361 research outputs found
Cavitation-induced ignition of cryogenic hydrogen-oxygen fluids
The Challenger disaster and purposeful experiments with liquid hydrogen (H2)
and oxygen (Ox) tanks demonstrated that cryogenic H2/Ox fluids always
self-ignite in the process of their mixing. Here we propose a
cavitation-induced self-ignition mechanism that may be realized under these
conditions. In one possible scenario, self-ignition is caused by the strong
shock waves generated by the collapse of pure Ox vapor bubble near the surface
of the Ox liquid that may initiate detonation of the gaseous H2/Ox mixture
adjacent to the gas-liquid interface. This effect is further enhanced by H2/Ox
combustion inside the collapsing bubble in the presence of admixed H2 gas
Strongly Time-Variable Ultra-Violet Metal Line Emission from the Circum-Galactic Medium of High-Redshift Galaxies
We use cosmological simulations from the Feedback In Realistic Environments
(FIRE) project, which implement a comprehensive set of stellar feedback
processes, to study ultra-violet (UV) metal line emission from the
circum-galactic medium of high-redshift (z=2-4) galaxies. Our simulations cover
the halo mass range Mh ~ 2x10^11 - 8.5x10^12 Msun at z=2, representative of
Lyman break galaxies. Of the transitions we analyze, the low-ionization C III
(977 A) and Si III (1207 A) emission lines are the most luminous, with C IV
(1548 A) and Si IV (1394 A) also showing interesting spatially-extended
structures. The more massive halos are on average more UV-luminous. The UV
metal line emission from galactic halos in our simulations arises primarily
from collisionally ionized gas and is strongly time variable, with
peak-to-trough variations of up to ~2 dex. The peaks of UV metal line
luminosity correspond closely to massive and energetic mass outflow events,
which follow bursts of star formation and inject sufficient energy into
galactic halos to power the metal line emission. The strong time variability
implies that even some relatively low-mass halos may be detectable. Conversely,
flux-limited samples will be biased toward halos whose central galaxy has
recently experienced a strong burst of star formation. Spatially-extended UV
metal line emission around high-redshift galaxies should be detectable by
current and upcoming integral field spectrographs such as the Multi Unit
Spectroscopic Explorer (MUSE) on the Very Large Telescope and Keck Cosmic Web
Imager (KCWI).Comment: 16 pages, 8 figures, accepted for publication in MNRA
Multiplicity of supercritical fronts for reaction-diffusion equations in cylinders
We study multiplicity of the supercritical traveling front solutions for
scalar reaction-diffusion equations in infinite cylinders which invade a
linearly unstable equilibrium. These equations are known to possess traveling
wave solutions connecting an unstable equilibrium to the closest stable
equilibrium for all speeds exceeding a critical value. We show that these are,
in fact, the only traveling front solutions in the considered problems for
sufficiently large speeds. In addition, we show that other traveling fronts
connecting to the unstable equilibrium may exist in a certain range of the wave
speed. These results are obtained with the help of a variational
characterization of such solutions
Self-replication and splitting of domain patterns in reaction-diffusion systems with fast inhibitor
An asymptotic equation of motion for the pattern interface in the
domain-forming reaction-diffusion systems is derived. The free boundary problem
is reduced to the universal equation of non-local contour dynamics in two
dimensions in the parameter region where a pattern is not far from the points
of the transverse instabilities of its walls. The contour dynamics is studied
numerically for the reaction-diffusion system of the FitzHugh-Nagumo type. It
is shown that in the asymptotic limit the transverse instability of the
localized domains leads to their splitting and formation of the multidomain
pattern rather than fingering and formation of the labyrinthine pattern.Comment: 9 pages (ReVTeX), 5 figures (postscript). To be published in Phys.
Rev.
Influence of Structural Features and Physico-chemical Properties of Metal-carbon Nanocomposites with Ferromagnetic Metal Inclusions on Microwave Radiation
Metal-carbon nanocomposites on the basis of polyacrylonitrile and compounds of metals (Fe, Ni, Co)
synthesized at IR-heating and studied by SEM, X-ray phase analysis, Raman scattering, IR Fourier spec-troscopy are characterized by the carbon nanostructured amorphous graphite matrix with uniformly dis-tributed nanoparticles of metals (10-30 nm), their oxides and compounds – FeNi3 and FeCo, multilayered
carbon nanotubes (~ 7-22 nm), and in the composition of Fe-Co / C fullerene-like formations – C60. All
nanocomposites feature high absorption of electromagnetic waves in the frequency range 20-40 GHz. Two
absorption mechanisms are proposed: dielectric loss in the amorphous carbon matrix and scattering of
electric and magnetic components by ferromagnetic inclusions. Absorption was – 8.68 dB for Fe-Ni / C,
– 12.93 dB for Fe / C, and – 7.07 dB for Ni / C and for Fe-Co / C was found to be maximum in the whole
range studied (more than – 40 dB) with a peak of – 52.83 dB at 24.27 GHz, which is explained probably by
both high nanocomposite electric conductivity 2 S / m and high specific magnetization of phase FeCo.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3625
Direct Evidence of Two Superconducting Gaps in FeSeTe: SnS-Andreev Spectroscopy and Lower Critical Field
We present direct measurements of the superconducting order parameter in
nearly optimal FeSeTe single crystals with critical temperature
K. Using intrinsic multiple Andreev reflection effect (IMARE)
spectroscopy and measurements of lower critical field, we directly determined
two superconducting gaps, meV and meV, and their temperature dependences. We show that a two-band
model fits well the experimental data. The estimated electron-boson coupling
constants indicate a strong intraband and a moderate interband interaction
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