47 research outputs found
INVERSE SCATTERING TRANSFORM ANALYSIS OF STOKES-ANTI-STOKES STIMULATED RAMAN SCATTERING
Zakharov-Shabat--Ablowitz-Kaup-Newel-Segur representation for
Stokes-anti-Stokes stimulated Raman scattering is proposed. Periodical waves,
solitons and self-similarity solutions are derived. Transient and bright
threshold solitons are discussed.Comment: 16 pages, LaTeX, no figure
МОДЕЛИРОВАНИЕ ВЛИЯНИЯ ВНУТРЕННИХ МЕХАНИЧЕСКИХ НАПРЯЖЕНИЙ НА СКОРОСТЬ РОСТА КИСЛОРОДНЫХ ПРЕЦИПИТАТОВ В КРЕМНИИ
In the work an approach to modeling the influence of mechanical stresses generated in a silicon matrix by an oxygen precipitate (SiO2) on the rates of the main processes determining the precipitation kinetics. The time dependences of the sizes of a spherical precipitate and the number of oxygen atoms inside it has been obtained and analyzed with the stress factor taken into account. Предложен подход для моделирования влияния механических напряжений, возникающих в системе «кремниевая матрица — кислородный преципитат (SiO2)», на скорость основных процессов,определяющих кинетику преципитации. Найдены и проанализированы полученные с учетом этого фактора зависимости от времени размеров сферическогопреципитата и количества атомов кислорода в нем.
Relativistic outflow from two thermonuclear shell flashes on neutron stars
We study the exceptionally short (32-41 ms) precursors of two
intermediate-duration thermonuclear X-ray bursts observed with RXTE from the
neutron stars in 4U 0614+09 and 2S 0918-549. They exhibit photon fluxes that
surpass those at the Eddington limit later in the burst by factors of 2.6 to
3.1. We are able to explain both the short duration and the super-Eddington
flux by mildly relativistic outflow velocities of 0.1 to 0.3 subsequent
to the thermonuclear shell flashes on the neutron stars. These are the highest
velocities ever measured from any thermonuclear flash. The precursor rise times
are also exceptionally short: about 1 ms. This is inconsistent with predictions
for nuclear flames spreading laterally as deflagrations and suggests
detonations instead. This is the first time that a detonation is suggested for
such a shallow ignition column depth ( = 10 g cm).
The detonation would possibly require a faster nuclear reaction chain, such as
bypassing the alpha-capture on C with the much faster
C(p,)N(,p)O process previously proposed.
We confirm the possibility of a detonation, albeit only in the radial
direction, through the simulation of the nuclear burning with a large nuclear
network and at the appropriate ignition depth, although it remains to be seen
whether the Zel'dovich criterion is met. A detonation would also provide the
fast flame spreading over the surface of the neutron star to allow for the
short rise times. (...) As an alternative to the detonation scenario, we
speculate on the possibility that the whole neutron star surface burns almost
instantly in the auto-ignition regime. This is motivated by the presence of 150
ms precursors with 30 ms rise times in some superexpansion bursts from 4U
1820-30 at low ignition column depths of ~10 g cm.Comment: 11 pages, 6 figures, accepted by Astronomy and Astrophysic
Comparing two approaches to Hawking radiation of Schwarzschild-de Sitter black holes
We study two different ways to analyze the Hawking evaporation of a
Schwarzschild-de Sitter black hole. The first one uses the standard approach of
surface gravity evaluated at the possible horizons. The second method derives
its results via the Generalized Uncertainty Principle (GUP) which offers a yet
different method to look at the problem. In the case of a Schwarzschild black
hole it is known that this methods affirms the existence of a black hole
remnant (minimal mass ) of the order of Planck mass
and a corresponding maximal temperature also of the order of
. The standard dispersion relation is, in the GUP
formulation, deformed in the vicinity of Planck length which is
the smallest value the horizon can take. We generalize the uncertainty
principle to Schwarzschild-de Sitter spacetime with the cosmological constant
and find a dual relation which, compared to
and , affirms the existence of a maximal mass
of the order , minimum
temperature . As compared to the standard
approach we find a deformed dispersion relation close to
and in addition at the maximally possible horizon approximately at
. agrees with the standard results at
(or equivalently at ).Comment: new references adde
Heat Explosion In A Two-Phase Medium
Introduction In this work we study heat explosion in a heterogeneous medium consisting of reacting particles surrounded by a gas. Chemical reaction can occur inside the particles or between the particles and the gas, but it does not occur inside the gaseous phase. The particles are sufficiently small and there is no heat conduction in this phase. The gas is heat conducting and there is heat exchange between the two phases. Under the gravity conditions the temperature distribution can be influenced by convection. Convective motion of particles is determined by the gas motion in the sense that both phases have the same velocity field. We consider the two-temperature model in terms of dimensionless variables oe ` @` 1 @t + (ur)` 1 ' = ke Z` 1 \Gamma ff(` 1 \Gamma ` 2 );<