13,548 research outputs found
X-ray film holder permits single continuous picture of tubing joint
X ray technique produces a clear continuous picture of a welded brazed tubing joint on a single film with one exposure. A stationary X ray source located in the plane of the joint to be inspected, a means of rotating the tube, and a unique internal film holder and positioning fixture are used
VLBI Astrometry of the Stellar Image of U Herculis, Amplified by the 1667 OH Maser
The OH 1667 MHz maser in the circumstellar shell around the Mira variable U
Herculis has been observed with the NRAO Very Long Baseline Array (VLBA) at 6
epochs, spread over 4 years. Using phase referencing techniques the position of
the most blue-shifted maser spot was monitored with respect to two
extra-galactic radio sources. The absolute radio positions of the maser can be
compared with the stellar optical position measured by the Hipparcos satellite
to 15 mas accuracy. This confirms the model in which one of the maser spots
corresponds to the stellar continuum, amplified by the maser. The stellar
proper motion and the annual parallax (5.3 +/- 2.1 mas) were measured.Comment: 6 pages, 4 figures; to be published in A&
Circular Polarization of Circumstellar Water Masers around S Per
We present the first circular polarization measurements of circumstellar H2O
masers. Previously the magnetic field in circumstellar envelopes has been
estimated using polarization observations of SiO and OH masers. SiO masers are
probes of the high temperature and density regime close to the central star. OH
masers are found at much lower densities and temperatures, generally much
further out in the circumstellar envelope. The detection of the circular
polarization of the (6_16 - 5_23) rotational transition of the H2O maser could
be attributed to Zeeman splitting due to the magnetic field in the intermediate
temperature and density regime. The fields inferred here agree well with
predicted values for a combination of the r^{-2} dependence of a solar-type
magnetic field, and the coupling of the field to the high density masing
regions. We also discuss the unexpected narrowing of the circular polarization
spectrum.Comment: 4 pages, 4 figures; accepted for publication in Astronomy and
Astrophysics Letter
A MERLIN Study of 6 GHz Excited-state OH & 6.7 GHz Methanol Masers in ON1
MERLIN observations of 6.668-GHz methanol and both 6.031- and 6.035-GHz
hydroxyl (OH) emission from the massive star-formation region ON1 are
presented. These are the first methanol observations made in full polarization
using 5 antennas of MERLIN, giving high resolution and sensitivity to extended
emission. Maser features are found to lie at the southern edge of the
ultra-compact HII region, following the known distribution of ground-state OH
masers. The masers cover a region ~1 arcsec in extent, lying perpendicular to
the H13CO+ bipolar outflow. Excited-state OH emission demonstrates consistent
polarization angles across the strongest linearly polarized features which are
parallel to the overall distribution. The linear polarizations vary between
10.0 and 18.5 per cent, with an average polarization angle of -60 deg +/- 28
deg. The strongest 6.668-GHz methanol features provide an upper limit to linear
polarization of ~1 per cent. Zeeman splitting of OH shows magnetic fields
between -1.1 to -5.8 mG, and a tentative methanol magnetic field strength of
-18 mG is measured.Comment: 10 Pages, 5 Figure
Collateral and Debt Maturity Choice. A Signaling Model
This paper derives optimal loan policies under asymmetric information where banks offer loan contracts of long and short duration, backed or unbacked with collateral. The main novelty of the paper is that it analyzes a setting in which high quality firms use collateral as a complementary device along with debt maturity to signal their superiority. The least-cost signaling equilibrium depends on the relative costs of the signaling devices, the difference in firm quality and the proportion of good firms in the market. Model simulations suggest a non-monotonic relationship between firm quality and debt maturity, in which high quality firms have both long-term secured debt and short-term secured or non-secured debt.
How Well Do Medical Students Understand the Consequences of the Debt They Are Accumulating?
No abstract available
Circular Polarization of Water Masers in the Circumstellar Envelopes of Late Type Stars
We present circular polarization measurements of circumstellar H_2O masers.
The circular polarization detected in the (6_{16}-5_{23}) rotational transition
of the H_{2}O maser can be attributed to Zeeman splitting in the intermediate
temperature and density regime. The magnetic fields are derived using a
general, LTE Zeeman analysis as well as a full radiative transfer method
(non-LTE), which includes a treatment of all hyperfine components
simultaneously as well as the effects of saturation and unequal populations of
the magnetic substates. The differences and relevances of these interpretations
are discussed extensively. The field strengths are compared with previous
detections of the magnetic field on the SiO and OH masers. We show that the
magnetic pressure dominates the thermal pressure by a factor of 20 or more.Comment: 15 pages, 15 figures; accepted for publication in A&A; (Abstract
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