Open Access. Powered by Scholars. Published by Universities.®

Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

Discipline
Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 180721 - 180750 of 197973

Full-Text Articles in Engineering

Design And Fabrication Of An Implantable Cortical Semiconductor Integrated Circuit Electrode Array, Pierre K. Lefevre Dec 1990

Design And Fabrication Of An Implantable Cortical Semiconductor Integrated Circuit Electrode Array, Pierre K. Lefevre

Theses and Dissertations

This research furthered the processing steps of the AFIT 16 by 16 implantable cortical semiconductor integrated circuit electrode array, or brain chip. The areas of interest include the brain chip electron ics, metallization, ionic permeation, and implantation. The electronics and metallization are heavily covered. A high speed, single clock divide-by-two circuit was modified with a reset transistor and cascaded to form a ripple counter. This device had stable operation at specific source voltage and clock voltage and frequency. A 7-stage inverter with 10 unmodified divide-by-two circuits cascaded operated between 1.7 and 8 volts, and between 39 Khz and 1 Mhz, …

Go to article

Analysis And Testing Of A Bistatic Radar Cross Section Measurement Capability For The Afit Anechoic Chamber, Timothy D. Mccool Dec 1990

Analysis And Testing Of A Bistatic Radar Cross Section Measurement Capability For The Afit Anechoic Chamber, Timothy D. Mccool

Theses and Dissertations

This research effort examined the feasibility of performing bistatic radar cross section (RCS) measurements in the AFIT anechoic chamber. The capability was established to measure the bistatic RCS of a target versus frequency and versus target azimuth angle. In either case, one of three bistatic angles (angle between transmit and receive antennas) is available: 45 degrees, 90 degrees, and 135 degrees. Accurate bistatic RCS measurements were obtained using a CW radar and utilizing background subtraction, bistatic calibration, and software range gating. Simple targets were selected for validation purposes since their bistatic RCS could be predicted. These consisted of spheres and …

Go to article

Rule-Based Frequency Domain Speech Coding, Vance M. Mcmillan Dec 1990

Rule-Based Frequency Domain Speech Coding, Vance M. Mcmillan

Theses and Dissertations

A speech processing system is designed to simulate the transmission of speech signals using a speech coding scheme. The transmitter portion of the simulation extracts a minimized set of frequencies in Fourier space which represents the essence of each of the speech timeslices. These parameters are then adaptively quantized and transmitted to a receiver portion of the coding scheme. The receiver then generates an estimate of the original timeslice from the transmitted parameters using a sinusoidal speech model. After initial design, the thesis investigates how each of the design parameters affect the human perceived quality of speech. This is done …

Go to article

Multi-Input Multi-Output Flight Control System Design For The Yf-16 Using Nonlinear Qft And Pilot Compensation, Russell B. Miller Dec 1990

Multi-Input Multi-Output Flight Control System Design For The Yf-16 Using Nonlinear Qft And Pilot Compensation, Russell B. Miller

Theses and Dissertations

Nonlinear Quantitative Feedback Theory (QFT) and pilot compensation techniques are used to design a 2x2 flight control system for the YF-16 aircraft over a large range of plant uncertainty. The design is based on numerical input- output time histories generated with a FORTRAN implemented nonlinear simulation of the YF-16. The first step of the design process is the generation of a set of equivalent linear time-invariant (LTI) plant models to represent the actual nonlinear plant. It has been proven that the solution to the equivalent plant problem is guaranteed to solve the original nonlinear problem. Standard QFT techniques are then …

Go to article

Moving-Bank Multiple Model Adaptive Estimation And Control Applied To A Large Flexible Space Structure, Robert B. Moyle Dec 1990

Moving-Bank Multiple Model Adaptive Estimation And Control Applied To A Large Flexible Space Structure, Robert B. Moyle

