134 research outputs found
Thermal radiation of various gravitational backgrounds
We present a simple and general procedure for calculating the thermal
radiation coming from any stationary metric. The physical picture is that the
radiation arises as the quasi--classical tunneling of particles through a
gravitational barrier. We show that our procedure can reproduce the results of
Hawking and Unruh radiation. We also show that under certain kinds of
coordinate transformations the temperature of the thermal radiation will change
in the case of the Schwarzschild black holes. In addition we apply our
procedure to a rotating/orbiting system and show that in this case there is no
radiation, which has experimental implications for the polarization of
particles in circular accelerators.Comment: 6 pages revtex, added references, publication version. To be
published IJMP
Professional competence of graduates as employment guarantee
In the article the basic problems of employment of graduates and their solutions in the current market conditionsРассмотрены основные проблемы трудоустройства выпускников вузов и пути их решения в современных рыночных условия
How often does the Unruh-DeWitt detector click? Regularisation by a spatial profile
We analyse within first-order perturbation theory the instantaneous
transition rate of an accelerated Unruh-DeWitt particle detector whose coupling
to a massless scalar field on four-dimensional Minkowski space is regularised
by a spatial profile. For the Lorentzian profile introduced by Schlicht, the
zero size limit is computed explicitly and expressed as a manifestly finite
integral formula that no longer involves regulators or limits. The same
transition rate is obtained for an arbitrary profile of compact support under a
modified definition of spatial smearing. Consequences for the asymptotic
behaviour of the transition rate are discussed. A number of stationary and
nonstationary trajectories are analysed, recovering in particular the Planckian
spectrum for uniform acceleration.Comment: 30 pages, 1 figure. v3: Added references and minor clarification
Giant Anharmonic Phonon Scattering in PbTe
Understanding the microscopic processes affecting the bulk thermal
conductivity is crucial to develop more efficient thermoelectric materials.
PbTe is currently one of the leading thermoelectric materials, largely thanks
to its low thermal conductivity. However, the origin of this low thermal
conductivity in a simple rocksalt structure has so far been elusive. Using a
combination of inelastic neutron scattering measurements and first-principles
computations of the phonons, we identify a strong anharmonic coupling between
the ferroelectric transverse optic (TO) mode and the longitudinal acoustic (LA)
modes in PbTe. This interaction extends over a large portion of reciprocal
space, and directly affects the heat-carrying LA phonons. The LA-TO anharmonic
coupling is likely to play a central role in explaining the low thermal
conductivity of PbTe. The present results provide a microscopic picture of why
many good thermoelectric materials are found near a lattice instability of the
ferroelectric type
Observer Dependent Horizon Temperatures: a Coordinate-Free Formulation of Hawking Radiation as Tunneling
We reformulate the Hamilton-Jacobi tunneling method for calculating Hawking
radiation in static, spherically-symmetric spacetimes by explicitly
incorporating a preferred family of frames. These frames correspond to a family
of observers tied to a locally static timelike Killing vector of the spacetime.
This formulation separates the role of the coordinates from the choice of
vacuum and thus provides a coordinate-independent formulation of the tunneling
method. In addition, it clarifies the nature of certain constants and their
relation to these preferred observers in the calculation of horizon
temperatures. We first use this formalism to obtain the expected temperature
for a static observer at finite radius in the Schwarzschild spacetime. We then
apply this formalism to the Schwarzschild-de Sitter spacetime, where there is
no static observer with 4-velocity equal to the static timelike Killing vector.
