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Articles 4561 - 4590 of 5699
Full-Text Articles in Engineering
Residual Strength And Fatigue Characterization Of Scs-6/Ti-6-4, Sang-Myung Lee
Residual Strength And Fatigue Characterization Of Scs-6/Ti-6-4, Sang-Myung Lee
Theses and Dissertations
Metal matrix composite have potential in a variety of aerospace applications, but they should be better understood before they can be employed. Despite the many studies that have contributed to characterizing the fatigue response of titanium alloy MMCs, few have researched the residual strength. The purpose of this study was to investigate the residual strength and the frequency effects on the residual strength of an unidirectional laminate of SCS-6/Ti-6-4, a titanium alloy matrix based composite under tension-tension, load-controlled conditions at elevated temperatures and different frequencies. Specimens were fatigued at frequencies of 1 and 0.01Hz, and at maximum stress of 900MPa …
Influence Of Tip Clearance On The Flowfield In A Compressor Cascade With A Moving Endwall, Richard J. Mcmullan
Influence Of Tip Clearance On The Flowfield In A Compressor Cascade With A Moving Endwall, Richard J. Mcmullan
Theses and Dissertations
The effects of changing the blade tip clearances on the velocity and pressure flowfields within a compressor cascade were investigated in this experimental thesis. All moving endwall measurements were taken at a constant flow coefficient of 0.5 and tip clearances of 0.5, 1.0 and 2.0 percent chord. Hot-wire/film probes were used to determine the three-dimensional velocity vector components in various transverse planes - one upstream of the leading edges of the blades, three within the blade cascade and one downstream of the trailing edges of the blades. The transverse velocity vector plots showed a scraping of the tip leakage vortex …
Optimization Of A Gps-Based Navigation Reference System, Jason B. Mckay
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 …
Data-Driven Process Discovery: A Discrete Time Algebra For Relational Signal Analysis, David M. Conrad
Data-Driven Process Discovery: A Discrete Time Algebra For Relational Signal Analysis, David M. Conrad
Theses and Dissertations
This research presents an autonomous and computationally tractable method for scientific process analysis, combining an iterative algorithmic search and a recognition technique to discover multivariate linear and non-linear relations within experimental data series. These resultant data-driven relations provide researchers with a potentially real-time insight into experimental process phenomena and behavior. This method enables the efficient search of a potentially infinite space of relations within large data series to identify relations that accurately represent process phenomena. Proposed is a time series transformation that encodes and compresses real-valued data into a well-defined, discrete-space of 13 primitive elements where comparative evaluation between variables …
Adaptive Neural Network Controller For Atm Traffic, Jeffrey E. Larson
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 …
Microelectromechanical Isolation Of Acoustic Wave Resonators, James R. Reid Jr.
Microelectromechanical Isolation Of Acoustic Wave Resonators, James R. Reid Jr.
Theses and Dissertations
Microelectromechainical systems (MEMS) is a rapidly expanding field of research into the design and fabrication of actuated mechanical systems on the order of a few micrometers to a few millimeters. MEMS potentially offers new methods to solve a variety of engineering problems. A large variety of MEMS systems including flip-up platforms, scanning micromirrors, and rotating micromirrors are developed to demonstrate the types of MEMS that can be fabricated. The potential of MEMS for reducing the vibration sensitivity of surface acoustic wave and surface transverse wave resonators is then evaluated. A micromachined vibration isolation system is designed and modeled. A fabrication …
Countering The Effects Of Measurement Noise During The Identification Of Dynamical Systems, Odell R. Reynolds
Countering The Effects Of Measurement Noise During The Identification Of Dynamical Systems, Odell R. Reynolds
Theses and Dissertations
Sensor noise is an unavoidable fact of life when it comes to measurements on physical systems, as is the case in feedback control. Therefore, it must be properly addressed during dynamic system identification. In this work, a novel approach is developed toward the treatment of measurement noise in dynamical systems. This approach hinges on proper stochastic modeling, and it can be adapted easily to many different scenarios, where it yields consistently good parameter estimates. The Generalized Minimum Variance algorithm developed and used in this work is based on the theory behind the minimum variance identification process, and the estimate produced …
Experimental Investigation Of Compressible Boundary Layers Under The Influence Of Pressure Gradients, Raymond C. Wier
Experimental Investigation Of Compressible Boundary Layers Under The Influence Of Pressure Gradients, Raymond C. Wier
Theses and Dissertations
