Statistical thermodynamic approach to vibrational solitary waves in acetanilide

We analyze the behavior of the macroscopic thermodynamic state of polymers, centering on acetanilide. The nonlinear equations of evolution for the populations and the statistically averaged field amplitudes of CO-stretching modes are derived. The existence of excitations of the solitary wave type is evidenced. The infrared spectrum is calculated and compared with the experimental data of Careri et al. [Phys. Rev. Lett. 51, 104 (1983)], resulting in a good agreement. We also consider the situation of a nonthermally highly excited sample, predicting the occurrence of a large increase in the lifetime of the solitary wave excitation. [S0031-9007(98)05407-6].8092008201

MICROSCOPIC APPROACH TO IRREVERSIBLE THERMODYNAMICS .2. AN EXAMPLE FROM SEMICONDUCTOR PHYSICS

The general theory described in the preceding article [Phys. Rev. A 43, 6622 (1991)] based on the nonequilibrium-statistical-operator method, which provides mechano-statistical foundations for phenomenological irreversible thermodynamics, is applied to a specific problem. This is the case of a highly excited plasma in a semiconductor, where fluxes of mass and energy naturally appear, as well as other higher-order fluxes, as basic variables necessary for the description of the macroscopic state of the system. A criterion for the truncation of the basic set of variables is presented. The equations of motion for the macrovariables are derived for the case of a simple model. They have the structure of nonlinear and nonlocal transport equations, which fit into a natural extension of those of linear irreversible thermodynamics. In particular, Maxwell-Cattaneo-Vernotte-type equations of extended irreversible thermodynamics are recovered, having relaxation times and transport coefficients that may be calculated from the microscopic dynamics of the system composed of averages over the nonequilibrium ensemble.43126633664

A nonequilibrium ensemble formalism: Criterion for truncation of description

In the framework of a nonequilibrium statistical ensemble formalism, consisting of the so-called Nonequilibrium Statistical Operator Method, we discuss the question of the choice of the space of thermohydrodynamic states. We consider in particular the relevant question of the truncation of description (reduction of the dimension of the state space). A criterion for justifying the different levels of truncation is derived. It depends on the range of wavelengths and frequencies which are the relevant ones for the characterization, in terms of normal modes, of the thermohydrodynamic motion in a nonequilibrium open system. Applications to the cases of thermal-sensitive resins and of n-doped polar semiconductors are done, numerical results are presented, and experimental observation is discussed. (C) 2000 American Institute of Physics. [S0021-9606(00)50705-3].11262692270

NONLINEAR TRANSPORT IN PHOTOEXCITED PLASMA IN SEMICONDUCTORS - NONOHMIC MOBILITY AND A GENERALIZED EINSTEIN RELATION

Resorting to a theory of responses to thermal and mechanical perturbations, based on statistical irreversible thermodynamics for systems arbitrarily away from equilibrium, we obtain the diffusion and mobility coefficients in a highly photoexcited plasma in semiconductors in the presence of an electric field. They are dependent on the evolution of the nonequilibrium thermodynamic state of the system. From these transport coefficients we derived a generalized Einstein relation for ultrafast transient regimes and for non-Ohmic conditions. In all cases this generalized Einstein law acquires values that are field dependent and larger than those in its original form only valid in steady-state conditions and the limit of weak fields. Numerical results appropriate for the case of a GaAs sample are presented.5219139361394

Nonlinear hole transport and nonequilibrium thermodynamics in group III-nitrides under the influence of electric fields

A theoretical study on the nonlinear transport of holes and of the nonequilibrium thermodynamic characteristics of p-doped wurtzite gallium nitride (GaN), aluminium nitride (AlN), and indium nitride (InN), under the influence of moderate to high electric fields, is presented. It is based on a nonlinear quantum kinetic theory which provides a description of the dissipative phenomena developing in the system. The ultrafast time evolution of the hole drift velocity and of the quasitemperatures of holes and longitudinal optical phonons are obtained. The steady state is analyzed by determining the dependence on the electric field of the nonequilibrium thermodynamic state and of the non-Ohmic mobility. A velocity overshoot is evidenced. (C) 2007 American Institute of Physics.102

Ultrafast kinetics of evolution of optical phonons in a photoinjected highly excited plasma in semiconductors

