3,504 research outputs found
First principles numerical model of avalanche-induced arc discharges in electron-irradiated dielectrics
The model consists of four phases: single electron dynamics, single electron avalanche, negative streamer development, and tree formation. Numerical algorithms and computer code implementations are presented for the first three phases. An approach to developing a code description of fourth phase is discussed. Numerical results are presented for a crude material model of Teflon
Values and aspirations for coastal waters of the Kimberley: social values and participatory mapping using interviews. Technical Report. Kimberley Marine Research Program Node of the Western Australian Marine Science Institution
This is the first report from the “Values and aspirations for coastal waters of the Kimberley” research project funded by the Western Australian Government and administered by the Western Australian Marine Science Institution (Kimberley Research Node Project 2.1.2). The study area extends from the south western end of Eighty Mile Beach to the Northern Territory Border, a coastline 13,296 km in length at low water mark including the islands. The aim of this 3-year research project is to document and analyse the social values and aspirations of people associated with the existing and proposed marine parks at Eighty Mile Beach, Roebuck Bay, Lalang-garram (Camden Sound) and North Kimberley, and with other coastal waters of the Kimberley
Chemical Abundances Of Open Clusters From High-Resolution Infrared Spectra. I. NGC 6940
We present near-infrared spectroscopic analysis of 12 red giant members of
the Galactic open cluster NGC 6940. High-resolution (R45000) and high
signal-to-noise ratio (S/N > 100) near-infrared H and K band spectra were
gathered with the Immersion Grating Infrared Spectrograph (IGRINS) on the 2.7m
Smith Telescope at McDonald Observatory. We obtained abundances of H-burning
(C, N, O), (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group
(Sc, Ti, Cr, Fe, Co, Ni) and neutron-capture (Ce, Nd, Yb) elements. We report
the abundances of S, P, K, Ce, and Yb in NGC 6940 for the first time. Many OH
and CN features in the H band were used to obtain O and N abundances. C
abundances were measured from four different features: CO molecular lines in
the K band, high excitation C I lines present in both near-infrared and
optical, CH and bands in the optical region. We have also determined
ratios from the R-branch band heads of first overtone (2-0) and
(3-1) (2-0) lines near 23440
\overset{\lower.5em\circ}{\mathrm{A}} and (3-1) lines at about
23730 \overset{\lower.5em\circ}{\mathrm{A}}. We have also investigated the HF
feature at 23358.3 \overset{\lower.5em\circ}{\mathrm{A}}, finding solar
fluorine abundances without ruling out a slight enhancement. For some elements
(such as the group), IGRINS data yield more internally
self-consistent abundances. We also revisited the CMD of NGC 6940 by
determining the most probable cluster members using Gaia DR2. Finally, we
applied Victoria isochrones and MESA models in order to refine our estimates of
the evolutionary stages of our targets.Comment: 16 pages, 10 figure
Properties of Galactic Outflows: Measurements of the Feedback from Star Formation
Properties of starburst-driven outflows in dwarf galaxies are compared to
those in more massive galaxies. Over a factor of roughly 10 in galactic
rotation speed, supershells are shown to lift warm ionized gas out of the disk
at rates up to several times the star formation rate. The amount of mass
escaping the galactic potential, in contrast to the disk, does depend on the
galactic mass. The temperature of the hottest extended \x emission shows little
variation around K, and this gas has enough energy to escape
from the galaxies with rotation speed less than approximately 130 km/s.Comment: 11 pages + 3 figues. Accepted for publication in the Astrophysical
Journa
Observational Constraints on Superbubble X-ray Energy Budgets
The hot, X-ray-emitting gas in superbubbles imparts energy and enriched
material to the interstellar medium (ISM) and generates the hot ionized medium,
the ISM's high-temperature component. The evolution of superbubble energy
budgets is not well understood, however, and the processes responsible for
enhanced X-ray emission in superbubbles remain a matter of debate. We present
Chandra ACIS-S observations of two X-ray-bright superbubbles in the Large
Magellanic Cloud (LMC), DEM L50 (N186) and DEM L152 (N44), with an emphasis on
disentangling the true superbubble X-ray emission from non-related diffuse
emission and determining the spatial origin and spectral variation of the X-ray
emission. An examination of the superbubble energy budgets shows that on the
order of 50% of the X-ray emission comes from regions associated with supernova
remnant (SNR) impacts. We find some evidence of mass-loading due to swept-up
clouds and metallicity enrichment, but neither mechanism provides a significant
contribution to the X-ray luminosities. We also find that one of the
superbubbles, DEM L50, is likely not in collisional ionization equilibrium. We
compare our observations to the predictions of the standard Weaver et al. model
and to 1-D hydrodynamic simulations including cavity supernova impacts on the
shell walls. Our observations show that mass-loading due to thermal evaporation
from the shell walls and SNR impacts are the dominant source of enhanced X-ray
luminosities in superbubbles. These two processes should affect most
superbubbles, and their contribution to the X-ray luminosity must be considered
when determining the energy available for transport to the ISM.Comment: 25 pages, 11 figures, accepted for publication in Ap
Very Extended X-ray and H-alpha Emission in M82: Implications for the Superwind Phenomenon
We discuss the properties and implications of a 3.7x0.9 kpc region of
spatially-coincident X-ray and H-alpha emission about 11.6 kpc to the north of
the galaxy M82 previously discussed by Devine and Bally (1999). The PSPC X-ray
spectrum is fit by thermal plasma (kT=0.80+-0.17 keV) absorbed by only the
Galactic foreground column density. We evaluate the relationship of the
X-ray/H-alpha ridge to the M82 superwind. The main properties of the X-ray
emission can all be explained as being due to shock-heating driven as the
superwind encounters a massive ionized cloud in the halo of M82. This encounter
drives a slow shock into the cloud, which contributes to the excitation of the
observed H-alpha emission. At the same time, a fast bow-shock develops in the
superwind just upstream of the cloud, and this produces the observed X-ray
emission. This interpretation would imply that the superwind has an outflow
speed of roughly 800 km/s, consistent with indirect estimates based on its
general X-ray properties and the kinematics of the inner kpc-scale region of
H-alpha filaments. The gas in the M82 ridge is roughly two orders-of-magnitude
hotter than the minimum "escape temperature" at this radius, so this gas will
not be retained by M82.
(abridged)Comment: 24 pages (latex), 3 figures (2 gif files and one postscript),
accepted for publication in Part 1 of The Astrophysical Journa
Ferromagnetic redshift of the optical gap in GdN
We report measurements of the optical gap in a GdN film at temperatures from
300 to 6K, covering both the paramagnetic and ferromagnetic phases. The gap is
1.31eV in the paramagnetic phase and red-shifts to 0.9eV in the spin-split
bands below the Curie temperature. The paramagnetic gap is larger than was
suggested by very early experiments, and has permitted us to refine a
(LSDA+U)-computed band structure. The band structure was computed in the full
translation symmetry of the ferromagnetic ground state, assigning the
paramagnetic-state gap as the average of the majority- and minority-spin gaps
in the ferromagnetic state. That procedure has been further tested by a band
structure in a 32-atom supercell with randomly-oriented spins. After fitting
only the paramagnetic gap the refined band structure then reproduces our
measured gaps in both phases by direct transitions at the X point.Comment: 5 pages, 4 figure
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