2,665 research outputs found
Thermal conduction and particle transport in strong MHD turbulence, with application to galaxy-cluster plasmas
We investigate field-line separation in strong MHD turbulence analytically
and with direct numerical simulations. We find that in the
static-magnetic-field approximation the thermal conductivity in galaxy clusters
is reduced by a factor of about 5-10 relative to the Spitzer thermal
conductivity of a non-magnetized plasma. We also estimate how the thermal
conductivity would be affected by efficient turbulent resistivity.Comment: Major revision: higher resolution simulations lead to significantly
different conclusions. 26 pages, 10 figure
The divergence of neighboring magnetic field lines and fast-particle diffusion in strong magnetohydrodynamic turbulence, with application to thermal conduction in galaxy clusters
We investigate field-line separation in strong MHD turbulence using direct
numerical simulations. We find that in the static-magnetic-field approximation
the thermal conductivity in galaxy clusters is reduced by a factor of about 50
relative to the Spitzer thermal conductivity of a non-magnetized plasma. This
value is too small for heat conduction to balance radiative cooling in
clusters.Comment: Major revision: higher resolution simulations lead to significantly
different conclusions. 4 pages, 4 figures, submitted to Physical Review
Letter
Acceleration of energetic particles by large-scale compressible magnetohydrodynamic turbulence
Fast particles diffusing along magnetic field lines in a turbulent plasma can
diffuse through and then return to the same eddy many times before the eddy is
randomized in the turbulent flow. This leads to an enhancement of particle
acceleration by large-scale compressible turbulence relative to previous
estimates in which isotropic particle diffusion is assumed.Comment: 13 pages, 3 figures, accepted for publication in Ap
Speciation in Golden-Plovers, Pluvialis dominica and P. fulva: Evidence from the Breeding Grounds
Two forms of golden-plover have long been considered subspecies, Pluvialisdominica dominica and P. d. fulva. Prior studies have shown differences between forms in breeding distributions, wintering distributions, plumage, morphology, molt, and maturation schedules. We report clear and consistent differences in breeding vocalizations and nesting habitat, and strict assortative mating in areas of sympatry in western Alaska. These results indicate a greater degree of differentiation between the forms than was previously appreciated. They are appropriately treated as separate species and should be referred to under the names Pluvialis dominica, for the American Golden-Plover, and Pluvialis fulva, for the Pacific Golden-Plover
Breeding Ground Fidelity and Mate Retention in the Pacific Golden-Plover
We found male-biased site fidelity in Pacific Golden-Plovers (Phviah fulva)on breeding grounds in western Alaska. Males (8 of 8) returned to the same territories annually, while few females (1 of 4) were seen in subsequent seasons. Nest sites in successive years were usually within 100 m, and the same nest cup may be used in more than one year. First-year birds of both sexes mated with older birds and also with each other, but first-year females may breed less commonly than first-year males. The numbers of nesting birds on our study sites varied sharply both within and between seasons
Gradient Particle Magnetohydrodynamics
We introduce Gradient Particle Magnetohydrodynamics (GPM), a new Lagrangian
method for magnetohydrodynamics based on gradients corrected for the locally
disordered particle distribution. The development of a numerical code for MHD
simulation using the GPM algorithm is outlined. Validation tests simulating
linear and nonlinear sound waves, linear MHD waves, advection of magnetic
fields in a magnetized vortex, hydrodynamical shocks, and three-dimensional
collapse are presented, demonstrating the viability of an MHD code using GPM.
The characteristics of a GPM code are discussed and possible avenues for
further development and refinement are mentioned. We conclude with a view of
how GPM may complement other methods currently in development for the next
generation of computational astrophysics.Comment: 26 pages, 11 figure
1-Butanol dehydration and oxidation over vanadium phosphate catalysts
The transformation of 1-butanol into either butenes or maleic anhydride was carried out both with and without oxygen, using V/P/O catalysts. With vanadyl pyrophosphate prepared by coprecipitation, at temperature lower than 240 â—¦C and without oxygen, selectivity to butenes was higher than 90%, but a slow deactivation took place.
At temperature higher than 300 ◦C and in the presence of air, maleic and phthalic anhydrides were the prevailing products, with selectivity of 60% and 14%, respectively. Catalytic performance was affected by crystallinity and acidity. αI-VOPO4 showed a poor performance in the absence of air, with a quick deactivation due to coke
accumulation; but it displayed an excellent selectivity to butenes (close to 98%) at temperatures lower than 320 ◦C in the presence of air, with stable performance. At temperature higher than 360 ◦C, α I-VOPO4 was reduced to vanadyl pyrophosphate and catalyzed the direct oxidation of 1-butanol into maleic anhydride, but with 35% selectivit
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