868 research outputs found
Parsec-scale evolution of the gigahertz-peaked spectrum quasar PKS 0858-279
We conducted multi-epoch, multi-frequency parsec-scale studies on the
gigahertz-peaked spectrum quasar PKS 0858-279 with the Very Long Baseline Array
(VLBA). Our observations on 2005-11-26 elucidated a weak core, characterized by
an inverted spectrum, and a distinctly bent jet that exhibited a notable bright
feature in its Stokes I emission. Through comprehensive analysis of
polarization and spectral data, we inferred the formation of a shock wave
within this feature, stemming from interactions with a dense cloud in the
ambient medium. In this paper, VLBI-Gaia astrometry further reinforces the core
identification. With a deep analysis of six additional VLBA epochs spanning
from 2007 to 2018, we observed that while the quasar's parsec-scale structure
remained largely consistent, there were discernible flux density changes. These
variations strongly imply the recurrent ejection of plasma into the jet.
Complementing our VLBA data, RATAN-600 observations of the integrated spectra
suggested an interaction between standing and travelling shock waves in 2005.
Moreover, our multi-epoch polarization analysis revealed a drastic drop in
rotation measure values from 6000 rad/m^2 to 1000 rad/m^2 within a single year,
attributable to diminishing magnetic fields and particle density in an external
cloud. This change is likely instigated by a shock in the cloud, triggered by
the cloud's interaction with the jet, subsequently prompting its expansion.
Notably, we also observed a significant change in the magnetic field direction
of the jet, from being perpendicular post its observed bend to being
perpendicular prior to the bend - an alteration possibly induced by the
dynamics of shock waves.Comment: 14 pages, 10 figures, accepted for publication in MNRA
Group analysis and renormgroup symmetries
An original regular approach to constructing special type symmetries for
boundary value problems, namely renormgroup symmetries, is presented. Different
methods of calculating these symmetries, based on modern group analysis are
described. Application of the approach to boundary value problems is
demonstrated with the help of a simple mathematical model.Comment: 17 pages, RevTeX LATeX file, to appear in Journal of Mathematical
Physic
Determining the Young's modulus of a cellular titanium implant by FEM simulation
The role of additive manufacturing is noted for the construction of titanium medical implants. The purpose of the study is to determine the Young's modulus of cellular titanium implants, which is based on calculations performed by finite element analysis. A honeycomb structure from intersecting cylinder surfaces is offered for the implant made of the Ti-6Al-4V alloy. Boundary conditions are stated for the loading of the implant structure. It is demonstrated that the Young's modulus can be reduced more than three times comparing to a solid titanium alloy. Zones of strain and stress localization located near the abutment of the cylindrical surfaces. Recommendations for the further improvement of the implant architecture are generated. © 2017 Author(s).Ministry of Education and Science of the Russian Federation, Minobrnauka: 218We hereby acknowledge the support of the Ministry of Science and Education of the Russian Federation, in accordance with the decree of the Government of April 9, 2010, No. 218, project number 03.G25.31.0234
X-ray Diffraction Study of Superstructure in GdBaCo2O5.5
A single crystal of GdBaCo2O5.47(2) has been studied by means of X-ray
diffraction. Appearance of superstructure reflections at T = 341.5(7) K gives
an evidence of continuous transition to the phase with unit cell doubled along
the shortest edge a1. Critical exponent for the order parameter is found to be
beta=0.33(1). The superstructure reflections are about 2-4 orders of magnitude
weaker than the basic ones. Their systematic extinction indicates the crystal
symmetry change from Pmmm to Pmma. The integrated intensities allow to
calculate displacements of atoms from the positions in the high-temperature
phase. The cobalt-ligand distances in the ordered phase are discussed in terms
of the spin-state/orbital ordering of Co3+ ions.Comment: 4 page
Survey of Instantaneous 1-22 GHz Spectra of 550 Compact Extragalactic Objects with Declinations from -30deg to +43deg
We present observational results for extragalactic radio sources with
milliarcsecond components, obtained with the 600 meter ring radio telescope
RATAN-600 from 1st to 22nd December, 1997. For each source, a six frequency
broad band radio spectrum was obtained by observing simultaneously with an
accuracy up to a minute at 1.4, 2.7, 3.9, 7.7, 13 and 31 cm. The observed list
is selected from Preston et al. (1985) VLBI survey and contains all the sources
in the declinations between -30deg and +43deg with a correlated flux density
exceeding 0.1 Jy at 13 cm. The sample includes the majority of sources to be
studied in the current VSOP survey and the future RadioAstron Space VLBI
mission.Comment: 26 pages, 4 figures, 5 tables, published in the A&AS; figure 4 with
the broad-band spectra plots is included in the preprint; tables 1 and 5, in
electronic form, as well as the ReadMe file can be extracted from the
preprint sourc
Fabrication of bismuth films by a melt spinning method and the influence of annealing on their microstructure
The conditions of fabrication of bismuth films with thickness from 5 to 30 μm by a melt spinning method were studied. The microstructure of the fabricated films in the cross section was analyzed using SEM. The Bi films with thickness more than 5 μm consisted of crystallites with sizes up to 30 μm and had a layered structure with crystal twin
Nonlinear acoustic waves in channels with variable cross sections
The point symmetry group is studied for the generalized Webster-type equation
describing non-linear acoustic waves in lossy channels with variable cross
sections. It is shown that, for certain types of cross section profiles, the
admitted symmetry group is extended and the invariant solutions corresponding
