Nonequilibrium Media Research Articles

On the formation of structures in nonequilibrium media in the resonant three-wave interaction

A mechanism of formation of flat and spiral solitary structures in nonequilibrium media allowing the resonant three-wave interaction of eigenmodes is proposed. A bifurcations diagram on the 'pump wave amplitude - initial profile width' plane is plotted

Climate changing and non-equilibrium atmosphere

This work is a first step to solve the problem on creation of the theory of evolution of non-equilibrium open systems. The mean factors forming atmospheric structures are radiation fluxes. So in order to understand atmospheric evolutional processes it is a necessary to consider atmospheric gas in continuity with radiation. This problem couldn’t be solved in the frames of traditional gas dynamics equations because of dissipative structures in any systems including atmosphere and radiation causes by entropy production and interchange and this don’t describing in the frames of traditional gas dynamics. But for this aim we could use more complex non-equilibrium thermodynamics equations which taking into account exchange processes in such systems. The behavior of wave disturbances in non-equilibrium medium: atmospheric gas – solar radiation taking into account atmospheric structures and radiation flux interrelations was investigated in this work. The dispersion relation of acoustic-gravity waves was found from reductive atmospheric gas – solar radiation system dynamic equations set in the frames of non-equilibrium thermodynamics. Calculations show that the taking into account of solar radiation leads to slowly decreasing of pressure with height than without taking it into account. The maximum deviation of pressure comes to heights of 10-15 km and amounts about 3 percents. The dependence of AGW spectra deviation in non-equilibrium atmosphere from the spectra in equilibrium atmosphere from the height was estimated. It was found that in the frames of non-equilibrium spectra shifts into high-frequency region. Numerical calculations also shows that in the heights of ionosphere these effects shown up sharply at transitionally times at abrupt change of solar energy influx into atmosphere. Analysis of pressure variations shows the experimental prove of existing of obvious trend of spectra shift into high-frequency region of daytime spectra relatively to nighttime spectra and the difference made 10 percents and proves the correctness of theoretical calculations.

Self-refraction of acoustic pulses with shock fronts in some nonequilibrium media

The nonlinear self-refraction of acoustic pulsed beams, which include shock fronts, is studied. The medium of sound propagation is a gas where thermodynamically nonequilibrium processes take place, such as exothermic chemical reaction or excitation of vibrational degrees of a molecule’s freedom. Comparative analysis of the features of sound propagation over gases where pure nonlinear attenuation of the shock wave occurs, and gases with nonequilibrium and equilibrium processes, is performed.

Blast wave mitigation by dry aqueous foams

This paper presents results of experiments and numerical modeling on the mitigation of blast waves using dry aqueous foams. The multiphase formalism is used to model the dry aqueous foam as a dense non-equilibrium two-phase medium as well as its interaction with the high explosion detonation products. New experiments have been performed to study the mass scaling effects. The experimental as well as the numerical results, which are in good agreement, show that more than an order of magnitude reduction in the peak overpressure ratio can be achieved. The positive impulse reduction is less marked than the overpressures. The Hopkinson scaling is also found to hold particularly at larger scales for these two blast parameters. Furthermore, momentum and heat transfers, which have the main dominant role in the mitigation process, are shown to modify significantly the classical blast wave profile and thereafter to disperse the energy from the peak overpressure due to the induced relaxation zone. In addition, the velocity of the fireball, which acts as a piston on its environment, is smaller than in air. Moreover, the greater inertia of the liquid phase tends to project the aqueous foam far from the fireball. The created gap tempers the amplitude of the transmitted shock wave to the aqueous foam. As a consequence, this results in a lowering of blast wave parameters of the two-phase spherical decaying shock wave.

On the significance of developing boundary layers in integrated water cooled 3D chip stacks

We present in this paper a fundamental hydrothermal investigation of the next generation interlayer integrated water cooled three-dimensional (3D) chip stacks, with high volumetric heat generation. Such investigation of flow through microcavities with embedded heat transfer structures such as micro pin-fin arrays and microchannels is crucial for the successful realization of 3D chip stacks. We focus mainly on the complex physics of the entrance region of the cooling microcavities in order to assess its importance. The flow and heat transfer in the entrance region is strongly influenced by developing boundary layers and, as we show herein, the development lengths can occupy a significant portion of the microcavity due to the size restrictions of the 3D chip stack. These effects make a fundamental understanding of conjugate heat transfer in microcavities with heat transfer structures a necessity. The flow field and heat transfer in the entrance region are characterized by means of correlations determining the effective coolant permeability as well as the heat transfer coefficient as a function of the streamwise coordinate x, the flow Reynolds number (Re) and the Prandtl number. Based on a thermal non-equilibrium porous medium model relying on these results, a substantially improved estimation of pressure drop and temperature distribution inside the chip stack is realized. The modeling results are validated against measurements on a 3D chip stack simulator. The range of flow rates and thermal loads in the hot spots of the chip stack, over which it is crucial to consider the developing hydrothermal effects, are analyzed and discussed in detail. Moreover, microchannel and micro pin-fin structures are compared, showing more than 20% increased performance of the latter for all operating conditions investigated.

