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Air Force Institute of Technology

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Articles 1261 - 1290 of 1328

Full-Text Articles in Electrical and Computer Engineering

An Investigation Of A Design For A Finite-Difference Time Domain (Fdtd) Hardware Accelerator, James R. Marek Dec 1991

An Investigation Of A Design For A Finite-Difference Time Domain (Fdtd) Hardware Accelerator, James R. Marek

Theses and Dissertations

This study investigated increasing the speed of Finite-Difference Time Domain (FDTD) cell calculations through a special purpose architecture using Very Large Scale Integration (VLSI). These FDTD cell equations model inhomogeneous, isotropic, lossy magnetic and dielectric materials. Special attention was given to simplicity and performance, using the fastest components generally available in AFIT VLSI programs, while attempting to minimize component count. A VHSIC Hardware Description Language simulation of the proposed chip established design feasibility and provided performance estimates: 350 ns to generate the first cell value, 200 ns thereafter (30 MFLOPS maximum double-precision). This study also implemented boundary conditions in hardware …

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Sensing Refractive Turbulence Profiles Using Wave Front Slope Measurements From Two Reference Sources, Michael D. Rejack Dec 1991

Sensing Refractive Turbulence Profiles Using Wave Front Slope Measurements From Two Reference Sources, Michael D. Rejack

Theses and Dissertations

This thesis examines a remote sensing technique for measuring the atmospheric structure constant as a function of altitude by performing spatial correlation or wavefront sensor measurements. Two point sources are used to irradiate two wavefront sensors in the aperture plane of an optical system. The geometric relationship between the sources and the sensors gives rise to crossed optical paths. At the point where the paths cross, the correlation value of the turbulence contributions will be at a peak. The correlation is shown to be mathematically related to the structure constant in terms of an integral of the structure constant multiplied …

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Image Segmentation Using Affine Wavelets, Steven E. Smiley Dec 1991

Image Segmentation Using Affine Wavelets, Steven E. Smiley

Theses and Dissertations

This thesis discusses the use of the multiresolution representation and Radial Basis Function (RBF) neural networks to segment both FLIR and SAR imagery. The multiresolution approximation coefficients are used as features into the RBF network which learns to distinguish between different cultural and natural regions or objects. The wavelets used are Mallat's spline wavelet and Daubechies' compactly supported wavelets. Additionally, this thesis provides an explanation of wavelets in a tutorial manner. It introduces wavelet theory and discusses two different approaches to generating the multiresolution or wavelet representation.

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Face Recognition With The Karhunen-Loeve Transform, Pedro F. Suarez Dec 1991

Face Recognition With The Karhunen-Loeve Transform, Pedro F. Suarez

Theses and Dissertations

The major goal of this research was to investigate machine recognition of faces. The approach taken to achieve this goal was to investigate the use of Karhunen-Loe've Transform (KLT) by implementing flexible and practical code. The KLT utilizes the eigenvectors of the covariance matrix as a basis set. Faces were projected onto the eigenvectors, called eigenfaces, and the resulting projection coefficients were used as features. Face recognition accuracies for the KLT coefficients were superior to Fourier based techniques. Additionally, this thesis demonstrated the image compression and reconstruction capabilities of the KLT. This theses also developed the use of the KLT …

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Electromagnetic Scattering From Dielectric Pyramidal Tips, Albert D. Tyson Iv Dec 1991

Electromagnetic Scattering From Dielectric Pyramidal Tips, Albert D. Tyson Iv

Theses and Dissertations

This thesis investigated the electromagnetic scattering from conducting, lossless dielectric, and lossy dielectric (absorber) pyramids. The backscatter from pyramids was measured and a time gate was applied to isolate the scattering from the tips. The measured results were compared to predictions from an approximate Uniform Theory of Diffraction (UTD) solution for scattering by a dielectric corner. The accuracy of the corner diffraction solution was found to be dependent on the polarization of the incident electric field. The accuracy of the UTD solution was also dependent on the aspect angle to the pyramid: the UTD solution gave a nominally correct answer …

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An Investigation Of The Application Of Artificial Neural Networks To Adaptive Optics Imaging Systems, Andrew H. Suzuki Dec 1991

An Investigation Of The Application Of Artificial Neural Networks To Adaptive Optics Imaging Systems, Andrew H. Suzuki

Theses and Dissertations

Recurrent and feedforward artificial neural networks are developed as wavefront reconstructors. The recurrent neural network studied is the Hopfield neural network and the feedforward neural network studied is the single layer perceptron artificial neural network. The recurrent artificial neural network input features are the wavefront sensor slope outputs and neighboring actuator feedback commands. The feedforward artificial neural network input features are just the wavefront sensor slope outputs. Both artificial neural networks use their inputs to calculate deformable mirror actuator commands. The effects of training are examined.

