Engineering Commons^™

Growth And Behaviors Of Inn/Gan Multiple Quantum Wells By Plasma-Assisted Molecular Beam Epitaxy, Chen Li

Graduate Theses and Dissertations

Fully realizing the potential of InGaN semiconductors requires high quality materials with arbitrary In-content. To this date the growth of In-rich InGaN films is still challenging since it suffers from the low growth temperatures and many detrimental alloying problems. InN/GaN multiple quantum wells (MQWs) and super lattices (SLs) are expected to be promising alternatives to random InGaN alloys since in principle they can achieve the equivalent band gap of InGaN random alloys with arbitrarily high In-content and at the same time bypass many growth difficulties.

This dissertation focuses on studying the growth mechanisms, structural properties and energy structures of InN/GaN …

Fabrication And Characterization Of Electrochemical Glucose Sensors, Mohammed Marie

Graduate Theses and Dissertations

Electrochemical sensors based on the nanostructure of the semiconductor materials are of tremendous interest to be utilized for glucose monitoring. The sensors, based on the nanostructure of the semiconductor materials, are the third generations of the glucose sensors that are fast, sensitive, and cost-effect for glucose monitoring.

Glucose sensors based on pure zinc oxide nanorods (NRs) grown on different substrates, such ITO, FTO, and Si/SiO2/Au, were investigated in this research. Silicon nanowire (NW)- based glucose sensors were also studied. First, an enzyme-based glucose sensor was fabricated out of glass/ITO/ZnO NRs/BSA/GOx/nafion membrane. The sensor was tested amperometrically at different glucose concentrations. …

Photochemical Etching Of Nitrided Stainless Steel Piston Rings, Steven Sonntag

Mechanical Engineering Undergraduate Honors Theses

Piston rings are designed to provide a seal between the piston and the cylinder wall of internal combustion engines, keeping oil from the crankcase from getting into the combustion chamber. This means piston rings are the main point of contact between the piston and the cylinder wall, which causes the piston to experience high amounts of friction and wear. By texturing the surfaces of the cylinder wall and/or the piston ring, the amount of contact area can be reduced, allowing for less friction, slower wear, and better gas mileage. In this thesis experiments, photochemical etching processes were developed to etch …

Optimizing The Plasmonic Enhancement Of Light In Metallic Nanogap Structures For Surface-Enhanced Raman Spectroscopy, Stephen Joseph Bauman

Graduate Theses and Dissertations

Technology based on the interaction between light and matter has entered something of a renaissance over the past few decades due to improved control over the creation of nanoscale patterns. Tunable nanofabrication has benefitted optical sensing, by which light is used to detect the presence or quantity of various substances. Through methods such as Raman spectroscopy, the optical spectra of solid, liquid, or gaseous samples act as fingerprints which help identify a single type of molecule amongst a background of potentially many other chemicals. This technique therefore offers great benefit to applications such as biomedical sensors, airport security, industrial waste …

Impedance Sensing Of Cancer Cells Directly On Sensory Bioscaffolds Of Bioceramics Nanofibers, Hanan Alismail

Graduate Theses and Dissertations

Cancer cell research has been growing for decades. In the field of cancer pathology, there is an increasing and long-unmet need to develop a new technology for low-cost, rapid, sensitive, selective, label-free (i.e. direct), simple and reliable screening, diagnosis, and monitoring of live cancer and normal cells in same shape and size from the same anatomic region. For the first time on using an impedance signal, the breast cancer and normal cells have been thus screened, diagnosed and monitored on a smart bioscaffold of entangled nanowires of bioceramics titanate grown directly on the surface of implantable Ti-metal and characterized by …

Stability Analysis Of A High-Power Microgrid, David Manuel Carballo Rojas

Graduate Theses and Dissertations

The objective of this thesis is to perform the modeling and stability analysis of a high-power microgrid with multiple parallel-and grid connected voltage source converters using the system parameters from the high-power microgrid testbed at the National Center for Reliable Electric Power Transmission (NCREPT) at the University of Arkansas in order to identify, minimize, if not eliminate, the potential instabilities that can affect the proper operation of the microgrid testbed. To achieve this objective, the mathematical modeling of the high-power microgrid considering the adverse effects of resonances due to interactions among the converter LCL output filters is presented and analyzed. …

