40,509 research outputs found
STOL Simulation Requirements for Development of Integrated Flight/propulsion Control Systems
The role and use of simulation as a design tool in developing integrated systems where design criteria is largely unavailable is well known. This paper addresses additional simulation needs for the development of Integrated Flight/Propulsion Control Systems (IFPCS) which will improve the probability of properly interpreting simulation results. These needs are based on recent experience with power approach flying qualities evaluations of an advanced fighter configuration which incorporated Short Takeoff and Landing (STOL) technologies and earlier experiences with power approach flying qualities evaluations on the AFTI/F-16 program. The use of motion base platforms with axial and normal degrees of freedom will help in evaluating pilot coupling and workload in the presence of high frequency low amplitude axial accelerations produced by high bandwidth airspeed controllers in a gusty environment
Registration of Heat Capacity Mapping Mission day and night images
Neither iterative registration, using drainage intersection maps for control, nor cross correlation techniques were satisfactory in registering day and night HCMM imagery. A procedure was developed which registers the image pairs by selecting control points and mapping the night thermal image to the daytime thermal and reflectance images using an affine transformation on a 1300 by 1100 pixel image. The resulting image registration is accurate to better than two pixels (RMS) and does not exhibit the significant misregistration that was noted in the temperature-difference and thermal-inertia products supplied by NASA. The affine transformation was determined using simple matrix arithmetic, a step that can be performed rapidly on a minicomputer
The Pauli principle in collective motion: Reimagining and reinterpreting Cooper pairs, the Fermi sea, Pauli blocking and superfluidity
Typically visualized from an independent particle viewpoint, the Pauli
principle's role in collective motion is analyzed leading to a reimagination of
the microscopic dynamics underlying superfluidity/superconductivity and a
reinterpretation of several interrelated phenomena: Cooper pairs, the Fermi
sea, and Pauli blocking. The current approach, symmetry-invariant perturbation
theory is a first principles method with no adjustable parameters. An adiabatic
evolution is employed to transfer the well-known Pauli restrictions for
identical, independent particles with two spin values to restrictions on the
collective modes of an ensemble of ``spin up'' ``spin down'' particles. The
collective modes, analytic N-body normal modes, are obtained from a group
theoretic exact solution of the first-order equations. Cooper pairing is
reinterpreted not as the pairing of two fermions with total zero momentum, but
as the convergence of the momentum of the entire ensemble to two values, +k and
-k, as the particles in the normal mode move back and forth with a single
frequency and phase. The Fermi sea and Pauli blocking, commonly described using
independent fermions that occupy lower states to create a ``sea'' in energy
space and block occupation is redescribed as a collective energy phenomena of
the entire ensemble. Superfluidity, which has always been viewed as a
collective phenomena as Cooper pairs are assumed to condense into a macroscopic
occupation of a single lowest state, is now reimagined without two-body pairing
in real space, but as a macroscopic occupation of a low-energy phonon normal
mode resulting in the convergence of the momentum to two equal and opposite
values. The expected properties of superfluidity including the rigidity of the
wave function, interactions between fermions in different pairs, convergence of
the momentum and the gap in the excitation spectrum are discussed
Thermal expansion method for lining tantalum alloy tubing with tungsten
A differential-thermal expansion method was developed to line T-111 (tantalum - 8 percent tungsten - 2 percent hafnium) tubing with a tungsten diffusion barrier as part of a fuel element fabrication study for a space power nuclear reactor concept. This method uses a steel mandrel, which has a larger thermal expansion than T-111, to force the tungsten against the inside of the T-111 tube. Variables investigated include lining temperature, initial assembly gas size, and tube length. Linear integrity increased with increasing lining temperature and decreasing gap size. The method should have more general applicability where cylinders must be lined with a thin layer of a second material
High Redshift Standard Candles: Predicted Cosmological Constraints
We investigate whether future measurements of high redshift standard candles
(HzSCs) will be a powerful probe of dark energy, when compared to other types
of planned dark energy measurements. Active galactic nuclei and gamma ray
bursts have both been proposed as potential HzSC candidates. Due to their high
luminosity, they can be used to probe unexplored regions in the expansion
history of the universe. Information from these regions can help constrain the
properties of dark energy, and in particular, whether it varies over time.
We consider both linear and piecewise parameterizations of the dark energy
equation of state, , and assess the optimal redshift distribution a
high-redshift standard-candle survey could take to constrain these models.
The more general the form of the dark energy equation of state being
tested, the more useful high-redshift standard candles become. For a linear
parameterization of , HzSCs give only small improvements over planned
supernova and baryon acoustic oscillation measurements; a wide redshift range
with many low redshift points is optimal to constrain this linear model.
However to constrain a general, and thus potentially more informative, form of
, having many HzSCs can significantly improve limits on the nature of
dark energy.Comment: Accepted MNRAS, 27 Pages, 15 figures, matches published versio
Information extraction and transmission techniques for spaceborne synthetic aperture radar images
Information extraction and transmission techniques for synthetic aperture radar (SAR) imagery were investigated. Four interrelated problems were addressed. An optimal tonal SAR image classification algorithm was developed and evaluated. A data compression technique was developed for SAR imagery which is simple and provides a 5:1 compression with acceptable image quality. An optimal textural edge detector was developed. Several SAR image enhancement algorithms have been proposed. The effectiveness of each algorithm was compared quantitatively
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