10,525 research outputs found
Measurements over distributed high performance computing and storage systems
A strawman proposal is given for a framework for presenting a common set of metrics for supercomputers, workstations, file servers, mass storage systems, and the networks that interconnect them. Production control and database systems are also included. Though other applications and third part software systems are not addressed, it is important to measure them as well
A Contracting, Turbulent, Starless Core in the Serpens Cluster
We present combined single-dish and interferometric CS(2--1) and N2H+(1--0)
observations of a compact core in the NW region of the Serpens molecular cloud.
The core is starless according to observations from optical to millimeter
wavelengths and its lines have turbulent widths and ``infall asymmetry''. Line
profile modeling indicates supersonic inward motions v_in>0.34 km/s over an
extended region L>12000AU. The high infall speed and large extent exceeds the
predictions of most thermal ambipolar diffusion models and points to a more
dynamical process for core formation. A short (dynamic) timescale, ~1e5
yr=L/v_in, is also suggested by the low N2H+ abundance ~1e-10.Comment: 11 pages including 2 figures. Accepted for publication in the
Astrophysical Journal Letter
Seasonal changes in photosynthesis of eight savanna tree species
Seasonal variations in carbon assimilation of eight tree species of a north Australian tropical savanna were examined over two wet seasons and one dry season (18 months). Assimilation rates (A) in the two evergreen species, Eucalyptus tetrodonta F. Muell. and E. miniata A. Cunn. ex Schauer, were high throughout the study although there was a 10-20% decline in the dry season compared with the wet season. The three semi-deciduous species (Erythrophleum chlorostachys (F. Muell.) Baillon, Eucalyptus clavigera A. Cunn. ex Schauer, and Xanthostemon paradoxus F. Muell.) showed a 25-75% decline in A in the dry season compared with the wet season, and the deciduous species (Terminalia ferdinandiana Excell, Planchonia careya (F. Muell.) Kunth, and Cochlospermum fraseri Planchon) were leafless for several months in the dry season. Generally, the ratio of intercellular CO2 concentration to ambient CO2 concentration (C(i):C(a)) was larger in the wet season than in the dry season, indicating a smaller stomatal limitation of photosynthesis in the wet season compared with the dry season. In all species, the C(i):C(a) ratio and A were essentially independent of leaf-to-air vapor pressure difference (LAVPD) during the wet season, but both parameters generally declined with increasing LAVPD in the dry season. The slope of the positive correlation between A and transpiration rate (E) was less in the wet season than in the dry season. There was no evidence that high E inhibited A. Instantaneous transpiration efficiency was lowest in the wet season and highest during the dry season. Nitrogen-use efficiency (NUE) was higher in the wet season than in the dry season because the decline in A in the dry season was proportionally larger than the decline in foliar nitrogen content. In the wet season, evergreen species exhibited higher NUE than semi-deciduous and deciduous species. In all species, A was linearly correlated with specific leaf area (SLA) and foliar N content. Foliar N content increased with increasing SLA. All species showed a decline in midday leaf water potential as the dry season progressed. Dry season midday water potentials were lowest in semi-deciduous species and highest in the deciduous species, with evergreen species exhibiting intermediate values
The Circumstellar Environment of High Mass Protostellar Objects. III Evidence of Infall?
The results are presented of a molecular line survey to search for the
spectral signature of infall towards 77 850 micron continuum sources believed
to be candidate high mass protostellar objects. Up to six different
transitions, HCO+ 1-0, 3-2 and 4-3, H2CO 2_12-1_11, N2H+ and H13CO+ 3-2, were
observed towards each source. Towards the peak of the 850 micron emission, N2H+
was typically strong, with a peak antenna temperature of ~1.5K, with a typical
linewidth of ~2km/s. The good agreement between the velocity and velocity width
of the N2H+ and H13CO+ emission suggests that both species are tracing similar
material in the sources. With respect to the velocity of the N2H+, there is a
statistically significant excess of blue asymmetric line profiles in both the
HCO+ 1-0 and H2CO transitions. This excess reaches levels similar to that seen
towards samples of low mass protostars, and suggests that the material around
these high mass sources is infalling. We identify 22 promising candidate infall
sources which show at least one blue asymmetric line profile and no red
asymmetric profiles. The infall velocity is estimated to be in the range of 0.1
km/s to 1 km/s with an implied mass accretion rate of between 2x10^{-4} Msol/yr
and 10^{-3}Msol/yr.Comment: Accepted for publication in Astronomy and Astrophysics. Higher
resolution versions of Figures 1 and 2 are available from
http://www.jb.man.ac.uk/~gaf/Papers.htm
A High Resolution Study of the Slowly Contracting, Starless Core L1544
We present interferometric observations of N2H+(1--0) in the starless, dense
core L1544 in Taurus. Red-shifted self-absorption, indicative of inward
motions, is found toward the center of an elongated core. The data are fit by a
non-spherical model consisting of two isothermal, rotating, centrally condensed
layers. Through a hybrid global-individual fit to the spectra, we map the
variation of infall speed at scales ~1400AU and find values ~0.08 km/s around
the core center. The inward motions are small in comparison to thermal,
rotational, and gravitational speeds but are large enough to suggest that L1544
is very close to forming a star.Comment: 11 pages, 2 figures Accepted for publication in Astrophysical Journal
Letter
Celebration of Brockport Faculty & Staff Scholarship : 2014-2017
Compiled by College at Brockport faculty member Linda Hacker, and professional staff member Kim Myers, with assistance from Grants Development Director Patricia Williams. Foreword by Drake Library Director, Mary Jo Orzech.
... [a bibliography that] represents over 200 publications from the faculty and staff of The College at Brockport during 2014-2016, as well as 123 creative works and 139 grants.... is not exhaustive, but is intended as a representative sample...https://digitalcommons.brockport.edu/bookshelf/1422/thumbnail.jp
Constraints on star formation theories from the Serpens molecular cloud and protocluster
We have mapped the large-scale structure of the Serpens cloud core using
moderately optically thick (13CO(1--0) and CS(2--1)) and optically thin tracers
(C18O(1--0), C34S(2--1), and N2H+(1--0)), using the 16-element focal plane
array operating at a wavelength of 3mm at the Five College Radio Astronomy
Observatory. Our main goal was to study the large-scale distribution of the
molecular gas in the Serpens region and to understand its relation with the
denser gas in the cloud cores, previously studied at high angular resolution.
All our molecular tracers show two main gas condensations, or sub-clumps,
roughly corresponding to the North-West and South-East clusters of
submillimeter continuum sources. We also carried out a kinematical study of the
Serpens cloud. The 13CO and C18O(1--0) maps of the centroid velocity show an
increasing, smooth gradient in velocity from East to West, which we think may
be caused by a global rotation of the Serpens molecular cloud whose rotation
axis is roughly aligned in the SN direction. Although it appears that the cloud
angular momentum is not sufficient for being dynamically important in the
global evolution of the cluster, the fact that the observed molecular outflows
are roughly aligned with it may suggest a link between the large-scale angular
momentum and the circumstellar disks around individual protostars in the
cluster. We also used the normalized centroid velocity difference as an infall
indicator. We find two large regions of the map, approximately coincident with
the SE and NW sub-clumps, which are undergoing an infalling motion. Although
our evidence is not conclusive, our data appear to be in qualitative agreement
with the expectation of a slow contraction followed by a rapid and highly
efficient star formation phase in localized high density regions.Comment: 17 pages, A&A in press, full resolution figures available at
http://www.arcetri.astro.it/~lt/preprints/preprints.htm
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