Controlling Relative Humidity Using Glycerin, Juan Martinez

Civil Engineering Undergraduate Honors Theses

A series of tests were conducted to control relative humidity (RH) using a bubbler system that contained a series of glass jars and glass vials filled with different concentrations of glycerin. The relative humidity within the glass jars was measured. The total time interval for each laboratory test was 48 hours. During the first 24 hours a pump was used to bubble air through the glycerin solution. During the second 24 hours, the pump was turned off, and the RH within the system was monitored within the closed system. Target RH measurements from 100% to a 0% were obtained. The …

Fully Analog Laser Driver With Robust Active Feedback Control, John Petrilli

Graduate Theses and Dissertations

The objective of this project was to go through a real life engineering development cycle, document and justify the design choices, and use background experience in electronic design and control systems to implement the best design possible. The laser driver implemented in this project is designed for the general use of a large variety of diodes in continuous wave mode, much like off the shelf laser drivers. The design goals included improving upon off the shelf laser drivers by decreasing steady state error, setting time, response time, and overshoot. Many different feedback control systems were evaluated, and a modified PID …

Smart Surge Irrigation Using Microcontroller Based Embedded Systems And Internet Of Things, Prashant Dinkar Borhade

Graduate Theses and Dissertations

Surge Irrigation is a type of furrow irrigation and one of many efficient irrigation techniques. It is one of the economical techniques and requires minimum labor for monitoring it. In surge irrigation, water is applied intermittently to a field to achieve uniform distribution of water along the furrows, which is important while irrigating, as it ensures that there is enough water near the root zone of the crop. The uneven distribution can cause a loss in crop productivity.

Surge irrigation uses a surge valve, which is an electro-mechanical device that irrigates a field. The commercial surge valves available on the …

A Scalable, Chunk-Based Slicer For Cooperative 3d Printing, Jace J. Mcpherson

Computer Science and Computer Engineering Undergraduate Honors Theses

Cooperative 3D printing is an emerging technology that aims to increase the 3D printing speed and to overcome the size limit of the printable object by having multiple mobile 3D printers (printhead-carrying mobile robots) work together on a single print job on a factory floor. It differs from traditional layer-by-layer 3D printing due to requiring multiple mobile printers to work simultaneously without interfering with each other. Therefore, a new approach for slicing a digital model and generating commands for the mobile printers is needed, which has not been discussed in literature before. We propose a chunk-by-chunk based slicer that divides …

Collaborative Robotic Path Planning For Industrial Spraying Operations On Complex Geometries, Steven Brown

Graduate Theses and Dissertations

Implementation of automated robotic solutions for complex tasks currently faces a few major hurdles. For instance, lack of effective sensing and task variability – especially in high-mix/low-volume processes – creates too much uncertainty to reliably hard-code a robotic work cell. Current collaborative frameworks generally focus on integrating the sensing required for a physically collaborative implementation. While this paradigm has proven effective for mitigating uncertainty by mixing human cognitive function and fine motor skills with robotic strength and repeatability, there are many instances where physical interaction is impractical but human reasoning and task knowledge is still needed. The proposed framework consists …

Investigation Of A Gan-Based Power Supply Topology Utilizing Solid State Transformer For Low Power Applications, Akrem Mohamed Elrajoubi

Graduate Theses and Dissertations

Gallium nitride (GaN) power devices exhibit a much lower gate capacitance for a similar on-resistance than its silicon counterparts, making it highly desirable for high-frequency operation in switching converters, which leads to their significant benefits on power density, cost, and system volume. High-density switching converters are being realized with GaN power devices due to their high switching speeds that reduce the size of energy-storage circuit components. The purpose of this dissertation research is to investigate a new isolated GaN AC/DC switching converter based on solid-state transformer configuration with a totem-pole power factor corrector (PFC) front-end, a half-bridge series-resonant converter (SRC) …

