3,109 research outputs found
GRB 110709A, 111117A and 120107A: Faint high-energy gamma-ray photon emission from Fermi/LAT observations and demographic implications
Launched on June 11, 2008, the LAT instrument onboard the Gamma-ray
Space Telescope has provided a rare opportunity to study high energy photon
emission from gamma-ray bursts. Although the majority of such events (27) have
been iden tified by the Fermi LAT Collaboration, four were uncovered by using
more sensiti ve statistical techniques (Akerlof et al 2010, Akerlof et al 2011,
Zheng et al 2 012). In this paper, we continue our earlier work by finding
three more GRBs ass ociated with high energy photon emission, GRB 110709A,
111117A and 120107A. To s ystematize our matched filter approach, a pipeline
has been developed to identif y these objects in near real time. GRB 120107A is
the first product of this anal ysis procedure. Despite the reduced threshold
for identification, the number of GRB events has not increased significantly.
This relative dearth of events with low photon number prompted a study of the
apparent photon number distribution. W e find an extremely good fit to a simple
power-law with an exponent of -1.8 0.3 for the differential
distribution. As might be expected, there is a substa ntial correlation between
the number of lower energy photons detected by the GBM and the number observed
by the LAT. Thus, high energy photon emission is associ ated with some but not
all of the brighter GBM events. Deeper studies of the pro perties of the small
population of high energy emitting bursts may eventually yi eld a better
understanding of these entire phenomena.Comment: accepted to Ap
Effects of Contrarians in the Minority Game
We study the effects of the presence of contrarians in an agent-based model
of competing populations. Contrarians are common in societies. These
contrarians are agents who deliberately prefer to hold an opinion that is
contrary to the prevailing idea of the commons or normal agents. Contrarians
are introduced within the context of the Minority Game (MG), which is a binary
model for an evolving and adaptive population of agents competing for a limited
resource. Results of numerical simulations reveal that the average success rate
among the agents depends non-monotonically on the fraction of
contrarians. For small , the contrarians systematically outperform the
normal agents by avoiding the crowd effect and enhance the overall success
rate. For high , the anti-persistent nature of the MG is disturbed and
the few normal agents outperform the contrarians. Qualitative discussion and
analytic results for the small and high regimes are also
presented, and the crossover behavior between the two regimes is discussed.Comment: revtex, 11 pages, 4 figure
Distances and classification of amino acids for different protein secondary structures
Window profiles of amino acids in protein sequences are taken as a
description of the amino acid environment. The relative entropy or
Kullback-Leibler distance derived from profiles is used as a measure of
dissimilarity for comparison of amino acids and secondary structure
conformations. Distance matrices of amino acid pairs at different conformations
are obtained, which display a non-negligible dependence of amino acid
similarity on conformations. Based on the conformation specific distances
clustering analysis for amino acids is conducted.Comment: 15 pages, 8 figure
Molecular Mechanism of Z α1-Antitrypsin Deficiency.
The Z mutation (E342K) of α1-antitrypsin (α1-AT), carried by 4% of Northern Europeans, predisposes to early onset of emphysema due to decreased functional α1-AT in the lung and to liver cirrhosis due to accumulation of polymers in hepatocytes. However, it remains unclear why the Z mutation causes intracellular polymerization of nascent Z α1-AT and why 15% of the expressed Z α1-AT is secreted into circulation as functional, but polymerogenic, monomers. Here, we solve the crystal structure of the Z-monomer and have engineered replacements to assess the conformational role of residue Glu-342 in α1-AT. The results reveal that Z α1-AT has a labile strand 5 of the central β-sheet A (s5A) with a consequent equilibrium between a native inhibitory conformation, as in its crystal structure here, and an aberrant conformation with s5A only partially incorporated into the central β-sheet. This aberrant conformation, induced by the loss of interactions from the Glu-342 side chain, explains why Z α1-AT is prone to polymerization and readily binds to a 6-mer peptide, and it supports that annealing of s5A into the central β-sheet is a crucial step in the serpins' metastable conformational formation. The demonstration that the aberrant conformation can be rectified through stabilization of the labile s5A by binding of a small molecule opens a potential therapeutic approach for Z α1-AT deficiency
Autofocus for multispectral camera using focus symmetry
Author name used in this publication: Si-Jie ShaoAuthor name used in this publication: John H. Xin2011-2012 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
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