278 research outputs found
Contribution of One-Time Pair Correlation Function to Kinetic Phenomena in Nonequilibrium Gas
It has been established in nineteen seventies that in nonequilibrium case the
pair collisions generate non-zero two-particle correlations which are
non-diagonal in momentum space and give the essential contribution to the
current fluctuations of hot electrons. It is shown here that this correlations
give also a contribution to the collision integral, i.e., to kinetic properties
of nonequilibrium gas. The expression for electron energy loss rate P via
phonons is re-derived in detail from this point of view. The contribution of
the non-diagonal part of the nonequilibrium pair correlator to phonon-electron
collision integral and to P is obtained and explicitly calculated in the
electron temperature approximation. It is shown that these results can be
obtained from stochastic non-linear kinetic equation with Langevin fluctuation
force. Such an approach allows to formulate the simple general conditions under
that a contribution of two-particle correlations might be essential in
kinetics. The contribution obtained does not contain the extra powers of small
gas parameter unlike the equilibrium virial decompositions.Comment: 6 pages, based on the report presented at the conference ``Progress
in Nonequilibrium Green's Functions'', Dresden, Germany, 19.-22. August 200
Genuine converging solution of self-consistent field equations for extended many-electron systems
Calculations of the ground state of inhomogeneous many-electron systems
involve a solving of the Poisson equation for Coulomb potential and the
Schroedinger equation for single-particle orbitals. Due to nonlinearity and
complexity this set of equations, one believes in the iterative method for the
solution that should consist in consecutive improvement of the potential and
the electron density until the self-consistency is attained. Though this
approach exists for a long time there are two grave problems accompanying its
implementation to infinitely extended systems. The first of them is related
with the Poisson equation and lies in possible incompatibility of the boundary
conditions for the potential with the electron density distribution. The
analysis of this difficulty and suggested resolution are presented for both
infinite conducting systems in jellium approximation and periodic solids. It
provides the existence of self-consistent solution for the potential at every
iteration step due to realization of a screening effect. The second problem
results from the existence of continuous spectrum of Hamiltonian eigenvalues
for unbounded systems. It needs to have a definition of Hilbert space basis
with eigenfunctions of continuous spectrum as elements, which would be
convenient in numerical applications. The definition of scalar product
specifying the Hilbert space is proposed that incorporates a limiting
transition. It provides self-adjointness of Hamiltonian and, respectively, the
orthogonality of eigenfunctions corresponding to the different eigenvalues. In
addition, it allows to normalize them effectively to delta-function and to
prove in the general case the orthogonality of the 'right' and 'left'
eigenfunctions belonging to twofold degenerate eigenvalues.Comment: 12 pages. Reported on Interdisciplinary Workshop "Nonequilibrium
Green's Functions III", August 22 - 26, 2005, University Kiel, Germany. To be
published in Journal of Physics: Conference Series, 2006; Typos in Eqs. (37),
(53) and (54) are corrected. The content of the footnote is changed.
Published version available free online at
http://www.iop.org/EJ/abstract/1742-6596/35/1/01
Observation of anomalously strong penetration of terahertz electric field through terahertz-opaque gold films into a GaAs/AlGaAs quantum well
We observe an anomalously high electric field of terahertz (THz) radiation
acting on a two-dimensional electron gas (2DEG) placed beneath a thin gold
film, which, however, is supposed to be opaque at THz frequencies. We show that
the anomalously strong penetration of the THz electric field through a very
high conductive gold film emerges if two conditions are fulfilled
simultaneously: (i) the film's thickness is less than the skin depth and (ii)
the THz electric field is measured beneath the film at distances substantially
smaller than the radiation wavelength. We demonstrate that under these
conditions the strength of the field acting on a 2DEG is almost the same as it
would be in the absence of the gold film. The effect is detected for
macroscopically homogeneous perforation-free gold films illuminated by
THz-laser radiation with a spot smaller than the film area. This eliminates the
near-field of the edge diffraction as a possible cause of the anomalous
penetration. The microscopic origin of the effect remains unexplained in its
details, yet. The observed effect can be used for the development of THz
devices based on two-dimensional materials requiring robust highly conducting
top gates placed at less than nanometer distance from the electron gas
location
Laplace transformations of hydrodynamic type systems in Riemann invariants: periodic sequences
The conserved densities of hydrodynamic type system in Riemann invariants
satisfy a system of linear second order partial differential equations. For
linear systems of this type Darboux introduced Laplace transformations,
generalising the classical transformations in the scalar case. It is
demonstrated that Laplace transformations can be pulled back to the
transformations of the corresponding hydrodynamic type systems. We discuss
periodic Laplace sequences of with the emphasize on the simplest nontrivial
case of period 2. For 3-component systems in Riemann invariants a complete
discription of closed quadruples is proposed. They turn to be related to a
special quadratic reduction of the (2+1)-dimensional 3-wave system which can be
reduced to a triple of pairwize commuting Monge-Ampere equations. In terms of
the Lame and rotation coefficients Laplace transformations have a natural
interpretation as the symmetries of the Dirac operator, associated with the
(2+1)-dimensional n-wave system. The 2-component Laplace transformations can be
interpreted also as the symmetries of the (2+1)-dimensional integrable
equations of Davey-Stewartson type. Laplace transformations of hydrodynamic
type systems originate from a canonical geometric correspondence between
systems of conservation laws and line congruences in projective space.Comment: 22 pages, Late
Development of low-temperature thermochemical conversion reactors for coal power engineering
The main principles applied in developing a technology for low-temperature thermochemical conversion of brown coals to obtain fuel gas and semicoke intended for being fired in two-fuel power installations are considered on the basis of a set of experimental and calculated investigations. The obtained results are compared with the experimental data obtained using other methods and with the results of previous industrial tests. © 2013 Pleiades Publishing, Inc
Evaluation of myocardial damage in different types of rheumatoid arthritisduring disease-modifying antirheumatic drug or biological therapy (with infliximab)
Objective. To estimate the extent and pattern of myocardial damage in different types of rheumatoid arthritis (RA) during disease-modifying antirheumatic drug (DMARD) or biological therapy. Subjects and methods. Seventy-one patients with RA were examined; some of them received biological therapy with infliximab, while the others took DMARDs. A group of patients with incipient RA was also identified. B-type brain natriuretic peptide levels were estimated and electrocardiography, echocardiography (EchoCG), and cardiac magnetic resonance imaging (MRT) using the contrast medium Dotarem were conducted in all the patients. The follow-up totaled 6 months. A control examination was made at the moment of randomization and 6 months posttreatment. Results. Tn the bulk of patients, the level of B-type brain natriuretic peptide did not differ from the reference values, however, its lower level was observed in the incipient RA group, which was associated with the absence of cardiovascular diseases and with a younger age group. There were no negative EchoCG changes in myocardial viability values. Cardiac MRT demonstrated that the majority of patients had the similar changes that failed to affect myocardial kinetics and ejection fraction. These changes were not found in incipient RA patients without cardiovascular diseases. No improvement in myocardial viability was recorded in the patients receiving the biological therapy. Conclusion. Thus, cardiac MRT showed the similar changes that failed to affect myocardial kinetics and ejection fraction in patients with RA during both methotrexate and infliximab therapy
Effects of digestible protein to energy ratios on growth and carcass chemical composition of siamese fighting fish (Betta splendens)
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