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Design And Testing Of A Lightweight, Planar Microwave Lens, Paul M. Proudfoot Dec 1991

Design And Testing Of A Lightweight, Planar Microwave Lens, Paul M. Proudfoot

Theses and Dissertations

This thesis documents the design, fabrication, and testing of a lightweight, planar microwave lens. The lens consists of two planar arrays of lightweight printed circuit antennas interconnected by microstrip lines whose length varies as a function of position on the lens. Microwave energy is coupled from one face of the lens to the other by means of a slot etched in the ground plane. At 8.0 GHz the lens is ten wavelengths across, is less than 1/8 inch thick, and weighs less than 4 pounds. The lens can scan a beam over a +/- 30 degree region in both the …

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Back-Contact Vertical-Junction Solar Cell And Method, Michael W. Carver, Edward S. Kolesar Jr. Nov 1991

Back-Contact Vertical-Junction Solar Cell And Method, Michael W. Carver, Edward S. Kolesar Jr.

AFIT Patents

An interdigitated back-contact vertical-junction solar cell which utilizes an anisotropically etched 110-oriented silicon crystal wafer. The cell structure includes rounded corner top edges of the between cell channel walls in order to improve light capturing ability and also has pn-junctions disposed over all of the cavity internal surfaces. Additional pn-junctions are located on the rear surface of the cell array to assist in generated carrier collection into a rear mounted metallic conductor grid. The disclosed cell has desirable transducer efficiency, without the use of anti-reflection coatings, and previous improved physical robustness, and radiation hardening. Fabrication of the cell array includes …

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Comparative Analysis Of Guidance Algorithms For The Hyper Velocity Missile And Afti/F-16, Edward G. Rice Nov 1991

Comparative Analysis Of Guidance Algorithms For The Hyper Velocity Missile And Afti/F-16, Edward G. Rice

Theses and Dissertations

This project has provided me with endless intrigue. In considering the problem of guiding a hyper-velocity missile from a moving platform to a moving target, a common perception said it was just another Kalman Filtration design challenge. I began with lofty intentions of running a full up extended Kalman filter simulation but I became enthralled with the limited work available on the physical limitations of basic guidance algorithms. This became the emphasis of this project. The best filter scheme cannot overcome a guidance algorithms physical limitation. Only with an understanding of these limitations can one effectively integrate a guidance scheme …

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Steady-State Production And Quenching Of Br(2P½), Ralph F. Tate Nov 1991

Steady-State Production And Quenching Of Br(2P½), Ralph F. Tate

Theses and Dissertations

The spin orbit relaxation of atoms has been investigated in a steady state infrared fluorescence experiment. A CW argon ion laser operating at 488 nm was used to photodissociate gas-phase Br into equal quantities of Bromine and Bromine atoms. The resulting 2.7 µm emission was observed as a function of added quenching gas. A steady-state analysis was used to determine quenching rates for SF6, N2, O2, He, Ne, Ar, Kr, and Xe, relative to quenching by the parent molecule. Limitations in the apparatus prevented determination of the quenching rate coefficient for Br2. …

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Application Of Mixed H2/H∞ Optimization, John J. Kusnierek Nov 1991

Application Of Mixed H2/H∞ Optimization, John J. Kusnierek

Theses and Dissertations

A non-conservative optimization technique is utilized to examine the problem of minimizing the 2 norm of one transfer function subject to an ∞-norm bound on another transfer function. For single exogenous input/ single exogenous output systems this non conservative mixed solution is shown to be up to 5% better in a specific example. For single exogenous input/two exogenous output systems the mixed solution is shown to be up to 27% better than a previous technique for a specific example. Finally, a two exogenous input/two exogenous output practical system is examined to demonstrate the utility of this mixed optimization technique.

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Gaseous Component Identification With Polymeric Film Sensor, Edward S. Kolesar Jr. Sep 1991

Gaseous Component Identification With Polymeric Film Sensor, Edward S. Kolesar Jr.

