Dovich Theory Research Articles

Quantum Theory of Triboelectricity.

We propose a microphysical theory of the triboelectric effect by which mechanical rubbing separates charges across the interface between two materials. Surface electrons are treated as an open system coupled to two baths, corresponding to the bulks. Extending Zel'dovich's theory of bosonic superradiance, we show that motion-induced population inversion can generate an electromotive force. We argue that this is consistent with the basic phenomenology of triboelectrification and triboluminescence as irreversible processes, and we suggest how to carry out more precise experimental tests.

Numerical investigation of spontaneous flame propagation under RCCI conditions

This paper presents results from one and two-dimensional direct numerical simulations under Reactivity Controlled Compression Ignition (RCCI) conditions of a primary reference fuel (PRF) mixture consisting of n-heptane and iso-octane. RCCI uses in-cylinder blending of two fuels with different autoignition characteristics to control combustion phasing and the rate of heat release. These simulations employ an improved model of compression heating through mass source/sink terms developed in a previous work by Bhagatwala et al. (2014), which incorporates feedback from the flow to follow a predetermined experimental pressure trace. Two-dimensional simulations explored parametric variations with respect to temperature stratification, pressure profiles and n-heptane concentration. Statistics derived from analysis of diffusion/reaction balances locally normal to the flame surface were used to elucidate combustion characteristics for the different cases. Both deflagration and spontaneous ignition fronts were observed to co-exist, however it was found that higher n-heptane concentration provided a greater degree of flame propagation, whereas lower n-heptane concentration (higher fraction of iso-octane) resulted in more spontaneous ignition fronts. A significant finding was that simulations initialized with a uniform initial temperature and a stratified n-heptane concentration field, resulted in a large fraction of combustion occurring through flame propagation. It was also found that the proportion of spontaneous ignition fronts increased at higher pressures due to shorter ignition delay when other factors were held constant. For the same pressure and fuel concentration, the contribution of flame propagation to the overall combustion was found to depend on the level of thermal stratification, with higher initial temperature gradients resulting in more deflagration and lower gradients generating more ignition fronts. Statistics of ignition delay are computed to assess the Zel’dovich (1980) theory for the mode of combustion propagation based on ignition delay gradients.

Laminar, cellular, transverse, and multiheaded pulsating detonations in condensed phase energetic materials from molecular dynamics simulations.

The development of condensed-phase detonation instabilities is simulated using moving window molecular dynamics and a generic AB model of a high explosive. It is found that an initially planar detonation front with one-dimensional flow can become unstable through development of transverse perturbations resulting in highly inhomogeneous and complex two- and three-dimensional distributions of pressure and other variables within the detonation front. Chemical reactions are initiated in localized transverse shock fronts and Mach stems with a pressure and temperature higher than those predicted by classic Zel'dovich, von Neumann, and Doering detonation theory. The two-dimensional cellular and transverse and three-dimensional pulsating detonation structures are found by varying the physico-chemical properties of AB energetic material, sample geometry, and boundary conditions. The different regimes of condensed-phase detonation that can develop from instabilities within a planar detonation front exhibit structures, although at a much smaller scale, that are similar to those observed in gases and diluted liquids.

Weak detonation in mixtures of phlegmatized RDX with aluminum

The Zel’dovich theory predicts the possibility of realization of self-sustained weak detonation in systems with nonmonotonic energy release. The present paper describes experiments aimed at detecting such a regime of detonation in mixtures of phlegmatized RDX with PP-1 and PAP-2 aluminum powders. The mass fraction of aluminum was 20%. To examine the detonation regimes, 70-mm-in-diameter charges of these mixtures were initiated with powerful triangular pressure pulses, which gave rise to attenuating overdriven detonation waves. The pressure profiles were recorded at various distances from the initiation plane (from 10 to 80 mm). Specific features of the time evolution of the detonation wave profile indicative of the existence of a supersonic flow region arising not later than 0.15 μs behind the shock front were revealed. The supersonic character of the flow behind an intermediate C-J plane is an inherent characteristic of self-sustained weak detonation; i.e., direct experimental evidence for the existence of weak detonation in RDX-aluminum mixtures was obtained.

