Van Maldeghem aankondigde in de laatste OCW-vergadering zouden we een vergadering annex brainstormsessie willen houden om het verleden te evalueren en de toekomst uit te tekenen op het gebied van Wiskunde-PR. Op dit initiatief, dat eigenlijk adviserend is voor de OCW, zouden we graag veel OCW-leden willen verwelkomen, alsook iedereen die hierin geïnteresseerd is. Wat we zouden moeten bespreken, is

  • Uitgebreide evaluatie van UniMath + (hoe) gaan we ermee verder?
  • Wat plannen we in de toekomst?

Daarom stellen Hendrik Van Maldeghem, Andreas Weiermann en Bert Seghers voor om samen te komen op donderdag 22 december 2011, om 14:30 in de Vergaderzaal van S22. Als je niet kan komen maar wel interesse hebt, laat dan zeker iets weten.

Het zou niet de bedoeling zijn om ons weer tot over onze oren in het werk te schieten met vele nieuwe projecten, maar eerder om stil te staan bij publiciteit en met de wiskunde een doordachte strategie in communicatie en PR te ontwikkelen.

Plaats: S22, Vergaderzaal
Organisator: Opleiding Wiskunde
Datum: 21/12/2011
Tijd: 15:00

Multi-momentum maps in multi-symplectic geometry

This is a talk by Prof Frans Cantrijn in the Differential Geometry and Mechanics seminar. Everyone is cordially invited!

Plaats: zaal C
Organisator: Tom Mestdag
Datum: 16/12/2011
Tijd: 10:00 - 11:00

Reverse mathematics of complex analysis

Speaker: Yoshihiro Horihata (Tohoku University)

Reverse mathematics, which was pioneered by Harvey Friedman in the 1970s, is one program in mathematical logic.
The purpose of reverse mathematics program is to classify mathematical theorems by the strength of the axioms which are sufficient and necessary to prove it.

In this talk, some weak versions of Riemann's mapping theorem are considered in second order arithmetic.
Then, we apply one of them to prove Picard's little theorem within second order arithmetic.

Additionally, we will discuss about the identity theorem and Taylor expandability of holomorphic functions in second order arithmetic.

Plaats: Auditorium A
Organisator: Andreas Weiermann
Datum: 14/12/2011
Tijd: 18:15

Facultaire infosessie Internationalisering

Beste student(e)

Het Erasmus programma maakt het mogelijk om een deel van jouw studies te
volgen aan een buitenlandse Universiteit in het academiejaar 2012-2013.
Overweeg je een studie in het buitenland? Of klinkt ‘Erasmus’ je voorlopig
vaag in de oren? Wens je vrijblijvend wat meer informatie?
Wij organiseren een facultaire infosessie op woensdag 14 december 2011 van
18u15 tot 19u15 in Aud. 4 (K.L. Ledeganckstraat 35) waar we vnl. het luik
‘academische en praktische voorbereiding’ toelichten.

U kan zich inschrijven via volgende link vóór 1 december 2011:

https://webapps.ugent.be/eventManager/events/FacWetErasmus

Met vriendelijke groeten

Regine Coolen / Anja Sandrap
Internationalisering
Faculteit Wetenschappen

Email: international.sci@ugent.be

Plaats: K.L. Ledeganckstraat 35, aud. 4
Organisator: Faculteit Wetenschappen
Datum: 14/12/2011
Tijd: 14:30 - 17:00

Seminarie Algebra: A brief introduction to model theory

Jan-Christoph Schlage-Puchta: A brief introduction to model theory

If one avoids using phrases like "there exists a bijection", which cannot be made precise without developing huge parts of set theory, different mathematical objects suddenly look the same. For example, all infinite sets, or all algebraically closed fields of given characteristics essentially look the same. In this talk I shall first give a precise meaning to this concept, and then apply this notion to examples such as algebraically closed fields.

I assume some basic knowledge in algebra and topology, but no knowledge of logic.

