Presence Of Thermal Field Research Articles

On Bleustein-Gulyaev waves in thermo-piezoelectricity and in thermo-piezoelectromagnetism

In 1968-69 Bleustein and Gulyaev discovered a new type of piezoelectric surface waves, for any material in class having no counterpart in a purely elastic homogeneous material of the same elastic symmetry as the piezoelectric material. This discovery generated an extensive literature on the subject, with extensions to piezoelectromagnetism too. Here we study generalizations of this type of surface waves in the presence of thermal fields for thermo-piezoelectric materials with hexagonal symmetry. The exact solutions are written for a class of stationary waves varying harmonically with time, which couple both modes of propagation.

Stochastic ejection of nanocontact droplet solitons via drift instability

The magnetic droplet soliton is a large amplitude, coherently precessing wave state that exists in ferromagnetic thin films with perpendicular magnetic anisotropy. To effectively sustain a droplet, magnetic damping can be locally compensated in a nanocontact region that imparts spin-transfer torque; this has been successfully deployed in experiment to directly image the droplet and probe its dynamics electrically. However, theory predicts and experiments indicate the existence of a drift instability whereby the droplet is ejected from the spin-transfer-torque-active region and subsequently decays, an effect that may be enhanced or possibly induced by thermal fluctuations. Using soliton perturbation theory and large deviation theory, this work determines the soliton ejection rate and the most likely path an ejected soliton tracks in the presence of thermal fields. These results lead to an effective lower bound on the stability of magnetic droplet solitons in spin-transfer torque nanocontact devices operating at finite temperature and point to ways in which droplets can be made more robust.

Modeling and analysis of free vibrations in thermoelastic hollow spheres

Purpose– The purpose of this paper is to present a model to analyze free vibrations in a transradially isotropic, thermoelastic hollow sphere subjected to stress free, thermally insulated or stress free, isothermal and rigidly fixed, thermally insulated or rigidly fixed, isothermal boundary conditions.Design/methodology/approach– The potential functions along with spherical wave solution have been used to reduce the system of governing partial differential equations to a coupled system of ordinary differential equations in radial coordinates after employing non-dimensional quantities. Matrix Frobenius method of extended power series has been employed to obtain accurate solution of coupled differential equations in terms of radial coordinates. The mathematical model of the considered problem has been solved analytically to obtain the characteristics equations after imposing the appropriate boundary conditions at the outer and inner surfaces of the hollow sphere. The characteristic equations which govern various types of vibration modes expected to exist have been derived in the compact form. The special cases of spheroidal and toroidal modes of vibrations have been deduced from the characteristic equations and discussed.Findings– The toroidal mode has been found to be independent of temperature change. The magnitude of lowest frequency and damping factor are significantly affected in the presence of thermal field and increase with an increase in the spherical harmonics in addition to geometry of the structure.Originality/value– The matrix Frobenius method has been used to develop analytical solutions and functional iteration technique to carry out numerical simulations of such structures for the first time. The simulated results are presented graphically and compared with the available literature.

Particle deposition with thermal and electrical effects in turbulent flows

Development of relationships for the particle concentration and convection velocity profile has been obtained by the adaptation of the surface renewal model to the particle continuity and momentum equations of the turbulence boundary-layer flow in the presence of thermal field [1]. The predictions obtained on the basis of this model for nonisothermal deposition velocity of particles have been found to be in good agreement with the experimental measurements for fully-developed turbulence tube flow conditions. The aim of this work is to extend the previous model for an applied electric field, with the inclusion of the effect of Coulombic force in addition to the Brownian and turbulent diffusion, the eddy impaction, the turbophoresis, and the thermophoresis. The calculations show an interaction between thermophoresis and turbophoresis in the presence of an applied electric field. The effect of electric force in nonisothermal flows can have a dramatic effect on thermophoretic deposition for τ p + < 0.02 , where turbophoretic effect has ceased. The effect of axial pressure gradient is also included.

Thermal and electric transport in semiconductors under a thermal field: emergence of nonequilibrium charge carriers

A new point of view on thermoelectric phenomena as a transport process of non- equilibrium charge carriers is presented. It is shown that Fermi quasilevels which characterise transport in systems far from equilibrium can be nonmonotonic functions of position. The role of recombination in forming thermoelectric phenomena is discussed for the first time. It is shown that in the presence of thermal fields a new term in the expression for recombination appears which depends on the inhomogeneity of the temperature field. If electron and hole temperatures are different, which is typical of semiconductors, then one more new term appears in the expres- sion for recombination proportional to the difference of electron and hole temperatures. A new method for the characterisation of scmiconductor materials connected with the measurement of thcrmopower is proposed. It is shown that nonstationary thermal fields are best suited for this purpose.