Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Engineering (5731)
- Physical Sciences and Mathematics (2947)
- Aerospace Engineering (1674)
- Electrical and Computer Engineering (1343)
- Operations Research, Systems Engineering and Industrial Engineering (1244)
-
- Computer Sciences (1234)
- Business (993)
- Physics (919)
- Operational Research (609)
- Signal Processing (459)
- Civil and Environmental Engineering (422)
- Computer Engineering (414)
- Aviation (353)
- Electrical and Electronics (351)
- Social and Behavioral Sciences (349)
- Operations and Supply Chain Management (346)
- Materials Science and Engineering (335)
- Optics (330)
- Oceanography and Atmospheric Sciences and Meteorology (278)
- Navigation, Guidance, Control and Dynamics (252)
- Other Operations Research, Systems Engineering and Industrial Engineering (233)
- Human Resources Management (231)
- Systems Engineering (228)
- Atomic, Molecular and Optical Physics (198)
- Electromagnetics and Photonics (195)
- Aerodynamics and Fluid Mechanics (188)
- Environmental Sciences (188)
- Environmental Engineering (185)
- Nuclear Engineering (180)
- Applied Mathematics (178)
- Keyword
-
- #antcenter (380)
- #csra (134)
- Machine learning (93)
- Decision making (89)
- Algorithms (75)
-
- Global Positioning System (75)
- Image processing (73)
- Kalman filtering (65)
- Optimization (64)
- #afcec (62)
- Computer networks--Security measures (62)
- Drone aircraft (59)
- Computer security (57)
- Target acquisition (57)
- Neural networks (Computer science) (54)
- Software engineering (54)
- Additive manufacturing (52)
- Remote sensing (49)
- Flight control (48)
- Microelectromechanical systems (45)
- Computer vision (44)
- Artificial satellites (43)
- Decision support systems (43)
- #ctisr (42)
- Adaptive optics (42)
- Composite materials (42)
- Neural networks (41)
- Simulation (41)
- Wireless communication systems (41)
- Scheduling (40)
- Publication Year
- Publication
- Publication Type
- File Type
Articles 8641 - 8670 of 8785
Full-Text Articles in Entire DC Network
Analysis Of Hypersonic Blunt-Body Flows Using A Total Variation Diminishing Scheme And The Maccormack Scheme, Montgomery C. Hughson
Analysis Of Hypersonic Blunt-Body Flows Using A Total Variation Diminishing Scheme And The Maccormack Scheme, Montgomery C. Hughson
Theses and Dissertations
An explicit second-order accurate, total variation diminishing (TVD) scheme and the MacCormack scheme are applied to the Euler equations in axisymmetric form to study hypersonic blunt body flows. The modified flux approach of Harten, with modification by Yee, for two-dimensional flows is extended to treat axisymmetric flows. Calculated flow properties for the steady state, blunt body problem such as shock standoff distance, bow shock shape, surface pressure distribution and entropy jump conditions are compared to theory, results from the MacCormack scheme, and experimental data for Mach numbers of 3.0, 4.03, 5.06, 6.03 and 8.1. Additionally, the TVD and MacCormack schemes …
Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel
Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel
Theses and Dissertations
The introduction of two-beam coupling in photorefractive materials has resulted in an extensive amount of research into their use as optical processing/computing elements. This dissertation develops the theoretical equations for two-beam coupling in barium titanate as an optical amplifier. One of the factors which limits the optical gain in photorefractive crystals is the loss of pump beam power to the amplification of parasitic light (beam fanning). This parasitic light is produced by light scattered from the pump beam by imperfections on both the crystal face and within the crystal. Through the analysis of signal and noise amplification as functions of …
Implementation Of The Modified Monte Carlo Technique Using Importance Sampling On The Block Oriented System Simulator, John B. Bennett
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 …
Model-Based 3-D Recognition System Using Gabor Features And Neural Networks, Phung D. Le
Model-Based 3-D Recognition System Using Gabor Features And Neural Networks, Phung D. Le
Theses and Dissertations
A different approach to pattern recognition was attempted using Gabor features, artificial neural nets, and an image generator. The Gabor features and artificial neural nets are sound biological-based, and the image generator provides complete access to any view of an object. This thesis tested the idea that their integration could form a robust 3-D recognition system. The results of the research showed that the Gabor features together with a neural net were used successfully in classifying objects regardless of their positions, out-of- plane rotations, and to a lesser extent in-plane rotations. The Gabor features were obtained by correlating the image …
Realistic Orbits About The Martian Moons, Samuel R. Bryant
