14,490 research outputs found
Spectral analysis of Swift long GRBs with known redshift
We study the spectral and energetics properties of 47 long-duration gamma-ray
bursts (GRBs) with known redshift, all of them detected by the Swift satellite.
Due to the narrow energy range (15-150 keV) of the Swift-BAT detector, the
spectral fitting is reliable only for fitting models with 2 or 3 parameters. As
high uncertainty and correlation among the errors is expected, a careful
analysis of the errors is necessary. We fit both the power law (PL, 2
parameters) and cut--off power law (CPL, 3 parameters) models to the
time-integrated spectra of the 47 bursts, and present the corresponding
parameters, their uncertainties, and the correlations among the uncertainties.
The CPL model is reliable only for 29 bursts for which we estimate the nuf_nu
peak energy Epk. For these GRBs, we calculate the energy fluence and the rest-
frame isotropic-equivalent radiated energy, Eiso, as well as the propagated
uncertainties and correlations among them. We explore the distribution of our
homogeneous sample of GRBs on the rest-frame diagram E'pk vs Eiso. We confirm a
significant correlation between these two quantities (the "Amati" relation) and
we verify that, within the uncertainty limits, no outliers are present. We also
fit the spectra to a Band model with the high energy power law index frozen to
-2.3, obtaining a rather good agreement with the "Amati" relation of non-Swift
GRBs.Comment: 16 pages. To appear in MNRAS. Minor changes were introduced in this
last versio
The Washington 2004 Gubernatorial Election Crisis: The Necessity of Restoring Public Confidence in the Electoral Process
This Article details the plethora of problems associated with Washington State\u27s 2004 gubernatorial election and explores the proposed electoral reforms in light of prior threats to the electoral process. The Article postulates that electoral reforms in the administration of elections also present an important opportunity to provide minority communities with greater access to the political process. Part II of this Article begins with a history ofvoting discrimination in the United States. This history provides a context to the 2004 gubernatorial election in Washington. In addition, this history provides an important background context for assessing whether reforms in the administration of elections will have a corresponding impact on the political integration of minority communities. Part II closes with a brief discussion of the possible convergence of efforts to reform the electoral process and to incorporate minority communities into the body politic. Part III discusses the events that unfolded in the 2004 gubernatorial election and describes the crisis that ensued. Finally, Part IV provides a brief overview of legislation enacted in the Washington State 2005 Regular Legislative Session in order to assess whether all of the major problems identified in the 2004 gubernatorial election have been addressed
Cage-size control of guest vibration and thermal conductivity in Sr8Ga16Si30-xGex
We present a systematic study of thermal conductivity, specific heat,
electrical resistivity, thermopower and x-ray diffraction measurements
performed on single-crystalline samples of the pseudoquaternary type-I
clathrate system Sr8Ga16Si30-xGex, in the full range of 0 < x < 30. All the
samples show metallic behavior with n-type majority carriers. However, the
thermal conductivity and specific heat strongly depend on x. Upon increasing x
from 0 to 30, the lattice parameter increases by 3%, from 10.446 to 10.726 A,
and the localized vibrational energies of the Sr guest ions in the
tetrakaidekahedron (dodecahedron) cages decrease from 59 (120) K to 35 (90) K.
Furthermore, the lattice thermal conductivity at low temperatures is largely
suppressed. In fact, a crystalline peak found at 15 K for x = 0 gradually
decreases and disappears for x > 20, evolving into the anomalous glass-like
behavior observed for x = 30. It is found that the increase of the free space
for the Sr guest motion directly correlates with a continuous transition from
on-center harmonic vibration to off-center anharmonic vibration, with
consequent increase in the coupling strength between the guest's low-energy
modes and the cage's acoustic phonon modes.Comment: 7 pages, 7 figures, submitted to PR
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