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Events - Page 4

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

Cavitation is a ubiquitous and sometimes destructive, phenomenon. For instance, cavitation bubbles may interrupt water flow in plants or severely damage the surfaces of machines such as pumps and propellers. The so-called tribonucleation of vapor bubbles has been proposed to be responsible for the cracking sound produced by the manipulation of human synovial joints. To study cavitation up close we have developed an experimental setup where a sphere in water abruptly leaves a flat surface starting from a separation of only 10 nm.

Upon upward movement of the spherical surface, a cavitation bubble forms and develops branched fingers through the Saffmann-Taylor instability. Simultaneously, negative liquid pressures in the range of ∼10atm are observed. These large tension values occasionally lead to secondary nucleation events. The bubble sizes satisfy a predicted Familiy-Vicsek scaling law where the bubble area is proportional to the inverse bubble lifetime. The fact that creeping flow cavitation bubbles are more short lived the larger they are separate them from bubbles that are governed by inertial dynamics.

Time and place: , NHA 723 and Online
Time and place: , Abels Utsikt (NHA 1259)
Time and place: , NHA 108

QOMBINE seminar by Satvik Singh (University of Cambridge): The PPT2 conjecture for diagonal unitary covariant map

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

Doctoral candidate Michele Giordano at the Department of Mathematics will be defending the thesis On stochastic control for Volterra type dynamics for the degree of Philosophiae Doctor.

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

Self-assembly is the spontaneous generation of order in systems driven by thermal agitation and interactions. At the molecular level, self-assembly plays an important role in the formation of giant com- plex macromolecules, being quite relevant for living systems. At the mesoscopic level, capillary driven self-assembly has been proposed for building structures in the gap between classical bottom-up and top-down fabrication methods, i.e. at the scales in between 10 micrometers and 1 millimeter. Although the method was proposed 20 years ago, only regular or simple structures were achieved so far. Using both experimental and statistical physics ideas, we demonstrate how to exploit subtle capillary interactions to create elaborate complex structures, as well as functional micromachines. On top of that, we show how such mescoscopic systems can be the analogues of many different physical systems such as folding molecules, molecular locks and keys, and crystal formation.

Time and place: , NHA108

C*-algebra seminar talk by Suvrajit Bhattacharjee (University of Oslo)

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

Active solids consume energy to allow for actuation and shape change not possible in equilibrium. In this talk, I will focus on the elasticity of systems as wide-ranging as far-from-equilibrium hydrogels, nanoparticles, and mechanical structures composed of active robotic components. First, I will introduce our recent work on hydrogel spheres being lowered onto a hot plate. As the bottom vaporises, the resulting flow couples tightly to elastic deformations within the sphere, giving either spontaneous bouncing or steady-state floating as manifestations of the so-called elastic Leidenfrost effect. I will present theory and simulations of the floating case, which demonstrate a remarkable phenomenon: the heavier the solid, the higher it floats. I will then discuss the general competition between active boundary stresses and an elastic bulk, giving rise to so-called active elastocapillarity. Finally, I will discuss our current work on using non-reciprocal interactions in active elastic media to program robust mechanical actuation and locomotion. In each case, our results provide theoretical underpinning for recent experimental advances, and point to the design of novel soft machines.

 
Time and place: , NHA 723 and Online
Time and place: , NHA B1120

I will discuss the “geometric method” for syzygies and discuss applications to the study of tautological bundles of linear spaces. From this, I will explain how to pass from realizable matroids to all matroids via initial degenerations. This is joint work in progress with Alex Fink and Chris Eur.

Time and place: , NHA B1020

A finite graph determines a Kirchhoff polynomial, which is a squarefree, homogeneous polynomial in a set of variables indexed by the edges. The Kirchhoff polynomial appears in an integrand in the study of particle interactions in high-energy physics, and this provides some incentive to study the motives and periods arising from the projective hypersurface cut out by such a polynomial.

From the geometric perspective, work of Bloch, Esnault and Kreimer (2006) suggested that the most natural object of study is a polynomial determined by a linear matroid realization, for which the Kirchhoff polynomial is a special case.

I will describe some ongoing joint work with Delphine Pol, Mathias Schulze, and Uli Walther on the interplay between geometry and matroid combinatorics for this family of objects.

Time and place: , NHA108

QOMBINE seminar by Roy Araiza (University of Illinois Urbana-Champaign)

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

Innovations in fluid mechanics are leading to better food since ancient history, while creativity in cooking inspires applied and fundamental science. In this talk, I will discuss how recent advances in hydrodynamics are changing food science, and how the surprising phenomena that arise in the kitchen lead to discoveries and technologies across the disciplines, including rheology and soft matter. Central topics include cocktails and champagne (multiphase flows), whipped cream (complex fluids) and pancake making (viscous flows). For every topic, I will present the state-of-the-art knowledge, the open problems, and likely directions for future research.

Publications:
Mathijssen, A. J., Lisicki, M., Prakash, V. N., & Mossige, E. J. (2023). Culinary fluid mechanics and other currents in food science. Reviews of Modern Physics, 95(2), 025004.

Fuller, G. G., Lisicki, M., Mathijssen, A. J., Mossige, E. J., Pasquino, R., Prakash, V. N., & Ramos, L. (2022). Kitchen flows: Making science more accessible, affordable, and curiosity driven. Physics of Fluids, 34(11).

Time and place: , Abels Utsikt (NHA 1259)
Time and place: , NHA108

C*-algebra seminar talk by Valerio Proietti (University of Oslo)

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».