Nonequilibrium Features Research Articles

An Interface-Sensitive Conversion Electron Mössbauer Spectroscopic Study of the Ion Beam Induced Reactions at Fe-Si Interface.

ABSTRACTThe ion beam induced reactions at Fe-Si interface are studied for the first time using a novel interface-sensitive Mössbauer probe.The samples used in these studies are prepared by depositing a thin layer (<450A°) of enriched Fe57 isotope (95.45% by composition) on a freshly cleaned silicon (111) substrate followed by a deposition of a 150Ao film of natural iron (Fe 57 only 2.2%).These samples are subjected to Xetion bombardment at an incident ion energy of 100 keV and a dose of 6 × 1015 ions/cm2 The technique of Conversion Electron Mössbauer Spectroscopy (CEMS) is used to characterize the formation and growth of different phases as a function of annealing treatment. The spectra are leastsquare fitted using the MOSFIT programme.The MHssbauer lines for as-deposited and ion bombarded samples show a considerable broadening, which is a clear signature of a large concentration of defects formed at the interface due to ion beam induced collision cascades. As the samples are annealed the resonance lines are sharpened indicating recovery of stoichiometrically well-defined phases from an initial defective state. The present study indicates formation of FeSi and Fe3 Si phases after the annealing treatment-RBS measurements are used to confirm the mixing.These results are analyzed in terms of the non-equilibrium features of the directed energy processing of interface.

Phase Transformation Under Intense Shock Pressure Loading

ABSTRACTSolids subjected to high velocity impact or explosive loading may undergo polymorphic phase transformation or melting within time periods appreciably less than 10-8s due to the intense shock-pressure environment. Although criteria for equilibrium phase transformation on the Hugoniot are satisfied, other nonequilibrium features unique to the shock-wave environment have been identified in the shock transformation process. These features include shear and heterogeneous deformation effects which control the transformation kinetics and microstructure of the transformed material. Transformation under shock loading leads to unusual microstructure in the recovered materials and can result in interesting and useful changes in physical and mechanical properties.

On the use of statistical concepts in grand unified theories

The study raises the question - whether the use of traditional statistical mechanical concepts is legitimate in the early epochs of the development of the universe (from ≈10 -40s after the big bang, until about 10 -30s). Several current procedures are examined in detail; the use of the equilibrium notion, the use of Boltzmann-like rate equations, the use of ideas from the theory of phase transitions. It is stressed that from the general viewpoint of statistical mechanics there is no convincing evidence that dynamical systems described by spontaneously broken gauge theories necessarily approach equilibrium. Techniques are suggested whereby this question might be approached. It is noted that the usual treatment by starting from the assumption of a homogeneous, isotropic universe is in principle incapable of discussing local non-equilibrium features. It is very questionable whether this assumption is valid for the epochs considered. Attention is called to the circumstance that if the phase transition picture is taken literally, the presence of both fermions and bosons indicates that a consistent treatment requires the existence of a critical line T c(ξ), rather than a critical temperature. ξ is the ratio of the Fermi to Bose concentrations. This might well alter the qualitative picture of successive stages in the development of the universe.

Dielectric tensor of a weakly relativistic, nonequilibrium, and magnetized plasma

The dielectric tensor of a weakly relativistic magnetized plasma is discussed for wave frequencies very close to the fundamental or higher harmonics of the electron or ion cyclotron frequency. Since in real situations the plasmas of interest are often in nonequilibrium states, the present paper generalizes Shkarofsky’s result to include three nonequilibrium features; namely, a loss-cone distribution, anisotropic temperatures, and a field-aligned drift. The discussion is motivated by current interest in the study of absorption and emission of radiation near the electron cyclotron harmonics.

