Engineering Commons^™

Bridge Maintenance To Enhance Corrosion Resistance And Performance Of Steel Girder Bridges, Luis M. Moran Yanez

Open Access Dissertations

The integrity and efficiency of any national highway system relies on the condition of the various components. Bridges are fundamental elements of a highway system, representing an important investment and a strategic link that facilitates the transport of persons and goods. The cost to rehabilitate or replace a highway bridge represents an important expenditure to the owner, who needs to evaluate the correct time to assume that cost. Among the several factors that affect the condition of steel highway bridges, corrosion is identified as the main problem. In the USA corrosion is the primary cause of structurally deficient steel bridges. …

Laser-Processed Parchment Paper For Fabrication Of Chronic Wound Dressings With Selective Oxygenation, Manuel Ochoa

Open Access Dissertations

Chronic non-healing wounds (e.g., diabetic foot ulcers and bed sores) impact over 6.5 million Americans per year, costs in excess of $25 billion to treat on an annual basis, and are on the rise due to increasing levels of obesity and diabetes compounded by an aging population. A major inhibitor of healing is suboptimal oxygenation of the wound bed. Unlike acute injuries that receive sufficient oxygen via a functional blood vessel network, chronic wounds often suffer from the lack of a proper vascular network; thus being incapable of providing sufficient oxygen for tissue growth. Typical medical treatment of hypoxic chronic …

Development Of Inverse Methods For Reconstruction Of Flight Environments On Ablators, A. Brandon Oliver

Open Access Dissertations

Obtaining measurements of flight environments on ablative heatshields is both critical for spacecraft development and extremely challenging due to the harsh heating environment and surface recession. Thermocouples installed several millimeters below the surface are commonly used to measure the heatshield temperature response, but an ill-posed inverse heat conduction problem must be solved to reconstruct the surface heating environment from the embedded thermocouple measurements. The material properties of typical ablators make the reconstruction process more challenging when the measurements are deep, but measurements often must be located deep to allow for surface recession. Compounding the complexity of the surface reconstruction problem, …

Microstructural Evolution During The Homogenization Heat Treatment Of 6xxx And 7xxx Aluminum Alloys, Pikee Priya

Open Access Dissertations

Homogenization heat treatment of as-cast billets is an important step in the processing of aluminum extrusions. Microstructural evolution during homogenization involves elimination of the eutectic morphology by spheroidisation of the interdendritic phases, minimization of the microsegregation across the grains through diffusion, dissolution of the low-melting phases, which enhances the surface finish of the extrusions, and precipitation of nano-sized dispersoids (for Cr-, Zr-, Mn-, Sc-containing alloys), which inhibit grain boundary motion to prevent recrystallization. Post-homogenization cooling reprecipitates some of the phases, changing the flow stress required for subsequent extrusion. These precipitates, however, are deleterious for the mechanical properties of the alloy …

Towards Building A Prototype Spin-Logic Device, Ashish Verma Penumatcha

Open Access Dissertations

Since the late 1980s, several key discoveries, such as Giant and Tunneling Magne- toresistance, and advances in magnetic materials have paved the way for exponentially higher bit-densities in magnetic storage. In particular, the discovery of Spin-Transfer Torque (STT) has allowed information to be written to individual magnets using spin-currents. This has replaced the more traditional Oersted-field control used in field-MRAMs and allowed further scaling of magnetic-memories. A less obvious con- sequence of STT is that it has made possible a logic-technology based on magnets controlled by spin-polarized currents. Charge-coupled Spin Logic (CSL) is one such device proposal that couples a …

Experimentally Validated 3d Md Model For Afm-Based Tip-Based Nanomanufacturing, Rapeepan Promyoo

Open Access Dissertations

In order to control AFM-based TBN to produce precise nano-geometry efficiently, there is a need to conduct a more focused study of the effects of different parameters, such as feed, speed, and depth of cut on the process performance and outcome. This is achieved by experimentally validating a MD simulation model of nanomachining, and using it to conduct parametric studies to guide AFM-based TBN. A 3D MD model with a larger domain size was developed and used to gain a unique insight into the nanoindentation and nanoscratching processes such as the effect of tip speed (e.g. effect of tip speed …

Race, Class And Gender In Engineering Education: A Quantitative Investigation Of First Year Enrollment, Canek Moises Luna Phillips

Open Access Dissertations

Research explanations for the disparity across both race and gender in engineering education has typically relied on a deficit model, whereby women and people of color lack the requisite knowledge or psychological characteristics that Whites and men have to become engineers in sufficient numbers. Instead of using a deficit model approach to explain gender and race disparity, in the three studies conducted for this dissertation, I approach gender and race disparity as the result of processes of segregation linked to the historic and on-going perpetuation of systemic sources of oppression in the United States. In the first study, I investigate …

