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Articles 173521 - 173550 of 198025

Full-Text Articles in Engineering

Model Predictive Control Of Aerospace Systems, Derek W. Ebdon Dec 1996

Model Predictive Control Of Aerospace Systems, Derek W. Ebdon

Theses and Dissertations

The primary objective of this thesis is to explore the fault tolerance capabilities of a state space formulation of MPC. Subsequent to a simulated control surface failure on the F-18 High Alpha Research Vehicle (HARV), the MPC controller will attempt to maintain stability and nominal performance while tracking a setpoint. Secondary objectives include studying the effect of data sample rate and MPC horizon lengths on system performance. These objectives will be accomplished using Matlab to develop the MPC controller and Simulink to demonstrate its effectiveness through simulation.

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Influence Of Tip Clearance On The Flowfield In A Compressor Cascade With A Moving Endwall, Richard J. Mcmullan Dec 1996

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 …

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Multidisciplinary And Multiobjective Optimization In Conceptual Design For Mixed-Stream Turbofan Engines, Luc J. J. P. Nadon Dec 1996

Multidisciplinary And Multiobjective Optimization In Conceptual Design For Mixed-Stream Turbofan Engines, Luc J. J. P. Nadon

Theses and Dissertations

Despite major advances in design tools such as engine cycle analysis software and computer aided design, conceptual gas turbine engine design is essentially a trial-and-error process based on the experience of engineers. Modern optimization concepts, such as multidisciplinary optimization (MDO), and multiobjective optimization (MOO), linked with sequential quadratic programming (SQP) methods and genetic algorithms (GA), were applied to the conceptual engine design process to automate the conceptual design phase. Robust integrated computer codes were created to find the optimal values of eight engine parameters in order to minimize fuel usage, aircraft cost and engine annulus area over a given mission. …

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Residual Strength And Fatigue Characterization Of Scs-6/Ti-6-4, Sang-Myung Lee Dec 1996

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 …

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Experimental Investigation Of Transverse Supersonic Gaseous Injection Enhancement Into Supersonic Flow, Mark P. Wilson Dec 1996

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. …

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Demonstrating Optical Aberration Correction With A Mems Micro-Mirror Device, Shaun R. Hick Dec 1996

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 …

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Data-Driven Process Discovery: A Discrete Time Algebra For Relational Signal Analysis, David M. Conrad Dec 1996

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 …

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Pulse Coupled Neural Networks For The Segmentation Of Magnetic Resonance Brain Images, Shane L. Abrahamson Dec 1996

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 …

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Evaluation Of Segmentation For Bone Structures In 3d Rendering Of Ultrasound Residual Limb Images, Min C. Baker Dec 1996

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 …

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Requirements, Design, And Development Of A Rapidly Reconfigurable, Photo-Realistic, Virtual Cockpit Prototype, Terry A. Adams Dec 1996

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. …

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Artificial Cochlea Design Using Micro-Electro-Mechanical Systems, George C. Dalton Ii Dec 1996

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 …

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An Investigation Of Instantaneous Plume Rise From Rocket Exhaust, Paul F. Sand Dec 1996

An Investigation Of Instantaneous Plume Rise From Rocket Exhaust, Paul F. Sand

Theses and Dissertations

Rocket launches at Vandenburg Air Force Base and Cape Canaveral Air Station produce exhaust clouds containing several toxic by-products, including HC1 and A12O3. These clouds rise to atmospheric stabilization heights, and then start dispersing and diffusing through the air. Upon reaching the ground, concentration levels of the toxins may present a human health risk. To predict these risks and concentration levels, range officials use a computer program titled the Rocket Effluent Exhaust Diffusion Model (REEDM). The version currently in use has been shown to underpredict the stabilization height of the exhaust cloud. This thesis examines the theory and algorithms used …

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Independent Verification And Validation Of The Hazardous Material Cost Trade-Off Analysis Tool Developed By The Human Systems Center At Brooks Air Force Base, Thomas S. Choi Dec 1996

Independent Verification And Validation Of The Hazardous Material Cost Trade-Off Analysis Tool Developed By The Human Systems Center At Brooks Air Force Base, Thomas S. Choi

Theses and Dissertations

The Air Force realizes that the life cycle cost (LCC) associated with hazardous materials is a significant cost in the acquisition of major weapon systems. In trying to mitigate the growth of environmental LCC for future weapon systems, the Air Force has developed a tool called the Hazardous Material Cost Trade-off Analysis Tool (HAZMAT CTAT). The HAZMAT CTAT estimates the LCC for weapon system hazardous materials, so that intelligent decisions can be made in the early stages of the acquisition process. The problem with implementing this program into the acquisition process is that an independent computer model evaluation has never …

