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Events

Ongoing

Time and place: , Quality Hotel Fredrikstad

University of Oslo and University of Gothenburg invite to an informal workshop within machine learning with a focus on statistical aspects related to Machine Learning.

Upcoming

Time and place: , NHA B1120

Donaldson-Thomas and Pandharipande-Thomas theory are two approaches to counting curves on projective threefolds in terms of their moduli spaces of sheaves. An important special case in understanding the DT/PT correspondence the equivariant geometry of affine three-space with the natural coordinate action of the rank 3 torus. I will show how one can use new wall-crossing techniques to prove the equivariant K-theoretic DT/PT correspondence in this situation, which was previously known only in the Calabi-Yau limit.

This is part of an ongoing project with Felix Thimm and Henry Liu in which we aim to prove wall-crossing for virtual enumerative invariants associated to equivariant CY3 geometries by extending a vertex algebra formalism for wall-crossing developed by Joyce.

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

his talk discusses a nonparametric inference framework for occupation time curves derived from wearable device data. Such curves provide the total time a subject maintains activity above a given level as a function of that level. Taking advantage of the monotonicity and smoothness properties of these curves, we develop a likelihood ratio approach to construct confidence bands for mean occupation time curves.  An extension to fitting concurrent functional regression models is also developed. Application to wearable device data from an ongoing study of an experimental gene therapy for mitochondrial DNA depletion syndrome will be discussed. Based on joint work with Hsin-Wen Chang (Academia Sinica).

 

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

Structural equation models are simultaneous equation regression models, whose variables are latent, and measured via a confirmatory factor model (that is, with measurement error and repeated measurements). When the functional form of the simultaneous equation system is unknown, it has previously been observed in simulations that factor scores inputted into non-parametric regression methods approximate the true functional form. Factor scores estimate the latent variables (per person), and several types exist. We provide a theoretical (though population-based) analysis of this procedure, and provide assumptions under which it is theoretically justified in using Bartlett factor scores, which are simple linear transformations of the data. In simulations, we compare this suggestion to an already available though understudied non-linear and computationally heavy procedure, and observe that the simple Bartlett approach appears to work better.

Time and place: , Abels Utsikt (NHA 1259)
Time and place: , NHA B1120


Abstract: Tropical curves are piecewise linear objects arising as degenerations of algebraic curves. The close connection between algebraic curves and their tropical limits persists when considering moduli. This exhibits certain spaces of tropical curves as the tropicalizations of the moduli spaces of stable curves. It is, however, still unclear which properties of the algebraic moduli spaces of curves are reflected in their tropical counterparts.

In work with Renzo Cavalieri and Hannah Markwig we defined, in a purely tropical way, tropical psi classes in arbitrary genus. They are operational cocycles on a stack of tropical curves, which enjoy several properties that we know from their algebraic ancestors. We also computed two examples in genus one and gave a tropical explanation for the psi class on the moduli space of 1-marked stable genus-1 curves to be 1/24 times a point.

In my talk, I will report on joint work in progress with Renzo Cavalieri, where we explore the missing piece in the story: the link to algebraic geometry. I will explain how to obtain, if we are lucky, a family of tropical curves from a family of algebraic curves. Naturally, there also is a correspondence-type theorem that equates algebraic and tropical intersection products with psi classes, thus showing that the tropical computations done with Cavalieri and Markwig faithfully reflect the algebraic world.

Time and place: , Abels Utsikt (NHA 1259)
Time:

The purpose of this workshop is to bring together communities in dynamical systems, harmonic analysis and operator algebras whose research relates to point sets in Euclidean space and general locally compact groups.

Time:

C*-algebra seminar by Eduard Vilalta (Chalmers University of Technology / University of Gothenburg)

Time and place: , University of Oslo

The 5th Scandinavian Gathering Around Remarkable Discrete Mathematics

Time and place: , UE32

C*-seminar by John Quigg (Arizone State University).

Time and place: , Abels Utsikt (NHA 1259)
Time and place: , University of Oslo

Welcome to the third Norwegian meeting on PDEs!

Time and place: , UE32

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

Time and place: , Abels Utsikt (NHA 1259)

Previous

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

Bone stress injuries affect athletic populations who undertake activities in which bones are repeatedly loaded. In order to understand and reduce the risk of bone stress injuries, we need to quantify the loading experienced by the bones during activities such as running. Bone loading is difficult to quantify as the magnitudes of stress are influenced to a large extent by the magnitude of muscular forces acting on the bone. Musculoskeletal modelling, ranging from very simple to very complex approaches, can be used to estimate the internal loading experienced by the bone during running. This has allowed us to explore factors such as speed, slope and step length and their influence on bone loading during running. However, in order to truly understand risk of stress injuries this needs to be taken out of the lab and in-field. This talk will consider what we know and the limitations to current understanding.

 
Time and place: , NHA B1120

Gromov—Witten invariants are virtual counts of curves with prescribed conditions in a given algebraic variety. One of the main techniques to study Gromov—Witten invariants is degeneration. The degeneration formula expresses absolute Gromov—Witten invariants in terms of relative Gromov—Witten invariants of algebraic varieties with tangency conditions along boundary divisors.

Relative Gromov—Witten invariants with only one relative marking are relative invariants with maximal contacts along the unique relative marking. The local-relative correspondence proved by van Garrel—Graber—Ruddat states that genus zero relative invariants with maximal contacts are equal to local Gromov—Witten invariants of a line bundle. Local invariants are usually easier to compute. However, The degeneration formula usually involves relative invariants beyond maximal contacts (i.e. with several relative markings). I will explain a generalization of the local-relative correspondence beyond maximal contacts, hence determine all the genus zero relative invariants that appear in the degeneration formula.

This is based on joint work with Yu Wang.

Time and place: , NHA 723 and Online
Time and place: , NHA building, UE32

Qombine seminar by Joakim Bergli, Department of Physics (UiO)

Time and place: , Erling Sverdrups plass, Niels Henrik Abels hus, 8th floor and zoom: https://uio.zoom.us/j/68412228703?pwd=Y2FFZDlCSzBZbDZ4Rkw0S2NQWHpTQT09

The climatic ocean wave spectrum serves as a pivotal tool in comprehending the long-term characteristics and variations of wave patterns across different regions of the world's oceans. The presentation explores the methodologies employed to derive wave spectra from observational data. Basically, consists of a statistical approach that provides a quantitative understanding of the variability and extremes of wave conditions. In essence, an ocean wave spectrum is a representation of the distribution of energy among different wave frequencies and wavelengths. So, engineers rely on this valuable information to mitigate risks and design solutions that can withstand the dynamic forces of ocean waves. However, it is necessary to present such information in a robust and practical mode to better comprehend the variations. In this way, a robust and resistant approach will be presented to define such variabilities, thus reducing uncertainties and representing the climatic wave spectrum in a compact and informative way.

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

Future robots need to be robust and adaptable, and new design approaches are needed for new production methods. I will talk about my research in using evolutionary algorithms and biologically inspired methods with the aim of having more intelligent, robust, and adaptive behavior in robots. I will give a short introduction to some of the algorithms and show how we apply them in our robotic platforms for exploring automatic design and adaptation.

 
Time and place: , NHA 108 University of Oslo
Time and place: , room 1259 (Abels Utsikt) - Niels Henrik Abels hus

Doctoral candidate Edvard Aksnes at the Department of Mathematics will be defending the thesis Tropical homology manifolds for the degree of Philosophiae Doctor.

Time and place: , UE32

C*-algebra seminar by Gaute Schwartz (University of Oslo)