101,314 research outputs found
Simulator evaluation of the effects of reduced spoiler and thrust authority on a decoupled longitudinal control system during landings in wind shear
The effect of reduced control authority, both in symmetric spoiler travel and thrust level, on the effectiveness of a decoupled longitudinal control system was examined during the approach and landing of the NASA terminal configured vehicle (TCV) aft flight deck simulator in the presence of wind shear. The evaluation was conducted in a fixed-base simulator that represented the TCV aft cockpit. There were no statistically significant effects of reduced spoiler and thrust authority on pilot performance during approach and landing. Increased wind severity degraded approach and landing performance by an amount that was often significant. However, every attempted landing was completed safely regardless of the wind severity. There were statistically significant differences in performance between subjects, but the differences were generally restricted to the control wheel and control-column activity during the approach
A note on Volterra integral equations and topological dynamics
Topological dynamics theory applied to nonlinear Volterra equation
Computer program documentation for the pasture/range condition assessment processor
The processor which drives for the RANGE software allows the user to analyze LANDSAT data containing pasture and rangeland. Analysis includes mapping, generating statistics, calculating vegetative indexes, and plotting vegetative indexes. Routines for using the processor are given. A flow diagram is included
Simulator study of the effect of control-system time delays on the occurrence of pilot-induced oscillations and on pilot tracking performance with a space-shuttle-orbiter configuration
Using a six degree-of-freedom motion-base simulator, the effect of control-system time delays on the occurrence of pilot-induced oscillations (PIO's) on the vehicle handling qualities and on pilot tracking performance for a landing-approach configuration of the Space Shuttle orbiter was studied. A linearized math model was employed which represented a 300-knot orbiter with almost all time delays removed. Additional time delays were then inserted following the pilot's hand-controller signals. Only pitch and roll commands were used for vehicle control. The simulation employed an air to air tracking task as a means of emphasizing PIO tendencies. Two astronauts, two research pilots, and one simulation engineer served as test subjects. Results showed that PIO's occurred when the amount of added time delay approximated that existing for the orbiter configuration flown in the approach and landing tests. Increasing the amount of delay increased PIO occurrences and resulted in degraded tracking performance. Decreasing the amount of time delay eliminated the PIO's
Moving-base visual simulation study of decoupled controls during approach and landing of a STOL transport aircraft
The simulation employed all six rigid-body degrees of freedom and incorporated aerodynamic characteristics based on wind-tunnel data. The flight instrumentation included a localizer and a flight director which was used to capture and to maintain a two-segment glide slope. A closed-circuit television display of a STOLport provided visual cues during simulations of the approach and landing. The decoupled longitudinal controls used constant prefilter and feedback gains to provide steady-state decoupling of flight-path angle, pitch angle, and forward velocity. The pilots were enthusiastic about the decoupled longitudinal controls and believed that the simulator motion was an aid in evaluating the decoupled controls, although a minimum turbulence level with root-mean-square gust intensity of 0.3 m/sec (1 ft/sec) was required to mask undesirable characteristics of the moving-base simulator
Comparison of analytical predictions of longitudinal short period pilot-induced oscillations with results from a simulation study of the space shuttle orbiter
An analytical analysis of conditions producing pilot induced oscillations (PIO's) was made for the space shuttle orbiter in a landing approach configuration for the task of milling the elevation angle of the line of sight to a target vehicle. The analysis yielded a value of PIO frequency and a value for the amount of total system time delay (pilot + control system) that can be tolerated before instability results. Calculations were performed showing the effect of varying the range to the target and of varying the handling qualities of the orbiter vehicle. Analytical predictions were compared with simulation results obtained using a visual motion simulator
Simulator study of the effect of visual-motion time delays on pilot tracking performance with an audio side task
The effect of time delay was determined in the visual and motion cues in a flight simulator on pilot performance in tracking a target aircraft that was oscillating sinusoidally in altitude only. An audio side task was used to assure the subject was fully occupied at all times. The results indicate that, within the test grid employed, about the same acceptable time delay (250 msec) was obtained for a single aircraft (fighter type) by each of two subjects for both fixed-base and motion-base conditions. Acceptable time delay is defined as the largest amount of delay that can be inserted simultaneously into the visual and motion cues before performance degradation occurs. A statistical analysis of the data was made to establish this value of time delay. Audio side task provided quantitative data that documented the subject's work level
Composition profiling InAs quantum dots and wetting layers by atom probe tomography and cross-sectional scanning tunnelling microscopy
This study compares cross-sectional scanning tunnelling microscopy (XSTM) and
atom probe tomography (APT). We use epitaxially grown self-assembled InAs
quantum dots (QDs) in GaAs as an exemplary material with which to compare these
two nanostructural analysis techniques. We studied the composition of the
wetting layer and the QDs, and performed quantitative comparisons of the indium
concentration profiles measured by each method. We show that computational
models of the wetting layer and the QDs, based on experimental data, are
consistent with both analytical approaches. This establishes a link between the
two techniques and shows their complimentary behaviour, an advantage which we
exploit in order to highlight unique features of the examined QD material.Comment: Main article: 8 pages, 6 figures. Appendix: 3 pages, 5 figure
Bounds on the Compactness of Neutron Stars from Brightness Oscillations
The discovery of high-amplitude brightness oscillations at the spin frequency
or its first overtone in six neutron stars in low-mass X-ray binaries during
type~1 X-ray bursts provides a powerful new way to constrain the compactness of
these stars, and hence to constrain the equation of state of the dense matter
in all neutron stars. Here we present the results of general relativistic
calculations of the maximum fractional rms amplitudes that can be observed
during bursts. In particular, we determine the dependence of the amplitude on
the compactness of the star, the angular dependence of the emission from the
surface, the rotational velocity at the stellar surface, and whether there are
one or two emitting poles. We show that if two poles are emitting, as is
strongly indicated by independent evidence in 4U 1636-536 and KS 1731-26, the
resulting limits on the compactness of the star can be extremely restrictive.
We also discuss the expected amplitudes of X-ray color oscillations and the
observational signatures necessary to derive convincing constraints on neutron
star compactness from the amplitudes of burst oscillations.Comment: 8 pages plus one figure, AASTeX v. 4.0, submitted to The
Astrophysical Journal Letter
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