Digital Commons Network^™

The Effect Of Incorporating End-User Customization Into Additive Manufacturing Designs, Jonathan D. Ashley

Graduate Theses and Dissertations

In the realm of additive manufacturing there is an increasing trend among makers to create designs that allow for end-users to alter them prior to printing an artifact. Online design repositories have tools that facilitate the creation of such artifacts. There are currently no rules for how to create a good customizable design or a way to measure the degree of customization within a design. This work defines three types of customizations found in additive manufacturing and presents three metrics to measure the degree of customization within designs based on the three types of customization. The goal of this work …

Developing Computer Codes For Analyzing Bridge Response Due To Wim Data Truck Loading, Kenneth Patrick Pasley

Graduate Theses and Dissertations

Despite actual truck demographics evolving over the past 30 years, the Arkansas legal loads for bridge posting have not been updated. Custom computer codes were developed.to facilitate comparison between the current Arkansas legal loads for bridge posting and the actual Arkansas truck traffic to ensure that actual reactions are enveloped by the state'. The program, WIMFluence, calculates shear and moment influence lines for a bridge and the resulting shear and moment reactions based on weigh-in-motion data. With supporting scripts, the reactions due to actual Arkansas truck traffic were compared to those due to the current Arkansas legal loads for bridge …

Development Of A Rapid Fatigue Life Testing Method For Reliability Assessment Of Flip-Chip Solder Interconnects, Cody Jackson Marbut

Graduate Theses and Dissertations

The underlying physics of failure are critical in assessing the long term reliability of power packages in their intended field applications, yet traditional reliability determination methods are largely inadequate when considering thermomechanical failures. With current reliability determination methods, long test durations, high costs, and a conglomerate of concurrent reliability degrading threat factors make effective understanding of device reliability difficult and expensive. In this work, an alternative reliability testing apparatus and associated protocol was developed to address these concerns; targeting rapid testing times with minimal cost while preserving fatigue life prediction accuracy. Two test stands were fabricated to evaluate device reliability …

On The Development Of 8,000 Psi Geopolymer Mortar For Practical Use In Field Applications, Remington Gabriel Reed

Graduate Theses and Dissertations

Although there are several perceived benefits from the use of geopolymer binder as an alternative to ordinary portland cement in concrete materials, it is not widely used in field applications. Geopolymer materials have no set guidelines for mixture design and often require heat curing to facilitate strength gain. Additionally, many geopolymers are created using carefully controlled and high quality materials and activator chemicals. These factors greatly affect the practicality of the material. The goal of this research was to create a geopolymer material capable of achieving high compressive strengths at 28 days without heat curing, and using only readily available …

Developing Ultra-High Performance Concrete (Uhpc) With Locally Available Materials, Ali Alsalman

Graduate Theses and Dissertations

Ultra-High Performance Concrete (UHPC) can enhance the durability and resilience of concrete structures. The use of local materials is a fundamental step to save energy and reduce the cost of concrete. The main focus of this research was to develop a UHPC with compressive strength of 150 MPa using locally sources materials. In this study, the effect of fine materials, binder type and content, type of mixer, steel fibers and curing regimes on concrete’s compressive strength were investigated. The relationship between compressive strength and elastic modulus was also studied. This study synthesizes all relevant experimental data in the literature to …

Towards Environmentally Sustainable And Cost-Effective Food Distribution In The U.S., Jasmina Burek

Graduate Theses and Dissertations

Distribution centers (DCs) and supermarkets have an important role in food sustainability, but no previous research has accounted for their environmental impact. The purpose of this research was to assess environmental sustainability of grocery, perishables, and general merchandise DCs; to estimate food storing and retailing impact; and to provide cost-effective strategies to reduce DCs’ environmental impacts. The importance and relevance of the research is threefold: improving sustainability of DCs, food storing, and food retailing. The main method used in this research was the life cycle assessment (LCA) method. An initial study calculated environmental impacts of the Wal-Mart Stores, Inc. DCs, …

Effect Of Continuity Plate Eccentricity On The Performance Of Welded Beam-To-Column Connections, Jason Thomas Norwood

