3,322 research outputs found
SGR J1550–5418 Bursts Detected with the Fermi Gamma-Ray Burst Monitor during its Most Prolific Activity
We have performed detailed temporal and time-integrated spectral analysis of 286 bursts from SGR J1550–5418 detected with the Fermi Gamma-ray Burst Monitor (GBM) in 2009 January, resulting in the largest uniform sample of temporal and spectral properties of SGR J1550–5418 bursts. We have used the combination of broadband and high time-resolution data provided with GBM to perform statistical studies for the source properties. We determine the durations, emission times, duty cycles, and rise times for all bursts, and find that they are typical of SGR bursts. We explore various models in our spectral analysis, and conclude that the spectra of SGR J1550–5418 bursts in the 8-200 keV band are equally well described by optically thin thermal bremsstrahlung (OTTB), a power law (PL) with an exponential cutoff (Comptonized model), and two blackbody (BB) functions (BB+BB). In the spectral fits with the Comptonized model, we find a mean PL index of –0.92, close to the OTTB index of –1. We show that there is an anti-correlation between the Comptonized E_(peak) and the burst fluence and average flux. For the BB+BB fits, we find that the fluences and emission areas of the two BB functions are correlated. The low-temperature BB has an emission area comparable to the neutron star surface area, independent of the temperature, while the high-temperature BB has a much smaller area and shows an anti-correlation between emission area and temperature. We compare the properties of these bursts with bursts observed from other SGR sources during extreme activations, and discuss the implications of our results in the context of magnetar burst models
On the design of a real-time volume rendering engine
An architecture for a Real-Time Volume Rendering Engine (RT-VRE) is given, capable of computing 750 × 750 × 512 samples from a 3D dataset at a rate of 25 images per second. The RT-VRE uses for this purpose 64 dedicated rendering chips, cooperating with 16 RISC-processors. A plane interpolator circuit and a composition circuit, both capable to operate at very high speeds, have been designed for a 1.6 micron VLSI process. Both the interpolator and composition circuit are back from production. They have been tested and both complied with our specifications
Applying an accurate spherical model to gamma-ray burst afterglow observations
We present results of model fits to afterglow data sets of GRB970508,
GRB980703 and GRB070125, characterized by long and broadband coverage. The
model assumes synchrotron radiation (including self-absorption) from a
spherical adiabatic blast wave and consists of analytic flux prescriptions
based on numerical results. For the first time it combines the accuracy of
hydrodynamic simulations through different stages of the outflow dynamics with
the flexibility of simple heuristic formulas. The prescriptions are especially
geared towards accurate description of the dynamical transition of the outflow
from relativistic to Newtonian velocities in an arbitrary power-law density
environment. We show that the spherical model can accurately describe the data
only in the case of GRB970508, for which we find a circumburst medium density
consistent with a stellar wind. We investigate in detail the implied spectra
and physical parameters of that burst. For the microphysics we show evidence
for equipartition between the fraction of energy density carried by
relativistic electrons and magnetic field. We also find that for the blast wave
to be adiabatic, the fraction of electrons accelerated at the shock has to be
smaller than 1. We present best-fit parameters for the afterglows of all three
bursts, including uncertainties in the parameters of GRB970508, and compare the
inferred values to those obtained by different authors
Exploring the electron density in plasmas induced by extreme ultraviolet radiation in argon
The new generation of lithography tools use high energy EUV radiation which
ionizes the present background gas due to photoionization. To predict and
understand the long term impact on the highly delicate mirrors It is essential
to characterize these kinds of EUV-induced plasmas. We measured the electron
density evolution in argon gas during and just after irradiation by a short
pulse of EUV light at 13.5 nm by applying microwave cavity resonance
spectroscopy. Dependencies on EUV pulse energy and gas pressure have been
explored over a range relevant for industrial applications.
Our experimental results show that the maximum reached electron density
depends linearly on pulse energy. A quadratic dependence - caused by
photoionization and subsequent electron impact ionization by free electrons -
is found from experiments where the gas pressure is varied. This is
demonstrated by our theoretical estimates presented in this manuscript as well.Comment: submitted to J. Phys. D. 16 pages, 8 figure
Broadband modelling of short gamma-ray bursts with energy injection from magnetar spin-down and its implications for radio detectability
The magnetar model has been proposed to explain the apparent energy injection
in the X-ray light curves of short gamma-ray bursts (SGRBs), but its
implications across the full broadband spectrum are not well explored. We
investigate the broadband modelling of four SGRBs with evidence for energy
injection in their X-ray light curves, applying a physically motivated model in
which a newly formed magnetar injects energy into a forward shock as it loses
angular momentum along open field lines. By performing an order of magnitude
search for the underlying physical parameters in the blast wave, we constrain
the characteristic break frequencies of the synchrotron spectrum against their
manifestations in the available multi-wavelength observations for each burst.
