428 research outputs found
Shear viscosity of degenerate electron matter
We calculate the partial electron shear viscosity limited by
electron-electron collisions in a strongly degenerate electron gas taking into
account the Landau damping of transverse plasmons. The Landau damping strongly
suppresses in the domain of ultrarelativistic degenerate electrons
and modifies its %asymptotic temperature behavior. The efficiency of the
electron shear viscosity in the cores of white dwarfs and envelopes of neutron
stars is analyzed.Comment: 16 pages, 4 figures, accepted to Journal of Physics
Anaerobic conversion of biomass upon disintegration in ultrasonic fields of low intensity
Disintegration is the destruction of the cell structure to release all its contents. This process facilitates bacteria access to nutrients and it results in a substrate decomposition rate increase. We can use thermal (the brief heating below one hundred degrees temperature at normal pressure or higher one hundred degrees temperature at enhanceable pressure) and chemical (enzymes and catalysts addition, which can positively influence the process speed), biochemical and physical-mechanical methods (the sonication). © 2014 WIT Press
Large collection of astrophysical S-factors and its compact representation
Numerous nuclear reactions in the crust of accreting neutron stars are
strongly affected by dense plasma environment. Simulations of superbursts, deep
crustal heating and other nuclear burning phenomena in neutron stars require
astrophysical S-factors for these reactions (as a function of center-of-mass
energy E of colliding nuclei). A large database of S-factors is created for
about 5000 non-resonant fusion reactions involving stable and unstable isotopes
of Be, B, C, N, O, F, Ne, Na, Mg, and Si. It extends the previous database of
about 1000 reactions involving isotopes of C, O, Ne, and Mg. The calculations
are performed using the Sao Paulo potential and the barrier penetration
formalism. All calculated S-data are parameterized by an analytic model for
S(E) proposed before [Phys. Rev. C 82, 044609 (2010)] and further elaborated
here. For a given reaction, the present S(E)-model contains three parameters.
These parameters are easily interpolated along reactions involving isotopes of
the same elements with only seven input parameters, giving an ultracompact,
accurate, simple, and uniform database. The S(E) approximation can also be used
to estimate theoretical uncertainties of S(E) and nuclear reaction rates in
dense matter, as illustrated for the case of the 34Ne+34Ne reaction in the
inner crust of an accreting neutron star.Comment: 13 pages, 2 figures, Phys. Rev. C, accepte
The determination of the thermal properties of unconsolidated materials
Heat transfer in a composite cylindrical region is considered. An approximate analytical solution of the direct problem is obtained. It is shown that, beginning at the instant t > t , the relative error of the solution obtained does not exceed 1%. On the basis of this, algorithms are constructed which enable inverse problems to be solved effectively. Examples of the use of the algorithms to determine the thermal properties of unconsolidated materials are presented. © 2012 Springer Science+Business Media, Inc
Observability of HOFNARs with SRG/eROSITA
Neutron stars can appear as sources of different nature. In this paper we
address observability of a hypothetical class of neutron stars -- HOt and Fast
Non Accreting Rotators, HOFNARs. These objects are heated due to the r-mode
instability. With surface temperatures ~K they are expected to be
thermal soft X-ray emitters. We perform a population synthesis modeling of
HOFNARs to predict the number of potentially detectable sources in the eROSITA
all-sky survey. For surface temperatures ~K we obtain
sources above the detection limit 0.01~cts~s and easier
identifiable sources with ~cts~s. Temperatures ~K start to be in contradiction with non-detection of HOFNARs by ROSAT.
Only for ~K numbers predicted for eROSITA turn out to
be so low that identification does not look possible. We conclude that eROSITA
has good chances to discover HOFNARs, if they exist. Non-detection will put
very stringent limits on the properties of this type of neutron stars.Comment: 17 pages, submitted to Univers
Modeling AlGaN p-i-n photodiodes
Ternary AlGaN alloys with a band gap of 3.4 to 6.2 eV are very promising for photodetectors in the UV wavelength range. Using the COMSOL MULTIPHYSICS software based on AlGaN, a p-i-n photodiode model was developed, including its I–V characteristic, spectral sensitivity of the received radiation, absorption coefficient as a function of the aluminum fraction and the depletion layer thickness. To calculate the process of interaction of a semiconductor with EM radiation, we used a model based on the use of an element of the transition matrix through the carrier lifetime during spontaneous recombination. In this case, the peak sensitivity of the photodiode is from 0.08 to 0.18 A/W at wavelengths of 0.2–0.33 µm. This is in line with experimental results taken from the relevant literature.Ternary AlGaN alloys with a band gap of 3.4 to 6.2 eV are very promising for photodetectors in the UV wavelength range. Using the COMSOL MULTIPHYSICS software based on AlGaN, a p-i-n photodiode model was developed, including its I–V characteristic, spectral sensitivity of the received radiation, absorption coefficient as a function of the aluminum fraction and the depletion layer thickness. To calculate the process of interaction of a semiconductor with EM radiation, we used a model based on the use of an element of the transition matrix through the carrier lifetime during spontaneous recombination. In this case, the peak sensitivity of the photodiode is from 0.08 to 0.18 A/W at wavelengths of 0.2–0.33 µm. This is in line with experimental results taken from the relevant literature
SU(2) Skyrme Vortices
A regular method for constructing vortex-like solutions with cylindrical
symmetry to the equations of the SU(2) Skyrme chiral model is proposed. A
numerical estimate for the length density of mass is given
Mathematical description and calculation of contact melting
Heat- and mass-transfer processes are investigated in the contact melting of solids with large specific loads and energy rates appropriate to conditions of thermal drilling. © 1985 Plenum Publishing Corporation
Reactive rimming flow of non-Newtonian fluids
The steady and non-steady flows of a liquid polymer treated as a non-Newtonian fluid on the inner surface of a horizontal rotating cylinder are investigated. Since the Reynolds number is small and the liquid film is thin, a simple lubrication approximation is applied. Governing equations for non-steady Power-Law and Ellis fluids are solved numerically and the time of transition from non-steady to steady-state mode for various model parameters and flow conditions are defined. The stabilization effect of a chemical reaction within the polymeric fluid (reactive flow) is examined.© 2013 Elsevier Inc. All rights reserved
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