A transformation between minimum dimension adjoint variables and redundant adjoint variables is derived in this dissertation. The transformation is then applied between the adjoint variables associated with Cartesian position and velocity vectors and a set of redundant adjoint variables associated with certain regularized variables (Schumacher variables). This transformation proves to be very beneficial when it is applied to minimum-fuel space rendezvous and intercept problems. It facilitates using attributes from the two systems simultaneously; a new necessary condition in Schumacher adjoints is derived in this dissertation, and this together with classical necessary conditions for fuel-optimal transfer (existing in the position and velocity space) leads to a numerical algorithm which seems to be quite robust in finding candidate optimal control solutions for space transfer problems. / Ph. D.

This dissertation presents a new approach to the generation of integration systems for CAD/CAM application programs which enlists the tools and methodologies of computer aided software engineering, also referred to as CASE. A CASE workbench is described which aids in the design, analysis and automatic generation of program code for the integration of CAD/CAM applications based on a variety of integration models. The requirements and detail design of a CASE integration toolkit, which will be incorporated into the CAD/CAM CASE workbench, is presented. This toolkit assists with the identification of vital information from the CAD/CAM application programs, such as code structure, comment blocks and explicit information about the occurrence and location of variables, arrays and subprograms, that is not normally supplied by compilers or other source code analysis tools. This specialized toolkit helps to quickly acquaint the integration system designer with unfamiliar application programs and greatly assists in the integration process. The information obtained by the CASE integration toolkit is subsequently passed into the CASE design and analysis toolkits and used to assist in the semi-automatic generation of the integration system. As a basis for many of the ideas in this research, a survey of CAD/CAM integration in industry was undertaken. A wide variety of Fortune 500 companies participated in this project, providing important information on current integration methods, problems and needs. A synopsis of the survey questions and responses is presented. Additionally, a new integration model, referred to as the High-level Autonomous Integration Model (HAIM), is also described. The autonomous integration model allows a higher-level of integration than is normally considered through the utilization of the X Window System and database methods. This model includes the transfer of necessary data as well as simultaneous execution of application programs and the ability to share menus and functions between applications. The CAD/CAM CASE workbench and integration toolkit are designed to assist an integration system designer with the tedious tasks necessary in any CAD/CAM applications integration. This is not meant to infer that the workbench allows complete automation of the integration process. A skilled and knowledgeable designer, however, can save a great deal of time through the utilization of the analysis, design and generation capabilities provided by the CAD/CAM CASE workbench. A description of the necessary skills and tasks performed by the systems integration designer is also included. / Ph. D.

We develop a systematic approach to the problem of finding the perturbative expansion for the topological pressure for an analytic expanding dynamics (/, M) on a Riemannian manifold M. The method is based on the spectral analysis of the transfer operator C. We show that in typical cases, when / depends real-analytically on a set of perturbing parameters ,", the related operators C~ form an analytic family. This gives rise to the rigorous construction of the power series expansion for the pressure via the analytic perturbation theory for eigenvalues, [Kato]. Consequently, the pressure and related dynamical indices, such as dimension spectra, Lyapunov exponents, escape rates and Renyi entropies inherit the real-analyticity in ~ from (I,M). / Ph. D.

A measurement tool has been developed to estimate errors in relaying current transformers and voltage transformers. The tool has been developed to collect data in a substation and send it to a remote location over a telephone line. Different schemes were evaluated and tested in the laboratory. The final choice was made on the basis of the hardware and transmission cost constraints. The measurement unit was developed using hardware similar to that used in a computer relay. The signals from the current and voltage transducers were sampled using a microprocessor and an analog to digital converter in real-time. The measurement device has been installed in the field. The data from the field was collected remotely and analyzed in the Virginia Tech Power Systems laboratory. The analysis of the data is presented at the end. / Master of Science

The current study compared the performance of six commonly used cursor devices (absolute touchpad, mouse, trackball, relative touchpad, force joystick, and displacement joystick) on three types of tasks (target acquisition, text editing, and graphics). Prior to these comparisons, each of the devices was optimized for display/control dynamics in independent experiments. A total of 30 subjects were used in the five optimization studies. For each device, the optimization experiment compared a range of control dynamics using a target acquisition task (i.e., positioning a cross-hair cursor over square targets of varying sizes and screen distances). An analysis of variance procedure was used to determine the best control dynamics, of the range studied, for each device. Performance was based on a time-to-target (TT) measure. A comparison of the six optimized devices was then performed on the three task environments. For the target acquisition, text editing, and graphics tasks, a total of 12, seven, and six subjects were required, respectively. For the target acquisition study, the six devices were compared on a task identical to the optimization task; that is, cursor positioning performance for various target sizes and distances. In addition to the TT dependent measure, bipolar scale and subjective rank data were also collected. The text editing task required subjects to perform document correction on the computer using each of the six devices, with cursor keys added as a baseline device. Task completion time (TCT), bipolar scale response, and subjective rank data were collected. For the graphics task, subjects were required to perform basic graphics editing tasks with the six devices. As with the text editing task, TCT, bipolar scale, and rank data were collected. Results indicated a wide variation in the cursor positioning performance of the devices on the three tasks. Without exception, the mouse and trackball performed the best of the six devices, across all tasks. In addition, these devices were most preferred. In general, the two joysticks performed worse on the target acquisition and graphics tasks than the two touchpads. On the text editing task, however, the rate—controlled joysticks performed better than the touchpads. / Ph. D.