This study examined the effect of mild pressure gradients on the mean and turbulent flow of high-speed boundary layers. Three Mach numbers (1.7, 3.0 and 5.0) were investigated. Three pressure gradients were examined; a zero pressure gradient (ZPG), a favorable pressure gradient (FPG), and a combined pressure gradient (CPG). The CPG consisted of an adverse pressure gradient followed by a favorable pressure gradient. Conventional pressure probes, hot-wire and particle image velocimetry (PIV) were used to examine the flow. Measurement included mean velocity, velocity turbulence intensity, mass flux turbulence intensity and energy spectra. Instantaneous (10 nsec) Mie scattering flow visualizations were …
Experimental Investigation Of Transverse Supersonic Gaseous Injection Enhancement Into Supersonic Flow, Mark P. Wilson
Experimental Investigation Of Transverse Supersonic Gaseous Injection Enhancement Into Supersonic Flow, Mark P. Wilson
Theses and Dissertations
In pursuit of more efficient and effective fuel-air mixing for a SCRAMJET combustor, this study was conducted to investigate relative near field enhancements of penetration and mixing of a discrete low-angled (25°) injected air jet into a supersonic (M=2.9) cross flow. The enhancements were achieved by injecting the transverse air jet parallel to the compression face of eight different ramp geometries. The jet-ramp interactions created collinear shock structures, baroclinic torque vorticity enhancement, ramp spillage enhanced vorticity, magnus effect penetration enhancement, and increased total pressure loss. Shadowgraph photography was used to identify the shock structures and interactions in the flow field. …
Demonstrating Optical Aberration Correction With A Mems Micro-Mirror Device, Shaun R. Hick
Demonstrating Optical Aberration Correction With A Mems Micro-Mirror Device, Shaun R. Hick
Theses and Dissertations
This research conducted the first demonstrated use of a micro-electro-mechanical structure (MEMS) mirror array to correct a static optical aberration. A well-developed technique in adaptive optics imaging systems uses a deformable mirror to reflect the incident wave front to the imaging stage of the system. By matching the surface of the deformable mirror to the shape of the wave front phase distortion, the reflected wave front will be less aberrated before it is imaged. Typical adaptive optics systems use piezo-electric actuated deformable mirrors. This research used an electrostatically actuated, segmented mirror array, constructed by standard MEMS fabrication techniques, to investigate …
Pulse Coupled Neural Networks For The Segmentation Of Magnetic Resonance Brain Images, Shane L. Abrahamson
Pulse Coupled Neural Networks For The Segmentation Of Magnetic Resonance Brain Images, Shane L. Abrahamson
Theses and Dissertations
This research develops an automated method for segmenting Magnetic Resonance (MR) brain images based on Pulse Coupled Neural Networks (PCNN). MR brain image segmentation has proven difficult, primarily due to scanning artifacts such as interscan and intrascan intensity inhomogeneities. The method developed and presented here uses a PCNN to both filter and segment MR brain images. The technique begins by preprocessing images with a PCNN filter to reduce scanning artifacts. Images are then contrast enhanced via histogram equalization. Finally, a PCNN is used to segment the images to arrive at the final result. Modifications to the original PCNN model are …
Evaluation Of Segmentation For Bone Structures In 3d Rendering Of Ultrasound Residual Limb Images, Min C. Baker
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 …
Requirements, Design, And Development Of A Rapidly Reconfigurable, Photo-Realistic, Virtual Cockpit Prototype, Terry A. Adams
Requirements, Design, And Development Of A Rapidly Reconfigurable, Photo-Realistic, Virtual Cockpit Prototype, Terry A. Adams
Theses and Dissertations
The United States Air Force uses aircraft flight simulators for pilot training and mission rehearsal. They use a variety of simulators for this task ranging with prices ranging from $400,000 to $30,000,000. These simulators have specialized hardware that restricts reuse of their components and increases maintenance costs. Air Education and Training Command wants to reduce simulators cost and improve availability to the operational commands by supporting research in virtual reality flight simulators. This thesis looks at the development of a reconfigurable virtual cockpit in a distributed virtual environment that can be used for different aircraft as well as training scenarios. …
Artificial Cochlea Design Using Micro-Electro-Mechanical Systems, George C. Dalton Ii
Artificial Cochlea Design Using Micro-Electro-Mechanical Systems, George C. Dalton Ii
Theses and Dissertations
The use of Micro-Electro-Mechanical Systems (MEMS) in the design of an artificial cochlea is investigated in depth. Interdigitated finger (comb), cantilever, bridge, and mirror resonators are presented as possible devices used to implement the artificial cochlea. These resonators are demonstrated to be extremely high Q devices, capable of being tuned with a simple DC bias. This suggests a possible change to existing cochlea models that claim highly complex AC feedback as being responsible for changes in the damping of the basilar membrane. The new cochlea model presented here, using MEMS to approximate the tuning of the basilar membrane, may be …
