10,739 research outputs found
Analysis of DSN software anomalies
A categorized data base of software errors which were discovered during the various stages of development and operational use of the Deep Space Network DSN/Mark 3 System was developed. A study team identified several existing error classification schemes (taxonomies), prepared a detailed annotated bibliography of the error taxonomy literature, and produced a new classification scheme which was tuned to the DSN anomaly reporting system and encapsulated the work of others. Based upon the DSN/RCI error taxonomy, error data on approximately 1000 reported DSN/Mark 3 anomalies were analyzed, interpreted and classified. Next, error data are summarized and histograms were produced highlighting key tendencies
Crowded-Field Astrometry with the Space Interferometry Mission - I. Estimating the Single-Measurement Astrometric Bias Arising from Confusion
The accuracy of position measurements on stellar targets with the future
Space Interferometry Mission (SIM) will be limited not only by photon noise and
by the properties of the instrument (design, stability, etc.) and the overall
measurement program (observing strategy, reduction methods, etc.), but also by
the presence of other "confusing" stars in the field of view (FOV). We use a
simple "phasor" model as an aid to understanding the main effects of this
"confusion bias" in single observations with SIM. This analytic model has been
implemented numerically in a computer code and applied to a selection of
typical SIM target fields drawn from some of the Key Projects already accepted
for the Mission. We expect that less than 1% of all SIM targets will be
vulnerable to confusion bias; we show that for the present SIM design,
confusion may be a concern if the surface density of field stars exceeds 0.4
star/arcsec^2. We have developed a software tool as an aid to ascertaining the
possible presence of confusion bias in single observations of any arbitrary
field. Some a priori knowledge of the locations and spectral energy
distributions of the few brightest stars in the FOV is helpful in establishing
the possible presence of confusion bias, but the information is in general not
likely to be available with sufficient accuracy to permit its removal. We
discuss several ways of reducing the likelihood of confusion bias in crowded
fields. Finally, several limitations of the present semi-analytic approach are
reviewed, and their effects on the present results are estimated. The simple
model presented here provides a good physical understanding of how confusion
arises in a single SIM observation, and has sufficient precision to establish
the likelihood of a bias in most cases.Comment: 28 pages, 20 figures, 1 table; to appear in December 2007 issue of
PAS
Computer Simulation of Particle Suspensions
Particle suspensions are ubiquitous in our daily life, but are not well
understood due to their complexity. During the last twenty years, various
simulation methods have been developed in order to model these systems. Due to
varying properties of the solved particles and the solvents, one has to choose
the simulation method properly in order to use the available compute resources
most effectively with resolving the system as well as needed. Various
techniques for the simulation of particle suspensions have been implemented at
the Institute for Computational Physics allowing us to study the properties of
clay-like systems, where Brownian motion is important, more macroscopic
particles like glass spheres or fibers solved in liquids, or even the pneumatic
transport of powders in pipes. In this paper we will present the various
methods we applied and developed and discuss their individual advantages.Comment: 31 pages, 11 figures, to appear in Lecture Notes in Applied and
Computational Mechanics, Springer (2006
Development of sputtered techniques for thrust chambers, task 1
Filler materials proposed for use in the sputter fabrication regeneratively cooled thrust chambers were evaluated. Low melting castable alloys, CERROBEND. CERROCAST, and CERROTRU, slurry applied SERMETEL 481 and flame-sprayed aluminum were investigated as filler materials. Sputter deposition from a cylindrical cathode inverted magnestron was used to apply an OFHC copper closeout layer to filled OFHC copper ribbed-wall cylindrical substrates. The sputtered closeout layer structure was evaluated with respect to filler material contamination, predeposition machining and finishing operations, and deposition parameters. The application of aluminum by flame-spraying resulted in excessiver filler porosity. Though the outgassing from this porosity was found to be detrimental to the closeout layer structure, bond strengths in excess of 10,500 psi were achieved. Removal of the aluminum from the grooves was readily accomplished by leaching in a 7.0 molar solution of sodium hydroxide at 353 K. Of the other filler materials evaluated, CERROTRU was found to be the most suitable material with respect to completely filling the ribbed-wall cylinders and vacuum system compatibility. However, bond contamination resulted in low closeout layer bond strength with the CERROTRU filler. CERROBEND, CERROCAST, and SERMETEL 481 were found to be unacceptable as filler materials
Pairing and Isospin Symmetry in Proton-Rich Nuclei
Unlike their lighter counterparts, most odd-odd N=Z nuclei with mass A > 40
40 have ground states with isospin T=1, suggesting an increased role for the
isovector pairing interaction. A simple SO(5) seniority-like model of this
interaction reveals a striking and heretofore unnoticed interplay between
like-particle and neutron-proton isovector pairing near N=Z that is reflected
in the number of each kind of pair as a function of A and T. Large scale
shell-model calculations exhibit the same trends, despite the simultaneous
presence of isoscalar pairs, deformation, and other correlations.Comment: 8 pages + 2 postscript figures, in RevTeX. Discussion of isospin
projection in HFB added. This version to appear in Phys. Lett.
Amplitude control of quantum interference
Usually, the oscillations of interference effects are controlled by relative
phases. We show that varying the amplitudes of quantum waves, for instance by
changing the reflectivity of beam splitters, can also lead to quantum
oscillations and even to Bell violations of local realism. We first study
theoretically a generalization of the Hong-Ou-Mandel experiment to arbitrary
source numbers and beam splitter transmittivity. We then consider a Bell type
experiment with two independent sources, and find strong violations of local
realism for arbitrarily large source number ; for small , one operator
measures essentially the relative phase of the sources and the other their
intensities. Since, experimentally, one can measure the parity of the number of
atoms in an optical lattice more easily than the number itself, we assume that
the detectors measure parity.Comment: 4 pages; 4 figure
Development of sputtered techniques for thrust chambers
Procedures for closing out coolant passages in regeneratively cooled thrust chambers by triode sputtering, using post and hollow Cu-0.15 percent Zr cathodes are described. The effects of aluminum composite filler materials, substrate preparation, sputter cleaning, substrate bias current density and system geometry on closeout layer bond strength and structure are evaluated. High strength closeout layers were sputtered over aluminum fillers. The tensile strength and microstructure of continuously sputtered Cu-0.15 percent Zr deposits were determined. These continuous sputtered deposits were as thick as 0.75 cm. Tensile strengths were consistently twice as great as the strength of the material in wrought form
Construction of SU(3) irreps in canonical SO(3)-coupled bases
Alternative canonical methods for defining canonical SO(3)-coupled bases for
SU(3) irreps are considered and compared. It is shown that a basis that
diagonalizes a particular linear combination of SO(3) invariants in the SU(3)
universal enveloping algebra gives basis states that have good quantum
numbers in the asymptotic rotor-model limit.Comment: no figure
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