2,207 research outputs found
Masses, luminosities and dynamics of galactic molecular clouds
Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies
The Cool ISM in S0 Galaxies. I. A Survey of Molecular Gas
Lenticular galaxies remain remarkably mysterious as a class. Observations to
date have not led to any broad consensus about their origins, properties and
evolution, though they are often thought to have formed in one big burst of
star formation early in the history of the Universe, and to have evolved
relatively passively since then. In that picture, current theory predicts that
stellar evolution returns substantial quantities of gas to the interstellar
medium; most is ejected from the galaxy, but significant amounts of cool gas
might be retained. Past searches for that material, though, have provided
unclear results. We present results from a survey of molecular gas in a
volume-limited sample of field S0 galaxies, selected from the Nearby Galaxies
Catalog. CO emission is detected from 78 percent of the sample galaxies. We
find that the molecular gas is almost always located inside the central few
kiloparses of a lenticular galaxy, meaning that in general it is more centrally
concentrated than in spirals. We combine our data with HI observations from the
literature to determine the total masses of cool and cold gas. Curiously, we
find that, across a wide range of luminosity, the most gas rich galaxies have
about 10 percent of the total amount of gas ever returned by their stars. That
result is difficult to understand within the context of either monolithic or
hierarchical models of evolution of the interstellar medium.Comment: 26 pages of text, 15 pages of tables, 10 figures. Accepted for
publication in the Astrophysical Journa
Optimal Pacing for Running 400 m and 800 m Track Races
Physicists seeking to understand complex biological systems often find it
rewarding to create simple "toy models" that reproduce system behavior. Here a
toy model is used to understand a puzzling phenomenon from the sport of track
and field. Races are almost always won, and records set, in 400 m and 800 m
running events by people who run the first half of the race faster than the
second half, which is not true of shorter races, nor of longer. There is
general agreement that performance in the 400 m and 800 m is limited somehow by
the amount of anaerobic metabolism that can be tolerated in the working muscles
in the legs. A toy model of anaerobic metabolism is presented, from which an
optimal pacing strategy is analytically calculated via the Euler-Lagrange
equation. This optimal strategy is then modified to account for the fact that
the runner starts the race from rest; this modification is shown to result in
the best possible outcome by use of an elementary variational technique that
supplements what is found in undergraduate textbooks. The toy model reproduces
the pacing strategies of elite 400 m and 800 m runners better than existing
models do. The toy model also gives some insight into training strategies that
improve performance.Comment: 14 pages, 4 figures, submitted to the American Journal of Physic
Triviality and the (Supersymmetric) See-Saw
For the D=5 Majorana neutrino mass operator to have a see-saw ultraviolet
completion that is viable up to the Planck scale, the see-saw scale is bounded
above due to triviality limits on the see-saw couplings. For supersymmetric
see-saw models, with realistic neutrino mass textures, we compare constraints
on the see-saw scale from triviality bounds, with those arising from
experimental limits on induced charged-lepton flavour violation, for both the
CMSSM and for models with split supersymmetry.Comment: 27 pages, 7 figures, references adde
Increased levels of type VIII collagen in human brain tumours compared to normal brain tissue and non-neoplastic cerebral disorders.
