Stationary Solutions of the Fractional Kinetic Equation with a Symmetric Power-Law Potential

The properties of stationary solutions of the one-dimensional fractional Einstein--Smoluchowski equation with a potential of the form x ^2m+2, m=1,2,..., and of the Riesz spatial fractional derivative of order , 12, are studied analytically and numerically. We show that for 1<2, the stationary distribution functions have power-law asymptotic approximations decreasing as x ^–(+2m+1) for large values of the argument. We also show that these distributions are bimodal.     

Lévy Flights in a Steep Potential Well

Lévy flights in steeper than harmonic potentials have been shown to exhibit finite variance and a critical time at which a bifurcation from an initial monomodal to a terminal bimodal distribution occurs (Chechkin et al., Phys. Rev. E 67:010102(R) (2003)). In this paper, we present a detailed study of Lévy flights in potentials of the type U(x)∝|x| ^c with c>2. Apart from the bifurcation into bimodality, we find the interesting result that for c>4 a trimodal transient exists due to the temporal overlap between the decay of the central peak around the initial δ-condition and the building up of the two emerging side-peaks, which are characteristic for the stationary state. Thus, for certain system parameters there exists a transient trimodal distribution of the Lévy flight. These properties of Lévy flights in external potentials of the power-law type can be represented by certain phase diagrams. We also present details about the proof of multimodality and the numerical procedures to establish the probability distribution of the process.     

Theory of diffusive decomposition of supersaturated solid solution under the condition of simultaneous operation of several mass-transfer mechanisms

The kinetics of diffusive decomposition of a supersaturated solid solution under the condition of simultaneous operation of several mass-transfer mechanisms are developed. It is shown that the expressions for the growth rate of the precipitate and for the size distribution function have one peak. The location of these peaks, which slowly changes with time, can be considered a slowly changing parameter.     

Collisional super-Penrose process and Wald inequalities

We consider collision of two massive particles in the equatorial plane of an axially symmetric stationary spacetime that produces two massless particles afterwards. It is implied that the horizon is absent but there is a naked singularity or another potential barrier that makes possible the head-on collision. The relationship between the energy in the center of mass frame \(E_{c.m.}\) and the Killing energy E measured at infinity is analyzed. It follows immediately from the Wald inequalities that unbounded E is possible for unbounded \(E_{c.m.}\) only. This can be realized if the spacetime is close to the threshold of the horizon formation. Different types of spacetimes (black holes, naked singularities, wormholes) correspond to different possible relations between \(E_{c.m.}\) and E. We develop a general approach that enables us to describe the collision process in the frames of the stationary observer and zero angular momentum observer. The escape cone and escape fraction are derived. A simple explanation of the existence of the bright spot is given. For the particular case of the Kerr metric, our results agree with the previous ones found in Patil et al. (Phys Rev D 93:104015, 2016).     

The density of energy flow of quasiparticles with arbitrary energy–momentum relation

In this paper, we consider the energy conservation law in a continuous medium with arbitrary energy–momentum relation. We use a new theoretical approach in which both the long wavelength and short wavelength thermal excitations are described in a unified way. The theory is based on the fact that in a quantum fluid, the thermal de Broglie wavelengths of the atoms overlap each other. In this case, the atoms are delocalized in space and we can treat a quantum fluid as a continuous medium without any restriction on length scale. So, in quantum liquids, we can determine the probabilistic values of the parameters of the continuous medium in every mathematical point of space. From the Hamiltonian of this system, we derive a system of linear equations for the general case of an ideal liquid, which has a nonlocal relationship between pressure and density. In the frame of this model from the energy conservation law, a general expression for the energy density flow is obtained. It is shown that for the wave packet, it is not affected by the freedom in its definition. A clear relation for the energy density flow of a wave packet is derived that generalizes the ordinary form of it to the case of arbitrary dispersion.     

On the role of ascending diffusion of a gas flowing into the drift

We investigate the effect of ascending diffusion associated with the distribution of the hydrostatic pressure over the depth on the methane flow to the coal drift. The diffusion problem is solved analytically with the help of integral transformations. It is shown that the integrated gas flux is an exponential function of the drift depth. In view of the competition between transport modes associated with concentration and pressure gradients, the flux decays exponentially over a long time. The expressions for the integrated flux and for the flux at a preset instant are obtained. The role of symmetry in the problem of stress distribution in the medium surrounding the drift is considered.