Graduate Theses and Dissertations

Beam-to-column connections in structural steel buildings may have varying degrees of rotational restraint and varying degrees of moment transfer. In fully restrained moment connections, shear is typically transferred through the beam web, while the moment is mostly transferred through the beam flanges which create tension/compression force couples. Column sections that are incapable of resisting these flange forces are often retrofitted with continuity plates within the connection region to improve capacity. In cases of unequal beam depths on either side of the column, an eccentricity between the framed-in beam flange and continuity plate may be required; however, limited research exists to …

Effect Of Cement Content On Concrete Performance, Caleb Joshua Lebow

Graduate Theses and Dissertations

Of all the traditional concrete materials, portland cement has the greatest impact on mixture cost and the environment. Cement is in many ways the glue holding concrete together (Weiss, 1999), and as such, it plays a major role in fresh and hardened concrete properties. Without the proper range of cement in the mixture, low strength development or excessive shrinkage may occur leading to premature deterioration. The Arkansas Department of Transportation (ARDOT) recognizes two types of concrete for use in bridge construction, Class S and Class S(AE). This paper focuses on the findings from testing of Class S(AE) concrete, short for …

Utilizing 3d Printed Analogue Soils To Investigate Specimen Size Effects In Triaxial Testing, Claire Louise Stewart

Graduate Theses and Dissertations

Triaxial testing is one of the fundamental laboratory tests used in geotechnical engineering to determine strength parameters, such as shear strength and friction angle. Investigating the minimum representative elementary volume (REV) can verify the independence of size effects on strength parameters and ensure that the scaled laboratory tests results are consistent, repeatable, and representative of field conditions. Although, REV has been studied for many applications, there is disagreement within geotechnical engineering of a minimum particle diameter to specimen diameter to minimize the size effects related to the REV in consolidated drained (CD) triaxial tests. This research study compared the strength …

Assessing Biofiltration Without Ozonation For Removal Of Trihalomethane Precursors In Drinking Water At The Beaver Water District Drinking Water Treatment Plant, Sana Ajaz

Graduate Theses and Dissertations

Biofiltration without pre-ozonation has the capability to remove natural organic matter (NOM) fractions that serve as precursors of disinfection byproducts (DBPs), which include the four regulated trihalomethanes (THMs) and dichloroacetonitrile (DCAN). Rapid small-scale column tests (RSSCTs) and Pilot Plant filters operated at empty-bed contact times (EBCTs) of 4, 8, and 16 minutes were used to evaluate the performance of nutrient-amended (free ammonia and phosphorus) biofiltration for THM and DCAN precursor removal, as measured using formation potential (FP) tests. NOM surrogates – which include dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA254) and fluorescence-PARAFAC components – were measured weekly throughout the …

Subsurface Analysis Of Mississippian Tripolitic Chert In Northwest Arkansas, Thomas Jason Liner

Graduate Theses and Dissertations

Over the past 70 years the Mississippian strata of Northwest Arkansas have been studied in great detail. The study area is located on the escarpment between the Boston Mountains Plateau and the Springfield Plateau where a surface occurrence of Mississippian age rock allows for access to outcrops in close proximity to gas wells that encounter subsurface Mississippian strata. Many outcrops found in Northwest Arkansas expose Lower Mississippian (Kinderhookian-Osagean) strata that represent a full third order transgressive/regressive sequence that is unconformity bounded. These Mississippian outcrops are commonly treated as surface analogs to the Mississippi Lime Play in North Central Oklahoma. This …

Diversification Across A Dynamic Landscape: Phylogeography And Riverscape Genetics Of Speckled Dace (Rhinichthys Osculus) In Western North America, Steven Michael Mussmann

Graduate Theses and Dissertations

Evolution occurs at various spatial and temporal scales. For example, speciation may occur in historic time, whereas localized adaptation is more contemporary. Each is required to identify and manage biodiversity. However, the relative abundance of Speckled Dace (Rhinichthys osculus), a small cyprinid fish in western North America (WNA) and the study species for this dissertation, establishes it an atypical conservation target, particularly when contrasted with the profusion of narrowly endemic forms it displays. Yet, the juxtaposition of ubiquity versus endemism provides an ideal model against which to test hypotheses regarding the geomorphic evolution of WNA. More specifically, it also allows …

Working-Class Graduates’ Perceptions Of The 7 Habits Of Highly Effective Teens Training And Its Impact On Their Life Choices And Future Success, Andrew Kenneth Ashley