The application of the magnetar energy injection profile restricts the
successful matches to a limited family of models that are self-consistent
within the magnetic dipole spin-down framework.We produce synthetic light
curves that describe how the radio signatures of these SGRBs ought to have
looked given the restrictions imposed by the available data, and discuss the
detectability of these signatures with present-day and near-future radio
telescopes. Our results show that both the Atacama Large Millimetre Array and
the upgraded Very Large Array are now sensitive enough to detect the radio
signature within two weeks of trigger in most SGRBs, assuming our sample is
representative of the population as a whole. We also find that the upcoming
Square Kilometre Array will be sensitive to depths greater than those of our
lower limit predictions.Comment: 15 pages, 4 figures, 6 tables, accepted for publication in MNRA
ASAS/WHO ICF Core Sets for ankylosing spondylitis (AS): how to classify the impact of AS on functioning and health
Objective: To report on the results of a standardised consensus process agreeing on concepts typical and/or relevant when classifying functioning and health in patients with ankylosing spondylitis (AS) based on the International Classification of Functioning and Health (ICF).Methods: Experts in AS from different professional and geographical backgrounds attended a consensus conference and were divided into three working groups. Rheumatologists were selected from members of the Assessment of SpondyloArthritis international Society (ASAS). Other health professionals were recommended by ASAS members. The aim was to compose three working groups with five to seven participants to allow everybody's contribution in the discussions. Experts selected ICF categories that were considered typical and/or relevant for AS during a standardised consensus process by integrating evidence from preceding studies in alternating working group and plenary discussions. A Comprehensive ICF Core Set was selected for the comprehensive classification of functioning and a Brief ICF Core Set for application in trials.Results: The conference was attended by 19 experts from 12 countries. Eighty categories were included in the Comprehensive Core Set, which included 23 Body functions, 19 Body structures, 24 Activities and participation and 14 Environmental factors. Nineteen categories were selected for the Brief Core Set, which included 6 Body functions, 4 Body structures, 7 Activities and participation and 2 Environmental factors.Conclusion: The Comprehensive and Brief ICF Core Sets for AS are now available and aim to represent the external reference to define consequences of AS on functioning
Constraining properties of GRB magnetar central engines using the observed plateau luminosity and duration correlation
An intrinsic correlation has been identified between the luminosity and
duration of plateaus in the X-ray afterglows of Gamma-Ray Bursts (GRBs;
Dainotti et al. 2008), suggesting a central engine origin. The magnetar central
engine model predicts an observable plateau phase, with plateau durations and
luminosities being determined by the magnetic fields and spin periods of the
newly formed magnetar. This paper analytically shows that the magnetar central
engine model can explain, within the 1 uncertainties, the correlation
between plateau luminosity and duration. The observed scatter in the
correlation most likely originates in the spread of initial spin periods of the
newly formed magnetar and provides an estimate of the maximum spin period of
~35 ms (assuming a constant mass, efficiency and beaming across the GRB
sample). Additionally, by combining the observed data and simulations, we show
that the magnetar emission is most likely narrowly beamed and has 20%
efficiency in conversion of rotational energy from the magnetar into the
observed plateau luminosity. The beaming angles and efficiencies obtained by
this method are fully consistent with both predicted and observed values. We
find that Short GRBs and Short GRBs with Extended Emission lie on the same
correlation but are statistically inconsistent with being drawn from the same
distribution as Long GRBs, this is consistent with them having a wider beaming
angle than Long GRBs.Comment: MNRAS Accepte
Who benefits from tax competition in the European Union?
This memo documents version 7 of the model, which is used in in Bettendorf et al. (2006). The
first chapter documents the derivation of the equations. The calibration of the model is described
in chapter 2. Section 1.1 derives the first-order conditions for consumption and labour supply
from utility-maximising households. Section 1.2 derives from profit maximisation, the demand
for labour, capital, location specific capital, intermediate inputs and financial assets for domestic
and multinational firms. Taxes on corporate income, labour income, consumption and wealth are
introduced when appropriate. The tax revenues have to meet the government expenditures on
consumption, transfers and debt, see section 1.3. The market equilibria and the linkages with the
Rest of the World are presented in section 1.4. Section 1.5 presents the solution procedure.
Notation follows some simple rules. Upper case symbols are used for aggregated values
whereas lower case characters are reserved for per capita variables (in terms of the young
generation in the country of origin). In the case of variables with two dimensions, the first index
refers to the country which owns the resource (residence), whereas the second index denotes the
using country (destination). Time subscripts and country indices are dropped in the exposition
whenever this is possible.
The rates of return on bonds ( ˆ rwb) and equities ( ˆ rwe) are assumed fixed. The considered
countries are small in the sense that they can import (or export) capital from the Rest of the
World (ROW) without affecting the world interest rates. In other words, the net supply of capital
by the ROW is perfectly elastic. Multinationals are assumed to operate only in the other ‘small’
countries, but not in the ROW (and vice versa). The ROW block does not need to be fully
modelled. International capital and good flows are restricted by the current account for each
country
New insights in understanding the pathogenesis of spondyloarthropathies
Spondyloarthropathies (SpA) are characterised by dysregulation of the inflammatory processes and bone metabolism which may be clarified by gene expression profiles. Sharma and colleagues showed associations of axial SpA with the innate immune system, inflammation markers and markers of bone remodeling. Drawbacks of this study are the patient selection based on uveitis, which limits the extrapolation of these data, and the racial difference between index cases and controls, which contributes to differences in gene expression. Nevertheless, this study provides a direction for unraveling the intriguing balance between inflammation and ossification in ankylosing spondylitis
The hidden X-ray breaks in afterglow light curves
Gamma-Ray Burst (GRB) afterglow observations in the Swift era have a
perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift
era. Specifically, relatively few breaks, consistent with jet breaks, are
observed in the X-ray light curves of these bursts. If these breaks are truly
missing, it has serious consequences for the interpretation of GRB jet
collimation and energy requirements, and the use of GRBs as standard candles.
Here we address the issue of X-ray breaks which are possibly 'hidden' and
hence the light curves are misinterpreted as being single power-laws. We show
how a number of precedents, including GRB 990510 & GRB 060206, exist for such
hidden breaks and how, even with the well sampled light curves of the Swift
era, these breaks may be left misidentified. We do so by synthesising X-ray
light curves and finding general trends via Monte Carlo analysis. Furthermore,
in light of these simulations, we discuss how to best identify achromatic
breaks in afterglow light curves via multi-wavelength analysis.Comment: 4 pages, contributed talk, submitted to the proceedings of Gamma Ray
Bursts 2007, Santa Fe, New Mexico, November 5-9 200
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