53,870 research outputs found
Radar spectral measurements of vegetation
Spectral data of 4-8 GHz radar backscatter were gathered during the 1972 growing season at look angles between 0 and 70 deg and for all four possible polarization linear combinations. The data covers four crop types (corn, milo, alfalfa, and soybeans) and a wide range of soil moisture content. To insure statistical representation of the results, measurements were conducted over 128 fields corresponding to a total of about 40,000 data points. The use of spectral response signatures to separate different crop types and to separate healthy corn from blighted corn was investigated
Evaluation criteria for commercially oriented materials processing in space proposals
An approach and criteria for evaluating NASA funded experiments and demonstrations which have commercial potential were developed. Methods for insuring quick initial screening of commercial proposals are presented. Recommendations are given for modifying the current evaluation approach. New criteria for evaluating commercially orientated materials processing in space (MPS) proposals are introduced. The process for selection of qualified individuals to evaluate the phases of this approach and criteria is considered and guidelines are set for its implementation
Space shuttle: Supersonic aerodynamic characteristics of the MSC 040A orbiter (M equals 2.0 to 4.0)
A wind tunnel test of the space shuttle orbiter configuration 040A was run in a 20 in. supersonic wind tunnel. Basic aerodynamic data for this vehicle were determined at Mach 2.0, 2.4, 3.0 and 4.0
Small quantity production of complex chromium alloy sheet /Cr-7Mo-2Ta-0.09C-0.1Y/ Final report
Fabrication of Cr-Mo-Ta-C-Y alloy shee
Continuous-wave Cascaded-Harmonic Generation and Multi-Photon Raman Lasing in Lithium Niobate Whispering-Gallery Resonators
We report experimental demonstration of continuous-wave cascaded-harmonic
generation and Raman lasing in a millimeter-scale lithium niobate
whispering-gallery resonator pumped at a telecommunication-compatible infrared
wavelength. Intensity enhancement through multiple recirculations in the
whispering-gallery resonator and quasi phase-matching through a nonuniform
crystal poling enable simultaneous cascaded-harmonic generation up to the
fourth-harmonic accompanied by stimulated Raman, two-photon, three-photon, and
four-photon Raman scattering corresponding the molecular vibrational
wavenumbers 632 cm-1 and 255 cm-1 in z-cut lithium niobate at pump power levels
as low as 200mW. We demonstrate simultaneous cascaded-harmonic generation and
Raman lasing by observing the spectrum of the scattered light from the
resonator and by capturing the image of the decoupled light from the resonator
on a color CCD camera
5D Black Rings and 4D Black Holes
It has recently been shown that the M theory lift of a IIA 4D BPS Calabi-Yau
black hole is a 5D BPS black hole spinning at the center of a Taub-NUT-flux
geometries, and a certain linear relation between 4D and 5D BPS partition
functions was accordingly proposed. In the present work we fortify and enrich
this proposal by showing that the M-theory lift of the general 4D multi-black
hole geometry are 5D black rings in a Taub-NUT-flux geometry.Comment: 8 pages; version 2, with additional references and explanation
Mechanism for the failure of the Edwards hypothesis in the SK spin glass
The dynamics of the SK model at T=0 starting from random spin configurations
is considered. The metastable states reached by such dynamics are atypical of
such states as a whole, in that the probability density of site energies,
, is small at . Since virtually all metastable states
have a much larger , this behavior demonstrates a qualitative failure of
the Edwards hypothesis. We look for its origins by modelling the changes in the
site energies during the dynamics as a Markov process. We show how the small
arises from features of the Markov process that have a clear physical
basis in the spin-glass, and hence explain the failure of the Edwards
hypothesis.Comment: 5 pages, new title, modified text, additional reference
Resolving the Structure of Cold Dark Matter Halos
We examine the effects of mass resolution and force softening on the density
profiles of cold dark matter halos that form within cosmological N-body
simulations. As we increase the mass and force resolution, we resolve
progenitor halos that collapse at higher redshifts and have very high
densities. At our highest resolution we have nearly 3 million particles within
the virial radius, several orders of magnitude more than previously used and we
can resolve more than one thousand surviving dark matter halos within this
single virialised system. The halo profiles become steeper in the central
regions and we may not have achieved convergence to a unique slope within the
inner 10% of the virialised region. Results from two very high resolution halo
simulations yield steep inner density profiles, . The
abundance and properties of arcs formed within this potential will be different
from calculations based on lower resolution simulations. The kinematics of
disks within such a steep potential may prove problematic for the CDM model
when compared with the observed properties of halos on galactic scales.Comment: Final version, to be published in the ApJLetter
Fatigue testing a plurality of test specimens and method
Described is a fatigue testing apparatus for simultaneously subjecting a plurality of material test specimens to cyclical tension loading to determine the fatigue strength of the material. The fatigue testing apparatus includes a pulling head having cylinders defined therein which carry reciprocating pistons. The reciprocation of the pistons is determined by cyclical supplies of pressurized fluid to the cylinders. Piston rods extend from the pistons through the pulling head and are attachable to one end of the test specimens, the other end of the test specimens being attachable to a fixed base, causing test specimens attached between the piston rods and the base to be subjected to cyclical tension loading. Because all the cylinders share a common pressurized fluid supply, the breaking of a test specimen does not substantially affect the pressure of the fluid supplied to the other cylinders nor the tension applied to the other test specimens
Wind tunnel turning vanes of modern design
Rehabilitation of the Altitude Wind Tunnel includes the need for new corner turning vanes to match its upgraded performance. The design and experimental performance results from a 0.1-full scale model of the highest speed corner (M = 0.35) are presented and discussed along with some two dimensional inviscid analyses of two vaned corners. With a vane designed by an inverse two dimensional technique, the overall corner loss was about 12% of the inlet dynamic pressure of which about 4% was caused by vane skin friction. Comparable values with a conventionally designed circular arc vane were about 14% overall with about 7% due to skin friction
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