Statistical characteristics of large scale structure

We generalize and extend the statistical description of formation and evolution of Large Scale matter distribution in the Universe proposed in our previous papers. We investigate the impact of transverse motions – expansion and/or compression – on properties of the Large Scale Structure elements – walls, pancakes, filaments and clouds – and, generalizing the Press-Schechter formalism, derive their mass functions. Using the Zel'dovich theory of gravitational instability we show that these mass functions are approximately the same and the mass of each type of elements is found to be concentrated near the corresponding mean mass. At high redshifts, both the mass function and the mean mass of formed elements depend upon the small scale part of the initial power spectrum and, in particular, upon the mass of dominant fraction of dark matter (DM) particles. Using these results we obtain independent estimates of probable redshifts of the reionization and reheating periods of the Universe. We show that the transverse motions do not significantly change the redshift evolution of the observed mass function and the mean linear number density of low mass pancakes related to absorption lines in the spectra of the farthest quasars. Application of this approach to the observed Lyman–α forest allows one to directly estimate the shape of initial power spectrum on small scales.

Large scale structure in the SDSS galaxy survey

The Large Scale Structure in the galaxy distribution is investigated using Data Release 1 of the Sloan Digital Sky Survey. Using the Minimal Spanning Tree technique we have extracted sets of filaments, of wall-like structures, of galaxy groups, and of rich clusters from this unique sample. The physical properties of these structures were then measured and compared with the statistical expectations based on Zel'dovich theory. The measured characteristics of galaxy walls were found to be consistent with those for a spatially flat ΛCDM cosmological model with Ωm ≈ 0. 3a ndΩΛ ≈ 0.7, and for Gaussian initial perturbations with a Harrison - Zel'dovich power spectrum. Furthermore, we found that the mass functions of groups and of unrelaxed structure elements generally fit well with the expec- tations from Zel'dovich theory. We also note that both groups and rich clusters tend to prefer the environments of walls, which tend to be of higher density, rather than the environments of filaments, which tend to be of lower density.

Microscopic structure of travelling wave solutions in a class of stochastic interactingparticle systems

We obtain exact travelling wave solutions for three families of stochastic one-dimensionalnon-equilibrium lattice models with open boundaries. These solutions describe the diffusivemotion and microscopic structure of (i) shocks in the partially asymmetric exclusionprocess with open boundaries, (ii) a lattice Fisher wave in a reaction–diffusion system, and(iii) a domain wall in non-equilibrium Glauber–Kawasaki dynamics with magnetizationcurrent. For each of these systems we define a microscopic shock position and calculate theexact hopping rates of the travelling wave in terms of the transition rates of themicroscopic model. In the steady state a reversal of the bias of the travelling wave marks afirst-order non-equilibrium phase transition, analogous to the Zel’dovich theory of kineticsof first-order transitions. The stationary distributions of the exclusion process withn shocks can be describedin terms of n-dimensionalrepresentations of matrix product states.

Statistical characteristics of the observed Ly α forest and the shape of initial power spectrum

