Effect of a bounding surface on the rotational viscosity of liquid crystals

The effect of a surface, bounding a nematic-liquid phase, on the rotational viscosity γ ₁ is investigated on the basis of a statistical approach employing direct correlation functions. Specific calculations are performed for a model system consisting of ellipsoidal molecules interacting via a Gay-Berne potential near the bounding surface. Fiz. Tverd. Tela (St. Petersburg) 40, 1945–1949 (October 1998)     

Exact Connections between Current Fluctuations and the Second Class Particle in a Class of Deposition Models

We consider a large class of nearest neighbor attractive stochastic interacting systems that includes the asymmetric simple exclusion, zero range, bricklayers’ and the symmetric K-exclusion processes. We provide exact formulas that connect particle flux (or surface growth) fluctuations to the two-point function of the process and to the motion of the second class particle. Such connections have only been available for simple exclusion where they were of great use in particle current fluctuation investigations. MSC: 60K35, 82C41     

Periodic evolution of an ensemble of defects in crystals under dry friction conditions

A model of the frictional destruction of the surface layer of solids is proposed. The main elements of the model are ensembles of interacting dislocations and microcracks, whose kinetics is described by a system of coupled nonlinear differential equations. The periodic change in the wear parameters of the contacting materials is explained. Fiz. Tverd. Tela (St. Petersburg) 39, 497–498 (March 1997)     

Roughening of a Si(100) surface induced by the adsorption of oxygen near the solid-oxide nucleation threshold

An investigation of the processes on a Si(100) surface interacting with oxygen near the solid-oxide nucleation threshold using x-ray photoelectron spectroscopy and atomic-force microscopy is described. The nucleation threshold is the boundary between the temperature and oxygen pressure regions where a phase transition with the formation of a submonolayer oxide and a roughening transition caused by oxygen adsorption occur. Near the nucleation threshold, either a random rough relief or a quasiperiodic structure is formed on a surface coated with chemisorbed oxygen. The formation of the rough relief due to oxygen adsorption has been interpreted within the theory of phase transitions as a result of vacancy clustering. A model that allows one to describe the dynamics of processes on the surface near the nucleation threshold in qualitative and in some cases in quantitative terms has been suggested. Zh. éksp. Teor. Fiz. 114, 239–262 (July 1998)     

The angular dislocation parallel to a free surface. Application to a (1 1 1)Si low-angle twist boundary

The elastic displacement field of a sharply angular dislocation with its two legs parallel to a planar free surface is given in a practical analytical form. Its expression gives access, in transmission electron microscopy (TEM), to computed images of numerous interacting dislocations all located at a distance h close to the free surface. As an application, this field is used repeatedly to study, in dark-field TEM and a g(3g) diffraction mode with g{2?2?0}, the contrast of dissociated triple nodes of a low-angle twist boundary in silicon extended over a (1?1?1) plane. It is shown that free surface elastic effects can influence the contrasts of some 30° partials if h is at the nanometer scale.     

Quantum theory of van der Waals interactions between excited atoms and birefringent dielectric surfaces

A theory of van der Waals (vdW) interaction between an atom (in ground or excited state) and a birefringent dielectric surface with an arbitrary orientation of the principal optic axis (C-axis) is presented. Our theoretical approach is based on quantum-mechanical linear response theory, using generalized susceptibilities for both atom and electromagnetic field. Resonant atom-surface coupling is predicted for excited-state atoms interacting with a dispersive dielectric surface, when an atom de-excitation channel gets into resonance with a surface polariton mode. In the non-retarded regime, this resonant coupling can lead to enhanced attractive or repulsive vdW surface forces, as well as to a dissipative coupling increasing the excited-state relaxation. We show that the strongly non-scalar character of the interaction with the birefringent surface produces a C-axis-dependent symmetry-breaking of the atomic wavefunction. Changes of the C-axis orientation may also lead to a frequency shift of the surface polariton mode, allowing for tuning on or off the resonant coupling, resulting in a special type of engineering of surface forces. This is analysed here in the case of cesium 6D _3/2 level interacting with a sapphire interface, where it is shown that an adequate choice of the sapphire C-axis orientation allows one to transform vdW surface attraction into repulsion, and to interpret recent experimental observations based on selective reflection methods [H. Failache etal., Phys. Rev. Lett. 83, 5467 (1999)]. Received 24 January 2001     

Superconductivity in the presence of fermion condensation

Fermion condensation (FC) is studied within the density functional theory. FC can fulfill the role of a boundary, separating the region of strongly interacting electron liquid from the region of strongly correlated electron liquid. Consideration of the superconductivity in the presence of FC shows that, under certain circumstances, at temperatures above T _c the superconductivity vanishes and the superconducting gap smoothly transforms into a pseudogap. The pseudogap occupies only a part of the Fermi surface, and one that shrinks with increasing temperature and vanishes at T=T*, and the single-particle excitations of the gapped area of the Fermi surface have a width γ ∼(T-T _c ). Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 491–496 (25 September 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Chemical reactions at surfaces: Application of the reaction ensamble monte carlo method

