8,566 research outputs found
C^+ distribution around S1 in rho Ophiuchi
We analyze a [C II] 158 micron map obtained with the L2 GREAT receiver on
SOFIA of the emission/reflection nebula illuminated by the early B star S1 in
the rho-OphA cloud core. This data set has been complemented with maps of
CO(3-2), 13CO(3-2) and C18O(3-2), observed as a part of the JCMT Gould Belt
Survey, with archival HCO^+(4-3) JCMT data, as well as with [O I] 63 and 145
micron imaging with Herschel/PACS. The [C II] emission is completely dominated
by the strong PDR emission from the nebula surrounding S1 expanding into the
dense Oph A molecular cloud west and south of S1. The [C II] emission is
significantly blue shifted relative to the CO spectra and also relative to the
systemic velocity, particularly in the northwestern part of the nebula. The [C
II] lines are broader towards the center of the S1 nebula and narrower towards
the PDR shell. The [C II] lines are strongly self-absorbed over an extended
region in the S1 PDR. Based on the strength of the [13C II] F = 2-1 hyperfine
component, [C II] is significantly optically thick over most of the nebula. CO
and 13CO(3-2) spectra are strongly self-absorbed, while C18O(3-2) is single
peaked and centered in the middle of the self-absorption. We have used a simple
two-layer LTE model to characterize the background and foreground cloud
contributing to the [C II] emission. From this analysis we estimate the
extinction due to the foreground cloud to be ~9.9 mag, which is slightly less
than the reddening estimated towards S1. Since some of the hot gas in the PDR
is not traced by low J CO emission, this result appears quite plausible. Using
a plane parallel PDR model with the observed [OI(145)]/[C II] brightness ratio
and an estimated FUV intensity of 3100-5000 G0 suggests that the density of the
[C II] emitting gas is ~3-4x10^3 cm^-3.Comment: Accepted for publication in Astronomy & Astrophysic
Extremal Problems for Roman Domination
A Roman dominating function of a graph G is a labeling f: V(G) â{0,1,2} such that every vertex with a label 0 has a neighbor with label 2. The Roman domination number ÎłR(G) of G is the minimum of âÊÏ”V(G)f(v) over such functions. Let G be a connected n-vertex graph. We prove that ÎłR(G) †4n/5, and we characterize the graphs achieving equality. We obtain sharp upper and lower bounds for ÎłR(G) + ÎłR(áž ) and ÎłR(G)ÎłR(áž ), improving known results for domination number. We prove that ÎłR(G) †8n/11 when á”(G) â„ 2 and n â„ 9, and this is sharp
Forest disturbance and recovery: A general review in the context of spaceborne remote sensing of impacts on aboveground biomass and canopy structure
Abrupt forest disturbances generating gaps \u3e0.001 km2 impact roughly 0.4â0.7 million km2aâ1. Fire, windstorms, logging, and shifting cultivation are dominant disturbances; minor contributors are land conversion, flooding, landslides, and avalanches. All can have substantial impacts on canopy biomass and structure. Quantifying disturbance location, extent, severity, and the fate of disturbed biomass will improve carbon budget estimates and lead to better initialization, parameterization, and/or testing of forest carbon cycle models. Spaceborne remote sensing maps large-scale forest disturbance occurrence, location, and extent, particularly with moderate- and fine-scale resolution passive optical/near-infrared (NIR) instruments. High-resolution remote sensing (e.g., âŒ1 m passive optical/NIR, or small footprint lidar) can map crown geometry and gaps, but has rarely been systematically applied to study small-scale disturbance and natural mortality gap dynamics over large regions. Reducing uncertainty in disturbance and recovery impacts on global forest carbon balance requires quantification of (1) predisturbance forest biomass; (2) disturbance impact on standing biomass and its fate; and (3) rate of biomass accumulation during recovery. Active remote sensing data (e.g., lidar, radar) are more directly indicative of canopy biomass and many structural properties than passive instrument data; a new generation of instruments designed to generate global coverage/sampling of canopy biomass and structure can improve our ability to quantify the carbon balance of Earth\u27s forests. Generating a high-quality quantitative assessment of disturbance impacts on canopy biomass and structure with spaceborne remote sensing requires comprehensive, well designed, and well coordinated field programs collecting high-quality ground-based data and linkages to dynamical models that can use this information
Origin of positive magnetoresistance in small-amplitude unidirectional lateral superlattices
We report quantitative analysis of positive magnetoresistance (PMR) for
unidirectional-lateral-superlattice samples with relatively small periods
(a=92-184 nm) and modulation amplitudes (V_0=0.015-0.25 meV). By comparing
observed PMR's with ones calculated using experimentally obtained mobilities,
quantum mobilities, and V_0's, it is shown that contribution from streaming
orbits (SO) accounts for only small fraction of the total PMR. For small V_0,
the limiting magnetic field B_e of SO can be identified as an inflection point