Properties of approximately 4500 observed Ly α absorbers are investigated using the model of formation and evolution of dark matter (DM) structure elements based on the modified Zel’dovich theory. This model is generally consistent with simulations of absorber formation, describes the large-scale structure (LSS) observed in the galaxy distribution at small redshifts reasonably well and emphasizes the generic similarity of the LSS and absorbers. The simple physical model of absorbers asserts that they are composed of DM and gaseous matter. It allows us to estimate the column density and overdensity of DM and gaseous components and the entropy of the gas trapped within the DM potential wells. The parameters of the DM component are found to be consistent with theoretical expectations for the Gaussian initial perturbations with the warm dark matter-like power spectrum. The basic physical factors responsible for the evolution of the absorbers are discussed. The analysis of redshift distribution of absorbers confirms the self-consistency of the adopted physical model, Gaussianity of the initial perturbations and allows one to estimate the shape of the initial power spectrum at small scales that, in turn, restricts the mass of the dominant fraction of DM particles to M DM 1.5‐5 keV. Our results indicate possible redshift variations of intensity of the ultraviolet background by approximately a factor of 2‐3 at redshifts z ∼ 2‐3. One of the most promising methods for studying the processes responsible for the formation and evolution of the structure of the Universe is the analysis of properties of absorbers observed in the spectra of the furthest quasars. The great potential of such investigations has been discussed by Oort (1981, 1984) just after Sargent et al. (1980) established the intergalactic nature of the Ly α forest. The available Keck and VLT high-resolution observations of the forest provide a reasonable data base and allow one to apply statistical methods for such investigations. The essential progress achieved recently through numerous highresolution simulations of absorber formation and evolution confirms that this process is closely connected with the initial power spectrum of perturbations. These results allow us to consider the properties of absorbers in the context of the non-linear theory of gravitational instability (Zel’dovich 1970; Shandarin & Zel’dovich 1989) and to apply the statistical description of structure formation and evolu

Beyond the Kuramoto-Zel’dovich theory: Steadily rotating concave spiral waves and their relation to the echo phenomenon

In numerical experiments with the Fitzhugh-Nagumo set of reaction-diffusion equations describing two-dimensional excitable media, unusual solutions are found that correspond to a concave spiral wave steadily rotating round a circular obstacle in a finite-size medium. Such a wave arises in the region of parameters corresponding to the solitonlike regime (see text); it appears due to the interaction between the peripheral areas of a “seed” spiral wave with a convex front and the echo waves incoming from the outer boundaries of a medium. The solutions obtained are in contradiction with intuition and represent a numerical counterexample to the known theories that forbid steadily moving excitation waves with concave fronts. Nevertheless, a concave spiral wave is a stable object; being transformed to the usual spiral wave with a convex front by suppressing echo at the outer boundaries of the medium, it is again recovered upon restoring the echo conditions. In addition to the single-arm spiral concave wave, solutions are obtained that describe multiarm waves of this type; for this reason, the concave fronts of these waves are a coarse property.

Statistical characteristics of the observed Ly forest and the shape of the initial power spectrum

Properties of $\sim$ 5000 observed Ly-$\alpha$ absorbers are investigated using the model of formation and evolution of DM structure elements based on the Zel'dovich theory. This model is generally consistent with simulations of absorbers formation, accurately describes the Large Scale Structure observed in the galaxy distribution at small redshifts and emphasizes the generic similarity of the LSS and absorbers. The simple physical model of absorbers asserts that they are composed of DM and gaseous matter and it allows us to estimate the column density and overdensity of DM and gaseous components and the entropy of the gas trapped within the DM potential wells. The parameters of DM component are found to be consistent with theoretical expectations for the Gaussian initial perturbations with the WDM--like power spectrum. We demonstrate the influence of the main physical factors responsible for the absorbers evolution. The analysis of redshift distribution of absorbers confirms the self consistence of the assumed physical model and allows to estimate the shape of the initial power spectrum at small scales what in turn restricts the mass of dominant fraction of DM particles to $M_{DM}\approx 0.6 - 2$ keV. Our results verify the redshift variations of intensity of the UV background by about $4 - 6$ times and indicate that, perhaps, the available observations underestimate the intensity of this background.