Realistic Orbits About The Martian Moons, Samuel R. Bryant
Theses and Dissertations
Orbits about the Martian moons, Phobos and Deimos, previously found to be stable by the Poincare surface of section technique in a restricted three- body system, were investigated with non-zero eccentricity of the moons added to the dynamics of the planar four-body system (Mars, moon sun, artificial satellite). Although not strictly applicable to this case, the surface of section technique was used to verify whether or not the previously found stable orbits were realistic when a real world perturbation was added to the system dynamics. The surface of section technique involves the numerical integration of several orbits with the same …
A Low-Cost Part-Task Flight Training System: An Application Of A Head Mounted Display, David A. Dahn
A Low-Cost Part-Task Flight Training System: An Application Of A Head Mounted Display, David A. Dahn
Theses and Dissertations
To investigate the feasibility of using head-mounted display(HMD) and Computer Image Generators(CIG) in a low cost part-task trainer, we created a prototype system. Our approach was to build a virtual world interface using a HMD to an existing flight simulator application. This allowed a CIG with only one graphics channel to drive the display. To investigate which class of computing platform was suitable for use as the CIG, a cooperative thesis effort was launched to host the simulator on a mini-computer and micro-computer platform. The appropriate CIG could then be determined through demonstration and comparison between the systems. A software …
Autonomous Navigation Of A Satellite Cluster, Stephen C. Johnston
Autonomous Navigation Of A Satellite Cluster, Stephen C. Johnston
Theses and Dissertations
The relative position determination of a cluster of satellites operating in a low earth orbit is investigated. A U-D Covariance Factorization Kalman Filter is used for the on-board estimator with dynamics based on the Clohessy-Wiltshire equations. Measurements consist of range data between a single host satellite and the remaining cluster. Therefore only relative position and velocity states with respect to the host satellite can be determined. A 15 sample Monte Carlo simulation was conducted with clusters of 2, 5, and 10 satellites, respectively. Performance results consists of average error, average true error and filter covariance as a function of time.
Adaptive Filtering And Smoothing For Tracking A Hypersonic Aircraft From A Space Platform, Kenneth A. Gotski
Adaptive Filtering And Smoothing For Tracking A Hypersonic Aircraft From A Space Platform, Kenneth A. Gotski
Theses and Dissertations
This study took a previously developed six state Kalman filter (designed for space-based tracking of a hypersonic transatmospheric vehicle), tuned it, and performed a Monte Carlo analysis. Three multiple model adaptive filters were then developed, with sub-filters designed for quiescent periods and periods with apparent acceleration. Next, a smoother was developed using the six state filter as the forward filter and a form of that same filter as the backward filter. The smoother and all of the above filters were compared for their ability to most accurately estimate the transatmospheric vehicle's state, with special emphasis on the acceleration states. This …
A Comparison Of The Optimization And Analysis Of Doubly Curved Shells Using Msc/Nastran And Astros, John R. Dewsnap
A Comparison Of The Optimization And Analysis Of Doubly Curved Shells Using Msc/Nastran And Astros, John R. Dewsnap
Theses and Dissertations
This study identified techniques and software available for the optimization of doubly curved shells and applied them in the context of a large nozzle shape. An optimality criteria scheme that can reduce solution time was evaluated and compared to the Method of Feasible Directions. MSC/NASTRAN and ASTROS were used to perform finite element analysis and optimization, and the results were compared to the theory. The programs give virtually identical results, and if plates and shells are carefully modeled, then stresses, displacements and modes are accurate to within ten percent. A Mindlin-type axisymmetric finite element was implemented in ASTROS that preserved …
Analysis Of Periodic Orbits About The Martian Moons By Continuation Techniques, Frank Luria
Analysis Of Periodic Orbits About The Martian Moons By Continuation Techniques, Frank Luria
Theses and Dissertations
From a few known periodic orbits of Phobos and Deimos, continuation techniques were used to find entire families of stable orbits. These techniques involved varying a parameter, the Hamiltonian, of the system and analyzing how the orbital behavior changed with the parameter. Floquet multipliers, for stability analysis, were also computed. AUTO86, a continuation/bifurcation software package, was used in this study. Artificial energy dissipation had to be added to the conservative Hamiltonian system to enable use of AUTO.