AFIT Patents

A sensor having an interdigitated gate electrode field effect transistor (IGEFET) coupled to an electron beam evaporated copper phthalocyanine thin film is used to selectively detect parts-per-billion concentration levels of atmosphere contaminants such as nitrogen dioxide (NO2) and diisopropyl methylphosphonate (DIMP). The sensor is excited with a voltage pulse, and its time- and frequency-domain response are examined. The envelopes of the magnitude of the normalized difference frequency spectrums reveal features which unambiguously distinguish the NO2 and DIMP exposures.

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A Prolog System For Converting Vhdl-Based Models To Generalized Extraction System (Ges) Rules, Michael A. Dukes, Frank M. Brown, Joanne E. Degroat Jun 1991

A Prolog System For Converting Vhdl-Based Models To Generalized Extraction System (Ges) Rules, Michael A. Dukes, Frank M. Brown, Joanne E. Degroat

AFIT Documents

With the advent of VHDL accurate documentation of hardware designs is a practical reality. In the past, schematics were typically used for documentation of hardware designs. However, these schematics would usually become obsolete as the hardware design was being constructed. Deviations in the hardware design would sometimes not be reflected in the schematics. For design groups, failure to update schematics could lead to different parts of a hardware design becoming incompatible. A system to ensure compliance of hardware with its VHDL documentation is presented in this paper. The system, vhdl2ges, is meant to help guide the development of hardware by …

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A Multiple Model Adaptive Estimator Using First And Second-Order Acceleration Models For Use In A Forward-Looking Infrared Tracker, Barbara J. Niblett Jun 1991

A Multiple Model Adaptive Estimator Using First And Second-Order Acceleration Models For Use In A Forward-Looking Infrared Tracker, Barbara J. Niblett

Theses and Dissertations

The performance of a multiple model adaptive estimator (MMAE) for an enhanced correlator/forward-looking-infrared tracker for airborne targets is analyzed in order to improve its performance. Performance evaluation is based on elemental filter selection and MMAE estimation error sizes and trends. The elemental filters are based on either first or second-order acceleration models. Improved filter selection is achieved by using acceleration models that separate the frequency content of acceleration power spectral densities into non- overlapping regions with second-order models versus the more traditional overlapping regions with first-order models. A revised tuning method is presented. The maximum a posteriori (MAP) versus the …

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Investigation Of Adaptive Controllers For Puma Trajectory Tracking, Daniel J. Sims Jun 1991

Investigation Of Adaptive Controllers For Puma Trajectory Tracking, Daniel J. Sims

Theses and Dissertations

Two robust model-based controllers and two decentralized adaptive controllers are experimentally evaluated. Algorithm evaluation is motivated by the need for controllers with good high speed tracking under varying payload conditions. The test case is a PUMA-560 robotic manipulator operating over the standard test suite. The model-based controllers are made robust by the addition of either an auxiliary input term or an adaptive feedforward compensator based on Lyapunov Theory. The model-based auxiliary input controller (MBAIC) adapts the gain matrices used in computing an additional torque to be combined with model-based feedforward and PD feedback torques. The adaptive model-based controllers adapt the …

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A Vision System Model, Erik J. Fretheim Jun 1991

A Vision System Model, Erik J. Fretheim

Theses and Dissertations

This dissertation provides four major contributions to the field of vision research. The first contribution is a general vision system model. The model, which blends biological as well as technological methods into a coherent approach to vision, will provide a basis for implementing vision systems. The second contribution of this dissertation is to demonstrate particular implementations of portions of the model. These implementations will include methods for using Gabor wavelets in edge detection, in preprocessing images for use as feature vectors in backpropagation neural networks, and as basis functions in a recognition/reconstruction network, as well as methods for integrating color …

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High Frequency Scattering Code In A Distributed Processing Environment, Scott Suhr Jun 1991

High Frequency Scattering Code In A Distributed Processing Environment, Scott Suhr

Theses and Dissertations

Government agencies and academic institutions are very interested programming for concurrent processing to cut computer processing time. However, many of the world's problems have already been coded for conventional serial computers. This research demonstrates the feasibility of modifying existing serial codes for execution in a concurrent processing environment. A electromagnetic scattering prediction code known as NECBSC is incrementally modified to incorporated various levels of concurrent computing. The data processed by the code are completely independent, providing an avenue for data decomposition of the process. Portions of the data set are processed on each mode and the results combined for final …

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Development Of A Personal Computer Simulation Program Of The Ln-94 Inertial Navigation System, Thomas E. Flynn Jun 1991

