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2007

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Articles 1 - 30 of 4101

Full-Text Articles in Engineering

Metal Modulation Epitaxy Growth For Extremely High Hole Concentrations Above 10(19) Cm(-3) In Gan, Gon Namkoong, Elaissa Trybus, Kyung Keun Lee, Michael Moseley, W. Alan Doolittle, David C. Look Dec 2007

Metal Modulation Epitaxy Growth For Extremely High Hole Concentrations Above 10(19) Cm(-3) In Gan, Gon Namkoong, Elaissa Trybus, Kyung Keun Lee, Michael Moseley, W. Alan Doolittle, David C. Look

Applied Research Center Publications

The free hole carriers in GaN have been limited to concentrations in the low 1018 cm−3 range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ~10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ~1.5 x 1019 cm−3.

© 2008 American Institute of Physics.


Temperature Dependence Of A Macrobending Edge Filter Based On A High-Bend Loss Fiber, Pengfei Wang, Ginu Rajan, Yuliya Semenova, Gerald Farrell Dec 2007

Temperature Dependence Of A Macrobending Edge Filter Based On A High-Bend Loss Fiber, Pengfei Wang, Ginu Rajan, Yuliya Semenova, Gerald Farrell

Articles

The temperature dependence of a macrobending bare fiber based edge filter is investigated both theoretically and experimentally. The fiber used is a high bend loss fiber, type 1060XP. The experimental results show a good agreement with the proposed theoretical model over a temperature range from 0 to 80oC. It is shown that the strong temperature dependence of a high-bend loss fiber has a significant influence on the performance of a fiber edge filter used in a wavelength measurement application. However it is also concluded that such a temperature dependent performance can be beneficially utilized in a fiber temperature sensing application.


Interactive Visualization Of Information Hierarchies And Applications On The Web, Confesor Santiago Iii Dec 2007

Interactive Visualization Of Information Hierarchies And Applications On The Web, Confesor Santiago Iii

Theses and Dissertations

The visualization of information hierarchies is concerned with the presentation of abstract hierarchical information about relationships between various entities. It has many applications in diverse domains such as software engineering, information systems, biology, and chemistry. Information hierarchies are typically modeled by an abstract tree, where vertices are entities and edges represent relationships between entities. The aim of visualizing tree drawings is to automatically produce drawings of trees which clearly reflect the relationships of the information hierarchy.

This thesis is primarily concerned with problems related to the automatic generation of area-efficient grid drawings of trees, interactively visualizing information hierarchies, and applying ...


Optimization Of Optical Computed Tomography Techniques For The Synthesis Of Particle Aggregate Models, Patrick Anthony Giordano Jr. Dec 2007

Optimization Of Optical Computed Tomography Techniques For The Synthesis Of Particle Aggregate Models, Patrick Anthony Giordano Jr.

Theses and Dissertations

The characterization of 3-D shapes of particles in geomaterial aggregate mixtures is important for understanding the micro-mechanics of granular materials. Also, numerical synthesis of 3-D particle shapes from their corresponding shape descriptors is required for developing discrete element models (DEMs) that can be used to predict particle contact-forces, and ultimately the shear strength of the aggregate mixture.

Previous work has shown that Fourier-based 3-D shape descriptors can be constructed for aggregate mixtures, using a statistical combination of 2-D projections. Furthermore, optical tomography methods using the Algebraic Reconstruction Technique (ART) algorithm has proved capable of synthesizing 3-D shapes from 2-D projections ...


Soft Ground Improvement By Vacuum-Assisted Preloading, Cholachat Rujikiatkamjorn, Buddhima Indraratna Dec 2007

Soft Ground Improvement By Vacuum-Assisted Preloading, Cholachat Rujikiatkamjorn, Buddhima Indraratna

Faculty of Engineering - Papers (Archive)

This paper describes the behaviour of soft soil foundation stabilized with vacuum-assisted preloading at the New Bangkok International Airport, Thailand. An analytical solution considering the variation of soil permeability and compressibility and a finite element analysis based on an equivalent plane strain model developed by the authors are employed to investigate the performance of the test embankment. The converted equivalent plane strain parameters are incorporated in the finite element code ABAQUS. The associated settlement, excess pore pressure and lateral movement are predicted and compared with the available field measurement. The data indicate that the efficiency of the prefabricated vertical drains ...


