100,609 research outputs found
Development of non-linear finite element computer code
Recent work has shown that the use of separable symmetric functions of the principal stretches can adequately describe the response of certain propellant materials and, further, that a data reduction scheme gives a convenient way of obtaining the values of the functions from experimental data. Based on representation of the energy, a computational scheme was developed that allows finite element analysis of boundary value problems of arbitrary shape and loading. The computational procedure was implemental in a three-dimensional finite element code, TEXLESP-S, which is documented herein
An analysis of bi-directional use of frequencies for satellite communications
The bi-directional use of frequencies allocated for space communications has the potential to double the orbit/spectrum capacity available. The technical feasibility of reverse band use (RBU) at C-band (4 GHz uplinks and 6 GHz downlinks) is studied. The analysis identifies the constraints under which both forward and reverse band use satellite systems can share the same frequencies with terrestrial, line of sight transmission systems. The results of the analysis show that RBU satellite systems can be similarly sized to forward band use (FBU) satellite systems. In addition, the orbital separation requirements between RBU and FBU satellite systems are examined. The analysis shows that a carrier to interference ratio of 45 dB can be maintianed between RBU and FBU satellites separated by less than 0.5 deg., and that a carrier to interference ratio of 42 dB can be maintained in the antipodal case. Rain scatter propagation analysis shows that RBU and FBU Earth stations require separation distances fo less than 10 km at a rain rate of 13.5 mm/hr escalating to less than 100 km at a rain rate of 178 mm/hr for Earth station antennas in the 3 to 10 m range
On the problems of measuring transient temperature in cryogenic fluids
Cryogenic sensor errors in measuring transient temperature in cryogenic fluid
Impulse approximation in the n p --> d pi^0 reaction reexamined
The impulse approximation (one-body operator) in the n p --> d pi^0 reaction
is reexamined with emphasis on the issues of reducibility and recoil
corrections. An inconsistency when one pion exchange is included in the
production operator is demonstrated and then resolved via the introduction of
"wave function corrections" which nearly vanish for static nucleon propagators.
Inclusion of the recoil corrections to the nucleon propagators is found to
change the magnitude and sign of the impulse production amplitude, worsening
agreement with the experimental cross section by approximately 30%. A cutoff is
used to account for the phenomenological nature of the external wave functions,
and is found to have a significant impact up to approximately 2.5 GeV.Comment: Published versio
Image data processing system requirements study. Volume 2: Appendixes
Supporting information for the ERS loading study contains computer simulation loading output including printout description, and similar output representing data that include night station contacts
Excitation of the auroral green line by dissociative recombination of O plus over 2 - Analysis of two rocket experiments
Excitation of auroral green line by dissociative recombination of oxygen ion
Image data processing system requirements study. Volume 1: Analysis
Digital image processing, image recorders, high-density digital data recorders, and data system element processing for use in an Earth Resources Survey image data processing system are studied. Loading to various ERS systems is also estimated by simulation
Solvent coarse-graining and the string method applied to the hydrophobic collapse of a hydrated chain
Using computer simulations of over 100,000 atoms, the mechanism for the
hydrophobic collapse of an idealized hydrated chain is obtained. This is done
by coarse-graining the atomistic water molecule positions over 129,000
collective variables that represent the water density field and then using the
string method in these variables to compute the minimum free energy pathway
(MFEP) for the collapsing chain. The dynamical relevance of the MFEP (i.e. its
coincidence with the mechanism of collapse) is validated a posteriori using
conventional molecular dynamics trajectories. Analysis of the MFEP provides
atomistic confirmation for the mechanism of hydrophobic collapse proposed by
ten Wolde and Chandler. In particular, it is shown that lengthscale-dependent
hydrophobic dewetting is the rate-limiting step in the hydrophobic collapse of
the considered chain.Comment: 11 pages, 7 figures, including supporting informatio
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