The Monte Carlo simulation method introduced by Smith and Triska [J. Chem. Phys.100 (1994) 3019] is extended to the case of a reacting fluid in contact with a hard wall. The fluid structure for both spherical and nonspherical reaction products is discussed for simple models of reacting hard spheres near a hard wall and near a wall interacting via Lennard-Jones (9,3) potential. In the latter case the investigated model assumes that the probability of a chemical reaction changes with a distance from the surface. It is shown that the applied technique is suitable for the study of reacting nonuniform fluids. This work is supported by KBN under the Grant No. 3 T09A 062 10.     

Kinetics of impurity segregation at grain boundaries in polycrystals. II. Concentrated solution

The isothermal impurity segregation from a finite-size grain into an intergrain boundary region or at an external free surface is investigated when the impurity concentration in the boundary region is not small. Simple algebraic equations are obtained that describe the impurity concentration for the case of several competing and interacting impurities. The process of segregation of two impurities is discussed in detail, and it is shown that the concentration of one of them can have a maximum as a function of time. Fiz. Tverd. Tela (St. Petersburg) 40, 251–253 (February 1998)     

X-ray spectral analysis of the degradation of Au/Si interphase boundaries in air

The dependence on the energy of primary electrons of the form of the ultrasoft x-ray Si L _2,3 and Au N _6,7 emission bands is studied in Au/Si structures interacting with the oxygen in air. A method for quantitatively estimating the phase chemical composition and its depth distribution was used, based on an analysis of the shape of the bands and employing the most general integral form for the dependence of the intensity of the x-ray spectra on the energy of the primary electrons. Oxidation was found to cause diffusion of silicon atoms to the surface and produce a fundamental change in the phase composition of the structures that were studied. A characteristic feature of the structure of all the samples was the appearance on their surface of a relatively thick layer of SiO₂, whose thickness depends on the initial phase composition of the Au/Si interface. Fiz. Tverd. Tela (St. Petersburg) 39, 2101–2105 (November 1997)     

On the boson-fermion model of superconductivity

Summary The existence of pair excitations in a Fermi gas interacting via a short-range attractive potential is investigated. Within the ladder approximation to the Bethe-Salpeter equation for the effective two-particle interaction, evidence of pair excitation is found at energies slightly larger than the chemical potential. The link between those excitations and a boson-fermion model of superconductivity (Phys. Lett. A,196 (1995) 359) is discussed. In particular it is shown that the charge carrier density dependence of the pair excitation (boson) energy, assumed phenomenologically in the boson-fermion model, is consistent with the properties of the interacting Fermi gas studied. These results give support to the microscopic origin of the phenomenological boson-fermion model of superconductivity. Within the polaron-bipolaron theory the assumption that bosons and fermions can be described as mobile particles has found support in ref.[6] where the small bipolaron (boson) delocalization is discussed and in ref.[7] where the large polaron delocalization is analysed.     

Effect of magnetic field pulses on the anelastic properties of nitrogen-containing steel

The effect of weak magnetic field pulses on the dynamic properties of dislocations interacting with impurity-defect complexes is determined by the internal-friction method. The effect is characterized by an increase in the plasticity of a material under the conditions of microplastic deformation and slowing of strain hardening. Zh. Tekh. Fiz. Zh. Tekh. Fiz. 69, 122–123 (August 1999)     

Long-range order and magnetic relaxation in a system of single-domain particles

The paramagnetic-ferromagnetic phase transition and distinctive characteristics of relaxation of the magnetization in a system of interacting single-domain ferromagnetic particles distributed randomly in a nonmagnetic matrix are investigated in the mean-field approximation. Fiz. Tverd. Tela (St. Petersburg) 41, 1822–1827 (October 1999)     

Depth Profiling of Polymer Surfaces with FT-IR Spectroscopy

INTRODUCTION

The composition and structure at the surface of polymeric materials can vary with depth as a result of surface treatments, surface-specific processing variables, or thermodynamic forces active at the surface. For example, low molecular weight oils are applied to the surface of polymers for lubrication purposes. The distribution or depth gradient of the oil in the polymer depends on a variety of interacting factors, such as diffusion, solubility, temperature, chemical or physical interaction, porosity, etc. In the coatings and lamination industries, gradients can occur as a result of the direct deposition of Material A on the surface of Material B. When A does not mix with B, as is often desirable, the integrity of the surface is of importance. The thickness of the layer(s) and the sharpness of the interface(s) can be critical to the intended application of the material. Polymer surfaces are often treated to obtain specific surface properties. An example of this is in the corona poling of such surfaces to improve the printability in commercial applications. Material properties are based on the depth to which the surface treatment propagates, the chemistry of the reactions, and the resulting products.     

