827 research outputs found
Peculiarities of phonon spectra and lattice heat capacity in Ir and Rh
A simple pseudopotential model is proposed, which allows the phonon spectra
and temperature dependence of the lattice heat capacity of Ir and Rh be
described with a high enough accuracy. A careful comparison of the calculated
and experimental values of the lattice heat capacity is carried out, with the
procedure of the identification of the phonon contribution to the heat capacity
and determination of the characteristics (momenta) of the phonon density of
states from the experimental values of the total heat capacity of metal at a
constant pressure being described in detail. The results of the theoretical
calculations explain, in particular, such peculiar feature of Ir and Rh,
unusual for cubic metals, as a sharp (more than by a factor of 1.5) decrease in
the effective Debye temperature with increasing termperature. The temperature
dependence of the mean square amplitude of atomic displacements in Ir and Rh
has been calculated. Basing on the band calculations the manifestation of the
Kohn singularities in the phonon spectra of Ir are discussed.Comment: 15 pages, LaTeX2e, 12 figures in postscrip
Synthesis, Single Crystal Growth, and Properties of Cobalt Deficient Double Perovskite EuBaCo2-xO6-delta (x=0-0.1)
The cobalt deficient double perovskites EuBaCo2−xO6−δ with x=0–0.1 were obtained both as powders and as single crystal. Formation of cobalt vacancies in their crystal lattice was shown to be accompanied by the formation of oxygen ones. Chemical lattice strain caused by this cooperative disordering of cobalt and oxygen sublattices was found to be isotropic contrary to that caused by the formation of oxygen vacancies only. Cobalt deficiency was also shown to lead to lowering overall conductivity and Seebeck coefficient of EuBaCo2−xO6−δ double perovskites as a result of simultaneous decrease of charge carriers’ concentration and their mobility as well as number of sites available for electrons and holes transfer. Strong anisotropy of the overall conductivity of the single crystal double perovskites EuBaCo2−xO6−δ was found and explained on the basis of preferential location of oxygen vacancies in the rare-earth-oxygen- (REO-) planes
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
Electrical and optical properties of a PtSn 4 single crystal
A topological semimetal PtSn4 single crystal was grown by method of crystallization from a solution in a melt. Then the electrical resistivity and galvanomagnetic properties (magnetoresistivity and the Hall effect) were studied in the temperature range from 4.2 to 80 K and in magnetic fields up to 100 kOe. The optical measurements were carried out at room temperature. The residual resistivity is shown to be low enough and amount to ∼ 0.5 μOhm•cm. The temperature dependence of the electrical resistivity has a metallic type, increasing monotonically with temperature. A sufficiently large magnetoresistance of 750% is observed. The majority carriers are supposed to be holes with a concentration of ∼ 6.8•10 21 cm -3 and mobility of ∼ 1950 cm 2 /Vs at T = 4.2 K as a result of the Hall effect studies. The optical properties of PtSn 4 have features characteristic of "bad" metals. © 2019 Published under licence by IOP Publishing Ltd.This work was partly supported by the state assignment of Russia (theme “Spin” No. АААА-А18-18020290104-2 and theme “Electron” No. АААА-А18-118020190098-5), by the RFBR (project No.17-52-52008) and by the Government of the Russian Federation (state contract No. 02.A03.21.0006)
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
Design and Performance of the GAMMA-400 Gamma-Ray Telescope for Dark Matter Searches
The GAMMA-400 gamma-ray telescope is designed to measure the fluxes of gamma-rays and cosmic-ray electrons (+) positrons, which can be produced by annihilation or decay of the dark matter particles, as well as 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 approximately 0.01deg (E(sub gamma) greater than 100 GeV), the energy resolution approximately 1% (E(sub gamma) greater than 10 GeV), and the proton rejection factor approximately 10(exp 6). GAMMA-400 will be installed on the Russian space platform Navigator. The beginning of observations is planned for 2018
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