to these profiles are obtained. Approximate analytic solutions to the
generalized Webster equation are derived for channels with smoothly varying
cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to
Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic
corrections introduced mainly in the Introduction and References. Several
typos were also correcte
Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine Scale Structure
We have used VLBA fringe visibility data obtained at 15 GHz to examine the
compact structure in 250 extragalactic radio sources. For 171 sources in our
sample, more than half of the total flux density seen by the VLBA remains
unresolved on the longest baselines. There are 163 sources in our list with a
median correlated flux density at 15 GHz in excess of 0.5 Jy on the longest
baselines. For about 60% of the sources, we have at least one observation in
which the core component appears unresolved (generally smaller than 0.05 mas)
in one direction, usually transverse to the direction into which the jet
extends. BL Lacs are on average more compact than quasars, while active
galaxies are on average less compact. Also, in an active galaxy the
sub-milliarcsecond core component tends to be less dominant. IDV sources
typically have a more compact, more core-dominated structure on
sub-milliarcsecond scales than non-IDV sources, and sources with a greater
amplitude of intra-day variations tend to have a greater unresolved VLBA flux
density. The objects known to be GeV gamma-ray loud appear to have a more
compact VLBA structure than the other sources in our sample. This suggests that
the mechanisms for the production of gamma-ray emission and for the generation
of compact radio synchrotron emitting features are related. The brightness
temperature estimates and lower limits for the cores in our sample typically
range between 10^11 and 10^13 K, but they extend up to 5x10^13 K, apparently in
excess of the equipartition brightness temperature, or the inverse Compton
limit for stationary synchrotron sources. The largest component speeds are
observed in radio sources with high observed brightness temperatures, as would
be expected from relativistic beaming (abridged).Comment: 31 pages, 13 figures, 4 tables, accepted for publication in the
Astronomical Journal; minor changes to the text are mad
Оценка боковой силы при взаимодействии колеса автомобиля с дорожной колеёй
The operation of roads under modern conditions associated with high speeds and traffic density results in wear of pavement and formation of a rut. When crossing the ruts, instability can occur when relatively small steering inputs lead to large changes in the trajectory. The lateral force acting on a wheel of a car is of particular importance in the study of stability and controllability. The magnitude of this force is determined by various factors: tire stiffness, speed, change in the angle of rotation of the wheel, the geometry of the transverse profile of the rut.The objective of the study refers to the problem of determining the angles of inclination of side walls of the rut that are safe for movement at different speeds. The paper considers the interaction of a car wheel with the road surface, proposes a mathematical model for interaction of a tire with ruts, considers the angle of the wheel running on the rut wall. To describe the elastic response of a tire in contact with a rut, an elastic foundation model and a plane section method are used. The lateral force was estimated based on equations of motion of the wheel when crossing the rut. The dependences of the ratio of the lateral force to the normal load for various rut depths and angles of inclination of its walls on the angle of rotation of the wheel and the speed of the vehicle were obtained. It is shown that at a rut inclination angle exceeding five degrees, the lateral force begins to increase significantly with an increase in the angle of rotation of the wheel, as well as the speed of the vehicle, and may exceed the applied normal load. According to the condition of vehicle stability against skidding on a wet surface, limiting average angles of inclination of the side walls of the rut are estimated for various values of the vehicle speed and wheel rotation angles.Эксплуатация дорог в современных условиях, связанных с высокими скоростями и плотностью потоков, приводит к изнашиванию покрытия и образованию дорожной колеи. При пересечении колеи может возникать неустойчивость движения, когда относительно небольшие воздействия при управлении приводят к большим изменениям траектории. Особое значение при изучении устойчивости и управляемости приобретает боковая сила, действующая на колесо автомобиля. Величина этой силы определяется различными факторами: жёсткостью шины, скоростью, изменением угла поворота колеса, геометрией поперечного профиля колеи.Цель настоящего исследования связана с проблемой определения безопасных для движения углов наклона боковых стенок дорожной колеи при разных скоростных режимах. В работе рассмотрено взаимодействие колеса автомобиля с дорожным покрытием, предложена математическая модель взаимодействия шины с колеёй, принимая во внимание угол набегания колеса на стенку колеи. Для описания упругого отклика шины в контакте с колеёй используется модель упругого основания и метод плоских сечений. На основе уравнений движения колеса при пересечении колеи проведена оценка боковой силы. Получены зависимости отношения боковой силы к нормальной нагрузке для различной глубины колеи и углов наклона её стенок от угла поворота колеса и скорости движения автомобиля. Показано, что при угле наклона колеи, превышающем пять градусов, боковая сила начинает существенно возрастать с ростом угла поворота колеса, а также скорости движения автомобиля и может превысить приложенную нормальную нагрузку. По условию устойчивости автомобиля против заноса на мокром покрытии дана оценка предельных средних углов наклона боковых стенок колеи при различных значениях скорости движения автомобиля и углов поворота колеса
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