arXiv subjects

E. V. Vakarin

Publications and source records attributed to E. V. Vakarin.

14 recordsLinked to original sources

arXiv2013

On the origin of power-law distributions in systems with constrained phase space

Behavior of condensed matter systems deviating from the standard equilibrium conditions is discussed. Statistical properties of coupled dynamic-stochastic systems are studied within a combination of the maximum information principle and the superstatistical approach. The conditions at which the Shannon entropy functional leads to a power-law statistics are investigated. It is demonstrated that, from a quite general point of view, the power-law dependencies may appear as a consequence of "global" constraints restricting both the dynamic phase space and the stochastic fluctuations. As a result, at sufficiently long observation times, the dynamic counterpart is driven into a non-equilibrium steady state whose deviation from the usual exponential statistics is given by the distance from the conventional equilibrium.

cond-mat.stat-mech↗

arXiv2013

Modeling of aging processes in the insertion compounds

The aging phenomena occurring in the course of cycling processes in the insertion host-guest compounds are discussed in the framework of a simple model. It takes into account two types of effects. One can be attributed to modifications of the host/guest solution interface in a form of an effective energetic barrier. The other is associated with the host matrix disordering that is translated into a change in the distribution of the host site energies as a function of the applied potential or the concentration of the guest species. It is found that the aging properties depend on the preparation mode, the cycling conditions and the insertion induced transformations. The impact of these transformations on the aging is determined by the matrix sensibility.

cond-mat.mtrl-sci↗

arXiv2013

Phase behavior under the averaging over disorder realizations

Effects of the averaging over disorder realizations (samples) on the phase behavior are analyzed in terms of the mean field approximation for the random field Ising model with infinite range interactions. It is found that the averaging is equivalent to a drastic modification in the statistics of the quenched variables. In its turn, this lowers the critical temperature of a second-order phase transition or, depending on the sampling, even suppresses the ordered phase. Possible first order transitions are shown to be softened by the sample averaging. Common issues and differences in the interpretation of these effects in the context of the simulation and experimental studies are discussed.

cond-mat.stat-mech↗

arXiv2010

A link between the maximum entropy approach and the variational entropy form

The maximum entropy approach operating with quite general entropy measure and constraint is considered. It is demonstrated that for a conditional or parametrized probability distribution $f(x|μ)$ there is a "universal" relation among the entropy rate and the functions appearing in the constraint. It is shown that the recently proposed variational formulation of the entropic functional can be obtained as a consequence of this relation, that is from the maximum entropy principle. This resolves certain puzzling points appeared in the variational approach.

cond-mat.stat-mech↗

arXiv2009

On the mechanism of negative compressibility in layered compounds

A mechanism of negative compressibility occurring in compressed layered compounds in the presence of a pressure transmitting fluid medium is discussed within a simple model. It takes into account the excluded volume effects and soft fluid-matrix repulsion. It is demonstrated that a non-monotonic behavior of the interlayer spacing with the applied pressure results from a competition between the applied pressure and the internal one induced by the adsorbed fluid. Recent experimental data on the graphite oxide "structure breathing" under compression in the presence of water are analyzed in the light of these theoretical results.

cond-mat.stat-mech↗

arXiv2006

Constrained equilibrium as a tool for characterization of deformable porous media

A new method for characterizing the deformable porous materials with non-critical adsorption probes is proposed. The mechanism is based on a driving the adsorbate through a sequence of constrained equilibrium states with the insertion isotherms forming a pseudo-critical point or a van der Waals-type loop. In the framework of a perturbation theory and Monte Carlo simulations we have found a link between the loop parameters and the host morphology. This allows one to characterize porous matrices through analyzing a shift of the pseudo-critical point and a shape of the pseudo-spinodals.

cond-mat.stat-mech↗

arXiv2006

On a mechanism low-pressure insertion of chain molecules into crystalline matrices

A microscopic mechanism of low-pressure insertion and separation of chain-like molecules in host matrices is proposed. It is shown that the intramolecular correlations combined to appropriate host activities are responsible for a low-pressure condensation of chain molecules. This allows recover a fine structure of the isotherms and to explain recent experiments on the insertion of $C_2H_2$ and $CO_2$ guest species. We argue that the mechanism should be dominant in low-dimensional host geometries, where the entropic effects are strongly suppressed and the major factors are the chain connectivity and packing.

