Response of a Lorentzian gas to an a. c. pulse

The response of a “Lorentz gas” to a pulsed a.c. electric field and its relaxation after the cessation of this field has been studied by solving the Boltzmann's transfer equation. Explicit expressions for the electron distribution function and the current density are obtained under the assumption that the collision frequency is independent of the electron velocity.     

Fluctuations in a fluid under a stationary heat flux. III. Brillouin lines

We present a general theory of the Brillouin lines in a fluid subject to a strong stationary heat flux. The combined effects of sound-absorbing walls and of large spatial inhomogeneities induced by the temperature gradient are computed for the first time. Nonequilibrium sound modes, constructed by WKB techniques, are used. No restrictions have to be made in the theory concerning the scattering geometry and the thermal equations of state.     

Fluctuations in a fluid under a stationary heat flux. I. General theory

We present the basic formulas for a unified treatment of the correlation functions of the hydrodynamic variables in a fluid between two horizontal plates which is exposed to a stationary heat flux in the presence of a gravity field (Rayleigh-Bénard system). Our analysis is based on fluctuating hydrodynamics. In this paper (I) we show that in the nonequilibrium stationary state the hydrodynamic fluctuations evolve on slow and fast time scales that are widely separated. A time scale perturbation theory is used to diagonalize the hydrodynamic operator partially. This enables us to derive the eigenvalue equations for the nonequilibrium hydrodynamic modes. Therein we take into account the variation of the macroscopic quantities with position. The correlation functions are formally expressed in terms of the nonequilibrium modes. In paper II the slow hydrodynamic modes (viscous and viscoheat modes) will be determined explicitly for ideal heat-conducting plates with stick boundary conditions and used to compute the slow part of the correlation functions; in paper III the fast hydrodynamic modes (sound modes) will be explicitly determined for stick boundary conditions and used to compute the fast part of the correlation functions. In these papers we will also compute the shape and intensity of the lines measured in light scattering experiments.     

Einstein. a centenary volume

“At a meeting early in 1976, the International Commission on Physics Education took note of the fact that 14 March 1979 would be the centenary of the birth of Albert Einstein.…This book is the result. We hope that, in the spirit of our intentions, the book will appeal to a wide range of readers. In planning it, however, we had especially in mind both teachers and students of physics at secondary and undergraduate (tertiary) levels. Our main purpose has been to provide something of a picture of Einstein the man, of his scientific work and its subsequent significance, and of his role as a humanitarian and a World statesman.”     

The density of states of a single tight-binding band for a b.c.c. element

Summary An exact expression has been derived for the density of statesn(ε) of a single tight-binding band of a b.c.c. element, within the two-centred approximation with nearest-neighbour contribution. Using this expression, a simple approximate relation is suggested forn(ε), which can be useful in deriving various properties of transition metals. Supporting organization: Shahid Beheshty University.     

Constraints imposed upon a state of a system that satisfies the K.M.S. boundary condition

Using the uniqueness of the K.M.S. automorphism, we investigate the set of automorphisms that commutes with it. The results are applied to gauge invariant quasi-free states of a fermion system.Attaché de Recherche, C.N.R.S.On leave of absence from the Groningen University, the Netherlands.     

On a.c. conductivity in chalcogenide glasses

A simple model describing doubly occupied defect states in chalcogenide glasses is used to get the power frequency dependence of a.c. conductivity. The temperature dependence of the exponent is found to be linear for not too low temperatures.     

The a.c. Josephson effect in a resistive state of narrow superconducting channels

Current steps in the current-voltage characteristic of a narrow superconducting channel in the resistive state under microwave irradiation are calculated. The current steps appear when the frequency of microwave irradiation Ω satisfies the condition $\text{Ω = mω}$, where ω is the Josephson frequency of the phase-slippage and m is an integer.     

Relativistic precession of a gyroscope. I. Circular orbits

The relativistic precession of the rotation axis of a spherical gyroscope is treated in the framework of monadic specification of the frame of reference. It is found that the precession in the comoving frame compensates the rotation of the frame of reference itself. An exact expression is derived for the angular velocity of precession for motion of a gyroscope in circular epiequatorial orbits in the Kerr field. The results are compared with the approximate expression obtained by Schiff. Numerical examples are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 64–68, March, 1981.     

Reply to a note by T. G. Shepherd

Summary In a recent note by Shepherd it is claimed that the main conclusions discussed in a paper by Petroniet al. about certain instability mechanisms for steady equivalent barotropic flows are incorrect and, although no criticism is made regarding the analytical treatment, two counterexamples are presented to support this thesis. In addition to this it is asserted that the envisaged necessity for energy and enstrophy to be transferred in both spatial directions in a normal-mode instability is ?extremely well known?. Here we demonstrate that Shepherd's conclusions are without foundation and confirm the validity and originality of Petroniet al. results by showing that:a) the first counterexample describes a situation that is in fact provided for by Petroniet al.'s analysis;b) the second counterexample is not dynamically realizable and, even if it were, the related conclusions would not apply to flows defined in doubly periodic or bounded domains such as those considered by Petroniet al.; c) the mechanism cited above is not known at all in the specific context dealt with by Petroniet al. We emphasize this by pointing out that for steady equivalent barotropic flows the range of parameters for which such an instability mechanism is allowed complements exactly the range for which the steady states are stable according to Benziet al.