2,842 research outputs found
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
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
SDSS J170745+302056: a low surface brightness galaxy in a group
On the basis of the SDSS survey and spectral observations with the 6-m
telescope of SAO RAS, we have peformed a detailed study of SDSS J170745+302056.
By combination of its characteristics -- exponential surface brightness
distribution, central surface brightness of stellar disk \mu_0(B) =
23.25\,^m/\square", blue colors, low metallicity and low star formation rate
-- the galaxy is a typical low surface brightness spiral galaxy. Exponential
scalelength of the galaxy is 3 kpc, its optical diameter exceeds 20
kpc. SDSS J170745+302056 is a member of a group of five galaxies and probably
it is in interaction with UGC 10716. The existence of a large low surface
brightness galaxy in such a dense environment is very unusual.Comment: 8 pages, 4 figure
Kinematics of CMEs and associated shock waves as deduced from LASCO data: comparative analysis
From data by LASCO C2 and C3 coronagraphs, depending on time (distance), we
have determined positions and velocities of the front for fast limb CMEs' body
with their sources near the limb, and for the body of halo-type CME with the
sources near the solar disk center. These characteristics of CME body are
compared to similar kinematic characteristics obtained for CME body-associated
shock waves (shocks). For the body of halo-type CME with the sources near the
solar disk center and associated shocks, we determined and compared their
kinematic characteristics in 3D space. It has been shown that for all the
considered CME groups, the shock velocity is higher than the CME body velocity,
both velocities decrease as the mass ejection moves. As this takes place, the
distance between CME body and shock grows. On average, distance from CME body
to shock, and velocity difference of these structures is greater for a halo
CME, and even greater for a model CME in 3D
With no Color and Scent (part II): Metal and Alloy Microstructures-Handmade Replicas of Natural Objects
As a continuation of work on metal and alloy "plants" synthesis on porous
membranes by means of pulsed current electroplating volume metallic
microstructures resembling such natural objects as shells, cabbage leaves,
mushrooms are grown and presented in their modest elegance. Such structures are
formed from PdNi and PdCo alloys as well as Ag, Cu and Ni in conditions defined
by the shape of membrane pores and the parameters of the pulsed current. It is
shown that the obtained complex structures are formed by layers of metallic
nanowires as a result of their self-assembly while growing during the pulsed
current electroplating process. Depending on the shape of the membrane and the
regime of the pulsed current electroplating either one type of shell-like
structures or various structures can be grown.Comment: 11pages, 10 figure
Current-induced magnetization dynamics at the edge of a two-dimensional electron system with strong spin-orbit coupling
We experimentally investigate electron transport through the interface
between a permalloy ferromagnet and the edge of a two-dimensional electron
system with strong Rashba-type spin-orbit coupling. We observe strongly
non-linear transport around zero bias at millikelvin temperatures. The observed
nonlinearity is fully suppressed above some critical values of temperature,
magnetic field, and current through the interface. We interpret this behavior
as the result of spin accumulation at the interface and its current-induced
absorption as a magnetization torque.Comment: 6 pages, minor correction
Interacting galaxy NGC4656 and its unusual dwarf companion
We studied the nearby edge-on galaxy NGC4656 and its dwarf low surface
brightness companion with the enhanced UV brightness, NGC4656UV, belonging to
the interacting system NGC4631/56. Regular photometric structure and relatively
big size of NGC4656UV allows to consider this dwarf galaxy as a separate group
member rather than a tidal dwarf. Spectral long-slit observations were used to
obtain the kinematical parameters and gas-phase metallicity of NGC4656UV and
NGC4656. Our rough estimate of the total dynamical mass of NGC4656UV allowed us
to conclude that this galaxy is the dark-matter dominated LSB dwarf or ultra
diffuse galaxy. Young stellar population of NGC4656UV, as well as strong local
non-circular gas motions in NGC4656 and the low oxygen gas abundance in the
region of this galaxy adjacent to its dwarf companion, give evidence in favour
of the accretion of metal-poor gas onto the discs of both galaxies.Comment: 8 pages, 2 tables, 9 figures, accepted for publication in MNRA
Optical and infrared emission of H II complexes as a clue to the PAH life cycle
We present an analysis of optical spectroscopy and infrared aperture
photometry of more than 100 H II complexes in nine galaxies. Spectra obtained
with the 6-m telescope of SAO RAS are used along with archival data from
Spitzer and several ground-based telescopes to infer a strength of polycyclic
aromatic hydrocarbon (PAH) emission, age, properties of the UV radiation field,
and metallicity of studied H II complexes. Physical properties (age, radiation
field parameters, metallicity) are related to the ratio used as
a proxy for the PAH abundance in order to reveal factors that may influence the
PAH evolution in H II complexes. The well-known correlation between the
ratio and metallicity is confirmed in the studied complexes. The
infrared flux ratio also correlates with the [O III] ratio which is often considered as an indicator of the
radiation field hardness, but this correlation seems to be a mere reflection of
a correlation between [O III] and metallicity. In
separate metallicity bins, the ratio is found to correlate with
an age of an H II complex, which is estimated from the equivalent width of
line. The correlation is positive for low metallicity
complexes and negative for high metallicity complexes. Analysing various
mechanisms of PAH formation and destruction in the context of found
correlations, we suggest that PAH abundance is likely altered by the UV
radiation within H II complexes, but this is not necessarily due to their
destruction. If PAHs can also form in H II complexes due to some processes like
aromatisation, photodestruction, shattering and sputtering of very small
grains, the net ratio is determined by a balance between all
these processes that can be different at different metallicities.Comment: Accepted to MNRA
Dust Evolution in the Dwarf Galaxy Holmberg II
A detailed photometric study of star-forming regions (SFRs) in the galaxy
Holmberg II has been carried out using archival observational data from the far
infrared to ultraviolet obtained with the GALEX, Spitzer, and Herschel
telescopes. Spectroscopic observations with the 6-m telescope of Special
Astrophysical Observatory of the Russian Academy of Sciences are used to
estimate ages and metallicities of SFRs. For the first time, the ages of SFRs
have been related to their emission parameters in a wide spectral range and
with the physical parameters determined by fitting the observed spectra. It is
shown that fluxes at 8 and 24 micron characterizing the emission of polycyclic
aromatic hydrocarbons (PAHs) and hot dust grains decrease with age, but their
ratio increases. This implies that the relative PAH contribution to the total
infrared flux increases with age. It is suggested that the detected increase in
the ratio of the fluxes at 8 and 24 micron is related to the growth in the PAH
mass due to destruction of larger grains.Comment: 15 pages, 8 figures, 3 tables. Published in Astronomy Letter
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