Engineering Commons^™

Surface Wetting And Friction Studies Of Nano-Engineered Surfaces On Copper Substrate, Julius Sheldon Morehead

Graduate Theses and Dissertations

Nano-engineered-textures on a material surface can dramatically improve the wetting and non-wetting properties of a surface, and they also show promise to address friction issues that affect surfaces in contact. In this work, aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) was used to produce nano-textures on copper (Cu) substrates. A study was performed to examine the effects of changing the annealing conditions and a-Si thickness on nano-texture formation. The creation of various nano-topographies and chemically modifying them using octafluorocyclobutane (C4F8) was performed to control hydrophilicity, hydrophobicity, and oil affinity of nano-textured surfaces. A video-based contact angle measurement system was used …

Influence Of Recycled Asphalt Shingles On Asphalt Binder Content, Mixture Stiffness, And Laboratory Rutting Performance, Joshua David King

Graduate Theses and Dissertations

Recycled asphalt shingles (RAS) is a technology in which pavement costs can be reduced significantly and pavement properties may be enhanced. Also, incorporating shingles into pavements reduces the impacts of waste shingles in landfills, preserving our environment. However, for this new technology to be practical for implementation, a better understanding of how the ground shingles affect the properties of the asphalt is necessary. The purpose of this research was to examine the effects of recycled asphalt shingles on asphalt binder content, mixture stiffness, and laboratory rutting performance. For this project, shingles were added to hot mix asphalt mixtures at 2.5, …

Removal Of Disinfection By-Product Precursors Using Magnetic Ion Exchange (Miex(R)): The Effects Of Ph And Source Water Variability, Sarah Cousins

Graduate Theses and Dissertations

Disinfection by-products (DBPs) form as an unintended result of drinking water disinfection, from chemical reactions between disinfectants (e.g., free chlorine) and naturally occurring dissolved organic matter (DOM). At present, 11 DBPs are regulated in treated drinking waters due to potential adverse health effects, including four trihalomethanes (THMs). Despite nearly 40 years of DBP research, compliance with DBP regulations remains a challenge for many drinking water treatment plants (DWTPs), including the four DWTPs located on the Beaver Lake Reservoir in Northwest Arkansas. Due to the high net negative surface charge on DOM, anion exchange is one potentially viable method for removing …

The Marked Tree Site: Evaluation Of Geosynthetic Reinforcements In Flexible Pavements, Taylor Mitchell Goldman

Graduate Theses and Dissertations

This document presents findings from a three-year, full-scale, field research project aimed at determining the benefits of using geosynthetic reinforcements to improve the performance of flexible pavements constructed over poor subgrade soils. The test site, known as the Marked Tree site, is an 850-ft (258-m) long segment of low-volume frontage road along Highway 63 in the town of Marked Tree, Arkansas. The site, constructed in 2005, consists of seventeen 50-ft (15.2-m) long flexible pavement test sections with various types of geosynthetic reinforcements (woven and nonwoven geotextiles, and geogrids), which were all positioned at the base-subgrade interface, and two different nominal …

Powersearch: Augmenting Mobile Phone Search Through Personalization, Xiangyu Liu

Computer Science and Computer Engineering Undergraduate Honors Theses

Cell phone has become a fundamental element of people's life. People use it to call each other, browse websites, send text messages, etc. Among all the functionalities, the most important and frequently used is the search functionality. Based on ComScore, in July 2008, Google was estimated to host 235 millions searches per day. However, unlike the search on desktop, the search on cell phone has one critical constrain: battery. Cell phone performing a normal Google search, the battery drains very fast. The reason is that when sending a query to and fetching the results from Google, cell phone keeps communicating …

Inventory Models For Intermittent Highly Variable Demand And Policy Parameter Adjustments To Meet Desired Service Level Requirements, Yasin Unlu

Graduate Theses and Dissertations

This dissertation consists of three assays. The first assay examines the robustness of lead time demand models for the continuous review (r;Q) inventory policy. A number of classic distributions as well as distribution selection rules are examined under a wide variety of demand conditions. First, the models are compared to each other by assuming a known demand process and evaluating the errors associated with using a different model. Then, the models are examined using a large sample of simulated demand conditions. Approximation results of inventory performance measures - ready, rate excepted number of backorders and on-hand inventory levels are reported. …

