956 research outputs found
Comment: Microarrays, Empirical Bayes and the Two-Groups Model
Comment on ``Microarrays, Empirical Bayes and the Two-Groups Model''
[arXiv:0808.0572]Comment: Published in at http://dx.doi.org/10.1214/07-STS236A the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Cosmic Ray Spallation in Radio-Quiet Active Galactic Nuclei: A Case Study of NGC 4051
We investigate conditions for and consequences of spallation in radio-quiet
Seyfert galaxies. The work is motivated by the recent discovery of significant
line emission at 5.44 keV in Suzaku data from NGC 4051. The energy of the new
line suggests an identification as Cr I Ka emission, however the line is much
stronger than would be expected from material with cosmic abundances, leading
to a suggestion of enhancement owing to nuclear spallation of Fe by low energy
cosmic rays from the active nucleus. We find that the highest abundance
enhancements are likely to take place in gas out of the plane of the accretion
disk and that timescales for spallation could be as short as a few years. The
suggestion of a strong nuclear flux of cosmic rays in a radio-quiet Seyfert
galaxy is of particular interest in light of the recent suggestion from Pierre
Auger Observatory data that ultra-high-energy cosmic rays may originate in such
sources.Comment: 14 pages, 1 figure. Accepted for publication in The Astrophysical
Journa
Hyperconnectivity of Local Neocortical Microcircuitry Induced by Prenatal Exposure to Valproic Acid
Exposure to valproic acid (VPA) during embryogenesis can cause several teratogenic effects, including developmental delays and in particular autism in humans if exposure occurs during the third week of gestation. We examined the postnatal effects of embryonic exposure to VPA on microcircuit properties of juvenile rat neocortex using in vitro electrophysiology. We found that a single prenatal injection of VPA on embryonic day 11.5 causes a significant enhancement of the local recurrent connectivity formed by neocortical pyramidal neurons. The study of the biophysical properties of these connections revealed weaker excitatory synaptic responses. A marked decrease of the intrinsic excitability of pyramidal neurons was also observed. Furthermore, we demonstrate a diminished number of putative synaptic contacts in connection between layer 5 pyramidal neurons. Local hyperconnectivity may render cortical modules more sensitive to stimulation and once activated, more autonomous, isolated, and more difficult to command. This could underlie some of the core symptoms observed in humans prenatally exposed to valproic aci
Self-trapped bidirectional waveguides in a saturable photorefractive medium
We introduce a time-dependent model for the generation of joint solitary
waveguides by counter-propagating light beams in a photorefractive crystal.
Depending on initial conditions, beams form stable steady-state structures or
display periodic and irregular temporal dynamics. The steady-state solutions
are non-uniform in the direction of propagation and represent a general class
of self-trapped waveguides, including counterpropagating spatial vector
solitons as a particular case.Comment: 4 pages, 5 figure
Spatiotemporal pulses in a liquid crystal optical oscillator
A nonlinear optical medium results by the collective orientation of liquid
crystal molecules tightly coupled to a transparent photoconductive layer. We
show that such a medium can give a large gain, thus, if inserted in a ring
cavity, it results in an unidirectional optical oscillator. Dynamical regimes
with many interacting modes are made possible by the wide transverse size and
the high nonlinearity of the liquid crystals. We show the generation of
spatiotemporal pulses, coming from the random superposition of many coexisting
modes with different frequencies
Recommended from our members
Behavior of Sodium Oxide, Uranium Oxide and Mixed Sodium Oxide-Uranium Oxide Aerosols in a Large Vessel
Results are reported for experiments on the behavior of sodium oxide aerosols, uranium oxide aerosols, and various mixtures of these in the Nuclear Safety Pilot Plant (NSPP) vessel at Oak Ridge National Laboratory. The NSPP program, sponsored by the Nuclear Regulatory Commission, is to provide experimental qualification of the HAARM-3 aerosol behavioral code being independently developed at Battelle-Columbus Laboratories. The results of fourteen single-component and six mixed-component aerosol experiments are presented along with selected comparisons with code predictions
The Origin of Galactic Cosmic Rays
Motivated by recent measurements of the major components of the cosmic
radiation around 10 TeV/nucleon and above, we discuss the phenomenology of a
model in which there are two distinct kinds of cosmic ray accelerators in the
galaxy. Comparison of the spectra of hydrogen and helium up to 100 TeV per
nucleon suggests that these two elements do not have the same spectrum of
magnetic rigidity over this entire region and that these two dominant elements
therefore receive contributions from different sources.Comment: To be published in Physical Review D, 13 pages, with 3 figures,
uuencode
Fission-Residues Produced in the Spallation Reaction 238U+p at 1 A GeV
Fission fragments from 1 A GeV 238U projectiles irradiating a hydrogen target
were investigated by using the fragment separator FRS for magnetic selection of
reaction products including ray-tracing and DE-ToF techniques. The momentum
spectra of 733 identified fragments were analysed to provide isotopic
production cross sections, fission-fragment velocities and recoil momenta of
the fissioning parent nuclei. Besides their general relevance, these quantities
are also demanded for applications. Calculations and simulations with codes
commonly used and recently developed or improved are compared to the data.Comment: 60 pages, 21 figures, 4 tables, 2 appendices (15 pages
Spatiotemporally localized solitons in resonantly absorbing Bragg reflectors
We predict the existence of spatiotemporal solitons (``light bullets'') in
two-dimensional self-induced transparency media embedded in a Bragg grating.
The "bullets" are found in an approximate analytical form, their stability
being confirmed by direct simulations. These findings suggest new possibilities
for signal transmission control and self-trapping of light.Comment: RevTex, 3 pages, 2 figures, to be published in PR
- …