12,072 research outputs found
Low State of the X-ray Burster SLX 1732-304 in the Globular Cluster Terzan 1 According to RXTE Data
Observations of the X-ray burster SLX 1732-304 in the globular cluster Terzan
1 with the PCA/RXTE instrument in April 1997 are presented. The source was in a
low state; its flux in the standard X-ray band was half the flux recorded by
the ART-P/Granat telescope also during its low state. At the same time, its
spectrum was softer than the ART-P spectrum; it was well described by a power
law with a photon index of 2.3 without any evidence of a high-energy cutoff.Comment: 8 pages, 3 figures. Accepted to publication in Astronomy Letter
A Persistent High-Energy Flux from the Heart of the Milky Way : Integral's view of the Galactic Center
The Ibis/Isgri imager on Integral detected for the first time a hard X-ray
source, IGR J17456-2901, located within 1' of Sgr A* over the energy range
20-100 keV. Here we present the results of a detailed analysis of ~7 Ms of
Integral observations of the GC. With an effective exposure of 4.7 Ms we have
obtained more stringent positional constraints on this HE source and
constructed its spectrum in the range 20-400 keV. Furthermore, by combining the
Isgri spectrum with the total X-ray spectrum corresponding to the same physical
region around SgrA* from XMM data, and collected during part of the Integral
observations, we constructed and present the first accurate wide band HE
spectrum for the central arcmins of the Galaxy. Our complete analysis of the
emission properties of IGR shows that it is faint but persistent with no
variability above 3 sigma contrary to what was alluded to in our first paper.
This result, in conjunction with the spectral characteristics of the X-ray
emission from this region, suggests that the source is most likely not
point-like but, rather, that it is a compact, yet diffuse, non-thermal emission
region. The centroid of IGR is estimated to be R.A.=17h45m42.5,
decl.=-28deg59'28'', offset by 1' from the radio position of Sgr A* and with a
positional uncertainty of 1'. Its 20-400 keV luminosity at 8 kpc is L=5.4x10^35
erg/sec. Very recently, Hess detected of a source of ~TeV g-rays also located
within 1' of Sgr A*. We present arguments in favor of an interpretation
according to which the photons detected by Integral and Hess arise from the
same compact region of diffuse emission near the central BH and that the
supernova remnant Sgr A East could play an important role as a contributor of
very HE g-rays to the overall spectrum from this region.Comment: 14 pages, 11 figures, Accepted for publication in Ap
EXIST's Gamma-Ray Burst Sensitivity
We use semi-analytic techniques to evaluate the burst sensitivity of designs
for the EXIST hard X-ray survey mission. Applying these techniques to the
mission design proposed for the Beyond Einstein program, we find that with its
very large field-of-view and faint gamma-ray burst detection threshold, EXIST
will detect and localize approximately two bursts per day, a large fraction of
which may be at high redshift. We estimate that EXIST's maximum sensitivity
will be ~4 times greater than that of Swift's Burst Alert Telescope. Bursts
will be localized to better than 40 arcsec at threshold, with a burst position
as good as a few arcsec for strong bursts. EXIST's combination of three
different detector systems will provide spectra from 3 keV to more than 10 MeV.
Thus, EXIST will enable a major leap in the understanding of bursts, their
evolution, environment, and utility as cosmological probes.Comment: 25 pages, 10 figures, accepted by Ap
Enhancing Academic Engagement: Providing Opportunities for Responding and Influencing Students to Choose to Respond
Although educators often provide opportunities for students to engage in active academic responding, in many situations, students either cannot or will not respond. In the current article, we analyze the reasons students fail to respond. Practical procedures educators can use to prevent can\u27t do problems are provided. Won\u27t do problems are conceptualized as choice behaviors. Both applied and theoretical research on choice behavior provides the basis for recommendations designed to enhance the probability of students choosing to engage in active accurate academic (AAA) responding. Such procedures can increase skill development and achievement while decreasing inappropriate behaviors that are incompatible with AAA responding. School psychologists may utilize this information during the initial stages of collaborative problem solving (e.g., consultation) to help conceptualize problems. This conceptualization may then guide the assessment and intervention processes
Troubles with Bayesianism: An introduction to the psychological immune system
A Bayesian mind is, at its core, a rational mind. Bayesianism is thus well-suited to predict and explain mental processes that best exemplify our ability to be rational. However, evidence from belief acquisition and change appears to show that we do not acquire and update information in a Bayesian way. Instead, the principles of belief acquisition and updating seem grounded in maintaining a psychological immune system rather than in approximating
a Bayesian processor
Chondromyxoid fibroma management: a single institution experience of 22 cases
Background: Several different strategies have been reported for the treatment of chondromyxoid fibromas, all with variable outcomes and high recurrence rates. Methods: We report on 22 consecutive cases of chondromyxoid fibromas treated by intralesional curettage, four of which had adjuvant cementation at our institution between 2003 and 2010. We assessed the functional outcome using the Musculoskeletal Tumour Society (MSTS) scoring system. Results: Nine males and 16 females with a mean age of 36.5 years (range 11 to 73) and a mean follow-up of 60.7 months were included in the study. Local recurrence occurred in two patients (9%) within the first 2 years following the index procedure. This was treated by re-curettage only of the residual defect. Two postoperative complications occurred: a superficial wound infection in one patient and a transient deep peroneal nerve neurapraxia in the other. The mean postoperative MSTS score was 96.7%. Conclusions: Intralesional curettage and cementation is as an effective treatment strategy for chondromyxoid fibromas, providing satisfactory functional results with a low recurrence rate. Careful case selection with stringent clinical and radiographic follow-up is recommended
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