Plaats: S22, A
Organisator: Algebra
Datum: 13/12/2011
Tijd: 19:45

Grote getallen en geheime gegevens

Over codes en cryptografie

Wat is cryptografie precies? Waarvoor dienen de controlegetallen op het einde van een rekeningnummer? Hoe komt het dat cd's met (kleine) krassen toch nog goed afspelen?

Welke soorten geheimsschriften en codes bestaan er zoal? Hoe werden geheime codes gekraakt in tijden van oorlig? Kan je nog onjkraakbare codes maken?

Gratis toegang.

Gastheer: Joël De Ceulaer (De Standaard)
Met: Prof. Dr. Leo Storme (UGent)

Meer info: www.wetenschapscafegent.be.
Plaats: Zebrastraat 32
Organisator: Wetenschapscafé
Datum: 13/12/2011
Tijd: 10:00

Nonlinear inverse problems in magnetic field synthesis

Talk by Marcin Ziolkowski
(West Pomeranian University of Technology, Szczecin, Poland)

Abstract:

Magnetic field synthesis problems have been discussed at length in
scientific literature but they still remain as a topic of research in
electrical engineering, physics and medical applications. In these
disciplines, there is often a need to design an electromagnetic arrangement
which can generate a magnetic field of required distribution. Such an
arrangement can also work as an active shield. The aim of an active shield
is to generate a specified magnetic field which counteracts the external
magnetic fields in a protected region.
This presentation will describe the methods of magnetic field synthesis in
an axisymmetric region. It is assumed that the region of interest is
surrounded by a cylindrical solenoid with an electrical current. Two cases
will be considered, namely: magnetic field synthesis on a solenoid's axis
and magnetic field synthesis in an axisymmetric three-dimensional finite
region. Two independent methods of magnetic fields synthesis, i.e.
iteratively regularized Gauss-Newton method and Genetic Algorithm coupled
with Bezier curves-based method, will be discussed and compared in this
presentation.

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 9/12/2011
Tijd: 16:00

Wigner quantization and Lie superalgebra representations

Thesis defense of Gilles Regniers for obtaining a PhD degree in Mathematics.

Summary: Wigner quantization leads to algebraic relations for operators, which are difficult to solve in general. Using representations of Lie superalgebras such as gl(1|n) and osp(1|2n), particular solutions of certain Wigner quantum systems can be investigated. In the thesis, the following systems are considered in the framework of Wigner quantization: some one-dimensional Hamiltonians, harmonic oscillators coupled by an interaction matrix, an n-dimensional harmonic oscillator. The techniques used are, amongst others: representations and characters of Lie superalgebras, branching rules, generating functions, orthogonal polynomials and hypergeometric functions.

Plaats: Krijgslaan 281-S9 - A2
Organisator: J. Van der Jeugt
Datum: 9/12/2011
Tijd: 10:00 - 11:00

Asymptotic formulas for partitions III. On a multiplicative partition problem involving certain prime numbers

Talk by Jasson Vindas

Abstract:

We continue our series of talks on asymptotic formulas for partition problems. Lecture notes of the previous two talks are available ( at http://cage.ugent.be/~jvindas/talks.html).

We shall consider a multiplicative partition problem involving certain prime numbers; in particular, we will give answer to an open problem of A. Weiermann. The technique that we will employ has a general character, thus, the problem studied in this talk may serve as a model for finding strong asymptotic formulas for other similar multiplicative partition problems.

The counting problem under consideration arises naturally in several contexts, for instance, when coding non planar trees with prime numbers, at considering a certain norm complexity for ordinals, or even in some problems of chemistry.

We first discuss an extension of Ingham's theorem for partitions. In the remaining part of the talk, we will explain how to find the sought asymptotic formula for our counting function. The talk reports on collaborative work with H. Vernaeve.