Odometry Correction Of A Mobile Robot Using A Range-Finding Laser, Thomas Epton Dec 2007

Odometry Correction Of A Mobile Robot Using A Range-Finding Laser, Thomas Epton

All Theses

Two methods for improving odometry using a pan-tilt range-finding laser is considered. The first method is a one-dimensional model that uses the laser with a sliding platform. The laser is used to determine how far the platform has moved along a rail. The second method is a two-dimensional model that mounts the laser to a mobile robot. In this model, the laser is used to improve the odometry of the robot. Our results show that the one-dimensional model proves our basic geometry is correct, while the two-dimensional model improves the odometry, but does not completely correct it.


Algorithme D’Elaboration D’Un Reseau Electrique A Gestion Optimale D’Ecoulement Des Puissances, Tarek Mesbah Dec 2007

Algorithme D’Elaboration D’Un Reseau Electrique A Gestion Optimale D’Ecoulement Des Puissances, Tarek Mesbah

Boukhemis Chetate

Un des baromètres (indicateurs du niveau d’évolution ) de développement d’un pays, est sa consommation en énergie électrique ; dont tout industrie et mode de vie des résidents en dépend. Partant sur ce point capital nous avons organisé la thèse afin de gérer le parc énergétique national d’une manière rationnelle. Cette étude peut servir dans la compréhension et l’analyse approfondie de l’état de la stabilité de notre réseau électrique, qui a montré sa fragilité après l’incident vécu le 03/02/2003, qui a prouvé l’urgence de prendre en charge toutes les insuffisances enregistrées pour éviter ...


Architecture Design And Performance Analysis Of Practical Buffered-Crossbar Packet Switches, Ziqian Dong Dec 2007

Architecture Design And Performance Analysis Of Practical Buffered-Crossbar Packet Switches, Ziqian Dong

Dissertations

Combined input crosspoint buffered (CICB) packet switches were introduced to relax inputoutput arbitration timing and provide high throughput under admissible traffic. However, the amount of memory required in the crossbar of an N x N switch is N2x k x L, where k is the crosspoint buffer size and needs to be of size RTT in cells, L is the packet size. RTT is the round-trip time which is defined by the distance between line cards and switch fabric. When the switch size is large or RTT is not negligible, the memory amount required makes the implementation costly ...


Optimized Scheduling Of Highway Work Zones, Yimin Tang Dec 2007

Optimized Scheduling Of Highway Work Zones, Yimin Tang

Dissertations

Highway maintenance activities usually require lane closures and disrupt traffic operations. Because of budget constraints, project deadlines, and the resulting traffic impact, the objective of this dissertation is to improve the efficiencies of traffic operation and maintenance work, and minimize the total project cost (i.e., agency cost and road user cost) by optimizing work zone schedules.

This dissertation focuses on the maintenance projects on multiple-lane highways. The objective total cost function is formulated while considering a discrete maintenance time-cost function and time-dependent traffic diversions. However, the work zone scheduling problem is a combinatorial optimization problem and difficult to solve ...


Propagation And Scattering Of Beam Waves In Vegetation Using Scalar Transport Theory, Michael Yu-Chi Wu Dec 2007

Propagation And Scattering Of Beam Waves In Vegetation Using Scalar Transport Theory, Michael Yu-Chi Wu

Dissertations

Vegetation is a very complex propagation medium, and multiple scattering effects play a significant role in the propagation of microwave and millimeter (mm)-wave signals through foliage. At frequencies above 1 GHz,both the coherent and incoherent field components have to be taken into account and vegetation has to be modeled as a random medium of discrete scatterers having a wide variety of sizes and shapes. Multiscattering can be studied effectively by using transport theory. In prior studies, theories have been developed for microwave and mm-wave propagation in vegetation using transport theory for continuous wave and pulsed signals. In this ...


