Relativistic two-stream instability

We study the (local) propagation of plane waves in a relativistic, non- dissipative, two-fluid system, allowing for a relative velocity in the “background” configuration. The main aim is to analyze relativistic two-stream instability. This instability requires a relative flow—either across an interface or when two or more fluids interpenetrate—and can be triggered, for example, when one-dimensional plane-waves appear to be left-moving with respect to one fluid, but right-moving with respect to another. The dispersion relation of the two-fluid system is studied for different two-fluid equations of state: (i) the “free” (where there is no direct coupling between the fluid densities), (ii) coupled, and (iii) entrained (where the fluid momenta are linear combinations of the velocities) cases are considered in a frame-independent fashion (e.g.no restriction to the rest-frame of either fluid). As a by-product of our analysis we determine the necessary conditions for a two-fluid system to be causal and absolutely stable and establish a new constraint on the entrainment.     

Theory of Brownian motion in a Jeffreys fluid

We have constructed a kinetic theory of Brownian motion in a rheologically complex medium—a Jeffreys fluid that is characterized by a combination of two viscosity mechanisms: ordinary and delayed. This model is shown to be much better suited for the interpretation of experiments on the microrheology of viscoelastic media than the standard Maxwell model. In particular, no oscillations of the mean-square particle displacement arise in a Jeffreys fluid, which is a nonremovable artifact of the theory of Brownian motion in a Maxwell fluid. The developed approach can to be used also consider the diffusion of particles in other complex fluids whose rheology is described by phenomenological schemes.     

Extremes of nuclear structure

With the advent of medium and large gamma detector arrays, it is now possible to look at nuclear structure at high rotational forces. The role of pairing correlations and their eventual breakdown, along with the shell effects have showed us the interesting physics for nuclei at high spins — superdeformation, shape co-existence, yrast traps, alignments and their dramatic effects on nuclear structure and so on. Nuclear structure studies have recently become even more exciting, due to efforts and possibilities to reach nuclei far off from the stability valley. Coupling of gamma ray arrays with ‘filters’, like neutron wall, charged particle detector array, gamma ray total energy and multiplicity castles, conversion electron spectrometers etc gives a great handle to study nuclei produced online with ‘low’ cross-sections. Recently we studied, nuclei in mass region 80 using an array of 8 germanium detectors in conjunction with the recoil mass analyser, HIRA at the Nuclear Science Centre and, most unexpectedly came across the phenomenon of identical bands, with two quasi-particle difference. The discovery of magnetic rotation is another highlight. Our study of light In nucleus, 107In brought us face to face with the ‘dipole’ bands. I plan to discuss some of these aspects. There is also an immensely important development — that of the ‘radioactive ion beams’. The availability of RIB, will probably very dramatically influence our ‘conventional’ concept of nuclear structure. The exotic shapes of these exotic nuclei and some of their expected properties will also be touched upon.     

Equilibrium distribution of an ideal fluid in space-times permitting groups of concircular motions

A space — time with an ideal fluid as a source that permits groups of concircular motions is investigated. It is assumed that the velocity vector of the fluid is directed along a time-like group vector. A theorem on the properties of such a fluid and its relation with symmetries of the space — time is proven. Kazan’ State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 7–13, June, 1997.     

A Rayleigh-type wave at the plane interface of two homogeneous fluid half-spaces

It is shown that at the plane interface of two homogeneous fluid semi-infinite media, of which one is an ordinary fluid and the other a double negative—i.e., a fluid with negative density and negative compressibility—there can exist a Rayleigh-type wave propagating without attenuation, whose amplitude exponentially decreases with distance on both sides of the interface. In the parameter space of the media, the range of its existence is determined and the main properties are studied. A unique feature of this wave is the arbitrarily small propagation velocity, which does not depend on frequency, and the energy concentration in an arbitrarily thin layer close to the interface.     

