Showing papers by "Áurea R. Vasconcellos published in 2000"
Book•
11 Oct 2000
Abstract: We briefly, and partially, consider aspects of the present status of phenomenological irreversible thermodynamics and nonequilibrium statistical mechanics. After short comments on Classical Irreversible Thermodynamics, its conceptual and practical shortcomings are pointed out, as well as the efforts undertaken to go beyond its limits, consisting of particular approaches to a more general theory of Irreversible Thermodynamics. In particular, a search for statistical-mechanical foundations of Irreversible Thermodynamics, namely, the construction of a statistical thermodynamics, are based on the Non-equilibrium Statistical Operator Method. This important theory for the treatment of phenomena at the macroscopic level, is based on a microscopic molecular description in the context of a nonequilibrium ensemble formalism. We draw attention to the fact that this method may be considered to be emcompassed within Jaynes' Predictive Statistical Mechanics and based on the principle of maximization of informational entropy. Finally, we describe how, in fact, the statistical method provides foundations to phenomenological irreversible thermodynamics, thus giving rise to what can be referred to as Informational Statistical Thermodynamics.
73 citations
TL;DR: In this article, a kinetic theory providing bases for an analytical treatment of nonlinear quantum transport is described, based on a nonequilibrium statistical ensemble formalism, which constitutes a soundly approach for the study of dissipative manybody systems driven arbitrarily away from equilibrium.
Abstract: It is described a kinetic theory providing bases for an analytical treatment of nonlinear quantum transport. It is founded on a nonequilibrium statistical ensemble formalism, which constitutes a soundly approach for the study of dissipative many-body systems driven arbitrarily away from equilibrium. This theory is applied to the study of transport of charge in n- and p- type doped polar semiconductors. Evolution of the carriers’ quasitemperature and mobility as well as of the relaxation times for energy and momentum are derived. Some comparison with experimental data is done.
42 citations
TL;DR: The main six basic steps that are at the foundations of the formalism are presented and the fundamental concepts are discussed and there follows a good agreement between theory and experimental data in the cases in which the latter are presently available.
Abstract: We describe a particular approach for the construction of a nonequilibrium statistical ensemble formalism for the treatment of dissipative many-body systems. This is the so-called Nonequilibrium Statistical Operator Method, based on the seminal and fundamental ideas set forward by Boltzmann and Gibbs. The existing approaches can be unified under a unique variational principle, namely, MaxEnt, which we consider here. The main six basic steps that are at the foundations of the formalism are presented and the fundamental concepts are discussed. The associated nonlinear quantum kinetic theory and the accompanying Statistical Thermodynamics (the Informational Statistical Thermodynamics) are very briefly described. The corresponding response function theory for systems away from equilibrium allows to connected the theory with experiments, and some examples are summarized; there follows a good agreement between theory and experimental data in the cases in which the latter are presently available. We also present an overview of some conceptual questions and associated criticisms.
39 citations
TL;DR: In this article, a theoretical study on the electron drift velocity and some nonequilibrium thermodynamic characteristics of wurtzite GaN, AlN, and InN is presented.
Abstract: A theoretical study on the electron drift velocity and some nonequilibrium thermodynamic characteristics of wurtzite GaN, AlN, and InN 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 electron drift velocity and quasitemperature is obtained, and overshoot effects are evidenced on both. The overshoot onsets are shown to occur at 20 kV/cm in GaN, 60 kV/cm in AlN, and 10 kV/cm in InN, electric field intensities which are considerably smaller than those that have been recently derived resorting to Monte Carlo simulations.
34 citations
TL;DR: In this article, the authors consider the problem of the truncation of description (reduction of the dimension of the state space) in a nonequilibrium statistical ensemble formalism and derive a criterion for justifying different levels of truncation.
Abstract: 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.
26 citations
TL;DR: In this paper, the authors apply a statistical-thermodynamic approach to the study of a particular physical system (two sets of nonlinearly coupled oscillators), driven far away from equilibrium.
Abstract: We apply a statistical–thermodynamic approach to the study of a particular physical system (two sets of nonlinearly coupled oscillators), driven far away from equilibrium. Such a system displays a kind of complex behavior consisting in the so-called Frohlich effect leading in steady-state conditions to a nonequilibrium phase condensation resembling the Bose–Einstein condensation of systems in equilibrium. A kind of “two-fluid model” arises: the “normal nonequilibrium phase” and Frohlich condensate or “nonequilibrium superphase,” which is shown to be an attractor of the system. We work out some aspects of the irreversible thermodynamics of this dissipative complex system. Particular nonlinear properties are discussed and Lyapunov exponents determined. This kind of system gives a good modeling of polar vibration modes in polymers and biopolymers.