Sql/Nf Translator For The Triton Nested Relational Database System, Craig W. Schnepf
Sql/Nf Translator For The Triton Nested Relational Database System, Craig W. Schnepf
Theses and Dissertations
The problem addressed in this thesis concerns the design and implementation of a high level data base query language translator based on the nested relational data model. The objective of the model is to increase the performance of the relational model by modeling real-world objects in the problem domain into nested relations. The translator is designed within the EXODUS extensible architectural framework for building application-specific database systems. The SQL/NF query language used for the nested relational model is an extension of the popular relational model query language SQL. The query language is translated into a nested relational algebra (Colby algebra) …
Investigation Of Direct And Indirect Optimization Algorithms For Aerospace Structures, Harry Hopkins Iii
Investigation Of Direct And Indirect Optimization Algorithms For Aerospace Structures, Harry Hopkins Iii
Theses and Dissertations
This thesis investigated the performance of two direct and two indirect methods of structural optimization. A gradient calculator and overall design system was created with the finite element code FRAME. Three of the methods were employed using this system with the fourth being a commercial available code. The algorithms were applied to two different sized trusses using static constraints and were measured for accuracy, reliability, and efficiency. Results for the problems tested showed the Direct methods were sensitive to starting designs and their performance depended on the proper selection of internal parameters. They were also shown to have a high …
Model-Based Reasoning In Electronic Repair, Kenneth B. Cohen
Model-Based Reasoning In Electronic Repair, Kenneth B. Cohen
Theses and Dissertations
Diagnosis is the process of identifying the cause for an observed behavior of a system. Model-based reasoning uses knowledge of the behavior of the component and the interconnection of the components to diagnose a system. This thesis investigates the application of model-based reasoning to the problem of isolating faulty components of an analog electronic circuit. More specifically, this thesis describes an architecture for a model-based diagnostic system for electronic modules, implements an assumption-based truth maintenance system (one of the component parts of a model-based diagnostic system), and creates the interface between the truth maintenance system and the diagnostic system.
