462 research outputs found
Star formation in the S233 region
The main objective of this paper is to study the possibility of triggered
star formation on the border of the HII region S233, which is formed by a
B-star. Using high-resolution spectra we determine the spectral class of the
ionizing star as B0.5 V and the radial velocity of the star to be -17.5(1.4)
km/s. This value is consistent with the velocity of gas in a wide field across
the S233 region, suggesting that the ionizing star was formed from a parent
cloud belonging to the S233 region. By studying spatial-kinematic structure of
the molecular cloud in the S233 region, we detected an isolated clump of gas
producing CO emission red-shifted relative to the parent cloud. In the UKIDSS
and WISE images, the clump of gas coincides with the infrared source containing
a compact object and bright-rimmed structure. The bright-rimmed structure is
perpendicular to the direction of the ionizing star. The compact source
coincides in position with IRAS source 05351+3549. All these features indicate
a possibility of triggering formation of a next-generation star in the S233
region. Within the framework of a theoretical one-dimensional model we conclude
that the "collect-and-collapse" process is not likely to take place in the S233
region. The presence of the bright-rimmed structure and the compact infrared
source suggest that the "collapse of the pre-existing clump" process is taking
place.Comment: 12 pages, 10 figure
On the methanol emission detection in the TW Hya disc: the role of grain surface chemistry and non-LTE excitation
The recent detection of gas-phase methanol (CHOH) lines in the disc of TW
Hya by Walsh et al. provided the first observational constraints on the complex
O-bearing organic content in protoplanetary discs. The emission has a ring-like
morphology, with a peak at au and an inferred column density of
cm. A low CHOH fractional abundance of (with respect to H) is derived, depending on the
assumed vertical location of the CHOH molecular layer. In this study, we
use a thermo-chemical model of the TW Hya disc, coupled with the ALCHEMIC
gas-grain chemical model, assuming laboratory-motivated, fast diffusivities of
the surface molecules to interpret the CHOH detection. Based on this disc
model, we performed radiative transfer calculations with the LIME code and
simulations of the observations with the CASA simulator. We found that our
model allows to reproduce the observations well. The CHOH emission in our
model appears as a ring with radius of au. Synthetic and observed line
flux densities are equal within the rms noise level of observations. The
synthetic CHOH spectra calculated assuming local thermodynamic equilibrium
(LTE) can differ by up to a factor of 3.5 from the non-LTE spectra. For the
strongest lines, the differences between LTE and non-LTE flux densities are
very small and practically negligible. Variations in the diffusivity of the
surface molecules can lead to variations of the CHOH abundance and,
therefore, line flux densities by an order of magnitude.Comment: Accepted for publication in MNRAS, 8 pages, 8 figure
Towards detecting methanol emission in low-mass protoplanetary discs with ALMA:The role of non-LTE excitation
The understanding of organic content of protoplanetary discs is one of the
main goals of the planet formation studies. As an attempt to guide the
observational searches for weak lines of complex species in discs, we modelled
the (sub-)millimetre spectrum of gaseous methanol (CHOH), one of the
simplest organic molecules, in the representative T Tauri system. We used 1+1D
disc physical model coupled to the gas-grain ALCHEMIC chemical model with and
without 2D-turbulent mixing. The computed CHOH abundances along with the
CHOH scheme of energy levels of ground and excited torsional states were
used to produce model spectra obtained with the non-local thermodynamic
equilibrium (non-LTE) 3D line radiative transfer code LIME. We found that the
modelled non-LTE intensities of the CHOH lines can be lower by factor of
-- than those calculated under assumption of LTE. Though population
inversion occurs in the model calculations for many (sub-)millimetre
transitions, it does not lead to the strong maser amplification and noticeably
high line intensities. We identify the strongest CHOH (sub-)millimetre
lines that could be searched for with the Atacama Large Millimeter Array (ALMA)
in nearby discs. The two best candidates are the CHOH
(241.791 GHz) and (241.767 GHz) lines, which could possibly
be detected with the signal-to-noise ratio after hours of
integration with the full ALMA array.Comment: Accepted for publication in MNRAS, 15 figures, 3 table
Outpatient management of patients with dyscirculatory encephalopathy