23 citations
01 Mar 2000
TL;DR: In this paper, a statistical-thermodynamic theory of the phenomenon of stimulated amplification of the population of excitons which lie at the bottom of their lowest energy band is presented.
Abstract: A statistical-thermodynamic theory of the phenomenon of stimulated amplification of the population of excitons which lie at the bottom of their lowest-energy band is presented. The experimentally detected "packet" of excitons flowing ballistically is shown to consist of a Schrodinger-Davydov solitary wave, dressed with a cloud of incoherent excitons. Moreover, a secondary excitation by a c.w. laser beam promotes a Frohlich-Bose-Einstein–like condensation, which is responsible for the relevant phenomenon that the lifetime of the soliton is largely increased with increasing pumping power.
13 citations
TL;DR: In this article, the authors present an analysis of the nonequilibrium thermodynamics and a response function theory for the study of optical properties in ultrafast-spectroscopy pump-probe experiments.
Abstract: We present an analysis of the nonequilibrium thermodynamics and, mainly, a response function theory for the study of optical properties in ultrafast-spectroscopy pump-probe experiments. These experiments give rise to the formation of a photoinjected plasma in semiconductors in far-from-equilibrium conditions. The dissipative processes that evolve in this medium greatly influence optical and transport properties. The theory is centred on the application to the study of the phenomenon of modulated changes in the time-resolved reflectivity spectrum. In particular, we show that this phenomenon consists in the coupled effect of coherent-LO-phonon and carrier-charge-density motions, which are driven through the action of the coherent photons of the laser electromagnetic radiation. In the given conditions the modulation effect decays in time and has associated a frequency close to the zone-centre upper LO phonon-optical plasma hybrid mode, as experimentally observed.
9 citations
TL;DR: In this article, a quantum Boltzmann-style transport theory of a broad scope was derived by choosing the single and two-particle dynamical density operators as the basic informational-statistical variables.
Abstract: Within the framework of the nonequilibrium statistical ensemble formalism provided by the nonequilibrium statistical operator method, we derive a quantum Boltzmann-style transport theory of a broad scope. This is done by choosing the single- and two-particle dynamical density operators as the basic informational–statistical variables. The equations of evolution for their average values over the nonequilibrium ensemble, the nonequilibrium-reduced Dirac–Landau–Bogoliubov-type density matrices, are obtained. From the resulting generalized nonlinear quantum transport theory, after resorting to perturbative-like expansions, a far-reaching generalization of Boltzmann equation for the single-particle distribution function is derived. A type of traditional Boltzmann equation follows after using stringent approximations, whose limits of validity are evaluated.
6 citations
TL;DR: In this paper, it was shown that Davydov's solitary waves, strongly damped in near equilibrium conditions, can display long-range propagation when travelling in Frohlich's condensate.
Abstract: The particular question of transport of vibrational energy in biosystems is considered within the scope of Frohlich–Davydov's model. It is shown that Davydov's solitary waves, strongly damped in near equilibrium conditions, can display long-range propagation when travelling in Frohlich's condensate. The latter consists in the emergence of a self-organized dissipative structure (in Prigogine's sense), resembling a nonequilibrium Bose–Einstein-like condensation in the low-lying in frequency modes of vibration, once a critical level of pumping of metabolic energy is achieved.
6 citations
TL;DR: In this article, the nonlinear kinetics of a carrier system in a photoinjected plasma in semiconductors under the action of constant illumination with ultraviolet light were analyzed, and it was shown that the spatially homogeneous steady state becomes unstable, and a charge density wave emerges after a critical intensity of the incident radiation is achieved.
Abstract: We analyze in detail the nonlinear kinetics of a carrier system in a photoinjected plasma in semiconductors under the action of constant illumination with ultraviolet light. We show that the spatially homogeneous steady-state becomes unstable, and a charge density wave emerges after a critical intensity of the incident radiation is achieved. It is shown that this instability can only follow in doped p-type materials. In bulk systems the critical intensity was found to be too high making the phenomenon not observable under realistic experimental conditions. However, a more efficient electron excitation can be obtained in low dimensional p-type systems, like some molecular and biological polymers, where the interaction may follow by chemical interaction with the medium. We show that for intensities beyond the critical threshold an increasing number of modes provide further contributions (subharmonics) to the space inhomogeneity. It is conjectured that this process could lead the system to display chaotic-like behavior.