A New Approach To Modeling Aviation Accidents, Arjun Harsha Rao

Open Access Dissertations

General Aviation (GA) is a catchall term for all aircraft operations in the US that are not categorized as commercial operations or military flights. GA aircraft account for almost 97% of the US civil aviation fleet. Unfortunately, GA flights have a much higher fatal accident rate than commercial operations. Recent estimates by the Federal Aviation Administration (FAA) showed that the GA fatal accident rate has remained relatively unchanged between 2010 and 2015, with 1566 fatal accidents accounting for 2650 fatalities. Several research efforts have been directed towards betters understanding the causes of GA accidents. Many of these efforts use National …

A Unicorn's Tale: Examining The Experiences Of Black Women In Engineering Industry, Monique S. Ross

Open Access Dissertations

Black women have recently been identified as the most educated demographic in the United States, and yet they are grossly underrepresented in engineering. They comprise 6.4 % of the U.S. population and only 0.72 % of engineering industry. Meanwhile, engineers have been identified as the key to the United States’ ability to maintain its prominence and leadership in a competitive global economy due to their contribution to maintaining and improving our infrastructures and standard of living. This significance to society has spawned national initiatives geared towards broadening participation in engineering. This research study was designed to explore the experiences of …

Adaptive Sampling Trust-Region Methods For Derivative-Based And Derivative-Free Simulation Optimization Problems, Sara Shashaani

Open Access Dissertations

We consider unconstrained optimization problems where only “stochastic” estimates of the objective function are observable as replicates from a Monte Carlo simulation oracle. In the first study we assume that the function gradients are directly observable through the Monte Carlo simulation. We propose ASTRO, which is an adaptive sampling based trust-region optimization method where a stochastic local model is constructed, optimized, and updated iteratively. ASTRO is a derivative-based algorithm and provides almost sure convergence to a first-order critical point with good practical performance. In the second study the Monte Carlo simulation is assumed to provide no direct observations of the …

Investigation Of Methods For Reducing Aflatoxin Contamination In Distillers Grains, Hu Shi

Open Access Dissertations

The overall goal of this project was to reduce the aflatoxin level in the final coproduct of ethanol bioprocessing--DDGS. This was pursued by examining the effects of reduction of aflatoxin in the incoming corn prior to bioprocessing, the degradation of aflatoxin in the intermediate products, namely DWG and CDS, during processing, and aflatoxin degradation in the DDGS. Segregation techniques (size screening and density sorting) and detoxification methods (conventional and microwave heating, food additives, and high voltage atmospheric cold plasma) were evaluated for their effectiveness in aflatoxin reduction.

Effectiveness of physical segregation of aflatoxin contaminated corn was investigated by size screening …

Dynamic Holography In Semiconductors And Biomedical Optics, Hao Sun

Open Access Dissertations

Three-dimensional scanning and display are rapidly-advancing new technologies with important commercial drivers such as 3D printing and remote imaging for big data applications. Holography is a natural approach to recording and displaying three-dimensional information because it uses phase-sensitive interferometry to record interference patterns when a reference beam encounters coherent light arriving from an object. The 3D information is contained in the values of wave optics. Holography is a broad field that goes beyond recording and displaying. For instance, holographic optical elements, which take advantage of holographic imaging principles, perform the functions of lenses, gratings or mirrors. Holographic interferometry is also …

Characterizing The Effects Of Repetitive Head Trauma In Female Soccer Athletes For Prevention Of Mild Traumatic Brain Injury, Diana Otero Svaldi

Open Access Dissertations

As participation in women’s soccer continues to grow and the longevity of female athletes’ careers continues to increase, prevention of mTBI in women’s soccer has become a major concern for female athletes as the long-term risks associated with a history of mTBI are well documented. Among women’s sports, soccer exhibits the highest concussion rates, on par with those of men’s football at the collegiate level. Head impact monitoring technology has revealed that “concussive hits” occurring directly before symptomatic injury are not predictive of mTBI, suggesting that the cumulative effect of repetitive head impacts experienced by collision sport athletes should be …

Clustered-Dot Periodic Halftone Screen Design And Icc Profile Color Table Compression, Chuohao Tang

Open Access Dissertations

This dissertation studies image quality problems associated with rendering images in devices like printing or displaying. It mainly includes two parts: clustered-dot periodic halftone screen design, and color table compression.