Integrated Planning For Rural Rail Transportation, Jeffrey Cohan Gwaltney

Graduate Theses and Dissertations

Population growth in rural areas has led to new interest in rail transportation. Planning a passenger rail system involves numerous difficult decisions, most representing a trade-off between customer service and cost. In this work, we attempt to integrate many of these planning decisions. We consider strategic decisions such as station location and vehicle procurement, as well as tactical issues that include vehicle scheduling. Our integrated model exploits the linear network structure that best suits many rural American communities, including Northwest Arkansas. Due to the intractability of the integrated rail planning problem, we have developed a customized heuristic approach to solve …

Investigation Of A Floating Load Buck Dc-Dc Switching Converter, Hong Tan

Graduate Theses and Dissertations

A floating load buck DC-DC switching converter was analyzed, simulated, designed and prototyped. The floating load buck converter is first compared to the conventional buck converter. It was found that both the floating load buck converter and conventional buck converter exhibit similar conversion characteristics despite the differences in the placement of their output inductors. A floating load buck converter was designed to be used as a high-voltage off-line light-emitting diodes (LEDs) driver using a Texas Instruments' TPS92001 controller. Finally, the characteristics of this floating load buck converter LED driver were experimentally examined.

Design Of A Low Noise Amplifier For Wireless Sensor Networks, Ting Liu

Graduate Theses and Dissertations

CMOS technology becomes important in Radio Frequency (RF) communication systems which include both a receiver and a transmitter. In a high performance radio receiver, the Low Noise Amplifier (LNA) is the first circuit, and its noise performance dominates the entire receiver. Depending upon the system in which they are used, LNAs can be designed according to various topologies and structures. The LNA needs to have matched input impedance, and at the same time it should amplify the small amplitude input signal without adding too much noise and still have the minimal power consumption. It also needs a good interface with …

Design Of An 866 Mhz On-Chip Frequency Synthesizer, Phaniraj Joshi

Graduate Theses and Dissertations

There is a strong need for stable frequency references with large tuning ranges in today's communication systems. While the crystal oscillators assure good frequency stability, it is not possible to achieve a large frequency range by tuning the passive components attached to them. Frequency synthesizers are usually used for this purpose because of their ability to produce a variety of output frequencies. The Phase Locked Loop (PLL) based frequency synthesizer is the most preferred of all types of synthesizers available because of its additional features like programmability, low noise and low cost as well as high accuracy and stability. The …

Adaptive Intensity Modulated Radiation Therapy Planning Optimization With Changing Tumor Geometry And Biology Enforcing Both Cumulative And Fraction Size Dose Constraints, Behlul Saka

Graduate Theses and Dissertations

Intensity Modulated Radiation Therapy (IMRT) is a modern technique of delivering radiation treatments to cancer patients. In IMRT technology, intensities must be chosen for the many small unit grids into which the beams are divided to produce a desired distribution of dose at points throughout the body with the goal of maximizing dose delivered to the tumor while sparing healthy tissues from excessive radiation and keeping dose homogeneous across the tumor. Although IMRT plans are optimized as a single overall treatment plan, they are delivered over 30-50 treatment sessions (fractions) and both cumulative and per-fraction dose constraints apply. The extended …

Gesn Devices For Short-Wave Infrared Optoelectronics, Benjamin Ryan Conley

Graduate Theses and Dissertations

The electronics industry has a large silicon infrastructure for the manufacture of complementary-metal oxide semiconductor (CMOS) based electronics. The increasing density of Si based circuits has set a pace that is now pushing the physical limits of connectivity between devices over conventional wire based links. This has driven the increasing interest in Si based optoelectronics and to use the groundwork already established by the electronics industry for lower cost optical communications. The greatest limitation to this effort has been the incorporation of a Si based laser, which requires integration of a direct bandgap material within this CMOS process.