Plaats: S22, A
Organisator: Jasson Vindas
Datum: 8/12/2011
Tijd: 13:00

Electromagnetic heating of metals and its selected applications

Talk by Pavel Karban, Frantisek Mach and Ivo Dolezel
(University of West Bohemia, Pilsen, Czech Republic )


Abstract:

Physical backgrounds of electromagnetic heating of solid and molten metals. Examples of typical industrial and other applications (direct heating, induction heating, induction hardening and levitation melting of solid metals, dosing, pumping and stirring of molten metals). Continuous mathematical models of these processes, coupling of particular physical fields (current or electromagnetic field, temperature field, in specific cases also field of thermoelastic displacements). Possibilities of their numerical solution. Presentation of the fully adaptive higher-order finite element method developed in our group. Illustrative examples and further activities in the domain.

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 8/12/2011
Tijd: 11:00

Curve evolution models — numerical solution and applications

Talk by Jozef Urban
(Slovak University of Technology, Bratislava)


Abstract:

In this talk we present 2D and 3D Lagrangean curve evolution models
used for online semi-automatic medical image segmentation, simulations
of wind-driven forest fire fronts and finding an ideal path of camera
in virtual colonoscopy. In all these models, the curve is driven by a
properly designed external vector field, the motion is regularized by
curvature and numerical computations are stabilized by a suitable
asymptotically uniform tangential redistribution in 2D and in 3D. We
also present new fast algorithm for treatment of topological changes
in Lagrangean approach to curve evolution which is important e.g. in
forest fire simulations. Our formulations of 2D and 3D curve evolution
models are based on intrinsic advection-diffusion equations with a
driving force discretized by the flowing finite volume method allowing
large time steps without losing numerical stability. This is a common work with Karol Mikula and Martin Balazovjech.

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 8/12/2011
Tijd: 10:00

Application of level set method for groundwater flow problems

Talk by Peter Frolkovic
(Slovak University of Technology, Bratislava)

Abstract:

The possibilities of level set methods for modelling of moving interfaces and boundaries in groundwater flow and transport problems will be discussed. Particular application of groundwater flow with moving water table will be introduced in details. The main ingredients of level set methods like computations of signed distance function, extrapolation of missing data and solution of advection equation will be described. Several examples of practical relevance will be presented.

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 6/12/2011
Tijd: 11:00

Gelfand-Levitan-Krein method in inverse acoustic problems

Talk by Maxim Shishlenin
(Sobolev Institute of Mathematics, Russian Academy of Science, Novosibirsk)

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 6/12/2011
Tijd: 10:00

Numerical methods for solving inverse acoustic problems

Talk by Maxim Shishlenin
(Sobolev Institute of Mathematics, Russian Academy of Science, Novosibirsk)


Abstract:

The direct and iterations algorithms for the solutions of inverse hyperbolic problems are considered.
Methods for solving inverse and ill-posed problems can be divided into direct and iteration. Direct methods are linearization, finite-difference scheme inversion, Gel'fand-Levitan-Krein and singular value decomposition. Direct methods allow to determine unknown coeffcients in fixed point of medium when additional information is given by the trace of the direct problem solution on a (usually time-like) surface of the domain. The direct methods in multidimensional inverse problems seem to be very promising because in iteration algorithms (method of steepest descent, Landweber iteration, Newton-Kantorovich method and so on) we have to solve the corresponding direct (forward) and adjoint (or linear inverse) problems on every step of the iterative process and in multidimensional case solving direct problem is hard enough. Advantage of direct methods is easy way for algorithm parallelization, namely, value of unknown coeffients in fixed point can be determined independently of values in other points.

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 5/12/2011
Tijd: 17:30

Workshop Ongelijkheden

Workshop over ongelijkheden door Bart De Bruyn.

Iedereen heeft al wel eens gehoord van ongelijkheden, maar dat wil niet zeggen dat ze zich gemakkelijk laten oplossen. Integendeel: wiskundige problemen met zo'n ongelijkheden vragen veel creativiteit en ervaring. Gelukkige zijn er enkele handige tips en oplossingstechnieken die je een heel eind verderhelpen.

