Search results for "Statistical physics"

Moment Equations for a Spatially Extended System of Two Competing Species

2005

The dynamics of a spatially extended system of two competing species in the presence of two noise sources is studied. A correlated dichotomous noise acts on the interaction parameter and a multiplicative white noise affects directly the dynamics of the two species. To describe the spatial distribution of the species we use a model based on Lotka-Volterra (LV) equations. By writing them in a mean field form, the corresponding moment equations for the species concentrations are obtained in Gaussian approximation. In this formalism the system dynamics is analyzed for different values of the multiplicative noise intensity. Finally by comparing these results with those obtained by direct simulat…

Focus on statistical physics modeling in economics and finance

2011

This focus issue presents a collection of papers on recent results in statistical physics modeling in economics and finance, commonly known as econophysics. We touch briefly on the history of this relatively new multi-disciplinary field, summarize the motivations behind its emergence and try to characterize its specific features. We point out some research aspects that must be improved and briefly discuss the topics the research field is moving toward. Finally, we give a short account of the papers collected in this issue.

Erratum: “Fitted dosimetric parameters of high dose-rate 192Ir sources according to the AAPM TG43 formalism” [Med. Phys. 28 (4), 654-660 (2001)]

2001

Fractional-Order Thermal Energy Transport for Small-Scale Engineering Devices

2014

Fractional-order thermodynamics has proved to be an efficient tool to describe several small-scale and/or high-frequency thermodynamic processes, as shown in many engineering and physics applications. The main idea beyond fractional-order physics and engineering relies on replacing the integer-order operators of classical differential calculus with their real-order counterparts. In this study, the authors aim to extend a recently proposed physical picture of fractional-order thermodynamics to a generic 3D rigid heat conductor where the thermal energy transfer is due to two phenomena: a short-range heat flux ruled by stationary and nonstationary transport equations, and a long-range thermal …

Coarse-grained models and collective phenomena in membranes: Computer simulation of membrane fusion

2003

We discuss the role coarse-grained models play in in- vestigating collective phenomena in bilayer membranes and place them in the context of alternative approaches. By reducing the de- grees of freedom and applying simple effective potentials, coarse- grained models can address the large time scales and length scales of collective phenomena in mem- branes. Although the mapping from a coarse-grained model onto chemi- cally realistic models is a challenge, such models provide a direct view on the phenomena that occur on the length scales of a few tens of nano- meters. Their relevance is exempli- ied by the study of fusion of model membranes. ' 2003 Wiley Periodicals,

Point field models for the galaxy point pattern modelling the singularity of the two-point correlation function

2002

There is empirical evidence that the two-point correlation function of the galaxy distribution follows, for small scales, reasonably well a power-law expression $\xi(r)\propto r^{-\gamma}$ with $\gamma$ between 1.5 and 1.9. Nevertheless, most of the point field models suggested in the literature do not have this property. This paper presents a new class of models, which is produced by modifying point fields commonly used in cosmology to mimic the galaxy distribution, but where $\gamma=2$ is too large. The points are independently and randomly shifted, leading to the desired reduction of the value of $\gamma$.

Aging effects manifested in the potential-energy landscape of a model glass former

2010

We present molecular dynamics simulations of a model glass-forming liquid (the binary Kob-Anderson Lennard-Jones model) and consider the distributions of inherent energies and metabasins during aging. In addition to the typical protocol of performing a temperature jump from a high temperature to a low destination temperature, we consider the temporal evolution of the distributions after an 'up-jump', i.e. from a low to a high temperature. In this case the distribution of megabasin energies exhibits a transient two-peak structure. Our results can qualitatively be rationalized in terms of a trap model with a Gaussian distribution of trap energies. The analysis is performed for different syste…

Rotational Motion of Linear Molecules in Three Dimensions. A Path-Integral Monte Carlo Approach

1994

Abstract A path-integral Monte Carlo (PIMC) simulation method for the rotational motion of linear molecules in three dimensions is presented. The technique is applied to an H2 impurity in a static crystal-field. The resulting orientational distributions from quantum and classical simulations are obtained and discussed. The algorithm suffers from the “sign problem” of quantum simulations. However, as can be seen by comparing the low temperature simulation result to the variational solution of the Schrodinger equation, the PIMC method captures the quantum fluctuations.

A minimal Gō-model for rebuilding whole genome structures from haploid single-cell Hi-C data

2020

Abstract We present a minimal computational model, which allows very fast, on-the-fly construction of three dimensional haploid interphase genomes from single-cell Hi-C contact maps using the HOOMD-blue molecular dynamics package on graphics processing units. Chromosomes are represented by a string of connected beads, each of which corresponds to 100,000 base pairs, and contacts are mediated via a structure-based harmonic potential. We suggest and test two minimization protocols which consistently fold into conformationally similar low energy states. The latter are similar to previously published structures but are calculated in a fraction of the time. We find evidence that mere fulfillment…

Spin-orbit couplings within the equation-of-motion coupled-cluster framework: Theory, implementation, and benchmark calculations.

2015

We present a formalism and an implementation for calculating spin-orbit couplings (SOCs) within the EOM-CCSD (equation-of-motion coupled-cluster with single and double substitutions) approach. The following variants of EOM-CCSD are considered: EOM-CCSD for excitation energies (EOM-EE-CCSD), EOM-CCSD with spin-flip (EOM-SF-CCSD), EOM-CCSD for ionization potentials (EOM-IP-CCSD) and electron attachment (EOM-EA-CCSD). We employ a perturbative approach in which the SOCs are computed as matrix elements of the respective part of the Breit-Pauli Hamiltonian using zeroth-order non-relativistic wave functions. We follow the expectation-value approach rather than the response-theory formulation for p…