Development Of Synthetic Soils For Sorption Mass Transfer Model Validation, Thomas P. De Venoge
Development Of Synthetic Soils For Sorption Mass Transfer Model Validation, Thomas P. De Venoge
Theses and Dissertations
Existing sorption models often fail to describe grain scale sorption because of an inability to define the diffusion domain. A proposed improved model required testing to determine model validity. The testing method used a synthetic media of known geometry such that the distribution of sorption sites was known. Sorption rate data was obtained using batch experiments with the media. Data was used in comparison against model predicted rates. Fined sorption site distributions were compared to real distributions obtained by controlling sorbent geometries. Comparison determined model performance in fitting known distributions. The focus of this study was to (1) determine what …
Investigation Of Sorption Mass Transfer Models Using Synthetic Soils, Karla K. Mika
Investigation Of Sorption Mass Transfer Models Using Synthetic Soils, Karla K. Mika
Theses and Dissertations
Grain-scale sorption mass transfer is an important process that must be considered when predicting clean-up time and choosing remediation techniques for subsurface hazardous waste contamination. Rate-limited sorption is responsible for the rebound effect, where remediated groundwater is recontaminated by desorption. Sorbed contaminants are not available for microbial degradation, and the desorption rate may govern the effectiveness of natural attenuation by biodegradation. Grain-scale sorption nonequilibrium is generally attributed to diffusive transport, either in SOM or in mineral micropores. Typically used sorption mass transfer models either fail to reproduce long-term slow desorption (first-order models), or are based on diffusion in assumed (often …
Modeling Plant Uptake Of Metal In Constructed Wetlands Supported By Experimentally Derived Uptake Rates, Michael B. Peake
Modeling Plant Uptake Of Metal In Constructed Wetlands Supported By Experimentally Derived Uptake Rates, Michael B. Peake
Theses and Dissertations
Many communities and Air Force installations are using constructed wetlands to filter trace metals from their stormwater runoff. Constructed wetlands are attractive to industry for runoff mitigation because they are relatively cheap to build and operate and require little or no energy for operation. The purpose of this research project is to develop quantitative concepts for understanding the dynamics of metal uptake in constructed wetland plants by constructing a system dynamics model supported by experimental observation and offer environmental managers a tool to simulate, under a broad range of conditions, long term wetland exposure to stormwater runoff contaminated with trace …
Environmental Restoration Project, Peer Review Process Assessment, Paul A. Schantz
Environmental Restoration Project, Peer Review Process Assessment, Paul A. Schantz
Theses and Dissertations
Installation Restoration Program (IRP) projects often cost over $250 thousand, and projects over $1.5 million are common. To ensure these projects are risk based, technically sound, and cost effective, the Air Force instituted a peer review program in 1992. The objective of this research is to describe and analyze the peer review process. Through triangulation of data from interviews, observations, official and academic documents, and surveys, seven constructs were discovered: focus, agenda, facilitator, written preparation, oral presentation, team characteristics, and reviewer characteristics. A questionnaire was used to gather perceptions of peer review effectiveness--the criterion variable--and of the seven constructs. A …
Development Of A Basis For A Hazardous Materials And Waste Management System For Air Force Contingency Deployments, Christopher J. West
Development Of A Basis For A Hazardous Materials And Waste Management System For Air Force Contingency Deployments, Christopher J. West
Theses and Dissertations
Increased awareness of the potential for adverse mission impact on deployments, recent experience on such deployments, and Air Force and Major Command interest establish the need for an integrated hazardous materials and waste management system for contingency environments. This research was focused toward establishing a basis for developing such a system. An intensive literature review was accomplished to justify the necessity of the research, characterize the contingency environment, review legal and regulatory requirements, review proper hazardous substance handling and processing procedures, and review existing and new material resources which may be employed in such a system. Further literature review led …
Performance Analysis Of Dynamic Routing Protocols In A Low Earth Orbit Satellite Data Network, Richard F. Janoso
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. …
Clustered Microcalcification Detection Using Optimized Difference Of Gaussians, Edward M. Ochoa
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.
