Designed as the first mission to explore the ultra-high energy universe from space, JEM-EUSO observes the Earth’s atmosphere at night to record the ultraviolet tracks generated by the extensive air ...showers. We present the expected geometrical aperture and annual exposure in the nadir and tilt modes for ultra-high energy cosmic rays observation as a function of the altitude of the International Space Station.
Accretion-powered X-ray pulsars exhibit significant variability of the cyclotron resonance scattering feature (CRSF) centroid energy on pulse-to-pulse timescales, and also on much longer timescales. ...Two types of spectral variability are observed. For sources in group 1, the CRSF energy is negatively correlated with the variable source luminosity, and for sources in group 2, the opposite behavior is observed. The authors explore the hypothesis that the accretion dynamics in the group 1 sources is dominated by radiation pressure near the stellar surface, and that Coulomb interactions decelerate the gas to rest in the group 2 sources. They derive a new expression for the critical luminosity, ..., such that radiation pressure decelerates the matter to rest in sources with X-ray luminosity ... . The results confirm that the group 1 sources are supercritical and the group 2 sources are subcritical, although the situation is less clear for those highly variable sources that cross over the line ... . (ProQuest: ... denotes formulae/symbols omitted.)
During acute regional myocardial ischemia, a “current of injury” flows between the ischemic and the normal tissue. Its direction and magnitude change during the cardiac cycle. During diastole, the ...injury current flows intracellularly from the ischemic cells toward the normal cells and tends to depolarize the latter. To gain insight into the possible role of the injury current in arrhythmogenesis, we simultaneously determined diastolic stimulation threshold, K+o, and TQ potential at multiple sites closely spaced across the cyanotic border in Langendorff-perfused pig hearts during the first 10 minutes after occlusion of the left anterior descending coronary artery. The position of the electrodes relative to the border was validated by their response to 1) regional ischemia and 2) selective perfusion with a high-K perfusate of the left anterior descending coronary artery. A temporary decrease of diastolic stimulation threshold preceded a rapid increase in the central ischemic zone; a lasting reduction (by ±20%) without a concomitant increase of Ko was observed at seven sites (of 39 sites tested), five of which were less than 2 mm outside the electrophysiological border. Moreover, up to 4 mm inside the electrophysiological border, a similar lasting decrease of diastolic stimulation threshold was accompanied by a moderate increase of Ko. We conclude that 1) the injury current causes increased excitability in normal tissue close to the “ischemic” border and 2) increased excitability related to a moderately increased Ko may persist up to 10 minutes of ischemia at the ischemic side of the border. Both factors may facilitate the induction of life-threatening arrhythmias in acute myocardial ischemia.
We are conducting tests of optical and electronics components of JEMEUSO at the Telescope Array site in Utah with a ground-based “EUSO-TA” detector. The tests will include an engineering validation ...of the detector, cross-calibration of EUSO-TA with the TA fluorescence detector and observations of air shower events. Also, the proximity of the TA’s Electron Light Source will allow for convenient use of this calibration device. In this paper, we report initial results obtained with the EUSO-TA telescope.
INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Centaurus A in 2003 March, 2004 January, and 2004 February with the goals of investigating the geometry and ...emission processes via the spectral/temporal variability of the X-ray/low-energy gamma-ray flux, and intercalibration of the INTEGRAL instruments with respect to those on RXTE. Cen A was detected by both sets of instruments from 3 to 240 keV. When combined with earlier archival RXTE results, we find the power-law continuum flux and the line-of-sight column depth varied independently by 60% between 2000 January and 2003 March. Including the three archival RXTE observations, the iron-line flux was essentially unchanging, and from this we conclude that the iron-line-emitting material is distant from the site of the continuum emission, and that the origin of the iron-line flux is still an open question. Taking X-ray spectral measurements from satellite missions since 1970 into account, we discover a variability in the column depth between 1.0 x 10 super(23) and 1.5 x 10 super(23) cm super(-2) separated by approximately 20 yr, and suggest that variations in the edge of a warped accretion disk viewed nearly edge-on might be the cause. The INTEGRAL OSA 4.2 calibration of JEM-X, ISGRI, and SPI yields power-law indices consistent with the RXTE PCA and HEXTE values, but the indices derived from ISGRI alone are about 0.2 greater. Significant systematics are the limiting factor for INTEGRAL spectral parameter determination.
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