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Applying Probabilistic Risk Assessment And Decision Analysis Techniques To Avoid Excessive Remedial Investigation Costs, Alejandro Hinojos Dec 1996

Applying Probabilistic Risk Assessment And Decision Analysis Techniques To Avoid Excessive Remedial Investigation Costs, Alejandro Hinojos

Theses and Dissertations

The majority of remediation resources have been consumed by costly and lengthy remedial investigation studies to characterize the human health risk. Unable to deal directly with the uncertainty resulting from the convolution of the uncertainties in a multitude of variables, and heavily persuaded by the liabilities, decision makers and regulators have relied on conservative assumptions and more studies to take appropriate actions. The main objective of this research is to provide tools and techniques to aid risk analysts in determining whether it would be beneficial to gather additional information or whether the decision to take an appropriate action can be …

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Determining The Optimum Strategy Of Techniques From The Municipal Solid Waste Management Hierarchy To Maximize Social Value, Camille M. Still Dec 1996

Determining The Optimum Strategy Of Techniques From The Municipal Solid Waste Management Hierarchy To Maximize Social Value, Camille M. Still

Theses and Dissertations

Environmental managers must make difficult decisions regarding how to manage solid waste generation and disposal. The primary waste management alternatives are source reduction, recycling, composting, incineration, and landfilling often, waste management policies are based entirely on technical considerations and ignore that actual disposal practices depend on individuals' attitudes and behaviors. This research formulated a decision analysis model that incorporates social value measures to determine the waste management strategy that maximizes the individuals' willingness to participate. The social values that are important and that were considered in the decision support model to assist with making decisions about solid waste management were …

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Development Of Synthetic Soils For Sorption Mass Transfer Model Validation, Thomas P. De Venoge Dec 1996

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 …

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Habitat Suitability Mapping Through Integration Of Multicriteria Evaluation Techniques With A Geographic Information System (Gis), Anthony A. Ference Dec 1996

Habitat Suitability Mapping Through Integration Of Multicriteria Evaluation Techniques With A Geographic Information System (Gis), Anthony A. Ference

Theses and Dissertations

The presence of an endangered species, the Pacific Pocket Mouse (PPM), in critical Marine Corps training areas aboard Camp Pendleton may adversely affect training activities that are crucial to meeting the Marine Corps' mission. Camp Pendleton must focus limited budgetary assets for live trapping surveys of the PPM in the areas of best habitat suitability and the purpose of this study was to develop a PPM habitat suitability map of Camp Pendleton. Suitability maps were developed by integrating expert opinion with the Camp Pendleton Geographic Information System (GIS) database.

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Economic Valuation Of Air Force Environmental Resources: A Contingent Valuation Case Study, Timothy P. Haynie Dec 1996

Economic Valuation Of Air Force Environmental Resources: A Contingent Valuation Case Study, Timothy P. Haynie

Theses and Dissertations

The Air Force spends $1 billion each year to preserve, maintain, and restore environmental resources under its control (Budget of the United States Government, 1994). Assessing the benefit of this spending is a central issue in federal environmental management. As federal environmental management moves from a "clean it up at any cost" mentality to one which carefully considers the costs and benefits of spending, a fundamental question arises: What value of environmental resources does our environmental spending provide? As in any rational economic exchange benefits must exceed costs; the value of an environmental resource which benefits from public spending must …

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Study Of Desorption Of Contaminant From Synthetic Soil, Kung-Fu Hwang Dec 1996

Study Of Desorption Of Contaminant From Synthetic Soil, Kung-Fu Hwang

Theses and Dissertations

A better understanding of sorption and desorption processes could improve estimates of time and cost required for remedial activities, exposure times and health risk, and bioavailability. Conventional rate-limited sorption models do not accurately define the diffusion domain at the grain scale. Heyse (1994) proposed the multiple sites in series (MSS) model, which allows more general description of the geometry of the sorption domain than the classical spherical or discrete distributions. A version of this model was tested by deVenoge (1996). The model was able to accurately simulate sorption rate data, but could not estimate unique geometry parameters. This research is …

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A Decision Support Model For Municipal Solid Waste Recycling At United States Air Force Installations, Gergory A. Williams Dec 1996

A Decision Support Model For Municipal Solid Waste Recycling At United States Air Force Installations, Gergory A. Williams

Theses and Dissertations

The United States Air Force requires each installation to operate a municipal solid waste recycling program. Two inherently conflicting objectives, waste material diversion and financial result, have been established for the program. Reducing landfill disposal is the primary objective, but the incentive for profit is strong because each installation can retain profits from the program. Installations can be divided into two distinct areas, commercial and residential, based on the waste stream composition and funding. Structuring of the recycling program is often done in an ad-hoc manner. A decision support model was developed to evaluate four methods for each area. The …

