1,145 research outputs found
Statistical Properties of Multiple Optical Emission Components in Gamma-Ray Bursts and Implications
Well-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are complied
from the literature. Multiple optical emission components are extracted with
power-law function fits to these lightcurves. We present a systematical
analysis for statistical properties and their relations to prompt gamma-ray
emission and X-ray afterglow for each component. We show that peak luminosity
in the prompt and late flares are correlated and the evolution of the peak
luminosity may signal the evolution of the accretion rate. No tight correlation
between the shallow decay phase/plateau and prompt gamma-ray emission is found.
Assuming that they are due to a long-lasting wind injected by a compact object,
we show that the injected behavior favors the scenarios of a long-lasting wind
after the main burst episode. The peak luminosity of the afterglow onset is
tightly correlated with Eiso, and it is dimmer as peaking later. Assuming that
the onset bump is due to the fireball deceleration by the external medium, we
examine the Gamma_0-Eiso relation and find that it is confirmed with the
current sample. Optical re-brightening is observed in 30 GRBs in our sample. It
shares the same relation between the width and the peak time as found in the
onset bump, but no clear correlation between the peak luminosity and Eiso as
observed in the onset bumps is found. Although its peak luminosity also decays
with time, the slope is much shallower than that of the onset peak. We get L
t^{-1}_{p}$, being consistent with off-axis observations to an expanding
external fireball in a wind-like circum medium. The late re-brightening may
signal another jet component. Mixing of different emission components may be
the reason for the observed chromatic breaks in different energy bands.Comment: 10 pages, 5 figures, to be published by IJMPD (Proceedings of "The
Third Galileo - Xu Guangqi meeting", Beijing, October 11-15, 2011
Nuclear Hartree-Fock calculations on parallel computers
Hartree-Fock (HF) calculations have had remarkable success in describing large nuclei at
high spin, temperature and deformation. To allow full range of possible deformations,
the Skyrme HF equations can be discretized on a three-dimensional mesh. However, such
calculations are currently limited by the computational resources provided by traditional
supercomputers. To take advantage of recent developments in massively parallel computing
technology, we have implemented the LLNL Skyrme-force static and rotational
HF codes on Intel's DELTA and GAMMA systems at Caltech.
We decomposed the HF code by assigning a portion of the mesh to each node, with
nearest neighbor meshes assigned to nodes connected by communication· channels. This
kind of decomposition is well-suited for the DELTA and the GAMMA architecture because
the only non-local operations are wave function orthogonalization and the boundary
conditions of the Poisson equation for the Coulomb field.
Our first application of the HF code on parallel computers has been the study of
identical superdeformed (SD) rotational bands in the Hg region. In the last ten years,
many SD rotational bands have been found experimentally. One very surprising feature
found in these SD rotational bands is that many pairs of bands in nuclei that differ
by one or two mass units have nearly identical deexcitation gamma-ray energies. Our
calculations of the five rotational bands in ^(192)Hg and ^(194)Pb show that the filling of
specific orbitals can lead to bands with deexcitation gamma-ray energies differing by at
most 2 keV in nuclei differing by two mass units and over a range of angular momenta comparable to that observed experimentally. Our calculations of SD rotational bands
in the Dy region also show that twinning can be achieved by filling or emptying some specific orbitals.
The interpretation of future precise experiments on atomic parity nonconservation
(PNC) in terms of parameters of the Standard Model could be hampered by uncertainties
in the atomic and nuclear structure. As a further application of the massively parallel
HF calculations, we calculated the proton and neutron densities of the Cesium isotopes
from A = 125 to A = 139. Based on our good agreement with experimental charge
radii, binding energies, and ground state spins, we conclude that the uncertainties in
the ratios of weak charges are less than 10^(-3), comfortably smaller than the anticipated experimental error.</p
Synthesis of chiral α-hydroxy acids via palladium-catalyzed C(sp^3)–H alkylation of lactic acid
Herein we report a Pd-catalyzed alkylation of lactic acid with the assistance of 8-aminoquinoline auxiliary. A wide range of alkyl iodides bearing β-hydrogen atoms are compatible with the reaction conditions, providing a practical and straightforward alternative to access chiral α-hydroxy acids (AHAs). The new reactions have been applied for the synthesis of isotope-labeled AHAs and a sugar-containing complex AHA
contribution in at small
Two-photon annihilate contributions in the process including and intermediate are discussed in a simple
hadronic model. The corrections to the unpolarized cross section and polarized
observables are presented. The results show the two-photon annihilate
correction to unpolarized cross section is small and its angle dependence
becomes weak at small after considering the and
contributions simultaneously, while the correction to is enhanced.Comment: 5 page
Improving Classification of Protein Interaction Articles Using Context Similarity-Based Feature Selection
Protein interaction article classification is a text classification task in the biological domain to determine which articles describe protein-protein interactions. Since the feature space in text classification is high-dimensional, feature selection is widely used for reducing the dimensionality of features to speed up computation without sacrificing classification performance. Many existing feature selection methods are based on the statistical measure of document frequency and term frequency. One potential drawback of these methods is that they treat features separately. Hence, first we design a similarity measure between the context information to take word cooccurrences and phrase chunks around the features into account. Then we introduce the similarity of context information to the importance measure of the features to substitute the document and term frequency. Hence we propose new context similarity-based feature selection methods. Their performance is evaluated on two protein interaction article collections and compared against the frequency-based methods. The experimental results reveal that the context similarity-based methods perform better in terms of the 1 measure and the dimension reduction rate. Benefiting from the context information surrounding the features, the proposed methods can select distinctive features effectively for protein interaction article classification
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