The Ge1-xSnx …

Fabrication Of Horizontal Silicon Nanowires Using A Thin Aluminum Film As A Catalyst, Khaja Hafeezuddin Mohammed

Graduate Theses and Dissertations

Silicon nanowires have been the topic of research in recent years for their significant attention from the electronics industry to grow even smaller electronic devices. The semiconductor industry is built on silicon. Silicon nanowires can be the building blocks for future nanoelectronic devices. Various techniques have also been reported in fabricating the silicon nanowires. But most of the techniques reported, grow vertical silicon nanowires. In the semiconductor industry, integrated circuits are designed and fabricated in a horizontal architecture i.e. the device layout is flat compared to the substrate. When vertical silicon nanowires are introduced in the semiconductor industry, a whole …

Location-Aware Traffic Management On Mobile Phones, Sarath Krishna Mandava

Graduate Theses and Dissertations

The growing number of mobile phone users is a primary cause of congestion in cellular networks. Therefore, cellular network providers have turned to expensive and differentiated data plans. Unfortunately, as the number of smartphone users keeps increasing, changing data plans only provides a temporary solution. A more permanent solution is offloading 3G traffic to networks in orthogonal frequency bands. One such plausible network is open Wi-Fi, which is free by definition. As Wi-Fi networks become ubiquitous, there are several areas where there is simultaneous Wi-Fi and 3G coverage. In this thesis, we study the feasibility of offloading 3G traffic to …

Proteome Based Development Of Novel Affinity Tail For Immobilized Metal Affinity Chromatography And Hydrophobic Interaction Chromatography, Neha Tiwari

Graduate Theses and Dissertations

At industrial scale, reducing the step in purification and recovery is desired; this not only decreases the cost but also increases the yield. Hydrophobic Interaction Chromatography (HIC) and Immobilized Metal Affinity Chromatography (IMAC) both are not harsh on biological structure or activity of proteins; also both the techniques are economical and therefore a suitable choice at industrial level. This dissertation comprises of three parts. Purpose for the Part I was to identify and characterize Escherichia coli proteins which display affinity towards both IMAC and Hydrophobic Interaction Chromatography (HIC). Co (II) IMAC was chosen as the primary capture step, followed by …

Development Of A Structured Concrete Thermocline Thermal Energy Storage System, Bradley M. Brown

Graduate Theses and Dissertations

The past couple of decades have shown a concern when considering the way the world obtains its power. The focus has been switching from fossil fuels that have been used for hundreds of years to renewable energy sources, such as the sun. Solar energy is readily and infinitely available for harnessing. One problem with solar energy, though, is its inability to be used during the night time and during cloud covered weather. A solution to this problem is the use of energy storage mechanisms. For solar plants that use solar thermal energy (concentrating solar power plants), thermal energy storage (TES) …

Degradation Of Polystyrene Foam Under Radiant Heat Flux, James Butler

Graduate Theses and Dissertations

As the demand for liquefied natural gas has increased, safety concerns about the performance of transport vessels under fire conditions have been raised. Current codes for the sizing of the pressure relief systems require that the vessels are able to withstand an emmissive heat flux of 108kW/m2 and do not take into account the effects of insulation loss due to thermal decomposition of the insulation materials. To address this possible oversight in the current code models were presented to a working group organized by the Society of International Gas Tanker and Terminal Operators Ltd. focusing on the decomposition rate of …

Improvements On Just-About-Right (Jar) Scales As Product Optimization Tools Using Kano Modeling Concepts, Bangde Li

Graduate Theses and Dissertations

Attribute Kano characteristics are useful in product design to prioritize development efforts. However, attribute Kano characteristics have not been discussed and applied to product optimization when using Just-About-Right (JAR) scales. Product optimizations without identifying attributes Kano characteristics can be misleading. The two objectives in this research were: 1. Determine attribute Kano categories using a modified classic Kano classification methodology. 2. Propose a method to measure attribute performance and identify attribute Kano characteristics to direct product optimization. Two methodologies of attribute Kano classification were investigated. In experiment one, a modified classic Kano methodology was employed to determine attribute Kano categories through …

Water Quality Trends For Section 319 Priority Watersheds In Northwest Arkansas, 1997-2010, Bryan William Bailey