Theses and Dissertations

The performance of moving-bank multiple model adaptive estimation (MMAE) and control (MMAC) algorithms for large space structure control is analyzed in this thesis. The performance of a six-state filter model and associated controller are evaluated on the basis of estimation/control performance against a 24-estate truth model. A model developed using finite element analysis is used to approximate a large flexible space structure. The space structure is configured as a two-bay truss which is attached to a large central hub, where the mass of the hub is considered to be much more larger than the mass of the flexible structure. The …

Go to article

Analysis Of Visual Illusions Using Gabor Filters, Richard A. Oberndorf Dec 1990

Analysis Of Visual Illusions Using Gabor Filters, Richard A. Oberndorf

Theses and Dissertations

This thesis has demonstrated the correctness of using spatial filters in the analysis of various visual illusions; the specific form of filter has been derived from a Gabor equation model of simple cell response on the visual cortex. The Gabor Low Pass Filter (GLPF) applied to these anomalies was derived from proposals made that simple cell response on the visual cortex may be modeled by a set of equations originally proposed by Gabor in the 1940's. Based upon the extension of these equations into two dimensions, a GLPF process was applied to computer-generated black and white illusions (the Kanizsa Triangle, …

Go to article

Digital Control Of The Utah/Mit Dexterous Hand: Initial Evaluation And Analysis, Lloyd W. Rainey Iii Dec 1990

Digital Control Of The Utah/Mit Dexterous Hand: Initial Evaluation And Analysis, Lloyd W. Rainey Iii

Theses and Dissertations

An experimental digital platform is developed as an environment on which to evaluate digital control strategies for dexterous manipulation with a pneumatically actuated tendon-driven manipulator. This environment is used to begin the study of advanced control methods that are suitable for providing the tracking accuracy required for grasping and dexterous manipulation with a pneumatically actuated tendon-driven end-effector. The digital platform consists of a PC/AT-386 and a single board MC68020 microcomputer in a VME chassis with shared RAM between the two processors to control the Utah/MIT Dexterous Hand (UMDH). The MC68020 controls the A/D and D/A access for the UMDH, while …

Go to article

Speech Coding And Compression Using Wavelets And Lateral Inhibitory Networks, Richard Ricart Dec 1990

Speech Coding And Compression Using Wavelets And Lateral Inhibitory Networks, Richard Ricart

Theses and Dissertations

The purpose of this thesis is to introduce the concept of lateral inhibition as a generalized technique for compressing time/frequency representations of electromagnetic and acoustical signals, particularly speech. This requires at least a rudimentary treatment of the theory of frames-which generalizes most commonly known time/frequency distributions--the biology of hearing, and digital signal processing. As such, this material, along with the interrelationships of the disparate subjects, is presented in a tutorial style. This may leave the mathematician longing for more rigor, the neurophysiological psychologist longing for more substantive support of the hypotheses presented, and the engineer longing for a reprieve from …

Go to article

Pulsed Compression For Aerosol Ranging With Coherent Pulse-Doppler Lidar Systems, Jerry L. Rogers Dec 1990

Pulsed Compression For Aerosol Ranging With Coherent Pulse-Doppler Lidar Systems, Jerry L. Rogers

Theses and Dissertations

This thesis provides a thorough review of conventional matched filter radar theory as it applies to aerosol sensing lidar. Basic matched-filter radar theory and the complex, dense aerosol target model eventually lead to a general derivation of the matched-filter radar receiver response to a dense aerosol target environment. The matched-filter response is obtained in terms of a two dimensional convolution of the target scattering function and the radar ambiguity function. The range and radial velocity resolution of various radar signals were compared using the matched-filter radar receiver and scattering function models. Pulse compression radar signals were compared to the simple …

Go to article

The Radar Range Equation For The Detection Of Steady Targets In Weibull Clutter, Leon C. Rountree Dec 1990

The Radar Range Equation For The Detection Of Steady Targets In Weibull Clutter, Leon C. Rountree

