700 research outputs found
A digital computer simulation of high-altitude parachute response to wind gradients
Digital computer rigid body simulation of impervious hemisphere and disk-gap-band parachute systems response to high altitude wind shea
Optimal Mass Configurations for Lensing High-Redshift Galaxies
We investigate the gravitational lensing properties of lines of sight
containing multiple cluster-scale halos, motivated by their ability to lens
very high-redshift (z ~ 10) sources into detectability. We control for the
total mass along the line of sight, isolating the effects of distributing the
mass among multiple halos and of varying the physical properties of the halos.
Our results show that multiple-halo lines of sight can increase the magnified
source-plane region compared to the single cluster lenses typically targeted
for lensing studies, and thus are generally better fields for detecting very
high-redshift sources. The configurations that result in optimal lensing cross
sections benefit from interactions between the lens potentials of the halos
when they overlap somewhat on the sky, creating regions of high magnification
in the source plane not present when the halos are considered individually. The
effect of these interactions on the lensing cross section can even be
comparable to changing the total mass of the lens from 10^15 M_sun to 3x10^15
M_sun. The gain in lensing cross section increases as the mass is split into
more halos, provided that the lens potentials are projected close enough to
interact with each other. A nonzero projected halo angular separation, equal
halo mass ratio, and high projected halo concentration are the best mass
configurations, whereas projected halo ellipticity, halo triaxiality, and the
relative orientations of the halos are less important. Such high mass,
multiple-halo lines of sight exist in the SDSS.Comment: Accepted for publication in ApJ; emulateapj format; 24 pages, 13
figures, 1 table; plots updated to reflect erratu
Astrometric performance of the Gemini multi-conjugate adaptive optics system in crowded fields
The Gemini Multi-conjugate adaptive optics System (GeMS) is a facility
instrument for the Gemini-South telescope. It delivers uniform,
near-diffraction-limited image quality at near-infrared wavelengths over a 2
arcminute field of view. Together with the Gemini South Adaptive Optics Imager
(GSAOI), a near-infrared wide field camera, GeMS/GSAOI's combination of high
spatial resolution and a large field of view will make it a premier facility
for precision astrometry. Potential astrometric science cases cover a broad
range of topics including exo-planets, star formation, stellar evolution, star
clusters, nearby galaxies, black holes and neutron stars, and the Galactic
center. In this paper, we assess the astrometric performance and limitations of
GeMS/GSAOI. In particular, we analyze deep, mono-epoch images, multi-epoch data
and distortion calibration. We find that for single-epoch, un-dithered data, an
astrometric error below 0.2 mas can be achieved for exposure times exceeding
one minute, provided enough stars are available to remove high-order
distortions. We show however that such performance is not reproducible for
multi-epoch observations, and an additional systematic error of ~0.4 mas is
evidenced. This systematic multi-epoch error is the dominant error term in the
GeMS/GSAOI astrometric error budget, and it is thought to be due to
time-variable distortion induced by gravity flexure.Comment: 16 pages, 22 figures, accepted for publication in MNRA
Comparison of polymerase chain reaction and bacterial culture for Salmonella detection in the Muscovy duck in Trinidad and Tobago
Objectives: The purpose of this study was to investigate the presence and serovar identity of Salmonella, at the national level, in farmed Muscovy ducks (Cairina moschata) in Trinidad and Tobago, and to compare the relative benefits of bacterial culture to those of polymerase chain reaction (PCR) for use in the routine detection and surveillance of Salmonella in these ducks.
Methods: From March-September 2003, 110 fecal samples were collected from 82 farms across the islands of Trinidad and Tobago. Salmonella was isolated from fresh and frozen samples and the serotype of each was determined through bacterial culture. An in-house, nested PCR that detects all pathogenic Salmonella species was utilized in analyzing the samples.
