4,192 research outputs found
Discovery of a Planar Waveguide for an X-Ray Radiation
A simple model of X-Ray standing waves (XSW) formation in the slit of a
planar waveguide of X-Ray radiation beam for the angle area restricted by the
critical total reflection angle is developed. It is shown that the model is
true for a case of the Bragg reflection. The conditions required for XSW to
appear in the space between two polished parallel plane plates are formulated
and a slit size interval conforming to these conditions is evaluated. A
mechanism of a XSW intensity decrease in a planar waveguide is proposed. This
mechanism explains a high efficiency of slitless collimator application for the
transportation of narrow X-Ray beams.
Some recommendations on the application of the planar X-Ray waveguide in
X-Ray structural and spectral studies of surface are presented.Comment: 15 pages, 2 figures, 1 tabl
Riemannian Spin(7) holonomy manifold carries octonionic-Kahler structure
We prove that Riemannian holonomy manifolds carry
octonionic-K\"{a}hler structure.Comment: 5 page
Symplectic analog of Calabi's conjecture for Calabi--Yau threefolds
In this paper we state an analog of Calabi's conjecture proved by Yau. The
difference with the classical case is that we propose deformation of the
complex structure, whereas the complex Monge--Amp\`{e}re equation describes
deformation of the K\"{a}hler (symplectic) structure.Comment: 4 pages. This is a revised version of "Mirror Kaehler potential on
Calabi-Yau threefolds" arXiv:1110.473
Metallicity and ionization state of the gas in polar-ring galaxies
The ionization state and oxygen abundance distribution in a sample of
polar-ring galaxies (PRGs) were studied from the long-slit spectroscopic
observations carried out with the SCORPIO-2 focal reducer at the Russian 6-m
telescope. The sample consists of 15 PRGs classified as `the best candidates'
in the SDSS-based Polar Ring Catalogue. The distributions of line-of-sight
velocities of stellar and gaseous components have given kinematic confirmation
of polar structures in 13 galaxies in the sample. We show that ionization by
young stars dominates in the external parts of polar discs, while shocks have a
significant contribution to gas excitation in the inner parts of polar
structures. This picture was predicted earlier in a toy model implying the
collision between gaseous clouds on polar orbits with the stellar disc
gravitational potential well. The exception is a moderately inclined ring to
the host galaxy NGC 5014: the accreted gas in the centre has already settled on
the main plane and ionized by young stars, while the gas in the internal part
of the ring is excited by shocks. The present study three times increases the
number of polar structures with an available oxygen abundance estimation. The
measured values of the gas metallicity almost do not depend on the galaxy
luminosity. The radial [O/H] gradient in the considered polar rings is shallow
or absent. No metal-poor gas was detected. We ruled out the scenario of the
formation of polar rings due to cold accretion from cosmic filaments for the
considered sample of PRGs.Comment: 13 pages, accepted for publication in MNRA
Memory effects in permalloy-niobium hybrid structures
The kineticts of magnetization reversal of stripe-shaped permalloy-niobium
hybrid nanofilms is studied in 6-300 K temperature range by means of
magneto-optics visualization technique. The niobium influence on magnetic
domain walls type and on magnetic domain structure of permalloy via the
interface quality and via the distortion of stray fields is found. The memory
effect, which is the superconducting niobium memory about an initial magnetic
domain structure of permalloy at cooling below T_c, is found. The memory is
razed only by hybrid heating over T_c
Current and field stimulated motion of domain wall in narrow permalloy stripe
Of the new types of cryoelectronic devices under development, including phase
shifters, giant magnetoresistance switches, diodes, transistors, and memory
cells, some are based on hybrid superconductor-normal metal or
superconductor-ferromagnet films. Control of these devices is realized by means
of pulses of voltage, light, or magnetic field. Spin-polarized current may be
used to switch low-temperature devices, as in spin-electronic devices. In the
superconducting layer, the current is dissipation less, which would bring large
reduction of energy consumption. We demonstrate that mag-netic domain walls in
bilayer niobium-permalloy stripes are shifted by electrical current along the
stripe even at low tem-perature, with the niobium in the superconducting state.
