Digital Commons Network^™

Analysis Of Multimode Low-Probability-Of-Intercept (Lpi) Communications With Atmospheric Effects, Ala Ghordlo

Theses and Dissertations

This research expanded Low Probability of Intercept (LPI) communications analysis in two areas. First, multimode communication was included to account for ground to ground and air to ground links in addition to the standard air to air links traditionally used in LPI analysis. The propagation equations for the three modes of interest were derived and included in LPI analytic models in the form of a mode quality factor to account for multimode LPI scenarios. This new quality factor was used in studying several communication and interception link combinations. Variations due to differences between the communication and interception modes were presented …

Performance Analysis Of Preemption Algorithms In An Idnx Circuit Switch Communications Network, Eric C. Gumbs

Theses and Dissertations

Access to communication networks is increasing rapidly. The increase access to these networks results in delays and at times loss of data. At times of peak traffic or when trunks or nodes are down, very important customers' communications requirements are not met. One way to combat this problem is to prioritize the network and provide different levels of grade of service (GOS) for each priority. Call preemption provides an effective method of obtaining different levels of GOS. This research seeks to design the best circuit switch communications network preemption model for the DoD by analyzing previously developed preemption algorithms. Four …

Application Of A Finite-Volume Time-Domain Maxwell Equation Solver To Three-Dimensional Objects, Frederick G. Harmon

Theses and Dissertations

Concurrent engineering approaches for the disciplines of computational fluid dynamics (CFD) and electromagnetics (CEM) are necessary for designing future high-performance, low-observable aircraft. A characteristic-based finite-volume time-domain (FVTD) computational algorithm, developed for CFD and now applied to CEM, is implemented to analyze the radar cross section (RCS) of two three-dimensional objects, the ogive and cone-sphere. The FVTD formulation implements a Monotone Upstream-Centered Scheme for Conservation Laws (MUSCL) algorithm for the flux evaluation and a Runge-Kutta multi-stage scheme for the time integration. Developmental FVTD work for the thesis focused on algorithm development to analyze scattering and obtain RCS data for closed-surface perfect …

Performance Analysis Of Dynamic Routing Protocols In A Low Earth Orbit Satellite Data Network, Richard F. Janoso

Theses and Dissertations

Modern warfare is placing an increasing reliance on global communications. Currently under development are several Low Earth Orbit (LEO) satellite systems that propose to deliver voice and data traffic to subscribers anywhere on the globe. However, very little is known about the performance of conventional routing protocols under orbital conditions where the topology changes on a scale of minutes rather than days. This thesis compares two routing protocols in a LEO environment. One (Extended Bellman-Ford) is a conventional terrestrial routing protocol, while the other (Darting) is a new protocol which has been proposed as suitable for use in LEO networks. …

Adaptive Neural Network Controller For Atm Traffic, Jeffrey E. Larson

Theses and Dissertations

Broadband-Integrated Services Digital Networks (B-ISDN), along with Asynchronous Transfer Mode (ATM), were designed to meet the requirements of modern communication networks to handle multiple users and a wide variety of diverse traffic including voice, data and video. ATM responds to requests for admission to the network by analyzing whether or not the grade of service (GOS) requirement, specified in the admission request, can be guaranteed without violating the GOS guaranteed to traffic already accepted into the network. The GOS is typically a parameter such as cell loss rate (CLR), average delay, or some other measurement associated with network performance. In …

Analysis And Simulation Of A New Code Tracking Loop For Gps Multipath Mitigation, Mark C. Laxton

Theses and Dissertations

This thesis proposes a new direct sequence spread spectrum (DS/SS) code phase tracking loop which mitigates the effects of multipath interference on code phase tracking error; such errors can translate to significant range measurement errors in DS/SS ranging systems such as Global Positioning System (GPS). The new code tracking loop, called the modified RAKE delay lock loop (MRDLL), uses maximum likelihood (ML) signal parameter estimation to determine the amplitude, carrier phase, and relative propagation delay of both a direct path and a reflected signal; a multiple correlator code phase tracking loop then exploits these ML signal estimates to remove the …

Multiple Model Adaptive Estimation And Control Redistribution For The Vista F-16, Robert W. Lewis Sr.