of the magnetoresistance trace. The major part of PMR is ascribed to drift
velocity arising from incompleted cyclotron orbits obstructed by scatterings.Comment: 12 pages, 9 figures, REVTe
Spinning Down a Black Hole With Scalar Fields
We study the evolution of a Kerr black hole emitting scalar radiation via the
Hawking process. We show that the rate at which mass and angular momentum are
lost by the black hole leads to a final evolutionary state with nonzero angular
momentum, namely .Comment: 4 pages (including 3 postscript figures), Revtex, uses epsf.tex,
twocolumn.sty and header.sty (included). Submitted to Physical Review Letter
A Probe Particle in Kerr-Newman-deSitter Cosmos
We consider the force acting on a spinning charged test particle (probe
particle) with the mass m and the charge q in slow rotating the
Kerr-Newman-deSitter(KNdS) black hole with the mass M and the charge Q. We
consider the case which the spin vector of the probe particle is parallel to
the angular momentum vector of the KNdS space-time. We take account of the
gravitational spin-spin interaction under the slow rotating limit of the KNdS
space-time. When Q=M and q=m, we show that the force balance holds including
the spin-spin interaction and the motion is approximately same as that of a
particle in the deSitter space-time. This force cancellation suggests the
possibility of the existence of an exact solution of spinning multi-KNdS black
hole.Comment: 7 pages, Classical and Quantum Gravity accepte
Einstein Cluster Alignments Revisited
We have examined whether the major axes of rich galaxy clusters tend to point
toward their nearest neighboring cluster. We have used the data of Ulmer,
McMillan, and Kowalski, who used position angles based on X-ray morphology. We
also studied a subset of this sample with updated positions and distances from
the MX Northern Abell Cluster Survey (for rich clusters () with well
known redshifts). A Kolmogorov-Smirnov (KS) test showed no significant signal
for nonrandom angles on any scale Mpc. However, refining the
null hypothesis with the Wilcoxon rank-sum test, we found a high confidence
signal for alignment. Confidence levels increase to a high of 99.997% as only
near neighbors which are very close are considered. We conclude there is a
strong alignment signal in the data, consistent with gravitational instability
acting on Gaussian perturbations.Comment: Minor revisions. To be published in Ap
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SNL/NM weapon hardware characterization process development report
This report describes the process used by Sandia National Laboratories, New Mexico to characterize weapon hardware for disposition. The report describes the following basic steps: (1) the drawing search process and primary hazard identification; (2) the development of Disassembly Procedures (DPs), including demilitarization and sanitization requirements; (3) the generation of a ``disposal tree``; (4) generating RCRA waste disposal information; and (5) documenting the information. Additional data gathered during the characterization process supporting hardware grouping and recycle efforts is also discussed
Extent of pollution in planet-bearing stars
(abridged) Search for planets around main-sequence (MS) stars more massive
than the Sun is hindered by their hot and rapidly spinning atmospheres. This
obstacle has been sidestepped by radial-velocity surveys of those stars on
their post-MS evolutionary track (G sub-giant and giant stars). Preliminary
observational findings suggest a deficiency of short-period hot Jupiters around
the observed post MS stars, although the total fraction of them with known
planets appears to increase with their mass. Here we consider the possibility
that some very close- in gas giants or a population of rocky planets may have
either undergone orbital decay or been engulfed by the expanding envelope of
their intermediate-mass host stars. If such events occur during or shortly
after those stars' main sequence evolution when their convection zone remains
relatively shallow, their surface metallicity can be significantly enhanced by
the consumption of one or more gas giants. We show that stars with enriched
veneer and lower-metallicity interior follow slightly modified evolution tracks
as those with the same high surface and interior metallicity. As an example, we
consider HD149026, a marginal post MS 1.3 Msun star. We suggest that its
observed high (nearly twice solar) metallicity may be confined to the surface
layer as a consequence of pollution by the accretion of either a planet similar
to its known 2.7-day-period Saturn-mass planet, which has a 70 Mearth compact
core, or a population of smaller mass planets with a comparable total amount of
heavy elements. It is shown that an enhancement in surface metallicity leads to
a reduction in effective temperature, in increase in radius and a net decrease
in luminosity. The effects of such an enhancement are not negligible in the
determinations of the planet's radius based on the transit light curves.Comment: 25 pages, 8 figures, submitted to Ap
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