The wall motion in response to current pulses is quite different from that
induced by a magnetic field pulses only. The effect could be used to create a
new type of sequentially switched serial devices because of very high value of
the wall velocity, which excides by many orders of magnitude the velocity of
the wall moved with magnetic field pulses.Comment: 5 pages, 6 figure
Super pulses of orbital angular momentum in fractional-order spiroid vortex-beams
We consider optical properties of Hypergeometric-Gaussian beam compositions
with spiral-like intensity and phase distributions that were called the spiroid
beams. Their orbital angular momentum as a function of a fractional-order
topological charge has a chain of supper-pulses (bursts and dips).The form of
the supper-pulses can be controlled by the spiral parameters. Such a phenomenon
can be used in optical switches and triggers for optical devices and
communication systems.Comment: 4 pages, 7 figure
Study of CME properties using high resolution data
The joint use of high-resolution data from PROBA2 and SDO satellites and
LASCO/SOHO coronographs enabled us to examine early stages of initiation and
propagation of six limb CMEs registered in June 2010 - June 2011. For five
events under consideration, the CME initiation is marked by filament
(prominence) eruption or by a loop-like structure having another nature.
Subsequently, several loop-like structures having higher brightness and
following each other at different velocities appear in the region of the CME
initiation. The CME frontal structure is formed by these loop-like structures.
The time-dependent velocities and acceleration of the ejection front have been
obtained for all CMEs under consideration. We have drawn a conclusion about the
possible existence of two CME types dependent on the time profile of their
velocity. The first CME type comprises the ejections whose velocity decreases
abruptly by more than 100 km/s after having reached the maximum; it thereupon
passes to slow deceleration/variation. The second CME type is formed by the
ejections whose velocity varies insignificantly after reaching the maximum. The
CME angular size is shown to increase up to threefold at the initial stage of
propagation; it increases twofold 3.5-11 minutes after the first measurement of
this parameter. When considering 3 CMEs, we see that their broadening exceeds
their extension in the longitudinal direction during a certain period of time
at the initial propagation stage.Comment: 16 pages, 8 figure
Origin of a CME-related shock within the LASCO C3 field-of-view
We study the origin of a CME-related shock within the LASCO C3 field-of-view
(FOV). A shock originates, when a CME body velocity on its axis surpasses the
total velocity , where is the Alfv\'en velocity,
is the slow solar wind velocity. The formed shock appears collisionless,
because its front width is manifold less, than the free path of coronal plasma
charged particles. The Alfv\'en velocity dependence on the distance was found
by using characteristic values of the magnetic induction radial component and
of the proton concentration in the Earth orbit, and by using the known
regularities of the variations in these solar wind characteristics with
distance. A peculiarity of the analyzed CME is its formation at a relatively
large height, and the CME body slow acceleration with distance. We arrived at a
conclusion that the formed shock is a bow one relative to the CME body moving
at a super Alfv\'en velocity. At the same time, the shock formation involves a
steeping of the front edge of the coronal plasma disturbed region ahead of the
CME body, which is characteristic of a piston shock
Search for gas accretion imprints in voids: I. Sample selection and results for NGC 428
We present the first results of a project aimed at searching for gas
accretion events and interactions between late-type galaxies in the void
environment. The project is based on long-slit spectroscopic and scanning
Fabry-Perot interferometer observations performed with the SCORPIO and
SCORPIO-2 multimode instruments at the Russian 6-m telescope, as well as
archival multiwavelength photometric data. In the first paper of the series we
describe the project and present a sample of 18 void galaxies with oxygen
abundances that fall below the reference `metallicity-luminosity' relation, or
with possible signs of recent external accretion in their optical morphology.
To demonstrate our approach, we considered the brightest sample galaxy NGC 428,
a late-type barred spiral with several morphological peculiarities. We analysed
the radial metallicity distribution, the ionized gas line-of-sight velocity and
velocity dispersion maps together with WISE and SDSS images. Despite its very
perturbed morphology, the velocity field of ionized gas in NGC 428 is well
described by pure circular rotation in a thin flat disc with streaming motions
in the central bar. We also found some local non-circular gas motions clearly
related to stellar feedback processes. At the same time, we revealed a
circumnuclear inclined disc in NGC 428 and a region with significant residual
velocities that could be considered as a result of a recent (<0.5 Gyr)
accretion event. The observed oxygen abundance gradient does not contradict
this conclusion.Comment: Accepted for publication in MNRAS; 13 pages, 10 figures, 4 table
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