Norwegian version of this page

Events - Page 5

Time and place: , NHA B1120
In this talk, I explain how we explicitly construct a motivic analog of the fundamental group of the circle. We construct a group structure on the set of pointed naive homotopy classes of maps from the Jouanolou device to the projective line. The group operation is defined via matrix multiplication on generating sections of line bundles and only requires basic algebraic geometry. In particular, it is completely independent of the construction of the motivic homotopy category. Based on joint work with William Hornslien, Gereon Quick, and Glen Matthew Wilson.
Time and place: , NHA108

QOMBINE seminar talk by Ruben Bassa (SINTEF)

Time and place: , Abels utsikt, 12. etasje, Niels Henrik Abels hus

Doctoral candidate Mari Dahl Eggen at the Department of Mathematics will be defending the thesis Stochastic differential equations with memory and relations - Modelling of stratospheric dynamics for the degree of Philosophiae Doctor.

Time and place: , NHA 108

Franz Fuchs (Sintef/UiO) will give a talk with title "Hamiltonians with time evolution restricted to subspaces"

Time and place: , room 1259 (Abels Utsikt) - Niels Henrik Abels hus

Doctoral candidate Juvenal Murwanashyaka at the Department of Mathematics will be defending the thesis Papers on Weak First-Order Theories and Decidability Problems for the degree of Philosophiae Doctor.

Time and place: , Niels Henrik Abels hus, 9th floor

We have developed a pump-less recirculation Organ-on-Chip (rOoC) platform that generates a directional gravity-driven flow. This platform can be adapted to various flow conditions and enables the study of endothelial lining, blood vessel sprouting, circulation of immune cells, pathogens or other particles, and incorporation of 3D cell models like organoids. Additionally, we have developed a computational model to predict shear stress and mass transport within the rOoC, allowing for customization of the platform for various use-cases.

The rOoC platform is very versatile and can be used to model for instance drug-induced liver-injury (DILI) that mimics the complex interaction between resident human stem cell-derived liver organoids (3D-HLO) and circulating immune cells. Moreover, we show the functional crosstalk between 3D-HLOs and human pancreatic islets to model the onset of type-2 diabetes.

Time and place: , NHA 723 and Online
Time and place: , Auditorium 4

Doctoral candidate Erik Habbestad at the Department of Mathematics will be defending the thesis C∗-algebras with quantum group symmetry -Noncommutative boundaries and equivariant subproduct systems for the degree of Philosophiae Doctor.

Time and place: , NHA B1120

Markus Spitzweck (Universität Osnabrück) will present the talk «Representation categories and motives».

Time and place: , Niels Henrik Abels hus, 9th floor

This seminar will consist of two separate presentations, each about 15-minute long.

1) Magnetic Quincke Rollers with tunable single particle dynamics and collective states
2) Electrically controllable ferrofluids

Time and place: , room 1259 (Abels Utsikt) - Niels Henrik Abels hus

Doctoral candidate Bastian Zapf at the Department of Mathematics will be defending the thesis Inverse mathematical modeling of solute transport in the human brain for the degree of Philosophiae Doctor.

Time and place: , Niels Henrik Abels hus, 9th floor
It is well known that if the singular values of a matrix are distinct, then its best rank-n approximation in the Frobenius norm is uniquely determined and given by the truncated singular value decomposition. On the other hand, this uniqueness is in general not true for best rank-n approximations in the spectral norm. In this talk we relate the problem of finding best rank-n approximations in the spectral norm to Kolmogorov n-widths and corresponding optimal spaces. By providing new criteria for optimality of subspaces with respect to the n-width, we describe a large family of best rank-n approximations to a given matrix. This results in a variety of solutions to the best low-rank approximation problem and provides alternatives to the truncated singular value decomposition. This variety can be exploited to obtain best low-rank approximations with problem-oriented properties.
We further discuss the generalization of these results to compact operators in L2, and explain how they can be used to both describe the out-performance of smooth spline approximations of solutions to differential equations when compared to classical finite element methods, and to solve the outlier-problem in isogeometric analysis.
This talk is based on work done in collaboration with Michael Floater, Carla Manni and Hendrik Speleers.
Time and place: , Niels Henrik Abels Hus and Zoom

This Stochastic Analysis and Applications Workshop aims to provide a professional platform for young researchers in stochastics from China and Norway to convene, exchange ideas, and potentially establish new collaborations.

