3,303 research outputs found
Gamma-Ray Observations of GRO J1655-40
The bright transient X-ray source GRO J1655-40 = XN Sco 1994 was observed by the OSSE instrument on the Compton Gamma Ray Observatory (GRO). Preliminary results are reported here. The initial outburst from GRO J1655-40 was detected by BATSE on 27 Jul 1994. OSSE observations were made in five separate viewing periods starting between 4 Aug 1994 and 4 Apr 1995. The first, third, and fifth observations are near the peak luminosity. In the second observation, the source flux had dropped by several orders of magnitude and we can only set an upper limit. The fourth observation is a weak detection after the period of maximum outburst. In contrast with other X-ray novae such as GRO J0422+32, the spectrum determined by OSSE is consistent with a simple power law over the full range of detection, about 50 - 600 keV. The photon spectral index is in the range of -2.5 to 2.8 in all of the observations. We set an upper limit on fractional rms variation \u3c5% in the frequency range 0.01 â 60 Hz. No significant narrow or broad line features are observed at any energy
Kidney transplantation in children
Transplantation in children with kidney failure once presented many technical, immunologic, and logistic problems that led to worse patient and allograft survival, as compared with adults. Advances in all these areas and the development of pediatric-trial groups have resulted in dramatic improvements, such that young children now have the best long-term graft survival among all age groups, including adults
Effective Bandgap Shrinkage in GaAs
Electrical measurements of the equilibrium np product (n2ie) in heavily doped nâ and pâGaAs were performed. The n2ieDproduct (where D is the diffusivity) was measured by fitting the collector currentâvoltage characteristic of a homojunction bipolar transistor to an ideal diode equation modified to account for transport in thin base transistors.The n2ie product was then extracted from n2ieD by utilizing diffusivity results obtained with the zeroâfield timeâofâflight technique. Our results show significant effective bandâgap shrinkage in heavily doped pâGaAs, and very little effective bandâgap shrinkage in heavily doped nâGaAs. At extremely heavy dopings, an effective bandâgap widening is observed for both nâ and pâGaAs and is attributed to the effects of degeneracy
Image of dynamic local exchange interactions in the dc magnetoresistance of spin-polarized current through a dopant
We predict strong, dynamical effects in the dc magnetoresistance of current
flowing from a spin-polarized electrical contact through a magnetic dopant in a
nonmagnetic host. Using the stochastic Liouville formalism we calculate
clearly-defined resonances in the dc magnetoresistance when the applied
magnetic field matches the exchange interaction with a nearby spin. At these
resonances spin precession in the applied magnetic field is canceled by spin
evolution in the exchange field, preserving a dynamic bottleneck for spin
transport through the dopant. Similar features emerge when the dopant spin is
coupled to nearby nuclei through the hyperfine interaction. These features
provide a precise means of measuring exchange or hyperfine couplings between
localized spins near a surface using spin-polarized scanning tunneling
microscopy, without any ac electric or magnetic fields, even when the exchange
or hyperfine energy is orders of magnitude smaller than the thermal energy
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Advancing the remote sensing of precipitation
Satellite-based global precipitation data has addressed the limitations of rain gauges and weather radar systems in forecasting applications and for weather and climate studies. Inspite of this ability, a number of issues that require the development of advanced concepts to address key challenges in satellite-based observations of precipitation were identified during the Advanced Concepts Workshop on Remote Sensing of Precipitation at Multiple Scales at the University of California. These include quantification of uncertainties of individual sensors and their propagation into multisensor products warrants a great deal of research. The development of metrics for validation and uncertainty analysis are of great importance. Bias removal, particularly probability distribution function (PDF)-based adjustment, deserves more in-depth research. Development of a near-real-time probabilistic uncertainty model for satellitebased precipitation estimates is highly desirable
Unusual temperature dependence of band dispersion in Ba(Fe(1-x)Ru(x))2As2 and its consequences for antiferromagnetic ordering
We have performed detailed studies of the temperature evolution of the
electronic structure in Ba(Fe(1-x)Ru(x))2As2 using Angle Resolved Photoemission
Spectroscopy (ARPES). Surprisingly, we find that the binding energy of both
hole and electron bands changes significantly with temperature in pure and Ru
substituted samples. The hole and electron pockets are well nested at low
temperature in unsubstituted (BaFe2As2) samples, which likely drives the spin
density wave (SDW) and resulting antiferromagnetic order. Upon warming, this
nesting is degraded as the hole pocket shrinks and the electron pocket expands.
Our results demonstrate that the temperature dependent nesting may play an
important role in driving the antiferromagnetic/paramagnetic phase transition.Comment: 5 pages, 6 figure
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