Search results for "Statistical physics"
showing 10 items of 1402 documents
Some results on the dynamics and transition probabilities for non self-adjoint hamiltonians
2015
We discuss systematically several possible inequivalent ways to describe the dynamics and the transition probabilities of a quantum system when its hamiltonian is not self-adjoint. In order to simplify the treatment, we mainly restrict our analysis to finite dimensional Hilbert spaces. In particular, we propose some experiments which could discriminate between the various possibilities considered in the paper. An example taken from the literature is discussed in detail.
Cluster Embedding Method with Non-orthogonal Wave Functions for Simulation of Nanodevices
2012
Applicability of cluster embedding method with non-orthogonal wave functions for theoretical study of processes in nanodevices has been studied. Processes in nanodevices are treated in the framework of time-dependent DFT. We demonstrate that our cluster embedding method is compatible with DFT Kohn-Sham method and quantum transport theory based on time-dependent DFT. We conclude that the approach for electric current calculation developed for orthogonal wave functions may be applied for non-orthogonal wave functions if we transform the initial equations assuming that overlaps are small (S2 ≪ S).
Analyzing the Boer-Mulders function within different quark models
2009
A general formalism for the evaluation of time reversal odd parton distributions is applied here to calculate the Boer-Mulders function. The same formalism when applied to evaluate the Sivers function led to results which fulfill the Burkardt sum rule quite well. The calculation here has been performed for two different models of proton structure: a constituent quark model and the MIT bag model. In the latter case, important differences are found with respect to a previous evaluation in the same framework, a feature already encountered in the calculation of the Sivers function. The results obtained are consistent with the present wisdom, i.e., the contributions for the $u$ and $d$ flavors t…
Linear response in multipolar glasses
1988
We consider the unified hamiltonian with a bilinear coupling, describing the Ising-, vector-, Potts-, octupolar-glass and other glasses [1, 2]. We systematically derive the response to a homogeneous tensor-field as well as the response to an inhomogeneous random tensor-field. We investigate the overlap distribution function and its first and second moment. In all these considerations, we recover the results of the Ising spin glass for sufficiently symmetric multipolar glasses, but we also obtain differnt results for less symmetric glasses.
Spin-one-Ising model for (CO)1?x (N2) x mixtures: A finite size scaling study of random-field-type critical phenomena
1995
A qualitative model for solid mixtures of diatomic molecules, where one species (called CO, to be specific) carries both a dipole moment and a quadrupole moment, while the other species (calledN 2) has only a quadrupole moment, is studied by Monte Carlo methods. We use spinsS i =±1 to represent the orientations of the CO electric dipole moment, if the lattice sitei is taken by a CO molecule, whileS i =0 if the site is taken by anN 2 molecule. Assuming nearest-neighbor antiferroelectric interactions between CO molecules, and a bilinear dipole-quadrupole coupling between CO andN 2, the randomly quenchedN 2 molecules act like random fields do in the random field Ising model. In previous work i…
KINETICS OF CRYSTAL GROWTH LIMITED BY RANDOM VELOCITY FIELDS
2008
A spherical growth process controlled by velocity fluctuations of particles of a saturated solution is investigated. Velocity fluctuations are modeled by a Gaussian random field. The interface evolution is determined by a Langevin-type equation with a multiplicative random field, which in the case of the quasi-homogeneous random Gaussian field is equivalent to Fokker–Planck dynamics. We analyze numerically the Fokker–Planck equation and compare growth kinetics in the case of noisy (i.e. space-independent) fluctuations. It is shown that for a large class of spatially correlated velocity fluctuations, the growth kinetics is universal, i.e. it does not depend on the details of statistics of f…
Continuum limit in random sequential adsorption.
1991
We develop analytical estimates of the late-stage (long-time) asymptotic behavior of the coverage in the D-dimensional lattice models of irreversible deposition of hypercube-shaped particles. Our results elucidate the crossover from the exponential time dependence for the lattice case to the power-law behavior with a multiplicative logarithmic factor, in the continuum deposition. Numerical Monte Carlo results are reported for the two-dimensional (2D) deposition, both lattice and continuum. Combined with the exact 1D results, they are used to test the general theoretical expectations for the late-stage deposition kinetics. New accurate estimates of the jamming coverages in 2D rule out some e…
STOCHASTIC ANALYSIS OF ONE-DIMENSIONAL HETEROGENEOUS SOLIDS WITH LONG-RANGE INTERACTIONS
2011
Random mass distribution in one-dimensional (1D) elastic solids in the presence of long-range interactions is studied in this paper. Besides the local Cauchy contact forces among adjacent elements, long-range forces depending on the product of interacting masses, as well as on their relative displacements, are considered. In this context, the random fluctuations of the mass distribution involve a stochastic model of the nonlocal interactions, and the random displacement field of the body is provided as the solution of a stochastic integro-differential equation. The presence of the random field of mass distribution is reflected in the random kernel of the solving integro-differential equatio…
Four-time rotational correlation functions
1998
A scheme to analyze four-time rotational correlation functions of any rank is developed and details for rank L = 1 and 2 are given. The scheme provides a transparent way for identifying deviations from simple Markovian dynamics as observed, e.g., in complex liquids close to the glass transition. The method should be applicable to NMR and optical multiple-pulse techniques as well as to photon correlation spectroscopy. Results are given for 2H-NMR multiple-pulse data in supercooled glycerol. We identify and analyze the dynamical heterogeneity of molecular reorientation in a range of 205 − 215 K close to the glass temperature Tg = 190 K.
The dynamics of optically pumped molecular lasers. On its relation with the Lorenz - Haken model
1997
In this paper we review the work on dynamical instabilities in optically pumped molecular lasers (OPLs) that has been carried out during the last 15 years. The main purpose of this review article is to survey and extend the authors' work on optically pumped molecular lasers and to place it in context with other research done in this area, without being a comprehensive review of all previous work done on this topic. In particular, we concentrate on the theoretical interpretation of the Lorenz dynamics observed in the far-infrared ammonia laser by reviewing the results obtained with different models of OPLs. New results corresponding to the dynamics obtained with the Doppler-broadened OPL mod…