3,239 research outputs found
A Flexible Evolvable Architecture for Constellation Mission Systems User Applications
While simulating a complex set of repair tasks to be performed by EVA crewmembers on an upcoming mission, flight controllers and astronauts determine that the repair will take much longer than originally anticipated. All equipment in the vicinity of the worksite must be powered off to maintain a safe environment for the astronauts. Because heater power will be unavailable, several critical components will now be at risk of freezing and permanent damage. If an impending thermal violation is detected, Mission Control will have very limited time to react. Therefore, flight controllers must not only modify their procedures to account for these risks, they must also incorporate into their displays outputs from thermal models, alternate temperature measurements, new alarm limits, and emergency power-on commands to enable the detection and response to freezing conditions. Current software for mission control systems makes scenarios like this difficult to address. Given the time frame for modifying software, operations teams are left with labor-intensive operational workarounds as their only options. NASA Ames Research Center (ARC) and NASA Johnson Space Center (JSC) are collaborating on the development of a flexible software system for mission operations that will enable greater user flexibility than has been available to date. Using composable software, end users in the scenario described above could recompose procedures and command and control displays to allow flight controllers to monitor temperature measurements, identify time-critical conditions, and execute the procedures required to respond to these conditions before flight hardware is permanently damaged
The symbiotic star CH Cygni. III. A precessing radio jet
VLA, MERLIN and Hubble Space Telescope imaging observations of the extended
regions of the symbiotic system CH Cygni are analysed. These extensions are
evidence of a strong collimation mechanism, probably an accretion disk
surrounding the hot component of the system. Over 16 years (between 1985 and
2001) the general trend is that these jets are seen to precess. Fitting a
simple ballistic model of matter ejection to the geometry of the extended
regions suggests a period of 6520 +/- 150 days, with a precession cone opening
angle of 35 +/- 1 degrees. This period is of the same order as that proposed
for the orbital period of the outer giant in the system, suggesting a possible
link between the two. Anomalous knots in the emission, not explained by the
simple model, are believed to be the result of older, slower moving ejecta, or
possibly jet material that has become disrupted through sideways interaction
with the surrounding medium.Comment: 9 pages, 4 figure
Oscillating Neutrinos from the Galactic Center
It has recently been demonstrated that the -ray emission spectrum of
the EGRET-identified, central Galactic source 2EG J1746-2852 can be well fitted
by positing that these photons are generated by the decay of 's produced
in p-p scattering at or near an energizing shock. Such scattering also produces
charged pions which decay leptonically.The ratio of -rays to neutrinos
generated by the central Galactic source may be accurately determined and a
well-defined and potentially-measurable high energy neutrino flux at Earth is
unavoidable. An opportunity, therefore, to detect neutrino oscillations over an
unprecedented scale is offered by this source. In this paper we assess the
prospects for such an observation with the generation of neutrino \v{C}erenkov
telescopes now in the planning stage. We determine that the next generation of
detectors may find an oscillation signature in the Galactic Center (GC) signal.Comment: 45 pages, LaTeX, uses ApJ style, some minor revisions, this final
version to be published in ApJ
New Pseudo-Phase Structure for -Pu
In this paper we propose a new pseudo-phase crystal structure, based on an
orthorhombic distortion of the diamond structure, for the ground-state
-phase of plutonium. Electronic-structure calculations in the
generalized-gradient approximation give approximately the same total energy for
the two structures. Interestingly, our new pseudo-phase structure is the same
as the Pu -phase structure except with very different b/a and c/a
ratios. We show how the contraction relative to the phase, principally
in the direction, leads to an -like structure in the [0,1,1] plane.
This is an important link between two complex structures of plutonium and opens
new possibilities for exploring the very rich phase diagram of Pu through
theoretical calculations
Hydrodynamic Coupling of Two Brownian Spheres to a Planar Surface
We describe direct imaging measurements of the collective and relative
diffusion of two colloidal spheres near a flat plate. The bounding surface
modifies the spheres' dynamics, even at separations of tens of radii. This
behavior is captured by a stokeslet analysis of fluid flow driven by the
spheres' and wall's no-slip boundary conditions. In particular, this analysis
reveals surprising asymmetry in the normal modes for pair diffusion near a flat
surface.Comment: 4 pages, 4 figure
Methyl 2-(methylthio)benzoate: the unique sulfur-containing sex pheromone of Phyllophaga crinita
The female-produced sex pheromone of Phyllophaga crinita (Burmeister) (Coleoptera: Scarabaeidae: Melolonthinae; the adult has no common name) is identified as methyl 2-(methylthio)benzoate. This is the first identification of a sulfur-containing, long-distance, female-produced sex attractant from any insect taxa. The root-feeding larvae of this species are serious pests in many crops in Texas and Mexico. In field tests, many P. crinita males were captured in traps baited with the authentic compound. Interestingly, a heteroatom analog, methyl 2-methoxybenzoate, also captured P. crinita males, but only at a dose 10,000 times higher than the lowest tested dose of the authentic pheromon
Phase behaviour of a model of colloidal particles with a fluctuating internal state
Colloidal particles are not simple rigid particles, in general an isolated
particle is a system with many degrees of freedom in its own right, e.g., the
counterions around a charged colloidal particle.The behaviour of model
colloidal particles, with a simple phenomenological model to account for these
degrees of freedom, is studied. It is found that the interaction between the
particles is not pairwise additive. It is even possible that the interaction
between a triplet of particles is attractive while the pair interaction is
repulsive. When this is so the liquid phase is either stable only in a small
region of the phase diagram or absent altogether.Comment: 12 pages including 4 figure
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