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A Comparative Analysis Of Two Alternatives To Chemical Aircraft Paint Stripping, George P. Joyce Ii Dec 1996

A Comparative Analysis Of Two Alternatives To Chemical Aircraft Paint Stripping, George P. Joyce Ii

Theses and Dissertations

The Air Force must periodically strip and paint its aircraft to prevent the damaging effects of corrosion. The paint removal process typically involves the use of toxic chemicals such as methylene chloride which are soon to be banned as a result of impending environmental regulations and increased costs associated with handling and disposing of such material. The Air Force must choose an alternative to methylene chloride chemical stripping which complies with environmental regulations and reduces costs. This thesis compares the life cycle costs and environmental impacts of two alternatives to chemical aircraft stripping. Plastic Media Blasting (PMB) and Modified Medium …

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Investigation Of Sorption Mass Transfer Models Using Synthetic Soils, Karla K. Mika Dec 1996

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 …

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Modeling Plant Uptake Of Metal In Constructed Wetlands Supported By Experimentally Derived Uptake Rates, Michael B. Peake Dec 1996

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 …

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An Activity Driver Based Analysis Of Hazardous Materials Usage At Wright-Patterson Afb, Charles D. Perham Dec 1996

An Activity Driver Based Analysis Of Hazardous Materials Usage At Wright-Patterson Afb, Charles D. Perham

Theses and Dissertations

As the Air Force has progressed and succeeded in the realm of pollution prevention, the opportunities for further progress have become more challenging. With the 'low-hanging fruit' now gone from the pollution prevention tree, new methods to identify opportunities must be adopted. This research effort applied a subset of activity based costing, activity driver analysis, to reveal pollution prevention opportunities in regards to hazardous materials usage. A sample of base organizations (civil engineering and aircraft maintenance), and a sample of the hazardous chemicals (Class C or most hazardous) used by those organizations were investigated to determine the drivers behind usage.

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Evaluation Of Hazardous Material Life Cycle Cost Tools For Use In Air Force Hazardous Material Pharmacies, Rowene J. Resler Dec 1996

Evaluation Of Hazardous Material Life Cycle Cost Tools For Use In Air Force Hazardous Material Pharmacies, Rowene J. Resler

Theses and Dissertations

This research focuses on evaluation of various tools that assist in the selection of hazardous material substitutes. Substitute material consideration is a function of the Hazardous Material Pharmacy (HMP) when a hazardous material is requested for purchase and use in a current base operation. The substitute material decision is complex, involving identification of potential substitutes and then comparison of factors, such as cost, performance, and environmental effects, between the potential substitute and the material being requested. Various tools such as life cycle cost models, databases, and other information services can provide assistance to HMPs making substitution decisions.

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Environmental Restoration Project, Peer Review Process Assessment, Paul A. Schantz Dec 1996

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 …

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Development Of A Basis For A Hazardous Materials And Waste Management System For Air Force Contingency Deployments, Christopher J. West Dec 1996

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 …

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Development Of Object-Based Teleoperator Control For Unstructured Applications, Hyunki Cho Dec 1996

Development Of Object-Based Teleoperator Control For Unstructured Applications, Hyunki Cho

Theses and Dissertations

For multi-fingered end effectors in unstructured applications, the main issues are control in the presence of uncertainties and providing grasp stability and object manipulability. The suggested concept in this thesis is object based teleoperator control which provides an intuitive way to control the robot in terms of the grasped object and reduces the operator's conceptual constraints. The general control law is developed using a hierarchical control structure, i.e., human interface I gross motion control level in teleoperation control and fine motion control/object grasp stability in autonomous control. The gross motion control is required to provide the position/orientation of the Super …

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Analysis Of Multimode Low-Probability-Of-Intercept (Lpi) Communications With Atmospheric Effects, Ala Ghordlo Dec 1996

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 …

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A Two-Phase Damped-Exponential Model For Speech Synthesis, H. Allan Arb Dec 1996

A Two-Phase Damped-Exponential Model For Speech Synthesis, H. Allan Arb

Theses and Dissertations

It is well known that there is room for improvement in the resultant quality of speech synthesizers in use today. This research focuses on the improvement of speech synthesis by analyzing various models for speech signals. An improvement in synthesis quality will benefit any system incorporating speech synthesis. Many synthesizers in use today use linear predictive coding (LPC) techniques and only use one set of vocal tract parameters per analysis frame or pitch period for pitch-synchronous synthesizers. This work is motivated by the two-phase analysis-synthesis model proposed by Krishnamurthy. In lieu of electroglottograph data for vocal tract model transition point …

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