Theses and Dissertations

In this thesis, the detection characteristics of a steady target immersed in radar clutter characterized by returns statistically modeled according to a Weibull probability density function are developed. A detector model is developed by modifying an envelope detection scheme used to detect deterministic signals in Gaussian noise. By examining the statistics of the detector output under alternate hypotheses, an expression for the probability of detection (P sub d) is developed in terms of the probability of false alarm (P sub fa), the signal-to-clutter ratio (SCR), and the Weibull skewness parameter (b), which is a function of the type of terrain …

Go to article

Radar Image Processing For The Afit Anechoic Chamber, Brian K. Sanders Dec 1990

Radar Image Processing For The Afit Anechoic Chamber, Brian K. Sanders

Theses and Dissertations

The purpose of this study was to begin development of an Inverse Synthetic Aperture Radar imaging capability for the AFIT anechoic chamber. This began with an evaluation of the capabilities and limitations of the existing radar system and the chamber itself for this application. Then, after deciding on the image processing approach, software had to be written to collect the data necessary for image processing. This constituted the majority of this study, and resulted in a versatile, user-friendly program that automates the process of collecting data for high-resolution radar images. The program checks that the data to be collected will …

Go to article

Characterization Of An Air-To-Air Optical Heterodyne Communication System, Rebecca N. Seeger Dec 1990

Characterization Of An Air-To-Air Optical Heterodyne Communication System, Rebecca N. Seeger

Theses and Dissertations

The primary goal of this research was to determine the feasibility of air-to-air optical communications systems using coherent detection in a turbulent environment. Secondary goals were to determine (1) the signal-to-noise ratio (SNR) degradation due to turbulence and (2) the effect of varying the wavelength (1.5, 830, 904 nm), altitude (5000-12500 m), path length (40-160 km) and aperture side length (1-15 cm) on the turbulence affected SNR. The research was conducted under the following assumptions: (1) ideal transmitter and receiver, (2) equally sized, uniformly weighted, square transmitter and receiver apertures, (3) ideal tracking by the receiver, and (4) zero losses …

Go to article

Establishment Of A Fabrication And Measurement Capability For Aperture-Fed Stacked Patch Microstrip Antennas At The Air Force Institute Of Technology, Christopher I. Terry Dec 1990

Establishment Of A Fabrication And Measurement Capability For Aperture-Fed Stacked Patch Microstrip Antennas At The Air Force Institute Of Technology, Christopher I. Terry

Theses and Dissertations

Much time and effort has been applied to accurately model aperture- fed stacked patch microstrip antennas at the Air Force Institute of Technology (AFIT). The results of this study provide AFIT with the capability to fabricate and measure these antennas for comparison of measured radiation characteristics to the predicted characteristics. Basic microstrip patch antenna theory is reviewed, as well as the motivation leading to the development of aperture-fed stacked patch microstrip antennas. The fabrication process used to produce the two antennas manufactured for this study is described in detail. The construction of a small anechoic chamber for pattern measurements is …

Go to article

Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas Dec 1990

Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas

Theses and Dissertations

The optical sensors of United States Air Force reconnaissance vehicles, such as satellites, are subject to temporary or permanent blinding from hostile (or threat) laser radiation. By detecting and determining the angle of arrival (AOA) of the hostile radiation, the reconnaissance vehicle may be able to protect its optical sensors by taking evasive maneuvers or by shutting down the optical sensor (such as closing a shutter) until the threat has passed. In addition, the vehicle can relay information to its ground terminal allowing the intelligence community to determine the source of the hostile laser radiation. This thesis demonstrated that an …

Go to article

Automatic Flight Control System Design For An Unmanned Research Vehicle Using Discrete Quantitative Feedback Theory, David G. Wheaton Dec 1990

Automatic Flight Control System Design For An Unmanned Research Vehicle Using Discrete Quantitative Feedback Theory, David G. Wheaton

Theses and Dissertations

This thesis presents the application of non-minimum phase (NMP) w'- plane discrete MIMO (multiple-input-multiple-output) Quantitative Feedback Theory (QFT) to the design of a three-axis rate-commanded automatic flight control system for an unmanned research vehicle (URV). The URV model used has seven inputs and three outputs derived from the small-angle perturbation equations of motion. Plant parameter uncertainty consists of six flight conditions derived from variations in the aircraft center of gravity, airspeed, and gross weight. A weighting matrix delts is used to post-multiply the plants for blending the seven effector inputs into three effective rate-command inputs and resulting in an effective …

Go to article

Te Scattering From A Dielectric Coated Conducting Strip, William D. Wood Jr. Dec 1990

Te Scattering From A Dielectric Coated Conducting Strip, William D. Wood Jr.

