The hopping rate equation for neutral particles, on an arbitrary periodical lattice, can be solved exactly. It is shown that if one scales the time t and the distances x(t→λ2t, x→λx) then, in the λ→∞ limit, the particle density tends to the solution of the diffusion equation faster...

This is a study of the equilibrium statistical mechanics of a mixed system of planar spins and Ising spins. The Ising spins σr are situated (one on each of the bonds connecting the planar spins sr so that the planar spins interact only via Ising spins. For a one-dimensional lattice the...

As is well known, the solution of the one-dimensional Schrödinger equation enables one to formulate simple models for the description of phenomena in condensed matter physics. This equation can be solved analytically only for particular potentials. In this paper we describe a new method to...

The possibility of the formation of a condensate with a finite absolute value of the momentum k0 in a strongly nonideal Bose system is considered. Such a condensate comes into existence when the one-particle spectrum of a normal system touches zero in the point k0 ≠ 0. The form of a...

We study the velocity autocorrelation function for the diffusion of a spherical macromolecule in solution. The diffusion is described by a generalized Langevin equation with memory character derived previously from fluctuation theory applied to the Debye-Bueche-Brinkman equation which describes...

A theory for nonequilibrium phenomena primarily associated with the molecular orientation in liquids and liquid crystals is developed within the framework of irreversible thermodynamics. The alignment tensors of rank 2 and 4 are taken into consideration as additional macroscopic variables. With...

We consider thermal fluctuations in a system with many degrees of freedom described by macroscopic equations and discuss the question how by elimination of variables one can arrive at a contracted stochastic equation for a subsystem. It is shown that for the validity of the...

We have calculated the Green function describing the physical process where a three level atom interacts with a strong pump field as well as with a weak perturbing signal field in the limit of high photon densities. The theory is then used to describe the cooperative two-photon resonance...

The Wigner function is calculated for a relativistic system of interacting scalar particles and anti-particles in thermal equilibrium. It is pointed out that the prerequisite for obtaining the correct result is normal ordering, as opposed to the customary process of symmetrization of the field...

By complex extension of a model for the harmonic oscillator a model is obtained which can be interpreted as a linearly damped harmonic oscillator. The quantized Hamiltonian with band-spectrum is explored.