Multiclass Intermodal Network Model : The Use Of Combined Model On System Evaluations, Yi Deng Dec 2007

Multiclass Intermodal Network Model : The Use Of Combined Model On System Evaluations, Yi Deng

Dissertations

United States transportation policy has generally addressed the negative economic and social effects of the standpoint of individual transportation modes and local government involvement. Therefore, there has been an increased focus on the development of intermodal transportation. Integrating the modes and using each of them to its best advantage are strategies to optimize the existing resources and to create new capabilities.

According to the literature review performed in this research, the research in intermodal transportation system evaluation is far from mature. Most transportation performance measurements are focused on one mode rather than a whole network. In practice, the data necessary ...


Design And Analysis Of Scalable Scheduling Schemes For High-Speed Input-Queued Packet Switches, Chuan-Bi Lin Dec 2007

Design And Analysis Of Scalable Scheduling Schemes For High-Speed Input-Queued Packet Switches, Chuan-Bi Lin

Dissertations

Single-stage input-queued (IQ) switches are attractive for implementation of high performance routers because they require no speedup in the used memory. It has been shown that IQ switches can provide 100% throughput under admissible traffic when using either maximum-weight matching schemes or iterative maximal-weight matching schemes with a significant speedup. These different approaches require either high computation complexity or high memory costs that can make them infeasible. Therefore, there is a need for low-complexity and fast matching schemes that provide high throughput under several admissible traffic patterns, without recurring to speedup nor multiple iterations. In this thesis. the concept of ...


Brain Segmentation Using Endogenous Contrast Mechanism Using Breath Holding Fmri Signal For Tissue Characterization, Samata Mukesh Kakkad Dec 2007

Brain Segmentation Using Endogenous Contrast Mechanism Using Breath Holding Fmri Signal For Tissue Characterization, Samata Mukesh Kakkad

Theses

MRL has fast become the modality of choice for the analysis of the complexity of the human brain. MRJ is a non-invasive method and gives high spatial resolution maps of the brain with soft tissue contrast. Conventional MRI technique modified to be used to image the functionality at high temporal resolution is known as fMRI. In fMRI the BOLD signal we measure is the hemodynamic response to neuronal and vascular changes at rest or in response to a stimulus where the various tissue types will have a different response.

While fMRI has been traditionally been used to detect and identify ...


Retransmission Strategies For Moving Networks Over Ricean Fading Channels, Alex Ruiz Lee Dec 2007

Retransmission Strategies For Moving Networks Over Ricean Fading Channels, Alex Ruiz Lee

Theses

The problem of designing retransmission protocols based on Hybrid Automatic Repeat reQuest (HARQ) for moving networks over Ricean fading channels has been considered. The scenario of interest consists of one receiver traveling at a given speed while connected to a wireless network based on OFDM (e.g., WiMax) through several base stations located along the path. Five different retransmission protocols that combine HARQ with handover between adjacent base stations are considered. Their performance in terms of number of retransmissions per packet via numerical simulations, considering both frequency selective and nonselective channels are presented. The results obtained show the relevant advantage ...


The Use Of Instrumented Measures To Describe Lower Extremity Joint Mechanics, Steven Thomas Kaufman Dec 2007

The Use Of Instrumented Measures To Describe Lower Extremity Joint Mechanics, Steven Thomas Kaufman

Theses

Currently, various biomechanical assessments are used in clinical settings that offer diagnostic information about the studied joint. These assessments, however, are based on the judgment and experience of the therapist conducting the test and have a high degree of inter and intra rater variability, decreasing the strength of the observation. A set of instrumented measures consisting of a force/torque sensor and an angle sensor was created to quantitatively assess the mechanics of the lower extremity joints as a possible solution to the low repeatability of commonly used clinical tests.