Poly-Essential and General Hyperelastic World (Brane) Models

This article provides a unified treatment of an extensive category of non-linear classical field models whereby the universe is represented (perhaps as a brane in a higher dimensional background) in terms of a structure of a mathematically convenient type describable as hyperelastic, for which a complete set of equations of motion is provided just by the energy-momentum conservation law. Particular cases include those of a perfect fluid in quintessential backgrounds of various kinds, as well as models of the elastic solid kind that has been proposed to account for cosmic acceleration. It is shown how an appropriately generalised Hadamard operator can be used to construct a symplectic structure that controles the evolution of small perturbations, and that provides a characteristic equation governing the propagation of weak discontinuities of diverse (extrinsic and extrinsic) kinds. The special case of a poly-essential model—the k-essential analogue of an ordinary polytropic fluid—is examined and shown to be well behaved (like the fluid) only if the pressure to density ratio w is positive.     

Analogue model for an expanding universe

Over the last few years numerous papers concerning analogue models of (and for) gravity have been published. It has been shown that the dynamical equations for several condensed matter systems, (e.g., simple fluids, superfluids, Bose–Einstein condensates with a sink or a vortex) permit perturbations that are governed by the same type of wave equation as light in a curved spacetime—the curved-space d'Alembertian equation. More recently, several papers have been released which use analogue models to simulate the expanding universe. In this article the de Sitter universe will be simulated using a freely expanding three-dimensional Bose–Einstein condensate with spherical symmetry. Initially the condensate is in a harmonic trap, which is then suddenly switched off. At the same time a small perturbation is injected in the center of the condensate cloud. The motion of this perturbation in the expanding condensate will be discussed, and (after some transformations) the similarity of this system to an expanding universe will be exhibited. Finally, we briefly discuss questions of experimental observability of these effects. Presented at the 4th Australasian conference on General Relativity and Cosmology, Monash University, Melbourne, 7–9 January 2004     

Extreme Covariant Observables for Type I Symmetry Groups

The structure of covariant observables—normalized positive operator measures (POMs)—is studied in the case of a type I symmetry group. Such measures are completely determined by kernels which are measurable fields of positive semidefinite sesquilinear forms. We produce the minimal Kolmogorov decompositions for the kernels and determine those which correspond to the extreme covariant observables. Illustrative examples of the extremals in the case of the Abelian symmetry group are given. Dedicated to Pekka J. Lahti in honor of his sixtieth birthday     

Heat transfer and fluid flow of benard-cell convection in rectangular container with free surface sensed by infrared thermography

The natural convection flow phenomena that occur inside an enclosed space are very interesting examples of complex fluid systems that may yield to analytical, empirical and numerical solutions, and many reports have looked into this basic problem. In the present study, heat transfer and fluid flow for natural convection in a horizontal rectangular container with a free surface are investigated using infrared thermography. The temperature field was measured and visualized at a gas-liquid (air — silicon oil) interface using infrared thermography. The heat transfer phenomena were also investigated by statistically analyzing the temperature data. The applicability of the infrared thermography to quantitative heat transfer measurement at the gas-liquid interface was evaluated. It is revealed that infrared thermography is effective not only in visualization of a gas-liquid interface but also in heat transfer measurement. A new heat transfer correlation is proposed for the gas-liquid interface of this flow system. The coefficient of heat transfer can be summarized by a specific heat transfer correlation formula regardless of several conditions, including container aspect ratio, fluid viscosity and fluid layer depth.     

Horses for courses: risk information and decision making in the regulation of nanomaterials

Despite the widespread commercial use of nanomaterials, regulators currently have a limited ability to characterize and manage risks. There is a paucity of data available on the current production and use of nanomaterials and extreme scientific uncertainty on most aspects of the risk assessment “causal chain.” Regulatory decisions will need to be made in the near-term in the absence formal quantitative risk assessments. The article draws on examples from three different regulatory contexts—baseline data monitoring efforts of the U.S. Environmental Protection Agency and California Department of Toxic Substances Control, prioritization of risk information in the context of environmental releases, and mitigation of occupational risks—to argue for the use of decision-analytic tools in lieu of formal risk assessment to help regulatory bodies. We advocate a “horses for courses” approach whereby existing analytical tools (such as risk ranking, multi-criteria decision analysis, and “control banding” approaches) might be adapted to regulators’ goals in particular decision contexts. While efforts to build new and modify existing tools are underway, they need greater support from funding and regulatory agencies because innovative approaches are needed for the “extreme” uncertainty problems that nanomaterials pose.     

Are Biological Systems Poised at Criticality?