Bart De Bruyn toont hieruit de belangrijkste en schotelt ons gepaste uitdagingen voor (van elke moeilijkheidsgraad). Er worden gratis brownies van Quetzal voorzien.

Plaats: S25, Emmy Noether
Organisator: PRIME
Datum: 2/12/2011
Tijd: 10:00 - 11:00

Asymptotic formulas for partitions II. Ingham's approach

Talk by Jasson Vindas

Abstract:

This is the second part of my series of talks on asymptotic formulas for partition problems. There are lecture notes of the previous talk (available at my website); however, I emphasize that this talk is independent from the previous one.

Let p(n) be the number of unrestricted partitions of a natural number n, that is, the number of ways of writing n as sums 1j +2m +3h+..., where j, m, h, .. are nonnegative integers. Hardy and Ramanujan (1918) discovered a celebrated asymptotic formula for p(n), which is certainly not easy to guess. In 1940, Ingham developed a method for finding strong asymptotic formulas for general partition problems. His method is based on a Tauberian theorem for Laplace transforms and easily recovers the formula of Hardy and Ramanujan.

We will discuss in this talk Ingham's approach in detail. There are no prerequisites, students and non-specialists are welcome!

Plaats: S22, A
Organisator: Jasson Vindas
Datum: 2/12/2011
Tijd: 9:30 - 17:30

Colloquium on Galois geometry

Tweede colloquium over Galoismeetkunde en verwante onderwerpen. Het programma in een notedop:

10:00: Anamari Nakic (University of Zagreb): "Kramer-Mesner with tactical decompositions"
11:00: Marcella Takáts (Eötvös Loránd University, Budapest): "Exploring new directions"
11:45: lunch
13:15: John Sheekey (University College Dublin): "Subspaces of matrices with restricted rank"
14:15: Klara Stokes (Universitat Rovira i Virgili, Tarragona): "The numerical semigroup of combinatorial configurations"
15:00: koffiepauze
15:30: Frédéric Vanhove (Universiteit Gent): "On geometry and distance-regular graphs"
16:30: Jan-Christoph Schlage-Puchta (Universiteit Gent): "Additive combinatorics in vector spaces over large finite fields"

Deelname en lunch gratis, registreer daartoe ten laatste op 20/11/2011 per e-mail. De abstracts zijn beschikbaar online.
Plaats: S25, Emmy Noether
Organisator: Jan De Beule en Leo Storme
Datum: 1/12/2011
Tijd: 13:00

A computational multiscale approach for multiphase porous media

Talk by: Lubomir Banas
(Department of Mathematics, Heriot-Watt University, Edinburgh)

Abstract:

We present a multiscale method for multiphase porous media flow based on
numerical homogenization. The multiscale algorithm consists of a pore
scale phase-field multiphase flow solver coupled to a macroscopic finite
volume solver. The coupling between the solvers is done through a
macroscopic pressure gradient which enters the pore-scale simulations
and averaged microscopic fluxes which are used in the finite volume
solver.
The method is able to handle arbitrary number of fluid phases and allows
to include nonlinear effects such as contact angles and surface
tension in a straightforward way. For single phase and simplified
two-phase flow problems the approach is consistent with existing
homogenization results.

Plaats: S22, Auditorium C
Organisator: Marian Slodicka
Datum: 28/11/2011
Tijd: 13:30 - 14:30

Homogeneous conformal Killing-Yano space-times

Talk of Prof Norbert Van den Bergh in the Differential Geometry and Mechanics seminar. Everyone is cordially invited!

Plaats: S22, computerzaal
Organisator: Tom Mestdag
Datum: 25/11/2011
Tijd: 10:00 - 11:00

Ideals and filters in a ring of generalized constants

Talk by the guest speaker Dimitris Scarpalezos (Paris 7) in the Logic and Analysis seminar. Everyone is welcome!

