619 research outputs found
Normal and Anomalous Averages for Systems with Bose-Einstein Condensate
The comparative behaviour of normal and anomalous averages as functions of
momentum or energy, at different temperatures, is analysed for systems with
Bose-Einstein condensate. Three qualitatively distinct temperature regions are
revealed: The critical region, where the absolute value of the anomalous
average, for the main energy range, is much smaller than the normal average.
The region of intermediate temperatures, where the absolute values of the
anomalous and normal averages are of the same order. And the region of low
temperatures, where the absolute value of the anomalous average, for
practically all energies, becomes much larger than the normal average. This
shows the importance of the anomalous averages for the intermediate and,
especially, for low temperatures, where these anomalous averages cannot be
neglected.Comment: Latex file, 17 pages, 6 figure
Temperature-Dependent Polarized Raman Spectra of CaFe2O4
The Raman spectra of CaFe2O4 were measured with several exact scattering
configurations between 20 and 520K and the symmetry of all observed Raman lines
was determined. The Ag and B2g lines were assigned to definite phonon modes by
comparison to the results of lattice dynamical calculations. No anomaly of
phonon parameters was observed near the magnetic ordering temperature TN =
160K.Comment: 4 pages, 1 table, 4 figure
Limits and Possible Consequences of the Development of Agricultural Production: Modeling Agricultural Situations in the Stavropol Territory, USSR
The Food and Agriculture Program at IIASA focuses its research activities on understanding the nature and dimension of the world's food situation and problems, on exploring possible alternative policies which could improve the present situation in the short and long term, and on investigating the consequences of such policies at various levels - global, national and regional -- and in various time horizons.
One part of the research activities focussed on investigations of alternative paths of technology transformation in agriculture with respect to resource limitations and environmental consequences in the long term. The general approach and methodology developed for this investigation is being applied in several case studies on the regional level. The reason for the studies is not only to validate the general methodology but also to develop an applicable tool for detailed investigations for a particular region which could then be applied on a number of similar regions.
Furthermore, some specific aspects are being addressed in all these case studies which has been initiated within the IIASA's Food and Agriculture Program. This will allow the behavior of various systems to be compared, according to the selected aspects, and analyzed (in different social, economic and natural resource conditions) according to the selected aspects. One of these case studies is of Stavropol, USSR, and covers the whole of this region.
This paper describes the first phase of the study, the problems in this region, the aims for solving them, and the first draft of the methodology which is based on the general framework developed at IIASA
Nonequilibrium Bose systems and nonground-state Bose-Einstein condensates
The theory of resonant generation of nonground-state Bose-Einstein
condensates is extended to Bose-condensed systems at finite temperature. The
generalization is based on the notion of representative statistical ensembles
for Bose systems with broken global gauge symmetry. Self-consistent equations
are derived describing an arbitrary nonequilibrium nonuniform Bose system. The
notion of finite-temperature topological coherent modes, coexisting with a
cloud of noncondensed atoms, is introduced. It is shown that resonant
generation of these modes is feasible for a gas of trapped Bose atoms at finite
temperature.Comment: Latex file, 16 pages, no figure
Self-consistent calculation of the coupling constant in the Gross-Pitaevskii equation
A method is proposed for a self-consistent evaluation of the coupling
constant in the Gross-Pitaevskii equation without involving a pseudopotential
replacement. A renormalization of the coupling constant occurs due to medium
effects and the trapping potential, e.g. in quasi-1D or quasi-2D systems. It is
shown that a simplified version of the Hartree-Fock-Bogoliubov approximation
leads to a variational problem for both the condensate and a two-body wave
function describing the behaviour of a pair of bosons in the Bose-Einstein
condensate. The resulting coupled equations are free of unphysical divergences.
