2,537 research outputs found
Characteristics of anomalously high multiplicity cosmic ray interactions
Six events with the number of secondaries ranging from 250 to several thousands were registered by an installation consisting of a thin graphite target, above and under which are placed photolayers followed by the usual lead X-ray film and emulsion chambers. Data concerning the number of secondaries and their angular distribution are given. The variance of the angular distribution is compared with data obtained at accelerator energies
Spectro-Polarimetric Properties of Sunquake Sources in X1.5 Flare and Evidence for Electron and Proton Beam Impacts
The first significant sunquake event of Solar Cycle 25 was observed during
the X1.5 flare of May 10, 2022, by the Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory. We perform a detailed
spectro-polarimetric analysis of the sunquake photospheric sources, using the
Stokes profiles of the FeI 6173A line, reconstructed from the HMI linear and
circular polarized filtergrams. The results show fast variations of the
continuum emission with rapid growth and slower decay lasting 3-4 min,
coinciding in time with the hard X-ray impulses observed by the Konus
instrument onboard the Wind spacecraft. The variations in the line core
appeared slightly ahead of the variations in the line wings, showing that the
heating started in the higher atmospheric layers and propagated downward. The
most significant feature of the line profile variations is the transient
emission in the line core in three of the four sources, indicating intense,
impulsive heating in the lower chromosphere and photosphere. In addition, the
observed variations of the Stokes profiles reflect transient and permanent
changes in the magnetic field strength and geometry in the sunquake sources.
Comparison with the radiative hydrodynamics models shows that the physical
processes in the impulsive flare phase are substantially more complex than
those predicted by proton and electron beam flare models currently presented in
the literature.Comment: 15 pages, 12 figures, accepted for publication in ApJ, for associated
mpeg file, see
https://spaceweather.com/images2022/12may22/Sunquake_X1.5_flare_051022_1.mp
The impact of globalization on higher education system in Russia: the principles of individual approach to students
Авторы рассматривают вопросы влияния глобализации на систему высшего образования в России, а также адаптации студентов-иностранцев к неродной среде с позиции необходимости индивидуального подхода в оценке их успеваемости.The authors consider the impact of globalization on higher education system in Russia, as well as adaptation of foreign students to non-native environment position required an individual approach in the assessment of their learning
Electrotransport and magnetic properies of Cr-GaSb spintronic materials synthesized under high pressure
Electrotarnsport and magnetic properties of new phases in the system Cr-GaSb
were studied. The samples were prepared by high-pressure (P=6-8 GPa)
high-temperature treatment and identified by x-ray diffraction and scanning
electron microscopy (SEM). One of the CrGaSb phases with an
orthorhombic structure has a combination of ferromagnetic and
semiconductor properties and is potentially promising for spintronic
applications. Another high-temperature phase is paramagnetic and identified as
tetragonal
The "Horizon-T" Experiment: Extensive Air Showers Detection
Horizon-T is an innovative detector system constructed to study Extensive Air
Showers (EAS) in the energy range above 10^16 eV coming from a wide range of
zenith angles (0 - 85 degrees). The system is located at Tien Shan
high-altitude Science Station of Lebedev Physical Institute of the Russian
Academy of Sciences at approximately 3340 meters above the sea level. It
consists of eight charged particle detection points separated by the distance
up to one kilometer as well as optical detector subsystem to view the
Vavilov-Cerenkov light from the EAS. The time resolution of charged particles
and Vavilov-Cerenkov light photons passage of the detector system is a few ns.