Abstract:

In the case of the algebra of continuous functions on a normal topological space A, there is a precise correspondence between maximal ideals and maximal filters of closed subsets of A (ultrafilters). More generally, to a given ideal in this algebra of continuous functions, we can associate the filter of the zero sets of elements of the ideal; on the other hand, to a given filter, we associate the ideal of functions whose zero sets belong to the filter.

In this talk we study ideals in the ring of "continuous" generalized constants, which in fact amounts to the same as studying ideals of moderate functions on the interval (0,1]. Our results extend earlier ones by Vernaeve, and Aragona and Juriaans, which were obtained in the setting of the ring of generalized constants without the continuity hypothesis. To each filter of "asymptotic" closed sets we associate two ideals, and to each ideal we associate one of such filters. We prove that the maximal and minimal prime ideals are precisely those that correspond to the choice of ultrafilters.

Plaats: S22, A
Organisator: Jasson Vindas
Datum: 23/11/2011
Tijd: 14:30 - 17:00

Groepen van eindige Morley rang, deel 2

Tom De Medts: Groepen van eindige Morley rang

Plaats: S22, A
Organisator: Algebra
Datum: 22/11/2011
Tijd: 10:00 - 11:00

Wave propagation on groupoids

Voordracht van gastspreker Shantanu Dave (Universiteit Wenen).

Abstract:
The propagation of singularities by solutions to wave operators describes many interesting phenomenons on various manifolds with boundaries/corners. We shall present a general result relating propagation of singularities on a Lie-groupoid with the propagation of singularities on the base manifolds, under suitable assumptions.

Plaats: S22, C
Organisator: Hans Vernaeve
Datum: 21/11/2011
Tijd: 16:00

Archimedes? Stomachion: The World

Lecture by Douglas G. Rogers

Abstract. Archimedes' Stomachion, a game based on a geometrical dissection, has been called "the World's Oldest Puzzle". It has been in the news in connection with the Archimedes Codex eliciting a novel combinatorial interpretation. No examples are known to have survived, making both moves and board something of a puzzle in themselves. The presumption that the board is a square is open to challenge: such a board is difficult to fabricate and awkward to use, on account of the sharp angles required; and most likely the Arabic text has been mistranslated. But, in reappraising the subject afresh, what tells most against the square board, and in favour of a double square board, is the geometry that, strangely enough, seems to be have been overlooked.

Our review also returns to focus gures from the previous century, notably Richard Oldham, FRS (1858-1936), better known for identifying the Earth's core, who proposed a double square board in a letter to Nature in 1926.

The Stomachion board also has suggestive Archimedean echoes. Whether square or double square, the board features several centroids of triangles that help determine the proportional areas of the pieces of the dissection. The principal lines of the dissection give a geometrical approach to recurrence relations and rational approximations, to the square root of 2 in the case of the double square board and to the Golden Ratio in the case of the square board.

Plaats: S25, Emmy Noether
Organisator: Albrecht Heeffer
Datum: 21/11/2011
Tijd: 13:30 - 14:30

Geometric aspects of Routh reduction for Lagrangian systems

Talk of Eduardo Garcia-Torano in the Differential Geometry and Mechanics seminar. Everyone is cordially invited!

Plaats: S22, computerzaal
Organisator: Tom Mestdag
Datum: 21/11/2011
Tijd: 10:00 - 11:00

Non-intersecting Brownian motions and complex analysis

Voordracht door Steven Delvaux (KULeuven)

Abstract:

In this expository talk, we discuss non-intersecting
1-dimensional Brownian motion paths with prescribed starting and ending
positions. We obtain some interesting phase transitions. We also discuss
the limiting distribution of the paths. These problems lead to techniques
from potential theory, orthogonal polynomials and complex analysis,
particularly jump problems for piecewise analytic functions.

