183 research outputs found
Muon puzzle in ultra-high energy EASs according to Yakutsk array and Auger experiment data
The lateral distribution of particles in extensive air showers from cosmic
rays with energy above eV registered at the Yakutsk complex array was
analyzed. Experimentally measured particle densities were compared to the
predictions obtained within frameworks of three ultra-high energy hadron
interaction models. The cosmic ray mass composition estimated by the readings
of surface-based and underground detectors of the array is consistent with
results based on the Cherenkov light lateral distribution data. A comparison
was made with the results of direct measurement of the muon component performed
at the Pierre Auger Observatory. It is demonstrated that the densities of muon
flux measured at Yakutsk array are consistent with results of fluorescent light
measurements and disagree with results on muons obtained at the Auger array.Comment: 14 pages, 6 figures, 2 tables. Accepted for publication in JETP
Letter
A Direct Comparison of Muon Measurements at the Yakutsk Array and the Pierre Auger Observatory
Here we consider the results of direct measurements of muons in extensive air
showers with zenith angles and energy above
eV, obtained at the Pierre Auger Observatory and Yakutsk array. In both
experiments muons were registered with underground scintillation detectors with
GeV energy threshold. Measured density values
were compared to theoretical predictions calculated within the framework of the
QGSJet-II.04 hadron interaction model. They differ by factor (stat). We demonstrate that this difference is due to overestimation of
muon densities by 1.22 times and underestimation of primary energy by 1.25
times in the Auger experiment.Comment: 9 pages, 11 figures, 3 tables. Presented at the 4th International
Symposium on Cosmic Rays and Astrophysics
(https://indico.nevod.mephi.ru/event/9/contributions/226/). To be published
in Physics of Atomic Nucle
Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure
The temperature and pressure dependence of the partial density of phonon
states of iron atoms in superconducting Fe1.01Se was studied by 57Fe nuclear
inelastic scattering (NIS). The high energy resolution allows for a detailed
observation of spectral properties. A sharpening of the optical phonon modes
and shift of all spectral features towards higher energies by ~4% with
decreasing temperature from 296 K to 10 K was found. However, no detectable
change at the tetragonal - orthorhombic phase transition around 100 K was
observed. Application of a pressure of 6.7 GPa, connected with an increase of
the superconducting temperature from 8 K to 34 K, results in an increase of the
optical phonon mode energies at 296 K by ~12%, and an even more pronounced
increase for the lowest-lying transversal acoustic mode. Despite these strong
pressure-induced modifications of the phonon-DOS we conclude that the
pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the
framework of classical electron-phonon coupling. This result suggests the
importance of spin fluctuations to the observed superconductivity
Results of the study of kinetic parameters of spontaneous combustion of coal dust
The article is devoted to the study of the problem of spontaneous combustion of energy grades of coal not only during storage, but also during transportation.
As the main samples for the study, the energy grades of SS and Zh coals were selected. The main task of the scientific research was to study the rate of cooling and heating of coal depending on their thermophysical parameters and environmental parameters.
To solve this problem, the authors used both the author's installations designed to study the thermophysical parameters of the spontaneous combustion process (the Ya.S.Kiselev method), and the NETZSCH STA 449 F3 Jupiter synchronous thermal analysis device, the NETZSCH Proteus Termal Analysis software package.
On the basis of a complex study of the spontaneous combustion process, the authors of the article obtained the kinetic characteristics of the spontaneous heating process (activation energy and pre-exponential multiplier). Nomograms of the permissible size of coal density of different types and shapes of accumulation depending on the ambient temperature are presented, practical recommendations for the prevention (avoidance) of spontaneous combustion of coal fuel are given
Geometric, electronic, and magnetic structure of CoFeSi: Curie temperature and magnetic moment measurements and calculations
In this work a simple concept was used for a systematic search for new
materials with high spin polarization. It is based on two semi-empirical
models. Firstly, the Slater-Pauling rule was used for estimation of the
magnetic moment. This model is well supported by electronic structure
calculations. The second model was found particularly for Co based Heusler
compounds when comparing their magnetic properties. It turned out that these
compounds exhibit seemingly a linear dependence of the Curie temperature as
function of the magnetic moment. Stimulated by these models, CoFeSi was
revisited. The compound was investigated in detail concerning its geometrical
and magnetic structure by means of X-ray diffraction, X-ray absorption and
M\"o\ss bauer spectroscopies as well as high and low temperature magnetometry.
The measurements revealed that it is, currently, the material with the highest
magnetic moment () and Curie-temperature (1100K) in the classes of
Heusler compounds as well as half-metallic ferromagnets. The experimental
findings are supported by detailed electronic structure calculations
Cosmic-ray acceleration in supernova remnants: non-linear theory revised
A rapidly growing amount of evidences, mostly coming from the recent
gamma-ray observations of Galactic supernova remnants (SNRs), is seriously
challenging our understanding of how particles are accelerated at fast shocks.
The cosmic-ray (CR) spectra required to account for the observed phenomenology
are in fact as steep as , i.e., steeper than the
test-particle prediction of first-order Fermi acceleration, and significantly
steeper than what expected in a more refined non-linear theory of diffusive
shock acceleration. By accounting for the dynamical back-reaction of the
non-thermal particles, such a theory in fact predicts that the more efficient
the particle acceleration, the flatter the CR spectrum. In this work we put
forward a self-consistent scenario in which the account for the magnetic field
amplification induced by CR streaming produces the conditions for reversing
such a trend, allowing --- at the same time --- for rather steep spectra and CR
acceleration efficiencies (about 20%) consistent with the hypothesis that SNRs
are the sources of Galactic CRs. In particular, we quantitatively work out the
details of instantaneous and cumulative CR spectra during the evolution of a
typical SNR, also stressing the implications of the observed levels of
magnetization on both the expected maximum energy and the predicted CR
acceleration efficiency. The latter naturally turns out to saturate around
10-30%, almost independently of the fraction of particles injected into the
acceleration process as long as this fraction is larger than about .Comment: 24 pages, 5 figures, accepted for publication in JCA
Search for TeV gamma-rays from SN 1987A in 2001
We searched for TeV gamma-rays from the remnant of SN 1987A around 5400 days
after the supernova. The observations were carried out in 2001, from November
16 to December 11, using the CANGAROO-II Imaging Atmospheric Cherenkov
Telescope. In total, 708 minutes of ON- and 1019 minutes of OFF-source data
were obtained under good conditions. The detection threshold was estimated to
be 1 TeV, due to the mean zenith angle of 39. The upper limits for the
gamma-ray flux were obtained and compared with the previous observations and
theoretical models. The observations indicate that the gamma-ray luminosity is
lower than erg s at TeV.Comment: 8 pages, 3 figures, submitted for publication, style file adde
High temperature superconductivity (Tc onset at 34K) in the high pressure orthorhombic phase of FeSe
We have studied the structural and superconducting properties of tetragonal
FeSe under pressures up to 26GPa using synchrotron radiation and diamond anvil
cells. The bulk modulus of the tetragonal phase is 28.5(3)GPa, much smaller
than the rest of Fe based superconductors. At 12GPa we observe a phase
transition from the tetragonal to an orthorhombic symmetry. The high pressure
orthorhombic phase has a higher Tc reaching 34K at 22GPa.Comment: 15 pages, 4 figure
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