Many of life’s most fascinating phenomena emerge from interactions among many elements—many amino acids determine the structure of a single protein, many genes determine the fate of a cell, many neurons are involved in shaping our thoughts and memories. Physicists have long hoped that these collective behaviors could be described using the ideas and methods of statistical mechanics. In the past few years, new, larger scale experiments have made it possible to construct statistical mechanics models of biological systems directly from real data. We review the surprising successes of this “inverse” approach, using examples from families of proteins, networks of neurons, and flocks of birds. Remarkably, in all these cases the models that emerge from the data are poised near a very special point in their parameter space—a critical point. This suggests there may be some deeper theoretical principle behind the behavior of these diverse systems.     

Vortex stretching and reconnection in a compressible fluid

Vortex stretching in a compressible fluid is considered. Two-dimensional (2D) and axisymmetric cases are considered separately. The flows associated with the vortices are perpendicular to the plane of the uniform straining flows. Externally-imposed density build-up near the axis leads to enhanced compactness of the vortices — “dressed" vortices (in analogy to “dressed" charged particles in a dielectric system). The compressible vortex flow solutions in the 2D as well as axisymmetric cases identify a length scale relevant for the compressible case which leads to the Kadomtsev-Petviashvili spectrum for compressible turbulence. Vortex reconnection process in a compressible fluid is shown to be possible even in the inviscid case — compressibility leads to defreezing of vortex lines in the fluid.     

A complete data base of kinematical data for early-type galaxies

Summary As a result of an exhaustive bibliographical search covering the period 1975–1988, a complete catalogue of kinematical data for early-type galaxies (ellipticals and lenticulars) has been compiled. The catalogue contains all data—both in tabular and in plotted form—appeared in specialized literature before December 1988 and includes central velocity dispersions, rotation curves, and velocity dispersion profiles for 846, 174 and 108 objects, respectively. The catalogue is also available on magnetic tape—made available to the astronomical community through the Strasbourg Data Center—and will be updated yearly. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Coherence vs. decoherence in (some) problems of condensed matter physics

We present an ‘overview’ of coherence-to-decoherence transition in certain selected problems of condensed matter physics. Our treatment is based on a subsystem-plus-environment approach. All the examples chosen in this paper have one thing in common — the environmental degrees of freedom are taken to be bosonic and their spectral density of excitations is assumed to be ‘ohmic’. The examples are drawn from a variety of phenomena in condensed matter physics involving, for instance, quantum diffusion of hydrogen in metals, Landau diamagnetism and c-axis transport in high T _c superconductors.     

Anyonic lie algebras

We introduce anyonic Lie algebras in terms of structure constants. We provide the simplest examples and formulate some open problems. Presented at the 6th International Colloquium on Quantum Groups: “Quantum Groups and Integrable Systems”, Prague, 19–21 June 1997. This paper is in final form and no version of it will be published elsewhere.     

Structural transformations of the cumulene form of amorphous carbyne at high pressure

Structural transformations of the cumulene form of amorphous carbyne which are induced by heating at high pressure (7.7 GPa) are investigated. These can be described by the sequence amorphous phase — crystal — amorphous phase — disordered graphite. Raman scattering shows that predominately the chain structure of carbyne remains at the first three stages. It was found that the intermediate crystalline phase is an unknown modification of carbon whose structure is identified as cubic (a=3.145 Å). A mechanism of structural transformations in carbyne that involves the formation of new covalent bonds between chains is discussed. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 237–242 (25 August 1997)     

Order—disorder phase transitions in domain structures of ferrite—garnet films

Order—order and order—disorder phase transitions in the domain structure of ferrite—garnet films upon a change in temperature or magnetic field were studied. It was shown that the structure of the domain boundaries affects the type of the phase transitions.     

Kerr-Newman metric in deSitter background

In addition to the Kerr-Newman metric with cosmological constant several other metrics are presented giving Kerr-Newman type solutions of Einstein-Maxwell field equations in the background of deSitter universe. The electromagnetic field in all the solutions is assumed to be source-free. A new metric of what may be termed as an electrovac rotating de-Sitter space-time—a space-time devoid of matter but containing source-free electromagnetic field and a null fluid with twisting rays—has been presented. In the absence of the electromagnetic field, our solutions reduce to those discussed by Vaidya.