It was shown through the use of instrumentation that the ...


Magnetically Assisted Impaction Mixing Of Nanosize Particles, James V. Scicolone Dec 2007

Magnetically Assisted Impaction Mixing Of Nanosize Particles, James V. Scicolone

Theses

Magnetically assisted impaction mixing (MAIM) is a novel dry mixing technique, which can be used to mix nanoparticles. Mixing of nanoparticles is usually conducted in solvent-based mixing techniques. The solvents used in these techniques are usually organic, which can be expensive and harmful to the environment. MAIM creates homogeneous nanoparticle mixtures while eliminating conditioning and drying steps associated with wet mixing techniques. To create the best mixing quality of nanoparticles, MAIM was optimized by studying the effects of magnet-to-sample ratio, time, magnet size, and constituents of the mixture. The results were then compared with other well-known mixing techniques.

To characterize ...


Design Of Three-Dimensional Axon Stretch Growth Device, Fayekah Assanah Dec 2007

Design Of Three-Dimensional Axon Stretch Growth Device, Fayekah Assanah

Theses

Spinal Cord Injury (SCI) causes destruction and degeneration of axons in the white matter of the spinal cord, resulting in functional loss and paralysis. A successful treatment of SCI requires axons to regenerate across damaged regions. Current studies focus on identifying mechanisms to promote axon regeneration in lesions and have yet to be successful in preventing nerve degeneration due to scar tissue formation. Establishing axonal bridges over long distances of SCI lesions remains a challenge, resulting in poor functional recovery. Instead of relying on promoting axon regeneration into lesions, Pfister et al. has developed a transplantable nervous tissue construct spanned ...


Ignition Of Metal Powder By Electrostatic Discharge Stimulation, Ervin Beloni Dec 2007

Ignition Of Metal Powder By Electrostatic Discharge Stimulation, Ervin Beloni

Theses

Energetic formulations with metal fuel additives are extensively used in propellants, explosives, pyrotechnics, and incendiaries. Currently, replacement of regular metal powders with nanocomposite metal-based materials is being considered. Such nanocomposite reactive materials are capable of very high reaction rates while maintaining the high combustion enthalpies characteristic of metals. However, such novel reactive nano-materials are often highly sensitive to impact, friction, and electrostatic discharge, making them difficult to handle. In particular, their high electrostatic discharge sensitivity (ESD) was reported. While ESD testing is very common and standardized, the mechanisms of powder ignition by electric spark remain unclear. This project is aimed ...


Fracture Healing : The Effects Of Local Insulin Delivery Via Calcium Sulfate And Tricalcium Phosphate, Sarah Elizabeth Buchala Dec 2007

Fracture Healing : The Effects Of Local Insulin Delivery Via Calcium Sulfate And Tricalcium Phosphate, Sarah Elizabeth Buchala

Theses

Previous studies have documented the major role played by insulin in osseous healing. This is the first study to examine local intramedullary insulin delivery to the fracture site and its effect upon the normal fracture healing process. Preceding results show that when administered at the fracture site of the impaired fracture healing model of the diabetic BB Wistar rat, insulin will regulate early cellular proliferation and chondrogenesis and late mineralized tissue, cartilage content and mechanical strength.

In this study, two novel delivery vehicles have been evaluated for sustained insulin release in the normal fracture model of the BB Wistar rat ...


Creating New Visualization And Human Interface Devices For Theraputic Video Games, Kunal Jayant Doshi Dec 2007

Creating New Visualization And Human Interface Devices For Theraputic Video Games, Kunal Jayant Doshi

Theses

Virtual reality (VR) gaming environment as a tool for rehabilitation of patients with upper extremity disorders is fast gaining momentum. VR based motor training systems provide an engaging, motivating and adaptable environment where the motion of the limb displayed in the virtual world is a replication of the motion produced in the real world by the patient's extremity.