This level of resolution allows conducting research of atmospheric development
of individual EAS.Comment: Initial technical note for Horizon-T experiment, updated with recent
detector upgrades, 11/2016. Updated 12/2017 with minor edits. Large upgrade
will be in another articl
Interplay between magnetism and superconductivity and appearance of a second superconducting transition in alpha-FeSe at high pressure
We synthesized tetragonal alpha-FeSe by melting a powder mixture of iron and
selenium at high pressure. Subsequent annealing at normal pressure results in
removing traces of hexagonal beta- FeSe, formation of a rather sharp transition
to superconducting state at Tc ~ 7 K, and the appearance of a magnetic
transition near Tm = 120 K. Resistivity and ac-susceptibility were measured on
the annealed sample at hydrostatic pressure up to 4.5 GPa. A magnetic
transition visible in ac-susceptibility shifts down under pressure and the
resistive anomaly typical for a spin density wave (SDW) antiferromagnetic
transition develops near the susceptibility anomaly. Tc determined by the
appearance of a diamagnetic response in susceptibility, increases linearly
under pressure at a rate dTc/dP = 3.5 K/GPa. Below 1.5 GPa, the resistive
superconducting transition is sharp; the width of transition does not change
with pressure; and, Tc determined by a peak in drho/dT increases at a rate ~
3.5 K/GPa. At higher pressure, a giant broadening of the resistive transition
develops. This effect cannot be explained by possible pressure gradients in the
sample and is inherent to alpha-FeSe. The dependences drho(T)/dT show a
signature for a second peak above 3 GPa which is indicative of the appearance
of another superconducting state in alpha-FeSe at high pressure. We argue that
this second superconducting phase coexists with SDW antiferromagnetism in a
partial volume fraction and originates from pairing of charge carriers from
other sheets of the Fermi surface
Holonomic functions of several complex variables and singularities of anisotropic Ising n-fold integrals
Lattice statistical mechanics, often provides a natural (holonomic) framework
to perform singularity analysis with several complex variables that would, in a
general mathematical framework, be too complex, or could not be defined.
Considering several Picard-Fuchs systems of two-variables "above" Calabi-Yau
ODEs, associated with double hypergeometric series, we show that holonomic
functions are actually a good framework for actually finding the singular
manifolds. We, then, analyse the singular algebraic varieties of the n-fold
integrals , corresponding to the decomposition of the magnetic
susceptibility of the anisotropic square Ising model. We revisit a set of
Nickelian singularities that turns out to be a two-parameter family of elliptic
curves. We then find a first set of non-Nickelian singularities for and , that also turns out to be rational or ellipic
curves. We underline the fact that these singular curves depend on the
anisotropy of the Ising model. We address, from a birational viewpoint, the
emergence of families of elliptic curves, and of Calabi-Yau manifolds on such
problems. We discuss the accumulation of these singular curves for the
non-holonomic anisotropic full susceptibility.Comment: 36 page
Specific Heat Discontinuity, deltaC, at Tc in BaFe2(As0.7P0.3)2 - Consistent with Unconventional Superconductivity
We report the specific heat discontinuity, deltaC/Tc, at Tc = 28.2 K of a
collage of single crystals of BaFe2(As0.7P0.3)2 and compare the measured value
of 38.5 mJ/molK**2 with other iron pnictide and iron chalcogenide (FePn/Ch)
superconductors. This value agrees well with the trend established by Bud'ko,
Ni and Canfield who found that deltaC/Tc ~ a*Tc**2 for 14 examples of doped
Ba1-xKxFe2As2 and BaFe2-xTMxAs2, where the transition metal TM=Co and Ni. We
extend their analysis to include all the FePn/Ch superconductors for which
deltaC/Tc is currently known and find deltaC/Tc ~ a*Tc**1.9 and a=0.083
mJ/molK**4. A comparison with the elemental superconductors with Tc>1 K and
with A-15 superconductors shows that, contrary to the FePn/Ch superconductors,
electron-phonon-coupled conventional superconductors exhibit a significantly
different dependence of deltaC on Tc, namely deltaC/Tc ~ Tc**0.9. However
deltaC/gamma*Tc appears to be comparable in all three classes (FePn/Ch,
elemental and A-15) of superconductors with, e. g., deltaC/gamma*Tc=2.4 for
BaFe2(As0.7P0.3)2. A discussion of the possible implications of these
phenomenological comparisons for the unconventional superconductivity believed
to exist in the FePn/Ch is given.Comment: some disagreement in reference and footnote numbering with the
published versio
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