Plaats: S22, Auditorium B
Organisator: Hendrik De Bie
Datum: 18/11/2011
Tijd: 10:00 - 11:00

Asymptotic formulas for partitions I. Tauberian methods

Talk by Jasson Vindas

Abstract:

This is the first of a series of talks that the speaker intends to give on the topic of analytical methods in combinatorial analysis. We will focus on partition problems.

Let p(n) be the number of unrestricted partitions of a natural number n, that is, the number of ways of writing n as sums 1j +2m +3h+..., where j, m, h, .. are nonnegative integers. In 1918, Hardy and Ramanujan discovered their celebrated asymptotic formula for p(n). Our aim in this talk is to discuss classical Tauberian methods for obtaining this remarkable asymptotic formula. We shall actually take a more comprehensive perspective and deal also with more general partition problems.

It should be pointed out that Tauberian theorems are very useful and valuable tools for non-specialists because their statements are very often relatively "easy" to understand and apply without having to have a particular specialized knowledge. Thus, students and non-specialists are welcome!

Plaats: S22, A
Organisator: Jasson Vindas
Datum: 10/11/2011
Tijd: 11:30 - 12:30

Reuniting the antipodes: bringing together Nonstandard Analysis

Talk by Sam Sanders (currently Tohoku University)

Constructive Analysis was introduced by Erret Bishop to identify the `computational meaning' of mathematics. In the spirit of intuitionistic mathematics, notions like `algorithm,' `explicit computation,' and `finite procedure' are central. The exact meaning of these vague terms was left open, to ensure the compatibility of Constructive Analysis with several traditions in mathematics. Constructive Reverse Mathematics (CRM) is a spin-off of Harvey Friedman's famous Reverse Mathematics program, based on Constructive Analysis. Bishop famously derided Nonstandard Analysis for its lack of computational meaning. In this talk, we introduce `Ω-invariance': a simple and elegant definition of `finite procedure' in (classical) Nonstandard Analysis. Using an intuitive interpretation, we obtain many results from CRM, thus showing that Ω-invariance is quite close to Bishop's notion of `finite procedure.'

Plaats: Vergaderzaal S22
Organisator: Andreas Weiermann
Datum: 9/11/2011
Tijd: 14:00 - 18:30

Internationalisation @ home

Op deze informele sessie zullen vijf sprekers vertellen over hun ervaringen met internationalisatie. We vragen om vooraf uw aanwezigheid te bevestigen op erasmus@cage.ugent.be.

Het volledige programma:

  • 14u00-14u20: Anamari Nakic (Zagreb, Croatia): A Hitchiker's Guide to the University of Zagreb.
  • 14u30-14u50: Prof. Dr. Marian Slodicka (UGent): A personal scienti c journey through Europe.
  • 15u10-15u30: Nursen Avci (UGent): Veni Vidi Amavi (I came, I saw, I loved it).
  • 15u40-16u: Nele Verbiest (UGent): Erasmus in Halle: small town - big experience.
  • 16u20-16u40: Sam Poppe (UGent): On ski's to the courses - studying above the Polar Circle.
  • 16u40-18u: Reception.
Plaats: S25, Aud. Emmy Noether
Organisator: Leo Storme
Datum: 8/11/2011
Tijd: 19:00

Stefaan Vaes: De Banach-Tarskiparadox

Zoals elk jaar organiseert PRIME ook dit jaar een lezing. We hebben Stefaan Vaes uitgenodigd om te vertellen over de Banach-Tarskiparadox.

Abstract:

De paradox van Banach en Tarski: twee blokken goud maken uit één enkele. Het is mogelijk om een massieve goudbol met 10 cm diameter in vijf stukken te verdelen en deze vijf stukken te verschuiven en te draaien om zo twee massieve goudbollen met 10 cm diameter te bekomen. Dit klinkt absurd en is ook niet praktisch haalbaar. Het is wel echt mogelijk in de wiskundige betekenis van het woord, waarbij je een bol in vijf deelverzamelingen verdeelt. Stefaan Vaes zal een bewijs van deze verrassende eigenschap schetsen en hierbij het verband uitleggen met de analyse op oneindige groepen en een eigenschap genaamd 'amenability'.

