7,252 research outputs found
Astrobiological Effects of F, G, K and M Main-Sequence Stars
We focus on the astrobiological effects of photospheric radiation produced by
main-sequence stars of spectral types F, G, K, and M. The photospheric
radiation is represented by using realistic spectra, taking into account
millions or hundred of millions of lines for atoms and molecules. DNA is taken
as a proxy for carbon-based macromolecules, assumed to be the chemical
centerpiece of extraterrestrial life forms. Emphasis is placed on the
investigation of the radiative environment in conservative as well as
generalized habitable zones.Comment: 3 pages, 3 figures; submitted to: Exoplanets: Detection, Formation
and Dynamics, IAU Symposium 249, eds. Y.S. Sun and S. Ferraz-Mello (San
Francisco: Astr. Soc. Pac.
Molecular clouds and clumps in the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
The Boston University-Five College Radio Astronomy Observatory (BU-FCRAO)
Galactic Ring Survey (GRS) of 13 CO (1-0) emission covers Galactic longitudes
18 deg < l < 55.7 deg and Galactic latitudes |b| <= 1 deg. Using the SEQUOIA
array on the FCRAO 14m telescope, the GRS fully sampled the 13 CO Galactic
emission (46 arcsec angular resolution on a 22 arcsec grid) and achieved a
spectral resolution of 0.21 km/s. Because the GRS uses 13 CO, an optically thin
tracer, rather than 12 CO, an optically thick tracer, the GRS allows a much
better determination of column density and also a cleaner separation of
velocity components along a line of sight. With this homogeneous, fully-sampled
survey of 13 CO, emission, we have identified 829 molecular clouds and 6124
clumps throughout the inner Galaxy using the CLUMPFIND algorithm. Here we
present details of the catalog and a preliminary analysis of the properties of
the molecular clouds and their clumps. Moreover, we compare clouds inside and
outside of the 5 kpc ring and find that clouds within the ring typically have
warmer temperatures, higher column densities, larger areas, and more clumps
compared to clouds located outside the ring. This is expected if these clouds
are actively forming stars. This catalog provides a useful tool for the study
of molecular clouds and their embedded young stellar objects.Comment: 29 pages. ApJ in pres
A Herschel/HIFI Legacy Survey of HF and H2O in the Galaxy: Probing Diffuse Molecular Cloud Chemistry
We combine Herschel observations of a total of 12 sources to construct the
most uniform survey of HF and H2O in our Galactic disk. Both molecules are
detected in absorption along all sight lines. The high spectral resolution of
the Heterodyne Instrument for the Far-Infrared (HIFI) allows us to compare the
HF and H2O distributions in 47 diffuse cloud components sampling the disk. We
find that the HF and H2O velocity distributions follow each other almost
perfectly and establish that HF and H2O probe the same gas-phase volume. Our
observations corroborate theoretical predictions that HF is a sensitive tracer
of H2 in diffuse clouds, down to molecular fractions of only a few percent.
Using HF to trace H2 in our sample, we find that the N(H2O)-to-N(HF) ratio
shows a narrow distribution with a median value of 1.51. Our results further
suggest that H2O might be used as a tracer of H2 -within a factor 2.5- in the
diffuse interstellar medium. We show that the measured factor of ~2.5 variation
around the median is driven by true local variations in the H2O abundance
relative to H2 throughout the disk. The latter variability allows us to test
our theoretical understanding of the chemistry of oxygen-bearing molecules in
the diffuse gas. We show that both gas-phase and grain-surface chemistry are
required to reproduce our H2O observations. This survey thus confirms that
grain surface reactions can play a significant role in the chemistry occurring
in the diffuse interstellar medium n_H < 1000 cm^-3.Comment: 53 pages; 12 figures, accepted for publication in ApJ main journa
Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?
The origin of striations aligned along the local magnetic field direction in
the translucent envelope of the Taurus molecular cloud is examined with new
observations of 12CO and 13CO J=2-1 emission obtained with the 10~m
submillimeter telescope of the Arizona Radio Observatory. These data identify a
periodic pattern of excess blue and redshifted emission that is responsible for
the striations. For both 12CO and 13CO, spatial variations of the J=2-1 to
J=1-0 line ratio are small and are not spatially correlated with the striation
locations. A medium comprised of unresolved CO emitting substructures (cells)
with a beam area filling factor less than unity at any velocity is required to
explain the average line ratios and brightness temperatures. We propose that
the striations result from the modulation of velocities and the beam filling
factor of the cells as a result of either the Kelvin-Helmholtz instability or
magnetosonic waves propagating through the envelope of the Taurus molecular
cloud. Both processes are likely common features in molecular clouds that are
sub-Alfvenic and may explain low column density, cirrus-like features similarly
aligned with the magnetic field observed throughout the interstellar medium in
far-infrared surveys of dust emission.Comment: 11 pages, 4 figures. Accepted for publication in MNRA
Contaminant removal from enclosed atmospheres by regenerable adsorbents
A system for removing contaminants from spacecraft atmospheres was studied, which utilizes catalyst-impregnated activated carbon followed by in-situ regeneration by low-temperature catalytic oxidation of the adsorbed contaminants. Platinum was deposited on activated carbon by liquid phase impregnation with chloroplatinic acid, followed by drying and high-temperature reduction. Results were obtained for the seven selected spacecraft contaminants by means of three experimental test systems. The results indicate that the contaminants could be removed by oxidation with very little loss in adsorptive capacity. The advantages of a catalyst-impregnated carbon for oxidative regeneration are found to be significant enough to warrent its use
Performance modeling of ultraviolet Raman lidar systems for daytime profiling of atmospheric water vapor
We describe preliminary results from a comprehensive computer model developed to guide optimization of a Raman lidar system for measuring daytime profiles of atmospheric water vapor, emphasizing an ultraviolet, solar-blind approach
Diabetic nephropathy: What does the future hold?
The consensus management of diabetic nephropathy (DN) in 2015 involves good control of glycaemia, dyslipidaemia and blood pressure (BP). Blockade of the renin–angiotensin–aldosterone system using angiotensin-converting enzyme inhibitors, angiotensin-2 receptor blockers or mineralocorticoid inhibitors are key therapeutic approaches, shown to be beneficial once overt nephropathy is manifest, as either, or both, of albuminuria and loss of glomerular filtration rate. Some significant additional clinical benefits in slowing the progression of DN was reported from the Remission clinic experience, where simultaneous intensive control of BP, tight glycaemic control, weight loss, exercise and smoking cessation were prioritised in the management of DN. This has not proved possible to translate to more conventional clinical settings. This review briefly looks over the history and limitations of current therapy from landmark papers and expert reviews, and following an extensive PubMed search identifies the most promising clinical biomarkers (both established and proposed). Many challenges need to be addressed urgently as in order to obtain novel therapies in the clinic; we also need to examine what we mean by remission, stability and progression of DN in the modern era
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