Results: Five samples were positive for Salmonella by bacterial culture, whereas 44 were positive by the nested PCR. Serovars isolated were Kiambu, Orion, Uganda, and two isolates from Group E1 whose H antigens could not be fully characterized. Of the samples, 87 (79%) gave equivalent PCR results for both enrichment broths-28 were positive for both and 59 were negative for both). However, 16 samples were positive for one broth, but not for the other, with the majority (14 of the 16) resulting positive for Selenite broth. PCR results for seven samples were inconclusive due to ambiguous band size or multiple bands near the expected band size.
Conclusions: In Trinidad and Tobago, the Muscovy duck does not appear to be a significant source of S. typhimurium or S. enteritidis, but it does harbor other Salmonella species. In-house, nested PCR represents a simple, relatively inexpensive and potentially more sensitive method than bacterial culture for the routine surveillance of pathogenic Salmonella in the Muscovy duck
An Exploratory Study of Methicillin-Resistant Staphylococcus aureus and SCCmec Elements Obtained from a Community Setting Along the Texas Border with Mexico
An exploratory study of methicillin-resistant Staphylococcus aureus (MRSA) and SCCmec elements in bacteria along the Mexican border of south Texas was performed. Between September and December of 2008, 375 swabs of anterior nares were self-collected by students attending the University of Texas-Pan American (UTPA) and cultured for MRSA. Fifty seven bacterial isolates were kept for further analysis that included suspected MRSA and other SCCmec-containing bacteria. Isolates were examined for the presence of nuc, mecA, lukS-PV, and spa genes using PCR. SCCmec and spa typing were also performed. Seven S. aureus isolates were found of which six were classified as MRSA. SCCmec typing showed five of the six MRSA strains to be type IV, while one MRSA strain, and most of the non-S. aureus strains, were untypeable, producing results that were indicative of mixed SCCmec types. Five of the six MRSA strains contained known spa types (two of which corresponded to USA300 and one to USA600), while one strain had a novel spa type. Only one isolate, a USA300 MRSA, was positive for lukS-PV. Easy access by the Texas border community to antibiotics in Mexico without a prescription, and the strong partition in SCCmec types between MRSA and non-S. aureus bacteria suggest that this border region of Texas may be uniquely suited for the study of emerging SCCmec types, their horizontal transfer, and perhaps other aspects of antibiotic resistance in bacteria
A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: The Group Catalog
With a large, unique spectroscopic survey in the fields of 28 galaxy-scale
strong gravitational lenses, we identify groups of galaxies in the 26
adequately-sampled fields. Using a group finding algorithm, we find 210 groups
with at least five member galaxies; the median number of members is eight. Our
sample spans redshifts of 0.04 0.76 with a median of 0.31,
including 174 groups with . Groups have radial velocity
dispersions of 60 1200 km s with a median of 350
km s. We also discover a supergroup in field B0712+472 at 0.29
consisting of three main groups. We recover groups similar to 85% of
those previously reported in these fields within our redshift range of
sensitivity and find 187 new groups with at least five members. The properties
of our group catalog, specifically 1) the distribution of , 2)
the fraction of all sample galaxies that are group members, and 3) the fraction
of groups with significant substructure, are consistent with those for other
catalogs. The distribution of group virial masses agrees well with theoretical
expectations. Of the lens galaxies, 12 of 26 (46%) (B1422+231, B1600+434,
B2114+022, FBQS J0951+2635, HE0435-1223, HST J14113+5211, MG0751+2716,
MGJ1654+1346, PG 1115+080, Q ER 0047-2808, RXJ1131-1231, and WFI J2033-4723)
are members of groups with at least five galaxies, and one more (B0712+472)
belongs to an additional, visually identified group candidate. There are groups
not associated with the lens that still are likely to affect the lens model; in
six of 25 (24%) fields (excluding the supergroup), there is at least one
massive ( 500 km s) group or group candidate projected
within 2 of the lens.Comment: 87 pages, 8 figures, a version of this was published in Ap
Research Notes, February 1965
This is issue 2: Glacier Park Chalet Visits; An Introduction to Wilderness Experiencehttps://scholarworks.umt.edu/montana_forestry_notes/1001/thumbnail.jp
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