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2007

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Articles 1 - 30 of 4418

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 ...


Friction Of Soft Elastomeric Surfaces With A Defect, Charles J. Rand, Alfred Crosby Dec 2007

Friction Of Soft Elastomeric Surfaces With A Defect, Charles J. Rand, Alfred Crosby

Alfred Crosby

We consider a simple problem that provides insight into the building blocks of friction for topographically patternedsurfaces and fundamental understanding into the general friction of coatings. The problem focuses on the effect of a line defect, such as a pattern’s edge, on the lateral force of a sliding soft interface. The line defect presents a discontinuity in the stress at the sliding interface, changing the lateral stiffness and decreasing the sliding force. We relate the decrease in sliding shear force to the changes in lateral stiffness through relationships that account for contact splitting and lateral confinement effects.


An Explanation Of Srs Beam Cleanup In Graded-Index Fibers And The Absence Of Srs Beam Cleanup In Step-Index Fibers, Nathan B. Terry, Thomas G. Alley, Timothy H. Russell Dec 2007

An Explanation Of Srs Beam Cleanup In Graded-Index Fibers And The Absence Of Srs Beam Cleanup In Step-Index Fibers, Nathan B. Terry, Thomas G. Alley, Timothy H. Russell

Faculty Publications

Beam cleanup via stimulated Raman scattering in multimode fibers is modeled by numerically considering the competition between the Stokes modes of graded-index and step-index fibers. The relative gain of each Stokes mode is calculated by considering the overlap the various pump and Stokes modes of the fibers. Mode competition in a graded-index fiber favors the LP01 Stokes mode while mode competition in a step-index fiber does not favor the LP01 Stokes mode. This model explains why beam cleanup has only been reported for graded-index fibers and not for step-index fibers.


Incorporating Grain Size Effects In Taylor Crystal Plasticity, Bradley S. Fromm Dec 2007

Incorporating Grain Size Effects In Taylor Crystal Plasticity, Bradley S. Fromm

Theses and Dissertations

A method to incorporate grain size effects into crystal plasticity is presented. The classical Hall-Petch equation inaccurately predicts the macroscopic yield strength for materials with non-equiaxed grains or materials that contain unequal grain size distributions. These deficiencies can be overcome by incorporating both grain size and orientation characteristics into crystal plasticity theory. Homogenization relationships based on a viscoplastic Taylor-like approach are introduced along with a new function, the grain size and orientation distribution function (GSODF). Estimates of the GSODF for high purity α-titanium are recovered through orientation imaging microscopy coupled with the chord length distribution. A comparison between the new ...


Forensics Image Background Matching Using Scale Invariant Feature (Sift)Transform And Speeded Up Robust Features (Surf), Paul N. Fogg Ii Dec 2007

Forensics Image Background Matching Using Scale Invariant Feature (Sift)Transform And Speeded Up Robust Features (Surf), Paul N. Fogg Ii

Theses and Dissertations

In criminal investigations, it is not uncommon for investigators to obtain a photograph or image that shows a crime being committed. Additionally, thousands of pictures may exist of a location, taken from the same or varying viewpoints. Some of these images may even include a criminal suspect or witness. One mechanism to identify criminals and witnesses is to group the images found on computers, cell phones, cameras, and other electronic devices into sets representing the same location. One or more images in the group may then prove the suspect was at the crime scene before, during, and/or after a ...


Acceleration Of The Maturation Of Tissue Engineered Grafts By Dynamic Force Stimulation Or Gene Therapy, Shila Taylor Dec 2007

Acceleration Of The Maturation Of Tissue Engineered Grafts By Dynamic Force Stimulation Or Gene Therapy, Shila Taylor

All Theses

Over 16 million people suffer from osteoarthritis (OA). As the body ages OA and other cartilage diseases create an imbalance of anabolic and catabolic cell activities in cartilage and or over time the cartilage is damaged and wears away which creates lesion that resulting in pain. Most clinical surgeries are either temporary or have not gone through trials to test their success. For a long term solution researchers have been looking at replacing cartilage with a tissue engineered graft. One of the major problems to date has been is the strength of the scaffold.
Natural cartilage needs loading for its ...


Project Valuation Using Real Options, Dimitrios V. Siskos Dec 2007

Project Valuation Using Real Options, Dimitrios V. Siskos

Dimitrios V. Siskos

No abstract provided.