Graduate Theses and Dissertations

The purpose of this phenomenological study was to examine working-class graduates’ perceptions of The 7 Habits of Highly Effective Teens training. This purpose was accomplished through a qualitative analysis of data. The data was collected from interviews of graduates and teachers. Following the coding process, graduate data was then reduced to the following categories: social awareness, relationship development, teamwork, communication skills, empathy, self-awareness, and self-confidence which created the themes of interpersonal skills and intrapersonal skills. Four additional graduate themes were created from decision-making data: weighing pros and cons, prioritizing outcomes, thinking long-term, and real-life applications. Additional graduate data was provided …

Decadal Land Surface Phenology And Water Quality In The Headwaters Illinois River Watershed, Justin Ray Rollans

Graduate Theses and Dissertations

Over 25 percent of the world’s population either lives on or obtains water from karst aquifers. The complex interactions between subsurface karst geologic features, the constant motion of the plant life cycle, and significant water resource demand all suggest the need to better define those interactions. The relationship of historical land surface phenology and water quality in karst topography were investigated in the Headwaters Illinois River watershed in Northwest Arkansas (NWA). This area represents high vulnerability to surface water and groundwater contamination, with both natural and anthropogenic processes such as over application of broil litter for enhanced cattle browse, affecting …

Ca2+ - Induced Structural Change Of Multi-Domain Collagen Binding Segments Of Collagenases Colg And Colh From Hathewaya Histolytica, Christopher Eric Ruth

Graduate Theses and Dissertations

Hathewaya histolytica, previously renamed as Clostridium histolyticum, secretes at least two collagenases, ColH and ColG, that allow for degradation of extracellular matrices of animal tissue. Hathewaya histolytica virulence factors are proposed to undergo domain rearrangement upon secretion from the bacteria to the host. In order to accomplish this, collagenases seek the least ordered regions in collagen to efficiently disassemble the fibril. Two types of domains, Polycystic Kidney Disease-like (PKD) and Collagen Binding Domain (CBD), direct the collagenases ability to disassemble the fibril. Calcium dependent structural change have been reported to increase in thermal stability and in tighter collagen binding for …

Effect Of Cooking Method On Meat Texture In Normal And Woody Broiler Breast Fillets Using Instrumental Analysis And Descriptive Sensory Analysis, Lynda D. Combs

Graduate Theses and Dissertations

Over the past few decades, broiler breast meat has changed in terms of meat quality. Meat quality has deteriorated with the rise in the occurrence of muscle myopathies. Conditions such as woody breast, which is described as pale and bulging areas of distinct hardness, compromise both the textural and technological traits that have been associated with breast meat. The Meullenet-Owens Razor Shear (MORS) method is a common method for indirectly assessing poultry meat tenderness. A blunt version of the MORS (BMORS) has been shown to be a more sensitive method at higher degrees of toughness. A slightly larger stainless steel …

Perceptions Of E-Learning By Management Trainees In A Small, Fast Food Restaurant, Anthony A. Longo

Graduate Theses and Dissertations

Small businesses account for a majority of U.S. jobs and play a vital role in the economy. However, the survival rate for small businesses is disconcerting. Only half of the small businesses will survive five years or more and one-third ten or more years. Fast food restaurants are part of the food and drinking industry. It is the second largest industry in the United States and the most vulnerable to business failure. Research has shown the capabilities of small business managers can play a significant role in the success or failure of a small business, but little research has been …

Undergraduate Students’ Perceptions Of Their International Teaching Assistants (Itas) And Perceptions Of Themselves In A Course(S) Instructed By An Ita, Nadia Hanayeen

Graduate Theses and Dissertations

The University of Arkansas is a large, diverse public university. International teaching assistants (ITAs) represent 20% of the total graduate teaching assistants at the University of Arkansas. In the Fall semester of 2015, the University of Arkansas ranked 9th among U.S. universities based on the number of ITAs instructing undergraduate classes. Combining quantitative and qualitative data collection and analysis methods, this study investigated domestic undergraduate students’ perceptions of their ITAs and of themselves in courses instructed by ITAs. The descriptive quantitative findings showed that the two most significant challenges facing ITAs are American students’ perceptions of their pedagogical skills and …

