National Research University – Higher School of Economics

About: National Research University – Higher School of Economics is a education organization based out in Moscow, Russia. It is known for research contribution in the topics: Population & Computer science. The organization has 12873 authors who have published 23376 publications receiving 256396 citations.

Fast radio bursts

Abstract: The phenomenon of fast radio bursts (FRBs) was discovered in 2007. These are powerful (0.1-100 Jy) single radio pulses with durations of several milliseconds, large dispersion measures, and record high brightness temperatures suggesting coherent emission mechanism. As of time of writing, 32 FRBs were recorded. There is also one repeating source from which already hundreds of bursts have been detected. The FRB rate is estimated to amount up to several thousand per day over the sky, and their isotropic sky distribution likely suggests a cosmological origin. Since the discovery, different hypotheses on the possible FRB nature have been proposed, however up to now the origin of these transient events remains obscure. The most prospective models treat them as being related to a bursting emission from magnetars -- neutron stars whose activity is due to their magnetic field dissipation, -- or as being analogs of giant pulses observed from several radio pulsars . Future increase in the statistics of the observed FRBs and an improvement upon the FRB population characteristics will make possible to use them as a new tool to probe the intergalactic medium and to test fundamental physical theories.

SWAN/SOHO Lyman- α Mapping: the Hydrogen Geocorona Extends Well Beyond The Moon

Abstract: The Earth's hydrogen exosphere Lyman‐α radiation was mapped with the SWAN/SOHO instrument in January 1996, 1997 and 1998 (low solar activity). The use of a hydrogen absorption cell allowed to disentangle the interplanetary emission from the geocoronal one and to assign the absorbed signal almost entirely to the geocorona. The geocorona was found to extend at least up to 100 Earth Radii (RE) with an intensity of 5 Rayleigh, an unprecedented distance well exceeding the recent results of LAICA imager (∼50 RE), and encompassing the orbit of the Moon (∼60 RE). We developed a numerical kinetic model of the hydrogen atoms distribution in the exosphere which includes the solar Lyman‐α radiation pressure and the ionization. The radiation pressure compresses the H exosphere on the day side, producing a bulge of H density between 3 and 20 RE which fits observed intensities very well. The SWAN Lyman‐α distribution of intensity was compared both to LAICA (2015) and to OGO‐5 (1968) measurements. Integrated H densities of SWAN at a tangent distance of 7 RE are larger than LAICA/OGO‐5 by factors 1.1‐2.5, while we should expect a stronger effect of the radiation pressure at solar max. We discuss the possible role of H atoms in satellite orbits to explain this apparent contradiction. An onion‐peeling technique is used to retrieve hydrogen number density in the exosphere for the three SWAN observations. They show an excess of density versus models at large distances, which is likely due to non‐thermal atoms (not in the model).

Statistical physics of balance theory

Abstract: Triadic relationships are accepted to play a key role in the dynamics of social and political networks. Building on insights gleaned from balance theory in social network studies and from Boltzmann-Gibbs statistical physics, we propose a model to quantitatively capture the dynamics of the four types of triadic relationships in a network. Central to our model are the triads’ incidence rates and the idea that those can be modeled by assigning a specific triadic energy to each type of triadic relation. We emphasize the role of the degeneracy of the different triads and how it impacts the degree of frustration in the political network. In order to account for a persistent form of disorder in the formation of the triadic relationships, we introduce the systemic variable temperature. In order to learn about the dynamics and motives, we propose a generic Hamiltonian with three terms to model the triadic energies. One term is connected with a three-body interaction that captures balance theory. The other terms take into account the impact of heterogeneity and of negative edges in the triads. The validity of our model is tested on four datasets including the time series of triadic relationships for the standings between two classes of alliances in a massively multiplayer online game (MMOG). We also analyze real-world data for the relationships between the “agents” involved in the Syrian civil war, and in the relations between countries during the Cold War era. We find emerging properties in the triadic relationships in a political network, for example reflecting itself in a persistent hierarchy between the four triadic energies, and in the consistency of the extracted parameters from comparing the model Hamiltonian to the data.