The Penn Discourse Treebank 2.0 Annotation Manual, Rashmi Prasad, Eleni Miltsakaki, Nikhil Dinesh, Alan Lee, Aravind Joshi, Livio Robaldo, Bonnie L. Webber Dec 2007

The Penn Discourse Treebank 2.0 Annotation Manual, Rashmi Prasad, Eleni Miltsakaki, Nikhil Dinesh, Alan Lee, Aravind Joshi, Livio Robaldo, Bonnie L. Webber

IRCS Technical Reports Series

This report contains the guidelines for the annotation of discourse relations in the Penn Discourse Treebank (http://www.seas.upenn.edu/~pdtb), PDTB. Discourse relations in the PDTB are annotated in a bottom up fashion, and capture both lexically realized relations as well as implicit relations. Guidelines in this report are provided for all aspects of the annotation, including annotation explicit discourse connectives, implicit relations, arguments of relations, senses of relations, and the attribution of relations and their arguments. The report also provides descriptions of the annotation format representation.


Electrical Activation Studies Of Silicon Implanted Aluminum Gallium Nitride With High Aluminum Mole Fraction, Elizabeth A. Moore Dec 2007

Electrical Activation Studies Of Silicon Implanted Aluminum Gallium Nitride With High Aluminum Mole Fraction, Elizabeth A. Moore

Theses and Dissertations

This research demonstrates a method for producing highly conductive Si-implanted n-type aluminum gallium nitride (AlxGa1-xN) alloys, and represents a comprehensive analysis of the resulting material's electrical and optical properties as a function of Al mole fraction, anneal temperature, anneal time, and implantation dose. Highly conductive alloys are critical to the fabrication of devices operating in deep UV, high-temperature, high-power, and high-frequency environments, and thus this research is significant in regard to the application of such devices. The AlxGa1-xN wafers of this study, with Al concentrations of 10 to 50%, were implanted ...


Elastic Properties Of Ca-Based Bulk Metallic Glasses Studied By Resonant Ultrasound, Zhiying Zhang, Veerle Keppens, Oleg Senkov, Daniel Miracle Dec 2007

Elastic Properties Of Ca-Based Bulk Metallic Glasses Studied By Resonant Ultrasound, Zhiying Zhang, Veerle Keppens, Oleg Senkov, Daniel Miracle

Veerle Keppens

We report measurements of the elastic properties and internal friction of Ca-based bulk metallic glasses (BMGs), Ca50Mg20Cu30, Ca55Mg18Zn11Cu16 and Ca65Mg15Zn20 (numbers indicate at.%), as a function of temperature between 5 and 400 K. Below the glass transition temperature, both Young's modulus and shear modulus decrease with increasing temperature, and the Poisson ratio increases with increasing temperature. Above the glass transition temperature, these trends reverse due to crystallization. At temperatures close to the glass transition temperature, we observe the onset of a peak in the internal friction Q−1, attributed to crystallization.


A Simple Model To Predict The Temperature Dependence Of Elastic Moduli Of Bulk Metallic Glasses, Zhiying Zhang, Veerle Keppens, Takeshi Egami Dec 2007

A Simple Model To Predict The Temperature Dependence Of Elastic Moduli Of Bulk Metallic Glasses, Zhiying Zhang, Veerle Keppens, Takeshi Egami

Veerle Keppens

We report a simple model to predict the temperature dependence of elastic moduli of bulk metallic glasses from room temperature measurements, using the Varshni equation and the basic assumption that between absolute zero and the melting point, the shear and bulk moduli change, respectively, by 45% and 22%. This model has been tested using experimental data obtained on a large variety of bulk metallic glasses, and the predicted values are found to be in very good agreement with the experimental results.


Metalloporphyrin Catalyzed Degradation Of Pce: Effects Of Reductants, Buffers And Cosolvent Concentration, Sowmya Suryanarayanan Dec 2007

Metalloporphyrin Catalyzed Degradation Of Pce: Effects Of Reductants, Buffers And Cosolvent Concentration, Sowmya Suryanarayanan

All Theses

Reductive dechlorination of chlorinated organic contaminants using metalloporphyrins as catalysts may be an effective approach to treat widespread contamination. However, most previous studies have examined water-soluble rather than insoluble metalloporphyrins despite the fact that the latter category makes up the largest fraction found in nature. Recent studies have shown that addition of different cosolvents to water can activate otherwise non-reactive metalloporphyrin catalysts and facilitate the reduction of tetrachloroethylene (PCE), presumably by the mere process of making the otherwise insoluble metalloporphyrins dissolve in solution. Therefore, solubility has been advanced as a key factor in the ability of metalloporphyrins to catalyze organic ...


Development Of The Impedance-Based Arc-Flash Determination Device (Iadd), Timothy Smith Dec 2007

Development Of The Impedance-Based Arc-Flash Determination Device (Iadd), Timothy Smith

All Theses

This thesis entitled, 'Development of the Impedance based Arc-Fault Determination Device (IADD)' details the development of a testing device that, when attached to an electrical node on the power system and through observations on voltage, current and phase shift with a step load change, determines the effective Thevenin or Norton impedance at the point of test. This thesis includes discussion of the theory and design process that enables the determination of an equivalent circuit, software development using National Instruments' LabView software development package and suggestions for future development.
The purpose of this thesis is to produce a device that can ...