Particular cases of this scheme that admit analytical estimations are
considered and compared to the literature. In addition to the well-known cases
of low-dimensional trapping, cross-over regimes can be studied. The values of
the kinetic, interaction, external, and release energies in low dimensions are
also evaluated and contributions due to short-range correlations are found to
be substantial.Comment: 15 pages, ReVTEX, no figure
The Measurement of the Asymmetry of Tensor-Polarized Deuteron Electrodisintegration at 180 MeV Electron Energy
The nucleon emission asymmetry in d(e, pn)e' reaction was measured using the tensor-polarized deuterium jet target in the VEPP-2 electron storage ring. At the present experimental accuracy, the results for the proton energy interval Ep= 12-100 MeV do not contradict the nonrelativistic calculations.
Carrier dynamics and infrared-active phonons in c-axis oriented RuSrGdCuO film
The conductivity spectra of c-axis oriented thin RuSrGdCuO film
on SrTiO substrate, prepared by pulsed-laser deposition, are obtained from
the analysis of the reflectivity spectra over broad frequency range and
temperatures between 10 and 300 K. The free charge carriers are found to be
strongly overdamped with their scattering rate (1.0 eV at room temperature)
exceeding the plasma frequency (0.55 eV). Four phonon lines are identified in
the experimental spectra and assigned to the specific oxygen related in-plane
polarized vibrations based on the comparison with the results of a lattice
dynamics shell model calculations.Comment: 3 pages, 4 figure
Singular potentials and annihilation
We discuss the regularization of attractive singular potentials , by infinitesimal imaginary addition to interaction
constant . Such a procedure enables unique
definition of scattering observables and is equal to an absorption (creation)
of particles in the origin. It is shown, that suggested regularization is an
analytical continuation of the scattering amplitudes of repulsive singular
potential in interaction constant . The nearthreshold properties of
regularized in a mentioned way singular potential are examined. We obtain
expressions for the scattering lengths, which turn to be complex even for
infinitesimal imaginary part of interaction constant. The problem of
perturbation of nearthreshold states of regular potential by a singular one is
treated, the expressions for level shifts and widths are obtained. We show,
that the physical sense of suggested regularization is that the scattering
observables are insensitive to any details of the short range modification of
singular potential, if there exists sufficiently strong inelastic short range
interaction. In this case the scattering observables are determined by
solutions of Schrodinger equation with regularized potential . We point out that the developed formalism can be applied for the
description of systems with short range annihilation, in particular low energy
nucleon-antinucleon scattering.Comment: 10 page
Dilute Bose gas in two dimensions: Density expansions and the Gross-Pitaevskii equation
A dilute two-dimensional (2D) Bose gas at zero temperature is studied by the
method developed earlier by the authors. Low density expansions are derived for
the chemical potential, ground state energy, kinetic and interaction energies.
The expansion parameter is found to be a dimensionless in-medium scattering
amplitude u obeying the equation 1/u+\ln u=-\ln(na^2\pi)-2\gamma, where na^2
and \gamma are the gas parameter and the Euler constant, respectively. It is
shown that the ground state energy is mostly kinetic in the low density limit;
this result does not depend on a specific form of the pairwise interaction
potential, contrary to 3D case. A new form of 2D Gross-Pitaevskii equation is
proposed within our scheme.Comment: 4 pages, REVTeX, no figure
Design of Drum Type Apparatus for Processing of Bulk Materials
The article presents the development and research of drum continuous mixers, most attention is paid to the results of theoretical (using of cybernetic approach) and experimental studies of longitudinal mixing particulate material in rotating drums of continuous action, the influence of internal recycles of material flows, intensifying the process of smoothing the input fluctuations. The authors analyzed the influence of internal recycles material flows, intensifying the process of smoothing the input fluctuations. The results presented in this paper were obtained by the experiments on the smoothing ability determination during which they change the frequency of the drum rotation, the location of the Г-shaped mixer blades on the drum mixer. The article reported that the studies were conducted on three mixtures which components have different physical and mechanical systems with various dispersed liquid additives and without it
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