The goal of this thesis was to create a generic gaming system which can be interfaced to a number of different Human interface devices (HID) and produce rich graphics to create a virtual environment which closely resembles the real world. This ...


Comparison Of Linear Parametric Models For Predicting Fmri Response, Parina Gandhi Dec 2007

Comparison Of Linear Parametric Models For Predicting Fmri Response, Parina Gandhi

Theses

In this study, five different linear parametric models including Autoregressive model (ARX), Autoregressive Moving Average Model (ARMAX), Box-Jenkins Model (BJ), Instrument Variable Model (IV) and Prediction Error Model (PEM) were used to predict the fMRI response and their performances compared. Transfer functions were computed for every voxel time series for every subject using all the parametric models. Cross-correlation was subsequently performed between the predicted response and the actual fMRI data to compare the performance of the five models. The consistency of the models and the transfer function was checked by doing a statistical analysis. Among the five models tested, PEM ...


A Stereoscopic System Using Knowledge Propagation To Achieve Accurate Depth Calculation, Chaitali Mulay Dec 2007

A Stereoscopic System Using Knowledge Propagation To Achieve Accurate Depth Calculation, Chaitali Mulay

Theses

With the advent of the twenty first century, stereoscopic systems have found a widespread use in the engineering industry. Several biomechanical analyses utilize this concept for efficient information extraction. Some examples of its applications are gait analysis, hand shape recognition, facial surface recognition etc.

The primary goal of this thesis was to optimize the existing stereoscopic system, to increase accuracy and precision of the depth information extracted. The process included redesign of the existing equipment set-up, automation of image acquisition unit and modification of conventionally used correspondence test to achieve higher accuracy. The acquired data was used to estimate depth ...


Finger Joint Impedance Control Applications To Investigate Spasticity, David Naisby Paglia Dec 2007

Finger Joint Impedance Control Applications To Investigate Spasticity, David Naisby Paglia

Theses

In order to investigate how spasticity disrupts the capabilities of the human body, a better understanding of how joint impedance control operates in healthy individuals is necessary. In this investigation, a second order rotary torque model was implemented to investigate the impedances at the metacarpophalangeal (MCP) joint of the index finger. The model was fit to approximately 25 milliseconds of force and displacement data to determine the mechanical impedances at the finger tip. Ranges of damping and stiffness were optimized over a range of mean finger tip force (0-12 N) for extension. The equilibrium-point hypothesis was examined when compared to ...


Phase Transfer In A Collision Between A Droplet And Solid Spheres, Zheng Shen Dec 2007

Phase Transfer In A Collision Between A Droplet And Solid Spheres, Zheng Shen

Theses

The hydrodynamics of a liquid droplet impinging on a particle is of direct relevance to many engineering applications. The mechanism of heat and mass transfer during the droplet solid collision is essential to the design and operation of many industrial systems. However, very limited systemic research is available to describe the droplet impact on hot solid spheres.

This paper aims to establish a systematic investigation of phase transfer due to the droplet-solid impact, by both experimental and modeling approaches. The targeted phase transfer includes the surface attachment, mass of vaporization, heat transfer to droplet and its partition between vaporization and ...


Fully Dense Aluminum-Rich Aluminum Copper Oxide Powders For Energetic Formulations, Demitrios Stamatis Dec 2007

Fully Dense Aluminum-Rich Aluminum Copper Oxide Powders For Energetic Formulations, Demitrios Stamatis

Theses

The thermite reaction between Al and CuO is well known and highly exothermic. For a conventional thermite mixture comprising mixed metal and oxide powders, this reaction is rate limited by the slow heterogeneous mass transfer at the metal and oxide interface. The relatively low reaction rate and a difficult ignition have restricted practical applications for this reaction. For newly developed, nano-composed thermites, the interface area can be substantially increased resulting in a much higher reaction rate and a new range of possible applications. Nanocomposite Al-CuO materials are produced using a technique referred to as arrested reactive milling. Regular metal and ...