This thesis investigates the relationship between semantic change and theory change in science. The study focuses on thirty years of developments in chaos theory. Because of measurement problems associated with certain nonlinear phenomena, the observability of chaotic systems is severely limited. In such cases, ongoing processes of language change may play a greater role in shaping scientific theories than in cases in which the phenomena are more easily observed. This study is interdisciplinary, drawing on theories from linguistics, philosophy, philology, and sociology. Several mechanisms of semantic change are explored in order to discover their possible influence on theory formation. Developments in chaos theory are described in terms of George Lakoff's radial model of conceptual categories. This model describes concepts in terms of (1) a central cluster which acts as a prototypical example, and (2) various non-central extensions from that center. I argue that in an emerging discipline, non-central extensions are made depending on the interests of the community. As Andrew Pickering observed, communities on the research front select a research direction that will intersect with the interests of more established research communities. This thesis explores several examples of historical developments in chaos research showing how conceptual change in science can be described in terms of Lakoff' s radial category model and Pickering's interest model. / Master of Science

For individuals requiring interactive access to online text, information storage and retrieval systems provide a way to retrieve desired documents and/or text passages. The CODER (COmposite Document Expert/effective/extended Retrieval) system is a testbed for determining how useful various artificial intelligence techniques are for increasing the effectiveness of information storage and retrieval systems. The system, designed previously, has three components: an analysis subsystem for analyzing and storing document contents, a central spine for manipulation and storage of world and domain knowledge, and a retrieval subsystem for matching user queries to relevant documents. This thesis discusses the implementation of the retrieval subsystem and portions of the spine and analysis subsystem. It illustrates that logic programming, specifically with the Prolog language, is suitable for development of an intelligent information retrieval system. Furthermore, it shows that system modularity provides a flexible research testbed, allowing many individuals to work on different parts of the system which may later be quickly integrated. The retrieval subsystem has been implemented in a modular fashion so that new approaches to information retrieval can be easily compared to more traditional ones. A powerful knowledge representation language, a comprehensive lexicon and individually tailored experts using standardized blackboard modules for communication and control allowed rapid prototyping, incremental development and ready adaptability to change. The system executes on a DEC VAX ll/785 running ULTRIX™, a variant of 4.2 BSD UNIX. It has been implemented as a set of MU-Prolog and C modules communicating through TCP/IP sockets. / Master of Science

Recent interest in three-dimensional (3-D) stereoscopic displays has prompted the need to assess the efficacy of retinal disparity depth cues. Accordingly, this study analyzed performance on two 3-D tasks under three levels of signal-to-clutter ratio as participants viewed three display formats portrayed with or without retinal disparity depth cues. Display formats included a plan view and two types of perspective formats. The two tasks assessed viewer ability to compare inter-object distances and extrapolate object positions given a known vector within a 3-D volume. Results indicate that retinal disparity depth cues reduce the number and magnitude of errors within a course prediction task, but did not affect search times or ratings of viewer confidence. Display format affected search times as follows. In a relative distance task, search times for the perspective format are lower than for either the plan view or enhanced perspective formats. In a course prediction task, search times for the plan view and perspective formats are lower than for the enhanced perspective format. Display format does not affect error rate, error magnitude, or ratings of viewer confidence. No interaction between depth cues and display format was observed. The inclusion of retinal disparity depth cues in a visual display system are suggested when the viewer task involves predictions of object position in a 3-D volume and when reducing the number and magnitude of errors is important. Perspective display formats are suggested when fast search times are important. / Master of Science

This work defines an expert machinability data system integrated with a CAD system, for computing complete machining parameters required for further processing with NC software. The main objective is to move toward the concept of a fully computerized system, from design to the generation of NC code which can be directly sent to a manufacturing unit. A typical example of such a system, MICADEX, is described in this thesis. MICADEX is capable of retrieving geometric description of components from their 2-D CADAM drawings using the IUE (CADAM Access) facilities and making decisions on machining parameters required for the turning operation, in consultation with the user. MICADEX is designed to be a representative example of an intelligent system capable of providing virtual machining facilities on a CAD system, and lt does not require its users to have a high level of engineering skills. / Master of Science

Just as image processing and image data bases have moved out of the lab and into the office environment, so has the need for image enhancement. Image scanners must to be able to capture and store a wide variety of information including faded documents, carbon copies, signatures, postmarks, etc. OCR systems put further demands on scanned image quality in terms of low noise, and unbroken disconnected characters. Straight thresholding techniques do not always meet the performance requirements, but by applying simple image processing techniques some of these problems can be solved. However, more burden is placed on the users to control the image enhancement techniques. The users, most of whom have little technical background, want no part in adjusting parameters. This paper proposes a method of examining small windows of the image to derive parameter settings autonomously. Histograms allow rudimentary measures to be used in setting parameters for edge detection, non-linear filters, and point operators such as non-linear gray scale mapping. Some examples of automatic parameter setting are given in chapter three. / Master of Science