Search results for "Statistical physic"
showing 10 items of 1403 documents
Non-LTE radiation hydrodynamics in PLUTO
2019
Modeling the dynamics of most astrophysical structures requires an adequate description of the radiation-matter interaction. Several numerical (magneto)hydrodynamics codes were upgraded with a radiation module to fulfill this request. However, those among them that use either the flux-limited diffusion (FLD) or the M1 radiation moment approaches are restricted to the local thermodynamic equilibrium (LTE). This assumption may be not valid in some astrophysical cases. We present an upgraded version of the LTE radiation-hydrodynamics module implemented in the PLUTO code, originally developed by Kolb et al. (2013), which we have extended to handle non-LTE regimes. Starting from the general freq…
Communication: Restoring full size extensivity in internally contracted multireference coupled cluster theory.
2012
The reason for the lack of size extensivity in the valence space in current implementations of internally contracted multireference coupled cluster theories is the procedure used to eliminate redundant components from the cluster operator. We present a simple way to restore full size extensivity by performing this critical step in a basis of excitation operators that are normal ordered with respect to the multiconfigurational reference function.
Analysis of the level-crossing rate and average duration of fades of WSSUS channels
2017
Studies of the level-crossing rate (LCR) and the average duration of fades (ADF) are so far only devoted to stochastic processes being a function of one independent variable, which is usually time or in some few cases frequency. In this paper, we study the LCR (ADF) of wide-sense stationary uncorrelated scattering (WSSUS) processes in the time-frequency domain. A closed-form solution will be derived for the so-called time-frequency LCR (ADF) of the absolute value of the time-variant transfer function (TVTF) of WSSUS processes. It is shown that the LCR (ADF) is circularly symmetric in the normalized time-frequency domain. The derived time-frequency LCR contains the time LCR and frequency LCR…
Statistical characterization of self-assembled charged nanoparticle structures
2013
We propose a novel approach for description of dynamics of nanostructure formation for a system consisting of oppositely charged particles. The combination of numerical solution of analytical Bogolyubov–Born–Green–Kirkwood–Yvon (BBGKY) type equation set with reverse Monte Carlo (RMC) method allows us to overcome difficulties of standard approaches, such as kinetic Monte Carlo or Molecular Dynamics, to describe effects of long-range Coulomb interactions. Moreover, this allows one to study the system dynamics on realistic time and length scales. We applied this method to a simple short-range Lenard–Jones (LJ)-like three- (3D) and two-dimensional (2D) system combining the long-range Coulomb an…
Comment on “How skew distributions emerge in evolving systems” by Choi M. Y. et al.
2010
Power-law distributions and other skew distributions, observed in various models and real systems, are considered. As an example, critical exponents determined from highly accurate experimental data very close to the λ-transition point in liquid helium are discussed in some detail. A model, describing evolving systems with increasing number of elements, is considered to study the distribution over element sizes. Stationary power-law distributions are found. Certain non-stationary skew distributions are obtained and analyzed, based on exact solutions. Validerad; 2010; 20100908 (weber)
Fick Diffusion Coefficients in Ternary Liquid Systems from Equilibrium Molecular Dynamics Simulations
2012
An approach for computing Fick diffusivities directly from equilibrium molecular dynamics (MD) simulations is presented and demonstrated for a ternary chloroform–acetone–methanol liquid mixture. In our approach, Fick diffusivities are calculated from the Maxwell–Stefan (MS) diffusivities and the so-called matrix of thermodynamic factors. MS diffusivities describe the friction between different molecular species and can be directly computed from MD simulations. The thermodynamic factor describes the deviation from ideal mixing behavior and is difficult to extract from both experiments and simulations. Here, we show that the thermodynamic factor in ternary systems can be obtained from density…
IDEA: interface dynamics and energetics algorithm.
2007
IDEA, interface dynamics and energetics algorithm, was implemented, in FORTRAN, under different operating systems to mimic dynamics and energetics of elementary events involved in interfacial processes. The code included a parallel elaboration scheme in which both the stochastic and the deterministic components, involved in the developed physical model, worked simultaneously. IDEA also embodied an optionally running VISUAL subroutine, showing the dynamic energy changes caused by the surface events, e.g., occurring at the gas-solid interface. Monte Carlo and ordinary differential equation system subroutines were employed in a synergistic way to drive the occurrence of the elementary events a…
Parallel simulation of dense two-dimensional polymer systems
1990
Abstract We present a parallel algorithm for the simulation of dense lattice polymer systems. The algorithm will be given for a two-dimensional system although the algorithm can be generalized to higher dimensions. We discuss timing results and applications.
Computer simulations of critical phenomena and phase behaviour of fluids
2010
Computer simulation techniques such as Monte Carlo (MC) and Molecular Dynamics (MD) methods yield numerically exact information (apart from statistical errors) on model systems of classical statistical mechanics. However, a systematic limitation is the restriction to a finite (and often rather small) particle number N (or box linear dimension L, respectively). This limitation is particularly restrictive near critical points (due to the divergence of the correlation length of the order parameter) and for the study of phase equilibria (possibly involving interfaces, droplets, etc.). Starting out with simple lattice gas (Ising) models, finite size scaling analyses have been developed to overco…
Cluster size distributions in particle systems with asymmetric dynamics
2001
We present exact and asymptotic results for clusters in the one-dimensional totally asymmetric exclusion process (TASEP) with two different dynamics. The expected length of the largest cluster is shown to diverge logarithmically with increasing system size for ordinary TASEP dynamics and as a logarithm divided by a double logarithm for generalized dynamics, where the hopping probability of a particle depends on the size of the cluster it belongs to. The connection with the asymptotic theory of extreme order statistics is discussed in detail. We also consider a related model of interface growth, where the deposited particles are allowed to relax to the local gravitational minimum.