466 research outputs found
Diffusionless (chemically partitionless) crystallization and subsequent decomposition of supersaturated solid solutions in Sn-Bi eutectic alloy
Results of a study on microstructural evolution of eutectic Sn-57wt.% Bi processed with cooling rates of 10-2, 1Ks-1 and approximately 105 Ks-1 are presented. In order to distinguish different mechanisms of microstructure formation, a comparison with microstructures of different hypoeutectic alloys with compositions down to below the maximum solubility of Bi in Sn-Bi is undertaken. It is found that at the cooling rates of 10-2 and 1Ks-1, coupled eutectic growth occurs, leading to lamellar structures with different length scales. At the rapid quenching rates of approximately 105 Ks-1, structure formation in the eutectic alloy is qualitatively different. Partitionless solidification resulting in a supersaturated solid solution with the initial composition is observed in both eutectic and hypoeutectic alloys. It is shown that the observed microstructure of the rapidly solidified alloys forms by the decomposition of the supersaturated solid solution. This article is part of the theme issue 'Heterogeneous materials: Metastable and non-ergodic internal structures'. ©2019 The Author(s) Published by the Royal Society
Cooling of Neutron Stars: Two Types of Triplet Neutron Pairing
We consider cooling of neutron stars (NSs) with superfluid cores composed of
neutrons, protons, and electrons (assuming singlet-state pairing of protons,
and triplet-state pairing of neutrons). We mainly focus on (nonstandard)
triplet-state pairing of neutrons with the projection of the total
angular momentum of Cooper pairs onto quantization axis. The specific feature
of this pairing is that it leads to a power-law (nonexponential) reduction of
the emissivity of the main neutrino processes by neutron superfluidity. For a
wide range of neutron critical temperatures , the cooling of NSs with
the superfluidity is either the same as the cooling with the superfluidity, considered in the majority of papers, or much faster. The
cooling of NSs with density dependent critical temperatures and
can be imitated by the cooling of the NSs with some effective
critical temperatures and constant over NS cores. The
hypothesis of strong neutron superfluidity with is inconsistent
with current observations of thermal emission from NSs, but the hypothesis of
weak neutron superfluidity of any type does not contradict to observations.Comment: 10 pages, 6 figure
Improved confinement transition in high density deuterium discharges at the FT-2 tokamak accompanied by onset of negative triangularity
Dark Matter Search Perspectives with GAMMA-400
GAMMA-400 is a future high-energy gamma-ray telescope, designed to measure
the fluxes of gamma-rays and cosmic-ray electrons + positrons, which can be
produced by annihilation or decay of dark matter particles, and to survey the
celestial sphere in order to study point and extended sources of gamma-rays,
measure energy spectra of Galactic and extragalactic diffuse gamma-ray
emission, gamma-ray bursts, and gamma-ray emission from the Sun. GAMMA-400
covers the energy range from 100 MeV to ~3000 GeV. Its angular resolution is
~0.01 deg(Eg > 100 GeV), and the energy resolution ~1% (Eg > 10 GeV). GAMMA-400
is planned to be launched on the Russian space platform Navigator in 2019. The
GAMMA-400 perspectives in the search for dark matter in various scenarios are
presented in this paperComment: 4 pages, 4 figures, submitted to the Proceedings of the International
Cosmic-Ray Conference 2013, Brazil, Rio de Janeir
The GAMMA-400 space observatory: status and perspectives
The present design of the new space observatory GAMMA-400 is presented in
this paper. The instrument has been designed for the optimal detection of gamma
rays in a broad energy range (from ~100 MeV up to 3 TeV), with excellent
angular and energy resolution. The observatory will also allow precise and high
statistic studies of the electron component in the cosmic rays up to the multi
TeV region, as well as protons and nuclei spectra up to the knee region. The
GAMMA-400 observatory will allow to address a broad range of science topics,
like search for signatures of dark matter, studies of Galactic and
extragalactic gamma-ray sources, Galactic and extragalactic diffuse emission,
gamma-ray bursts and charged cosmic rays acceleration and diffusion mechanism
up to the knee
A separation of electrons and protons in the GAMMA-400 gamma-ray telescope
The GAMMA-400 gamma-ray telescope is intended to measure the fluxes of gamma
rays and cosmic-ray electrons and positrons in the energy range from 100 MeV to
several TeV. Such measurements concern with the following scientific goals:
search for signatures of dark matter, investigation of gamma-ray point and
extended sources, studies of the energy spectra of Galactic and extragalactic
diffuse emission, studies of gamma-ray bursts and gamma-ray emission from the
active Sun, as well as high-precision measurements of spectra of high-energy
electrons and positrons, protons, and nuclei up to the knee. The main
components of cosmic rays are protons and helium nuclei, whereas the part of
lepton component in the total flux is ~10E-3 for high energies. In present
paper, the capability of the GAMMA-400 gamma-ray telescope to distinguish
electrons and positrons from protons in cosmic rays is investigated. The
individual contribution to the proton rejection is studied for each detector
system of the GAMMA-400 gamma-ray telescope. Using combined information from
all detector systems allow us to provide the proton rejection from electrons
with a factor of ~4x10E5 for vertical incident particles and ~3x10E5 for
particles with initial inclination of 30 degrees. The calculations were
performed for the electron energy range from 50 GeV to 1 TeV.Comment: 19 pages, 10 figures, submitted to Advances and Space Researc
Symmetry of the Neutron and Proton Superfluidity Effects in Cooling Neutron Stars
We investigate the combined effect of neutron and proton superfluidities on
the cooling of neutron stars whose cores consist of nucleons and electrons. We
consider singlet-state pairing of protons and triplet-state pairing of neutrons
in the cores of neutron stars. The critical superfluid temperatures T_c are
assumed to depend on the density of matter. We study two types of neutron
pairing with different components of the total angular momentum of Cooper pairs
along the quantization axis (|m_J| =0 or 2). Our calculations are compared with
observations of thermal emission from isolated neutron stars. We show that the
observations can be interpreted by using two classes of superfluidity models:
(1) strong proton superfluidity with a maximum critical temperature in the
stellar core T_c^{max} > 4 \times 10^9 K and weak neutron superfluidity of any
type (T_c^{max} < 2 \times 10^8 K); (2) strong neutron superfluidity (pairing
with |m_J|=0) and weak proton superfluidity. The two types of models reflect an
approximate symmetry with respect to an interchange of the critical
temperatures of neutron and proton pairing.Comment: 20 pages, 8 figure
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