Theses and Dissertations

Performance characteristics of a Multiple Model Adaptive Estimation and Control Redistribution (MMAE/CR) algorithm are evaluated against single and double actuator and sensor failures. MMAE alone can compensate for sensor failures, whereas Control Redistribution compensates for actuator failures by redistributing commands, initially intended for failed actuators, to the unfailed actuators in such a way that the desired system response is achieved. Both failure detection and compensation capabilities are developed and analyzed through an extensive amount of simulation data, particularly addressing multiple failures. Simulations are performed utilizing the high fidelity, non-linear six degree of freedom Simulation Rapid Prototyping Facility for the VISTA …

Clustered Microcalcification Detection Using Optimized Difference Of Gaussians, Edward M. Ochoa

Theses and Dissertations

The objective of this thesis is to design an automated microcalcification detection system to be used as an aid in radiologic mammogram interpretation. This research proposes the following methodology for clustered microcalcification detection. First, preprocess the digitized film mammogram to reduce digitization noise. Second, spatially filter the image with a difference of Gaussians (DoG) kernel. To detect potential microcalcifications, segment the filtered image using global and local thresholding. Next, cluster and index these detections into regions of interest (ROIs). Identify ROIs on the digitized image (or hardcopy printout) for final radiologic diagnosis.

Optimization Of A Gps-Based Navigation Reference System, Jason B. Mckay

Theses and Dissertations

The development of increasingly accurate new aircraft navigation systems has caused the Air Force to develop a new Navigation Reference System to test them, called the Submeter Accuracy Reference System (SARS). The SARS is an inverted GPS system which consists of an array of GPS receivers on the ground and an airborne pseudolite mounted on the test aircraft. The SARS will provide a proof position estimate that is used to check the navigation system under test. Unfortunately, ground based inverted GPS systems tend to suffer from high geometric sensitivity to measurement errors. This research tackles the problem of optimizing the …

Interference Suppression For Spread Spectrum Signals Using Adaptive Beamforming And Adaptive Temporal Filter, Wonjin Park

Theses and Dissertations

Interference and jamming signals are a serious concern in an operational military communication environment. This thesis examines the utility and performance of combining adaptive temporal filtering with adaptive spatial filtering (i.e. adaptive beamforming) to improve the signal-to-jammer ratio (SJR) in the presence of narrowband and wideband interference. Adaptive temporal filters are used for narrowband interference suppression while adaptive beamforming is used to suppress wideband interference signals. A procedure is presented for the design and implementation of a linear constraints minimum variance generalized sidelobe canceler (LCMV-GSC) beamformer. The adaptive beamformer processes the desired signal with unity gain while simultaneously and adaptively …

Evaluation Of Design Tools For Rapid Prototyping Of Parallel Signal Processing Algorithms, James C. Savage

Theses and Dissertations

Digital signal processing (DSP) has become a popular method for handling not only signal processing, but communications, and control system applications. A DSP application of interest to the Air Force is high speed avionics processing. The real time computing requirements of avionics processing exceed the capabilities of current single chip DSP processors, and parallelization of multiple DSP processors is a solution to handle such requirements. Designing and implementing a parallel DSP algorithm has been a lengthy process often requiring different design tools and extensive programming experience. Through the use of integrated software development tools, rapid prototyping becomes possible by simulating …

Experimental Investigation Of Radar Cross Section Spatial Correlation Properties For A Point Scattering Target, John D. Shannon

Theses and Dissertations

This research investigates the spatial correlation of RCS. In pulsed radar systems, probability of detection for partially correlated signals depends on the autocovariance of the target's RCS. The RCS changes pulse to pulse due to spatial and time fluctuations. Spatial fluctuation are due to the motion of all scatterers relative to the radar (i.e. changing aspect angle). Time fluctuations are due to relative motion of scatterers to each other (i.e. wings flexing, engines spinning). Theory developed at AFIT [9] can generate autocovariance estimates from a distribution of scatterers. Theory based autocovariance estimates are compared to static measurement based autocovariance estimates …