Performance Analysis Of A Hartman Wavefront Sensor Used For Sensing Atmospheric Turbulence Statistics, Toby D. Reeves
Performance Analysis Of A Hartman Wavefront Sensor Used For Sensing Atmospheric Turbulence Statistics, Toby D. Reeves
Theses and Dissertations
Atmospheric turbulence parameters, such as Fried's coherence diameter, the outer scale of turbulence, and the turbulence power law, are related to the wavefront slope structure function (SSF). The SSF is defined as the second moment of the wavefront slope difference as a function of both time and position. Knowledge of the SSF allows turbulence parameters to be estimated. Hartmann wavefront sensor (H-WFS) slope measurements composed of both signal and noise, allow the SSF to be estimated by computing a mean square difference of H-WFS slope measurements. The quality of the SSF estimate is quantified by the signal-to-noise ratio (SNR) of …
Mmae Detection Of Interference/Jamming And Spoofing In A Dpgs-Aided Inertial System, Nathan A. White
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 …
Development Of Site Characterization Simulator Specifications, Jeffrey L. Heiderscheidt
Development Of Site Characterization Simulator Specifications, Jeffrey L. Heiderscheidt
Theses and Dissertations
The purpose of this study was to develop a tool for evaluating data quality when characterizing a potentially contaminated groundwater aquifer, and to provide a basis for developing a simulator to allow environmental managers and engineers to practice and learn about the site characterization process. Specifically, this study characterized the uncertainty, estimation block size, and cost for the various methods of determining the value of each geological, hydrological, and contaminant parameter necessary to characterize a site. Research entailed identifying site characterization objectives and identifying parameters necessary to obtain those objectives. Methods of estimating each parameter were identified, then research was …
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
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 …
Optical Detection Properties Of Silicon-Germanium Quantum Well Structures, Michael R. Gregg
Optical Detection Properties Of Silicon-Germanium Quantum Well Structures, Michael R. Gregg
Theses and Dissertations
A study has been carried out on Si/SiGe multi quantum well structures to determine their applicability as normal incidence infrared detectors in the spectral range of 2-12 micrometers. The research effort was primarily experimental; however, extensive calculations were performed to initially explain the experimental data and then used to design subsequent structures. Multiple quantum well structures grown on both Si[001] and Si[110] substrates via molecular beam epitaxy were studied by photoluminescence, absorption, and photoresponse measurements over a wide parameter space. Variables included quantum well depth and width, well doping, number of wells and growth temperature. Well widths were varied from …
Maximum Likelihood Estimation Of Exponentials In Unknown Colored Noise For Target In Identification Synthetic Aperture Radar Images, Matthew P. Pepin
Maximum Likelihood Estimation Of Exponentials In Unknown Colored Noise For Target In Identification Synthetic Aperture Radar Images, Matthew P. Pepin
Theses and Dissertations
This dissertation develops techniques for estimating exponential signals in unknown colored noise. The Maximum Likelihood ML estimators of the exponential parameters are developed. Techniques are developed for one and two dimensional exponentials, for both the deterministic and stochastic ML model. The techniques are applied to Synthetic Aperture Radar SAR data whose point scatterers are modeled as damped exponentials. These estimated scatterer locations exponentials frequencies are potential features for model-based target recognition. The estimators developed in this dissertation may be applied with any parametrically modeled noise having a zero mean and a consistent estimator of the noise covariance matrix. ML techniques …
Nlo Waveguide "And" Switch And Method Therefor, John J. Kester, Iyad A. Dajani, Peter M. Ranon, Thomas G. Alley
Nlo Waveguide "And" Switch And Method Therefor, John J. Kester, Iyad A. Dajani, Peter M. Ranon, Thomas G. Alley
AFIT Patents
Method and apparatus are provided for NLO switching by first providing a phase-matched SHG grating which outputs a reinforced SHG beam only when two input beams of frequency (ω) are present in two modes of such wg. The so encoded NLO switch is operated by directing at least two input pulsed laser beams of frequency (ω) into the two modes of the wg to generate a reinforced pulsed output SHG beam and output same from the wg in an NLO switching process. The two input beams desirably have a separate pulse train and the spatial and temporal overlap of the …
Assessing User Requirements For An Automated System To Support Programmed Depot Maintenance Through Use Of A Rapid Prototype In A Group Support System Environment, Floyd A. Gwartney
Assessing User Requirements For An Automated System To Support Programmed Depot Maintenance Through Use Of A Rapid Prototype In A Group Support System Environment, Floyd A. Gwartney
Theses and Dissertations
The purpose of this thesis was to assess user requirements for an automated information system to support programmed depot maintenance (PDM). To accomplish this, the Integrated Technical Information for the Air Logistics Centers (ITI-ALC) program's rapid prototype was evaluated. The evaluation focused on users' perception of how well the prototype met system and human computer interface requirements for PDM technicians and managers. A group support system (GSS) was used as an analysis tool to evaluate the prototype and collect evaluation data. Using the prototype as a requirements baseline for the ITI-ALC system, this thesis had three objectives: to perform an …
Identifying Situational Constraints To Focus Quality Improvement In An Air Force Aerial Port, Timothy J. Pettit
Identifying Situational Constraints To Focus Quality Improvement In An Air Force Aerial Port, Timothy J. Pettit
Theses and Dissertations
This research analyzes the effects of situational constraints on individual performance within an Air Force Aerial Port squadron. Situational constraint research originated with laboratory studies by Peters and O'Connor in 1980 and was investigated in an Air Force field environment in 1984; mixed results were obtained. Laboratory studies identified direct performance inhibitors (Peters et al., 1980); however, field studies found little correlations with job performance (Kane, 1981; O'Connor et al., 1984a). Data collected in June 1995 (Dougherty, 1995) and March 1996, in this study, were used to accomplish a longitudinal analysis. Correlations between constraints and performance were also low in …