171 research outputs found
NASA industrial applications study. Industrial review for improved electrode for biopotential measurement at the skin
Electrode for measuring biopotentials at surface of human ski
EGRET Spectral Index and the Low-Energy Peak Position in the Spectral Energy Distribution of EGRET-Detected Blazars
In current theoretical models of the blazar subclass of active galaxies, the
broadband emission consists of two components: a low-frequency synchrotron
component with a peak in the IR to X-ray band, and a high-frequency inverse
Compton component with a peak in the gamma-ray band. In such models, the
gamma-ray spectral index should be correlated with the location of the
low-energy peak, with flatter gamma-ray spectra expected for blazars with
synchrotron peaks at higher photon energies and vice versa. Using the
EGRET-detected blazars as a sample, we examine this correlation and possible
uncertainties in its construction.Comment: 17 pages including 1 figure, accepted for publication in The
Astrophysical Journa
EGRET Observations of the Extragalactic Gamma Ray Emission
The all-sky survey in high-energy gamma rays (E30 MeV) carried out by the
Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma-Ray
Observatory provides a unique opportunity to examine in detail the diffuse
gamma-ray emission. The observed diffuse emission has a Galactic component
arising from cosmic-ray interactions with the local interstellar gas and
radiation as well an almost uniformly distributed component that is generally
believed to originate outside the Galaxy. Through a careful study and removal
of the Galactic diffuse emission, the flux, spectrum and uniformity of the
extragalactic emission is deduced. The analysis indicates that the
extragalactic emission is well described by a power law photon spectrum with an
index of -(2.10+-0.03) in the 30 MeV to 100 GeV energy range. No large scale
spatial anisotropy or changes in the energy spectrum are observed in the
deduced extragalactic emission. The most likely explanation for the origin of
this extragalactic high-energy gamma-ray emission is that it arises primarily
from unresolved gamma-ray-emitting blazars.Comment: 19 pages latex, 10 figures, accepted for publication in Ap
Search for Gamma Ray Bursts with the Argo-YBJ Detector in Scaler Mode
We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100
GeV in coincidence with the prompt emission detected by satellites using the
Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ)
air shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R.
China, 4300 m a.s.l.), active surface (about 6700 m**2 of Resistive Plate
Chambers), and large field of view (about 2 sr, limited only by the atmospheric
absorption), the ARGO-YBJ air shower detector is particularly suitable for the
detection of unpredictable and short duration events such as GRBs. The search
is carried out using the "single particle technique", i.e. counting all the
particles hitting the detector without measurement of the energy and arrival
direction of the primary gamma rays.
Between 2004 December 17 and 2009 April 7, 81 GRBs detected by satellites
occurred within the field of view of ARGO-YBJ (zenith angle < 45 deg). It was
possible to examine 62 of these for >1 GeV counterpart in the ARGO-YBJ data
finding no statistically significant emission. With a lack of detected spectra
in this energy range fluence upper limits are profitable, especially when the
redshift is known and the correction for the extragalactic absorption can be
considered. The obtained fluence upper limits reach values as low as 10**{-5}
erg cm**{-2} in the 1-100 GeV energy region.
Besides this individual search for a higher energy counterpart, a statistical
study of the stack of all the GRBs both in time and in phase was made, looking
for a common feature in the GRB high energy emission. No significant signal has
been detected.Comment: accepted for publication in Ap
In-Flight Calibration of the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory
The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory has been operating for over seven years since its launch in 1991 April. This span of time far exceeds the design lifetime of two years. As the instrument has aged, several changes have occurred due to spark chamber gas exchanges as well as some hardware degradation and failures, all of which have an influence on the instrument sensitivity. This paper describes post-launch measurements and analysis that are done to calibrate the instrument response functions. The updated instrument characteristics are incorporated into the analysis software
Gamma-Ray Burst Energy Spectra: Theoretical Models, Old and New
The modelling of gamma-ray burst (GRB) spectra has considerable potential for
increasing the understanding of these enigmatic sources. A diversity of ideas
and analyses has been generated over the last two decades to explain line
features and continuum shapes, encompassing both older galactic neutron star
and ``new age'' cosmological source models. This paper reviews some of the
highlights of these studies, discussing the merits and limitations of various
ideas, and in particular their compatibility with the observational data. The
first focus will be on continuum models for GRBs, which include optically thin
synchrotron emission and resonant Compton upscattering near galactic neutron
stars, while the synchrotron and non-magnetic inverse Compton scattering
mechanisms are prominent in the less well-developed cosmological scenarios.
Line formation scenarios will then be discussed, in particular the scattering
model for producing cyclotron features, which remains the only viable
explanation for the Ginga observations of double lines. Absorption-like line
production in cosmological burst models is generally difficult, though
interesting notions such as femtolensing interference patterns have been
proffered.Comment: 8 pages with no figures, as a compressed, uuencoded, Postscript file.
Invited review, to appear in Astrophysics and Space Science as part of the
proceedings of the 29th ESLAB Symposium ``Towards the Source of Gamma-Ray
Bursts'' held in Noordwijk, 199
Frequent CEO Turnover and Firm Performance: The Resilience Effect of Workforce Diversity
© 2020, Springer Nature B.V. CEO turnover (or succession) is a critical event in an organization that influences organizational processes and performance. The objective of this study is to investigate whether workforce diversity (i.e., age, gender, and education-level diversity) might have a resilience effect on firm performance under the frequency of CEO turnover. Based on a sample of 409 Korean firms from 2010 to 2015, our results show that firms with more frequent CEO turnover have a lower firm performance. However, firms with more gender and education-level diversity could buffer the disruptive effect of frequent CEO turnover on firm performance to offer a benefit to the organization. Our theory and findings suggest that effectively managing diverse workforce can be a resilience factor in an uncertain organizational environment because diverse workforce has complementary skills and behaviors that can cope better with uncertainty and signals social inclusion of an organization, thus fostering a long-term exchange relationship. These findings contribute to the literature on CEO turnover (or succession) and diversity
Gamma ray astrophysics: the EGRET results
Cosmic gamma rays provide insight into some of the most dynamic processes in
the Universe. At the dawn of a new generation of gamma-ray telescopes, this
review summarizes results from the Energetic Gamma Ray Experiment Telescope
(EGRET) on the Compton Gamma Ray Observatory, the principal predecessor mission
studying high-energy photons in the 100 MeV energy range. EGRET viewed a
gamma-ray sky dominated by prominent emission from the Milky Way, but featuring
an array of other sources, including quasars, pulsars, gamma-ray bursts, and
many sources that remain unidentified. A central feature of the EGRET results
was the high degree of variability seen in many gamma-ray sources, indicative
of the powerful forces at work in objects visible to gamma-ray telescopes.Comment: 23 pages, 24 figure
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