957 research outputs found
Paper Session I-A - A Strategy for Implementation of Integrated Vehicle Health Management into the Space Shuttle Program
A Strategy for Implementation of Integrated Vehicle Health Management (IVHM) into the Space Shuttle Program
Microwave Temperature Profiler Mounted in a Standard Airborne Research Canister
Many atmospheric research aircraft use a standard canister design to mount instruments, as this significantly facilitates their electrical and mechanical integration and thereby reduces cost. Based on more than 30 years of airborne science experience with the Microwave Temperature Profiler (MTP), the MTP has been repackaged with state-of-the-art electronics and other design improvements to fly in one of these standard canisters. All of the controlling electronics are integrated on a single 4 ~5-in. (.10 ~13- cm) multi-layer PCB (printed circuit board) with surface-mount hardware. Improved circuit design, including a self-calibrating RTD (resistive temperature detector) multiplexer, was implemented in order to reduce the size and mass of the electronics while providing increased capability. A new microcontroller-based temperature controller board was designed, providing better control with fewer components. Five such boards are used to provide local control of the temperature in various areas of the instrument, improving radiometric performance. The new stepper motor has an embedded controller eliminating the need for a separate controller board. The reference target is heated to avoid possible emissivity (and hence calibration) changes due to moisture contamination in humid environments, as well as avoiding issues with ambient targets during ascent and descent. The radiometer is a double-sideband heterodyne receiver tuned sequentially to individual oxygen emission lines near 60 GHz, with the line selection and intermediate frequency bandwidths chosen to accommodate the altitude range of the aircraft and mission
TA-13: Ground and Launch Systems, 2015 NASA Technology Roadmaps
This presentation is a summary of new content contained in the 2015 update of Technology Area-13, Ground and Launch Systems technology roadmap beyond the content contained in the 2010 version. Also included are brief assessments of benefits, alignments, challenges, technical risk and reasonableness, sequencing and timing, and time and effort to achieve goals. This presentation is part of overall presentations of new content only for the 2015 update of the 15 NASA Technology Roadmaps that will be conducted in a public forum managed by the National Research Council on September 28-29, 2015. The 15 roadmaps have already been publically released via the STI process
A Better Definition of the Kilogram
This article reviews several recent proposed redefinitions of the kilogram,
and compares them with respect to practical realizations, uncertainties
(estimated standard deviations), and educational aspects.Comment: 10 pages, no figure
Plasticization and antiplasticization of polymer melts diluted by low molar mass species
An analysis of glass formation for polymer melts that are diluted by
structured molecular additives is derived by using the generalized entropy
theory, which involves a combination of the Adam-Gibbs model and the direct
computation of the configurational entropy based on a lattice model of polymer
melts that includes monomer structural effects. Antiplasticization is
accompanied by a "toughening" of the glass mixture relative to the pure
polymer, and this effect is found to occur when the diluents are small species
with strongly attractive interactions with the polymer matrix. Plasticization
leads to a decreased glass transition temperature T_g and a "softening" of the
fragile host polymer in the glass state. Plasticization is prompted by small
additives with weakly attractive interactions with the polymer matrix. The
shifts in T_g of polystyrene diluted by fully flexible short oligomers are
evaluated from the computations, along with the relative changes in the
isothermal compressibility at T_g to characterize the extent to which the
additives act as antiplasticizers or plasticizers. The theory predicts that a
decreased fragility can accompany both antiplasticization and plasticization of
the glass by molecular additives. The general reduction in the T_g and
fragility of polymers by these molecular additives is rationalized by analyzing
the influence of the diluent's properties (cohesive energy, chain length, and
stiffness) on glass formation in diluted polymer melts. The description of
glass formation at fixed temperature that is induced upon change the fluid
composition directly implies the Angell equation for the structural relaxation
time as function of the polymer concentration, and the computed "zero mobility
concentration" scales linearly with the inverse polymerization index N.Comment: 12 pages, 15 figure