Screening is a widely used halftoning method. As a consequence of the lower resolution of digital presses and printers, the number of printer-addressable dots or holes in each microcell may be too few to provide the requisite number of tone lev- els between paper white and full colorant coverage. To address this limitation, the microcells can be grouped into supercells. The challenge is then to determine the desired supercell shape …

Fracture Analysis In Biomimetic Bouligand Architectures, Nobphadon Suksanqpanya

Open Access Dissertations

The Bouligand structure, which is found in many biological materials, is a hierarchical architecture that features uniaxial fiber layers assembled periodically into a helicoidal pattern. Many studies have highlighted the high damage-resistant performance of Bouligand structures and its biomimetic materials. One of the outstanding species with the Bouligand structures is the smashing Mantis Shrimp, Odontodactylus Scyllarus, (or stomatopod) due to its capability of generating high speed, high acceleration blows using its raptorial appendage to defeat highly armored preys. The load-bearing part of this appendage, the dactyl club, contains an interior region, which is mainly characterized by the Bouligand structure. This …

Geometric Accuracy Evaluation Of Mobile Terrestrial Lidar Surveys With Supporting Algorithms, Chisaphat Supunyachotsakul

Open Access Dissertations

Mobile Mapping System (MMS) technology is widely used for many applications, hence quantifying its accuracy is a very important and essential task and is a primary focus of this research. In general, to perfrom geometric accuracy evaluation of MMS data, validation points/features are needed. A method is needed to capture a point feature off the roadway in a position where a target on the ground surface would not be visible to the scanner. In this study, eight sphere targets with 14" diameter were placed on the shoulder of the roadway over validation points on the ground. The sphere targets were …

Policy Design Tool For Managing Indoor Residential Water Demand In Water-Scarce Regions, Mujahed M. Thneibat

Open Access Dissertations

In view of population growth; climate change; and economic evolution, water resources in numerous parts of the world have reached their natural capacities. Consequently, the ability of many countries to grow; meet the basic needs of inhabitants; and protect the environment will be endangered like never before unless water resources are smartly handled and managed. ^ In the past few decades, many developed and developing countries have suffered from water scarcity, and more are certain to follow. The water security dilemma is much more challenging in developing countries. Water utilities have had to follow regulatory plans to manage demand on …

Approximate Computing: An Integrated Cross-Layer Framework, Swagath Venkataramani

Open Access Dissertations

A new design approach, called approximate computing (AxC), leverages the flexibility provided by intrinsic application resilience to realize hardware or software implementations that are more efficient in energy or performance. Approximate computing techniques forsake exact (numerical or Boolean) equivalence in the execution of some of the application’s computations, while ensuring that the output quality is acceptable. While early efforts in approximate computing have demonstrated great potential, they consist of ad hoc techniques applied to a very narrow set of applications, leaving in question the applicability of approximate computing in a broader context.

The primary objective of this thesis is to …

Identifying And Prioritizing Critical Success Factors For Fixed Base Operators In The United States: A Mixed Method Approach, Yu Wang

Open Access Dissertations

Fixed Base Operators (FBOs) are major service providers for the general aviation (GA) sector, which closely connect the public with the aviation industry. However, over the past decade, the U.S. GA industry has experienced a decline in the numbers of registered aircraft, pilots, and airports. Due to the fact that FBOs significantly contribute to the aviation industry, further research studies regarding the FBO-sector at a national level are needed. The purpose of this dissertation was to identify and prioritize the critical success factors (CSFs) that promote the success of FBO operations in the United States.

The methodology consisted of a …

Fundamental Studies Of Flame Propagation In Lean-Burn Natural Gas Engines, Zhiyan Wang

Open Access Dissertations

Lean-burn natural gas engines offer enhanced thermal efficiencies and reduced soot and NOx emissions. However, cycle-to-cycle variability in combustion that can result from unreliable ignition, variability in equivalence ratio and quenching is a challenge. Reliability of ignition can be improved by employing a dual-fuel ignition strategy in which a small quantity of diesel fuel is injected to initiate ignition. Computational studies of n-heptane/methane-air mixing layers are performed to provide insight into the fundamental physics of dual-fuel ignition. The results show that the characteristic time required for steady premixed flame propagation has three components: time for autoignition to occur, time for …

On The Use Of Mechanical And Acoustical Excitations For Selective Heat Generation In Polymer-Bonded Energetic Materials, Daniel C. Woods

Open Access Dissertations

To address security issues in both military and civilian settings, there is a pressing need for improved explosives detection technologies suitable for trace vapor detection. In light of the strong dependence of vapor pressure on temperature, trace vapor detection capabilities may be enhanced by selectively heating target materials by external excitation. Moreover, polymer-bonded energetic materials may be particularly susceptible to heating by mechanical or acoustical excitation, due to the high levels of damping and low thermal conductivities of most polymers. In this work, the thermomechanical response of polymer-based energetic composites and methods for acoustical excitation are investigated in order to …

Matrix-Free Time-Domain Methods For General Electromagnetic Analysis, Jin Yan

Open Access Dissertations

Many engineering challenges demand an efficient computational solution of large-scale problems. If a computational method can be made free of matrix solutions, then it has a potential of solving very large scale problems. Among existing computational electromagnetic methods, the explicit finite-difference time-domain (FDTD) method is free of matrix solutions. However, it requires a structured orthogonal grid for space discretization. In this work, we develop a new time-domain method that naturally requires no matrix solution, regardless of whether the discretization is a structured grid or an unstructured mesh. No dual mesh, interpolation, projection and mass lumping are needed. Furthermore, a time-marching …