Evaluation Of A Computer Vision Traffic Surveillance System, Robert Graham Dec 2007

Evaluation Of A Computer Vision Traffic Surveillance System, Robert Graham

All Theses

This thesis presents an evaluation of the accuracy of a novel computer vision traffic sensor - developed by the Clemson University Electrical and Civil Engineering Departments - capable of collecting a variety of traffic parameters. More specific, the thesis examines how the camera height and distance from the travel way affects the accuracy. The details of the quantitative and qualitative evaluations used to validate the system are provided. The parameters chosen to evaluate were volume, vehicle classification, and speed. Experimental results of cameras mounted at heights of 20 and 30 feet and a lateral distance of 10 and 20 feet show accuracy ...


Bacterial Auto-Aggregation And Co-Aggregation In Activated Sludge, Fei Chen Dec 2007

Bacterial Auto-Aggregation And Co-Aggregation In Activated Sludge, Fei Chen

All Theses

Microbial auto-aggregation and co-aggregation, leading to biofilm or floc formation, widely occur in natural systems. This study was conducted to investigate the extent of bacterial auto-aggregation and co-aggregation in activated sludge and their contributions in activated sludge floc formation. In this study, an activated sludge sample was separated into a supernatant part (planktonic community) and a sediment part (floc community) by centrifugation at 650_g for 2 minutes. 197 strains were isolated from both communities. These isolates belong to 18 phylotypes based on molecular identifications. Similar phylogenetic distributions of these isolates were observed in planktonic and floc communities, suggesting a similar ...


Property Measurements And Evaluation Of Heat Leak, Nathan Race Dec 2007

Property Measurements And Evaluation Of Heat Leak, Nathan Race

All Theses

Heat transport in capillary wick structures is an important parameter in loop heat pipe (LHP) design. The purpose of this study was to investigate the conductive heat leak in operating capillary wick structures. The heat leak is the portion of applied heat load conducted through the wick in spite of the convection of working fluid. Four sintered 316 stainless steel wicks were tested for porosity, effective thermal conductivity, pore size, and heat leak. Pore sizes were found to correlate well with the nominal pore size and pores were very narrowly distributed within a size range of approximately 1-10μm. Effective thermal ...


N-Glycan Modification In Aspergillus Species, Elke Kainz, Andreas Gallmetzer, Christian Hatzl, Juergen H. Nett, Huijuan Li, Thorsten Schinko, Robert Pachlinger, Harald Berger, Yazmid Reyes-Dominguez, Andreas Bernreiter, Tillmann Gerngross, Stefan Wildt, Joseph Strauss Dec 2007

N-Glycan Modification In Aspergillus Species, Elke Kainz, Andreas Gallmetzer, Christian Hatzl, Juergen H. Nett, Huijuan Li, Thorsten Schinko, Robert Pachlinger, Harald Berger, Yazmid Reyes-Dominguez, Andreas Bernreiter, Tillmann Gerngross, Stefan Wildt, Joseph Strauss

Open Dartmouth: Peer-reviewed articles by Dartmouth faculty

The production by filamentous fungi of therapeutic glycoproteins intended for use in mammals is held back by the inherent difference in protein N-glycosylation and by the inability of the fungal cell to modify proteins with mammalian glycosylation structures. Here, we report protein N-glycan engineering in two Aspergillus species. We functionally expressed in the fungal hosts heterologous chimeric fusion proteins containing different localization peptides and catalytic domains. . This strategy allowed the isolation of a strain with a functional -1,2-mannosidase producing increased amounts of N-glycans of the Man 5 GlcNAc 2 type. This strain was further engineered by the introduction of ...


Bio-Surfaces And Geometric References For A Standardized Biomechanical Design Methodology For Mass Customization, Kimberly A. Jensen Dec 2007

Bio-Surfaces And Geometric References For A Standardized Biomechanical Design Methodology For Mass Customization, Kimberly A. Jensen

Theses and Dissertations

This dissertation presents a method for the design of customizable products that interface with the human body. The method presented involves first, a consistent method of capturing and representing the human model so that the model can be used with CAx tools and solid modeling techniques. Second, it provides a design methodology based on feature structure planning and assembly modeling that provides a consistent structure to the design process so that it can be reused and parameterized. Third, a strategy for identifying parametric variables that are referenced to the human body is introduced. The core of this method is the ...