Mmae Detection Of Interference/Jamming And Spoofing In A Dpgs-Aided Inertial System, Nathan A. White

Theses and Dissertations

Previous research at AFIT has resulted in the development of a DGPS-aided INS-based precision landing system (PLS) capable of meeting the FAA precision requirements for instrument landings. The susceptibility of DGPS transmissions to interference/jamming and spoofing must be addressed before DGPS may be used in such a safety-of-flight critical role. This thesis applies multiple model adaptive estimation (MMAE) techniques to the problem of detecting and identifying interference/jamming and spoofing failures in the DGPS signal. Such an MMAE is composed of a bank of parallel filters, each hypothesizing a different failure status, along with an evaluation of the current probability of …

Weighted Mahalanobis Distance For Hyper-Ellipsoidal Clustering, Khaled S. Younis

Theses and Dissertations

Cluster analysis is widely used in many applications, ranging from image and speech coding to pattern recognition. A new method that uses the weighted Mahalanobis distance (WMD) via the covariance matrix of the individual clusters as the basis for grouping is presented in this thesis. In this algorithm, the Mahalanobis distance is used as a measure of similarity between the samples in each cluster. This thesis discusses some difficulties associated with using the Mahalanobis distance in clustering. The proposed method provides solutions to these problems. The new algorithm is an approximation to the well-known expectation maximization (EM) procedure used to …

Inference Algorithm Performance And Selection Under Constrained Resources, Brett J. Borghetti

Theses and Dissertations

Knowing that reasoning over probabilistic networks is, in general, NP-hard, and that most reasoning environments have limited resources, we need to select algorithms that can solve a given problem as fast as possible. This thesis presents a method for predicting the relative performance of reasoning algorithms based on the domain characteristics of the target knowledge structure. Armed with this knowledge, the research shows how to choose the best algorithm to solve the problem. The effects of incompleteness of the knowledge base at the time of inference is explored, and requirements for reasoning over incompleteness are defined. Two algorithms for reasoning …

Evaluation Of Segmentation For Bone Structures In 3d Rendering Of Ultrasound Residual Limb Images, Min C. Baker

Theses and Dissertations

Prosthetists today widely practice manual socket fitting, which produces subjective, inconsistent results. To address this problem, the Computerized Anthropometry Research and Design (CARD) Laboratory is developing a computer-aided socket design system that acquires ultrasound datasets of an amputee's residual limb, creates a 3D model, and helps identify load- bearing and pressure-relief areas. This research project focuses on providing 3D visualization of a residual limb to support the CARD Laboratory's efforts. Creating the 3D model of the skin and two bone contours requires two major steps: segmentation to identify the objects of interest and a surface tracking algorithm to generate the …

A Voice From The Fire: The Authority Of Experience, Colleen C. Bernhard

Theses and Dissertations

Over all, this thesis was written to be a "ramble" of its own around and through three issues that are central to the writing of the personal essay-voice, authority, and experience-and central to the emergence of this author's own sense of "self."
Drawing upon years of voluminous journals, this collection of six personal essays demonstrates what the scholarly introduction proposes: that the personal essay is both a valid genre and a magnificent bridge from informal life-writing to genuine literary accomplishment. Drawing on Phillip Lopate's differentiation of "memoiristic" essays from the more classic autobiographical form, this collection includes three of each …

A Comparative Study Of The Sounds Of Kuo-Yu And Taiwanese, Chia-Jung Fan

Theses and Dissertations

This study was made to explore the pronunciation rules between Taiwanese and Kuo-yu, which are the two major languages used in Taiwan today, by comparing selected features of their phonological systems. The purpose was to provide the future researchers and Taiwanese learners more information on sounds, which will be helpful in the maintenance and future development of the Taiwanese language.