Development Of A Personal Computer Simulation Program Of The Ln-94 Inertial Navigation System, Thomas E. Flynn

Theses and Dissertations

This thesis develops a simulation that emulates a Litton LN-94 INS. Real time simulation is achieved for a stationary navigation case and a straight-and-level flight trajectory are provided to exercise the simulation dynamics. The user interface is simple and requires little previous knowledge to operate. The communication link with the MILSTD 1553B bus provide a realistic environment in which to collect and analyze data. The simulation is processed on an 80386 IBM compatible personal computer. A 23-state INS error model is implemented and integration is performed by a fifth-order Kutta-Merson routine. The simulation is interfaced to a plotting routine and …

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An Alternative Algorithm For Discrete-Time Filtering, Frederick H. Zeitz Iii Jun 1991

An Alternative Algorithm For Discrete-Time Filtering, Frederick H. Zeitz Iii

Theses and Dissertations

The discrete-time Kalman filter is a conditional mean estimator of the states of a linear stochastic process, conditioned on the previous state and current measurements. It assumes that the states and noise inputs can be represented as jointly Gaussian random variables. The influence diagram is a decision analysis tool. Under certain conditions, it can represent continuous, jointly Gaussian random variables. The conditioning order of the random variables may be changed (using Bayes' rule) so that any random variable can be conditioned on any other subset of random variables in the diagram. Under these conditions, an influence diagram can represent the …

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Hybrid Wafer Scale Microcircuit Integration -- [ 5008213 ], Edward S. Kolesar Jr. Apr 1991

Hybrid Wafer Scale Microcircuit Integration -- [ 5008213 ], Edward S. Kolesar Jr.

AFIT Patents

A wafer scale integration arrangement wherein integrated circuit die of varying size, fabrication processes, and function are commonly mounted in the same host wafer using a filled epoxy material of special characteristics. The mounting epoxy material also serves as a substrate for the die interconnecting conductors in regions adjacent the mounted die. The described assembly also includes a newly available photosensitive polyimide material as a planarization and passivation covering for the die and hose wafer and as a mounting surface for an interconnecting metal conductor array. Multiple levels of interconnection metal. Fabrication processes for the die to host wafer attachment …

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Afit/Afosr Symposium On Applications Of Wavelets To Signal Processing, Volume Ii, Tutorial Notes, Gregory T. Warhola, Mark E. Oxley, Steven K. Rogers, Matthew Kabrisky, Bruce W. Suter Mar 1991

Afit/Afosr Symposium On Applications Of Wavelets To Signal Processing, Volume Ii, Tutorial Notes, Gregory T. Warhola, Mark E. Oxley, Steven K. Rogers, Matthew Kabrisky, Bruce W. Suter

AFIT Documents

The Air Force Institute of Technology (AFIT) hosted the Symposium on Applications of Wavelets to Signal processing during 20-22 March 1991 at the AFIT Science and Research Center, Wright-Patterson AFB, OH. This was the first major academic meeting of its kind held at AFIT. The symposium was sponsored by the Air Force Office of Scientific Research (AFOSR), Bolling AFB, DC. It focused on applications of wavelets to problems in image and speech processing, communications, and graphics and opened with a one-day short course, 'A Tutorial on Wavelets.' The symposium was attended by more than 220 researchers worldwide. They represented 15 …

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Modifications To Mcnp, Version 3b: Incorporating A Variable Density Atmosphere. Addendum, David L. Monti, Kirk A. Mathews Mar 1991

Modifications To Mcnp, Version 3b: Incorporating A Variable Density Atmosphere. Addendum, David L. Monti, Kirk A. Mathews

AFIT Documents

MCNP version 3B was modified to incorporate a continuously variable density atmosphere. This was accomplished by representing the variation of air density as a function of altitude with a series of continuous piecewise exponential curves up to a maximum altitude of 1000 km. User-written subroutines and functions were written which incorporated these piecewise functions. These subroutines and functions were subsequently incorporated into a production version of MCNP. Several MCNP subroutines and files were modified in support of these modifications. This report discusses detailed information regarding the theoretical development of the variable density model, the user written subroutines and functions, the …

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A Fully Coupled, Automated Formation Control System For Dissimilar Aircraft In Maneuvering Formation Flight, Paul R. Rohs Mar 1991

A Fully Coupled, Automated Formation Control System For Dissimilar Aircraft In Maneuvering Formation Flight, Paul R. Rohs