Intelligent Application Of Flexible Ac Transmission System Components In An Evolving Power Grid, Robert Wall

Graduate Theses and Dissertations

The world revolves around energy and the energy sector is continually transforming and evolving. The status quo has been set by governing agencies in the United States for completely reliable power. The demand for energy efficiency continually rises for multiple reasons. Technology has improved for all sectors of the power grid, including renewable energy sources, fault protection, and SMART grid technology. The addition of new energy sources has led to the decommissioning of inefficient energy sources. The implementation of new technologies and power load on a large scale, coupled with the removal of grid stabilizers has posed different challenges that …

Classifying Interdependencies In The Food And Agriculture Critical Infrastructure Sector, John Doerpinghaus

Graduate Theses and Dissertations

This work classifies examples of infrastructure interdependencies found in the food and agriculture critical infrastructure sector. Interdependencies are identified through an examination of rice and poultry agriculture throughout the state of Arkansas. The subtleties of interdependence examples in the food and agriculture sector are inadequately captured by the well-studied interdependence classification taxonomies. Through 39 interviews, we develop an understanding of the subtle temporal, geographic, and productivity scales of interdependence in over 100 examples and present five new, distinct classifications of interdependence: (1) dynamic physical, (2) dynamic geographic, (3) deadline, (4) delay, and (5) human, economic, and natural resource interdependencies. An …

Comparative Study Of Power Semiconductor Devices In A Multilevel Cascaded H-Bridge Inverter, Kenneth Mordi

Graduate Theses and Dissertations

This thesis compares the performance of a nine-level transformerless cascaded H-bridge (CHB) inverter with integrated battery energy storage system (BESS) using SiC power MOSFETs and Si IGBTs. Two crucial performance drivers for inverter applications are power loss and efficiency. Both of these are investigated in this thesis. Power devices with similar voltage and current ratings are used in the same inverter topology, and the performance of each device is analyzed with respect to switching frequency and operating temperature. The loss measurements and characteristics within the inverter are discussed. The Saber® simulation software was used for the comparisons. The power MOSFET …

Budget-Constrained Regression Model Selection Using Mixed Integer Nonlinear Programming, Jingying Zhang

Graduate Theses and Dissertations

Regression analysis fits predictive models to data on a response variable and corresponding values for a set of explanatory variables. Often data on the explanatory variables come at a cost from commercial databases, so the available budget may limit which ones are used in the final model.

In this dissertation, two budget-constrained regression models are proposed for continuous and categorical variables respectively using Mixed Integer Nonlinear Programming (MINLP) to choose the explanatory variables to be included in solutions. First, we propose a budget-constrained linear regression model for continuous response variables. Properties such as solvability and global optimality of the proposed …

Growth And Characterization Of Silicon-Germanium-Tin Semiconductors For Future Nanophotonics Devices, Bader Saad Alharthi

Graduate Theses and Dissertations

The bright future of silicon (Si) photonics has attracted research interest worldwide. The ultimate goal of this growing field is to develop a group IV based Si foundries that integrate Si-photonics with the current complementary metal–oxide–semiconductor (CMOS) on a single chip for mid-infrared optoelectronics and high speed devices. Even though group IV was used in light detection, such as photoconductors, it is still cannot compete with III-V semiconductors for light generation. This is because most of the group IV elements, such as Si and germanium (Ge), are indirect bandgap materials. Nevertheless, Ge and Si attracted industry attention because they are …

Experimentation And Modeling Of The Effects Of Along-Wind Dispersion On Cloud Characteristics Of Finite-Duration Contaminant Releases In The Atmosphere, Jessica M. Morris

Graduate Theses and Dissertations

Along-wind dispersion, or stretching of the cloud in the direction of the wind, plays an important role in the concentration and modeling of contaminant releases in the atmosphere. Theoretical and empirical derivations were compared for appropriate parameterization of along-wind dispersion. Available field data were analyzed to evaluate and improve previous parameterizations of the along-wind dispersion coefficient, σ_x. An experimental test program was developed and executed in an ultra-low speed wind tunnel at the Chemical Hazards Research Center to determine the effects of the time distribution coefficient on true finite-duration releases from an original area source. Multiple wind speeds, release durations, …