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. …

Mitigating The Risk For Glufosinate Resistance, Christopher John Meyer

Graduate Theses and Dissertations

While glufosinate-resistant weeds have not yet been identified in U.S. row crops, rapid evolution of glyphosate-resistance, and resulting cost to U.S. farmers, demonstrates the need to responsibly steward the limited number of herbicides available in agricultural systems. Field and laboratory experiments were conducted to: 1) Identify herbicide interactions that can occur in Enlist™ and Roundup Ready® Xtend® systems; 2) Identify herbicide interactions that occur when glufosinate is mixed with fomesafen, clethodim, and glyphosate; 3) Determine the optimum rate structure and application timings when multiple POST applications of glufosinate are applied to LibertyLink soybean; 4) Use 14C techniques to determine why …

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, …

Influence Of Loss Of Function Of The Fatty Acid Desaturase 7 Gene On Photosynthetic Activity And Foliar Redox Status, Janithri Savindya Wickramanayake

Graduate Theses and Dissertations

Fatty Acid Desaturase7 (FAD7) is a chloroplast-localized enzyme that converts 16 and 18 carbon dienoic fatty acids to trienoic fatty acids. The suppressor of prosystemin-mediated response2 (spr2) mutant in tomato (Solanum lycopersicum) and the fad7-1 mutant in Arabidopsis (Arabidopsis thaliana) result in the loss of function of FAD7, which alter the fatty acid profiles of chloroplast membranes and enhance resistance against aphids. This research contributes toward the long-term goal of identifying factors that determine aphid resistance in FAD7 mutants. Previous data suggested constitutive differences between spr2 and WT including increased expression of genes associated with photosynthesis and differences in redox …

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 …

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 …

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 …

Counter-Revolution And Egypt’S Lower Middle Class, Keith Glenn Whitmire

Graduate Theses and Dissertations

The Egyptian lower middle class has been declining since the 1970s. Yet since the 2011 uprising and coup d’état the lower middle class has sat in the midst of an economic and political counter-revolution carried out by the police, the military, and Egypt’s intelligence services. In particular, President Abdel Fattah al-Sisi has responded to Egypt’s economic crisis in 2014 and onward by engaging in a program of austerity has sped the decline of the Egyptian lower middle class significantly. The Egyptian lower middle class is in increasing danger of becoming merely educated working poor. Therefore this dissertation will examine the …

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 …

Sequential Inference For Hidden Markov Models, Michael Ellis

Graduate Theses and Dissertations

In many applications data are collected sequentially in time with very short time intervals between observations. If one is interested in using new observations as they arrive in time then non-sequential Bayesian inference methods, such as Markov Chain Monte Carlo (MCMC) sampling, can be too slow. Increasingly, state space models are being used to model nonlinear and non-Gaussian systems. The structure of state space models allows for sequential Bayesian inference so that an approximation to the posterior distribution of interest can be updated as new observations arrive. In special cases, the exact posterior distribution can be updated through conjugate Bayesian …

Mindset, Mentor, And Money: How Each Influences College Success, Malachi Nichols

Graduate Theses and Dissertations

Across society, the consistent influx of students enrolling in higher education institutions without a comparable increase in degree attainment has produced a heightened awareness and a desire to identify the factors related to influencing college success. This dissertation aims to develop a greater understanding of three potentially relevant factors and their respective influences in facilitating college success at the University of Arkansas. First, I evaluate the Student Talent Enrichment Program (STEP) Grant program, designed to fulfill low-income first-year students’ financial needs and encourage their persistence on to their second year of college. Second, I study the effectiveness of the BounceBack …

Systems To Attract And Feed Pollinators In Warm-Season Lawns, Michelle Wisdom

Graduate Theses and Dissertations

Pollinating insects are responsible for the production of many agricultural crops and they require floral resources to fulfill their life-cycle. Ideally, pollinating insects will encounter a diversity of floral resources across their entire season of activity, and those floral resources can include both herbaceous and woody plant species. Managed turfgrass areas have been identified as potential locations for creating pollinator-friendly habitats. In the transition zone, where both warm- and cool-season turfgrass species are present, the persistence of herbaceous plants in warm-season turfgrasses such as bermudagrass (Cynodon spp.) and buffalograss (Buchloe dactyloides), may be affected not only by the competitive nature …