Theses and Dissertations

Consider a plane wave incident on a conducting strip of infinite length coated on one side with a thin, uniform coating of lossless dielectric, and let the incident magnetic field vector be parallel to the edges of the strip. From first principles we develop the integral equations relating the total, incident, and scattered fields in the dielectric. We expand the fields in the dielectric slab as the sum of three plane waves (the 'forced' wave and two oppositely-directed surface waves). The phase constants in the x and y directions are known and the wave amplitudes are found using least-squared- error-point-matching. …

Go to article

An Evaluation Of An Ada Implementation Of The Rete Algorithm For Embedded Flight Processors, F. Jesse Fanning Dec 1990

An Evaluation Of An Ada Implementation Of The Rete Algorithm For Embedded Flight Processors, F. Jesse Fanning

Theses and Dissertations

The purpose of this thesis was to design and develop an expert system shell in Ada, and to evaluate the shell's execution and size performance to determine its suitability for real-time operation on the MIL-STD-1750A embedded flight processor. The expert system shell uses the CLIPS/Ada inference engine, a forward-chaining Ada implementation of Rete. The expert system shell design is presented along with an overview of the target environment--the MIL-STD-1750A VHSIC Avionic Modular Processor (VAMP) running under the Ada Avionics Real-Time Software (AARTS) Operating System. Theoretical and empirical complexity analyses of the inference engine are presented and discussed in view of …

Go to article

Characterization Of Radar Signals Using Neural Networks, Daniel R. Zahirniak Dec 1990

Characterization Of Radar Signals Using Neural Networks, Daniel R. Zahirniak

Theses and Dissertations

Recent work concerning artificial neural networks has focused on decreasing network training times. Kernel Classifier networks, using radial basis functions (RBFs) as the kernel function, can be trained quickly with little performance degradation. Short training times are critical for systems which must adapt to changing environments. The function of Kernel Classifier networks is based on the principle that multivariate functions can be approximated via linear combinations of RBFs. RBFs can also perform probability density estimations, making classifications approximating a Baye's optimal descriminant. Methods used to set the RBF centers included matching the training data, Kohonen Training, K-Means Clustering and placement …

Go to article

Low Temperature Photoluminescence Study Of Holmium And Thulium Implanted Into Iii-V Semiconductors And Silicon, Eric Silkowski Dec 1990

Low Temperature Photoluminescence Study Of Holmium And Thulium Implanted Into Iii-V Semiconductors And Silicon, Eric Silkowski

Theses and Dissertations

Low temperature photoluminescence studies were performed on holmium implanted into InP, GaAs, and Si; and thulium implanted into AlGaAs, GaAs, and Si. Samples were annealed by the conventional furnace and rapid thermal techniques. None of the characteristic 4f emissions of holmium were found in the spectral region of .73 to 1.55 eV. AlGaAs:Tm showed strong thulium emissions in the .93 to 1.03 eV region. These emissions were studied and compared to those in GaAs:Tm. Low and high temperature annealed samples showed evidence of trivalent Tm centers. Temperature dependence studies showed that thulium 4f emissions were present above 200 K but …

Go to article

Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp Dec 1990

Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp

Theses and Dissertations

Lifetime measurements of the excited states of three GaAs semiconductors doped with the rare earth elements Erbium (ER), Praseodymium (Pr) , and Thulium (Tm) has been studied using a pulsed nitrogen laser and germanium detector. The measurements were made with an experimental set up with a system response time of 0.34 micro seconds. A 330 milliwatt nitrogen laser with a wavelength of 3370 angstrums was used to excite transitions of the rare earth elements.

