6,726 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
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
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
Refractive index of a transparent liquid measured with a concave mirror
This paper describes the spherical concave mirror method for measuring the
index of refraction of transparent liquids. We derived the refractive index
equation using Snell's law and the small-angle approximation. We also verified
the validity of this method using the traditional spherical mirror and
thin-lens Gaussian equations.Comment: IOPart, 8 pages, 4 figure
Coherent state triplets and their inner products
It is shown that if H is a Hilbert space for a representation of a group G,
then there are triplets of spaces F_H, H, F^H, in which F^H is a space of
coherent state or vector coherent state wave functions and F_H is its dual
relative to a conveniently defined measure. It is shown also that there is a
sequence of maps F_H -> H -> F^H which facilitates the construction of the
corresponding inner products. After completion if necessary, the F_H, H, and
F^H, become isomorphic Hilbert spaces. It is shown that the inner product for H
is often easier to evaluate in F_H than F^H. Thus, we obtain integral
expressions for the inner products of coherent state and vector coherent state
representations. These expressions are equivalent to the algebraic expressions
of K-matrix theory, but they are frequently more efficient to apply. The
construction is illustrated by many examples.Comment: 33 pages, RevTex (Latex2.09) This paper is withdrawn because it
contained errors that are being correcte
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Solid Freeform Fabrication of Functional Silicon Nitride Ceramics by Laminated Object Manufacturing 1
The processing of silicon nitride (Si3N4) structural ceramics by Laminated Object
Manufacturing (LOM) using ceramic tape preforms was investigated. The key processing stages
involved green shape formation (which used the LOM process), followed by the burnout of all
organics, and final densification by pressureless sintering. Two material systems were
considered. These were a) monolithic Si3N4 and b) a preceramic polymer infiltrated Si3N4. The
raw materials for the process were tape preforms of Si3N4, which were fabricated by standard
tape casting techniques.
Mechanical property data obtained for the LOM processed Si3N4 showed high strength and
fracture toughness values. The room temperature and high temperature (1260 o
C) flexural
strengths were in the range of 700-900 MPa and 360-400 MPa, respectively. The fracture
toughness averaged from 5.5-7.5 MPa.m1/2. These strength and fracture toughness values are
comparable to those reported for conventionally prepared Si3N4 ceramics. Thus, this research
demonstrated that the LOM technique is a viable method for preparing functional Si3N4 ceramics
with good physical and mechanical properties.Mechanical Engineerin
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