Nirt: Developing A Nanoscale Sensing Device For Measuring The Supply Of Iron To Phytoplankton In Marine Systems, Mark L. Wells, Karen Orcutt, D. Whitney King, Carl Tripp Dec 2007

Nirt: Developing A Nanoscale Sensing Device For Measuring The Supply Of Iron To Phytoplankton In Marine Systems, Mark L. Wells, Karen Orcutt, D. Whitney King, Carl Tripp

University of Maine Office of Research Administration: Grant Reports

There is increasing evidence that Fe has a singularly unique role in marine ecosystems, both regulating total phytoplankton production in high nitrate, low chlorophyll regions of the world, and influencing the predominant composition of the phytoplankton assemblages found in others. It is remarkable then that there is no agreement about how to define biologically available Fe, in contrast to the macronutrients nitrogen, phosphorous or silicon. Current attempts to attain predictive insights to how ocean ecosystems will influence the magnitude of climate change are blocked in large part by this question, along with an extreme shortage of data on Fe distributions ...


Thermal Diffusion Coefficient Modeling For High Pressure Combustion Simulations, Soundararaghavan Vasudevan Dec 2007

Thermal Diffusion Coefficient Modeling For High Pressure Combustion Simulations, Soundararaghavan Vasudevan

All Theses

The effects of Soret and Dufour diffusion on the behavior of high pressure laminar diffusion flames relevant to modern combustion devices are investigated. A novel model for thermal diffusion coefficients is developed based on experimental data found in the literature and the principle of corresponding states. The new model is first compared with existing models and experimental data and is shown to be more accurate and to exhibit correct behavior in the limit of high temperature relevant to combustion. The model furthermore does not exhibit sensitivity to the equation of state, its mixing rules, or unphysical sign changes observed in ...


The Role Of Computer Aided Engineering In Developing A Combined Trash And Recycling Truck : A Case Study, Peter Johnston Dec 2007

The Role Of Computer Aided Engineering In Developing A Combined Trash And Recycling Truck : A Case Study, Peter Johnston

All Theses

This work will illustrate how Environmental America Inc., EAI, and the Clemson University design team utilized lean manufacturing principles to revolutionize the curbside waste collection process. Through the application of lean manufacturing principles the number of non-value added steps was significantly reduced and the information gathered from the lean process tree acted as a framework to develop initial constraints and criteria for the vehicle's development. The design team was asked to construct the fifth iteration of the prototype collection vehicle in an effort to minimize vehicle cost, size and weight. An extensive case study will be presented which illustrates ...


Fabrication, Electrical Characterization, And Annealing Of Al/, Cu/, And Au/4h-Sic Schottky Diodes, Nikhil Karkhanis Dec 2007

Fabrication, Electrical Characterization, And Annealing Of Al/, Cu/, And Au/4h-Sic Schottky Diodes, Nikhil Karkhanis

All Theses

Schottky diodes were fabricated on n-type 4H-SiC with Nickel ohmic contacts and Aluminum, Copper, and Gold Schottky contacts. An improved and revised fabrication process was developed in the course of this research project. The Schottky diodes were electrically characterized using I-V and C-V measurements to extract electrical parameters which include Schottky barrier height, ideality factor, the diode series resistance, and substrate doping density. Al/4H-SiC and Au/4H-SiC were annealed at 600¼C and 500¼C respectively to improve the Schottky parameters. Schottky barrier height was raised and the ideality factor was reduced in both cases. Significant improvement was observed in the ...


Operational Strategies For Continuum Manipulators, Matt Csencsits Dec 2007

Operational Strategies For Continuum Manipulators, Matt Csencsits

All Theses

We introduce a novel, intuitive user interface for continuum manipulators through the use of various joystick mappings. This user interface allows for the effective use of continuum manipulators in the lab and in the field. A novel geometric approach is developed to produce a more intuitive understanding of continuum manipulator kinematics. Using this geometric approach we derive the first closed-form solution to the inverse kinematics problem for continuum robots. Using the derived inverse kinematics to convert from workspace coordinates to configuration space coordinates we develop a potential-field path planner for continuum manipulators.


Laboratory Evaluation Of Microbial Aggregation In Activated Sludge, Xiaoling Liu Dec 2007

Laboratory Evaluation Of Microbial Aggregation In Activated Sludge, Xiaoling Liu

All Theses

Microbial aggregation was investigated in this study using the activated sludge process as a model system, the performance of which is highly dependent on effective bioaggregation. This research includes two experiments. First, four laboratory-scale activated sludge sequencing batch reactors (SBRs) were constructed in order to evaluate the effect of solids retention time (SRT) on microbial aggregation. These SBRs were operated at SRT of 4, 8, 16, and 32 days, respectively, fed with a protein-based synthetic wastewater, and monitored over a period of 268 days for performance and sludge settling characteristics including soluble COD in the effluent (sCOD), sludge volume index ...