Localized Supersoft Supersymmetry Breaking
We consider supersymmetry breaking models in which the MSSM is extended to
include an additional chiral adjoint field for each gauge group with which the
the MSSM gauginos acquire Dirac masses. We investigate a framework in which the
Standard Model gauge fields propagate in the bulk of a warped extra dimension
while quarks and leptons are localized on the ultraviolet brane. The adjoint
fields are localized on the infrared brane, where supersymmetry is broken in a
hidden sector. This setup naturally suppresses potentially large flavor
violating effects, while allowing perturbative gauge coupling unification under
SU(5) to be realized. The Standard Model superpartner masses exhibit a
supersoft spectrum. Since the soft scalar masses are generated at very low
scales of order the gaugino masses these models are significantly less
fine-tuned than other supersymmetric models. The LSP in this class of models is
the gravitino, while the NLSP is the stau. We show that this theory has an
approximate R symmetry under which the gauginos are charged. This symmetry
allows several possibilities for experimentally distinguishing the Dirac nature
of the gauginos.Comment: 23 pages, 2 figure
Two-loop RGEs with Dirac gaugino masses
The set of renormalisation group equations to two loop order for general
supersymmetric theories broken by soft and supersoft operators is completed. As
an example, the explicit expressions for the RGEs in a Dirac gaugino extension
of the (N)MSSM are presented.Comment: 10 pages + 24 pages of RGEs in appendix; no figure
The Santa Fe Light Cone Simulation Project: II. The Prospects for Direct Detection of the WHIM with SZE Surveys
Detection of the Warm-Hot Intergalactic Medium (WHIM) using Sunyaev-Zeldovich
effect (SZE) surveys is an intriguing possibility, and one that may allow
observers to quantify the amount of "missing baryons" in the WHIM phase. We
estimate the necessary sensitivity for detecting low density WHIM gas with the
South Pole Telescope (SPT) and Planck Surveyor for a synthetic 100 square
degree sky survey. This survey is generated from a very large, high dynamic
range adaptive mesh refinement cosmological simulation performed with the Enzo
code. We find that for a modest increase in the SPT survey sensitivity (a
factor of 2-4), the WHIM gas makes a detectable contribution to the integrated
sky signal. For a Planck-like satellite, similar detections are possible with a
more significant increase in sensitivity (a factor of 8-10). We point out that
for the WHIM gas, the kinematic SZE signal can sometimes dominate the thermal
SZE where the thermal SZE decrement is maximal (150 GHz), and that using the
combination of the two increases the chance of WHIM detection using SZE
surveys. However, we find no evidence of unique features in the thermal SZE
angular power spectrum that may aid in its detection. Interestingly, there are
differences in the power spectrum of the kinematic SZE, which may not allow us
to detect the WHIM directly, but could be an important contaminant in
cosmological analyses of the kSZE-derived velocity field. Corrections derived
from numerical simulations may be necessary to account for this contamination.Comment: 9 pages, submitted to Astrophysical Journa
Microplastic distribution and characteristics across a large river basin:Insights from the Neuse River in North Carolina, USA
Elevated CO\u3csub\u3e2\u3c/sub\u3e further lengthens growing season under warming conditions
Observations of a longer growing season through earlier plant growth in temperate to polar regions have been thought to be a response to climate warming. However, data from experimental warming studies indicate that many species that initiate leaf growth and flowering earlier also reach seed maturation and senesce earlier, shortening their active and reproductive periods. A conceptual model to explain this apparent contradiction, and an analysis of the effect of elevated CO2—which can delay annual life cycle events—on changing season length, have not been tested. Here we show that experimental warming in a temperate grassland led to a longer growing season through earlier leaf emergence by the first species to leaf, often a grass, and constant or delayed senescence by other species that were the last to senesce, supporting the conceptual model. Elevated CO2 further extended growing, but not reproductive, season length in the warmed grassland by conserving water, which enabled most species to remain active longer. Our results suggest that a longer growing season, especially in years or biomes where water is a limiting factor, is not due to warming alone, but also to higher atmospheric CO2 concentrations that extend the active period of plant annual life cycles
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