In the introduction, there is a brief description of the background and formation of Taiwanese and Kuo-yu. In chapter two, the syllable structure and phonetic systems of Taiwanese and Kuo-yu are introduced. The following three chapters are about the three …

Transformational And Transactional Leadership Behaviors Of Administrators Of Performing And Visual Arts Schools, Angela F. Koppang

Theses and Dissertations

This study examined the extent to which administrators in performing and visual arts schools demonstrate transformational and transactional leadership behaviors. Administrator self-perceptions and teacher perceptions of transformational and transactional leadership behaviors of administrators in performing and visual arts schools were compared. Eight transformational and transactional leadership behaviors and four leadership effects were examined. The eight leadership behaviors examined were attributed charisma, idealized influence, inspirational motivation, intellectual stimulation, individual consideration, contingent reward, management-by-exception active, and management-byexception passive. The four leadership effects examined were laissez-faire, extra effort, effectiveness, and satisfaction.

Data were collected by obtaining responses to a survey instrument mailed to …

Mercury Sorption On Metal Oxides, Heidi L. Hitchcock

Theses and Dissertations

This project addresses the fundamental aspects of toxic metal (mercury) sorption by metal oxides. The emission of toxic trace elements from anthropogenic sources, such as combustion, has drawn attention to potential dangers for the ecosystem. Particular concern has been directed toward mercury species because of their high toxicity and tendency to convert into forms leading to mercury accumulation in mammals. Efforts to control mercury species release have centered on sorption technology using carbonaceous sorbents. However, it has been found, in some cases, that fly ash also has some sorptive properties towards mercury species. In order to further understand the sorption …

Censorship Of Textbooks And Supplemental Books In North Dakota Secondary Schools From 1989-1994, Jeffrey L. Lofthus

Theses and Dissertations

Censorship of school books and other materials has long been an issue in the United States. North Dakota has not been exempt from censorship, and the public schools in Drake, Minot, and Napoleon all experienced censorship battles.

This study examined the extent of censorship in North Dakota public high schools and determined what policies are used to handle challenges to textbooks and supplemental reading materials. A model policy for reconsideration of educational materials is recommended.

This study focuses on academic freedom, challenges to textbooks, library books, and other materials, humanistic education, the new age movement, reconsideration policies, secular humanism, and …

A Descriptive Study Of Preschool Children Learning Through Shared Activity, Carol Lynn Enger

Theses and Dissertations

The purpose of this study was to develop a better understanding of how preschool children learn from other children in shared activities. Shared activities provide opportunities for children to assist each other in a meaningful social context. The question directing the study was: how do preschool children assist other children to learn in teacher designed learning centers and in child directed free play activities?

In order to discover how and when children are learning from other children, an observational study of one universtiy campus child care center was conducted over a period of seven months. Initial investigations included observations of …

"Now She Understood": Free Indirect Discourse And Its Effects, Mary Margaret Dahlberg

Theses and Dissertations

While the discussion of Free Indirect Discourse is limited almost entirely to the twentieth, century, the technique has been used by writers from a variety of periods throughout literary history. Its effects vary, depending on the strength of the narrative voice and whether it is used to represent speech or thought. The first essay in this dissertation examines free indirect thought as it emerges in Chaucer's Troylus and Criseyde, Lyly's Euphues, and Gascoigne's Adventures of Master F.J. The effect in this early period seems to be primarily dramatic, a finding supported by further discussion of a prototype form identified in …

Waterfowl Nest Success In Two Habitat Types On Lonetree Wildlife Management Area, Jon Merril Roaldson

Theses and Dissertations

Land managers have long debated the efficacy of available options for replacement plant communities and planted cover on previously disturbed soils. I used waterfowl nest success to evaluate planted cover types of Dense Nesting Cover (DNC) and Native Grass Planting (NP) from late April-early August 1994-95 on 39 Lonetree WMA study areas in central North Dakota. I was unable to detect a significant difference in waterfowl nest success between DNC and NP during 1994-95, despite major differences in cover height and density by visual obstruction reading (VOR) (P=0.001) and maximum height (P=0.02) measures by cover-year interaction. The power of our …