TL;DR: In this article, an approach based on the statistical-mechanical foundations provided by a Gibbs ensemble-like algorithm in none-quilibrium situations is discussed, and a comparison of quasitemperatures that arise in different approximated nonequilibrium statistical-thermodynamic descriptions of the dissipative system is done.
Abstract: Several aspects of the Thermodynamics of systems away from equilibrium are considered. Particular attention is given to the question of the concepts of entropy and temperature in arbitrary nonequilibrium conditions. Even though such state function and thermodynamic variable are elusive in such conditions, it is elaborated and discussed an approach to them that can be obtained in the framework of the so-called Informational Statistical Thermodynamics. This is the approach to Thermodynamics based on the statistical-mechanical foundations provided by a Gibbs ensemble-like algorithm in nonequilibrium situations. The resulting nonequilibrium temperature-like variable - dubbed as quasitemperature - is shown to be a quantity measurable with appropriate "thermometric devices". A comparison of quasitemperatures that arise in different approximated nonequilibrium statistical-thermodynamic descriptions of the dissipative system is done. The validity of these different approximations is evaluated, and (in the framework of the theory) generalized Gibbs, Clausius, and Boltzmann's relations, as well as properties of the corresponding entropy-like function (or informational entropy in Jaynes-Shannon sense), that the theory introduces, are presented. Conceptual and physical aspects of the question are also discussed, and a partial comparison of these concepts with those arising in other approaches to irreversible thermodynamics is briefly attempted. This article is an enlargement of a paper in Fortschritte der Physik/Progress of Physics, 47, 9 (1999), where have been added extensive comments on the subject.
01 Jun 2000
TL;DR: In this article, a system of externally pumped nonequilibrium harmonic oscillators (vibrational modes) interacting through anharmonic effects with a harmonics with lower-lying frequencies (acoustic-like vibrations) composing a thermal bath for the former is considered.
Abstract: We consider a system of externally pumped nonequilibrium harmonic oscillators (vibrational modes) interacting through anharmonic effects with a system of harmonic oscillators with lower-lying frequencies (acoustic-like vibrations) composing a thermal bath for the former. We derive the equations of evolution for the population of the vibrational modes, introducing high order nonlinear relaxation processes. It is shown that complex behavior arises in this system, namely, after a certain critical intensity of the pumping source is achieved, the populations of the modes lowest in frequency increase enormously at the expense of the excitations of the other modes. In this way there follows what can be termed a Bose–Einstein-like condensation, not in a phase in equilibrium, but in a nonequilibrium dissipative structure.
TL;DR: In this article, the authors considered the behavior of the absorption coefficient and luminescence spectrum in the steady state when III-nitrides semiconductors (compounds GaN, AlN, and InN) are in far-from-equilibrium conditions created by an electric field.
Abstract: We consider the behavior of the absorption coefficient and luminescence spectrum in the steady state when III-nitrides semiconductors (compounds GaN, AlN, and InN) are in far-fromequilibrium conditions created by an electric field. We analyze the high frequency part of the spectra obtaining a generalization of the Roosbroeck-Schockley relation, δRS(ω, EF), the ratio between the frequency dependent luminescence I(ω) and the absorption coefficient α(ω), for nonequilibrium conditions which are dependent on the electric field intensity EF. We show that the carrier’s temperature within a small error is proportional to d ln[δ RS(ω, EF)]/dω.
TL;DR: The frequency and wave-vector-dependent dielectric function of a quasi-one-dimensional electron system under the action of an exciting external pumping source is derived and the optical responses of the system are obtained in terms of its nonequilibrium thermodynamic state.
Abstract: The optical properties of low-dimensional carrier systems ("quantum wire" type) driven away from equilibrium are studied. The frequency and wave-vector-dependent dielectric function of a quasi-one-dimensional electron system under the action of an exciting external pumping source is derived. The optical responses of the system are obtained in terms of its nonequilibrium thermodynamic state, the latter characterized resorting to a nonequilibrium statistical ensemble formalism.