Time and place: , Room 1119, Niels Henrik Abels hus

The Section 4 seminar for the Spring of 2023 will be held on Wednesdays at 10:15–12:00 (see the schedule)

Time and place: , NHA107

C*-algebra seminar talk by John Quigg (Arizona State University)

Time and place: , Niels Henrik Abels hus, 9th floor

I will discuss some of our recent results on active chiral and nematic membranes. The chiral stresses we consider give rise to a novel form of odd elasticity. To outline this phenomenology I will give explicit calculations outlining spontaneous flow transitions and shape instabilities. I will discuss the relevance of these results in developmental biology and their relation to active nematics, in particular how certain limits of active nematic membranes can reduce to a theory of an isotropic membrane with an active stress defined by the deviatoric part of the shape operator.

Time and place: , NHA107

C*-algebra seminar talk by Roberto Conti (Sapienza University of Rome)

Time and place: , NHA B1120

Many have tried to adapt Clemens and Griffiths's approach to irrationality of cubic threefolds to higher dimensions, using different invariants in place of H^3(X,Z): the transcendental part of H^4, derived categories, quantum cohomology... I will report on my attempt to use higher algebraic K-theory, which turns out to be strictly weaker than what Voisin and Colliot-Thélène have already gotten from Bloch-Ogus theory, but (I think) in an interesting way. For a positive result, I can show that the higher K-theory of Kuznetsov's K3 category for a cubic or Gushel-Mukai 4-fold looks the same as that of an honest K3 surface.

Time:

This is a half-day online workshop on PDEs in physical systems. Abstracts and Zoom link can be found here!

Time and place: , Erling Sverdrups plass, Niels Henrik Abels hus, 8th floor

This talk will focus on recent work about the sequential detection of anomalies within partially observed functional data, motivated by a problem encountered by an industrial collaborator. Classical sequential changepoint detection approaches look for changes in the parameters, or structure, of a data sequence and are not equipped to handle the complex non-stationarity and dependency structure of functional data. Conversely, existing functional data approaches require the full observation of the curve before anomaly detection can take place. We propose a new method, FAST, that performs sequential detection of anomalies in partially observed functional data. This talk will introduce the approach, and some associated theoretical results, and highlight its application on telecommunications data.

This is joint work with Idris Eckley and Lawrence Bardwell.

Time and place: , Niels Henrik Abels hus, 9th floor

The human brain has no lymphatic vessels, so how does the brain clear metabolic waste? In 2012, Iliff et al. proposed a theory about waste clearance of the brain, called the "glymphatic" theory. The theory suggest that the waste clearances is bio-mechanical, and that impaired clearance may be the cause of some neurodegenerative diseases and disorders. The inaccessibility of the human brain have been a hurdle in the research, as experiments on rat brains do not translate to the human brain. Researchers at Oslo university hospital Rikshospitalet have shown clearance using tracers visible in magnetic resonance images (MRI). However, the MRI only provide snapshots of different states in time, therefore computational modeling is needed to fill in the gaps. In this presentation, we will look at computational modeling with the MRI to infer material parameters in the brain.

Time and place: , Niels Henrik Abels hus, 9th floor

Stalagmites grow on the floor of caves by precipitation of calcium ions found in the residual water film covering the top of the stalagmite, which is progressively drained away. Drops dripping from stalactites ensure the renewal of these ions.
Previous models of stalagmite growth assumed that drops fall on a straight vertical line from stalactites. Through high-speed imaging during field experiments in caves, we however observe that the impact point position of the drops is scattered. Using a Langevin-like equation to describe the fall of drops in response to gravity and aerodynamic forces, we then propose a prediction of the impact point dispersal. We show that measured stalagmite widths are correlated to the impact point dispersal of the drops.
In a second time, we focus on the mixing of calcium ions between the drop and the film during impact. The drop produces a crown when impacting the film, accompanied by a large amount of secondary droplet ejections. This is at the very heart of the film thickness variability post-impact. We record high-speed imaging of drop impacts on films of controlled thickness in a lab environment and assess the mixing between the drop and the film. We deduce how much liquid coming from the initial drop remains in the film.

Time and place: , Abels Utsikt (NHA 1259)
Time and place: , Erling Sverdrups plass, Niels Henrik Abels hus, 8th floor

A flexible predictive density combination is introduced for large financial data sets which allows for model set incompleteness. Dimension reduction procedures that include learning allocate the large sets of predictive densities and combination weights to relatively small subsets.  Given the representation of the probability model in extended nonlinear state-space form, efficient simulation-based Bayesian inference is proposed using parallel dynamic clustering as well as nonlinear filtering, implemented on graphics processing units. The approach is applied to combine predictive densities based on a large number of individual US stock returns of daily observations over a period that includes the Covid-19 crisis period.  Evidence on dynamic cluster composition, weight patterns and model set incompleteness gives valuable signals for improved modelling. This enables higher predictive accuracy and better assessment of uncertainty and risk for investment fund management.