Relaxation spectrum of the asymmetric exclusion process with open boundaries

We calculate numerically the exact relaxation spectrum of the totally asymmetric simple exclusion process (TASEP) with open boundary conditions on lattices up to 16 sites. In the low- and high-density phases and along the nonequilibrium first-order phase transition between these phases, but sufficiently far away from the second-order phase transition into the maximal-current phase, the low-lying spectrum (corresponding to the longest relaxation times) agrees well with the spectrum of a biased random walker confined to a finite lattice of the same size. The hopping rates of this random walk are given by the hopping rates of a shock (a domain wall separating stationary low- and high-density regions), which are calculated in the framework of a recently developed non-equilibrium version of Zel'dovich's theory of the kinetics of first-order transitions. We conclude that the description of the domain wall motion in the TASEP in terms of this theory of boundary-induced phase transitions is meaningful for very small systems of the order of ten lattice sites.

Properties of the observed Ly forest

The main observed properties of Lyα absorbers are investigated on the basis of a theoretical model of formation and evolution of dark matter (DM) structure elements. This model is generally consistent with simulations of absorber formation and with the statistical description of structure evolution based on the Zel'dovich theory. The analysis of redshift variations of comoving linear number density of absorbers was performed in our previous paper. We show that the observed characteristics of the Doppler parameter can be related to the size of DM structure elements that allow us to explain the observed distribution of the Doppler parameter. This distribution is found to be consistent with the Gaussian initial perturbations. The observed characteristics of entropy and column density NH i confirm that the merging of pancakes is the main evolutionary process at redshifts z2. The observed sample of absorbers mainly characterizes the matter distribution within large low-density regions and therefore it is difficult to reconstruct the density field from the distribution of absorbers.

Statistical characteristics of simulated walls

Accepted 2000 May 1. Received 2000 March 17; in original form 1999 July 14 ABSTRA C T The large-scale matter distribution in three different simulations of CDM models is investigated and compared with corresponding results of the Zel’dovich theory of non-linear gravitational instability. We show that the basic characteristics of wall-like structure elements are well described by this theory, and that they can be expressed by the cosmological parameters and a few spectral moments of the perturbation spectrum. Therefore the characteristics of such elements provide reasonable estimates of these parameters. We show that the compressed matter is relaxed and gravitationally confined and manifests itself in the existence of walls as (quasi-)stationary structure elements with a lifetime restricted by their disruption into high-density clouds. The matter distribution is investigated in both real and redshift spaces. In both cases almost the same particles form the walls, and we estimate differences in corresponding wall characteristics. The same methods are applied to several mock catalogues of ‘galaxies’, which allows us to characterize a large-scale bias between the spatial distribution of dark matter and of simulated ‘galaxies’.

Statistical characteristics of formation and evolution of structure in the Universe

ABSTRA C T An approximate statistical description of the formation and evolution of structure of the Universe based on the Zel’dovich theory of gravitational instability is proposed. It is found that the evolution of dark matter (DM) structure shows features of self-similarity and the main structure characteristics can be expressed through the parameters of the initial power spectrum and cosmological model. For the CDM-like power spectrum and suitable parameters of the cosmological model the effective matter compression reaches the observed scales Rwall , 20‐25h 21 Mpc with the typical mean separation of wall-like elements DSLSS , 50‐70h 21 Mpc. This description can be directly applied to the deep pencil beam galactic surveys and absorption spectra of quasars. For larger 3D catalogues and simulations it can be applied to results obtained with the core-sampling analysis. It is shown that the interaction of large- and small-scale perturbations modulates the creation rate of early Zel’dovich pancakes and generates bias on the SLSS scale. For suitable parameters of the cosmological model and reheating process this bias can essentially improve the characteristics of simulated structure of the Universe. The models with 0:3 # Vm # 0:5 give the best description of the observed structure parameters. The influence of low-mass ‘warm’ dark matter particles, such as a massive neutrino, will extend the acceptable range of Vm and h.

