3,183 research outputs found
Cardiac myoglobin deficit has evolved repeatedly in teleost fishes
Peer reviewedPublisher PD
Statistical Evidence for Three classes of Gamma-ray Bursts
Two different multivariate clustering techniques, the K-means partitioning
method and the Dirichlet process of mixture modeling, have been applied to the
BATSE Gamma-ray burst (GRB) catalog, to obtain the optimum number of coherent
groups. In the standard paradigm, GRB are classified in only two groups, the
long and short bursts. However, for both the clustering techniques, the optimal
number of classes was found to be three, a result which is consistent with
previous statistical analysis. In this classification, the long bursts are
further divided into two groups which are primarily differentiated by their
total fluence and duration and hence are named low and high fluence GRB.
Analysis of GRB with known red-shifts and spectral parameters suggests that low
fluence GRB have nearly constant isotropic energy output of 10^{52} ergs while
for the high fluence ones, the energy output ranges from 10^{52} to 10^{54}
ergs. It is speculated that the three kinds of GRBs reflect three different
origins: mergers of neutron star systems, mergers between white dwarfs and
neutron stars, and collapse of massive stars.Comment: 7 pages, accepted for publication in the Astrophysical Journal. Minor
editorial change
Significance analysis and statistical mechanics: an application to clustering
This paper addresses the statistical significance of structures in random
data: Given a set of vectors and a measure of mutual similarity, how likely
does a subset of these vectors form a cluster with enhanced similarity among
its elements? The computation of this cluster p-value for randomly distributed
vectors is mapped onto a well-defined problem of statistical mechanics. We
solve this problem analytically, establishing a connection between the physics
of quenched disorder and multiple testing statistics in clustering and related
problems. In an application to gene expression data, we find a remarkable link
between the statistical significance of a cluster and the functional
relationships between its genes.Comment: to appear in Phys. Rev. Let
Essais d'introduction de quatre espÚces de bousiers Scarabaeinae en Nouvelle Calédonie et au Vanuatu
La Nouvelle CalĂ©donie et le Vanuatu Ă©taient initialement dĂ©pourvus de gros mammifĂšres et leur entomofaune ne comportait pas de bousiers susceptibles de fractionner et d'enfouir les dĂ©jections des ruminants importĂ©s par l'homme. En prolongement d'une vaste opĂ©ration d'introduction de bousiers effectuĂ©e en Australie par le CSIRO, on a essayĂ© d'implanter dans ces deux archipels quatre espĂšces de #Scarabaeinae appartenant aux tribus des Onthophagini (#Onthophagus gazella), des Oniticellini (#Euoniticellus intermedius et #Liatongus militaris) et des Sisyphini (#Sisyphus spinipes). Cinq ans aprĂšs ces tentatives, on peut estimer que trois espĂšces se sont Ă©tablies dans chacun de ces ensembles d'Ăźles : #O. gazella, #E. intermedius et #S. spinipes en Nouvelle CalĂ©donie; #O. gazella, #E. intermedius et #L. militaris au Vanuatu. Les enquĂȘtes effectuĂ©es ont Ă©galement permis de rĂ©colter deux espĂšces probablement introduites antĂ©rieurement : #Onthophagus consentaneus en Nouvelle CalĂ©donie et #Copris incertus$ au Vanuatu. (RĂ©sumĂ© d'auteur
A Dedicated M-Dwarf Planet Search Using The Hobby-Eberly Telescope
We present first results of our planet search program using the 9.2 meter
Hobby-Eberly Telescope (HET) at McDonald Observatory to detect planets around
M-type dwarf stars via high-precision radial velocity (RV) measurements.
Although more than 100 extrasolar planets have been found around solar-type
stars of spectral type F to K, there is only a single M-dwarf (GJ 876, Delfosse
et al. 1998; Marcy et al. 1998; Marcy et al. 2001) known to harbor a planetary
system. With the current incompleteness of Doppler surveys with respect to
M-dwarfs, it is not yet possible to decide whether this is due to a fundamental
difference in the formation history and overall frequency of planetary systems
in the low-mass regime of the Hertzsprung-Russell diagram, or simply an
observational bias. Our HET M-dwarf survey plans to survey 100 M-dwarfs in the
next 3 to 4 years with the primary goal to answer this question. Here we
present the results from the first year of the survey which show that our
routine RV-precision for M-dwarfs is 6 m/s. We found that GJ 864 and GJ 913 are
binary systems with yet undetermined periods, while 5 out of 39 M-dwarfs reveal
a high RV-scatter and represent candidates for having short-periodic planetary
companions. For one of them, GJ 436 (rms = 20.6 m/s), we have already obtained
follow-up observations but no periodic signal is present in the RV-data.Comment: 12 pages, 14 figures, accepted for publication in the Astronomical
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