We consider the ultrafast kinetics of evolution of optical phonons in a photoinjected highly excited plasma in semiconductors. The state of the nonequilibrium ('hot') phonon system is described in terms of the concept of a nonequilibrium temperature, referred to as quasitemperature, per mode, which can be experimentally characterized and measured. The phonon emission time shows that optical phonons are preferentially produced, well in excess of equilibrium, in a reduced off-center region of the Brillouin zone. The phonons in this region are responsible for the phenomenon referred to as 'hot-phonon temperature overshoot.' Most of the phonons, namely, those outside such a region, are only weakly to moderately excited, and mutual thermalization of the nonequilibrium carriers and optical phonons follows, typically, in the tenfold picosecond scale. All these results are influenced by the experimental conditions, which we discuss on the basis of calculations specialized for GaAs. Comparison with experimental data is presented.5416113111131

DIFFUSION OF PHOTOINJECTED CARRIERS IN PLASMA IN NONEQUILIBRIUM SEMICONDUCTORS

We consider effects of diffusion in the photogenerated carrier system in highly photoexcited polar semiconductors. We develop a quantum quasihydrodynamic description of the system based on the nonequilibrium statistical operator formalism. We derive a generalized Fick's diffusion equation for the charge density of the carriers, with the ambipolar diffusion coefficient obtained at the microscopic level and depending on the evolving macroscopic (nonequilibriium thermodynamic) state of the sample. A detailed numerical calculation for the case of GaAs is done, obtaining good agreement with experimental data.4815108731088

Solitons in highly excited matter: Dissipative-thermodynamic and supersonic effects

Solitary waves - arising out of nonlinearity-induced coherence of optical and acoustical vibrational modes in dissipative open systems (polymers and bulk matter) - are described in terms of a statistical thermodynamics based on a nonequilibrium ensemble formalism. The undistorted progressive wave is coupled to the normal vibrations, and three relevant phenomena follow in sufficiently away-from-equilibrium conditions: (i) A large increase in the populations of the normal modes lowest in frequency, (ii) accompanied by a large increase of the solitary-wave lifetime, and (iii) emergence of a Cherenkov-like effect, consisting in a large emission of phonons in privileged directions, when the velocity of propagation of the soliton is larger than the group velocity of the normal vibrations. Comparison with experiments is presented, which points out to the. corroboration of the theory. [S1063-651X(98)00412-7].586B7913792

AMPLIFICATION OF COHERENT POLAR VIBRATIONS IN BIOPOLYMERS - FROHLICH CONDENSATE

We consider the nonequilibrium and dissipative evolution, and the steady state of the population of vibrational polar modes in a chain of biomolecules. These polar modes are excited through a coupling with a metabolic pumping source and are in anharmonic interaction with an elastic continuum. Groups of polar modes are coupled in this way through nonlinear terms in the kinetic equations. This nonlinearity is shown to be the source of an unexpected phenomenon characterizing complex behavior in this kind of system: after a threshold of intensity of the pumping source is achieved, polar modes with the lowest frequencies increase enormously their population in a way reminiscent of a Bose-Einstein condensation (Frohlich effect). The transient time for the steady-state condensate to follow is very short (picosecond time scale) and the condensation appears even for weak values of the anharmonic coupling strength responsible for its occurrence. Further, it seemingly requires accessible levels of metabolic pumping power in order to be produced and sustained.4854049405

MICROSCOPIC APPROACH TO IRREVERSIBLE THERMODYNAMICS .1. GENERAL-THEORY

In this paper we show how an extension of the nonequilibrium-statistical-operator method, relying upon the maximum-entropy principle set up by Jaynes [Am. J. Phys. 33, 391 (1965)], may be used to describe the time evolution of an arbitrary many-body system. The Gibbs space of the observables describing the macrostates of the system is extended to include not only the conserved variables, but additional ones whose origin is directly related to the microscopic nature of the system manifested in its Hamiltonian. This allows us to go beyond linear irreversible thermodynamics and enter into the domain of what is now known as extended irreversible thermodynamics (EIT). Transport equations for the extended basic set of macrovariables are derived, showing that the Maxwell-Cattaneo-Vernotte equations of EIT are obtained. The relaxation times and transport coefficients contained therein can be calculated from the microscopic dynamics of the system averaged over an appropriate nonequilibrium coarse-grained probability density. Other outstanding features of the methods are emphasized and related to already-established results for nonequilibrium systems.43126622663