The expression of type VIII collagen was examined in the normal and diseased human brain. Focal immunoreactivity was seen in histologically abnormal vessels of all four angiomas and 40 of 52 brain tumours (gliomas, meningiomas and schwannomas). An extended staining pattern, as well as a punctate distribution, was frequently observed in affected vessels. Staining was not apparent in nine normal brains and in 15 pathologic brains showing various cerebrovascular abnormalities, including Alzheimer's, Leigh's and Wernicke's diseases. Immunoblotting of glioblastomas revealed two bands at 56 kD and 67 kD which were also present at low levels in normal frontal cortex. The extracellular distribution of type VIII collagen was different from that of the other collagen types which have been described in brain and resembles patterns of expression described for certain tissues during mammalian embryogenesis (Kapoor et al., 1988). Our results provide additional evidence for the participation of type VIII collagen in some types of angiogenesis
Concordance of Nuclear and Mitochondrial DNA Markers in Detecting a Founder Event in Lake Clark Sockeye Salmon
Genetic bottleneck effects can reduce genetic variation, persistence probability, and evolutionary potential of populations. Previous microsatellite analysis suggested a bottleneck associated with a common founding of sockeye salmon Oncorhynchus nerka populations of Lake Clark, Alaska, about 100 to 400 generations ago. The common founding event occurred after the last glacial recession and resulted in reduced allelic diversity and strong divergence of Lake Clark sockeye salmon relative to neighboring Six Mile Lake and Lake Iliamna populations. Here we used two additional genetic marker types (allozymes and mtDNA) to examine these patterns further. Allozyme and mtDNA results were congruent with the microsatellite data in suggesting a common founder event in Lake Clark sockeye salmon and confirmed the divergence of Lake Clark populations from neighboring Six Mile Lake and Lake Iliamna populations. The use of multiple marker types provided better understanding of the bottleneck in Lake Clark. For example, the Sucker Bay Lake population had an exceptionally severe reduction in allelic diversity at microsatellite loci, but not at mtDNA. This suggests that the reduced microsatellite variation in Sucker Bay Lake fish is due to consistently smaller effective population size than other Lake Clark populations, rather than a more acute or additional bottleneck since founding. Caution is urged in using reduced heterozygosity as a measure of genetic bottleneck effects because stochastic variance among loci resulted in an overall increase in allozyme heterozygosity within bottlenecked Lake Clark populations. However, heterozygosity excess, which assesses heterozygosity relative to allelic variation, detected genetic bottleneck effects in both allozyme and microsatellite loci
Resonant Coupling in the Heteronuclear Alkali Dimers for Direct Photoassociative Formation of X(0,0) Ultracold Molecules
Promising pathways for photoassociative formation of ultracold heteronuclear
alkali metal dimers in their lowest rovibronic levels (denoted X(0,0)) are
examined using high quality ab initio calculations of potential energy curves
currently available. A promising pathway for KRb, involving the resonant
coupling of the and states just below the lowest excited
asymptote (K()+Rb()), is found to occur also for RbCs and less
promisingly for KCs as well. The resonant coupling of the and
states, also just below the lowest excited asymptote, is found to be
promising for LiNa, LiK, LiRb, and less promising for LiCs and KCs. Direct
photoassociation to the state near dissociation appears promising in
the final dimers, NaK, NaRb, and NaCs, although detuning more than 100
cm below the lowest excited asymptote may be required.Comment: 20 pages, 12 figures, Submitted to Journal of Physical Chemistry
A Search for Molecular Gas in GHz Peaked Spectrum Radio Sources
We present searches for molecular gas (CO, OH, CS, and Ammonia) in six GHz
Peaked Spectrum (GPS) radio sources. We do not detect gas in any source and
place upper limits on the mass of molecular gas which are generally in the
range 1E9 to a few times 1E10 solar masses. These limits are consistent with
the following interpretations: (1) GPS sources do not require very dense gas in
their hosts, and (2) The GPS sources are unlikely to be confined by dense gas
and will evolve to become larger radio sources
The Regulation of Medical Device Representatives: A Question of Trust?
The introduction of new technologies in medical treatment has led to innovation in medical devices that are highly technical in their application and operation. The medical technology landscape is changeable and healthcare providers often turn to the medical device representatives (MDRs), employed by device manufacturers to help navigate the shifts and uncertainties. While the relationship between MDRs and healthcare providers can be a positive one focusing on appropriate use, selection and safety of devices, it is one that has evolved over time and is not independently regulated. In addition, patients, for the most part, are usually unaware of the involvement of MDRs in their healthcare. It is this knowledge gap with regard to the role of MDRs that is the focus of this paper. We argue that trust is at the heart of healthcare relationships and explore the nature of trust alongside the models of regulation of the medical device industry. We argue that MDRs may currently present a threat to both the interpersonal and the institutional trust of patients, and that regulation and policy responses are appropriate ways to address this risk. We consider potential regulatory frameworks and identify transparency and communication as the crucial characteristics of an appropriate response. We recommend that the polycentric nature of Australian healthcare regulation be cultivated through a multilayered approach, and that a positive obligation to inform the patient of the role of MDRs in their clinical care be established.Bernadette Richards, Susannah Sage Jacobson, Mianna Lotz, Wendy Roger
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