Lyman alpha emission from thick clouds photoionized by the metagalactic radiation

We present calculations of the expected Lyα surface brightness and emergent spectral line profiles from thick (N H ≥10 20 cm −2 ), massive (≥ 10 10 M ○ .) clouds at high redshift (z ≥ 3) photoionized by the metagalactic background radiation. Our results directly apply to the damped Lyα systems and to the «pancakes» that are expected to form at large redshift in the Sunyaev-Zel'dovich theory of cluster formation. We consider both quasar-dominated and stellar-dominated metagalactic fluxes. For the quasar-dominated metagalactic flux, we use two energy distributions: a power law with index − 1, which is representative of a «raw» (unfiltered) quasar energy distribution, and a distribution from Miralda-Escude and Ostriker [ApJ, 350, 1 (1990)] in which the ionizing background arises from quasar emission filtered by dust intervening galaxies and by Lyα forest clouds

Separation kinetics of ferrocolloids in the absence of a magnetic field

Formation of drop aggregates in ferrocolloids is described by using the general concepts of phase trnasition theory. The nucleation stage is analyzed within the framework of Frenkel-Zel'dovich's theory, allowing for diffusional mass transfer. The main focus is studying the evolution of the aggregate size density distribution function when the system supersaturation is intensively removed.

Dissociative Phase Transitions, Split Shock Waves, Rarefaction Shocks, and Detonations

AbstractWe present a comparative study of two different chemically-sustained shock waves. One shows behavior expected from the Zel'dovich, von Neumann, and Doering (ZND) continuum theory of planar detonations. The other exhibits the complexity of a split shock wave resulting from the presence of a polymorphic phase transition. This comparative study demonstrates the importance of carefully considering the high-pressure characteristics of the model in developing potentials for simulating detonations. This comparative study also raises the fascinating possibility of a first-order phase transition accompanying a condensed-phase detonation.

Homogeneous nucleation of supersaturated vapors

A theory of homogeneous nucleation from the vapor phase is presented. The classical Becker-Döring-Zel'dovich theory is contained as a limiting case. The theory is based on a semiphenomenological droplet model for the Gibbs free energy of formation of the cluster. Since this droplet model also allows the construction of a thermal equation of state for real gases below the critical point, all free parameters of the model can be determined from well-known macroscopic quantities. A new formulation of the surface free energy for small droplets is crucial. The theory gives a much better prediction of observed nucleation rates than the classical theory.

Effect of dissociation on the limting dimensions of the combustion of blended gaseous mixtures

Because of the fact that dissociation is significant for oxygen and oxygen-enriched mixtures, in this work the theory of limits is developed taking into account dissociation, and a constant critical Peclet number becomes a function of the energy and degree of dissociation. The authors found it useful to study simplified models which describe the limits of propagation of the flame in the presence of dissociation. The model developed in this work is based on Ya. B. Zel 'dovich's theory of combustion limits. It has been established that for the limiting dimensions of the combustion of air mixtures, the critical Peclet number is conserved. The authors maintain that the results obtained are inadequate for answering unequivocally the question of the effect of dissociation on the limits of combustion of mixed gaseous mixtures.

Solid propellant combustion in the presence of photoirradiation

Previous studies of the nonsteady processes associated with the irradiation of propellants with light have chiefly been devoted to the question of ignition [1–3]. It is also important to consider the effect of such an easily controlled influence as light on the propellant combustion process. We have attempted to estimate the dependence of the propellant burning rate on the intensity of the luminous radiation. Cases of steady-state combustion and combustion in the presence of a light flux varying harmonically with time are considered. It is assumed that the incident light flux is absorbed in the solid phase in accordance with the Bouguer-Lambert exponential law with constant transparency index. Steady-state combustion is considered within the framework of the Zel'dovich theory [4]. It is shown that in the steady state irradiation is equivalent to a certain increase in the initial temperature of the propellant. In the case of combustion with irradiation this makes it possible to use the data on steady-state combustion without irradiation. Nonsteady combustion in the presence of a periodically varying light flux is described with the aid of the Novozhilov model [5]. A correction to the mean burning rate (Δu °), proportional to the square of the light flux amplitude, is obtained. In the case of an exponential dependence of the burning rate on initial temperature the correction Δu ° is negative. The effect of irradiation on the stability of the steady-state propellant combustion mode is discussed.