342 research outputs found
К вопросу о пористости киля тороса (по поводу статьи В.В. Харитонова)
The article discusses whether the model of loose granular medium is applicable to the analysis of physical processes in the ridge keel. It is argued that the model is not valid for dealing with a number of problems such as the evolution of the ridge keel. It is also suggested that the decrease in keel porosity in time is primarily caused by thermodynamic factors.Обсуждается возможность применения модели сыпучей среды для анализа физических процессов в киле тороса. Высказано мнение, что для ряда задач, таких как эволюция киля тороса, такая модель не подходит. Также высказано мнение о том, что уменьшение пористости киля тороса во времени обусловлено в первую очередь термодинамическими факторами
«Царь-ледокол» академика А.Н. Крылова
The paper describes the GUSMP (North Sea Route Directorate) expert council session on the design of a powerful icebreaker of 18000–24000 HP held on June 15, 1935 in Leningrad, based on the archive documents. Analysis of the session materials sheds light on the state-of-the-art of icebreaker building in the mid-1930s. The standpoint of academician A.N. Krylov as well as GUSMP administration is particularly interesting.В работе на основании изучения архивных документов анализируется заседание экспертного совета ГУСМП по обсуждению проекта мощного ледокола в 18–24 тыс. л. с., состоявшееся 15 июня 1935 г. в Ленинграде. Материалы этого заседания позволяют оценить состояние ледоколостроения в середине 30-х годов прошлого века. Особый интерес представляет позиция по этому вопросу академика А.Н. Крылова, а также руководства ГУСМП
Движение судов в тертых льдах: результаты исследований
The paper gives a review of the studies concerned with operation of vessels in brash ice. Recently, the ice conditions have received an ever increasing attention of the researchers related to the fact that shipping in the Arctic regions and freezing seas, as well as in inland waterways has been scaled up. One of the important fields of brash ice studies is specifics of sailing under these conditions and primarily determination of the ship ice resistance. The paper shows that theoretical methods combined with physical modeling in ice basins are used for determination of the ship ice resistance under brash ice conditions. The paper traces the evolution of theoretical models utilized for calculations. It is mentioned that the models are mainly based on loose material mechanics. A rapidly developing computer modeling of ship motion in brash ice based on discrete element method is considered. Physical modeling techniques used for modeling brash ice in ice basin are described, and challenges of experimental investigations are discussed. It is pointed out that experimental studies in ice basin can provide valuable data not only about ship ice resistance but also about the mechanisms giving rise to ice channels filled with brash ice. The paper describes the methods for studying operation of ship propellers in brash ice conditions. It is concluded that further research into brash ice is needed.В статье приведен обзор исследований, посвященных изучению движения судов в тертых льдах. Показано, что для определения ледового сопротивления судна в указанных условиях используются теоретические методы исследования и метод физического моделирования в ледовых бассейнах. В работе прослежена эволюция теоретических моделей, применяемых для расчета. Описаны методы физического моделирования тертого льда в ледовом бассейне, обсуждены основные трудности, возникающие при экспериментальных исследованиях. Рассмотрено активно развивающееся в настоящее время компьютерное моделирование движения судна в тертых льдах на основе методов дискретных элементов. Дано описание методов изучения работы движителей судов в тертых льдах
New Kinds of Acoustic Solitons
We find that the modified sine-Gordon equation belonging to the class of the
soliton equations describes the propagation of extremely short transverse
acoustic pulses through the low-temperature crystal containing paramagnetic
impurities with effective spin S=1/2 in the Voigt geometry case. The features
of nonlinear dynamics of strain field and effective spins, which correspond to
the different kinds of acoustic solitons, are studied.Comment: 9 pages, 1 figur
Luminosity Function of High-Mass X-ray Binaries and Anisotropy in the Distribution of Active Galactic Nuclei toward the Large Magellanic Cloud
In 2003-2012, the INTEGRAL observatory has performed long-term observations
of the Large Magellanic Cloud (LMC). At present, this is one of the deepest
hard X-ray (20-60 keV) surveys of extragalactic fields in which more than 20
sources of different natures have been detected. We present the results of a
statistical analysis of the population of high-mass X-ray binaries in the LMC
and active galactic nuclei (AGNs) observed in its direction. The hard X-ray
luminosity function of high-mass X-ray binaries is shown to be described by a
power law with a slope alpha~1.8, that in agreement with the luminosity
function measurements both in the LMC itself, but made in the soft X-ray energy
band, and in other galaxies. At the same time, the number of detected AGNs
toward the LMC turns out to be considerably smaller than the number of AGNs
registered in other directions, in particular, toward the source 3C 273. The
