Light scattering from a fluid with a stationary temperature gradient

The spectrum of light, scattered from a fluid with a stationary temperature gradient, is calculated on the basis of fluctuating hydrodynamics. Explicit expressions are obtained for the spectrum of the scattered light which is no longer symmetric around the frequency of the incident light. In particular the difference in height and intensity of the Brillouin lines is given. Furthermore the shift in the position of the maximum of the Rayleigh line is calculated.     

Light scattering from a fluid with a stationary temperature gradient

The spectrum of light scattered from a system in which a stationary temperature gradient is maintained is calculated on the basis of fluctuating hydrodynamics. Explicit expressions are obtained for the frequency dependence of the intensity of the modified Brillouin lines.     

Features in the kinetics of lateral zone crystallization of semiconductor crystals in a temperature gradient field

Theoretical and experimental investigations of the kinetics of a lateral zone crystallization process in a temperature gradient field are given. Kinetic rules for the method are established which allow one to control the rate of the process and the configuration of the crystallization channel.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 67–71, January, 1996.     

Finite temperature field theory with boundaries: The photon field

We calculate the deviations from Planckian form of the photon field finite temperature stress tensor in a manifold with boundary, due to scattering from the boundary. Familiar non-integrable divergences are found in the photon stress tensor as the boundary is approached and these are shown to be an inescapable consequence of initial calculational assumptions. Modifications of these assumptions are discussed which serve to remove the divergences and to illustrate the importance of the role played by surface gravitational actions.     

Kinetic equations and brownian motion for a solid in a stationary temperature gradient

A kinetic equation for the distribution function for a subsystem s interacting with a bath b maintained in a stationary non-isothermal state by reservoirs is derived by using a projection operator formalism and a perturbation expansion parameter λ appropriate to some brownian motion problems. Thus, when s is a heavy particle of mass m ₀ and b a lattice of light particles of mass m then λ = (m m ₀)^1/2. By means of an assumption about the decay of correlations of b variables in the field of s, the terms are classified as destruction terms which vanish to arbitrary order in λ for long enough times and collision terms which give well-defined integrals for long times. For the heavy particle in a lattice the leading collision terms, after linearization in the temperature gradient, lead to an equation equivalent to the generalized nonisothermal Fokker-Planck equation of Nicolis.     

Edge dislocations near phase boundaries in the gradient theory of elasticity

A solution of the boundary-value problem in the gradient theory of elasticity concerning a rectilinear edge dislocation parallel to the interface between phases with different elastic moduli and gradient coefficients is obtained. The interaction between the dislocation and the interface is considered on a nanoscopic level. It is shown that the stress field has no singularities on the dislocation line and remains continuous at the interface, unlike the classical solution, which is singular at the dislocation line and allows a discontinuity of two stress components at the interface. The gradient solution also removes the classical singularity of the image force for the dislocation on the interface. An additional elastic image force associated with the difference in the gradient coefficients of contacting phases is also determined. It is found that this force, which has a short range and a maximum at the interface, expels the edge dislocation into the material with a smaller gradient coefficient.     

Anomalous reorientation processes in liquid-crystal cells with hybrid orientation in response to a temperature gradient

The orientational relaxation of the director field, the velocity field, the temperature field, and the stress tensor components in a liquid-crystal cell with a hybrid orientation in response to a temperature gradient is investigated. The anomalies of the orientational relaxation of these fields are numerically analyzed in the case where the temperature of one of the bonding surfaces is close to the nematic-smectic A phase transition temperature.     

Oscillatory melting temperature of the vortex smectic phase in layered superconductors

We report on transport measurements of YBa 2Cu 3O (7-delta) single crystals with different oxygen contents in the geometry B, J ||ab (J perpendicularB). Our data show that the vortices become confined between the Cu-O planes below a well-defined temperature at which the effective size 2xi of the vortex core is approximately equal to the period of the Cu-O layers. This confinement strongly increases the vortex liquid freezing temperature. A new melting line is found separating a vortex liquid and a smectic phase, which shows an oscillatory field dependence reflecting differences between commensurate and incommensurate smectic states.     

Electric field gradient at the Hf site and the phase transition in HfV2

The electric quadrupole interaction at the Hf site in the cubic HfV₂ compound, which shows lattice instability when cooled below 120 K, has been studied using the 482 keV (5/2⁺) state in¹⁸¹Ta. The time differential perturbed angular correlation (TDPAC) studies involving (133+136)-482 keV - cascade at room temperature show that only a fraction of¹⁸¹Ta nuclei see a cubic symmetry while the remaining experience a weak, randomly oriented, electric quadrupole interaction described by a Gaussian frequency distribution with _Q=6.1±1.0 Mrad/sec and the relative width =0.5. There is a dramatic change in TDPAC pattern indicating a phase transition when the compound is cooled down to 77 K. At this temperature the quadrupole interaction frequency is found to be _Q=40.6±3.0 Mrad/sec with =0.35. The experimentally observed EFG both at the Hf and the V sites are compared to the theoretical estimates based on point charge model.     