Graduate Theses and Dissertations

Northwest Arkansas contains two Section 319 Priority Watersheds that the Arkansas Natural Resources Commission (ANRC) has identified as being impacted by point and nonpoint sources of pollution (i.e., phosphorus, nitrogen, and sediment), and the Arkansas Water Resources Center (AWRC) has monitored the water quality at several sites within these watersheds. Water-quality data has been collected over the last decade within the Illinois River Watershed (HUC #11110103) and the Upper White River Basin (Beaver Reservoir HUC# 11010001), each watershed containing three sampling sites. The Illinois River Watershed sites are located on the Illinois River, Osage Creek, and Ballard Creek, and the …

Modeling And Characterization Of P-Type Silicon Carbide Gate Turn Off Thyristors, Osama Shihadeh Saadeh

Graduate Theses and Dissertations

Silicon carbide (SiC) power semiconductor devices have emerged in the past decade as the most promising technology for next generation power electronic applications ranging for electric vehicles to grid-connected power routing and conversion interfaces. Several devices have been developed, and even some have been released commercially, including diodes, MOSFETs, JFETs, thyristors, gate turn-off thyristors, and IGBTs. The model development, characterization and experimental validation of SiC p-type Gate Turn-off Thyristors (GTO) is presented in this work. The GTO device in this work is being used as part of a SiC-based solid-state fault current limiter under development at the University of Arkansas' …

Fabrication Of Composite Nanomaterials For Thin Film Amorphous Silicon Solar Cells, Benjamin Seth Newton

Graduate Theses and Dissertations

A material with the precise combination of amorphous silicon and polycrystalline silicon would be able to take advantage of the high absorption capabilities of amorphous silicon and the electron transport capabilities of polycrystalline silicon. Polycrystalline nanostructures in the form of wires can also take advantage of other properties of light absorption, trapping and scattering inherent in nanowire structures. These properties of high absorption and electron transport in one device would lead to advances in the search for highly efficient low cost solar cells and sensors. In this work a thin film material composed of an array of polycrystalline silicon nanostructures …

Development Of Spray Cooling For High Heat Flux Electronics, Jeremy Scott Junghans

Graduate Theses and Dissertations

The thermal demands of modern day electronic systems require innovative thermal solutions. Spray cooling has proven to be able to cool heat fluxes orders of magnitude higher than traditional cooling methodologies. This work includes a comparison of spray cooling to standard thermal management methodologies. Key system parameters and considerations are discussed. The properties of available packaging materials and their effect on the reliability of a spray cooled system are presented. Parameters such as fluid temperature, droplet size, fluid velocity and flow rate all directly impact performance and are detailed in this work. Finally, results from of a wide range of …

Design And Fabrication Of Nanofluidic Systems For Biomolecule Characterizations, Orain Ansel Hibbert

Graduate Theses and Dissertations

Nanofluidic channel systems were designed and fabricated by combining MEMS microfabrication with AFM nanolithography. In the fabrication process flow, photolithography was first utilized to pattern microfluidic channels and reservoirs on a 4" Pyrex substrate. Subsequently, atomic force microscopy (AFM) based nanolithography was used to mechanically fabricate nanochannels to connect the microreservoirs which formed the inlet and outlet of the nanofluidic system. A Tap190 Diamond-Like Carbon (DLC) AFM tip with a force constant of 48 N/m and a radius of less than 15 nm was used as the nanolithography tool. The resultant nanochannel ranges from 20 to 80 µm in length …

Modeling Of Sic P-Channel Insulated Gate Bipolar Transistors (Igbts), Mahmood Saadeh

Graduate Theses and Dissertations

A new physics-based IGBT compact model has been developed for circuit simulation of silicon (Si) or silicon carbide (SiC) devices. The model accurately predicts the steady-state output, transfer and switching characteristics of the IGBT under a variety of different conditions. This is the first IGBT model to predict the behavior of p-channel SiC IGBTs. Previous work on IGBT models has focused on Si n-channel IGBTs [1-3]. This unified model is not limited to SiC p-channel IGBTs; the user has the option to select between Si or SiC, and n-channel or p-channel, making it the first IGBT model that captures the …

Photodetectors And Photovoltaic Devices Based On Semiconductor Nanomaterials, Jiang Wu

Graduate Theses and Dissertations

Photodetectors based various nanostructures and plasmon enhanced solar cells are investigated in this dissertation. The motivation of the dissertation rise is driven by urgent need of both high efficiency photodetectors and solar cells.