Theses and Dissertations

This study developed a fully automated formulation control system, capable of controlling a number of like or dissimilar aircraft in maneuvering formation flight. C-130 fixed wing aircraft and H-53 helicopters were modelled in various formulations and simulated through a mix of maneuvers. External formation guidance was assumed as a single data burst of nominal function guidance commands and separation distances for each wing aircraft in the formation. No communication was assumed between formation aircraft. Wing aircraft track lead aircraft maneuvering with an ideal on-board sensor, maneuvering to maintain relative position. It was determined that lead aircraft inputs must be attenuated …

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A Navigation Reference System (Nrs) Using Global Positioning System (Gps) Aiding, Richard D. Stacey Mar 1991

A Navigation Reference System (Nrs) Using Global Positioning System (Gps) Aiding, Richard D. Stacey

Theses and Dissertations

To quantify the performance abilities of existing or proposed navigation systems, the U.S. Air Force has for the last several years compared the performance of the system under test to the performance of a baseline navigation system known as the Completely Integrated Reference Instrumentation System (CIRIS). CIRIS obtains a highly accurate navigation solution by combining the output from three major subsystems: inertial navigation system (INS) information, barometric altitude information, and range and range-rate data from ground transponders which have been precisely surveyed. Although the navigation solution produced by CIRIS is highly accurate, it will soon be inadequate as the standard …

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Hybrid Wafer Scale Microcircuit Integration -- [ 4989063 ], Edward S. Kolesar Jr. Jan 1991

Hybrid Wafer Scale Microcircuit Integration -- [ 4989063 ], Edward S. Kolesar Jr.

AFIT Patents

A wafer scale integration arrangement wherein integrated circuit die of varying size, fabrication processes, and function are commonly mounted in the same host wafer using a filled epoxy material of special characteristics. The mounting epoxy material also serves as a substrate for the die interconnecting conductors in regions adjacent the mounted die. The described assembly also includes a newly available photosensitive polyimide material as a planarization and passivation covering for the die and host wafer and as a mounting surface for an interconnecting metal conductor array. Multiple levels of interconnection metal. Fabrication processes for the die to host wafer attachment …

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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 …

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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 …

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Implementation Of The Modified Monte Carlo Technique Using Importance Sampling On The Block Oriented System Simulator, John B. Bennett Dec 1990

Implementation Of The Modified Monte Carlo Technique Using Importance Sampling On The Block Oriented System Simulator, John B. Bennett

Theses and Dissertations

The purpose of this thesis was to implement the Modified Monte Carlo technique using Importance Sampling on the Block Oriented System Simulator (BOSS). Computer simulation techniques of communications systems were reviewed. Next, conventional Monte Carlo techniques and Modified Monte Carlo techniques using Importance Sampling were reviewed. Models of Binary Phase Shift Keying (BPSK) systems using both Monte Carlo techniques were implemented and simulated. Reasons for the model using Importance Sampling not working correctly are postulated. The Monte Carlo technique is a method of ensuring the an inherently infinite procedure, such as determining system bit error rate (BER), can be determined …

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Predicting The Performance Of Airborne Antennas In The Microwave Regime, David P. Carroll Dec 1990

Predicting The Performance Of Airborne Antennas In The Microwave Regime, David P. Carroll

Theses and Dissertations

This study investigated the application of a high-frequency model (Uniform Geometrical Theory of Diffraction) of electromagnetic sources mounted on a curved surface of a complex structure. In particular, the purpose of the study was to determine if the model could be used to predict the radiation patterns of cavity-backed spiral antennas mounted on aircraft fuselages so that the optimum locations for the antennas could be chosen during the aircraft design phase. A review of literature revealed a good deal of work in modeling communications, navigation, identification antennas (blade monopoles and aperture slots) mounted on a wide variety of aircraft fuselages …

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Network Reduction Using Error Prediction, Michael V. Gilsdorf Dec 1990

Network Reduction Using Error Prediction, Michael V. Gilsdorf

Theses and Dissertations

This thesis investigates gradient descent learning algorithms for multi-layer feed forward neural networks. A technique is developed which uses error prediction to reduce the number of weights/nodes in a network. The research begins by studying the first and second order back-prop training algorithms along with their convergence properties. A network is reduced by making an estimate of the amount of error which would occur when a weight(s) is removed. This error estimate is then used to determine if a particular weight is essential to the operation of the network. If not, it is removed and the network retrained. The process …

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