962 research outputs found
Time Resolved GRB Spectroscopy
We present the main results of a study of time-resolved spectra of 43 intense
GRBs detected by BATSE. We considered the 4-parameter Band model and the
Optically Thin Synchrotron Shock model (OTSSM). We find that the large majority
of time-resolved spectra of GRBs are in remarkable agreement with the OTSSM.
However, about 15 % of initial GRB pulses show an apparent low-energy photon
suppression. This phenomenon indicates that complex radiative conditions
modifying optically thin emission may occur during the initial phases of some
GRBs.Comment: 5 pages, 3 figures, Paper presented at the 5th Huntsville Symposium,
Huntsville (Alabama) Oct. 199
Monte-Carlo simulations of thermal/nonthermal radiation from a neutron-star magnetospheric accretion shell
We discuss the space-and-time-dependent Monte Carlo code we have developed to
simulate the relativistic radiation output from compact astrophysical objects,
coupled to a Fokker-Planck code to determine the self-consistent lepton
populations. We have applied this code to model the emission from a magnetized
neutron star accretion shell near the Alfven radius, reprocessing the radiation
from the neutron sar surface. We explore the parameter space defined by the
accretion rate, stellar surface field and the level of wave turbulence in the
shell. Our results are relevant to the emission from atoll sources, soft-X-ray
transient X-ray binaries containing weakly magnetized neutron stars, and to
recently suggested models of accretion-powered emission from anomalous X-ray
pulsars.Comment: 24 pages, including 7 figures; uses epsf.sty. final version, accepted
for publication in ApJ. Extended introduction and discussio
When challenges hinder: An investigation of buyer-imposed stressors on supplier flexibility
Working with buyers may drive business growth but can also induce supplier stress. Drawing on Job Demands–Resources (JD-R) theory, this study explored how buyer-imposed work stressors affect supplier flexibility. Employing a scenario-based experiment involving 338 managers, we found that the imposition of challenge stressors increases supplier flexibility when hindrance stressors are low. Conversely, when hindrance stressors are high, imposing challenge stressors reduces supplier flexibility. We also found that supplier bricolage negatively moderates the relationship between buyer-imposed challenge stressors and supplier flexibility. Specifically, we confirmed that suppliers with higher bricolage are less willing to provide flexibility in response to challenge stressors. For practitioners, our study not only identified the type of work stressors they should impose on suppliers to boost flexibility but also highlighted bricolage as an important moderating factor
A variability analysis of low-latitude unidentified gamma-ray sources
We present a study of 40 low-latitude unidentified 3EG gamma-ray sources
which were found to be not positionally coincident with any known class of
potential gamma-ray emitters in the Galaxy (Romero, Benaglia & Torres, 1999).
We have performed a variability analysis which reveals that many of these 40
sources are variable. These sources have, in addition, a steep mean value of
the gamma-ray spectral index, , which, combined with
the high level of variability seems to rule out a pulsar origin. The positional
coincidences with uncatalogued candidates to supernova remnants were also
studied. Only 7 sources in the sample are spatially coincident with these
candidates, a result that is shown to be consistent with the expected level of
pure chance association. A complementary search for weak radio counterparts was
also conducted and the results are presented as an extensive table containing
all significant point-like radio sources within the 40 EGRET fields. We argue
that in order to produce the high variability, steep gamma-ray spectra, and
absence of strong radio counterparts observed in some of the gamma-ray sources
of our sample a new class of objects should be postulated, and we analyze a
viable candidate.Comment: Paper updated to match the accepted version to appear in Astronomy
and Astrophysics, 2001. Tables 5,6,7 and 8 are in ascii format and need to be
printed separately. they can also be obtained from
http://www.iar.unlp.edu.ar/garra Table 5 is 62 pages long. Download the
source to obtain the table
Classical and Keynesian models of inequality and stagnation
This paper studies two formal models of long run growth with a medium-run distributive cycle, both of which feature causal links from the rise in inequality to a deterioration of long run macroeconomic performance. Both versions feature an endogenous income-capital ratio: one through the Keynesian notion of effective demand, the other building on induced bias in technical change. A key focus of the analysis is on the assumptions necessary in both frameworks to generate policy implications consistent with the observed decline of the labor share, the income-capital ratio, and labor productivity growth during the neoliberal era. Importantly, both theories: (a) provide space for mutually reinforcing pro-labor and pro-growth policies in the long run, although they differ in the mechanisms at play in these processes; (b) imply a potential tradeoff between pro-labor policies and growth on one hand, and long-run employment on the other; (c) are consistent with the evidence on the distributive cycle at business cycle frequency
Virtual Outcrops in a Pocket: The Smartphone as a Fully Equipped Photogrammetric Data Acquisition Tool
Since the advent of affordable consumer-grade cameras over a century ago, photographic images have been the standard medium for capturing and visualizing outcrop-scale geological features. Despite the ubiquity of raster image data capture in routine fieldwork, the development of close-range 3D remote-sensing techniques has led to a paradigm shift in the representation and analysis of rock exposures from two- to three-dimensional forms. The use of geological 3D surface reconstructions in routine fieldwork has, however, been limited by the portability, associated learning curve, and/or expense of tools required for data capture, visualization, and analysis. Smartphones are rapidly becoming a viable alternative to conventional 3D close-range remote-sensing data capture and visualization platforms, providing a catalyst for the general uptake of 3D outcrop technologies by the geological community, which were up until relatively recently the purview of a relatively small number of geospatial specialists. Indeed, the continuous improvement of smartphone cameras, coupled with their integration with global navigation satellite system (GNSS) and inertial sensors provides 3D reconstructions with comparable accuracy to survey-grade systems. These developments have already led many field geologists to replace reflex cameras, as well as dedicated handheld GNSS receivers and compass clinometers, with smartphones, which offer the equivalent functionality within a single compact platform. Here we demonstrate that through the use of a smartphone and a portable gimbal stabilizer, we can readily generate and register high-quality 3D scans of outcropping geological structures, with the workflow exemplified using a mirror of a seismically active fault. The scan is conducted with minimal effort over the course of a few minutes with limited equipment, thus being representative of a routine situation for a field geologist
Long-Term Flux Monitoring of LSI +61 303 at 2.25 and 8.3 GHz
LSI +61 303 is an exotic binary system consisting of a ~10 Msun B star and a
compact object which is probably a neutron star. The system is associated with
the interesting radio source GT0236+610 that exhibits bright radio outbursts
with a period of 26.5 days. We report the results of continuous daily radio
interferometric observations of GT0236+610 at 2.25 and 8.3 GHz from 1994
January to 1996 February. The observations cover 25 complete (and 3 partial)
cycles with multiple observations each day. We detect substantial
cycle-to-cycle variability of the radio emission characterized by a rapid onset
of the radio flares followed by a more gradual decrease of the emission. We
detect a systematic change of the radio spectral index alpha which typically
becomes larger than zero at the onset of the radio outbursts. This behavior is
suggestive of expansion of material initially optically thick to radio
frequencies, indicating either that synchrotron or inverse Compton cooling are
important or that the free-free optical depth to the source is rapidly
changing. After two years of observations, we see only weak evidence for the
proposed 4-year periodic modulation in the peak flux of the outbursts. We
observe a secular trend in the outburst phases according the the best published
ephemeris. This trend indicates either orbital period evolution, or a drift in
outburst orbital phase in response to some other change in the system.Comment: 23 pages, LaTex, 7 figures, to appear in ApJ, v491, Dec 10th issue,
for associated info and preprints see
http://www.srl.caltech.edu/personnel/paulr/lsi.htm
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