Tidligere gjesteforelesninger og seminarer

Tid og sted: , Niels Henrik Abels hus, 9th floor

During this cold winter in Oslo, we certainly all have experienced the unsteady nature of friction and the sudden loss of stress bearing capacity that initiates catastrophic sliding. A similar kind of frictional rupture arises at the onset of a wide variety of natural disasters that includes earthquakes, landslides, as well as snow avalanches. In this talk, I will focus on the incipient stage of these catastrophic events that is characterized by the local nucleation of failure and its rapid propagation towards intact regions of the material. I will discuss how the analogy to fracture mechanics can be exploited to describe the dynamics of these rupture fronts and develop quantitative models to characterize the onset of failure in geomaterials.

 
Tid og sted: , Peisestua (room 304), Svein Rosselands Hus

Luis Teodoro, Centre for Space Sensors and Systems, Faculty of Mathematics and Natural Sciences, University of Oslo.

Tid og sted: , 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.

Tid og sted: , 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.

 
Tid og sted: , Peisestua (room 304), Svein Rosselands Hus

Cheng-Zong Ruan, Institute of Theoretical Astrophysics, University of Oslo.

Tid og sted: , 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.

Tid og sted: , Origo

Assoc. Prof. Tor Ole B. Odden, CCSE, UiO

Tid og sted: , NHA building, UE32

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

Tid og sted: , 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.

Tid og sted: , Kristine Bonnevies hus, Proteome 3627

By Knut Wiik Vollset, leader of the Bergen Telemetry Group within the Laboratory for Freshwater Ecology and Inland Fisheries (LFI), NORCE Bergen 

Tid og sted: , 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.

 
Tid og sted: , Peisestua (room 304), Svein Rosselands Hus

Frode Kristian Hansen, Cosmology and Extragalactic Astronomy research group, Institute of Theoretical Astrophysics, University of Oslo.

Tid og sted: , NHA 108 University of Oslo
Tid og sted: , UE32

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

Tid og sted: , Pollen (room 3205), Kristine Bonnevies hus

By Andrew Maccoll, the University of Nottingham, United Kingdom

Tid og sted: , Niels Henrik Abels hus, 9th floor

Engineering principles to develop advanced biomaterials and scaffolds. This study focuses on utilising engineering principles to facilitate new bone growth, specifically in designing and fabricating bone scaffolds. The core of our investigation lies in applying titanium dioxide (TiO2) scaffolds, which have emerged as promising candidates due to their osteoconductive properties and the potential for enhancing bone tissue engineering.

Our research aims to bridge the gap between engineering and biology by harnessing fluid mechanics and material science to create scaffolds that mimic the natural bone environment. By comparing TiO2 scaffolds with commercial porous calcium phosphate biomaterials under simulated perfusion culture conditions, we delve into the mechanical and fluidic stimuli that are crucial for bone regeneration. The study emphasises the role of fluid dynamics to make better “spare-parts” for the human body, highlighting the importance of permeability, mechanical load transfer and wall shear stress with a porous ceramic.

Furthermore, we validate our fluid mechanic simulations with the impact of dynamic seeding techniques. Our findings demonstrate the superiority of dynamic culture conditions in enhancing the expression of bone-related proteins and genes, thereby facilitating more effective bone regeneration. In addition, the study presents a clinical trial that shows that these porous bioceramic functions well in patients. The trial's outcomes confirm the potential of TiO2 scaffolds for in vivo bone formation and showcase the successful integration of engineering principles in the development of biomaterials for tissue engineering.

This research underscores the pivotal role of engineering in advancing tissue engineering and biomaterials science. By leveraging engineering principles to optimise scaffold design and functionality, we pave the way for innovative strategies in bone regeneration, offering new hope for patients requiring bone tissue reconstruction.

Tid og sted: , Niels Henrik Abels hus, 9th floor

Paper cuts are a minor nuisance, but they can lead to life-threatening microbial infections. The physical processes that determine whether paper cuts into the skin, however, remain poorly understood. To explore skin-paper interactions, we designed an experiment in which a piece of paper contacts an artificial finger made from ballistic gelatin. Our experiments suggest that the paper thickness is one of the most important parameters in determining cutting efficacy. A relatively thin sheet often buckles before cutting is initiated, whereas the predominant interaction with thick sheets is indentation. Our preliminary data indicate that a successful paper cut is physically impossible outside a relatively narrow range of thicknesses for a given angle. Finally, the optimal paper cut is explored, and the influence of skin properties and cutting angle is discussed.