First, quantum dot infrared photodetectors have been intensely investigated due to their promise in high performance photodetectors. However, the strain-driven growth of quantum dots has hindered the progress of quantum dot photodetectors. The presence of strain in the device presents complexity in designing as well as defects. Therefore, in this project, new designs of quantum dot photodetector structures are presented to improve the control over detection wavelength. …

Hydraulic Conductivity Of Environmentally Controlled Landfill Liner Test Pad, Camila Maldonado Soria Galvarro

Civil Engineering Undergraduate Honors Theses

Laboratory and field hydraulic conductivity tests have been conducted on soil samples to develop and verify the zone of acceptance for liner placement. Compaction testing and flexible wall hydraulic conductivity tests were performed on fifteen (15) samples to determine the dry unit weight, molding water content, and laboratory permeability. Five of the fifteen samples were compacted at Standard proctor energy, five were compacted at 75 percent of Standard proctor energy, and five were compacted at 50 percent of Standard proctor energy. The results obtained from the laboratory portion of the testing program (the zone of acceptance) are presented. A ten …

Application Of The Empirical Mode Decomposition On The Characterization And Forecasting Of The Arrival Data Of An Enterprise Cluster, Linh Bao Ngo

Graduate Theses and Dissertations

Characterization and forecasting are two important processes in capacity planning. While they are closely related, their approaches have been different. In this research, a decomposition method called Empirical Mode Decomposition (EMD) has been applied as a preprocessing tool in order to bridge the input of both characterization and forecasting processes of the job arrivals of an enterprise cluster. Based on the facts that an enterprise cluster follows a standard preset working schedule and that EMD has the capability to extract hidden patterns within a data stream, we have developed a set of procedures that can preprocess the data for characterization …

Mapping Device With Wireless Communication, Xiangyu Liu

Electrical Engineering Undergraduate Honors Theses

Wireless communication is one of the most powerful communication methods that people use nowadays. The key advantage of wireless communications is that it can cover large distances without having to run any cables from one end to the other. Based on this advantage, wireless communication has many important applications, such as remote controls, cell phones, and global positioning system (GPS). This senior design project is developed to use wireless communication technology to map the geographic characteristics of an unknown place. It contains two wireless communication modules with Atmega1281 microprocessor, two robots with the 8051 microcontroller, six pairs of infrared transmitters …

Synthesis Of Zinc Oxide Nanorods And Use In Biosensor Applications, Anishkumar Manoharan

Graduate Theses and Dissertations

The main aim of this research was to develop a nanorod based biosensor for biomedical applications. In this project I use zinc oxide nanorods as the bio-material for biosensor. I fabricated these nanorods using a solution-based technique. Initially I coated a zinc oxide seed layer as the base. This seed layer was then annealed at 350 degrees for almost 1 hour. As a next step, interdigitated electrodes were fabricated on the top of the seed layer using a lift off process. The zinc oxide nanorods were then grown at 90 degrees for almost 4 hours along the electrodes. In this …

Laboratory Evaluation Of Dynamic Characterization Methods For Rapid Condition Assessment Of Bridges, Jason Kyle Herrman

Graduate Theses and Dissertations

The objective of this thesis was to devise and refine Structural Health Monitoring methods and the associated quantitative characterization methods with the specific goal of enabling rapid and reliable safety evaluations of bridges following natural or manmade hazards. Presently, the safety and serviceability of these transportation infrastructure assets for use in emergency response and recovery operations are evaluated through on-site visual inspections of individual structures by teams of specially trained engineers or technicians; a process that is manpower-intensive, subjective, and slow. Specifically, the researcher was able to identify and evaluate strategies and procedures for using dynamic testing methods to rapidly …