Rural-Urban Student Differences On The Strong Interest Inventory For A Career Counseling Center Sample, Susan L. Pauly

Theses and Dissertations

The purpose of' his study was to explore whether differences existed between rural and urban students’ responses on the Strong Interest Inventory (SII). The subjects for this study were 665 students who had taken the SII as part of career counseling services received at the University of North Dakota. The subjects were classified as either rural or urban based on the population of their hometown. The rural and urban groups’ scores were compared on the SII General Occupational Theme (RIASEC), Academic Comfort and Introversion/Extroversion scales, the Iachan index of congruence between RIASEC scores and college major, measures of indifference in …

The Contribution Of Auditory Processing To Adult Age Differences In Memory Performance, Danae J. Lund

Theses and Dissertations

Recently, there has been increased interest in the changes in neuropsychological functioning which are associated with normal aging. Understanding age differences in neuropsychological functioning is of particular importance in the discrimination of normal aging from the early onset of Alzheimer’s Disease or other age-associated dementia. Older adults have been observed to perform more poorly than younger adults on several auditory memory measures which are commonly included in neuropsychological batteries. Age associated declines on these measures have been reported even in the absence of dementia or other health concerns.

To date, explanations for these age differences have focused on a decline …

Status Passage Of The Science Fiction Fan: Becoming A Member Of The Science Fiction Fan Subculture, B. Diane Miller

Theses and Dissertations

In the 1930's a middle class subculture developed around the popular culture genre literature known as science fiction. This subculture calls itself "Fandom" (Sanders, 1994; Bloch, 1962). I have chosen to investigate the status passage of the science fiction fan (Glaser and Strauss, 1971); or to phrase this as a question: What is the process of becoming a member of the subculture of science fiction fandom? Throughout this monograph, I refer to the members of the science fiction fan subculture as SF Fandom to distinguish them from other “fandoms” that have grown and branched off from the original group.

In …

Some Empirical Evidence On The Non-Normality Of Cost Variances On Defense Contracts, Robert J. Conley Iv

Theses and Dissertations

This study tested the hypothesis that defense cost variances reported on the Cost Performance Report are normally distributed. The DOD requires that all defense cost variances which breech a pre-specified threshold be investigated. The present variance investigation model has been criticized because it can prompt frivolous investigations. In theory, statistical models could reduce the number of frivolous investigations, but they are not used because they require too much information about the cost variance, including its distributional form. Often such models assume a normal distribution, but researchers have shown that the models do not work properly if the assumption is fallacious. …

The Preliminary Design Of A Standardized Spacecraft Bus For Small Tactical Satellites, Gerald Ashby, Darren Buck, Robert Carneal Iv, Tansel Cokuysal, Ahmet Donmez, James From, Todd Krueger, Brian Robinson

Theses and Dissertations

Current satellite design philosophies concentrate on optimizing and tailoring a particular satellite bus to a specific payload or mission. Today's satellites take a long time to build, checkout, and launch. An alternate approach shifts the design paradigm to one that focuses on access to space, enabling tactical deployment on demand and the capability to put current payload technology into orbit, versus several years by today's standards, by which time the technology is already obsolete. This design study applied systems engineering methods to create a satellite bus architecture that can accommodate a range of remote sensing mission modules. System-level and subsystem-level …

A 2-D Numerical Simulation And Analysis Of A Simple Band Model For The Priz Spatial Light Modulator, Gary D. Barmore

Theses and Dissertations

This dissertation discusses the development of and analyzes the first complete, 2-D numerical simulation of the PRIZ. The simulation is based upon a simple band model of the PRIZ: a single donor, a single trap, and free electron carriers. Modeled mechanisms include photogeneration, energy level transitions, injection, drift currents, diffusion currents, photorefraction and diffraction. The model goes beyond the previous charge and field dynamics of 1-D numerical models to include optical effects, and it eliminates the oversimplifications and assumptions used in earlier mathematical models with closed solutions. Sensitivity analyses and selected simulations provide a better understanding of the dynamic imaging …