Universities Space Research Association

About: Universities Space Research Association is a nonprofit organization based out in Columbia, Maryland, United States. It is known for research contribution in the topics: Gamma-ray burst & Galaxy. The organization has 1921 authors who have published 5412 publications receiving 255681 citations. The organization is also known as: USRA.

Response to Vitamin D Supplementation during Antarctic Winter Is Related to BMI, and Supplementation Can Mitigate Epstein-Barr Virus Reactivation

Abstract: Maintaining vitamin D status without sunlight exposure is difficult without supplementation. This study was designed to better understand interrelationships between periodic vitamin D supplementation and immune function in Antarctic workers. The effect of 2 oral dosing regimens of vitamin D supplementation on vitamin D status and markers of immune function was evaluated in people in Antarctica with no UV light exposure for 6 mo. Participants were given a 2000-IU (50 μg) daily (n = 15) or 10,000-IU (250 μg) weekly (n = 14) vitamin D supplement for 6 mo during a winter in Antarctica. Biological samples were collected at baseline and at 3 and 6 mo. Vitamin D intake, markers of vitamin D and bone metabolism, and latent virus reactivation were determined. After 6 mo, the serum 25-hydroxyvitamin D concentration (mean ± SD) increased from 56 ± 17 to 79 ± 16 nmol/L and from 52 ± 10 to 69 ± 9 nmol/L in the 2000-IU/d and 10,000-IU/wk groups, respectively (main effect over time, P < 0.001). Participants with a greater BMI (participant BMI range = 19–43 g/m2) had a smaller increase in 25-hydroxyvitamin D after 6-mo supplementation (P < 0.05). Participants with high serum cortisol and higher serum 25-hydroxyvitamin D were less likely to shed Epstein-Barr virus in saliva (P < 0.05). The doses given raised vitamin D status in participants not exposed to sunlight for 6 mo, and the efficacy was influenced by baseline vitamin D status and BMI. The data also provide evidence that vitamin D, interacting with stress, can reduce risk of latent virus reactivation during the winter in Antarctica.

Estimating Long GRB Jet Opening Angles and Rest-Frame Energetics

Abstract: We present a method to estimate the jet opening angles of long duration Gamma-Ray Bursts (GRBs) using the prompt gamma-ray energetics and an inversion of the Ghirlanda relation, which is a correlation between the timeintegrated peak energy of the GRB prompt spectrum and the collimationcorrected energy in gamma rays. The derived jet opening angles using this method and detailed assumptions match well with the corresponding inferred jet opening angles obtained when a break in the afterglow is observed. Furthermore, using a model of the predicted long GRB redshift probability distribution observable by the Fermi Gamma-ray Burst Monitor (GBM), we estimate the probability distributions for the jet opening angle and rest-frame energetics for a large sample of GBM GRBs for which the redshifts have not been observed. Previous studies have only used a handful of GRBs to estimate these properties due to the paucity of observed afterglow jet breaks, spectroscopic redshifts, and comprehensive prompt gamma-ray observations, and we potentially expand the number of GRBs that can be used in this analysis by more than an order of magnitude. In this analysis, we also present an inferred distribution of jet breaks which indicates that a large fraction of jet breaks are not observable with current instrumentation and observing strategies. We present simple parameterizations for the jet angle, energetics, and jet break distributions so that they may be used in future studies. Subject headings: gamma rays: bursts — methods: data analysis

Echo size and asymmetry : impact on NEXRAD storm identification

Abstract: The effects of echo shape and radar viewing angle on detecting small thunderstorms with the NEXRAD storm identification algorithms are examined. The amorphous low-level echo shapes are modeled as ellipses with major axes ranging from 5-15 km and minor axes varying between 2-5 km. The model echoes are then used to create a 'probability of detection' chart that demonstrates the impact of storm asymmetry on cell identification. The algorithm performance on small thunderstorms observed near Huntsville, Alabama and Kennedy Space Center, Florida is examined. A new algorithm based on the analysis of 15 storms observed in Florida, Alabama, and New Mexico is proposed that would identify storms as having lightning if 40 dBZ reflectivity is present at the -10 C level and the echo top exceeds 9 km. This algorithm would have a 100 percent probability of detecting lightning producing storms 4-33 min before the first flash, a 7 percent false alarm rate and a critical success index of 93 percent.

Exploring broadband GRB behavior during γ-ray emission

Abstract: S. A. Yost, H. F. Swan, E. S. Rykoff, F. Aharonian, C. W. Akerlof, A. Alday, M. C. B. Ashley, S. Barthelmy, D. Burrows, D. L. Depoy, R. J. Dufour, J. D. Eastman, R. D. Forgey, N. Gehrels, E. Gogus, T. Guver, J. P. Halpern, L. C. Hardin, D. Horns, U. Kizilolu, H. A. Krimm, S. Lepine, E. P. Liang, J. L. Marshall, T. A. McKay, T. Mineo, N. Mirabal, M. Ozel, A. Phillips, J. L. Prieto, R. M. Quimby, P. Romano, G. Rowell, W. Rujopakarn, B. E. Schaefer, J. M. Silverman, R. Siverd, M. Skinner, D. A. Smith, I. A. Smith, S. Tonnesen, E. Troja, W. T. Vestrand, J. C. Wheeler, J. Wren, F. Yuan, and B. Zhang

Impact fracturing and structural modification of sedimentary rocks at Meteor Crater, Arizona

Abstract: [1] Meteor Crater provides a rare opportunity to study impact deformation of sedimentary target rocks and isolate those features from preexisting tectonic deformation and impact-generated reactivation of preexisting tectonic features. This study reports over 2500 new measurements of orientations of bedding, faults, and fractures in crater walls and in surrounding bedrock. Target rocks are characterized by horizontal bedding planes that are cut by at least three prominent sets of preimpact tectonic fracture systems. The crater rim is also cut by three distinct groups of fractures: radial, concentric, and conical fractures. When the crater rim is restored to preimpact condition, the radial and concentric fractures resemble preimpact fracture populations, indicating that crater wall deformation and rim uplift were partly accommodated by activation of preexisting fractures. In contrast, the conical fractures are dissimilar to the preimpact fractures and apparently formed as a direct result of impact deformation. Some of the preimpact fractures were transformed into tear faults during the impact event, and motion along those faults appears to have controlled the geometry of the impact deformational features. The crater rim is, thus, square in plan view rather than circular. Faults occurring in the crater diagonals are prominent ones, allowing greater vertical displacement. The deformation pattern of Meteor Crater is different from that at Lonar Crater, which was excavated in basalt with fewer preimpact fractures. The differences between deformation at Meteor Crater and Lonar Crater may reflect the same disparities seen in simple craters produced in different target lithologies on Mars and other planetary surfaces.