11 research outputs found
The collective variables representation of simple fluids from the point of view of statistical field theory
The collective variable representation (CV) of classical statistical systems
such as simple liquids has been intensively developed by the Ukrainian school
after seminal works by Prof. Ihor Yukhnovskii. The basis and the structure of
the CV representation are reexamined here from the point of view of statistical
field theory and compared with another exact statistical field representation
of liquids based upon a Hubbard-Stratonovich transform. We derive a two-loop
expansion for the grand potential and free energy of a simple fluid in both
version of the theory. The results obtained by the two approaches are shown to
coincide at each order of the loop expansion. The one-loop results are
identical to those obtained in the framework of the random phase approximation
of the theory of liquids. However, at the second-loop level, new expressions
for the pressure and the free energy are obtained, yielding a new type of
approximation
A mesoscopic field theory of ionic systems versus a collective variable approach
We establish a link between the two functional approaches: a mesoscopic field
theory developed recently by A.Ciach and G.Stell [A. Ciach and G. Stell, J.
Mol. Liq. 87 (2000) 253] for the study of ionic models and an exact statistical
field theory based on the method of collective variables.Comment: 7 page
Crossover between hydrodynamic and kinetic modes in binary liquid alloys
Inelastic x-ray scattering (IXS) measurements of the dynamic structure factor
in liquid Na57K43, sensitive to the atomic-scale coarse graining, reveal a
sound velocity value exceeding the long wavelength, continuum value and
indicate the coexistence of two phonon-like modes. Applying Generalized
Collective Mode (GCM) analysis scheme, we show that the positive dispersion of
the sound velocity occurs in a wavelength region below the crossover from
hydrodynamic to atom-type excitations and, therefore, it can not be explained
as sound propagation over the light specie (Na) network. The present result
experimentally proves the existence of positive dispersion in a binary mixture
due to a relaxation process, as opposed to fast sound phenomena.Comment: 7 pages, 8 figures, to appear in "Physical Review B
Ionic fluids: charge and density correlations near gas-liquid criticality
The correlation functions of an ionic fluid with charge and size asymmetry
are studied within the framework of the random phase approximation. The results
obtained for the charge-charge correlation function demonstrate that the
second-moment Stillinger-Lovett (SL) rule is satisfied away from the gas-liquid
critical point (CP) but not, in general, at the CP. However in the special case
of a model without size assymetry the SL rules are satisfied even at the CP.
The expressions for the density-density and charge-density correlation
functions valid far and close to the CP are obtained explicitely
The war in Ukraine: Does physics have a future?
The war in Ukraine is still going on. The number of victims is increasing every day. Many research centers are destroyed, researchers are displaced, and the conditions and nature of work in almost all regions of Ukraine have undergone significant changes. Is it time to talk about the future of physics in Ukraine under such conditions now? It is our deep conviction that it is necessary
From Brownian motion to self-avoiding walks and Lévy flights
Among many notable jubilees brought by the year 2012, the one of a special importance for the community of statistical physicists was the 140th birth anniversary of Marian Smoluchowski (Maryan Ritter von Smolan Smoluchowski, 28.05.1872 - 5.09.1917), who was one of the pioneers of statistical physics and, on a larger scale, one of those who shaped modern physical science as a whole. The present issue of EPJ ST entitled From Brownian motion to self-avoiding walks and Lévy flights aims to reflect the evolution of Smoluchowski’s ideas in the field of statistics of interacting random and self-avoiding walks, stochastic equations for many-particle systems, physics of glass-forming and noise driven systems. Majority of papers in this issue were presented at the international conference in statistical physics that took place in Lviv (Ukraine) on July 3-6, 2012
Comment on “Universal Effect of Excitation Dispersion on the Heat Capacity and Gapped States in Fluids”
International audienceWe discuss the validity of recent results in [Phys. Rev. Lett. 125, 125501 (2020)] on an universalrelation between the heat capacity and dispersions of collective excitations in liquids