10,011 research outputs found
Linking of the BENSON graph-plotter with the Elektronika-1001 computer
A device, developed by the Institute of Space Research of the Academy of Sciences of the USSR, for linking the Elektronika-100I computer with the BENSON graph-plotter is described. Programs are compiled which provide display of graphic and alphanumeric information. Instructions for their utilization are given
Schwinger Pair Production in dS_2 and AdS_2
We study Schwinger pair production in scalar QED from a uniform electric
field in dS_2 with scalar curvature R_{dS} = 2 H^2 and in AdS_2 with R_{AdS} =
- 2 K^2. With suitable boundary conditions, we find that the pair-production
rate is the same analytic function of the scalar curvature in both cases.Comment: RevTex 6 pages, no figure; replaced by the version published in PR
Comparative Raman Studies of Sr2RuO4, Sr3Ru2O7 and Sr4Ru3O10
The polarized Raman spectra of layered ruthenates of the Srn+1RunO3n+1
(n=1,2,3) Ruddlesden-Popper series were measured between 10 and 300 K. The
phonon spectra of Sr3Ru2O7 and Sr4Ru3O10 confirmed earlier reports for
correlated rotations of neighboring RuO6 octahedra within double or triple
perovskite blocks. The observed Raman lines of Ag or B1g symmetry were assigned
to particular atomic vibrations by considering the Raman modes in simplified
structures with only one double or triple RuO6 layer per unit cell and by
comparison to the predictions of lattice dynamical calculations for the real
Pban and Pbam structures. Along with discrete phonon lines, a continuum
scattering, presumably of electronic origin, is present in the zz, xx and xy,
but not in the x'y' and zx spectra. Its interference with phonons results in
Fano shape for some of the lines in the xx and xy spectra. The temperature
dependencies of phonon parameters of Sr3Ru2O7 exhibit no anomaly between 10 and
300 K where no magnetic transition occurs. In contrast, two B1g lines in the
spectra of Sr4Ru3O10, corresponding to oxygen vibrations modulating the Ru-O-Ru
bond angle, show noticeable hardening with ferromagnetic ordering at 105 K,
thus indicating strong spin-phonon interaction.Comment: 9 pages, 12 figure
Infrared behavior and spectral function of a Bose superfluid at zero temperature
In a Bose superfluid, the coupling between transverse (phase) and
longitudinal fluctuations leads to a divergence of the longitudinal correlation
function, which is responsible for the occurrence of infrared divergences in
the perturbation theory and the breakdown of the Bogoliubov approximation. We
report a non-perturbative renormalization-group (NPRG) calculation of the
one-particle Green function of an interacting boson system at zero temperature.
We find two regimes separated by a characteristic momentum scale
("Ginzburg" scale). While the Bogoliubov approximation is valid at large
momenta and energies, |\p|,|\w|/c\gg k_G (with the velocity of the
Bogoliubov sound mode), in the infrared (hydrodynamic) regime |\p|,|\w|/c\ll
k_G the normal and anomalous self-energies exhibit singularities reflecting
the divergence of the longitudinal correlation function. In particular, we find
that the anomalous self-energy agrees with the Bogoliubov result
\Sigan(\p,\w)\simeq\const at high-energies and behaves as \Sigan(\p,\w)\sim
(c^2\p^2-\w^2)^{(d-3)/2} in the infrared regime (with the space
dimension), in agreement with the Nepomnyashchii identity \Sigan(0,0)=0 and
the predictions of Popov's hydrodynamic theory. We argue that the hydrodynamic
limit of the one-particle Green function is fully determined by the knowledge
of the exponent characterizing the divergence of the longitudinal
susceptibility and the Ward identities associated to gauge and Galilean
invariances. The infrared singularity of \Sigan(\p,\w) leads to a continuum
of excitations (coexisting with the sound mode) which shows up in the
one-particle spectral function.Comment: v1) 23 pages, 11 figures. v2) Changes following referee's comments.
To appear in Phys. Rev.A. v3) Typos correcte
Parameter selection for the supply system in a Pilger mill
The braking chamber in the supply system of a Pilger pipe mill is modernized. The influence of constant and variable parameters of the supply system on braking is studied. © 2013 Allerton Press, Inc
A nontrivial bosonic representation of large spin systems at high temperatures
We report on a nontrivial bosonization scheme for spin operators. It is shown
that in the large limit, at infinite temperature, the operators
behave like the creation and annihilation
operators, and , corresponding to a harmonic oscillator in thermal
equilibrium, whose temperature and frequency are related by . The component is found to be equivalent to the position variable
of another harmonic oscillator occupying its ground Gaussian state at zero
temperature. The obtained results are applied to the Heisenberg XY Hamiltonian
at finite temperature.Comment: 12 pages, preprint, we have included a brief discussion of the
antiferromagnetic cas
Types of corrosion damage of tubing in the oilfield
The accumulated research data of tubing fragments after operation made it possible to generalize and systematize information on the prevailing type of corrosion damage and operating conditions that determine the mechanism of their development. Understanding basic laws of the development of corrosion processes in specific operating conditions, allows to select the optimal type of tubing for these conditions more accurately. © The Authors, published by EDP Sciences, 2019
Properties of the strongly paired fermionic condensates
We study a gas of fermions undergoing a wide resonance s-wave BCS-BEC
crossover, in the BEC regime at zero temperature. We calculate the chemical
potential and the speed of sound of this Bose-condensed gas, as well as the
condensate depletion, in the low density approximation. We discuss how higher
order terms in the low density expansion can be constructed. We demonstrate
that the standard BCS-BEC gap equation is invalid in the BEC regime and is
inconsistent with the results obtained here. We indicate how our theory can in
principle be extended to nonzero temperature. The low density approximation we
employ breaks down in the intermediate BCS-BEC crossover region. Hence our
theory is unable to predict how the chemical potential and the speed of sound
evolve once the interactions are tuned towards the BCS regime. As a part of our
theory, we derive the well known result for the bosonic scattering length
diagrammatically and check that there are no bound states of two bosons.Comment: 16 pages, 15 figures. References added and typos correcte
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