Tid og sted: , Peisestua (room 304), Svein Rosselands Hus

Prasanta Gorai, Rosseland Centre for Solar Physics, Institute of Theoretical Astrophysics, University of Oslo.

Tid og sted: , UE32

C*-algebra seminar by Corey Jones (North Carolina State University)

Tid og sted: , Niels Henrik Abels hus, 9th floor

Controlling the spontaneous ruptures of nanoscale liquid thin films is crucial to various applications such as solar cell manufacturing. Over the past few decades, theoretical work based on the long-wave theory of thin liquid films has successfully identified a critical film height, below which the surface nanowaves become linearly unstable, leading to spontaneous rupture. This dewetting in the ‘spinodal regime’ has been repeatedly confirmed in experiments using atomic force microscopy on polymer films. However, ruptures are also observed for thicker films (linearly stable) in a different manner. It is believed that the random (Brownian) movement of particles is the cause of dewetting in this ‘thermal regime’ but the theoretical framework predicting the rupture is missing. In this talk, we present a theory to account for the rupture of a two dimensional linearly stable thin film by utilizing fluctuating hydrodynamics and rare events theory. By modelling the film dynamics with the stochastic thin-film equation (STF) and solving it numerically, we observe rupture in the linearly stable thermal regime and record the average waiting time for rupture. We show that the STF can be rearranged into the form of a gradient flow, which allows us to apply Kramer’s law from the rare events theory to obtain a theoretical prediction of the average waiting time. Molecular dynamics (MD) simulations are also performed and we find good agreements between the numerics, the prediction, and the MD.

 
Tid og sted: , Peisestua (room 304), Svein Rosselands Hus

Farbod Hassani, Cosmology and Extragalactic Astronomy research group, Institute of Theoretical Astrophysics, University of Oslo.

Tid og sted: , NHA B1120


Abstract: 

In this joint work in progress with Helge Ruddat and Bernd Siebert, we employ a particular type of Log Smooth Degeneration (LSD) to study the Geometry of Enumerative Mirror Symmetry (GEMS).
 
Mirror Symmetry is a broad conjecture that predicts that symplectic invariants of a Kähler manifold correspond to algebro-geometric invariants of a mirror-dual complex algebraic variety. This is generally proven by computing both sides.
 
In this work, we take the first steps towards a full enumerative correspondence that canonically identifies the invariants of both sides. To do so, we employ the Intrinsic Mirror Construction of Gross-Siebert. Then the enumerative correspondence passes through an intermediary tropical manifold and tropical invariants thereof.
 
I will start by briefly describing the string theory origins of mirror symmetry (Candelas-de la Ossa-Green-Parkes) followed by a brief description of the computational solution to the physics prediction (Givental Mirror Symmetry). Then I will outline our program which puts the physics intuition on firm ground and takes the first steps towards showing that Enumerative Mirror Symmetry follows from the geometric dualities of the Intrinsic Mirror Construction.
Tid og sted: , Room 1020 NHA

The Section 4 seminar for the Spring 2024 will be held Thursdays 14:15–15:00 in room 1020

Tid og sted: , Erling Sverdrups plass, Niels Henrik Abels hus, 8th floor

Our project partner Statkraft owns and operates several hydropower plants in Brazil and requires information about the future potential for hydropower production in this region. To provide inflow projections for the next several decades, we use climate model output in combination with a regression model that links meteorological variables such as precipitation and temperature to inflow over various catchments in the region. The relatively short time period for which observation data are available raises concerns about overfitting. We therefore explore an alternative model fitting approach that retains the original, easily interpretable regression model but estimates the regression coefficients within an artificial neural network (ANN) framework which permits spatial and temporal regularization and thus prevents overfitting. We show some examples of the inflow projections obtained with that methodology and discuss some caveats and limitations.