Computer Vision-Based Structural Assessment Exploiting Large Volumes Of Images, Chul Min Yeum

Open Access Dissertations

Visual assessment is a process to understand the state of a structure based on evaluations originating from visual information. Recent advances in computer vision to explore new sensors, sensing platforms and high-performance computing have shed light on the potential for vision-based visual assessment in civil engineering structures. The use of low-cost, high-resolution visual sensors in conjunction with mobile and aerial platforms can overcome spatial and temporal limitations typically associated with other forms of sensing in civil structures. Also, GPU-accelerated and parallel computing offer unprecedented speed and performance, accelerating processing the collected visual data. However, despite the enormous endeavor in past …

Photoelectrochemical And Photophysical Studies Of Carbon Nanotube And Molybdenum Disulfide Based Light Harvesting Devices, Hanyu Zhang

Open Access Dissertations

There is a critical need in utilizing solar radiation as a renewable energy source. While photovoltaic solar cells are widely used, much attention has been devoted in the past decade to developing nanotechnology for potential cost reduction and improved device efficiency and reliability. Low-dimensional materials offer unique physical properties which may be exploited for solar energy harvesting and conversion. Understanding their fundamental properties and developing relevant manufacturing strategies will thus pave the road toward high-performance, cost-effective, light-harvesting devices.

This thesis has investigated single-wall carbon nanotubes (SWCNTs) and molybdenum disulfide (MoS2) nanolayers for their light-harvesting ability in donor-acceptor systems. These materials …

Open Scholarly Publishing Plugin, Barry Bailey

Sabbatical Projects

Presentation reflecting author's sabbatical project, which reviewed the need for and developed a plugin to allow institutions to convert WordPress into an institutional repository.

Ballistic Resistance Of Plain Woven P-Aramid Fabrics, B Kusuktham, S Udon, M Jitjaicham

Journal of Metals, Materials and Minerals

This research investigated the ballistic resistance of p-Aramid fabric. Plain woven aramid fabrics were prepared to produce bulletproof vest having 5 kg of 32 fabric layers. The performance of the multilayer aramid fabrics in terms of ballistic resistance was evaluated by ballistic testing with the difference types of bullet. The damage of the fabric and the indentation of modeling clay behind the target were examined. The results showed that vests prepared from 18 - 32 fabric layers exhibited the ballistic resistance; the more the fabric layer the more the resistance performance. In addition, the indentation of the modeling clay decreased …

Compressive Properties And Imaging Analysis Of A New Metal Foam-Natural Rubber Hybrid Structure, A Chaturvedi, G Sanyal, S Chaturvedi, As Patil

Journal of Metals, Materials and Minerals

In this study an attempt has been made to create a new hybrid structure. The hybrid structure has been made by hierarchically combining closed cell Aluminum foam and natural rubber. The hybrid structure, when subjected to compressive loading, displayed improved energy absorption characteristics compared to its parent monoliths. It also displayed significant strain recovery post deformation. High resolution imaging was also carried out to compare the internal structure of hybrid samples before and after compression. Critical discussion of the experimental results has been made.

Hollow Fiber Membranes For Artificial Lung Applications, Lauren Reed

Chemical Engineering Undergraduate Honors Theses

Artificial lungs are in use, but difficult issues remain in the field of membrane development related to fouling issues. Currently there are external artificial lungs circulating blood outside the body, taking out the carbon dioxide, and inserting oxygenated blood back into the body. An example of this type of machine is the ExtraCorporeal Membrane Oxygenation (ECMO) machine currently used in hospitals. The ECMO takes over the functions for both the lungs and the heart but is only available for short term use by patients with respiratory failure due to infections [1]. The fibers in the machine develop fouling due to …

Outsourcing Of Building Information Modeling (Bim) Among General Contractors In The United States, James W. Fountain

Honors Theses

Building Information Modeling (BIM) is a process used by AEC industry members that simulates a construction project in a multidimensional digital model and provides multitudes of project benefits from inception to occupancy. However, a variety of barriers impede a holistic BIM implementation. Because of these barriers, some general contractors are choosing to outsource the creation and/or utilization of BIM models to specialized Information Technology (IT) firms instead of performing these processes in-house. Since little literature currently exists for BIM outsourcing, this online survey-based study aimed to identify BIM outsourcing patterns among the general contractors across the US and the perceived …

Continuous Long-Term Health Monitoring Using Ultrasonic Wave Propagation, Ece Erdogmus

Nebraska Department of Transportation: Research Reports

No abstract provided.