7,587 research outputs found
Mechanical properties and the electronic structure of transition of metal alloys
This interdiscipline research program was undertaken in an effort to investigate the relationship between the mechanical strength of Mo based alloys with their electronic structure. Electronic properties of these alloys were examined through optical studies, and the classical solid solution strengthening mechanisms were considered, based on size and molecular differences to determine if these mechanisms could explain the hardness data
Disentangling the spatial substructure of Cygnus OB2 from Gaia DR2
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyFor the first time, we have explored the spatial substructure of the Cygnus OB2 association using parallaxes from the recent second Gaia data release. We find significant line-of-sight substructure within the association, which we quantify using a parametrized model that reproduces the observed parallax distribution. This inference approach is necessary due to the non-linearity of the parallax distance transformation and the asymmetry of the resulting probability distribution. Using a Markov Chain Monte Carlo ensemble sampler and an unbinned maximum likelihood test, we identify two different stellar groups superposed on the association. We find the main Cygnus OB2 group at ∼1760 pc, further away than recent estimates have envisaged, and a foreground group at ∼1350 pc. We also calculate individual membership probabilities and identify outliers as possible non-members of the association.Peer reviewe
On the role of the UV and X-ray radiation in driving a disk wind in X-ray binaries
X-ray heating of the photosphere of an accretion disk is a possible mechanism
to produce strong, broad UV emission lines in low mass X-ray binaries (LMXBs).
However, detailed photoionization calculations show that this mechanism fails
to produce sufficient emission measure. We present the results of
hydrodynamical calculations of the disk photosphere irradiated by strong
X-rays. We attempt to determine whether LMXBs can harbor significant UV-driven
disk winds despite the effects of X-ray ionization. Such winds would be a
likely candidate for the site of emission of UV lines and may better explain
the observations than the X-ray heated disk photosphere. We find that the local
disk radiation cannot launch a wind from the disk because of strong ionizing
radiation from the central object. Unphysically high X-ray opacities would be
required to shield the UV emitting disk and allow the line force to drive a
disk wind. However the same X-ray radiation that inhibits line driving heats
the disk and can produce a hot bipolar wind or corona above the disk. To assess
the impact of X-ray heating upon driving of a disk wind by the line force in
any system with an accretion disk we derive analytic formulae. In particular,
we compare results of line-driven disk wind models for accretion disks in LMXBs
and active galactic nuclei. The latter show spectral features associated with a
strong and fast disk wind. The key parameter determining the role of the line
force is not merely the presence of the luminous UV zone in the disk and the
presence of the X-rays, but also the distance of this UV zone from the center.Comment: LaTeX, 34 pages, contains color figures, to appear in Ap
Time Response of Water-based Liquid Scintillator from X-ray Excitation
Water-based liquid scintillators (WbLS) present an attractive target medium
for large-scale detectors with the ability to enhance the separation of
Cherenkov and scintillation signals from a single target. This work
characterizes the scintillation properties of WbLS samples based on LAB/PPO
liquid scintillator (LS). X-ray luminescence spectra, decay profiles, and
relative light yields are measured for WbLS of varying LS concentration as well
as for pure LS with a range of PPO concentrations up to 90 g/L. The
scintillation properties of the WbLS are related to the precursor LAB/PPO:
starting from 90 g/L PPO in LAB before synthesis, the resulting WbLS have
spectroscopic properties that instead match 10 g/L PPO in LAB. This could
indicate that the concentration of active PPO in the WbLS samples depends on
their processing.Comment: 6 pages, 7 figures, 2 tables. Submitted to Materials Advances, a
journal of the Royal Society of Chemistr
New Species, Subgenus and Records of Bactrocera Macquart from the South Pacific (Diptera: Tephritidae: Dacinae)
ABSTRACT Bactrocera (Bulladacus) subgen.nov. is described to include nine species of Asian and Pacific Dacinae. B. (Afrodacus) grandistylus sp.nov., B. (Bulladacus) gnetum sp.nov. and B. (Notodacus) paraxanthodes sp.nov. are described and illustrated, the latter being closely related to B. xanthodes (Broun), an economic species with which it has been confused. B. (Bactrocera) passiflorae (Froggatt) and B. (Bulladacus) aenigmatica (Malloch) are revised and a new colour form of the former illustrated, while the male of the latter is described and illustrated for the first time
An equatorial wind from the massive young stellar object S140 IRS 1
The discovery of the second equatorial ionized stellar wind from a massive
young stellar object is reported. High resolution radio continuum maps of S140
IRS 1 reveal a highly elongated source that is perpendicular to the larger
scale bipolar molecular outflow. This picture is confirmed by location of a
small scale monopolar near-IR reflection nebula at the base of the blueshifted
lobe. A second epoch of observations over a five year baseline show little
ordered outward proper motion of clumps as would have been expected for a jet.
A third epoch, taken only 50 days after the second, did show significant
changes in the radio morphology. These radio properties can all be understood
in the context of an equatorial wind driven by radiation pressure from the
central star and inner disc acting on the gas in the surface layers of the disc
as proposed by Drew et al. (1998). This equatorial wind system is briefly
compared with the one in S106IR, and contrasted with other massive young
stellar objects that drive ionized jets.Comment: 19 pages, 5 figures, accepted by ApJ, minor changes in light of
referees repor
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