Determining Concurrency In Object-Oriented Design Of Real-Time Embedded Systems Using Ada, Kenneth D. Baum
Determining Concurrency In Object-Oriented Design Of Real-Time Embedded Systems Using Ada, Kenneth D. Baum
Theses and Dissertations
One of the characteristics of real-time systems is concurrency. Designers of real-time systems have traditionally determined system concurrency at implementation time using the facilities of a cyclic executive. With the advent of programming language constructs for specifying concurrency, determining concurrency at design time has become a possibility. Several design methods, all of which are extensions of either Structured Design or Jackson System Development, provide heuristics to help the designer make concurrency decisions. The object-oriented approach, however, has no corresponding heuristics to aid designers of real-time systems. The purpose of this thesis was to develop heuristics to help designers make concurrency …
An Empirical Evaluation Of Analytical Models For Parallel Relational Database Queries, Mark C. Denham
An Empirical Evaluation Of Analytical Models For Parallel Relational Database Queries, Mark C. Denham
Theses and Dissertations
This thesis documents the design and implementation of three parallel join algorithms to be used in the verification of analytical models developed by Kearns. Kearns developed a set of analytical models for a variety of relational database queries. These models serve as tools for the design of parallel relational database system. Each of Kearns' models is classified as either single step or multiple step. The single step models reflect queries that require only one operation while the multiple step models reflect queries that require multiple operations. Three parallel join algorithms were implemented based upon Kearns' models. Two are based upon …
Access And Operator Methods For The Triton Nested Relational Database System, Tina M. Harvey
Access And Operator Methods For The Triton Nested Relational Database System, Tina M. Harvey
Theses and Dissertations
Unique database requirements in the realm of non-standard applications (such as computer-aided design (CAD), computer-aided software engineering(CASE), and office information systems (OIS) have driven the development of new data models and database systems based on these new models. In particular, the goal of these new database systems is to exploit the advantages of complex data models that are more efficient (in terms of time and space) than their relationship counterparts. This research effort describes the relational design and implementation of the Triton nested relational database system, a prototype system based on the nested relational data model. Triton is intended to …
An Object Oriented Design And Implementation Of The Idef0 Essential Data Model Using Ada And An Ada Based Expert System, Terry L. Kitchen
An Object Oriented Design And Implementation Of The Idef0 Essential Data Model Using Ada And An Ada Based Expert System, Terry L. Kitchen
Theses and Dissertations
This thesis develops and implements an Ada based object oriented design (OOD) of the IDEF0 Essential Data Model called the Essential Subsystem, which includes an Ada based expert system for IDEF0 model syntax checking. IDEF0 is a graphic approach to system description development by SofTech, Inc. for the U.S. Air Force Program for Integrated Computer Aided Manufacturing (ICAM) and is a subset of the Structured Analysis (SA) language (30, 36). The IDEF0 Essential Data Model is an entity-relationship (E-R) model of the IDEF0 language and represents the fundamental (essential) information of an IDEF0 model. …
The Development Of A Graphical Notation For The Formal Specification Of Software, Gene A. Place
The Development Of A Graphical Notation For The Formal Specification Of Software, Gene A. Place
Theses and Dissertations
The program tranformations lifecycle model, proposed by Balzer in 1984, may hold the key to dramatic leap in software engineer productivity necessitated by the tremendous growth in the world's demand for software. This leap in productivity is made possible by the program transformation lifecycle's reliance on formal specifications rather than programs as the primary vehicle for the creation and maintenance of software systems. Because formal specifications are concerned only with system behaviors and not implementation details, formal specifications tend to present critical system characteristics much more concisely than programs. The major disadvantage of using formal specifications in a software development …
An Object-Oriented Military Simulation Baseline For Parallel Simulation Research, Robert J. Rizza
An Object-Oriented Military Simulation Baseline For Parallel Simulation Research, Robert J. Rizza
Theses and Dissertations
