562 research outputs found
The Arecibo Methanol Maser Galactic Plane Survey - II: Statistical and Multi-wavelength Counterpart Analysis
We present an analysis of the properties of the 6.7 GHz methanol maser sample
detected in the Arecibo Methanol Maser Galactic Plane Survey. The distribution
of the masers in the Galaxy, and statistics of their multi-wavelength
counterparts is consistent with the hypothesis of 6.7 GHz maser emission being
associated with massive young stellar objects. Using the detection statistics
of our survey, we estimate the minimum number of methanol masers in the Galaxy
to be 1275. The l-v diagram of the sample shows the tangent point of the
Carina-Sagittarius spiral arm to be around 49.6 degrees, and suggests
occurrence of massive star formation along the extension of the Crux-Scutum
arm. A Gaussian component analysis of the maser spectra shows the mean
line-width to be 0.38 km/s which is more than a factor of two larger than what
has been reported in the literature. We also find no evidence that faint
methanol masers have different properties than those of their bright
counterparts.Comment: Accepted by ApJ; Revised footnote number 3 on page 8 based on private
communicatio
ab-plane tunneling and Andreev spectroscopy of superconducting gap and pseudogap in (Bi,Pb)2Sr2Ca2Cu3O10 and Bi2Sr2CaCu2O8
We have measured the temperature dependence of gap features revealed by
Andreev reflection Delta_s and by tunneling Delta in the ab-plane of optimal
and slightly overdoped microcrystals of (BiPb)2Sr2Ca2Cu3O10 (Bi2223) with
critical temperature Tc=110-115 K, and Bi2Sr2CaCu2O8 (Bi2212) with Tc=80-84 K.
The tunneling conductance of Bi2223-Insulator-Bi2223 junction shows peaks at
the 2Delta gap voltage, as well as dips and broad humps at other voltages. In
Bi2223, similarly to the well known Bi2212 spectra, the energies corresponding
to 2Delta, to the dip, and to the hump structure are in the ratio of 2:3:4.
This confirms that the dip and hump features are generic to the high
temperature superconductors, irrespective of the number of CuO2 layers or the
BiO superstructure. On the other hand, in both compounds Delta(T) and
Delta_s(T) dependences are completely different, and we conclude that the two
entities have different nature.Comment: LaTeX 2e, 17 pages, 7 figures in .eps forma
The magnetic interactions in spin-glasslike Ge/1-x-y/Sn/x/Mn/y/Te diluted magnetic semiconductor
We investigated the nature of the magnetic phase transition in the
Ge/1-x-y/Sn/x/Mn/y/Te mixed crystals with chemical composition changing in the
range of 0.083 < x < 0.142 and 0.012 < y < 0.119. The DC magnetization
measurements performed in the magnetic field up to 90 kOe and temperature range
2-200 K showed that the magnetic ordering at temperatures below T = 50 K
exhibits features characteristic for both spin-glass and ferromagnetic phases.
The modified Sherrington - Southern model was applied to explain the observed
transition temperatures. The calculations showed that the spin-glass state is
preferred in the range of the experimental carrier concentrations and Mn
content. The value of the Mn hole exchange integral was estimated to be J/pd/ =
0.45+/-0.05 eV. The experimental magnetization vs temperature curves were
reproduced satisfactory using the non-interacting spin-wave theory with the
exchange constant J/pd/ values consistent with those calculated using modified
Sherrington - Southern model. The magnetization vs magnetic field curves showed
nonsaturating behavior at magnetic fields B < 90 kOe indicating the presence of
strong magnetic frustration in the system. The experimental results were
reproduced theoretically with good accuracy using the molecular field
approximation-based model of a disordered ferromagnet with long-range RKKY
interaction.Comment: 9 pages, 6 figure
VLBI study of maser kinematics in high-mass SFRs. II. G23.01-0.41
The present paper focuses on the high-mass star-forming region G23.01-0.41.
