10,339 research outputs found
Photoionization cross section calculations for the halogen-like ions Kr and Xe
Photoionization cross sections calculations on the halogen-like ions; Kr
and Xe have been performed for a photon energy range from each ion
threshold to 15 eV, using large-scale close-coupling calculations within the
Dirac-Coulomb R-matrix approximation. The results from our theoretical work are
compared with recent measurements made at the ASTRID merged-beam set-up at the
University of Aarhus in Denmark and from the Fourier transform ion cyclotron
resonance (FT-ICR) trap method at the SOLEIL synchrotron radiation facility in
Saint-Aubin, France and the Advanced Light Soure (ALS). For each of these
complex ions our theoretical cross section results over the photon energy range
investigated are seen to be in excellent agreement with experiment. Resonance
energy positions and quantum defects of the prominent Rydberg resonances series
identified in the spectra are compared with experiment for these complex
halogen like-ions.Comment: Accepted for publicatio
K-shell x-ray spectroscopy of atomic nitrogen
Absolute {\it K}-shell photoionization cross sections for atomic nitrogen
have been obtained from both experiment and state-of-the-art theoretical
techniques. Due to the difficulty of creating a target of neutral atomic
nitrogen, no high-resolution {\it K}-edge spectroscopy measurements have been
reported for this important atom. Interplay between theory and experiment
enabled identification and characterization of the strong
resonance features throughout the threshold region. An experimental value
of 409.64 0.02 eV was determined for the {\it K}-shell binding energy.Comment: 4 pages, 2 graphs, 1 tabl
Adaptive Bayesian decision feedback equalizer for dispersive mobile radio channels
The paper investigates adaptive equalization of time dispersive mobile ratio fading channels and develops a robust high performance Bayesian decision feedback equalizer (DFE). The characteristics and implementation aspects of this Bayesian DFE are analyzed, and its performance is compared with those of the conventional symbol or fractional spaced DFE and the maximum likelihood sequence estimator (MLSE). In terms of computational complexity, the adaptive Bayesian DFE is slightly more complex than the conventional DFE but is much simpler than the adaptive MLSE. In terms of error rate in symbol detection, the adaptive Bayesian DFE outperforms the conventional DFE dramatically. Moreover, for severely fading multipath channels, the adaptive MLSE exhibits significant degradation from the theoretical optimal performance and becomes inferior to the adaptive Bayesian DFE
PSR J0737-3039B: A probe of radio pulsar emission heights
In the double pulsar system PSR J0737-3039A/B the strong wind produced by
pulsar A distorts the magnetosphere of pulsar B. The influence of these
distortions on the orbital-dependent emission properties of pulsar B can be
used to determine the location of the coherent radio emission generation region
in the pulsar magnetosphere. Using a model of the wind-distorted magnetosphere
of pulsar B and the well defined geometrical parameters of the system, we
determine the minimum emission height to be ~ 20 neutron star radii in the two
bright orbital longitude regions. We can determine the maximum emission height
by accounting for the amount of deflection of the polar field line with respect
to the magnetic axis using the analytical magnetic reconnection model of Dungey
and the semi-empirical numerical model of Tsyganenko. Both of these models
estimate the maximum emission height to be ~ 2500 neutron star radii. The
minimum and maximum emission heights we calculate are consistent with those
estimated for normal isolated pulsars.Comment: 29 pages, 14 figures, Accepted by ApJ on 3 March 201
An Active-Sterile Neutrino Transformation Solution for r-Process Nucleosynthesis
We discuss how matter-enhanced active-sterile neutrino transformation in both
neutrino and antineutrino channels could enable the production of the rapid
neutron capture (r-process) nuclei in neutrino-heated supernova ejecta. In this
scheme the lightest sterile neutrino would be heavier than the electron
neutrino and split from it by a vacuum mass-squared difference roughly between
3 and 70 eV and vacuum mixing angle given by .Comment: 27 pages plus twelve figures. Submitted to Phys. Rev.
Modeling the non-recycled Fermi gamma-ray pulsar population
We use Fermi Gamma-ray Space Telescope detections and upper limits on
non-recycled pulsars obtained from the Large Area Telescope (LAT) to constrain
how the gamma-ray luminosity L depends on the period P and the period
derivative \dot{P}. We use a Bayesian analysis to calculate a best-fit
luminosity law, or dependence of L on P and \dot{P}, including different
methods for modeling the beaming factor. An outer gap (OG) magnetosphere
geometry provides the best-fit model, which is L \propto P^{-a} \dot{P}^{b}
where a=1.36\pm0.03 and b=0.44\pm0.02, similar to but not identical to the
commonly assumed L \propto \sqrt{\dot{E}} \propto P^{-1.5} \dot{P}^{0.5}. Given
upper limits on gamma-ray fluxes of currently known radio pulsars and using the
OG model, we find that about 92% of the radio-detected pulsars have gamma-ray
beams that intersect our line of sight. By modeling the misalignment of radio
and gamma-ray beams of these pulsars, we find an average gamma-ray beaming
solid angle of about 3.7{\pi} for the OG model, assuming a uniform beam. Using
LAT-measured diffuse fluxes, we place a 2{\sigma} upper limit on the average
braking index and a 2{\sigma} lower limit on the average surface magnetic field
strength of the pulsar population of 3.8 and 3.2 X 10^{10} G, respectively. We
then predict the number of non-recycled pulsars detectable by the LAT based on
our population model. Using the two-year sensitivity, we find that the LAT is
capable of detecting emission from about 380 non-recycled pulsars, including
150 currently identified radio pulsars. Using the expected five-year
sensitivity, about 620 non-recycled pulsars are detectable, including about 220
currently identified radio pulsars. We note that these predictions
significantly depend on our model assumptions.Comment: 26 pages, 10 figures, Accepted by ApJ on 8 September 201
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