latter confirms the previously made assumption that the distribution of matter
in the local Universe is nonuniform.Comment: 5 pages, 5 figures, will be published in Astronomy Letters, 2012,
Vol. 38, No. 8, p. 492--49
Polarization of X-ray lines from galaxy clusters and elliptical galaxies - a way to measure tangential component of gas velocity
We study the impact of gas motions on the polarization of bright X-ray
emission lines from the hot intercluster medium (ICM). The polarization
naturally arises from resonant scattering of emission lines owing to a
quadrupole component in the radiation field produced by a centrally peaked gas
density distribution. If differential gas motions are present then a photon
emitted in one region of the cluster will be scattered in another region only
if their relative velocities are small enough and the Doppler shift of the
photon energy does not exceed the line width. This affects both the degree and
the direction of polarization. The changes in the polarization signal are in
particular sensitive to the gas motions perpendicular to the line of sight. We
calculate the expected degree of polarization for several patterns of gas
motions, including a slow inflow expected in a simple cooling flow model and a
fast outflow in an expanding spherical shock wave. In both cases, the effect of
non-zero gas velocities is found to be minor. We also calculate the
polarization signal for a set of clusters, taken from large-scale structure
simulations and evaluate the impact of the gas bulk motions on the polarization
signal. We argue that the expected degree of polarization is within reach of
the next generation of space X-ray polarimeters.Comment: 25 pages, 18 figures, accepted to MNRA
X-ray line formation in the spectrum of SS 433
The mechanisms for the formation of X-ray lines in the spectrum of SS 433 are
investigated by taking into account the radiative transfer inside the jets. The
results of Monte Carlo numerical simulations are presented. The effect of a
decrease in line intensity due to scattering inside the jet turns out to be
pronounced, but it does not exceed 60% in magnitude on the entire grid of
parameters. The line broadening due to scattering, nutational motion, and the
contribution of satellites can lead to overestimates of the jet opening angle
from the line widths in Chandra X-ray observations. The fine structure
of the lines turns out to be very sensitive to the scattering effects. This
makes its investigation by planned X-ray observatories equipped with
high-resolution spectrometers (primarily Astro-H) a powerful tool for
diagnosing the parameters of the jets in SS 433.Comment: 23 pages, 14 figures, to be published in Astronomy Letters, v. 38, n.
7, p. 443 (2012
Lightweight amorphous silicon photovoltaic modules on flexible plastic substrate
Solar cells on lightweight and flexible substrates have advantages over glass-or wafer-based photovoltaic devices in both terrestrial and space applications. Here, we report on development of amorphous silicon thin film photovoltaic modules fabricated at maximum deposition temperature of 150 degrees C on 100 mu m thick polyethylene-naphtalate plastic films. Each module of 10 cm x 10 cm area consists of 72 a-Si:H n-i-p rectangular structures with transparent conducting oxide top electrodes with Al fingers and metal back electrodes deposited through the shadow masks. Individual structures are connected in series forming eight rows with connection ports provided for external blocking diodes. The design optimization and device performance analysis are performed using a developed SPICE model
Phase diagram of Eu magnetic ordering in Sn-flux-grown Eu(FeCo)As single crystals
The magnetic ground state of the Eu moments in a series of
Eu(FeCo)As single crystals grown from the Sn flux has
been investigated in detail by neutron diffraction measurements. Combined with
the results from the macroscopic properties (resistivity, magnetic
susceptibility and specific heat) measurements, a phase diagram describing how
the Eu magnetic order evolves with Co doping in
Eu(FeCo)As is established. The ground-state magnetic
structure of the Eu spins is found to develop from the A-type
antiferromagnetic (AFM) order in the parent compound, via the A-type canted AFM
structure with some net ferromagnetic (FM) moment component along the
crystallographic direction at intermediate Co doping levels,
finally to the pure FM order at relatively high Co doping levels. The ordering
temperature of Eu declines linearly at first, reaches the minimum value of
16.5(2) K around = 0.100(4), and then reverses upwards with
further Co doping. The doping-induced modification of the indirect
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the Eu moments,
which is mediated by the conduction electrons on the (Fe,Co)As
layers, as well as the change of the strength of the direct interaction between
the Eu and Fe moments, might be responsible for the change of the
magnetic ground state and the ordering temperature of the Eu sublattice. In
addition, for Eu(FeCo)As single crystals with 0.10
0.18, strong ferromagnetism from the Eu
sublattice is well developed in the superconducting state, where a spontaneous
vortex state is expected to account for the compromise between the two
competing phenomena.Comment: 10 pages, 9 figure
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