Measuring Characteristic Shrinkage Variability Due To Metal Loading Effects In Low Temperature Co-Fired Ceramic Using Image Processing, John Ezekiel Zumbro

Graduate Theses and Dissertations

Low temperature co-fired ceramic (LTCC) has many benefits when it comes to electronic packaging due to the low dielectric loss, reliability in extreme environments, and high breakdown voltage. Though the ceramic has a lot of benefits it is not widely used due to the high cost and complexities associated with manufacturing. One of these issues with manufacturing is compensating for the shrinkage of the ceramic, this is accomplished by using an expansion factor, creating the “green” or manufactured design. This expansion factor is approximated through knowledge of the ceramic factors such as the metal loading, layers of ceramic tape, firing …

Introduction To Data Analytics And Emerging Real-World Use Cases, Art Chaovalitwongse

Operations Management Presentations

Data analytics is a rapidly emerging interdisciplinary research area that involves advances in engineering, computer science, statistics and operations research. This webinar is focused on introducing the foundation of data analytics and emerging real-world use cases of data analytics. This presentation will begin with a discussion of the mathematical and statistical modeling aspects of various levels of data analytics (i.e., descriptive, predictive and prescriptive). In this webinar, you will hear an overview of data analytics in real world problems ranging from healthcare analytics, retail analytics and financial analytics.

Micro-Flow Nanocatalysis: Synergic Effect Of Tfoh@Spions And Micro-Flow Technology As An Efficient And Robust Catalytic System For The Synthesis Of Plasticizers, Maryam Tashi, Behnaz Shafiee, Yoshie Sakamaki, Ji-Yun Hu, Zachary Heidrick, Ahmad R. Khosropour, M. Hassan Beyzavi

Chemistry & Biochemistry Faculty Publications and Presentations

The combination of continuous flow technology with immobilizing of only 0.13 mol% of triflic acid (TfOH) on silica-encapsulated superparamagnetic iron oxide nanoparticles (SPIONs) under solvent-free conditions successfully provided a powerful, efficient, and eco-friendly route for the synthesis of plasticizers. The turnover frequency value in micro-flow conditions varied in the range of 948.7 to 7384.6 h−1 compared to 403.8 to 3099 h−1 for in-flask. This technique works efficiently, encouraging future applications of micro-flow nano-catalysis in green chemistry.

Stop “Droning” On About Unmanned Aircraft Systems And Do Something About It, Richard Ham

Operations Management Presentations

The use of Unmanned Aircraft Systems (UAS) is quickly becoming an expectation for inventory management, supply chain, engineering/construction and architectural inspections, agriculture assessment and surveillance. This webinar will provide an overview of compliance requirements, startup costs, and new use cases changing the way operations managers function and improve efficiency. Supply chain management and delivery, construction management, quality management inspections and homeland security requirements are already heavily invested in UAS integration. Learn how to use your knowledge as an operations manager to stay ahead of your competitors and discover creative ways to drive up productivity and reduce costs by adding UAS …

Leading Through Change, Travis Mcneal

Operations Management Presentations

In this webinar, you will learn how to leverage periods of change to develop better leaders. We all hear that "the only constant is change" and that "change is hard." What if there was a different narrative? What if organizations going through change actually resulted in higher performance, engagement and better leadership? It is widely known that effective change management requires sponsorship — this means every leader, from the C-Suite to the front-line supervisor. This webinar will share practical and repeatable ways to help all leaders improve the way they lead change.

