28,582 research outputs found
Six-man, self-contained carbon dioxide concentrator subsystem for Space Station Prototype (SSP) application
A six man, self contained, electrochemical carbon dioxide concentrating subsystem for space station prototype use was successfully designed, fabricated, and tested. A test program was successfully completed which covered shakedown testing, design verification testing, and acceptance testing
Scattering into Cones and Flux across Surfaces in Quantum Mechanics: a Pathwise Probabilistic Approach
We show how the scattering-into-cones and flux-across-surfaces theorems in
Quantum Mechanics have very intuitive pathwise probabilistic versions based on
some results by Carlen about large time behaviour of paths of Nelson
diffusions. The quantum mechanical results can be then recovered by taking
expectations in our pathwise statements.Comment: To appear in Journal of Mathematical Physic
Numerical Study of a Field Theory for Directed Percolation
A numerical method is devised for study of stochastic partial differential
equations describing directed percolation, the contact process, and other
models with a continuous transition to an absorbing state. Owing to the
heightened sensitivity to fluctuationsattending multiplicative noise in the
vicinity of an absorbing state, a useful method requires discretization of the
field variable as well as of space and time. When applied to the field theory
for directed percolation in 1+1 dimensions, the method yields critical
exponents which compare well against accepted values.Comment: 18 pages, LaTeX, 6 figures available upon request LC-CM-94-00
The Crystal and Molecular Structure and Absolute Configuration of (—)-(\u3ci\u3eS\u3c/i\u3e)-Warfarin
The crystal and molecular structure and the absolute configuration of (—)-(S)-warfarin, C19H1604, have been determined by X-ray crystallographic techniques. Crystals of (—)-(S)-warfarin are orthorhombic, space group P212121, with a=10·883 (3), b=9·562 (3), and c=14·902 (5) Å. Solution of the structure was by direct methods, and refinement by least-squares calculations led to a conventional R of 0·053 (Mo Kα data). The molecule crystallizes as the intramolecular hemiketal and thus may be described as (2S,4S)-2,3H-2-methyl-4-phenyl-5-oxobenzopyrano[3,4-e]dihydropyran-2-ol. The absolute configuration was confirmed by recollecting with Cu Kα radiation a group of reflect ions predicted to have the greatest observable Bijvoet differences based on the anomalous scattering of oxygen and the parameters from the refinement with Mo Kα data. A group of 51 Friedel pairs, 86% of which indicate the S enantiomer, gave a 17% decrease in the residual over the R enantiomer. Refinement of the imaginary part of the anomalous dispersion of oxygen gave a value of 0·037 for Δf
Investigation of external refrigeration systems for long term cryogenic storage Final report
Data on external refrigeration systems for space storage of cryogens for long period
Investigation of external refrigeration systems for long-term cryogenic storage
Evaluation of cryogenic refrigeration systems for space application
Changing shapes in the nanoworld
What are the mechanisms leading to the shape relaxation of three dimensional
crystallites ? Kinetic Monte Carlo simulations of fcc clusters show that the
usual theories of equilibration, via atomic surface diffusion driven by
curvature, are verified only at high temperatures. Below the roughening
temperature, the relaxation is much slower, kinetics being governed by the
nucleation of a critical germ on a facet. We show that the energy barrier for
this step linearly increases with the size of the crystallite, leading to an
exponential dependence of the relaxation time.Comment: 4 pages, 5 figures. Accepted by Phys Rev Let
Low-density series expansions for directed percolation IV. Temporal disorder
We introduce a model for temporally disordered directed percolation in which
the probability of spreading from a vertex , where is the time and
is the spatial coordinate, is independent of but depends on . Using
a very efficient algorithm we calculate low-density series for bond percolation
on the directed square lattice. Analysis of the series yields estimates for the
critical point and various critical exponents which are consistent with a
continuous change of the critical parameters as the strength of the disorder is
increased.Comment: 11 pages, 3 figure
Directed Percolation with a Wall or Edge
We examine the effects of introducing a wall or edge into a directed
percolation process. Scaling ansatzes are presented for the density and
survival probability of a cluster in these geometries, and we make the
connection to surface critical phenomena and field theory. The results of
previous numerical work for a wall can thus be interpreted in terms of surface
exponents satisfying scaling relations generalising those for ordinary directed
percolation. New exponents for edge directed percolation are also introduced.
They are calculated in mean-field theory and measured numerically in 2+1
dimensions.Comment: 14 pages, submitted to J. Phys.
Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4
We study dynamical properties of the anisotropic triangular quantum
antiferromagnet Cs_2CuCl_4. Inelastic neutron scattering measurements have
established that the dynamical spin correlations cannot be understood within a
linear spin wave analysis. We go beyond linear spin wave theory by taking
interactions between magnons into account in a 1/S expansion. We determine the
dynamical structure factor and carry out extensive comparisons with
experimental data. We find that compared to linear spin wave theory a
significant fraction of the scattering intensity is shifted to higher energies
and strong scattering continua are present. However, the 1/S expansion fails to
account for the experimentally observed large quantum renormalization of the
exchange energies.Comment: 13 pages, 11 figures, higher quality figures can be obtained from the
author
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