Classical-equations-of-motion calculations of high-energy heavy-ion collisions

Results are obtained with the classical-equations-of-motion approach which provides a complete microscopic, classical, description including finite-range interaction effects. Nonrelativistic classical-equations-of-motion calculations are made for equal mass projectile and target nuclei with ${A}_{P}={A}_{T}=20$ (Ne + Ne) at laboratory energies per projectile nucleon of ${E}_{L}=117, 400, \mathrm{and} 800$ MeV and at 400 MeV for ${A}_{P}={A}_{T}=40$ (Ca + Ca). A static two-body potential ${V}_{\mathrm{st}}$ is used which is fitted to ${\ensuremath{\sigma}}^{(2)}$, the ${sin}^{2}\ensuremath{\theta}$ weighted differential cross section. For ${A}_{P}={A}_{T}=20$ we also use a scattering equivalent momentum dependent potential ${V}_{\mathrm{tr}}$. ${V}_{\mathrm{st}}$ and ${V}_{\mathrm{tr}}$ give identical two-body scattering but are not equivalent for many-body scattering and are used to test for finite-range interaction effects in heavy-ion collisions. The evolution of central collisions is discussed. For these multiple scattering is large leading to high momentum components. Dissipation quite generally is larger at lower energies and is appreciable during the expansion phase of central collisions giving approximately thermalized distributions at the lower ${E}_{L}$. A peak at approximately the same momentum at all angles develops in the momentum distribution near the beginning of the expansion and changes roughly in step with the potential energy; for ${A}_{P}={A}_{T}=20$ at 800 MeV the peak persists to the final distributions. There are very appreciable differences in the densities, potential energies, and distributions between ${V}_{\mathrm{st}}$ and ${V}_{\mathrm{tr}}$ during the strong interaction stage. However, the final distributions are not significantly different even for ${A}_{P}={A}_{T}=20$ at 800 MeV. For ${A}_{P}={A}_{T}=40$ at 400 MeV a transverse peaking develops in the momentum distribution suggestive of collective effects. Noncentral collisions show typical nonequilibrium features and for larger impact parameters the final distributions show a strong single scattering component. This is true also of the impact parameter averaged distributions which are in fair agreement with experiment. A partial test of thermal models is made. Limitations and extensions of the classical-equations-of-motion approach are discussed. In particular we propose a new kinetic equation which includes finite-range interaction effects. Relativistic classical-equations-of-motion calculations to $O(\frac{{v}^{2}}{{c}^{2}})$ are briefly discussed.NUCLEAR REACTIONS Heavy ion (Ne + Ne, Ca + Ca); $\mathrm{laboratory}\mathrm{energy}/n=117, 400, 800$ MeV; classical microscopic many-body calculations.

Physico-chemical limitations in experimental investigations.

An element or compound in a natural water system is usually distributed between a variety of physico-chemical forms, both dissolved and particulate. The distribution is determined by the properties of the ion or molecule in question and by a number of major variables, including ionic strength, the nature and concentrations of major dissolved elements, particulate matter and organic complexing material, pH and the electron activity (pE); it may thus vary widely between different environments. The design of experiments to study sublethal effects of pollutants in sea water ideally requires that the test medium is closely matched to the environment for which information is needed, with respect to the ranges of concentration and activity, and the chemical speciation, of the pollutant and of any other constituents which may influence its effects. This in turn requires either that the pollutant can be added in the appropriate forms, implying a knowledge of the existing speciation, or that the added material rapidly exchanges with the forms already present. The implications of these requirements are most apparent for those pollutants that show complex chemical behaviour in sea water. This account concentrates on metals of toxicological significance. Consideration of particulate associations, redox speciation, and complex formation in the dissolved state with inorganic and organic ligands, suggests that physicochemical factors limit the usefulness, in terms of environmental predictions, of experimental studies of biological effects of metals, both inherently and through inadequate knowledge of environmental speciation and the mechanisms and rates of interconversion between species. Of particular importance are non-equilibrium features in speciation, such as the presence of thermodynamically unstable oxidation states and of kinetically non-labile associations. Interpretation of the nature of these associations is complicated by the presence of colloidal and organic macromolecular material in dissolved fractions as conventionally defined. While the chemical behaviour of some substances in sea water is considerably less complicated than that of the trace metals, there is a need with all types of pollutants for greater attention to physico-chemical factors in both the design and interpretation of experiments to investigate biological effects.

A hydrodynamic theory for homogeneous vapor nucleation in a carrier gas

A dynamical theory is constructed for the spontaneous development of a liquid drop out of an homogenous supersaturated vapor in a dense carrier gas. The work required to create intermediate state is estimated macroscopically, as in the classical theory of nucleation, but the dynamical equations are based upon hydrodynamic fluctuation theory. For the classical drop growth model the resulting nucleation rate is very similar to that traditionally assigned. The characterization of the mechanism is a little different from the traditional one, however, and nonequilibrium features of the process are described in greater detail. The vapor condensation process is also contrasted with the liquid– liquid separation process which occurs in binary mixtures.

Nonequilibrium reaction between N2O and CO in shock waves

The nonequilibrium features of decomposition reactions have been studied in detail by the example of HNs, NO, and other molecules [1-3]. The processes which take place in twocomponent systems differ considerably in their great complexity. The study of nonequillbrium energy distributions in these reactions is a complicated problem, The most suitable reaction for this investigation is the reaction between NzO and CO. Its kinetics in equilibrium conditions over the range T = 1400-2000~ are relatively slmpleand can be described by the following elementary stages [4, 5]:

Thermodynamics, the structure of integral membrane proteins, and transport.

Membranes are structures whose lipid and protein components are at, or close to, equilibrium in the plane of the membrane, but are not at equilibrium across the membrane. The thermodynamic tendency of ionic and highly polar molecules to be in contact with water rather than with nonpolar media (hydrophilic interactions) is important in determining these equilibrium and nonequilibrium states. In this paper, we speculate about the structures and orientations of integral proteins in a membrane, and about how the equilibrium and nonequilibrium features of such structures and orientations might be influenced by the special mechanisms of biosynthesis, processing, and membrane insertion of these proteins. The relevance of these speculations to the mechanisms of the translocation event in membrane transport is discussed, and specific protein models of transport that have been proposed are analyzed.