Breakdown voltage of p-n-junctions obtained by zone melting with a temperature gradient using linear zones

The breakdown voltage of planar p-n-junctions produced in plates of n-type silicon by zone melting with a temperature gradient using linear aluminum zones have been investigated. It is shown that a general the breakdown voltage of such p-n-junctions varies in the direction of motion of the zone, due to the variable conditions under which the p-n-junction is formed. A method of calculating the breakdown voltage along the p-n-junction perpendicular to the semiconductor plate is described. This method enables the necessary conditions for producing p-n-junctions with the same breakdown voltage to be chosen. The theoretical results are confirmed experimentally.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 1, pp. 91–95, January, 1969.     

The temperature and pressure dependence of the electric field gradient at tantalum in rhenium

The quadrupole interaction (QI) at substitutional Ta atoms in a Re matrix has been investigated by TDPAC between 1.2 K and 450 K. It was found to depend only weakly on temperature with a minium around 200 K. No change in the QI was observed when the sample was cooled into the superconducting state. The QI was found to increase with pressure with the coefficient (? lnq/?P)_T=+0.93(23)10^?3 kbar^?1 at 300 K. A discussion of the temperature and pressure variations in connection with published Mössbauer data reveals the role of the conduction electron contribution to the electric field gradient.     

Behavior of screw dislocations near phase boundaries in the gradient theory of elasticity

The solution of the boundary-value problem on a rectilinear screw dislocation parallel to the interface between phases with different elastic moduli and gradient coefficients is obtained in one of the versions of the gradient theory of elasticity. The stress field of the dislocation and the force of its interaction with the interface (image force) are presented in integral form. Peculiarities of the short-range interaction between the dislocation and the interface are described, which is impossible in the classical linear theory of elasticity. It is shown that neither component of the stress field has singularities on the dislocation line and remains continuous at the interface in contrast to the classical solution, which has a singularity on the dislocation line and permits a discontinuity of one of the stress components at the interface. This results in the removal of the classical singularity of the image force for the dislocation at the interface. An additional elastic image force associated with the difference in the gradient coefficients of contacting phases is also determined. It is found that this force, which has a short range and a maximum value at the interface, expels a screw dislocation into the material with a larger gradient coefficient. At the same time, new gradient solutions for the stress field and the image force coincide with the classical solutions at distances from the dislocation line and the interface, which exceed several atomic spacings.     

Electronic phenomena in semi-conductors with a temperature gradient

Phenomena connected with the transfer of current carrier concentrations as a result of a temperature gradient in semi-conductors with two kinds of current carriers are theoretically studied. The paper first deals with the general equations which are valid at a certain point of the semi-conductor with a temperature gradient for the concentrations of current carriers and density of electric and thermal current. From this the distribution of the concentrations of current carriers is found for a typical case, the phenomenon of thermal emission of minority current carriers is discussed, relations are derived for the dependence of the thermal emf on the magnitude of the temperature gradient, the possibility is discussed of thermal rectification and equations are given for the thermal conductivity of a semi-conductor with non-equilibrium concentrations of current carriers.     

Crystallization of a eutectic Pb-Sn melt in the thermal field of a temperature gradient

The crystallization of a eutectic Pb-Sn melt is investigated under nonuniform conditions in vacuum, in air, and in water. It is found that the structure of the solid-state systems formed depends on the cooling conditions. A structural inhomogeneity in volume and a correlation between the microstructure and the coordinate in a thermal field are revealed. Results of technological, electron-microscopic, and statistical investigations are reported. It is shown that the experiment is consistent with the crystallization theory of eutectic melts.     

Finite temperature field theory with boundaries: Stress tensor and surface action renormalisation

The local stress tensor is calculated for a scalar field at finite temperature in a static spacetime with boundaries. Results exact in the temperature are obtained which in the zero temperature limit exhibit known non-integrable divergences as the boundary is approached. Renormalisation of bare surface gravitational actions produces a delta function behaviour in the energy density on the boundary which exactly cancels the local divergences, thereby rendering finite the total renormalised energy in a cavity. The role played by boundary contributions to the integrated quantum mechanical propogator for a finite system is emphasised.     

Oscillatory behavior of spatial soliton in a gradient refractive index waveguide with nonlocal nonlinearity

Oscillatory behavior of spatial solitons in a transverse parabolic gradient refractive index distribution (GRIN) waveguide with both local and nonlocal nonlinearity is investigated. Dynamics of such solitons are analyzed by the effective-particle approach method. For weak nonlocal nonlinearity, solitons oscillate in transverse direction periodically during propagation. The normalized width and maximum of refractive index variation of the waveguide play a key role in determining the oscillating period while the position of soliton oscillatory center is slightly influenced by the nonlocal nonlinearity. Stronger nonlocal nonlinearity leads to instability of the oscillatory solitons. Furthermore, the dynamics of the solitons are simulated numerically and good agreements are obtained between the analysis and numerical results. This behavior may be used in all-optical routers, switches etc. PACS 42.65.Tg; 42.65.Jx; 42.65.Wi