Soluble Spin-Label as a NMR Relaxation Probe in the Study of the Enzyme-Substrate Complexes

Abstract

The paramagnetic contributions induced by TEMPOL soluble spin-label on gentiobiose carbon spin-lattice relaxation rates are analyzed. Selective effects in the β(1–6) glycosidic bond region were observed. The possibility of using soluble spin-label to determine the stereochemistry of the substrate-enzyme interaction was then explored.

The results obtained with different diamagnetic and paramagnetic systems enabled us to distinguish the region of gentiobiose most involved in interaction with the enzyme, and the region of the disaccharide molecule located on the surface of the enzyme and most exposed to the nitroxide.

The results obtained could be used to model the enzyme surface of the gentiobiose binding site.

Soluble spin-labels have been widely used in the investigation of the conformational and dynamical properties of biomolecules in solution (1–4). The main effects of nit oxide spin-labels, like TEMPO or TEMPOL, is the increase in NMR spin-lattice relaxation rates of solvent exposed nuclei. In small molecules like the disaccharide gentiobiose, the spin-label can be used to discriminate molecular regions with a different solvent accessibility and to investigate interaction with the enzyme are the C1s, C2s and C4s carbons (where s refers to α and β and to the reducing and most reducing moiety). It is interesting to observe that although the results come from four independent systems, complementary and self consistent information was obtained on the substrate region involved in the interaction with the enzyme and on the region of the substrate in contact with the surface of the enzyme and exposed to the solvent and nitroxide molecules.

This method proved useful for investigating the surface and the conformation of the enzyme interacting with the substrate molecule, and is a new application of soluble spin label in structural studies.     

Evolution of the width of the wave packet of a charged particle interacting with a quantum electromagnetic field

The path integral method is used to study the width of the wave packet of a relativistic charged particle interacting with a quantum electromagnetic field. A general expression is derived for the density distribution of a particle moving in arbitrary external potentials. An electron synchrotron with weak focusing is studied as a specific example, and the width of the wave packet of an electron moving in this accelerator is found. Zh. éksp. Teor. Fiz. 111, 1563–1578 (May 1997)     

Tensor structure of the stationary point of the radiative relaxation operator of an atom

We formulate the problem of the stationary point of the operator of radiative relaxation of an atom: the initial distribution among the sublevels of the excited state, whose nonzero eigenvalues (populations) coincide with the populations of the final distribution (after spontaneous decay) among the sublevels of the ground state. We show that these distributions can be expressed in terms of spherical functions of the complex direction. The results are then used to develop a compact analytical representation of the stationary density matrix of atoms interacting with an elliptically polarized monochromatic field. Zh. éksp. Teor. Fiz. 114, 125–134 (July 1998)     

Non-Lie and Discrete Symmetries of the Dirac Equation

Abstract

New algebras of symmetries of the Dirac equation are presented, which are formed by linear and antilinear first–order differential operators. These symmetries are applied to decouple the Dirac equation for a charged particle interacting with an external field.     

Properties of IR-active lattice vibrations in the vicinity of kinks in the Frenkel-Kontorova model

The properties of infrared lattice vibrations in the presence of kinks in the Frenkel-Kontorova model are analyzed. Our results show that the vibration of particles involved in kink formation is very similar to that in a gap mode around a force-constant defect. We found that the IR phonon mode intensity possesses a universal dependence on a certain combination of system parameters and kink concentration. On the basis of these results a criterion is proposed for separating the regime of weakly interacting kinks in the system from the regime of a kink lattice. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 10, 750–754 (25 May 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Vortex formation in a slowly rotating Bose-Einstein condensate confined in a harmonic-plus-Gaussian laser trap

Motivated by the recent experiment at ENS [V. Bretin, S. Stock, Y. Seurin and, J. Dalibard, Phys. Rev. Lett. 92, 050403 (2004)], we study a rotating (non-)interacting atomic Bose-Einstein condensate confined in a harmonic-plus-Gaussian laser trap potential. By adjusting the amplitude of the Gaussian laser potential, one can make quadratic-plus-quartic potential, purely quartic potential, and quartic-minus-quadratic potential. We show that an interacting Bose-Einstein condensate confined in a harmonic-plus-Gaussian laser trap breaks the rotational symmetry of the Hamiltonian when rotational frequency is greater than one-half of the lowest energy surface mode frequency. We also show that by increasing the amplitude of the Gaussian laser trap, a vortex appears in a slowly rotating Bose-Einstein condensate. Moreover, one can also create a vortex in a slowly rotating non-interacting Bose-Einstein condensate confined in harmonic-plus-Gaussian laser potential.Received: 24 June 2004, Published online: 24 August 2004PACS: 03.75.Lm Tunneling, Josephson effect, Bose-Einstein condensates in periodic potentials, solitons, vortices and topological excitations - 05.30.Jp Boson systems