587 research outputs found
Skylab vectorcardiograph: System description and in flight operation
A vectorcardiograph system was used to measure cardiac electrical activity of Skylab crewmen. This system was chosen because of its data-quantification advantages. The vectorcardiograph was required to meet recommended American Heart Association specifications, to withstand space environmental extremes, and to facilitate data gathering in the weightless environment. The vectorcardiograph system performed without failure, and all projected data were acquired. The appendix lists the design specifications used for the Skylab vectorcardiograph system
Determining the cosmic ray ionization rate in dynamically evolving clouds
The ionization fraction is an important factor in determining the chemical
and physical evolution of star forming regions. In the dense, dark starless
cores of such objects, the ionization rate is dominated by cosmic rays; it is
therefore possible to use simple analytic estimators, based on the relative
abundances of different molecular tracers, to determine the cosmic ray
ionization rate.
This paper uses a simple model to investigate the accuracy of two well-known
estimators in dynamically evolving molecular clouds. It is found that, although
the analytical formulae based on the abundances of H3+,H2,CO,O,H2O and HCO+
give a reasonably accurate measure of the cosmic ray ionization rate in static,
quiescent clouds, significant discrepancies occur in rapidly evolving
(collapsing) clouds. As recent evidence suggests that molecular clouds may
consist of complex, dynamically evolving sub-structure, we conclude that simple
abundance ratios do not provide reliable estimates of the cosmic ray ionization
rate in dynamically active regions.Comment: Accepted by A&A. 17 pages, 4 figure
The Ultraviolet Attenuation Law in Backlit Spiral Galaxies
(Abridged) The effective extinction law (attenuation behavior) in galaxies in
the emitted ultraviolet is well known only for actively star-forming objects
and combines effects of the grain properties, fine structure in the dust
distribution, and relative distributions of stars and dust. We use GALEX, XMM
Optical Monitor, and HST data to explore the UV attenuation in the outer parts
of spiral disks which are backlit by other UV-bright galaxies, starting with
candidates provided by Galaxy Zoo participants. Our analysis incorporates
galaxy symmetry, using non-overlapping regions of each galaxy to derive error
estimates on the attenuation measurements. The entire sample has an attenuation
law close to the Calzetti et al. (1994) form; the UV slope for the overall
sample is substantially shallower than found by Wild et al. (2011), a
reasonable match to the more distant galaxies in our sample but not to the
weighted combination including NGC 2207. The nearby, bright spiral NGC 2207
alone gives accuracy almost equal to the rest of our sample, and its outer arms
have a very low level of foreground starlight. This "grey" law can be produced
from the distribution of dust alone, without a necessary contribution from
differential escape of stars from dense clouds. The extrapolation needed to
compare attenution between backlit galaxies at moderate redshifts, and local
systems from SDSS data, is mild enough to allow use of galaxy overlaps to trace
the cosmic history of dust. For NGC 2207, the covering factor of clouds with
small optical attenuation becomes a dominant factor farther into the
ultraviolet, which opens the possibility that widespread diffuse dust dominates
over dust in star-forming regions deep into the ultraviolet. Comparison with
published radiative-transfer models indicates that the role of dust clumping
dominates over differences in grain populations, at this spatial resolution.Comment: In press, Astronomical Journa
City life makes females fussy : sex differences in habitat use of temperate bats in urban areas
Urbanization is a major driver of the global loss of biodiversity; to mitigate its adverse effects, it is essential to understand what drives species' patterns of habitat use within the urban matrix. While many animal species are known to exhibit sex differences in habitat use, adaptability to the urban landscape is commonly examined at the species level, without consideration of intraspecific differences. The high energetic demands of pregnancy and lactation in female mammals can lead to sexual differences in habitat use, but little is known of how this might affect their response to urbanization. We predicted that female Pipistrellus pygmaeus would show greater selectivity of forging locations within urban woodland in comparison to males at both a local and landscape scale. In line with these predictions, we found there was a lower probability of finding females within woodlands which were poorly connected, highly cluttered, with a higher edge : interior ratio and fewer mature trees. By contrast, habitat quality and the composition of the surrounding landscape were less of a limiting factor in determining male distributions. These results indicate strong sexual differences in the habitat use of fragmented urban woodland, and this has important implications for our understanding of the adaptability of bats and mammals more generally to urbanization.Publisher PDFPeer reviewe
Galaxy Zoo: Multimergers and the Millennium Simulation
We present a catalogue of 39 multiple mergers, found using the mergers catalogue of the Galaxy Zoo project for z <0.1, and compare them to corresponding semi-analytical galaxies from the Millennium Simulation. We estimate the (volume-limited) multimerger fraction of the local Universe using our sample and find it to be at least 2 orders of magnitude less than binary mergers - in good agreement with the simulations (especially the Munich group). We then investigate the properties of galaxies in binary mergers and multimergers (morphologies, colours, stellar masses and environment) and compare these results with those predicted by the semi-analytical galaxies. We find that multimergers favour galaxies with properties typical of elliptical morphologies and that this is in qualitative agreement with the models. Studies of multimergers thus provide an independent (and largely corroborating) test of the Millennium semi-analytical models.Peer reviewe
Predicting Interstellar Object Chemodynamics with Gaia
The interstellar object population of the Milky Way is a product of its
stars. However, what is in fact a complex structure in the Solar neighbourhood
has traditionally in ISO studies been described as smoothly distributed. Using
a debiased stellar population derived from the Gaia DR3 stellar sample, we
infer that the velocity distribution of ISOs is far more textured than a smooth
Gaussian. The moving groups caused by Galactic resonances dominate the
distribution. 1I/`Oumuamua and 2I/Borisov have entirely normal places within
these distributions; 1I is within the non-coeval moving group that includes the
Matariki (Pleiades) cluster, and 2I within the Coma Berenices moving group. We
show that for the composition of planetesimals formed beyond the ice line,
these velocity structures also have a chemodynamic component. This variation
will be visible on the sky. We predict that this richly textured distribution
will be differentiable from smooth Gaussians in samples that are within the
expected discovery capacity of the Vera C. Rubin Observatory. Solar
neighbourhood ISOs will be of all ages and come from a dynamic mix of many
different populations of stars, reflecting their origins from all around the
Galactic disk.Comment: Submitted to A
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