165,365 research outputs found
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BaBar simulation production - A millennium of work in under a year
The BaBar experiment requires simulated events beyond the ability of a single computing site to provide. This paper describes the evolution of simulation and job management methods to meet the physics community requirements and how production became distributed to use resources beyond any one computing center. The evolution of BaBar simulation along with the development of the distribution of the computing effort is described. As the computing effort is distributed to more sites there is a need to simplify production so the effort does not multiply with number of production centers. Tools are created to be flexible in handling errors and failures that happen in the system and respond accordingly, this reduces failure rates and production effort. This paper will focus on one cycle of simulation production within BaBar as a description of a large scale computing effort which was fully performed, and provided new simulation data to the users on time
The Grow-Shrink strategy for learning Markov network structures constrained by context-specific independences
Markov networks are models for compactly representing complex probability
distributions. They are composed by a structure and a set of numerical weights.
The structure qualitatively describes independences in the distribution, which
can be exploited to factorize the distribution into a set of compact functions.
A key application for learning structures from data is to automatically
discover knowledge. In practice, structure learning algorithms focused on
"knowledge discovery" present a limitation: they use a coarse-grained
representation of the structure. As a result, this representation cannot
describe context-specific independences. Very recently, an algorithm called
CSPC was designed to overcome this limitation, but it has a high computational
complexity. This work tries to mitigate this downside presenting CSGS, an
algorithm that uses the Grow-Shrink strategy for reducing unnecessary
computations. On an empirical evaluation, the structures learned by CSGS
achieve competitive accuracies and lower computational complexity with respect
to those obtained by CSPC.Comment: 12 pages, and 8 figures. This works was presented in IBERAMIA 201
Acceleration of convergence of vector sequences
A general approach to the construction of accelerated convergence methods for vector sequences is proposed. A simplified version of minimal polynomial extrapolation is emphasized. The convergence of this method is analyzed and it is shown that it is especially suitable for accelerating the convergence of vector sequences that are obtained when one solves linear systems of equations iteratively
The Very Massive Star Content of the Nuclear Star Clusters in NGC 5253
The blue compact dwarf galaxy NGC 5253 hosts a very young starburst
containing twin nuclear star clusters, separated by a projected distance of 5
pc. One cluster (#5) coincides with the peak of the H-alpha emission and the
other (#11) with a massive ultracompact H II region. A recent analysis of these
clusters shows that they have a photometric age of 1+/-1 Myr, in apparent
contradiction with the age of 3-5 Myr inferred from the presence of Wolf-Rayet
features in the cluster #5 spectrum. We examine Hubble Space Telescope
ultraviolet and Very Large Telescope optical spectroscopy of #5 and show that
the stellar features arise from very massive stars (VMS), with masses greater
than 100 Msun, at an age of 1-2 Myr. We further show that the very high
ionizing flux from the nuclear clusters can only be explained if VMS are
present. We investigate the origin of the observed nitrogen enrichment in the
circum-cluster ionized gas and find that the excess N can be produced by
massive rotating stars within the first 1 Myr. We find similarities between the
NGC 5253 cluster spectrum and those of metal poor, high redshift galaxies. We
discuss the presence of VMS in young, star-forming galaxies at high redshift;
these should be detected in rest frame UV spectra to be obtained with the James
Webb Space Telescope. We emphasize that population synthesis models with upper
mass cut-offs greater than 100 Msun are crucial for future studies of young
massive star clusters at all redshifts.Comment: 11 pages, 7 figures, accepted for publication in Astrophysical
Journa
The 50-horsepower solar-powered irrigation facility located near Gila Bend, Arizona
The 50 horsepower solar powered irrigation facility near Gila Bend, Arizona which includes a Rankine cycle demonstrates the technical feasibility of solar powered pumping. The design of a facility specifically for the irrigation farmer using the technology that has been developed over the last four years is proposed
Unpulsed UBV Optical Emission from the Crab Pulsar
Based on observations of the Crab pulsar using the TRIFFID high speed imaging
photometer in the UBV bands using the Special Astrophysical Observatory's 6m
telescope in the Russian Caucasus, we report the detection of pronounced
emission during the so-called `off' phase of emission. Following de-extinction,
this unpulsed component of emission is shown to be consistent with a power law
with an exponent of alpha = -0.60 +/- 0.37, the uncertainty being dominated by
the error associated with the independent CCD photometry used to reference the
TRIFFID data. This suggests a steeper power law form than that reported
elsewhere in the literature for the total integrated spectrum, which is
essentially flat with alpha ~ 0.1, although the difference in this case is only
significant at the ~ 2 sigma level. Deeper reference integrated and TRIFFID
phase-resolved photometry in these bands in conjunction with further
observations in the UV and R region would constrain this fit further.Comment: 26 pages, 2 figures, uses aasms4.sty, accepted for publication in the
Astrophysical Journa
Methodology for estimation of total body composition in laboratory mammals
A standardized dissection and chemical analysis procedure was developed for individual animals of several species in the size range mouse to monkey (15 g to 15 kg). The standardized procedure permits rigorous comparisons to be made both interspecifically and intraspecifically of organ weights and gross chemical composition in mammalian species series, and was applied successfully to laboratory mice, hamsters, rats, guinea pigs, and rabbits, as well as to macaque monkeys. The procedure is described in detail
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Chemistry and valency spectra of Chromite in SNC meteorites
Shergottite chromite core mantle sources were Al-poor, Fe-rich, low Fe^{3+}/Fe^{2+}, fO_{2} 1 to 4 unit
Wolf-Rayets in IC10: Probing the Nearest Starburst
IC10 is the nearest starburst galaxy, as revealed both by its Halpha surface
brightness and the large number of Wolf-Rayet stars (WRs) per unit area. The
relative number of known WC- to WN-type WRs has been thought to be unusually
high (~2), unexpected for IC10's metallicity. In this Letter we report the
first results of a new and deeper survey for WRs in IC10. We sucessfully
detected all of the spectroscopically known WRs, and based upon comparisons
with a neighboring control field, estimate that the total number of WRs in IC10
is about 100. We present spectroscopic confirmation of two of our WR
candidates, both of which are of WN type. Our photometric survey predicts that
the actual WC/WN ratio is ~0.3. This makes the WC/WN ratio of IC 10 consistent
with that expected for its metallicity, but greatly increases the already
unusually high number of WRs, resulting in a surface density that is about 20
times higher than in the LMC. If the majority of these candidates are
spectroscopically confirmed, IC10 must have an exceptional population of high
mass stars.Comment: Accepted by ApJL; only minor correction in this versio
Discovery of a Spin-Down State Change in the LMC Pulsar B0540-69
We report the discovery of a large, sudden, and persistent increase in the
spin-down rate of B0540-69, a young pulsar in the Large Magellanic Cloud, using
observations from the Swift and RXTE satellites. The relative increase in the
spin-down rate of 36% is unprecedented for B0540-69. No accompanying change in
the spin rate is seen, and no change is seen in the pulsed X-ray emission from
B0540-69 following the change in the spin-down rate. Such large relative
changes in the spin-down rate are seen in the recently discovered class of
'intermittent pulsars', and we compare the properties of B0540-69 to such
pulsars. We consider possible changes in the magnetosphere of the pulsar that
could cause such a large change in the spin-down rate.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter
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