Pattern Recognition Of Brain Fmri Images For Various Physiological States, Priyanka Bhatt Dec 2007

Pattern Recognition Of Brain Fmri Images For Various Physiological States, Priyanka Bhatt

Theses

The development of fMRI (functional Magnetic Resonance Imaging) has led many researchers to localize brain functions using different stimuli. The use of pattern recognition techniques have made it possible to predict the stimuli being presented from the corresponding brain images and activation patterns. The primary objective of the present study was to use pattern recognition methods to develop a model using available fMRJ images and then to use the model to identify the stimulus presented from a large number of unknown images. Two different experimental conditions were used involving both binary and multi-class classification. Bilateral finger tapping data which had ...


Mapping Inter-Subject And Inter-Regional Brain Connectivity During Free Viewing Of Novel Natural Scenes, Sheela Nagaraj Dec 2007

Mapping Inter-Subject And Inter-Regional Brain Connectivity During Free Viewing Of Novel Natural Scenes, Sheela Nagaraj

Theses

Traditional functional magnetic resonance imaging (fMRI) studies have used controlled tasks such as finger tapping to isolate function in distinct cortical. Recent studies have examined the mechanisms involved during natural conditions by asking subjects to freely view the presentation of a movie. The objective of our study was to further observe the extent to which similarities are present between subjects during natural vision. It was hypothesized that there would be a linear relationship between the percentage of region-specific overlap, which is the percent of the anatomical region of interest which contains spatial activation exhibited by all six subjects, and corresponding ...


Design Of Gait Rehabilitation System, Andriy Pletenetskyy Dec 2007

Design Of Gait Rehabilitation System, Andriy Pletenetskyy

Theses

This thesis describes the conceptual design of an innovative robotic rehabilitation machine whose purpose is to help in the recovery of people with motor function disabilities. The machine is smaller, simpler and cheaper than current solutions on the market yet it delivers same functionality.

The conceptual development of the gait rehabilitation system also features a human model with average anthropometric dimensions that allows better visualization and understanding of the actual machine operation. The human model is kinematically coupled to the machine and the whole assembly presents a complex mechanism that closely simulates gait training session.

Three-dimensional modeling and analysis techniques ...


Proactive Methods For Measurement Of Available Bandwidth And Link Capacity, Khondaker Musfakus Salehin Dec 2007

Proactive Methods For Measurement Of Available Bandwidth And Link Capacity, Khondaker Musfakus Salehin

Theses

With the continuous expansion of network infrastructure and deployment of applications sensitive to Quality-of-Service, network measurement plays a major role in both network planning and management. Accurate measurement of various network parameters, e.g., available bandwidth, link capacity, delay, packet loss and jitter, provides a positive impact for effective traffic engineering, Quality-of-Service (QoS) routing, optimization of end-to-end transport performance, and link capacity planning. For network measurement, there exists several proactive estimation tools based on either probe-gap model or probe-rate model that estimate path related attributes. Most of these tools that have been implemented can measure tight-link capacity (smallest available bandwidth ...


Ultra-Fine Particle Formation Using Principle Of Rapid Expansion Of Supercritical Solutions`, Miraj Minesh Sheth Dec 2007

Ultra-Fine Particle Formation Using Principle Of Rapid Expansion Of Supercritical Solutions`, Miraj Minesh Sheth

Theses

There are indications in the chemical and pharmaceutical industries that the reduction in size of a crystalline particle can lead to better performance of the drug compound, particularly for water insoluble drugs, in the final dosage form. Many particle formation techniques have been investigated in recent years by researchers to obtain desired particulate sizes and size distributions. Supercritical fluid technologies have been successfully investigated for particle formation due to its unique gas/liquid properties in the supereritical state. In this report, results of particle formation using the principles of Rapid Expansion of Supercritical Solutions (RESS) have been documented.

In the ...