73 research outputs found
Computer simulation of a pilot in V/STOL aircraft control loops
The objective was to develop a computerized adaptive pilot model for the computer model of the research aircraft, the Harrier II AV-8B V/STOL with special emphasis on propulsion control. In fact, two versions of the adaptive pilot are given. The first, simply called the Adaptive Control Model (ACM) of a pilot includes a parameter estimation algorithm for the parameters of the aircraft and an adaption scheme based on the root locus of the poles of the pilot controlled aircraft. The second, called the Optimal Control Model of the pilot (OCM), includes an adaption algorithm and an optimal control algorithm. These computer simulations were developed as a part of the ongoing research program in pilot model simulation supported by NASA Lewis from April 1, 1985 to August 30, 1986 under NASA Grant NAG 3-606 and from September 1, 1986 through November 30, 1988 under NASA Grant NAG 3-729. Once installed, these pilot models permitted the computer simulation of the pilot model to close all of the control loops normally closed by a pilot actually manipulating the control variables. The current version of this has permitted a baseline comparison of various qualitative and quantitative performance indices for propulsion control, the control loops and the work load on the pilot. Actual data for an aircraft flown by a human pilot furnished by NASA was compared to the outputs furnished by the computerized pilot and found to be favorable
Regulation of Leydig Cell Function by Prolactin, Growth Hormone and Luteinizing Hormone
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72585/1/j.1365-2605.1978.tb00026.x.pd
Computer simulation of a single pilot flying a modern high-performance helicopter
Presented is a computer simulation of a human response pilot model able to execute operational flight maneuvers and vehicle stabilization of a modern high-performance helicopter. Low-order, single-variable, human response mechanisms, integrated to form a multivariable pilot structure, provide a comprehensive operational control over the vehicle. Evaluations of the integrated pilot were performed by direct insertion into a nonlinear, total-force simulation environment provided by NASA Lewis. Comparisons between the integrated pilot structure and single-variable pilot mechanisms are presented. Static and dynamically alterable configurations of the pilot structure are introduced to simulate pilot activities during vehicle maneuvers. These configurations, in conjunction with higher level, decision-making processes, are considered for use where guidance and navigational procedures, operational mode transfers, and resource sharing are required
Computer simulation of multiple pilots flying a modern high performance helicopter
A computer simulation of a human response pilot mechanism within the flight control loop of a high-performance modern helicopter is presented. A human response mechanism, implemented by a low order, linear transfer function, is used in a decoupled single variable configuration that exploits the dominant vehicle characteristics by associating cockpit controls and instrumentation with specific vehicle dynamics. Low order helicopter models obtained from evaluations of the time and frequency domain responses of a nonlinear simulation model, provided by NASA Lewis Research Center, are presented and considered in the discussion of the pilot development. Pilot responses and reactions to test maneuvers are presented and discussed. Higher level implementation, using the pilot mechanisms, are discussed and considered for their use in a comprehensive control structure
Toward a statistical mechanics of four letter words
We consider words as a network of interacting letters, and approximate the
probability distribution of states taken on by this network. Despite the
intuition that the rules of English spelling are highly combinatorial (and
arbitrary), we find that maximum entropy models consistent with pairwise
correlations among letters provide a surprisingly good approximation to the
full statistics of four letter words, capturing ~92% of the multi-information
among letters and even "discovering" real words that were not represented in
the data from which the pairwise correlations were estimated. The maximum
entropy model defines an energy landscape on the space of possible words, and
local minima in this landscape account for nearly two-thirds of words used in
written English
Thermodynamics of natural images
The scale invariance of natural images suggests an analogy to the statistical
mechanics of physical systems at a critical point. Here we examine the
distribution of pixels in small image patches and show how to construct the
corresponding thermodynamics. We find evidence for criticality in a diverging
specific heat, which corresponds to large fluctuations in how "surprising" we
find individual images, and in the quantitative form of the entropy vs. energy.
The energy landscape derived from our thermodynamic framework identifies
special image configurations that have intrinsic error correcting properties,
and neurons which could detect these features have a strong resemblance to the
cells found in primary visual cortex
Imaging Spectroscopy for Extrasolar Planet Detection
Coronagraphic imaging in combination with moderate to high spectral
resolution may prove more effective in both detecting extrasolar planets and
characterizing them than a standard coronagraphic imaging approach. We envisage
an integral-field spectrograph coupled to a coronagraph to produce a 3D
datacube. For the idealised case where the spectrum of the star is well-known
and unchanging across the field, we discuss the utility of cross-correlation to
seek the extrasolar planet signal, and describe a mathematical approach to
completely eliminate stray light from the host star (although not its Poisson
noise). For the case where the PSF is dominated by diffraction and scattering
effects, and comprises a multitude of speckles within an Airy pattern typical
of a space-based observation, we turn the wavelength dependence of the PSF to
advantage and present a general way to eliminate the contribution from the star
while preserving both the flux and spectrum of the extrasolar planet. We call
this method `spectral deconvolution'. We illustrate the dramatic gains by
showing an idealized simulation that results in a 20-sigma detection of a
Jovian planet at 2 pc with a 2-m coronagraphic space telescope, even though the
planet's peak flux is only 1% that of the PSF wings of the host star. This
scales to detection of a terrestrial extrasolar planet at 2 pc with an 8-m
coronagraphic Terrestrial Planet Finder (TPF) in ~7 hr (or less with
appropriate spatial filtering). Data on the spectral characteristics of the
extrasolar planet and hence on its atmospheric constituents and possible
biomarkers are obtained naturally as part of this process.Comment: 62 pages 27 figures accepted for publication in Ap
Are biological systems poised at criticality?
Many of life's most fascinating phenomena emerge from interactions among many
elements--many amino acids determine the structure of a single protein, many
genes determine the fate of a cell, many neurons are involved in shaping our
thoughts and memories. Physicists have long hoped that these collective
behaviors could be described using the ideas and methods of statistical
mechanics. In the past few years, new, larger scale experiments have made it
possible to construct statistical mechanics models of biological systems
directly from real data. We review the surprising successes of this "inverse"
approach, using examples form families of proteins, networks of neurons, and
flocks of birds. Remarkably, in all these cases the models that emerge from the
data are poised at a very special point in their parameter space--a critical
point. This suggests there may be some deeper theoretical principle behind the
behavior of these diverse systems.Comment: 21 page
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