24,229 research outputs found
Finite element meshing of ANSYS (trademark) solid models
A large scale, general purpose finite element computer program, ANSYS, developed and marketed by Swanson Analysis Systems, Inc. is discussed. ANSYS was perhaps the first commercially available program to offer truly interactive finite element model generation. ANSYS's purpose is for solid modeling. This application is briefly discussed and illustrated
Research in orbit determination optimization for space trajectories
Research data covering orbit determination, optimization techniques, and trajectory design for manned space flights are summarized
The Composition of Dust in Jupiter-Family Comets as Inferred from Infrared Spectroscopy
We review the composition of Jupiter-family comet dust as inferred from
infrared spectroscopy. We find that Jupiter-family comets have 10 micron
silicate emission features with fluxes roughly 20-25% over the dust continuum
(emission strength 1.20-1.25), similar to the weakest silicate features in Oort
Cloud comets. We discuss the grain properties that change the silicate emission
feature strength (composition, size, and structure/shape), and emphasize that
thermal emission from the comet nucleus can have significant influence on the
derived silicate emission strength. Recent evidence suggests that porosity is
the dominant parameter, although more observations and models of silicates in
Jupiter-family comets are needed to determine if a consistent set of grain
parameters can explain their weak silicate emission features. Models of 8 m
telescope and Spitzer Space Telescope observations have shown that
Jupiter-family comets have crystalline silicates with abundances similar to or
less than those found in Oort Cloud comets, although the crystalline silicate
mineralogy of comets 9P/Tempel and C/1995 O1 (Hale-Bopp) differ from each other
in Mg and Fe content. The heterogeneity of comet nuclei can also be assessed
with mid-infrared spectroscopy, and we review the evidence for heterogeneous
dust properties in the nucleus of comet 9P/Tempel. Models of dust formation,
mixing in the solar nebula, and comet formation must be able to explain the
observed range of Mg and Fe content and the heterogeneity of comet 9P/Tempel,
although more work is needed in order to understand to what extent do comets
9P/Tempel and Hale-Bopp represent comets as a whole.Comment: 21 pages, 4 figures, 2 tables. Accepted for publication in Planetary
and Space Scienc
Alkaline battery separator characterization studies Quarterly report, 28 Apr. - 28 Jul. 1969
Absorber evaluation of alkaline battery separator systems with electrolyte wetting and wicking measuremen
Survey of cometary CO2, CO, and particulate emissions using the Spitzer Space Telescope: Smog check for comets
We surveyed 23 comets using the Infrared Array Camera on the Spitzer Space
Telescope in wide filters centered at 3.6 and 4.5 microns. Emission in the 3.6
micron filter arises from sunlight scattered by dust grains; these images
generally have a coma near the nucleus and a tail in the antisolar direction
due to dust grains swept back by solar radiation pressure. The 4.5 micron
filter contains the same dust grains, as well as strong emission lines from CO2
and CO gas; these show distinct morphologies, in which cases we infer they are
dominated by gas. Based on the ratio of 4.5 to 3.6 micron brightness, we
classify the survey comets as CO2+CO "rich" and "poor." This classification is
correlated with previous classifications by A'Hearn based on carbon-chain
molecule abundance, in the sense that comets classified as "depleted" in
carbon-chain molecules are also "poor" in CO2+CO. The gas emission in the IRAC
4.5 micron images is characterized by a smooth morphology, typically a fan in
the sunward hemisphere with a radial profile that varies approximately as the
inverse of projected distance from the nucleus, as would apply for constant
production and free expansion. There are very significant radial and azimuthal
enhancements in many of the comets, and these are often distinct between the
gas and dust, indicating that ejection of solid material may be driven either
by H2O or CO2. Notable features in the images include the following. There is a
prominent loop of gas emission from 103P/Hartley 2, possible due to an outburst
of CO2 before the Spitzer image. Prominent, double jets are present in the
image of 88P/Howell. A prominent single jet is evident for 3 comets. Spirals
are apparent in 29P and C/2006 W3; we measure a rotation rate of 21 hr for the
latter comet. Arcs (possibly parts of a spiral) are apparent in the images of
10P/Tempel 2, and 2P/Encke.Comment: accepted for publication in Icaru
New phenomena in the standard no-scale supergravity model
We revisit the no-scale mechanism in the context of the simplest no-scale
supergravity extension of the Standard Model. This model has the usual
five-dimensional parameter space plus an additional parameter . We show how predictions of the model may be extracted over
the whole parameter space. A necessary condition for the potential to be stable
is , which is satisfied if \bf m_{3/2}\lsim2 m_{\tilde
q}. Order of magnitude calculations reveal a no-lose theorem guaranteeing
interesting and potentially observable new phenomena in the neutral scalar
sector of the theory which would constitute a ``smoking gun'' of the no-scale
mechanism. This new phenomenology is model-independent and divides into three
scenarios, depending on the ratio of the weak scale to the vev at the minimum
of the no-scale direction. We also calculate the residual vacuum energy at the
unification scale (), and find that in typical models one must
require . Such constraints should be important in the search for the
correct string no-scale supergravity model. We also show how specific classes
of string models fit within this framework.Comment: 11pages, LaTeX, 1 figure (included), CERN-TH.7433/9
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