This thesis documents the design and implementation of a discrete event military simulation using a modular object-oriented design and the C programming language. The basis simulation is one of interacting objects. The objects move along a predetermined path until they encounter another object. Objects react to the encounter object according to the implemented algorithm. Object reaction options are fight, evade, or do nothing. In the code's current form it is generic enough to allow a user the flexibility of creating an infinite number of scenarios bounded in size by the hardware's memory capacity. The modularity of design will allow for …
Mapping An Object-Oriented Requirements Analysis To A Design Architecture That Supports Design And Component Reuse, Kelly L. Spicer
Mapping An Object-Oriented Requirements Analysis To A Design Architecture That Supports Design And Component Reuse, Kelly L. Spicer
Theses and Dissertations
Design reuse has more potential for increasing the productivity of software development and maintenance than do traditional approaches to software reuse that emphasize reuse of smaller components. Current software development methods do not promote design reuse. The literature contains limited documented research on the subject, but enough that some design reuse principles can be gleaned. Among these principles are that reusable designs should be applicable within some domain of application, have a consistent structure, provide a method for instantiating the design, avoid object nesting, and promote reuse of smaller components as well. A design mapping method from an object-oriented requirements …
An Ada-Based Framework For An Idef0 Case Tool Using The X Window System, Jay-Evan J. Tevis Ii
An Ada-Based Framework For An Idef0 Case Tool Using The X Window System, Jay-Evan J. Tevis Ii
Theses and Dissertations
This thesis documents the design strategy, implementation methodology, testing, and evaluation used in developing an Ada-based framework for SAtool II using the X Window System. SAtool II is an IDEF0 graphical project editor and data dictionary editor. An Ada-Based Framework for an IDEF0 Case Tool Using the X Window System is the ICAM Definition Method Zero graphical notation language adopted by the U.S. Air Force to produce a function model of a manufacturing system or environment (23:1-1). The Air Force Institute of Technology is conducting on-going research in the use of IDEF0 in the requirements analysis phase …
A Hypermedia Implementation For Reusable Software Component Representation, Gary G. Worrall
A Hypermedia Implementation For Reusable Software Component Representation, Gary G. Worrall
Theses and Dissertations
This study investigated software component representation methods. Hypermedia was chosen as the implementation method to represent a collection of reusable software components. The hypermedia implementation organizes knowledge about the component collection into a web of small information chunks called frames. The set of software components was represented using a hybrid classification scheme composed of enumerated and faceted parts. The enumerated part enables the user to progress along a path in a taxonomic tree, narrowing the scope of eligible components. Each leaf node in this tree denotes a class of components, members of which are distinguished by their time and space …
A Remote Visual Interface Tool For Simulation Control And Display, William J. Derouchey
A Remote Visual Interface Tool For Simulation Control And Display, William J. Derouchey
Theses and Dissertations
This thesis discusses the design and development of the Visual Interactive Simulation Interface Tool (VISIT). VISIT was designed to provide the graphical representation and user interface for a simulation that is running on another processor utilizing internet communications. The system provides support for various input devices to control the simulation display and environment. Simulation objects are displayed using either a three-dimensional wireframe representation or a Gouraud shaded representation. Viewer interaction to the simulation is provided by a collection of commands that allow the viewer to initialize, start, stop, abort, and restart the simulations. The viewer also has the ability to …
Brightness Invariant Port Recognition For Robotic Aircraft Refueling, Richard A. Bennett
Brightness Invariant Port Recognition For Robotic Aircraft Refueling, Richard A. Bennett
Theses and Dissertations
The purpose of this thesis effort was to develop and test a brightness invariant recognition algorithm that would locate and identify the half-scale mock up of a Universal Aerial Refueling Receptacle Slipway Installation (UARRSI) aerial refueling port in different lightening conditions. This was accomplished by developing a brightness invariant port recognition of identifiable attributes of the refueling port to locate and identify the UARRSI port. Based on this approach, a brightness invariant port recognition system (BIPRS) was demonstrated which identified the refueling receptacle in different lightening conditions. The BIPRS was also invariant to orientation and size of the UARRSI port. …
