5,732 research outputs found
Pumping of a Planetesimal Disc by a Rapidly Migrating Planet
We examine the effect of a rapidly migrating protoplanet on a ring of
planetesimals. The eccentricities of the planetesimals are usually increased by
, with the exact increase being proportional to the
protoplanet's mass, and inversely proportional to its migration rate. The
eccentricity distribution is also substantially changed from a Rayleigh
distribution. We discuss the possible implications for further planet
formation, and suggest that the rapid passage of a protoplanet may not prevent
the planetesimal disc from forming further planets.Comment: Five pages, two figures, accepted by MNRA
Inhibitory Plasticity in a Lateral Band Improves Cortical Detection of Natural Vocalizations
SummaryThe interplay between excitation and inhibition in the auditory cortex is crucial for the processing of acoustic stimuli. However, the precise role that inhibition plays in the distributed cortical encoding of natural vocalizations has not been well studied. We recorded single units (SUs) and local field potentials (LFPs) in the awake mouse auditory cortex while presenting pup isolation calls to animals that either do (mothers) or do not (virgins) recognize the sounds as behaviorally relevant. In both groups, we observed substantial call-evoked inhibition. However, in mothers this was earlier, longer, stronger, and more stereotyped compared to virgins. This difference was most apparent for recording sites tuned to tone frequencies lower than the pup calls' high-ultrasonic frequency range. We hypothesize that this auditory cortical inhibitory plasticity improves pup call detection in a relatively specific manner by increasing the contrast between call-evoked responses arising from high-ultrasonic and lateral frequency neural populations
Toxicity of radiotherapy in patients with collagen vascular disease
BACKGROUND. A diagnosis of collagen vascular disease (CVD) may predispose to radiotherapy (RT) toxicity. The objective of the current study was to identify factors that influence RT toxicity in the setting of CVD. METHODS. A total of 86 RT courses for 73 patients with CVD were delivered between 1985 and 2005. CVD subtypes include rheumatoid arthritis (RA; 33 patients), systemic lupus erythematosus (SLE; 13 patients), scleroderma (9 patients), dermatomyositis/polymyositis (5 patients), ankylosing spondylitis (4 patients), polymyalgia rheumatica/temporal arteritis (4 patients), Wegener granulomatosis (3 patients), and mixed connective tissue disorders (MCTD)/other (2 patients). Each patient with CVD was matched to 1 to 3 controls with respect to sex, race, site irradiated, RT dose (±2 Gray), and age (±5 years). RESULTS. There was no significant difference between CVD patients (65.1%) and controls (72.5%) experiencing any acute toxicity. CVD patients had a higher incidence of any late toxicity (29.1% vs 14%; P = .001), and a trend toward an increased rate of severe late toxicity (9.3% vs 3.7%; P = .079). RT delivered to the breast had increased risk of severe acute toxicity, whereas RT to the pelvis had increased risk of severe acute and late toxicity. RT administered in the setting of scleroderma carried a higher risk of severe late toxicity, whereas RT to SLE patients carried a higher risk of severe acute and late toxicity. CONCLUSIONS. Although generally well tolerated, RT in the setting of CVD appears to carry a higher risk of late toxicity. RT to the pelvis or in the setting of SLE or scleroderma may predispose to an even greater risk of severe toxicity. These issues should be considered when deciding whether to offer RT for these patients. Cancer 2008. © 2008 American Cancer Society.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60460/1/23591_ftp.pd
A Super-Earth caught in a trap
This paper is an extension of the work done by Pierens & Nelson (2008) in
which they have investigated the behaviour of a two-planet system embedded in a
protoplanetary disc. They have put a Jupiter mass gas giant on the internal
orbit and a lower mass planet on the external one. We consider here a similar
problem taking into account a gas giant with masses in the range of 0.5 to 1
Jupiter mass and a Super-Earth as the outermost planet. By changing disc
parameters and planet masses we have succeeded in getting the convergent
migration which allows for the possibility of their resonant locking. However,
in the case in which the gas giant has the mass of Jupiter, before any mean
motion first order commensurability could be achieved, the Super-Earth is
caught in a trap when it is very close to the edge of the gap opened by the
giant planet. This confirms the result obtained by Pierens & Nelson (2008) in
their simulations. Additionally, we have found that, in a very thin disc, an
apsidal resonance is observed in the system if the Super-Earth is captured in
the trap. Moreover, the eccentricity of the small planet remains low, while
that of the gas giant increases slightly due to the imbalance between Lindblad
and corotational resonances. We have also studied analogous systems in which
the gas giant is allowed to take Sub-Jupiter masses. In this case, after
performing an extensive survey over all possible parameters, we have succeeded
in getting the 1:2 mean motion resonant configuration only in a disc with low
aspect ratio and low surface density. However, the resonance is maintained just
for few thousand orbits. Thus, we conclude that for typical protoplanetary
discs the mean motion commensurabilities are rare if the Super-Earth is located
on the external orbit relative to the gas giant. (abridged)Comment: 10 pages, 11 figures, accepted for publication in MNRA
Gas Accretion by Star Clusters and the Formation of Ultraluminous X-ray Sources from Cusps of Compact Remnants
Here we show that the overabundance of ultra-luminous, compact X-ray sources
(ULXs) associated with moderately young clusters in interacting galaxies such
as the Antennae and Cartwheel can be given an alternative explanation that does
not involve the presence of intermediate mass black holes (IMBHs). We argue
that gas density within these systems is enhanced by the collective potential
of the cluster prior to being accreted onto the individual cluster members and,
as a result, the aggregate X-ray luminosity arising from the neutron star
cluster members can exceed . Various observational
tests to distinguish between IMBHs and accreting neutron star cusps are
discussed.Comment: 4 pages, 3 figures, accepted to ApJ
CASIMIR, The Caltech airborne submillimeter interstellar medium investigations receiver
CASIMIR, the Caltech Airborne Submillimeter Interstellar Medium Investigations Receiver is a multiband, far infrared and submillimeter, high resolution, heterodyne spectrometer under development for SOFIA. It is a first generation, PI class instrument. CASIMIR is designed for detailed, high sensitivity observations of warm (100 K) interstellar gas both in external galaxies and Galactic sources, including molecular clouds, circumstellar envelopes, and protostellar cores. Combining the 2.5 m SOFIA mirror with state of the art superconducting mixers, will give CASIMIR unprecedented sensitivity. Initially, CASIMIR will have two bands, at 1000 and 1250 GHz, and a further three bands, 550, 750, 1400 GHz, will be added soon after. Any four bands will be available on each flight. The availability of multiple bands during each flight will allow for efficient use of flight time. For example, searches for weak lines from rare species in bright sources can be carried out on the same flight with observations of abundant species in faint or distant objects
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