21,682 research outputs found
Design, fabrication, and bench testing of a solar chemical receiver
Solar thermal energy can be effectively collected, transported, stored, and utilized by means of a chemical storage and transport system employing the reversible SO2 oxidation reaction. A solar chemical receiver for SO3 thermal decomposition to SO2 and oxygen was analyzed. Bench tests of a ten foot section of a receiver module were conducted with dissociated sulfuric acid (SO3 and H2O) in an electrical furnace. Measured percent conversion of SO3 was 85% of the equilibrium value. Methods were developed to fabricate and assemble a complete receiver module. These methods included applying an aluminide coating to certain exposed surfaces, assembling concentric tubes with a wire spacer, applying a platinum catalyst to the tubing wall, and coiling the entire assembly into the desired configuration
On-shell Techniques and Universal Results in Quantum Gravity
We compute the leading post-Newtonian and quantum corrections to the Coulomb
and Newtonian potentials using the full modern arsenal of on-shell techniques;
we employ spinor-helicity variables everywhere, use the Kawai-Lewellen-Tye
(KLT) relations to derive gravity amplitudes from gauge theory and use
unitarity methods to extract the terms needed at one-loop order. We stress that
our results are universal and thus will hold in any quantum theory of gravity
with the same low-energy degrees of freedom as we are considering. Previous
results for the corrections to the same potentials, derived historically using
Feynman graphs, are verified explicitly, but our approach presents a huge
simplification, since starting points for the computations are compact and
tedious index contractions and various complicated integral reductions are
eliminated from the onset, streamlining the derivations. We also analyze the
spin dependence of the results using the KLT factorization, and show how the
spinless correction in the framework are easily seen to be independent of the
interacting matter considered.Comment: 34 pages, 7 figures, typos corrected, published versio
Global General Relativistic Magnetohydrodynamic Simulations of Accretion Tori
This paper presents an initial survey of the properties of accretion flows in
the Kerr metric from three-dimensional, general relativistic
magnetohydrodynamic simulations of accretion tori. We consider three fiducial
models of tori around rotating, both prograde and retrograde, and nonrotating
black holes; these three fiducial models are also contrasted with axisymmetric
simulations and a pseudo-Newtonian simulation with equivalent initial
conditions to delineate the limitations of these approximations.Comment: Submitted to ApJ. 30 pages, 21 figures. Animations and
high-resolution version of figures available at
http://www.astro.virginia.edu/~jd5
A microscopic approach to nonlinear Reaction-Diffusion: the case of morphogen gradient formation
We develop a microscopic theory for reaction-difusion (R-D) processes based
on a generalization of Einstein's master equation with a reactive term and we
show how the mean field formulation leads to a generalized R-D equation with
non-classical solutions. For the -th order annihilation reaction
, we obtain a nonlinear reaction-diffusion equation
for which we discuss scaling and non-scaling formulations. We find steady
states with either solutions exhibiting long range power law behavior (for
) showing the relative dominance of sub-diffusion over reaction
effects in constrained systems, or conversely solutions (for )
with finite support of the concentration distribution describing situations
where diffusion is slow and extinction is fast. Theoretical results are
compared with experimental data for morphogen gradient formation.Comment: Article, 10 pages, 5 figure
Non Equilibrium Noise as a Probe of the Kondo Effect in Mesoscopic Wires
We study the non-equilibrium noise in mesoscopic diffusive wires hosting
magnetic impurities. We find that the shot-noise to current ratio develops a
peak at intermediate source-drain biases of the order of the Kondo temperature.
The enhanced impurity contribution at intermediate biases is also manifested in
the effective distribution. The predicted peak represents increased inelastic
scattering rate at the non-equilibrium Kondo crossover.Comment: 4+ pages, 4 figures, published versio
Dephasing by extremely dilute magnetic impurities revealed by Aharonov-Bohm oscillations
We have probed the magnetic field dependence of the electron phase coherence
time by measuring the Aharonov-Bohm conductance oscillations of
mesoscopic Cu rings. Whereas determined from the low-field
magnetoresistance saturates below 1 K, the amplitude of Aharonov-Bohm
oscillations increases strongly on a magnetic field scale proportional to the
temperature. This provides strong evidence that a likely explanation for the
frequently observed saturation of at low temperature in weakly
disordered metallic thin films is the presence of extremely dilute magnetic
impurities.Comment: Accepted for publication in Physical Review Letter
Energy relaxation due to magnetic impurities in mesoscopic wires: Logarithmic approach
The transport in mesoscopic wires with large applied bias voltage has
recently attracted great interest by measuring the energy distribution of the
electrons at a given point of the wire, in Saclay. In the diffusive limit with
negligible energy relaxation that shows two sharp steps at the Fermi energies
of the two contacts, which are broadened due to the energy relaxation. In some
of the experiments the broadening is reflecting an anomalous energy relaxation
rate proportional to instead of valid for Coulomb
electron-electron interaction, where is the energy transfer. Later it has
been suggested that such relaxation rate can be due to electron-electron
interaction mediated by Kondo impurities. In the present paper the latter is
systematically studied in the logarithmic approximation valid above the Kondo
temperature. In the case of large applied bias voltage Kondo resonances are
formed at the steps of the distribution function and they are narrowed by
increasing the bias. An additional Korringa energy broadening occurs for the
spins which smears the Kondo resonances, and the renormalized coupling can be
replaced by a smooth but essentially enhanced average coupling (factor of
8-10). Thus the experimental data can be described by formulas without
logarithmic Kondo corrections, but with enhanced coupling. In certain regions
of large bias, that averaged coupling depends weakly on the bias. In those
cases the distribution function depends only on the ratio of the electron
energy and the bias, showing scaling behavior. The impurity concentrations
estimated from those experiments and other dephasing experiments can be very
different, and a possible explanation considering the surface spin anisotropy
due to strong spin-orbit interaction is the subject of our earlier paper.Comment: 12 pages, RevTex
Magnetodielectric effect of Bi6Fe2Ti3O18 film under an ultra-low magnetic field
Good quality and fine grain Bi6Fe2Ti3O18 magnetic ferroelectric films with
single-phase layered perovskite structure have been successfully prepared via
metal organic decomposition (MOD) method. Results of low-temperature
magnetocapacitance measurements reveal that an ultra-low magnetic field of 10
Oe can produce a nontrivial magnetodielectric (MD) response in
zero-field-cooling condition, and the relative variation of dielectric
constants in magnetic field is positive, i.e., MD=0.05, when T<55K, but
negative with a maximum of MD=-0.14 when 55K<T<190K. The magnetodielectric
effect appears a sign change at 55K, which is due to transition from
antiferromagnetic to weak ferromagnetic; and vanishes abruptly around 190K,
which is thought to be associated with order-disorder transition of iron ion at
B site of perovskite structures. The ultra-low-field magnetodielectric
behaviour of Bi6Fe2Ti3O18 film has been discussed in the light of
quasi-two-dimension unique nature of local spin order in ferroelectric film.
Our results allow expectation on low-cost applications of detectors and
switches for extremely weak magnetic fields in a wide temperature range
55K-190K.Comment: 10 pages 4 figures, planned to submit to J. Phys.: Condensed Matte
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