Go to article

An Aluminum Salvage Station For The External Tank (Asset), James N. Haislip Jr., William C. Raynes Jr., David L. Van Matte, Roger E. Linscott, Michael A. Skinner Dec 1990

An Aluminum Salvage Station For The External Tank (Asset), James N. Haislip Jr., William C. Raynes Jr., David L. Van Matte, Roger E. Linscott, Michael A. Skinner

Theses and Dissertations

The external tank is currently the only non-reusable portion of the National Space Transportation System. The tank has 98% of the energy required to be placed in orbit at the point it is jettisoned. The purpose of this study is to develop techniques which would transform this throw-away item into a source of construction material at low earth orbit. A simulation is developed to verify the reduction timelines and peak power requirements for manual and automated reduction. The required tools to accomplish the tasks of initial cutting, product transport, spray on foam insulation removal, and product storage are developed. A …

Go to article

Multidisciplinary Modeling And Design Of A Space Structure, Brian K. Cassiday, Lawrence L. Gatchet, John T. Tester, Stephen O. Gaines Ii, Mario N. Moya Dec 1990

Multidisciplinary Modeling And Design Of A Space Structure, Brian K. Cassiday, Lawrence L. Gatchet, John T. Tester, Stephen O. Gaines Ii, Mario N. Moya

Theses and Dissertations

A method is needed to simultaneously integrate several engineering disciplines into one complete model to determine the performance of the system as a whole during the design development. System engineering methodologies are particularly suited to this problem. These methods provide a structured approach to problem formulation and system parameter identification. Bond graphs are also well suited as bond graphs model power flow and energy relationships within subsystems, a characteristic inherent to all dynamic systems. The intent of this research was to demonstrate the use of concurrent engineering theory to systematically model a large flexible space structure involving several engineering disciplines. …

Go to article

A Procedure For Performance Assessment Of Drugs Hypothesized To Be Effective In Controlling Motion Sickness, Zainab N. Ahmed Dec 1990

A Procedure For Performance Assessment Of Drugs Hypothesized To Be Effective In Controlling Motion Sickness, Zainab N. Ahmed

Theses and Dissertations

The Air Force Institute of Technology (AFIT) is conducting research into the effectiveness of certain drugs for controlling motion sickness. If the drugs are found to be useful, they must still be proven to have no harmful effects on the operator's performance abilities. There are many methods for assessing performance effects of drugs but very little standardization exists. The Unified Tri-Services Cognitive Performance Assessment Battery (UTC-PAB) is a performance assessment method designed to be used by all military branches. This will encourage standardization of drug testing, exchange of data, and comparability of methods. Five tests were chosen from the UTC-PAB …

Go to article

Model-Based Reasoning In The Detection Of Satellite Anomalies, Ralph W. Dries Dec 1990

Model-Based Reasoning In The Detection Of Satellite Anomalies, Ralph W. Dries

Theses and Dissertations

Automatic fault detection and recovery would be a mandatory requirement for a satellite where some degree of autonomy is required. This thesis reviews some AI techniques used for the detection of satellite anomalies, and concludes that the model-based reasoning paradigm is best suited for automated on-board fault detection because it can cope with situations not necessarily programmed into the knowledge base. Using the Scheme language and its SCOOPS object oriented extension, development of software is described that models the pitch control channel in the attitude and velocity control subsystem of a typical geo-stationary communications satellite. This model is used by …

Go to article

An Analysis Of The Effects Of Phenytoin In Treating Motion Sickness And The Effects Of Motion Sickness On The Human Electroencephalogram, Todd M. Banducci Dec 1990

An Analysis Of The Effects Of Phenytoin In Treating Motion Sickness And The Effects Of Motion Sickness On The Human Electroencephalogram, Todd M. Banducci