cond-mat.stat-mech↗

arXiv2006

Maximum entropy approach to power-law distributions in coupled dynamic-stochastic systems

Statistical properties of coupled dynamic-stochastic systems are studied within a combination of the maximum information principle and the superstatistical approach. The conditions at which the Shannon entropy functional leads to a power-law statistics are investigated. It is demonstrated that, from a quite general point of view, the power-law dependencies may appear as a consequence of "global" constraints restricting both the dynamic phase space and the stochastic fluctuations. As a result, at sufficiently long observation times the dynamic counterpart is driven into a non-equilibrium steady state whose deviation from the usual exponential statistics is given by the distance from the conventional equilibrium.

cond-mat.stat-mech↗

arXiv2006

Negative linear compressibility in confined dilatating systems

The role of a matrix response to a fluid insertion is analyzed in terms of a perturbation theory and Monte Carlo simulations applied to a hard sphere fluid in a slit of fluctuating density-dependent width. It is demonstrated that a coupling of the fluid-slit repulsion, spatial confinement and the matrix dilatation acts as an effective fluid-fluid attraction, inducing a pseudo-critical state with divergent linear compressibility and non-critical density fluctuations. An appropriate combination of the dilatation rate, fluid density and the slit size leads to the fluid states with negative linear compressibility. It is shown that the switching from positive to negative compressibility is accompanied by an abrupt change in the packing mechanism.

cond-mat.stat-mech↗

arXiv2005

On the double criticality of fluids adsorbed in disordered porous media

The phase transition of a fluid adsorbed in a heterogeneous system is studied with two simple lattice gas models within the framework of a mean-field theory. Despite the different origin of the heterogeneity (spatial variation of binding energy or fluid coordination numbers), the fluid can undergo two phase transitions if the hosting system is sufficiently heterogeneous. It is clearly shown that such a polymorphism in the confined fluid results from the successive condensations in distinct spatial regions of the host. We have found the precise conditions at which one two phase transitions occur. The insight gained from the present study allows one to understand better some recent puzzling simulation results.

cond-mat.stat-mech↗

arXiv2004

Surface rearrangement at complex adsorbate-substrate interfaces

On the basis of the information theory approach we propose a novel statistical scheme for analyzing the evolution of coupled adsorbate-substrate systems, in which the substrate undergoes the adsorbate-induced transformations. A relation between the substrate morphology and the adsorbate thermodynamic state is established. This allows one to estimate the surface structure in terms of incomplete experimental information and the one concerning the adsorbate thermodynamic response to the structural modifications.

cond-mat.stat-mech↗

arXiv2003

Role of structural fluctuations in the insertion into complex host matrices

A coupling of structural and thermodynamic fluctuations in the course of various-type insertion processes is investigated within a combination of Gibbsian statistics and the information theory approach. It is shown that the coupling makes it possible to restore (at least partially) the information, inaccessible from experimental tests. This enables one to make physically reasonable predictions under limited information on the system.

cond-mat.stat-mech↗

arXiv2003

A correlation between the equilibrium and transport properties of intercalation systems

Employing the lattice gas model, combined with the linear elasticity theory, a correlation between the equilibrium and transport properties of intercalated species is investigated. It is shown that the major features of the intercalation isotherms and the concentration dependence of the chemical diffusion coefficient can be well understood in terms of the change of the host volume in the course of intercalation. Theoretical predictions are compared to the experimental observations on PdH_x, Li_xWO_3 and Li-graphite systems.

cond-mat.stat-mech↗

arXiv2003

Thermodynamic non-additivity in disordered systems

It is shown that there is a mapping of the replica approach to disordered systems with finite replica index $n$ on the Tsallis non-extensive statistics, if the average thermodynamic entropy differs from the information entropy for the probability distribution. In the case of incomplete information the entropic index $q=1-n$ is shown to be related to the degree of lost information.

cond-mat.stat-mech↗