Non-steady Mode Research Articles

Spontaneous symmetry breaking in nonsteady modes of open quantum many-body systems

In a quantum many-body system coupled to the environment, its steady state can exhibit spontaneous symmetry breaking when a control parameter exceeds a critical value. In this study, we consider spontaneous symmetry breaking in non-steady modes of an open quantum many-body system. Assuming that the time evolution of the density matrix of the system is described by a Markovian master equation, the dynamics of the system is fully characterized by the eigenmodes and spectrum of the corresponding time evolution superoperator. Among the non-steady eigenmodes with finite lifetimes, we focus on the eigenmodes with the highest frequency, which we call the most coherent mode. For a dissipative spin model, it is shown that the most coherent mode exhibits a transition from a disordered phase to a symmetry-broken ordered phase, even if the steady state does not show singular behavior. We further argue that the phase transition of the most coherent mode induces a qualitative change in the decoherence dynamics of highly entangled states, i.e., the Schr\"odinger's cat states.

Two-body model for the spatial distribution of dust ejected from an atmosphereless body

Aims. We present a model for the configuration of noninteracting material that is ejected in a continuous manner from an atmosphereless gravitating body for a given distribution of sources. The model is applicable to material on bound or unbound trajectories and to steady and nonsteady modes of ejection. Methods. For a jet that is inclined to the surface normal, we related the distributions of ejection direction, velocity, and size to the phase-space number density at the distance from the source body. Integrating over velocity space, we obtained an expression from which we inferred the density, flux, or optical depth of the ejected material. Results. As examples for the application of the code, we calculate profiles of the dust density in the Enceladus plume, the pattern of mass deposition rates around a plume on Europa, and images of optical depth following the nonstationary emission of material from a volcano on Io. We make the source code of a Fortran-95 implementation of the model freely available.

Research of the modern absorbing apparatus power characteristics influence on the freight train inter-car forces

A mathematical model of the inter-car connections used in the long and heavy train is presented. It takes into account the elastic-frictional properties of absorbing devices and gaps in automatic coupler devices connecting the train cars. There are demonstrated the calculation results of a homogeneous train motion along a straight horizontal track section at such non-steady modes as at starting, braking by the locomotive electrodynamic brakes and passing along a track profile section of a complex shape. A comparative assessment of the influence of the kind of the absorbing devices power characteristic on the maximal longitudinal forces arising in the train inter-car connections is carried out using the MSC ADAMS engineering software package. Transients with a smooth and sharp change in traction and braking forces are considered. Based on the obtained results, the main positive and negative properties of rigid, linear and soft power characteristics of the automatic couplers’ absorbing devices used on the railway rolling stock are determined. The results of performed computer simulation can be applied to the sphere of design and modernization of absorbing devices of automatic couplers and to the process of composition of various types of cars in trains of any length and weight.

The asymptotic theory of gasless combustion synthesis

The gasless, self-propagating, high-temperature synthesis of refractory materials is generally associated with a thin reaction zone that propagates through the material, converting the unburned reactant powders into a product alloy. The reactions themselves are characterized by large overall activation energies, a fact that can be exploited to derive asymptotic models in which the reaction zone becomes an infinitesimally thin sheet. Such models have been derived for both kinetically and diffusion-limited reactions, as well as for the intermediate case in which both chemical reaction and mass diffusion occur on comparable time scales. These models are amenable to analytical analysis, yielding formulas for the propagation speed of a steady, planar combustion wave and, in agreement with experiments, predicting critical parameter values above which stability is lost to one or more nonsteady modes of burning. In particular, nonlinear stability analyses have demonstrated the transition from steady to various periodic, quasi-periodic, and even chaotic combustion modes as a parameter related to the activation energy increases beyond the neutral stability threshold.

New Routes to Quasi-Periodic Combustion of Solids and High-Density Fluids Near Resonant Hopf Bifurcation Points

Steady, planar combustion waves propagating through solids and high-density fluids can lose stability to a time-periodic mode of burning via Hopf bifurcation as an activation-energy parameter increases past a critical value. However, if the combustion wave is confined in a long channel, there exist critical values of the transverse channel dimensions such that stability is simultaneously lost to two (or more) nonsteady modes of burning at a multiple eigenvalue of this parameter. In the present work, the case of bifurcation near a point of strong resonance from which multiple primary branches corresponding to a single pulsation frequency (but different spatial structures) emanate from the basic solution is considered. In contrast to the multiple-frequency case, the resulting amplitude equations contain transcendental terms which can lead to both secondary and isolated branches of multimodal time-periodic motions. In addition, the higher-order bifurcation of quasi-periodic waves can arise either through a classical Hopf bifurcation from a multimodal branch, or through a new type of nonlinear mechanism from a single-mode primary branch.

Flame propagation in solids and high-density fluids with Arrhenius reactant diffusion

The combustion of solids and high-density fluids, such as the combustion synthesis of refractory materials or the high-pressure oxidation of organic compounds in supercritical water, is often characterized by a highly temperature-dependent mass diffusivity. In particular, the case of an Arrhenius dependence of this quantity on temperature is considered, where the activation energy of reactant diffusion is of the same order as that of the overall chemical reaction. Exploiting the asymptotic limit of large activation energies, it is shown that reactant diffusion becomes significant in the thin reaction zone, where a balance among convection, reaction, and diffusion is maintained. Relative to the case of either a zero or constant mass diffusion coefficient, this leads to modifications in the steady, planar flame-speed eigenvalue. A new asymptotic model is then derived that predicts corresponding shifts in the neutral stability boundary that marks the transition from steady to nonsteady modes of flame propagation.

Stability Boundaries of Periodic Models of Propagation in Burner-Stabilized Methane-Air Flames

Abstract Our previous experiments on burner-stabilized laminar premixed flames have identified four nonsteady modes of propagation:axial,radial,spiral and nonplanar.In this paper we present stability boundaries for the occurrence of these modes,at a fixed pressure,as a function of total flow rate and equivalence ratio.We also specify the character of one of the four modes,the nonplanar mode,in which the flame front vibrates like a circular drumhead.

Trapping, emission and generation in MNOS memory devices

This study is concerned with trapping phenomena occuring at the semiconductor-oxide interface and in the nitride layer of variable-threshold metal-nitride-oxide-semiconductor (MNOS) memory devices. The technique consits of biasing the device in such a manner as to charge or discharge either the interface traps or the nitride traps, or both sets of traps simultaneously. The device is then cooled to low temperature with the bias still applied, and at the low temperature the biasing condition is changed, in order to induce the device into a non-steady mode that is quasi-stable at the low temperature. The temperature of the device is then raised at a constant rate, and the resulting current vs temperature ( I- T) characteristics is found to be rich in structure. By means of a series of systematic experiments the various portions of the I- T characteristic are identified with emission of electrons from interface states and the nitride traps, and surface generation. From this data the energy distribution of interface states is determied. It is shown that the memory charge in the nitride is distributed throughout the nitride, and temporary memory charge and semi-permanent memory charge are distinguished.