Fractal Geometry Segmentation Of High Resolution Polarimetric Synthetic Aperture Radar Data, Joseph L. Brickey
Fractal Geometry Segmentation Of High Resolution Polarimetric Synthetic Aperture Radar Data, Joseph L. Brickey
Theses and Dissertations
This thesis investigated the potential of fractal dimension estimation for segmenting high resolution polarimetric synthetic aperture radar. The data used during this research were collected with the Advanced Detection Technology Sensor (ADTS) developed by Massachusetts Institute of Technology Lincoln Laboratory with Defense Advanced Research Projects Agency funding. ADTS is a fully polarimetric calibrated 35 GHz SAR with one foot impulse response. A method of applying the correlation dimension algorithm developed by Grassberger and Procaccia for estimating the dimension of time series data was implemented to estimate the correlation dimension of polarimetric SAR data. A threshold sensitivity study was performed to …
Interference Cancellation In Rf Signals Using Adaptive Array Techniques, Mark E. Brown
Interference Cancellation In Rf Signals Using Adaptive Array Techniques, Mark E. Brown
Theses and Dissertations
This study investigated the effectiveness of the Least Means Squared (LMS) algorithm against various types of common jammers. The LMS algorithm was implemented using the Block Oriented Systems Simulator (BOSS). The LMS algorithm was inserted at the output of a two element antenna array. The array was configured so as to have one-half wavelength spacing. A quadrature hybrid signal structure was used. The array was then tested against a barrage and sweep jammer. The barrage jammer testing consisted of varying each of the three available jammer parameters; power, frequency and angle of arrival individually. The sweep jammer testing consisted of …
Evaluation Of An Interdigitated Gate Electrode Field-Effect Transistor For Detecting Organophosphorus Compounds, Charles P. Brothers Jr.
Evaluation Of An Interdigitated Gate Electrode Field-Effect Transistor For Detecting Organophosphorus Compounds, Charles P. Brothers Jr.
Theses and Dissertations
This study used integrated circuit microsensors to detect organophosphorus compounds. Chemically-sensitive thin films, copper phthalocyanine, DFPase, succinyl chloride, succinylcholine chloride, 2- naphthol(B), and L-histidine dihydrochloride,were deposited on interdigitated gate electrode (IGE) structures, with an average thickness of 2000A. Thin film electrical performance characteristics were measured for several parameters, including: DC resistance, AC impedance, time-domain, and spectral responses from 10 Hz to 1 MHz. Each microsensor contained nine IGEs; each IGE possessed an in situ field-effect transistor amplifier. After purging each sensor with filtered air, it was exposed to one or two of the following gases: diisopropyl fluorophosphate (DFP), diisopropyl methylphosphonate, …
Predicting The Performance Of Airborne Antennas In The Microwave Regime, David P. Carroll
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 …
Classification Of Correlation Signatures Of Spread Spectrum Signals Using Neural Networks, Richard A. Chapman
Classification Of Correlation Signatures Of Spread Spectrum Signals Using Neural Networks, Richard A. Chapman
Theses and Dissertations
The major goals of this thesis were to determine if Artificial Neural Networks (ANNs) could be trained to classify the correlation signatures of two classes of spread spectrum signals and four classes of spread spectrum signals. Also, the possibility of training an ANN to classify features of the signatures other than signal class was investigated. Radial Basis Function Networks and Back-Propagation Networks were used for the classification problems. Correlation signatures of four types or classes were obtained from United States Army Harry Diamond Laboratories. The four types are as follows: direct sequence (DS), linearly-stepped frequency hopped (LSFH), randomly-driven frequency hopped …
Numerical Approximations Of The Green's Functions For A Theoretical Model Of An Aperture Fed Stacked-Patch Microstrip Antenna, Ronald E. Erwert
Numerical Approximations Of The Green's Functions For A Theoretical Model Of An Aperture Fed Stacked-Patch Microstrip Antenna, Ronald E. Erwert
Theses and Dissertations
The numerical approximations of the Green's functions for a theoretical model of an aperture fed stacked patch microstrip antenna are presented. The Green's functions approximated are those developed by Nazar (AFIT Thesis GE-89D-37), Green's Functions for a Theoretical Model of an Aperture Fed Stacked-Patch Microstrip Antenna. Each complex valued Green's function was written as a function of the source-observer separation. The behavior of each Green's function was analyzed, and it was found that they could all be approximated by three separate functions. The approximating functions were either polynomials or rational functions composed of polynomials. One component could be approximated by …