738 research outputs found
NICMOS Imaging of the Nuclei of Arp 220
We report high resolution imaging of the ultraluminous infrared galaxy Arp
220 at 1.1, 1.6, and 2.22 microns with NICMOS on the HST. The
diffraction-limited images at 0.1--0.2 arcsecond resolution clearly resolve
both nuclei of the merging galaxy system and reveal for the first time a number
of luminous star clusters in the circumnuclear envelope. The morphologies of
both nuclei are strongly affected by dust obscuration, even at 2.2 microns :
the primary nucleus (west) presents a crescent shape, concave to the south and
the secondary (eastern) nucleus is bifurcated by a dust lane with the southern
component being very reddened. In the western nucleus, the morphology of the
2.2 micron emission is most likely the result of obscuration by an opaque disk
embedded within the nuclear star cluster. The morphology of the central
starburst-cluster in the western nucleus is consistent with either a
circumnuclear ring of star formation or a spherical cluster with the bottom
half obscured by the embedded dust disk. Comparison of cm-wave radio continuum
maps with the near-infrared images suggests that the radio nuclei lie in the
dust disk on the west and near the highly reddened southern component of the
eastern complex. The radio nuclei are separated by 0.98 arcseconds
(corresponding to 364 pc at 77 Mpc) and the half-widths of the infrared nuclei
are approximately 0.2-0.5 arcseconds. At least 8, unresolved infrared sources
-- probably globular clusters -- are also seen in the circumnuclear envelope at
radii 2-7 arcseconds . Their near-infrared colors do not significantly
constrain their ages.Comment: LaTex, 15 pages with 1 gif figure and 5 postscript figures. ApJL
accepte
Very Isolated Early-Type Galaxies
We use the Karachentseva (1973) ``Catalogue of Very Isolated Galaxies'' to
investigate a candidate list of >100 very isolated early-type galaxies.
Broad-band imaging and low resolution spectroscopy are available for a large
fraction of these candidates and result in a sample of 102 very isolated
early-type galaxies, including 65 ellipticals and 37 S0 galaxies. Many of these
systems are quite luminous and the resulting optical luminosity functions of
the Es and early-types (E+S0s) show no statistical differences when compared to
luminosity functions dominated by group and cluster galaxies. However, whereas
S0s outnumber Es 4:1 in the CfA survey, isolated Es outnumber S0s by nearly
2:1. We conclude that very isolated elliptical galaxies show no evidence for a
different formation and/or evolution process compared to Es formed in groups or
clusters, but that most S0s are formed by a mechanism (e.g., gas stripping)
that occurs only in groups and rich clusters. Our luminosity function results
for ellipticals are consistent with very isolated ellipticals being formed by
merger events, in which no companions remain.
CHANDRA observations were proposed to test specifically the merger hypothesis
for isolated ellipticals. However, this program has resulted in the observation
of only one isolated early-type galaxy, the S0 KIG 284, which was not detected
at a limit well below that expected for a remnant group of galaxies. Therefore,
the hypothesis remains untested that very isolated elliptical galaxies are the
remains of a compact group of galaxies which completely merged.Comment: 19 pages, 3 figures; AJ in pres
The ROTSE-III Robotic Telescope System
The observation of a prompt optical flash from GRB990123 convincingly
demonstrated the value of autonomous robotic telescope systems. Pursuing a
program of rapid follow-up observations of gamma-ray bursts, the Robotic
Optical Transient Search Experiment (ROTSE) has developed a next-generation
instrument, ROTSE-III, that will continue the search for fast optical
transients. The entire system was designed as an economical robotic facility to
be installed at remote sites throughout the world. There are seven major system
components: optics, optical tube assembly, CCD camera, telescope mount,
enclosure, environmental sensing & protection and data acquisition. Each is
described in turn in the hope that the techniques developed here will be useful
in similar contexts elsewhere.Comment: 19 pages, including 4 figures. To be published in PASP in January,
2003. PASP Number IP02-11
Neutrophil C5a receptor and the outcome in a rat model of sepsis
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154259/1/fsb2fj030009fje.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154259/2/fsb2fj030009fje-sup-0001.pd
Statistical Properties of Share Volume Traded in Financial Markets
We quantitatively investigate the ideas behind the often-expressed adage `it
takes volume to move stock prices', and study the statistical properties of the
number of shares traded for a given stock in a fixed time
interval . We analyze transaction data for the largest 1000 stocks
for the two-year period 1994-95, using a database that records every
transaction for all securities in three major US stock markets. We find that
the distribution displays a power-law decay, and that the
time correlations in display long-range persistence. Further, we
investigate the relation between and the number of transactions
in a time interval , and find that the long-range
correlations in are largely due to those of . Our
results are consistent with the interpretation that the large equal-time
correlation previously found between and the absolute value of
price change (related to volatility) are largely due to
.Comment: 4 pages, two-column format, four figure
GYES, a multifibre spectrograph for the CFHT
We have chosen the name of GYES, one of the mythological giants with one
hundred arms, offspring of Gaia and Uranus, for our instrument study of a
multifibre spectrograph for the prime focus of the Canada-France-Hawaii
Telescope. Such an instrument could provide an excellent ground-based
complement for the Gaia mission and a northern complement to the HERMES project
on the AAT. The CFHT is well known for providing a stable prime focus
environment, with a large field of view, which has hosted several imaging
instruments, but has never hosted a multifibre spectrograph. Building upon the
experience gained at GEPI with FLAMES-Giraffe and X-Shooter, we are
investigating the feasibility of a high multiplex spectrograph (about 500
fibres) over a field of view 1 degree in diameter. We are investigating an
instrument with resolution in the range 15000 to 30000, which should provide
accurate chemical abundances for stars down to 16th magnitude and radial
velocities, accurate to 1 km/s for fainter stars. The study is led by
GEPI-Observatoire de Paris with a contribution from Oxford for the study of the
positioner. The financing for the study comes from INSU CSAA and Observatoire
de Paris. The conceptual study will be delivered to CFHT for review by October
1st 2010.Comment: Contributed talk at the Gaia ELSA conference 2010, S\`evres 7-11 June
2010, to be published on the EAS Series, Editors: C. Turon, F. Arenou & F.