Design Of Wind Turbine Tower Height And Blade Length: An Optimization Approach, Ryan Wass

Mechanical Engineering Undergraduate Honors Theses

The wind industry is a fast growing market and is quickly becoming competitive with traditional non-renewable energy resources. As with any developing industry, research must continually be redefined as more complex understandings of design variables are learned. Optimization studies are common ways to quickly refine design variable selections. Historical wind turbine data shows that the tower hub height to rotor diameter ratio scales almost linearly. However there is no specific rule that dictates the optimum hub height for a given diameter. This study addresses this question by using an Excel based optimization program to determine the height to diameter ratio …

Presenting To Senior Decision Makers: Clear, Concise & Complete, Kirk Michealson

Operations Management Presentations

Your manager just assigned you to lead a new project for your Vice President. You have many questions! What are the details of the project? What does the VP want to see in briefings? Does the VP have an advocate for pre-briefs? What information is important to include in the presentation? How detailed should the information be? How should the information be presented? Are there any best practices in developing presentations? In this webinar, you will learn strategies for sharing important information with key stakeholders in your career – and how to actually get them to listen!

Imaging Characterization Of Current Generating Lipid-Protein Membranes, Joel D. Kamwa

Microelectronics-Photonics Student Works

Imaging Characterization of Current Generating Lipid-protein Membranes

Geophysical Assessment Of Subsurface Soil Conditions Using Capacitively Coupled Resistivity, Folaseye Coker

Graduate Theses and Dissertations

The purpose of this research is to explore the applicability of Capacitively-Coupled Resistivity (CCR) as an improvement on traditional drilling and sampling methods for subsurface soil investigations. The CCR method could be used to identify critical locations for drilling and sampling such as expansive clay layers and anomalies (sinkholes, unknown landfills, etc.) rather than uniformly sampling across a site. CCR surveys were performed at Alpena, Arkansas along a highway expansion project changing US 62 from a two lane to four lane highway, and at Alton, Illinois along the Mel Price Levee, a 5.2 mile levee along a portion of the …

Computer Modeling Of Close-To-Ground Tornado Wind-Fields For Different Tornado Widths, Mohammadhossein Kashefizadeh

Graduate Theses and Dissertations

Tornadoes induce different wind forces on buildings than straight-line (SL) winds. The tangential velocity (Vθ) of tornados is the main parameter that causes damage to the buildings. In-field tornado measurements cannot evaluate the tornado’s Vθ at less than 20m above ground level (AGL). The laboratory tornado simulators suggest that the Swirl ratio (S) and the radius (ro) are the most influential factors affecting Vθ. However, due to scaling problems, laboratory simulators cannot report the Vθ for elevations less than 10m AGL. Well refined computational fluid dynamics (CFD) models can evaluate the Vθ at less than 10m AGL. However, the CFD …

Proposed Astm Standard For The Stokoe-Type Resonant Column Torsional Shear Device, Anh Tuan Tran

Graduate Theses and Dissertations

Resonant Column Torsional Shear (RCTS) testing has become one of the most commonly used methods for determining laboratory soil stiffness and soil damping. The RCTS test has been accepted and is commonly utilized during the permitting of new nuclear facilities. However, there is still no available public standard for performing RCTS tests using the Stokoe-type device. Therefore, an ASTM standard for calibration and performance of RCTS tests using the Stokoe-type RCTS device is presented herein. Data collected using the Stokoe-type RCTS devices at the University of Arkansas (UofA) and at the Norwegian Geotechnical Institute (NGI) also aided in the development …

Testing And Development Of Pre-Stressed Cfrp Retrofit Strategies For Controlling Fatigue Cracking In Steel Waterway Lock Gate Structures, Maggie Langston

Graduate Theses and Dissertations

Steel waterway lock gates across the national inland waterway transportation network are reaching and exceeding their intended service life, often experiencing component failures that lead to service interruptions. Unscheduled maintenance and repair of lock gates can be expensive and cause economic ripples throughout the entire inland waterway network. These lock gate component failures are often caused by fatigue cracking from repeated loading during operation. This thesis develops and tests a prestressed carbon fiber reinforced polymer (CFRP) fatigue retrofit for controlling fatigue demands within lock gate components. The study expands upon a recent analytical work by Lozano (2017) by experimentally investigating …