Unified description of ballistic and diffusive carrier transport in semiconductor structures

A unified theoretical description of ballistic and diffusive carrier transport in parallel-plane semiconductor structures is developed within the semiclassical model. The approach is based on the introduction of a thermo-ballistic current consisting of carriers which move ballistically in the electric field provided by the band edge potential, and are thermalized at certain randomly distributed equilibration points by coupling to the background of impurity atoms and carriers in equilibrium. The sum of the thermo-ballistic and background currents is conserved, and is identified with the physical current. The current-voltage characteristic for nondegenerate systems and the zero-bias conductance for degenerate systems are expressed in terms of a reduced resistance. For arbitrary mean free path and arbitrary shape of the band edge potential profile, this quantity is determined from the solution of an integral equation, which also provides the quasi-Fermi level and the thermo-ballistic current. To illustrate the formalism, a number of simple examples are considered explicitly. The present work is compared with previous attempts towards a unified description of ballistic and diffusive transport.Comment: 23 pages, 10 figures, REVTEX

Propagation of Plane Waves in a Generalized Thermo-magneto-electro-elastic Medium

In the present paper, the governing equations of a generalized thermo-magneto-electro-elastic medium are formulated in the x-z plane. The plane wave solution of these equations indicates the existence of three quasi plane waves, namely, quasi-P, quasi-T and quasi-SV waves. The thermo-magneto-electro-elastic medium is modeled with LiNbO3 for computing the speeds of these plane waves. Effects of the frequency, thermal relaxation time, electric coupling coefficient, magnetic coupling coefficient and angle of propagation on the speeds of these plane waves are observed and shown graphically

Nonlinear diffusion & thermo-electric coupling in a two-variable model of cardiac action potential

This work reports the results of the theoretical investigation of nonlinear dynamics and spiral wave breakup in a generalized two-variable model of cardiac action potential accounting for thermo-electric coupling and diffusion nonlinearities. As customary in excitable media, the common Q10 and Moore factors are used to describe thermo-electric feedback in a 10-degrees range. Motivated by the porous nature of the cardiac tissue, in this study we also propose a nonlinear Fickian flux formulated by Taylor expanding the voltage dependent diffusion coefficient up to quadratic terms. A fine tuning of the diffusive parameters is performed a priori to match the conduction velocity of the equivalent cable model. The resulting combined effects are then studied by numerically simulating different stimulation protocols on a one-dimensional cable. Model features are compared in terms of action potential morphology, restitution curves, frequency spectra and spatio-temporal phase differences. Two-dimensional long-run simulations are finally performed to characterize spiral breakup during sustained fibrillation at different thermal states. Temperature and nonlinear diffusion effects are found to impact the repolarization phase of the action potential wave with non-monotone patterns and to increase the propensity of arrhythmogenesis

Multiphysics Analysis of a Thermo Acoustic MHD Inductive Generator

This paper fits in the multi-physics analysis of an innovative conceptual design of Magneto-Hydrodynamic (MHD) inductive generator, coupled with a Thermo-Acoustic (TA) resonator. The thermo-acoustic effect occurs when an intense gradient of temperature is present along the axial direction of a duct containing a gas. Such effect allows the heat to be statically converted into mechanical energy of vibration. If the gas is ionized and the charges of opposite sign are separated into two clouds, an alternate electric current is associated to the thermo-acoustic vibration. That current, in its turn, can induce an electromotive force into a magnetically coupled coil. In this way, a thermo-electric conversion is performed, without solid moving parts or matter transport. A FEM analysis has been performed to assess the suitability of the complete energy transformation chain. In particular, the possibility that the charge carriers are involved in the vibration motion is investigated. An acoustic analysis has been done, in a glass tube containing a ionized gas, in order to study the velocity profiles within the duct in presence of viscous and thermal effects. Then, a multiphysics simulation has been performed by using the same geometry, by coupling the acoustic module with the electrostatic module, and the particle tracing module, in order to study the behavior of the unbalanced charge carriers when they are subject to a vibration and to an electric force, for a given set of design parameters