# Seminars at the Landau Institute scientific council

Seminars are held on Fridays in the conference hall of Landau Institute for Theoretical Physics in Chernogolovka, beginning at 11:30.

You can subscribe and receive announcements about ITP seminars. If you have any questions, please contact the scientific secretary Sergey Krashakov.

## Spetsial’naya Kelerova geometriya i teorii Landau-Ginzburga

17 May in 11:30

Konstantin Aleshkin

Doklad po teme predstavlyaemoi k zashchite kandidatskoi dissertatsii.

## Aspects of quarkonium propagation in a thermal medium as seen by string models

17 May in 11:30 (short)

Oleg Andreev

We use gauge/string duality to model a heavy quark-antiquark pair in a color singlet moving through a thermal plasma. In particular, we explore the effect of velocity on the string tension and Debye screening mass. Then we apply the results to the analysis of heavy quarkonium bound states. With some assumptions, we estimate the characteristic size of quarkonium and its dissociation temperature.

## Parallel SPH modeling using dynamic domain decomposition and load balancing displacement of Voronoi subdomains

14 June in 11:30

__Maria S. Egorova__, Sergey A. Dyachkov, Anatoliy N. Parshikov, Vasily V. Zhakhovsky

A highly adaptive load balancing algorithm for parallel simulations using particle methods, such as molecular dynamics and smoothed particle hydrodynamics (SPH), is developed. Our algorithm is based on the dynamic spatial decomposition of simulated material samples between Voronoi subdomains, where each subdomain with all its particles is handled by a single computational process which is typically run on a single CPU core of a multiprocessor computing cluster. The algorithm displaces the positions of neighbor Voronoi subdomains in accordance with the local load imbalance between the corresponding processes. It results in particle transfers from heavy-loaded processes to less-loaded ones. Iteration of the algorithm puts into alignment the processor loads. Convergence to a well-balanced decomposition from imbalanced one is improved by the usage of multi-body terms in the balancing displacements. The high adaptability of the balancing algorithm to simulation conditions is illustrated by SPH modeling of the dynamic behavior of materials under extreme conditions, which are characterized by large pressure and velocity gradients, as a result of which the spatial distribution of particles varies greatly in time. The higher parallel efficiency of our algorithm in such conditions is demonstrated by comparison with the corresponding static decomposition of the computational domain. Our algorithm shows almost perfect strong scalability in tests using from tens to several thousand processes.

Publications: arXiv:1805.05128v2 [physics.comp-ph] ; Computer Physics Communications, Volume 234, January 2019, Pages 112-125

Publications: arXiv:1805.05128v2 [physics.comp-ph] ; Computer Physics Communications, Volume 234, January 2019, Pages 112-125