186 research outputs found
Bigger Buffer k-d Trees on Multi-Many-Core Systems
A buffer k-d tree is a k-d tree variant for massively-parallel nearest neighbor search. While providing valuable speed-ups on modern many-core devices in case both a large number of reference and query points are given, buffer k-d trees are limited by the amount of points that can fit on a single device. In this work, we show how to modify the original data structure and the associated workflow to make the overall approach capable of dealing with massive data sets. We further provide a simple yet efficient way of using multiple devices given in a single workstation. The applicability of the modified framework is demonstrated in the context of astronomy, a field that is faced with huge amounts of data
Numerical Simulations of Globular Cluster Formation
We examine various physical processes associated with the formation of
globular clusters by using the three-dimensional Smoothed Particle
Hydrodynamics (SPH) code. Our code includes radiative cooling of gases, star
formation, energy feedback from stars including stellar winds and supernovae,
and chemical enrichment by stars. We assume that, in the collapsing galaxy,
isothermal cold clouds form through thermal condensations and become
proto-globular clouds. We calculate the size of proto-globular clouds by
solving the linearized equations for perturbation. We compute the evolution of
the inner region of the proto-cloud with our SPH code for various initial
radius and initial composition of gases. When the initial gases contain no
heavy elements, the evolution of proto-clouds sensitively depends on the
initial radius. For a smaller initial radius, the initial star burst is so
intense that the subsequent star formation occurs in the central regions to
form a dense star cluster as massive as the globular cluster. When the initial
gases contain some heavy elements, the metallicity of gases affects the
evolution and the final stellar mass. If the initial radius of the
proto-globular clouds was relatively large, the formation of a star cluster as
massive as the globular clusters requires the initial metallicity as high as
[Fe/H] . The self-enrichment of heavy elements in the star cluster
does not occur in all cases.Comment: Accpeted for publication in the ApJ. Correctiong errors in Table
Nucleosynthesis in Type II Supernovae
Presupernova evolution and explosive nucleosynthesis in massive stars for
main-sequence masses from 13 to 70 are calculated. We
examine the dependence of the supernova yields on the stellar mass,
^{12}C(\alpha, \gamma) ^{16}O} rate, and explosion energy. The supernova
yields integrated over the initial mass function are compared with the solar
abundances.Comment: 1 Page Latex source, 10 PostScript figures, to appear in Nuclear
Physics A, Vol. A616 (1997
Benchmarks for Pir\'a 2.0, a Reading Comprehension Dataset about the Ocean, the Brazilian Coast, and Climate Change
Pir\'a is a reading comprehension dataset focused on the ocean, the Brazilian
coast, and climate change, built from a collection of scientific abstracts and
reports on these topics. This dataset represents a versatile language resource,
particularly useful for testing the ability of current machine learning models
to acquire expert scientific knowledge. Despite its potential, a detailed set
of baselines has not yet been developed for Pir\'a. By creating these
baselines, researchers can more easily utilize Pir\'a as a resource for testing
machine learning models across a wide range of question answering tasks. In
this paper, we define six benchmarks over the Pir\'a dataset, covering closed
generative question answering, machine reading comprehension, information
retrieval, open question answering, answer triggering, and multiple choice
question answering. As part of this effort, we have also produced a curated
version of the original dataset, where we fixed a number of grammar issues,
repetitions, and other shortcomings. Furthermore, the dataset has been extended
in several new directions, so as to face the aforementioned benchmarks:
translation of supporting texts from English into Portuguese, classification
labels for answerability, automatic paraphrases of questions and answers, and
multiple choice candidates. The results described in this paper provide several
points of reference for researchers interested in exploring the challenges
provided by the Pir\'a dataset.Comment: Accepted at Data Intelligence. Online ISSN 2641-435
Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants
We obtained FLAMES-GIRAFFE spectra (R=22,500) at the ESO Very Large Telescope
for 650 bulge red giant branch (RGB) stars and performed spectral synthesis to
measure Mg, Ca, Ti, and Si abundances. This sample is composed of 474 giant
stars observed in 3 fields along the minor axis of the Galactic bulge and at
latitudes b=-4, b=-6, b=-12. Another 176 stars belong to a field containing the
globular cluster NGC 6553, located at b=-3 and 5 degrees away from the other
three fields along the major axis. Our results confirm, with large number