Plaats: Emmy Noether
Organisator: PRIME
Datum: 4/11/2011
Tijd: 10:00 - 11:00

Telfuncties voor oneindige getallen

Ik geef een voordracht over de samenhang van oneindige ordinalgetallen met de analyse.
De voordracht gaat over mijn visie over misschien interessante beweringen.

Plaats: Auditorium A
Organisator: Andreas Weiermann
Datum: 28/10/2011
Tijd: 10:00 - 11:00

New bounds on Ramsey numbers

The finite version of Ramsey's theorem states that if we are given
integers $r_1, \ldots, r_k$, then there exists an integer $N$, such
that no matter how we colour the edges of a complete graph with $N$
vertices in $k$ colours, there is always some $i$ and $r_i$ vertices
of the graph, such that all edges between these points have the $i$-th
colour. The least integer $N$ with this property is called the Ramsey
number $R(r_1, \ldots, r_k)$. As computing this number is notorious
difficult, one tries to give at least bounds for these numbers.
In this talk I will describe the basic methods for bounding Ramsey
numbers, at the end I will also give a new result on $R(3, n)$.

Plaats: Auditorium A
Organisator: Jan Christoph Schlage Puchta
Datum: 25/10/2011
Tijd: 14:30 - 17:00

On jugera — de verjaardag van Galois

Evariste Galois is geboren op 25 oktober 1811 in Bourg-La-Reine. Op 25 oktober 2011 is het dus zijn 200ste verjaardag. Ter gelegenheid daarvan vertellen we iets over zijn leven en zijn werk.

We doen dit op 25 oktober in auditorium Emmy Noether van 14:30 – 17:00. Het is een onderdeel van de cursus Algebra II, maar iedereen die interesse heeft is hartelijk welkom.

Lees hier de uitnodiging met programma na.

Plaats: S25, aud. Emmy Noether
Organisator: Leo Storme & Jan Van Geel
Datum: 24/10/2011
Tijd: 14:00

Driven cofactor systems and Hamilton-Jacobi separability

Goedele Waeyaert spreekt over Driven cofactor systems and Hamilton-Jacobi separability.

Plaats: S22, computerklas
Organisator: Onderzoeksgroep Differentiaalmeet- kunde en Mechanica
Datum: 19/10/2011
Tijd: 14:30

The Steinberg group of a rational function field

Karim Becher (Univerisität Konstanz) spreekt over de Steinberg groep van een rationaal functieveld.

Het seminarie duurt van 14:30 tot ongeveer 17:00, met een pauze.

Abstract: We study the cokernel of the scalar extension map between the Steinberg groups of a field and its rational function field in terms of the isomorphic ramification group. For a given ramification, we give a bound in terms of the degree on the number of symbols needed for its representation. Moreover, we show that this bound is generally optimal. We further relate this problem to the study of central simple algebras and the Fadeev index. (Joint work with Melanie Raczek, Universite de Louvain, Belgium)

Plaats: Sterre, S25, aud. Emmy Noether
Organisator: Onderzoeksgroep algebra
Datum: 14/10/2011
Tijd: 10:00

Point behavior of Fourier series and conjugate series

Jasson Vindas spreekt over Puntgedrag van Fourierreeksen en toegevoegde reeksen.

Students and non-specialists are welcome!

Abstract. The study of the relationship between the point behavior of a periodic function and the convergence or summability of its Fourier and conjugate series is an old and interesting problem. This classical problem has been studied, among many others, by Fatou, Fejer, Loomis, Lukacs, Hardy, Littlewood, and Zygmund long time ago.

We discuss a recent result concerning simultaneous Abel summability of Fourier series and conjugate series at a given point. We characterize this situation for functions, measures, and even Schwartz distributions, which are bounded from below near the point. The characterization is given in terms of "average'' point values.

