2,527 research outputs found
Contamination assessment for OSSA space station IOC payloads
The results are presented from a study for the Space Station Planners Group of the Office of Space Sciences and Applications. The objectives of the study are: (1) the development of contamination protection requirements for protection of Space Station attached payloads, serviced payloads and platforms; and (2) the determination of unknowns or major impacts requiring further assessment. The nature, sources, and quantitative properties of the external contaminants to be encountered on the Station are summarized. The OSSA payload contamination protection requirements provided by the payload program managers are reviewed and the level of contamination awareness among them is discussed. Preparation of revisions to the contamination protection requirements are detailed. The comparative impact of flying the Station at constant atmospheric density rather than constant altitude is assessed. The impact of the transverse boom configuration of the Station on contamination is also assessed. The contamination protection guidelines which OSSA should enforce during their development of payloads are summarized
The Role of Final State Interactions in Quasielastic Fe Reactions at large
A relativistic finite nucleus calculation using a Dirac optical potential is
used to investigate the importance of final state interactions [FSI] at large
momentum transfers in inclusive quasielastic electronuclear reactions. The
optical potential is derived from first-order multiple scattering theory and
then is used to calculate the FSI in a nonspectral Green's function doorway
approach. At intermediate momentum transfers excellent predictions of the
quasielastic Fe experimental data for the longitudinal response
function are obtained. In comparisons with recent measurements at ~GeV/c the theoretical calculations of give good agreement for
the quasielastic peak shape and amplitude, but place the position of the peak
at an energy transfer of about ~MeV higher than the data.Comment: 13 pages typeset using revtex 3.0 with 6 postscript figures in
accompanying uuencoded file; submitted to Phys. Rev.
Total Cross Sections for Neutron Scattering
Measurements of neutron total cross-sections are both extensive and extremely
accurate. Although they place a strong constraint on theoretically constructed
models, there are relatively few comparisons of predictions with experiment.
The total cross-sections for neutron scattering from O and Ca are
calculated as a function of energy from ~MeV laboratory energy with a
microscopic first order optical potential derived within the framework of the
Watson expansion. Although these results are already in qualitative agreement
with the data, the inclusion of medium corrections to the propagator is
essential to correctly predict the energy dependence given by the experiment.Comment: 10 pages (Revtex 3.0), 6 fig
Relativistic Coulomb Sum Rules for
A Coulomb sum rule is derived for the response of nuclei to
scattering with large three-momentum transfers. Unlike the nonrelativistic
formulation, the relativistic Coulomb sum is restricted to spacelike
four-momenta for the most direct connection with experiments; an immediate
consequence is that excitations involving antinucleons, e.g., pair
production, are approximately eliminated from the sum rule. Relativistic recoil
and Fermi motion of target nucleons are correctly incorporated. The sum rule
decomposes into one- and two-body parts, with correlation information in the
second. The one-body part requires information on the nucleon momentum
distribution function, which is incorporated by a moment expansion method. The
sum rule given through the second moment (RCSR-II) is tested in the Fermi gas
model, and is shown to be sufficiently accurate for applications to data.Comment: 32 pages (LaTeX), 4 postscript figures available from the author
Full-Folding Optical Potentials for Elastic Nucleon-Nucleus Scattering based on Realistic Densities
Optical model potentials for elastic nucleon nucleus scattering are
calculated for a number of target nuclides from a full-folding integral of two
different realistic target density matrices together with full off-shell
nucleon-nucleon t-matrices derived from two different Bonn meson exchange
models. Elastic proton and neutron scattering observables calculated from these
full-folding optical potentials are compared to those obtained from `optimum
factorized' approximations in the energy regime between 65 and 400 MeV
projectile energy. The optimum factorized form is found to provide a good
approximation to elastic scattering observables obtained from the full-folding
optical potentials, although the potentials differ somewhat in the structure of
their nonlocality.Comment: 21 pages, LaTeX, 17 postscript figure
Energy Dependence of the NN t-matrix in the Optical Potential for Elastic Nucleon-Nucleus Scattering
The influence of the energy dependence of the free NN t-matrix on the optical
potential of nucleon-nucleus elastic scattering is investigated within the
context of a full-folding model based on the impulse approximation. The
treatment of the pole structure of the NN t-matrix, which has to be taken into
account when integrating to negative energies is described in detail. We
calculate proton-nucleus elastic scattering observables for O,
Ca, and Pb between 65 and 200 MeV laboratory energy and study
the effect of the energy dependence of the NN t-matrix. We compare this result
with experiment and with calculations where the center-of-mass energy of the NN
t-matrix is fixed at half the projectile energy. It is found that around 200
MeV the fixed energy approximation is a very good representation of the full
calculation, however deviations occur when going to lower energies (65 MeV).Comment: 11 pages (revtex), 6 postscript figure
A Temporal Expert System for Engineering Design Change Workflow
Workflow management, which is concerned with the coordination and control of business processes using information technology, has grown from its origins in document routing to include the automation of process logic in business process engineering. Workflow also has a strong temporal aspect. Activity sequencing, deadlines, routing conditions,and scheduling all involve the element of time. Temporal expert systems, which use knowledge-based constructs to represent and reason about time, can be used to enhance the capabilities of workflow software. This paper presents a temporal expert system workflow component for tracking engineering design changes. We use Allen\u27s theory of temporal intervals in our model to enhance the decision-making, timing, and routing activities in a workflow application. We test the model using information from a real-world engineering design situation and suggest further research opportunitie
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