statistics, the chemical similarity between the Galactic bulge and thick disk,
which are both enhanced in alpha elements when compared to the thin disk. In
the same context, we analyze [alpha/Fe] vs. [Fe/H] trends across different
bulge regions. The most metal rich stars, showing low [alpha/Fe] ratios at b=-4
disappear at higher Galactic latitudes in agreement with the observed
metallicity gradient in the bulge. Metal-poor stars ([Fe/H]<-0.2) show a
remarkable homogeneity at different bulge locations. We have obtained further
constrains for the formation scenario of the Galactic bulge. A metal-poor
component chemically indistinguishable from the thick disk hints for a fast and
early formation for both the bulge and the thick disk. Such a component shows
no variation, neither in abundances nor kinematics, among different bulge
regions. A metal-rich component showing low [alpha/Fe] similar to those of the
thin disk disappears at larger latitudes. This allows us to trace a component
formed through fast early mergers (classical bulge) and a disk/bar component
formed on a more extended timescale.Comment: 13 pages, 17 figures. Accepted for publication in Astronomy and
Astrophysic
Monoallelic maternal expression of STAT5A affects embryonic survival in cattle
<p>Abstract</p> <p>Background</p> <p>Reproductive disorders and infertility are surprisingly common in the human population as well as in other species. The decrease in fertility is a major cause of cow culling and economic loss in the dairy herd. The conception rate has been declining for the past 30–50 years. Conception rate is the product of fertilization and embryonic survival rates. In a previous study, we have identified associations of several single nucleotide polymorphisms (SNPs) in the signal transducer and activator 5A (<it>STAT5A</it>) with fertilization and survival rates in an <it>in </it>vitro experimental system. The objectives of this study are to fine map the <it>STAT5A </it>region in a search for causative mutations and to investigate the parent of origin expression of this gene.</p> <p>Results</p> <p>We have performed a total of 5,222 fertilizations and produced a total of 3,696 in vitro fertilized embryos using gametes from 440 cows and eight bulls. A total of 37 SNPs were developed in a 63.4-kb region of genomic sequence that includes <it>STAT5A</it>, <it>STAT3</it>, and upstream and downstream sequences of these genes. SNP153137 (G/C) in exon 8 of <it>STAT5A </it>was associated with a significant variability in embryonic survival and fertilization rate compared to all other examined SNPs. Expression analysis revealed that <it>STAT5A </it>is primarily monoallelically expressed in early embryonic stages but biallelically expressed in later fetal stages. Furthermore, the occurrence of monoallelic maternal expression of <it>STAT5A </it>was significantly higher in blastocysts, while paternal expression was more frequent in degenerative embryos.</p> <p>Conclusion</p> <p>Our results imply that <it>STAT5A </it>affects embryonic survival in a manner influenced by developmental stage and allele parent of origin.</p
Formation of Multiple Populations in Globular Clusters: Another Possible Scenario
While chemical composition spreads are now believed to be a universal
characteristic of globular clusters (GCs), not all of them present multiple
populations in their color-magnitude diagrams (CMDs). Here we present a new
scenario for the formation of GCs, in an attempt to qualitatively explain this
otherwise intriguing observational framework. Our scenario divides GCs into
three groups, depending on the initial mass (M_I) of the progenitor structure
(PS), as follows. i) Massive PSs can retain the gas ejected by massive stars,
including the ejecta of core-collapse SNe. ii) Intermediate-mass PSs can retain
at least a fraction of the fast winds of massive stars, but none of the
core-collapse SNe ejecta. iii) Low-mass PSs can only retain the slow winds of
intermediate-mass stars. Members of the first group would include omega
Centauri (NGC 5139), M54 (NGC 6715), M22 (NGC 6656), and Terzan 5, whereas NGC
2808 (and possibly NGC 2419) would be members of the second group. The
remaining GCs which only present a spread in light elements, such as O and Na,
would be members of the third group. According to our scenario, the different
components in omega Cen should not display a sizeable spread in age. We argue
that this is consistent with the available observations. We give other simple
arguments in favor of our scenario, which can be described in terms of two main
analytical relations: i) Between the actual observed ratio between first and
second generation stars (R_SG^FG) and the fraction of first generation stars
that have been lost by the GC (S_L); and ii) Between S_L and M_I. We also
suggest a series of future improvements and empirical tests that may help
decide whether the proposed scenario properly describes the chemical evolution
of GCs.Comment: Accepted for publication in Astronomy and Astrophysic
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