Cusp catastrophe in slowly varying equilibriums

Solutions of the equations v _x+v ³?tv+x=0 and v _xx=v ³? tv+x, which describe the nucleation of domain walls occurring in the neighborhood of cusps of slowly varying equilibriums, are analyzed. Examples related to the diffusion in smoothly inhomogeneous media are considered.     

Ionization of Hydrogen and Helium Atoms in Collisions with Relativistic Structural Heavy Ions

Based on the eikonal approximation, cross sections for single and double ionization of hydrogen and helium atoms in collisions with structural multiply charged heavy ions moving with relativistic velocities are calculated. In the present paper, the structural ions are taken to mean the ions with partially filled electronic shells. It is demonstrated that a consideration of the ion charge extension may noticeably change the corresponding cross sections compared to the cross sections for ionization by point ions having the same charges and energies.     

Interaction of charged dust particles in clouds of thermodynamically equilibrium charges

The solution of the Poisson-Boltzmann equation for a cloud of charges surrounding two charged dust particles treated as Debye atoms forming a Debye molecule is investigated numerically using Cassini coordinates. The electric force exerted on a dust particle by the other dust particle was determined by integrating the electrostatic pressure on the surface of the dust particle. It is shown that attractive forces appear when the following two conditions are satisfied. First, the Debye radius (corresponding to the electron density at half the mean distance between the dust particles) must be approximately equal to half the mean distance between the dust particles. Attraction between the dust particles emerges at a distance equal approximately to half the mean distance between the dust particles. Second, attraction takes place when like charges are concentrated predominantly on the dust particles. If the particles carry a small fraction of charge of the same polarity, repulsion between the particles takes place at all distances.     

Weighted Monte Carlo Methods for Approximate Solution of a Nonlinear Boltzmann Equation

We construct weighted modifications of statistical modeling of an ensemble of interacting particles which is connected with approximate solution of a nonlinear Boltzmann equation.     

Disintegration of a drop in an external electrostatic field

Regular features of the disintegration of both a drop of a perfectly conducting liquid and a drop of a dielectric liquid into two or three parts in an external uniform electric field are studied using the principle of minimizing the potential energy of the final state of a closed system with spontaneous processes.     

Influence of <Emphasis Type="Italic">CP</Emphasis> and <Emphasis Type="Italic">CPT</Emphasis> on production and decay of Dirac and Majorana fermions

The consequences of CP and CPT invariance for production and subsequent decay of Dirac and Majorana fermions in polarized fermion-antifermion annihilation are analytically studied. We derive general symmetry relations for the production spin density matrix and for the three-particle decay matrices and obtain constraints for the polarization and the spin-spin correlations of Dirac and Majorana fermions. We prove that only for Majorana fermions the energy and opening angle distribution factorizes exactly into contributions from production and decay if CP is conserved. Received: 6 November 2001 / Revised version: 23 April 2002 / Published online: 12 July 2002     

Relaxation dynamics of a broadband nanosecond acoustic pulse in a bubbly medium

The first experimental observation of the propagation dynamics of a short broadband acoustic pulse in a resonance medium with gas bubbles is carried out. The probing pulse is generated using the optoacoustic effect. It is shown that the theory of short pulse propagation in media with generalized resonance relaxation adequately and accurately describes the dynamics of short pulse dispersion. A possibility to determine the relaxation and resonance parameters of media by the pulsed testing technique is demonstrated.     

The epitaxial sexiphenyl (0 0 1) monolayer on TiO2(1 1 0): A grazing incidence X-ray diffraction study

A para-sexiphenyl monolayer of near up-right standing molecules (nominal thickness of 30 Å) is investigated in-situ by X-ray diffraction using synchrotron radiation and ex-situ by atomic force microscopy. A terrace like morphology is observed, the step height between the terraces is approximately one molecular length. The monolayer terraces, larger than 20 μm in size, are extended along the [0 0 1] direction of the TiO₂(1 1 0) substrate i.e. along the Ti-O rows of the reconstructed substrate surface. The structure of the monolayer and its epitaxial relationship to the substrate is determined by grazing incidence X-ray diffraction. Extremely sharp diffraction peaks reveal high crystalline order within the monolayer, which was found to have the bulk structure of sexiphenyl. The monolayer terraces are epitaxially oriented with the (0 0 1) plane parallel to the substrate surface (out-of-plane order). Four epitaxial relationships are observed. This in-plane alignment is determined by the arrangement of the terminal phenyl rings of the sexiphenyl molecules parallel to the oxygen rows of the substrate.