There is outpatient hyperdiagnosis of dyscirculatory encephalopathy (DE) frequently masked by other diseases. Objective: to improve the differential diagnosis of DE on the basis of a comprehensive patient examination, including neuropsychological testing. Patients and methods. Fifty patients, including 10 men and 40 women, aged 45 to 75 years (mean age 68.8±9.0 years), who had been followed up at the polyclinic with a diagnosis of DE for an average of 1.5 years, were examined. All the patients underwent evaluations of cognitive functions and emotional status and otoneurological examination (in case of headache); a psychiatrist consulted patients with anxiety and/or depressive disorders. Results and discussion. Only 9 (18%) patients were found to have vascular cognitive impairments (CIs) and signs of cerebrovascular lesions, as shown by neuroimaging, which may be regarded as DE. Five (10%) patients had CIs and neuroimaging changes that were more characteristic of Alzheimer’s disease (AD) than those of DE. The remaining 36 (72%) patients were established to have other diseases (primary headache, peripheral vestibulopathy, primary anxiety and depressive disorders, etc.), in which CIs were not detected. The diagnosis and effective treatment of these diseases yielded a rapid positive result in most cases. The management of patients with DE and AD was aimed at preventing stroke and improving cognitive functions; moreover, akatinol memantine was noted to be effective in the combination therapy of both DE and AD
Thermoelectric performance of weakly coupled granular materials
We study thermoelectric properties of inhomogeneous nanogranular materials
for weak tunneling conductance between the grains, g_t < 1. We calculate the
thermopower and figure of merit taking into account the shift of the chemical
potential and the asymmetry of the density of states in the vicinity of the
Fermi surface. We show that the weak coupling between the grains leads to a
high thermopower and low thermal conductivity resulting in relatively high
values of the figure of merit on the order of one. We estimate the temperature
at which the figure of merit has its maximum value for two- and
three-dimensional samples. Our results are applicable for many emerging
materials, including artificially self-assembled nanoparticle arrays.Comment: 4 pages, 3 figure
Thermoelectric performance of granular semiconductors
We study thermoelectric properties of granular semiconductors with weak
tunneling conductance between the grains, g_t < 1. We calculate the thermopower
and figure of merit taking into account the shift of the chemical potential and
the asymmetry of the density of states in the vicinity of the Fermi surface due
to n- or p-type doping in the Efros-Shklovskii regime for temperatures less
than the charging energy. We show that for weakly coupled semiconducting grains
the figure of merit is optimized for grain sizes of order 5nm for typical
materials and its values can be larger than one. We also study the case of
compensated granular semiconductors and show that in this case the thermopower
can be still finite, although two to three orders of magnitude smaller than in
the uncompensated regime.Comment: 4 pages, 4 figure
The Effect of High Background and Dead Time of an InGaAs/InP Single-Photon Avalanche Photodiode on the Registration of Microsecond Range Near-Infrared Luminescence
The effects of a high background count and a microsecond dead time interval on a gated InGaAs/InP single-photon avalanche photodiode (SPAD) during microsecond luminescence decay registration are discussed. It is shown that the background count rate of the SPAD limits its use for time-resolved and steady-spectral measurements, and that a “pile-up” effect appears in the microsecond range
ALMA sub-mm maser and dust distribution of VY Canis Majoris
Cool, evolved stars have copious, enriched winds. The structure of these
winds and the way they are accelerated is not well known. We need to improve
our understanding by studying the dynamics from the pulsating stellar surface
to about 10 stellar radii, where radiation pressure on dust is fully effective.
Some red supergiants have highly asymmetric nebulae, implicating additional
forces. We retrieved ALMA Science Verification data providing images of sub-mm
line and continuum emission from VY CMa. This enables us to locate water masers
with milli-arcsec precision and resolve the dusty continuum. The 658-, 321- and
325-GHz masers lie in irregular, thick shells at increasing distances from the
centre of expansion. For the first time this is confirmed as the stellar
position, coinciding with a compact peak offset to the NW of the brightest
continuum emission. The maser shells (and dust formation zone) overlap but
avoid each other on tens-au scales. Their distribution is broadly consistent
with excitation models but the conditions and kinematics appear to be
complicated by wind collisions, clumping and asymmetries.Comment: Letter 4 pages, 5 figures plus appendix with 3 figures. Accepted by
Astronomy and Astrophysics Letter
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