12,821 research outputs found
GRAPE - A Balloon-Borne Gamma-Ray Polarimeter Experiment
This paper reviews the development status of GRAPE (the Gamma-Ray Polarimeter
Experiment), a hard X-ray Compton Polarimeter. The purpose of GRAPE is to
measure the polarization of hard X-rays in the 50-300 keV energy range. We are
particularly interested in X-rays that are emitted from solar flares and
gamma-ray bursts (GRBs), although GRAPE could also be employed in the study of
other astrophysical sources. Accurately measuring the polarization of the
emitted radiation will lead to a better understating of both emission
mechanisms and source geometries. The GRAPE design consists of an array of
plastic scintillators surrounding a central high-Z crystal scintillator. The
azimuthal distribution of photon scatters from the plastic array into the
central calorimeter provides a measure of the polarization fraction and
polarization angle of the incident radiation. The design of the detector
provides sensitivity over a large field-of-view (>pi steradian). The design
facilitates the fabrication of large area arrays with minimal deadspace. This
paper presents the latest design concept and the most recent results from
laboratory tests of a GRAPE science model.Comment: 6 pages; paper presented at the FRASCATI Workshop 2005 on
Multifrequency Behaviour of High Energy Cosmic Sources; submitted to Chinese
Journal of Astronomy and Astrophysic
Influence of prior activity (warm-up) and inspiratory muscle training upon between- and within-day reliability of maximal inspiratory pressure measurement
This is the post-print version of the article. The official published version can be obtained from the link below.BACKGROUND: A specific inspiratory muscle ‘warm-up’ (IWU) prior to assessment of maximal inspiratory mouth pressure (PImax) may reduce the number of measurements required to obtain reproducible, representative estimates of PImax. The influence of inspiratory muscle training (IMT) upon this phenomenon is unknown. OBJECTIVE: Compare the impact of an IWU on the between- and within-day reliability of PImax before and after IMT. METHOD: Eight participants were assessed on 4 separate occasions: 2 trials preceded IMT and 2 followed it. At each assessment, the highest of 3 initial efforts was recorded as the pre-IWU value (PI). The highest of 9 subsequent efforts that followed 2 sets of 30 breaths at 40% PI was recorded as PImax. Following 4 weeks of IMT, the trials were repeated. RESULTS: IWU increased PI by 11–17% (p ≤ 0.01), irrespective of IMT status. After IWU, 5–6 efforts were required to determine PImax, irrespective of IMT status. PImax was similar between the 2 trials before IMT and the 2 trials after IMT (p ≥ 0.05), and was 21% higher after IMT (p ≤ 0.01). The coefficient of variation was excellent before and after IWU, both before (1.9 and 0.6%, respectively) and after IMT (1.1 and 0.3%, respectively). Limits of agreement and sample sizes for effect sizes ≤10% were substantially smaller after IWU in all trials. CONCLUSIONS: (1) IWU enhances the between-day reliability of PImax measurement, and this is unaffected by IMT, and (2) judgements regarding acceptability in relation to PImax reliability should be made in relation to analytical goals and we present data to facilitate this
Rethinking the value of initial claims as a forecasting tool
The weekly numbers on initial claims for unemployment insurance convey key information about the labor market. But how reliable are claims in predicting changes in the much anticipated monthly employment report? According to a simple forecasting model, claims consistently send an accurate signal about employment during recessions but not during expansions.Unemployment insurance ; Forecasting ; Employment (Economic theory)
Linear-Time Algorithms for Finding Tucker Submatrices and Lekkerkerker-Boland Subgraphs
Lekkerkerker and Boland characterized the minimal forbidden induced subgraphs
for the class of interval graphs. We give a linear-time algorithm to find one
in any graph that is not an interval graph. Tucker characterized the minimal
forbidden submatrices of binary matrices that do not have the consecutive-ones
property. We give a linear-time algorithm to find one in any binary matrix that
does not have the consecutive-ones property.Comment: A preliminary version of this work appeared in WG13: 39th
International Workshop on Graph-Theoretic Concepts in Computer Scienc
Time-scales of Radio Emission in PSR J0437-4715 at 327 MHz
Time-scales of radio emission are studied in PSR J0437-4715 at 327 MHz using
almost half a million periods of high quality data from Ooty Radio Telescope.
The radio emission in this milli second pulsar occurs on a short (s) time-scale
of approximately 0.026 +- 0.001 periods, and on a (l) time-scale that is much
longer than the widths of the components of the integrated profile
(approximately 0.05 periods). The width of the s emission increases with its
increasing relative contribution to the total radio emission. This may provide
constraints for the details of discharge of vacuum gaps above pulsar polar
caps. The s emission occasionally takes place in the form of intense spikes,
which are confined to the main component of the integrated profile for 90 per
cent of the time. The positions of spikes within a component of the integrated
profile have no simple relation to the shape of that component. This may have
impact on the interpretation of the integrated profile components in terms of
independent regions of emission on the polar cap.Comment: Accepted for publication in Vol 543 (1 Nov 2000) of The Astrophysical
Journa
The Formation and Evolution of Massive Black Holes
The past 10 years have witnessed a change of perspective in the way
astrophysicists think about massive black holes (MBHs), which are now
considered to have a major role in the evolution of galaxies. This appreciation
was driven by the realization that black holes of millions solar masses and
above reside in the center of most galaxies, including the Milky Way. MBHs also
powered active galactic nuclei known to exist just a few hundred million years
after the Big Bang. Here, I summarize the current ideas on the evolution of
MBHs through cosmic history, from their formation about 13 billion years ago to
their growth within their host galaxies.Comment: Review for Science Special Issue on black hole
COMPTEL solar flare measurements
We review some of the highlights of the COMPTEL measurements of solar flares. These include images of the Sun in γ rays and neutrons. One of the important features of the COMPTEL instrument is its capability to measure weak fluxes of γ rays and neutrons in the extended phase of flares. These data complement the spectra taken with the COMPTEL burst spectrometer and the telescope during the impulsive phase of flares. We focus our attention on some of these general capabilities of the instrument and the latest results of two long‐duration γ‐ray flares, i.e., 11 and 15 June 199
Has inventory volatility returned? A look at the current cycle
The massive liquidation of inventories during the 2001 recession contrasts sharply with the more moderate inventory movements observed in recent decades. While the rundown might be seen as evidence that firms are not managing their inventories as effectively as some economists have claimed, a careful analysis of inventory behavior in 2001 suggests that during much of the recession, firms were successfully regulating their inventories to avoid a large buildup of excess stock.Inventories ; Recessions
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