Theses and Dissertations

This research had two goals: to continue the ongoing research at AFIT to determine the efficacy of the anticonvulsant drug phenytoin in combating the onset and progression of motion sickness; and to note whether or not there is a discernable similarity in the brains of the test subjects to indicate a common point of origin (epicenter) and propagation pattern of the effects of motion sickness in the brain. Eight male DOD personnel were used as subjects to complete twelve trials. Four subjects completed the phenytoin verses placebo double-blind crossover experiment. These four subjects experienced a 99% mean increase in their …

Go to article

Development Of An Image Registration Technique For Polar-Orbiting Satellites, Jerry L. Mehlberg Dec 1990

Development Of An Image Registration Technique For Polar-Orbiting Satellites, Jerry L. Mehlberg

Theses and Dissertations

In this thesis, a means to perform spatial registration (gridding) of meteorological satellite data is developed. It is applicable to Automatic Picture Transmission (APT) data from the TIROS-N series polar-orbiting satellites operated by the National Oceanic and Atmospheric Administration (NOAA). This technique does not require the use of ground control points. Registration is accomplished using an advanced orbital model to precisely compute the satellite's location based on NORAD two-line element sets and the time of the image. This technique is examined for accuracy and sensitivity to errors in the element set and satellite attitude control. This study involves over 70 …

Go to article

Improving Reliability In A Stochastic Communication Network, William L. Gaught Dec 1990

Improving Reliability In A Stochastic Communication Network, William L. Gaught

Theses and Dissertations

This research investigated the behavior of increasing the reliability of components in stochastic communication networks. A stochastic communication network is one in which the components, links and nodes, are not 100 percent reliable. In addition the reliability value, each component also has a capacity value that limits the flow through the component. The throughput in a stochastic communication network can be improved by increasing the capacity or the reliability of the individual components. A set of linear and nonlinear models was developed to determine the best investment strategy for increasing the reliability of individual components. Once the models were developed, …

Go to article

A Correlation And Forecasting Analysis On Lost Satellites, Kenneth R. Norton Dec 1990

A Correlation And Forecasting Analysis On Lost Satellites, Kenneth R. Norton

Theses and Dissertations

The relationship between the size of the United States Air Force Space Command's lost satellite lists and thirteen other variables is investigated. The thirteen variables contain the Space Surveillance Center crew's effort to work the lost list, solar activity, geomagnetic field strength, and the number of observations received each day from seven space track sensors. To identify the relationship of cause and effect between the lost lists and the thirteen variables, simple and multiple linear regressions are used on a data set that begins on 1 January 1988 and ends on 31 December 1988. Multiple linear regression and basic time-series …

Go to article

Debris Production In Hypervelocity Impact Asat Engagements, Stephen K. Remillard Dec 1990

Debris Production In Hypervelocity Impact Asat Engagements, Stephen K. Remillard

Theses and Dissertations

This study reviews laboratory experiments on hypervelocity impacts and applies the results from those experiments to predict the mass of debris produced, the number of particles, and the size distribution of the debris particles produced in an ASAT engagement using kinetic energy weapons. The three possible types of hypervelocity collisions are discussed and parameters are provided that will help predict what type of collisions will occur between a given projectile and a target satellite. Once the collision type is determined, various equations are supplied which can be used to calculate debris mass, etc. Next, a notional attack between a miniature …

Go to article

Proposed Design Of A Tactical Reconnaissance Satellite System, John D. T. Severance Dec 1990

Proposed Design Of A Tactical Reconnaissance Satellite System, John D. T. Severance

Theses and Dissertations

Tactical reconnaissance is a much needed wartime asset, yet with the deactivation of all active-duty RF-4C squadrons world-wide there appears to be a gap in this country's war-fighting capability. This study proposes a system which utilizes a constellation of small tactical satellites and mobile ground receiving stations that can fulfill the tactical reconnaissance mission. A literature review gives background information on resolution variables, the RF-4C, space reconnaissance, and sensing technologies. After defining system requirements and constraints, a basic system concept is determined. Three alternative systems, separated mostly by threat scenario, technology, and cost, are evaluated using Athey's Systematic Systems Approach. …

Go to article

First Prev Next Last