Methods: Using the VLBA and the EVN arrays, we conducted phase-referenced
observations of the three most powerful maser species in G23.01-0.41: H2O at
22.2 GHz (4 epochs), CH3OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1
epoch). In addition, we performed high-resolution (> 0".1), high-sensitivity (<
0.1 mJy) VLA observations of the radio continuum emission from the HMC at 1.3
and 3.6 cm. Results: We have detected H2O, CH3OH, and OH maser emission
clustered within 2000 AU from the center of a flattened HMC, oriented SE-NW,
from which emerges a massive 12CO outflow, elongated NE-SW, extended up to the
pc-scale. Although the three maser species show a clearly different spatial and
velocity distribution and sample distinct environments around the massive YSO,
the spatial symmetry and velocity field of each maser specie can be explained
in terms of expansion from a common center, which possibly denotes the position
of the YSO driving the maser motion. Water masers trace both a fast shock (up
to 50 km/s) closer to the YSO, powered by a wide-angle wind, and a slower (20
km/s) bipolar jet, at the base of the large-scale outflow. Since the compact
free-free emission is found offset from the putative location of the YSO along
a direction consistent with that of the maser jet axis, we interpret the radio
continuum in terms of a thermal jet. The velocity field of methanol masers can
be explained in terms of a composition of slow (4 km/s in amplitude) motions of
radial expansion and rotation about an axis approximately parallel to the maser
jet. Finally, the distribution of line of sight velocities of the hydroxyl
masers suggests that they can trace gas less dense (n(H2) < 10^6 cm^-3) and
more distant from the YSO than that traced by the water and methanol masers,
which is expanding toward the observer. (Abridged)Comment: 23 pages, 8 figures, 4 tables, accepted by Astronomy and Astrophysic
Scattering series in mobility problem for suspensions
The mobility problem for suspension of spherical particles immersed in an
arbitrary flow of a viscous, incompressible fluid is considered in the regime
of low Reynolds numbers. The scattering series which appears in the mobility
problem is simplified. The simplification relies on the reduction of the number
of types of single-particle scattering operators appearing in the scattering
series. In our formulation there is only one type of single-particle scattering
operator.Comment: 11 page
Influence of Hydrodynamic Interactions on Mechanical Unfolding of Proteins
We incorporate hydrodynamic interactions in a structure-based model of
ubiquitin and demonstrate that the hydrodynamic coupling may reduce the peak
force when stretching the protein at constant speed, especially at larger
speeds. Hydrodynamic interactions are also shown to facilitate unfolding at
constant force and inhibit stretching by fluid flows.Comment: to be published in Journal of Physics: Condensed Matte
The Arecibo Methanol Maser Galactic Plane Survey--I: Data
We present the results of an unbiased survey for 6.7 GHz methanol masers in
the Galactic plane carried out using the 305 m Arecibo radio telescope. A total
of 18.2 square degrees was surveyed with uniform sampling at 35.2 deg < l <
53.7 deg, |b| < 0.41 deg. The large collecting area of Arecibo and the
sensitive C-Band High receiver allowed the survey to be complete at the level
of 0.27 Jy making this the most sensitive blind survey carried out to date. We
detected a total of 86 sources, 48 of which are new detections. Most of the new
detections have a peak flux density below 2 Jy. Many methanol masers are
clustered, reflecting the formation of massive stars in clusters.Comment: Accepted by Ap
12.2-GHz methanol maser MMB follow-up catalogue - II. Longitude range 186 to 330 degrees
We present the second portion of a catalogue of 12.2-GHz methanol masers
detected towards 6.7-GHz methanol masers observed in the unbiased Methanol
Multibeam (MMB) Survey. Using the Parkes radio telescope we have targeted all
207 6.7-GHz methanol masers in the longitude range 186 to 330 degrees for
12.2-GHz counterparts. We report the detection of 83 12.2-GHz methanol masers,
and one additional source which we suspect is thermal emission, equating to a
detection rate of 40 per cent. Of the 83 maser detections, 39 are reported here
for the first time. We discuss source properties, including variability and
highlight a number of unusual sources. We present a list of 45 candidates that
are likely to harbor methanol masers in the 107.0-GHz transition.Comment: Accepted MNRAS 19 July 201
12.2-GHz methanol masers associated with 1.2-mm dust clumps: Quantifying high-mass star formation evolutionary schemes
We report the results of a search for 12.2-GHz methanol maser emission,
targeted towards 113 known 6.7-GHz methanol masers associated with 1.2-mm dust
continuum emission. Observations were carried out with the Australia Telescope
National Facility (ATNF) Parkes 64-m radio telescope in the period 2008 June 20
- 25. We detect 68 12.2-GHz methanol masers with flux densities in excess of
our 5-sigma detection limit of 0.55 Jy, 30 of which are new discoveries. This
equates to a detection rate of 60 per cent, similar to previous searches of
comparable sensitivity. We have made a statistical investigation of the
properties of the 1.2-mm dust clumps with and without associated 6.7-GHz
methanol maser and find that 6.7-GHz methanol masers are associated with 1.2-mm
dust clumps with high flux densities, masses and radii. We additionally find
that 6.7-GHz methanol masers with higher peak luminosities are associated with
less dense 1.2-mm dust clumps than those 6.7-GHz methanol masers with lower
luminosities. We suggest that this indicates that more luminous 6.7-GHz
methanol masers are generally associated with a later evolutionary phase of
massive star formation than less luminous 6.7-GHz methanol maser sources.
Analysis of the 6.7-GHz associated 1.2-mm dust clumps with and without
associated 12.2-GHz methanol maser emission shows that clumps associated with
both class II methanol maser transitions are less dense than those with no
associated 12.2-GHz methanol maser emission; suggesting that 12.2-GHz methanol
masers are associated with a later evolutionary phase of massive star
formation. We present an evolutionary sequence for masers in high-mass star
formation regions, placing quantitative estimates on the relative lifetimes for
the first time.Comment: Accepted to MNRAS 2009 October
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