98,404 research outputs found
Adaptation of a modern medium helicopter (Sikorsky S-76) to higher harmonic control
Sikorsky Aircraft has performed analytical studies, design analyses, and risk reduction tests have been performed for Higher Harmonic Control (HHC) on the S-76. The S-76 is an 8 to 10,000 lb helicopter which cruises at 145 kts. Flight test hardware has been assembled, main servo frequency response tested and upgraded, aircraft control system shake tested and verified, open loop controllers designed and fabricated, closed loop controllers defined and evaluated, and rotors turning ground and flight tests planned for the near future. Open loop analysis shows that about 2 deg of higher harmonic feathering at the blade 75% radius will be required to eliminate 4P vibration in the cockpit
Cosmic Strings, Zero Modes and SUSY breaking in Nonabelian N=1 Gauge Theories
We investigate the microphysics of cosmic strings in Nonabelian gauge
theories with N=1 supersymmetry. We give the vortex solutions in a specific
example and demonstrate that fermionic superconductivity arises because of the
couplings and interactions dictated by supersymmetry. We then use supersymmetry
transformations to obtain the relevant fermionic zero modes and investigate the
role of soft supersymmetry breaking on the existence and properties of the
superconducting strings.Comment: 12 pages, RevTex, submitted to Phys. Rev.
Pairing mean-field theory for the dynamics of dissociation of molecular Bose-Einstein condensates
We develop a pairing mean-field theory to describe the quantum dynamics of
the dissociation of molecular Bose-Einstein condensates into their constituent
bosonic or fermionic atoms. We apply the theory to one, two, and
three-dimensional geometries and analyze the role of dimensionality on the atom
production rate as a function of the dissociation energy. As well as
determining the populations and coherences of the atoms, we calculate the
correlations that exist between atoms of opposite momenta, including the column
density correlations in 3D systems. We compare the results with those of the
undepleted molecular field approximation and argue that the latter is most
reliable in fermionic systems and in lower dimensions. In the bosonic case we
compare the pairing mean-field results with exact calculations using the
positive- stochastic method and estimate the range of validity of the
pairing mean-field theory. Comparisons with similar first-principle simulations
in the fermionic case are currently not available, however, we argue that the
range of validity of the present approach should be broader for fermions than
for bosons in the regime where Pauli blocking prevents complete depletion of
the molecular condensate.Comment: 16 pages, 10 figure
Quantum depletion of collapsing Bose-Einstein condensates
We perform the first numerical three-dimensional studies of quantum field
effects in the Bosenova experiment on collapsing condensates by E. Donley et
al. [Nature 415, 39 (2002)] using the exact experimental geometry. In a
stochastic truncated Wigner simulation of the collapse, the collapse times are
larger than the experimentally measured values. We find that a finite
temperature initial state leads to an increased creation rate of uncondensed
atoms, but not to a reduction of the collapse time. A comparison of the
time-dependent Hartree-Fock-Bogoliubov and Wigner methods for the more
tractable spherical trap shows excellent agreement between the uncondensed
populations. We conclude that the discrepancy between the experimental and
theoretical values of the collapse time cannot be explained by Gaussian quantum
fluctuations or finite temperature effects.Comment: 9 pages, 4 figures, replaced with published versio
Classical Region of a Trapped Bose Gas
The classical region of a Bose gas consists of all single-particle modes that
have a high average occupation and are well-described by a classical field.
Highly-occupied modes only occur in massive Bose gases at ultra-cold
temperatures, in contrast to the photon case where there are highly-occupied
modes at all temperatures. For the Bose gas the number of these modes is
dependent on the temperature, the total number of particles and their
interaction strength. In this paper we characterize the classical region of a
harmonically trapped Bose gas over a wide parameter regime. We use a
Hartree-Fock approach to account for the effects of interactions, which we
observe to significantly change the classical region as compared to the
idealized case. We compare our results to full classical field calculations and
show that the Hartree-Fock approach provides a qualitatively accurate
description of classical region for the interacting gas.Comment: 6 pages, 5 figures; updated to include new results with interaction
The use of Skylab data to study the early detection of insect infestations and density and distribution of host plants
The detection of insect infestations and the density and distribution of host plants were studied using Skylab data, aerial photography and ground truth simultaneously. Additional ground truth and aerial photography were acquired between Skylab passes. Three test areas were selected: area 1, of high density citrus, was located northwest of Mission, Texas; area 2, 20 miles north of Weslaco, Texas, irrigated pastures and brush-covered land; area 3 covered the entire Lower Rio Grande Valley and adjacent areas of Mexico. A color composite picture of S-190A data showed patterns of vegetation on both sides of the Rio Grande River clearly delineating the possible avenues of entry of pest insects from Mexico into the United States or from the United States into Mexico. Vegetation that could be identified with conventional color and color IR film included: citrus, brush, sugarcane, alfalfa, irrigated and unimproved pastures
A study of the early detection of insect infestations and density/distribution of host plants
There are no author-identified significant results in this report
Bringing remote sensing technology to the user community
The procedures and services available for educating and training potential users of remote sensing technology are discussed along with approaches for achieving an in-house capability for the analysis of remotely sensed data using numerical techniques based on pattern recognition principles. Cost estimates are provided where appropriate
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