Plaats: Sterre, S22 aud. A
Organisator: Onderzoeksgroep Logica en Analyse
Datum: 12/10/2011
Tijd: 17:30

Hans Vernaeve: Het verhaal achter Go

We beginnen deze avond met een lezing door Hans Vernaeve over het abstracte bordspel Go. Het is zeker niet erg als je nog nooit van Go gehoord hebt, dit is het ideale moment om er kennis mee te maken. Na de lezing kan men het spel Go ontdekken of andere spelletjes spelen.

Plaats: Emmy Noether
Organisator: PRIME
Datum: 30/9/2011
Tijd: 11:00 - 12:00

The decidability of the two-quantifier theory of the elm degrees

In subrecursive degree theory computable functions are ordered with respect to their complexity: A function $f$ is more complex than a function $g$, if one can easily compute $g$, provided that $f$ is already known. Here the notion of "easy" can be interpreted in an arbitrary number of ways, however, the practical experience shows that in many cases the structure of the resulting degrees does not depend on the particular notion chosen.

Here we present an axiomatic approach via lattice theory. A lattice is a partially ordered set, in which any two elements have a supremum and an infimum. We show that all lattices, which satisfy certain richness properties, have the same $\Pi_2$-theory, while they may differ in finer parts of their theory. In other words, all statements of the form "For all x_1, \dots, x_n$ there exist $y_1, \ldots, y_m$ such that \dots" either hold true in every rich lattice or in none of them, while there are simple statements of a slightly more complicated nature which hold in some rich lattice, fail in another one, and are not yet decided in another (in fact, one of the most interesting) example.

No prerequisites in logic or lattice theory are required beyond understanding the meaning of quantifiers.

Plaats: Auditorium B
Organisator: Andreas Weiermann
Datum: 22/9/2011
Tijd: 16:30

Inaugurale voordracht van professor Koen Thas

De Vakgroep Wiskunde van de Universiteit Gent (Faculteit Wetenschappen) heeft de eer u uit te nodigen voor de inaugurale voordracht van professor Koen Thas, die met ingang van 1 oktober 2010 benoemd werd.

Programma

16:30h Onthaal en koffie
17:00h Prof. Dr. Jan Van Geel
Inleiding
17:10h Prof. Dr. Koen Thas
De lange weg  — een verhaal over wiskundige problemen
             die denkers al eeuwenlang teisteren,
zonderlingen die in afgelegen berghutten
             de existentie van de duivel willen aantonen,
en een mythisch object dat niet bestaat,
             maar waar we toch naar zoeken.
18:00h Receptie aangeboden door de vakgroep

Registratie en meer informatie — http://java.ugent.be/inaugural-koen-thas

Plaats: Emmy Noether
Organisator: Vakgroep Wiskunde
Datum: 26/8/2011
Tijd: 14:00

Analysing Parity Games in Bounded Arithmetic

De spreker is Arnold Beckmann van Swansea. Hij is daar reader voor computer science.
De presentatie wordt aan het bord gegeven en de spreker belooft op de voorkennis van de aanwezigen in te spelen. De voordracht is in het Engels.

Abstract:

Parity games underlie the model checking problem for the modal μ-calculus, the complexity of which remains unresolved after more than two decades of intensive research. The community is split into those who believe this problem - which is known to be both in NP and coNP - has a polynomial-time solution (without the assumption that P = NP) and those who believe that it does not. (A third, pessimistic, faction believes that the answer to this question will remain unknown in their lifetime.)

In this talk we will discuss how Bounded Arithmetic can be used to analyse the complexity of parity games.

Plaats: Emmy Noether
Organisator: Onderzoeksgroep Logica en Analyse
Datum: 28/6/1917
Tijd: 9:00

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Plaats: onbekend
Organisator: ?
Datum: 27/6/1917
Tijd: 11:30

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Plaats: onbekend
Organisator: ?