For more details see: https://www.nature.com/articles/d41586-019-01155-0

Image of a black hole at the centre of the galaxy M87 obtained by the Event Horizon Telescope network.

The theory of critical behaviour states that universal characteristics of the systems under consideration (critical exponents, rations of the amplitudes, scaling functions) depends only on the tensor nature of the field and dimension of the space and can be calculated in the framework of the some systematical expansion. For the turbulent motion the multiscaling behavior is characteristic: the correlation functions of different orders are described by infinite set of different independent exponents. Moreover, the perturbation theory is constructed using the Reynolds number which is not small for the turbulent motion.

During the talk we will discuss how the initial stochastic problem with random noise can be reformulated via some quantum field theory and how renormalization group technique allows us to work with not small perturbation parameter and summarize infinite (asymptotical) series of divergent Feynman diagrams.

by N. Gulitskiy

Department of High Energy Physics and Elementary Particles, Saint Petersburg State University

at SJ1S24 (video conference room) Jesenná 5, PF UPJŠ Košice

on Thursday April 04, 2019

from 14:15

by Pavol Gajdoš

and

Modelling of eclipsing binaries with pulsating components

by Miroslav Fedurco

The Weyl semimetal Tantalum Arsenide has a colossal bulk photovoltaic effect – an intrinsic, or non-linear, generation of current from light more than ten times larger than ever previously achieved, according to researchers from Boston College, the University of California Los Angeles, and Ecole Polytechnique Federale de Lausanne. Credit: Kenneth Burch/Boston College

Read more here.

DOI: https://doi.org/10.1038/s41563-019-0297-4

AG Draconis belongs undoubtedly to the group of most well-known symbiotic stars. The first photographic observations date back to the 19th century. This system consists of a cool giant of spectral type K0-K4 and a hot white dwarf with high temperature and luminosity. The entire symbiotic system is surrounded by a circumbinary envelope created by the cool giant wind, which is partially ionized by the white dwarf’s radiation, and which generates observable emission lines. The talk will present some results of analysis of a unique observation material that covers a period of almost 130 years. We will focus on the properties of both components and the parameters of the whole system and also on the activity of this binary. The results obtained show that only long-term observations can help to understand the physical mechanisms that are responsible for the activity of these systems.

by Jaroslav Merc

Astronomical Institute, Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic

Institute of Physics, Faculty of Science, P. J. Šafárik University in Košice, Slovak Republic

at SA1A1 (P1 lecture hall) Institute of Physics, Park Angelinum 9, Košice, P. J. Šafárik University

on Thursday December 20, 2018

from 10:30

]]>by Oleg Derzhko

Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, L’viv Ukraine

at SA1A1 (P1 lecture hall) Institute of Physics, Park Angelinum 9, Košice, P. J. Šafárik University

on Thursday December 13, 2018

]]>by Viktor Khmara

at SA1A1 (P1 lecture hall) Institute of Physics, Park Angelinum 9, Košice, P. J. Šafárik University

on Thursday December 06, 2018

from 10:30

]]>An electric current flowing through a coil of copper wire induces a magnetic field in the coil. This magnetic field can then transfer to a nearby magnetic object, such as a second coil of wire. The laws of electromagnetism, and experimental demonstrations to date, predict that this transfer is symmetric, meaning that magnetic fields move both from coil A to coil B and from coil B to coil A. Prat-Camps and his colleagues wondered if they could break this so-called magnetic reciprocity and make the magnetic-field transfer one way. The answer, they found, is yes, if both coils are placed in between the two walls of a hollow, rotating, conducting cylinder, where the walls have a U-shaped cross section.

see: https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.121.213903

]]>In the first part, the XY model is generalized by inclusion of up to an infinite number of higher-order pairwise interactions with an exponentially decreasing strength. We demonstrate that at low temperatures the model displays QLRO phase with the exponent η = T/[2πJ(p,α)], nonlinearly dependent on parameters p and α that control the number of higher-order terms and the decay rate of their intensity, respectively. At higher temperatures the system shows a crossover from the continuous BKT to the first-order transition for the parameter values corresponding to a highly nonlinear shape of the potential well. The role of topological excitations (vortices) in changing the nature of the transition will be discussed.

In the second part, we will focus on critical properties of the XY model with solely nematic-like terms, cos(qφ) with q = 2, 3, and 4. We will demonstrate that, even though neither of the terms alone can induce ferromagnetic (FM) ordering, their coexistence and competition can lead to a complex phase diagram including the FM phase at low temperatures. In particular, in the model involving the first two terms the FM phase appears wedged between the two nematic-like phases induced by the respective couplings. The phase transitions between the FM and nematic-like phases belong to the Ising and three-state Potts universality classes. Inside the FM phase the spin pair correlation function decays even much more slowly than in the standard XY model and the vortex-antivortex pair density is extremely low. In the model including all three terms it is possible to observe up to three successive phase transitions: the order-disorder transition of the BKT type is followed by two more transitions, as the system passes through two nematic-like phases to the FM phase at low temperatures that are both of Ising type.

by Milan Žukovič

at SA1A1 (P1 lecture hall) Institute of Physics, Park Angelinum 9, Košice, P. J. Šafárik University

on Thursday November 08, 2018

from 10:30

]]>