It is shown that a preferred static observer, one whose trajectory is geodesic,
measures the lowest temperature from each horizon. Furthermore, this observer
measures horizon temperatures corresponding to the well-known Bousso-Hawking
normalization.Comment: 11 pages, 1 2-part figure, references added, appendix added,
discussion streamline
Black Hole Evaporation in a Noncommutative Charged Vaidya Model
The aim of this paper is to study the black hole evaporation and Hawking
radiation for a noncommutative charged Vaidya black hole. For this purpose, we
determine spherically symmetric charged Vaidya model and then formulate a
noncommutative Reissner-Nordstrm-like solution of this model which
leads to an exact dependent metric. The behavior of temporal component
of this metric and the corresponding Hawking temperature is investigated. The
results are shown in the form of graphs. Further, we examine the tunneling
process of the charged massive particles through the quantum horizon. It is
found that the tunneling amplitude is modified due to noncommutativity. Also,
it turns out that black hole evaporates completely in the limits of large time
and horizon radius. The effect of charge is to reduce the temperature from
maximum value to zero. It is mentioned here that the final stage of black hole
evaporation turns out to be a naked singularity.Comment: 25 pages, 36 figures, accepted for publication in J. Exp. Theor. Phy
COMPARISON OF THE STRUCTURE AND FRACTURES OF HARD ALLOYS
Проблему импортозамещения твердых сплавов для наплавок рабочих органов сельскохозяйственных машин невозможно решить без создания новых отечественных твердосплавных материалов. Решение такой задачи возможно только при условии достижения необходимой глубины понимания природы прочности, износостойкости и сопротивляемости разрушению существующих твердых сплавов, механизмов разрушения наблюдаемых в них разнородных структур.The problem of import substitution of hard alloys for pad weld work tool of agricultural machinery is impossible to solve without creation new domestic hard-alloy material. The solution of such task is possible only in condition of achievement of necessary depth of understanding of the nature of durability, wear resistance and the resilience to destruction of the existing solid alloys, mechanisms of destruction of the diverse structures observed in them.Работа выполнена в рамках Соглашения № 14.578.21.0129 о предоставлении субсидии для финансового обеспечения (возмещения) затрат, связанных с выполнением ПНИЭР по теме: «Разработка импортозамещающих твердых сплавов с повышенными износными и технологическими характеристиками для упрочнения быстроизнашиваемых деталей сельхозмашин, эксплуатирующихся в абразивной среде». Уникальный идентификатор ПНИЭР RFMEFI57815X0129
Back reaction, emission spectrum and entropy spectroscopy
Recently, an interesting work, which reformulates the tunneling framework to
directly produce the Hawking emission spectrum and entropy spectroscopy in the
tunneling picture, has been received a broad attention. However, during the
emission process, most related observations have not incorporated the effects
of back reaction on the background spacetime, whose derivations are therefore
not the desiring results for the real physical process. With this point as a
central motivation, in this paper we suitably adapt the \emph{reformulated}
tunneling framework so that it can well accommodate the effects of back
reaction to produce the Hawking emission spectrum and entropy spectroscopy.
Consequently, we interestingly find that, when back reaction is considered, the
Parikh-Wilczek's outstanding observations that, an isolated radiating black
hole has an unitary-evolving emission spectrum that is \emph{not} precisely
thermal, but is related to the change of the Bekenstein-Hawking entropy, can
also be reproduced in the reformulated tunneling framework, meanwhile the
entropy spectrum has the same form as that without inclusion of back reaction,
which demonstrates the entropy quantum is \emph{independent} of the effects of
back reaction. As our final analysis, we concentrate on the issues of the black
hole information, but \emph{unfortunately} find that, even including the
effects of back reaction and higher-order quantum corrections, such tunneling
formalism can still not provide a mechanism for preserving the black hole
information.Comment: 16 pages, no figure, use JHEP3.cls. to be published in JHE
Twenty-year clinical progression of dysferlinopathy in patients from Dagestan
© 2017 Umakhanova, Bardakov, Mavlikeev, Chernova, Magomedova, Akhmedova, Yakovlev, Dalgatov, Fedotov, Isaev and Deev.To date, over 30 genes with mutations causing limb-girdle muscle dystrophy have been described. Dysferlinopathies are a form of limb-girdle muscle dystrophy type 2B with an incidence ranging from 1:1,300 to 1:200,000 in different populations. In 1996, Dr. S. N. Illarioshkin described a family from the Botlikhsky district of Dagestan, where limb-girdle muscle dystrophy type 2B and Miyoshi myopathy were diagnosed in 12 members from three generations of a large Avar family. In 2000, a previously undescribed mutation in the DYSF gene (c.TG573/574AT; p. Val67Asp) was detected in the affected members of this family. Twenty years later, in this work, we re-examine five known and seven newly affected family members previously diagnosed with dysferlinopathy. We observed disease progression in family members who were previously diagnosed and noted obvious clinical polymorphism of the disease. A typical clinical case is provided
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