Magnetic Excitations in Locally Non-Equilibrium Media

The motion equation for magnetization in locally non-equilibrium media is derived. It is shown that in non-ordered media locally non-equilibrium excitations have peculiarities. There exist coupled waves of the magnetization and magnetic vector potential. Dispersion relation of the waves have frequencies corresponding to undamped waves or constant-phase damped waves and frequencies corresponding to change of real and imaginary parts of the wave number relation. Spectrum of the non-equilibrium fluctuations exhibits some pair of spin-electromagnetic modes without energy gap and electromagnetic-spin modes with energy gap branches.

GENERALIZED VAN HOVE FORMULA FOR SCATTERING OF NEUTRONS BY THE NONEQUILIBRIUM STATISTICAL MEDIUM

The theory of scattering of particles (e.g., neutrons) by statistical medium was recast for the nonequilibrium statistical medium. The correlation scattering function of the relevant variables give rise to a very compact and entirely general expression for the scattering cross-section of interest. The formula obtained by Van Hove provides a convenient method of analyzing the properties of slow neutron and light scattering by systems of particles such as gas, liquid or solid in the equilibrium state. In this paper the theory of scattering of particles by many-body system was reformulated and generalized for the case of nonequilibrium statistical medium. A new method of quantum-statistical derivation for the space and time Fourier transforms of the Van Hove correlation function was formulated. Thus in place of the usual Van Hove scattering function, a generalized one was deduced and the result was shown to be of greater potential utility than those previously given in the literature. This expression gives a natural extension of the familiar Van Hove formula for scattering of slow neutrons for the case in which the system under consideration is in a nonequilibrium state. The feasibility of light- and neutron-scattering experiments to investigate the appropriate problems in real physical systems was discussed briefly.

Localized Wave Structures in Nonequilibrium Media

Localized Wave Structures in Nonequilibrium Media

Conservation laws for a vortex in a compressible nonequilibrium medium

The problem of conservation of magnitudes is considered for a vortex in a relaxing compressible medium. Heat release due to the relaxation of a nonequilibrium medium leads to the propagation of compression waves, which remove material. Traditional integrals of motion are inapplicable in this case. We pro-pose the concept of integral quantity, which is conserved with an arbitrary degree of accuracy despite the fact that waves cross the boundary of the integration domain. Based on this concept, a broad class of conservation laws is derived for axisymmetric disturbances of columnar vortices, including conservation of the circulation and total angular momentum of the vortex. For nonaxisymmetric disturbances, it is shown that the total angular momentum and properly defined energy integral are conserved. Numerical verification of the derived conservation laws is performed and the perspectives for using these conservation laws in numerical simulations are discussed.

Locally nonequilibrium magnetic excitations in insulators

The equation of motion for the magnetic moment vector M in a locally nonequilibrium medium is derived. The dispersion and attenuation of the coupled modes of the magnetic vector potential and magnetization are determined. It is shown that the continuous spectrum contains frequencies corresponding to undamped waves or constant-phase damped waves.

Different approaches to fluid simulation of the longitudinal structure of the atmospheric-pressure microdischarge in helium

Numerical results for different versions of the fluid model of an atmospheric-pressure glow discharge in helium are compared. It is shown that efforts to improve the fluid model are to a large extent prospectless and often even impair previous results. This is because the fluid model has fundamental limitations when describing heavily nonequilibrium media, such as the gas discharge. In such systems, the properties of an ensemble of electrons cannot be reduced to the behavior of an “averaged particle,” which is characterized by the averaged concentration, averaged directional velocity, and averaged energy (temperature). In particular, the values of the electron temperature in the near-cathode plasma obtained by fluid simulation far exceed both the available experimental data and physical estimates. It is therefore necessary to develop consistent kinetic techniques to correctly describe the behavior of electrons in the near-cathode plasma.

Subterahertz self-oscillations of depletion of electron populations in the conduction band of GaAs in the presence of pumping and intrinsic stimulated radiation

It was previously found that, during picosecond optical pumping, ultrafast interrelated self-modulations of fundamental absorption of light and intrinsic stimulated picosecond radiation emerge in GaAs. In this study, quantitative evaluations confirming the assumption that the mentioned self-modulations are caused by self-oscillations of depletion of electron populations in the conduction band are made. The relation for the frequency of self-oscillations of depletion of populations is obtained. The presence of conditions for self-organization leading to the emergence of periodic nonlinear waves in nonequilibrium media, which is photogenerated electron-hole plasma with depletions of populations, is shown. As a result, in a series of studies, including this one, it is found that the collective excitation of charge carriers—self-oscillations of depletion of populations of the conduction band—emerges during pumping in GaAs under the effect of intrinsic stimulated radiation.

