2,583 research outputs found
Diagnosing GRB Prompt Emission Site with Spectral Cut-Off Energy
The site and mechanism of gamma-ray burst (GRB) prompt emission is still
unknown. Although internal shocks have been widely discussed as the emission
site of GRBs, evidence supporting other emission sites have been also suggested
recently, including the closer-in photosphere where the fireball becomes
transparent and further-out radii near the fireball deceleration radius where
magnetic dissipation may be important. With the successful operation of the
GLAST experiment, prompt high energy emission spectra from many GRBs would be
detected in the near future. We suggest that the cut-off energy of the prompt
emission spectrum from a GRB depends on both the fireball bulk Lorentz factor
and the unknown emission radius from the central engine. If the bulk Lorentz
factor could be independently measured (e.g. from early afterglow
observations), the observed spectral cutoff energy can be used to diagnose the
emission site of gamma-rays. This would provide valuable information to
understand the physical origin of the GRB promp emission.Comment: 6 pages,2 figures version to be published in MNRAS Letter
High Energy neutrino signals from the Epoch of Reionization
We perform a new estimate of the high energy neutrinos expected from GRBs
associated with the first generation of stars in light of new models and
constraints on the epoch of reionization and a more detailed evaluation of the
neutrino emission yields. We also compare the diffuse high energy neutrino
background from Population III stars with the one from "ordinary stars"
(Population II), as estimated consistently within the same cosmological and
astrophysical assumptions. In disagreement with previous literature, we find
that high energy neutrinos from Population III stars will not be observable
with current or near future neutrino telescopes, falling below both IceCube
sensitivity and atmospheric neutrino background under the most extreme
assumptions for the GRB rate. This rules them out as a viable diagnostic tool
for these still elusive metal-free stars.Comment: 9 pages, 5 figures
Allograft and Xenograft Acceptance under FK‐506 and Other Immunosuppressant Treatment
We will focus on two issues, both involving, but not confined to FK-506: first, the meaning of the graft acceptance, which is, after all, the objective of immunosuppression for the transplant surgeon; and second, how to take the next great step of xenotransplantation
Virulence of Escherichia coli Isolates Obtained from Layer Chickens with Colibacillosis Associated with Pericarditis, Perihepatitis, and Salpingitis in Experimentally Infected Chicks and Embryonated Eggs
To evaluate the virulence of avian pathogenic Escherichia coli (APEC) isolates obtained from colibacillosis cases associated with pericarditis, perihepatitis, and salpingitis, the embryo lethality assay and experimental infection model in chicks were used in this study. According to the established criteria based on mortality in the embryo lethality assay for evaluating the virulence of E. coli isolates, 23 of the 26 APEC isolates associated with pericarditis and perihepatitis and 8 of the 20 isolates associated with salpingitis were found to be virulent. Isolate D137, which had been obtained from a case with pericarditis and perihepatitis and had an embryo mortality of 92%, and isolate D445, which had been obtained from a case with pericarditis and perihepatitis and had an embryo mortality of 17%, were used for the experimental infection. Four of the five 11-day-old chickens inoculated through the air sac with isolate D137 died 1 day postinoculation, and the challenge strain was recovered from the air sac, pericardial sac, or liver; however, colibacillosis lesions were found in only one of the five birds postmortem. All five chicks inoculated with isolate D445 survived for 7 days postinoculation and exhibited airsacculitis or pericarditis lesions at 7 days postinoculation; the challenge strain was not recovered from the lesions postmortem. The results obtained in this study suggest that the different APEC isolates tested cause illness in chickens through distinct pathogenesis
Recommended from our members
Parametric Feature Detection
We propose an algorithm to automatically construct feature detectors for arbitrary parametric features. To obtain a high level of robustness we advocate the use of realistic multi-parameter feature models and incorporate optical and sensing effects. Each feature is represented as a densely sampled parametric manifold in a low dimensional subspace of a Hilbert space. During detection, the brightness distribution around each image pixel is projected into the subspace. If the projection lies sufficiently close to the feature manifold, the feature is detected and the location of the closest manifold point yields the feature parameters. The concepts of parameter reduction by normalization, dimension reduction, pattern rejection, and heuristic search are all employed to achieve the required efficiency. By applying the algorithm to appropriate parametric feature models, detectors have been constructed for five features, namely, step edge, roof edge, line, corner, and circular disc. Detailed experiments are reported on the robustness of detection and the accuracy of parameter estimation. In the case of the step edge, our results are compared with those obtained using popular detectors. We conclude with a brief discussion on the use of relaxation to rene outputs from multiple feature detectors, and sketch a hardware architecture for a general feature detection machine
A Universal Lifetime Distribution for Multi-Species Systems
Lifetime distributions of social entities, such as enterprises, products, and
media contents, are one of the fundamental statistics characterizing the social
dynamics. To investigate the lifetime distribution of mutually interacting
systems, simple models having a rule for additions and deletions of entities
are investigated. We found a quite universal lifetime distribution for various
kinds of inter-entity interactions, and it is well fitted by a
stretched-exponential function with an exponent close to 1/2. We propose a
"modified Red-Queen" hypothesis to explain this distribution. We also review
empirical studies on the lifetime distribution of social entities, and
discussed the applicability of the model.Comment: 10 pages, 6 figures, Proceedings of Social Modeling and Simulations +
Econophysics Colloquium 201
- …