Meynadie
Moisture susceptibility of high and low compaction dry process crumb rubber modified asphalt mixtures
The field performance of dry process crumb rubber-modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures
Does Lateral Transmission Obscure Inheritance in Hunter-Gatherer Languages?
In recent years, linguists have begun to increasingly rely on quantitative phylogenetic approaches to examine language evolution. Some linguists have questioned the suitability of phylogenetic approaches on the grounds that linguistic evolution is largely reticulate due to extensive lateral transmission, or borrowing, among languages. The problem may be particularly pronounced in hunter-gatherer languages, where the conventional wisdom among many linguists is that lexical borrowing rates are so high that tree building approaches cannot provide meaningful insights into evolutionary processes. However, this claim has never been systematically evaluated, in large part because suitable data were unavailable. In addition, little is known about the subsistence, demographic, ecological, and social factors that might mediate variation in rates of borrowing among languages. Here, we evaluate these claims with a large sample of hunter-gatherer languages from three regions around the world. In this study, a list of 204 basic vocabulary items was collected for 122 hunter-gatherer and small-scale cultivator languages from three ecologically diverse case study areas: northern Australia, northwest Amazonia, and California and the Great Basin. Words were rigorously coded for etymological (inheritance) status, and loan rates were calculated. Loan rate variability was examined with respect to language area, subsistence mode, and population size, density, and mobility; these results were then compared to the sample of 41 primarily agriculturalist languages in [1]. Though loan levels varied both within and among regions, they were generally low in all regions (mean 5.06%, median 2.49%, and SD 7.56), despite substantial demographic, ecological, and social variation. Amazonian levels were uniformly very low, with no language exhibiting more than 4%. Rates were low but more variable in the other two study regions, in part because of several outlier languages where rates of borrowing were especially high. High mobility, prestige asymmetries, and language shift may contribute to the high rates in these outliers. No support was found for claims that hunter-gatherer languages borrow more than agriculturalist languages. These results debunk the myth of high borrowing in hunter-gatherer languages and suggest that the evolution of these languages is governed by the same type of rules as those operating in large-scale agriculturalist speech communities. The results also show that local factors are likely to be more critical than general processes in determining high (or low) loan rates
Foodborne Campylobacter: Infections, Metabolism, Pathogenesis and Reservoirs
Campylobacter species are a leading cause of bacterial-derived foodborne illnesses worldwide. The emergence of this bacterial group as a significant causative agent of human disease and their propensity to carry antibiotic resistance elements that allows them to resist antibacterial therapy make them a serious public health threat. Campylobacter jejuni and Campylobacter coli are considered to be the most important enteropathogens of this genus and their ability to colonize and survive in a wide variety of animal species and habitats make them extremely difficult to control. This article reviews the historical and emerging importance of this bacterial group and addresses aspects of the human infections they cause, their metabolism and pathogenesis, and their natural reservoirs in order to address the need for appropriate food safety regulations and interventions
The Palomar Testbed Interferometer Calibrator Catalog
The Palomar Testbed Interferometer (PTI) archive of observations between 1998
and 2005 is examined for objects appropriate for calibration of optical
long-baseline interferometer observations - stars that are predictably
point-like and single. Approximately 1,400 nights of data on 1,800 objects were
examined for this investigation. We compare those observations to an
intensively studied object that is a suitable calibrator, HD217014, and
statistically compare each candidate calibrator to that object by computing
both a Mahalanobis distance and a Principal Component Analysis. Our hypothesis
is that the frequency distribution of visibility data associated with
calibrator stars differs from non-calibrator stars such as binary stars.
Spectroscopic binaries resolved by PTI, objects known to be unsuitable for
calibrator use, are similarly tested to establish detection limits of this
approach. From this investigation, we find more than 350 observed stars
suitable for use as calibrators (with an additional being
rejected), corresponding to sky coverage for PTI. This approach
is noteworthy in that it rigorously establishes calibration sources through a
traceable, empirical methodology, leveraging the predictions of spectral energy
distribution modeling but also verifying it with the rich body of PTI's on-sky
observations.Comment: 100 pages, 7 figures, 7 tables; to appear in the May 2008ApJS, v176n
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