Showing papers by "Áurea R. Vasconcellos published in 2002"

Predictive Statistical Mechanics: A Nonequilibrium Ensemble Formalism

Abstract: List of Figures. List of Tables. Preface. Acknowledgments. Prolegomena. Introduction. 1. Maxent-Nesom in Equilibrium Conditions. 2. Maxent-Nesom for Dissipative Processes in Open Systems. 3. Nonequilibrium Generalized Grand-Canonical Ensemble. 4. Maxent-Nesom-Based Kinetic Theory. 5. Response Function Theory. 6. Theory and Experiment. 7. Informational Statistical Thermodynamics. 8. Final Remarks. Appendices. Bibliography. Index. Name Index.

Higher-order hydrodynamics: Extended Fick’s Law, evolution equation, and Bobylev’s instability

Abstract: A higher-order hydrodynamics for material motion in fluids, under arbitrary nonequilibrium conditions, is constructed. We obtain what is a generalized—to that conditions—Fick-type Law. It includes a representation of Burnett-type contributions of all order, in the form of a continuous-fraction expansion. Also, the equation includes generalized thermodynamic forces, which are characterized and discussed. All kinetic coefficients are given as correlations of microscopic mechanical quantities averaged over the nonequilibrium ensemble, and then are time- and space-dependent as a consequence of accounting for the dissipative processes that are unfolding in the medium. An extended evolution equation for the density of particles is derived, and the conditions when it goes over restricted forms of the type of the telegraphist equation and Fick’s diffusion equation are presented.

Electron mobility in nitride materials

Abstract: We contribute here a theoretical study of the electron mobility in n-doped GaN, InN, and AlN at moderate to high electric fields. We solve the set of coupled nonlinear integro-differential equations of evolution to obtain the steady-state values of the basic intensive nonequilibrium thermodynamic variables for the three materials. The regions with ohmic and non-ohmic behavior in the electron drift velocity dependence on the electric field strength are characterized in the three nitrides. The electron mobility is calculated, and it is shown that the larger corresponds to InN, and the smaller to AlN.

Trying to Make Sense of Disorder

Abstract: In his article “a fresh take on disorder, or disorderly science?” (News Focus, 23 Aug, p 1268), Adrian Cho reports on a lively controversy presently raging over what is called “Tsallis entropy,” which has been wrongly suposed to be the physical entropy of the natural world, superseding the

Morphological ordering in biopolymers: informational statistical thermodynamic approach.

Abstract: We consider the question of the emergence of morphological ordering in an open far-from-equilibrium model of a biopolymer. We apply informational statistical thermodynamics, which was shown to be appropriate to deal with dissipative systems displaying complex behavior. The formation of nonlinear spatial ordering consisting in the emergence of static charge-density waves, producing a bioelectret-type state, is evidenced. This kind of behavior may arise in biopolymers under the influence of biochemical processes.

Carrier Dynamics Investigated by Time-Resolved Optical Spectroscopy

Abstract: An optical investigation of the transport properties of carriers in a thick GaAs layer is presented. The electron transport is monitored by time-resolved luminescence from the GaAs layer and an InGaAs quantum well beneath. The transients are mostly insensitive to the presence of external electric fields of both polarities, which indicates a carrier transport dominated by ambipolar diffusion. Spin measurements under a continuous-wave low-density regime show a strong conservation of the electron spin during the diffusion of electrons through the thick GaAs layer and their capture by the InGaAs well, but only for an applied field polarity that accelerates the electrons towards the well.

Response Function Theory

Abstract: We deal in this chapter with the question of a response function theory, which is fundamental for providing a way to relate theory and experiment. This introduces correlation functions over the given nonequilibrium ensemble, which are inevitable for the description of physical experiments [240]. Comparison with experiments provides the only way to validate a theory, with the connection of the two — theory and experiment — being indissoluble and the basis of the scientific method as it developed since the seventeenth century. As expressed by W. T. Grandy [119], in constructing a theory a first and fundamental step “consists of some kind of observation or experiment defining both the system and the problem. This is an essential procedure preceding any calculations, without which any real problem remains ill-defined. Though perhaps obvious, the point tends to be ignored in many theoretical discussions”. This point is the most pungent when dealing with not satisfactorily settled questions, as it is the thermodynamics of irreversible systems. In particular it is worth noticing the call of Ryogo Kubo [193], who stated that “statistical mechanics has been considered a theoretical endeavor. However, statistical mechanics exists for the sake of the real world, not for fictions. Further progress can only be hoped by close cooperation with experiment”. As noticed, the bridge between theory and measurement is provided by response function theory.