Information and knowledge: Nature and the conceptual model

Information is defined through the introduced concepts of an information object and an information interaction, in which the change in the state of objects-originals involves a change in their images. Information is a macro form that emerges in a nonequilibrium medium and has a dual nature as an object and as a reality. Knowledge is defined as information that is reduced to the superposition of possible states of the information object in different individual domains. Information fulfills communication functions, interactions in an individual domain, and its own functions that actualize its own validity. In terms of the mechanism of interaction, information, being a structured and not atomic object, should have "interface" elements that join it with communication objects.

Realization of a Brownian engine to study transport phenomena: A semiclassical approach

Brownian particles moving in a periodic potential with or without external load are often used as good theoretical models for the phenomenological studies of microscopic heat engines. The model that we propose here, assumes the particle to be moving in a nonequilibrium medium and we have obtained the exact expression for the stationary current density. We have restricted our consideration to the overdamped motion of the Brownian particle. We present here a self-consistent theory based on the system-reservoir coupling model, within a microscopic approach, of fluctuation induced transport in the semiclassical limit for a general system coupled with two heat baths kept at different temperatures. This essentially puts forth an approach to semiclassical state-dependent diffusion. We also explore the possibility of observing a current when the temperature of the two baths are different, and also envisage that our system may act as a Carnot engine even when the bath temperatures are the same. The condition for such a construction has been elucidated.

Evolution of a single vortex in a uniform nonequilibrium medium

The problem of the evolution of a single vortex in a nonequilibrium medium with a temperature-or density-dependent energy release was solved. In a medium that is stable against small perturbations, the vortex passes to a new stationary state, and no vortex breakdown occurs. For a temperature-dependent energy release, analytical solutions that define changes in the characteristics of the vortex were obtained for high and low relaxation times. The solutions were compared with the results of numerical simulation by the Godunov method.

On superluminal pulses in nonequilibrium media

The propagation and transverse dynamics of extremely short pulses in a nonequilibrium medium consisting of two-level atoms has been investigated. It is shown that, if the spectrum of such pulses does not overlap the characteristic frequency of quantum transitions, non-1D superluminal pulses with retained shape may exist.

Dynamic capillary pressure, hysteresis and gravity-driven fingering in porous media

Experimental data collected from the unstable, or fingered, flow of water through soils have shown that the traditional porous media equation is unable to explain the characteristic structure of the moisture distribution within these fingers. One and two-dimensional numerical solutions are presented for an alternative non-equilibrium porous medium equation as proposed by [1] which incorporates a dynamic hysteretic capillary pressure model. Computed profiles capture both the non-monotonic property of finger evolution as well as the limited lateral growth of the instabilities.

Explosive dynamics and localization of wave triads in a coupled magnetoelastic system

The dynamics of three-wave parametric coupling is considered on an example of nonequilibrium magnetostrictive medium under electromagnetic pumping. Subthreshold and supercritical mode of three-wave excitation are described analytically and simulated numerically for a triad of magnetoelastic waves. Theoretical analysis of the supercritical mode shows that space-time development of three-wave excitation in such a nonequilibrium system has the character of explosive instability and localization of "positive energy" waves.

SELF-ORGANIZATION AND NONEQUILIBRIUM STRUCTURES IN THE PHASE SPACE

We consider the possibilities of the formation of quasistationary distributions of particles over energy with power asymptotics in nonequilibrium systems and dynamical systems with couplings. It is shown that the Tsallis distribution is related to the exact solutions of a kinetic equation of the Boltzmann type and those of covariant kinetic equations of the Vlasov nonlocal statistical mechanics. We have studied the connection of the power-like solutions of kinetic equations with the eigenfunctions of fractional integro-differential operators and Jackson operators within quantum analysis, and that of nonextensiveness parameters in the framework of the Tsallis thermostatics, with flows in the phase space. It is shown that the processes running in a nonequilibrium nonconservative medium can be described by the solutions of the equation with fractional derivatives or Jackson derivatives for oscillations.

Two-particle Green’s functions in the diffusive approximation

The set of equations for the two-particle Green's functions in a nonequilibrium medium is derived in the diffusive approximation. Both the two- and single-particle Green's functions are calculated when matter is in the ground state. It is shown that the Landau Fermi-liquid consideration is correct when the interaction between particles in matter is rather weak or when matter is not too dense. In the opposite cases the energy spectrum of the particles is rearranged so that the step in the momentum distribution of the particles disappears. The applicability of the Landau Fermi-liquid theory is established in the general case.