1,795 research outputs found
Mechanization of and experience with a triplex fly-by-wire backup control system
A redundant three axis analog control system was designed and developed to back up a digital fly by wire control system for an F-8C airplane. The mechanization and operational experience with the backup control system, the problems involved in synchronizing it with the primary system, and the reliability of the system are discussed. The backup control system was dissimilar to the primary system, and it provided satisfactory handling through the flight envelope evaluated. Limited flight tests of a variety of control tasks showed that control was also satisfactory when the backup control system was controlled by a minimum displacement (force) side stick. The operational reliability of the F-8 digital fly by wire control system was satisfactory, with no unintentional downmodes to the backup control system in flight. The ground and flight reliability of the system's components is discussed
Mechanization of and experience with a triplex fly-by-wire backup control system
A redundant three-axis analog control system was designed and developed to back up a digital fly-by-wire control system for an F-8C airplane. Forty-two flights, involving 58 hours of flight time, were flown by six pilots. The mechanization and operational experience with the backup control system, the problems involved in synchronizing it with the primary system, and the reliability of the system are discussed. The backup control system was dissimilar to the primary system, and it provided satisfactory handling through the flight envelope evaluated. Limited flight tests of a variety of control tasks showed that control was also satisfactory when the backup control system was controlled by a minimum-displacement (force) side stick. The operational reliability of the F-8 digital fly-by-wire control system was satisfactory, with no unintentional downmodes to the backup control system in flight. The ground and flight reliability of the system's components is discussed
Effect of sampling rate and record length on the determination of stability and control derivatives
Flight data from five aircraft were used to assess the effects of sampling rate and record length reductions on estimates of stability and control derivatives produced by a maximum likelihood estimation method. Derivatives could be extracted from flight data with the maximum likelihood estimation method even if there were considerable reductions in sampling rate and/or record length. Small amplitude pulse maneuvers showed greater degradation of the derivative maneuvers than large amplitude pulse maneuvers when these reductions were made. Reducing the sampling rate was found to be more desirable than reducing the record length as a method of lessening the total computation time required without greatly degrading the quantity of the estimates
Quantum Mechanical Calculation of Molecular Radii. I. Hydrides of Elements of Periodic Groups IV through VII
The fraction of the total electron density within a sphere having the empirical van der Waals radius is calculated for the atoms of eight elements, using Hartree‐Fock atomic wavefunctions. The sphere is found to contain 97%–99% of the electron density, indicating that such calculations correlate well with atomic sizes. The procedure is extended to eight hydride molecules of the type AHn, with molecular size determined by the radius of the 98% contour as computed from published one‐center SCF molecular wave‐functions. The predicted molecular radii agree well with experimental values and support the usefulness of this method for describing effective molecular size.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70465/2/JCPSA6-56-9-4419-1.pd
The new HiVIS spectropolarimeter and spectropolarimetric calibration of the AEOS telescope
We designed, built, and calibrated a new spectropolarimeter for the HiVIS
spectrograph (R 12000-49000) on the AEOS telescope. We also did a polarization
calibration of the telescope and instrument. We will introduce the design and
use of the spectropolarimeter as well as a new data reduction package we have
developed, then discuss the polarization calibration of the spectropolarimeter
and the AEOS telescope. We used observations of unpolarized standard stars at
many pointings to measure the telescope induced polarization and compare it
with a Zemax model. The telescope induces polarization of 1-6% with a strong
variation with wavelength and pointing, consistent with the altitude and
azimuth variation expected. We then used scattered sunlight as a linearly
polarized source to measure the telescopes spectropolarimetric response to
linearly polarized light. We then made an all-sky map of the telescope's
polarization response to calibrate future spectropolarimetry.Comment: PASP 118, June 200
A Richness Study of 14 Distant X-ray Clusters From the 160 Square Degree Survey
We have measured the surface density of galaxies toward 14 X-ray-selected
cluster candidates at redshifts greater than z=0.46, and we show that they are
associated with rich galaxy concentrations. We find that the clusters range
between Abell richness classes 0-2, and have a most probable richness class of
one. We compare the richness distribution of our distant clusters to those for
three samples of nearby clusters with similar X-ray luminosities. We find that
the nearby and distant samples have similar richness distributions, which shows
that clusters have apparently not evolved substantially in richness since
redshift z =0.5. We compare the distribution of distant X-ray clusters in the
L_x--richness plane to the distribution of optically-selected clusters from the
Palomar Distant Cluster Survey. The optically-selected clusters appear overly
rich for their X-ray luminosities when compared to X-ray-selected clusters.
Apparently, X-ray and optical surveys do not necessarily sample identical mass
concentrations at large redshifts. This may indicate the existence of a
population of optically rich clusters with anomalously low X-ray emission. More
likely, however, it reflects the tendency for optical surveys to select
unvirialized mass concentrations, as might be expected when peering along
large-scale filaments.Comment: The abstract has been abridged. Accepted for publication in the
Astrophysical Journa
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Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces
Electron-hole excitations in the surface bands of GaAs(110) are analyzed
using constrained density-functional theory calculations. The results show that
Frenkel-type autolocalized excitons are formed. The excitons induce a local
surface unrelaxation which results in a strong exciton-exciton attraction and
makes complexes of two or three electron-hole pairs more favorable than
separate excitons. In such microscopic exciton "droplets" the
electron density is mainly concentrated in the dangling orbital of a surface Ga
atom whereas the holes are distributed over the bonds of this atom to its As
neighbors thus weakening the bonding to the substrate. This finding suggests
the microscopic mechanism of a laser-induced emission of neutral Ga atoms from
GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from:
[email protected]
Static charged perfect fluid spheres in general relativity
Interior perfect fluid solutions for the Reissner-Nordstrom metric are
studied on the basis of a new classification scheme. General formulas are found
in many cases. Explicit new global solutions are given as illustrations. Known
solutions are briefly reviewed.Comment: 23 pages, Revtex (galley), journal version, to appear in Phys.Rev.
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