4,293 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
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
Photospheric magnetic field variations accompanying the 2011 June 7 eruptive event
From vector measurements of the photospheric magnetic field with the SDO/HMI
instrument, we studied the field variations within the 2011 June 7 eruptive
event related to the filament eruption (FE), flare, and coronal mass ejection
(CME). We analyzed the variations in modulus (B), in radial (Br) and
transversal (Bt) magnetic induction components, as well as in the field line
inclination angle ({\alpha}) to the radial direction from the Sun center were.
The conclusion is that the most probable cause for the FE onset being the
trigger related to the flares and CME, as well as for Stage 1 of the filament
dramatic acceleration, is {\guillemotleft}magnetic flux
cancellation{\guillemotright} in several sites inside and around the filament
channel. We assumed that the flare and the stage of the filament fastest
acceleration are related to a spot emergence near the south-eastern filament
footpoint, in which the field polarity and value satisfy a possibility of this
field magnetic reconnection with the field surrounding the filament. We studied
in detail the time variations in the field line inclination angles within
different sites of the eruptive event. During the filament slow emergence, a
decrease in the field line inclination angles was revealed to occur in its
channel neighboring, whereas the field line inclination angles dramatically
grew in the neutral line neighboring within the flare region after the flare
onset. The flare ribbons at all the stages of their existence are shown to be
located under the photosphere sites with the field modulus local maxima and
with minima of the field line inclination angles. We show that, near the
photospheric magnetic field polarity inversion line (PIL), the azimuth
decreases after the flare onset, which means a decrease in the angle \b{eta}
between PIL and the magnetic induction vector projection onto the sky plane
Triggered star formation in giant HI supershells: ionized gas
We considered the regions of triggered star formation inside kpc-sized HI
supershells in three dwarf galaxies: IC 1613, IC 2574 and Holmberg II. The
ionized and neutral gas morphology and kinematics were studied based on our
observations with scanning Fabry-Perot interferometer at the SAO RAS 6-m
telescope and 21 cm archival data of THINGS and LITTLE THINGS surveys. The
qualitative analysis of the observational data performed in order to highlight
the two questions: why the star formation occurred very locally in the
supershells, and how the ongoing star formation in HI supershells rims
influence its evolution? During the investigation we discovered the phenomenon
never observed before in galaxies IC 2574 and Holmberg II: we found faint giant
(kpc-sized) ionized shells in H-alpha and [SII]6717,6731 lines inside the
supergiant HI shells.Comment: Published in proceedings of the conference "Galaxies" (Essentuki,
Russia, November 24-28, 2014). 9 pages, 4 figure
Emission spectrum of ionized gas in the Irr galaxy Holmberg II
We study the ionized gas spectrum of star forming regions in the Holmberg II
galaxy using the optical long-slit spectroscopic observations made at the 6-m
telescope of the Special Astrophysical Observatory of the Russian Academy of
Sciences (SAO RAS). We estimate the oxygen, nitrogen, sulphur, neon, and argon
abundances in individual HII regions and find the average metallicity in the
galaxy to be Z=0.1 or 0.3 Zsun depending on the estimation method employed. We
use these observations combined with the results of our earlier studies of the
Irr galaxy IC 10 and BCD galaxy VII Zw 403 to compare the currently most
popular methods of gas metallicity estimation in order to select among them the
techniques that are most reliable for analysing Irr galaxies. To this end, we
use the "direct" Te method and six empirical and theoretical methods. The
results of our observations mostly confirm the conclusions of Lopez-Sanchez et
al. (2012) based on the analysis of systematic deviations of metallicity
estimates derived by applying different methods to "model" HII regions.Comment: 17 pages, 8 figures, 4 tables. Landscape tables 2 and 3 are on the
last pages. Accepted by MNRA
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
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
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