Thema:

Ultrafast heat transfer in nanoscale materials

Datum:

27.05.19

Uhrzeit:

16:15

Ort:

H6

Vortragender:

Prof. David Cahill

University of Illinois

Inhalt:

On the macroscopic lengths scales of conventional engineering systems, heat transfer by conduction is generally a slow process well-described by the heat diffusion equation. The characteristic time-scale of diffusion scales with the square of length; therefore, at nanometer length scales, heat conduction can involve processes that occur on time-scales of picoseconds, i.e., a few trillionth of a second. We use ultrafast pump-probe optical techniques to directly study a variety of unconventional heat transfer mechanisms that are critical in nanoscale devices and nanoscale materials. Our studies encompass a diverse variety of systems (metallic nanoparticles for photothermal medical therapies, phase change materials for solid-state memory, and heat-assisted magnetic recording) and physical mechanisms (the thermal conductance of interfaces between dissimilar materials, the non-equilibrium between thermal excitations of electrons, phonons, and magnons, and the cross-terms in the transport of heat, charge, and spin). In this talk I will highlight three recent examples: i) ultrafast thermal transport in the surroundings of plasmonic nanostructures; ii) limitations on ultrafast heating of metallic multilayers imposed by electron-phonon coupling; and iii) the generation of currents of magnetization by the spin-dependent Seebeck effect and extreme heat fluxes exceeding 100 GW m^{-2}.

Ansprechpartner:

T. Kuschel

Thema:

The Widom-Rowlinson model: metastability, mesoscopic and microscopic fluctuations for the critical droplet

Datum:

24.05.19

Uhrzeit:

16:15

Ort:

V3-204

Vortragender:

Elena Pulvirenti

University of Bonn

Inhalt:

In this talk I will discuss the Widom-Rowlinson model on a finite two dimensional torus subject to a stochastic dynamics in which particles are randomly created and annihilated inside the torus according to an infinite reservoir with a given chemical potential. We are interested in the metastable behaviour of the system at low temperature when the chemical potential is supercritical. In particular, we compute the asymptotics of the average time the system needs to condensate and we describe the shape of the critical droplet. Our results rely on a precise analysis of the microscopic and mesoscopic fluctuations of the surface of the critical droplet. This is a joint work in progress with F. den Hollander, S. Jansen, R. Kotecky.

Ansprechpartner:

M. Baake

Thema:

The road to QUDA 1.0

Datum:

21.05.19

Uhrzeit:

14:15

Ort:

D6-135

Vortragender:

Matthias Wagner

NVIDIA Würselen

Inhalt:

Eleven years after its inception, the QUDA library for Lattice QCD on NVIDIA GPUs is nearing a historic 1.0 release. In this span, QUDA has evolved into an open-source framework for full QCD simulations. The library has been fully re-written in a new highly optimized C++11 framework, superseding python-generated routines and ushering in a new age of rapid algorithm prototyping and development. It supports nearly all fermion discretizations, features cutting-edge algorithms such as adaptive multigrid, deflation, and block Krylov-space methods, and contains native support for mixed precision and symmetry-inspired data compression. In preparation for the exascale era, the ability to strong scale is crucial for Lattice QCD simulations. We will discuss the techniques that QUDA implements to achieve the best scaling with MPI and novel improvements using NVSHMEM for GPU-centric communication.

Ansprechpartner:

O. Kaczmarek

Thema:

Matrix product states and matrix product operators

Datum:

13.06.19

Uhrzeit:

14:15

Ort:

D5-153

Vortragender:

Murod Bahohavinov

Bielefeld University

Inhalt:

Ansprechpartner:

Jürgen Schnack

Thema:

Critical behaviour and characteristic polynomials of non-Hermitian random matrices

Datum:

23.05.19

Uhrzeit:

16:15

Ort:

D5-153

Vortragender:

Nicholas Simm

University of Sussex

Inhalt:

I will discuss some recent developments regarding the normal matrix model. In particular my interest will be in certain critical models where the limiting support of the eigenvalues can radically change its topology by slightly adjusting an external parameter. I will discuss how aspects of the model can be explicitly mapped to the study of expectations of characteristic polynomials of non-Hermitian random matrices (e.g. Ginibre or truncated unitary). Many of these averages are related to Painlevé transcendents, and by exploiting this, a precise and non-trivial asymptotic expansion of partition functions can be calculated in the critical models. This is joint work with Alfredo Deaño (University of Kent).

Ansprechpartner:

Gernot Akemann

Thema:

tba

Datum:

19.06.19

Uhrzeit:

16:15

Ort:

V3-201

Vortragender:

Alfredo Deano

University of Kent

Inhalt:

Ansprechpartner:

Gernot Akemann