155 research outputs found
The Spectrum and Dips of RE 0751+14: A joint evaluation of ROSAT and ASCA Archival Data
Using archival ASCA and ROSAT observations of RE 0751+14, X-ray energy
spectra, pulse profiles and the results of pulse timing analysis are presented.
The energy spectra are well-fitted by a blackbody model at low energy and a
Raymond-Smith model at high energy, together with a partial covering absorber.
A fluorescence emission line at 6.4 keV with an equivalent width eV
was resolved for the first time.Comment: To appear on Astrophysics and Space Science, vol 259, pages 191-203,
January 199
Personal Lives? The Effects of nonwork behaviors on organizational image
Cataloged from PDF version of article.Organizational leaders may respond to employee nonwork behaviors because of the possible
influence on organizational image. We describe a typology of nonwork behaviors and discuss their
potential implications for organizational image. We explore conditions under which organizational
leaders may attempt to control employee nonwork behaviors and review the available alternatives
for organizational control. We conclude by discussing the theoretical and practical implications of
research on nonwork behavior
X-ray Spectral Variations of U Gem from Quiescence to Outburst
In this paper we report the discovery of a high energy component of the X-ray
spectra of U Gem, which can be observed while the source is in outburst. We
used Chandra and XMM-Newton observations to compare the quiescence and outburst
X-ray spectra of the source. The additional component may be the result of the
reflection of X-rays emitted from an optically thin plasma close to the white
dwarf, from the optically thick boundary layer during the outburst. Another
possible explanation is that some magnetically channeled accretion may occur
onto the equatorial belt of the primary causing shocks similar to the ones in
the intermediate polars as it was suggested by \citep{w2002}. We have also
found a timing structure at about 73 mHz (13.7 s.) in the RXTE
observation, resembling dwarf novae oscillations (DNOs).Comment: accepted by MNRAS, figure 1 replaced with a newer on
Patients With Kidney Cancer
To develop a preoperative prognostic model in order to predict recurrence-free survival in patients with nonmetastatic kidney cancer.A multi-institutional data base of 1889 patients who underwent surgical resection between 1987 and 2007 for kidney cancer was retrospectively analyzed. Preoperative variables were defined as age, gender, presentation, size, presence of radiological lymph nodes and clinical stage. Univariate and multivariate analyses of the variables were performed using the Cox proportional hazards regression model. A model was developed with preoperative variables as predictors of recurrence after nephrectomy. Internal validation was performed by Harrells concordance index.The median follow-up was 23.6 months (1222 months). During the follow-up, 258 patients (13.7) developed cancer recurrence. The median follow-up for patients who did not develop recurrence was 25 months. The median time from surgery to recurrence was 13 months. The 5-year freedom from recurrence probability was 78.6. All variables except age were associated with freedom from recurrence in multivariate analyses (P 0.05). Age was marginally significant in the univariate analysis. All variables were included in the predictive model. The calculated c-index was 0.747.This preoperative model utilizes easy to obtain clinical variables and predicts the likelihood of development of recurrent disease in patients with kidney tumors
John Schuster, Descartes-agonistes: Physico-mathematics, method and corpuscular-mechanism, 1618–1633
We report on a 10 ks simultaneous Chandra/HETG-NuSTAR observation of the
Bursting Pulsar, GRO J1744-28, during its third detected outburst since
discovery and after nearly 18 years of quiescence. The source is detected up to
60 keV with an Eddington persistent flux level. Seven bursts, followed by dips,
are seen with Chandra, three of which are also detected with NuSTAR. Timing
analysis reveals a slight increase in the persistent emission pulsed fraction
with energy (from 10% to 15%) up to 10 keV, above which it remains constant.
The 0.5-70 keV spectra of the persistent and dip emission are the same within
errors, and well described by a blackbody (BB), a power-law with an exponential
rolloff, a 10 keV feature, and a 6.7 keV emission feature, all modified by
neutral absorption. Assuming that the BB emission originates in an accretion
disc, we estimate its inner (magnetospheric) radius to be about 4x10^7 cm,
which translates to a surface dipole field B~9x10^10 G. The Chandra/HETG
spectrum resolves the 6.7 keV feature into (quasi-)neutral and highly ionized
Fe XXV and Fe XXVI emission lines. XSTAR modeling shows these lines to also
emanate from a truncated accretion disk. The burst spectra, with a peak flux
more than an order of magnitude higher than Eddington, are well fit with a
power-law with an exponential rolloff and a 10~keV feature, with similar fit
values compared to the persistent and dip spectra. The burst spectra lack a
thermal component and any Fe features. Anisotropic (beamed) burst emission
would explain both the lack of the BB and any Fe components.Comment: 15 pages, 11 figures, Accepted in Ap
A low-magnetic-field Soft Gamma Repeater
Soft gamma repeaters and anomalous x-ray pulsars form a rapidly increasing
group of x-ray sources exhibiting sporadic emission of short bursts. They are
believed to be magnetars, i.e. neutron stars powered by extreme magnetic
fields, B~10^{14}-10^{15} Gauss. We report on a soft gamma repeater with low
magnetic field, SGR 0418+5729, recently detected after it emitted bursts
similar to those of magnetars. X-ray observations show that its dipolar
magnetic field cannot be greater than 7.5x10^{12} Gauss, well in the range of
ordinary radio pulsars, implying that a high surface dipolar magnetic field is
not necessarily required for magnetar-like activity. The magnetar population
may thus include objects with a wider range of B-field strengths, ages and
evolutionary stages than observed so far.Comment: Accepted by Science. First published on-line in ScienceXpress on 2010
October 14th: http://www.sciencexpress.or
- …