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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Characteristics of CoZrTaB in the 5G Spectral Environment

January 2019 (has links)
abstract: The study of soft magnetic materials has been growing in popularity in recent years. Driving this interest are new applications for traditional electrical power-management components, such as inductors and transformers, which must be scaled down to the micro and nano scale while the frequencies of operation have been scaling up to the gigahertz range and beyond. The exceptional magnetic properties of the materials make them highly effective in these small-component applications, but the ability of these materials to provide highly-effective shielding has not been so thoroughly considered. Most shielding is done with traditional metals, such as aluminum, because of the relatively low cost of the material and high workability in shaping the material to meet size and dimensional requirements. This research project focuses on analyzing the variance in shielding effectiveness and electromagnetic field effects of a thin film of Cobalt Zirconium Tantalum Boron (CZTB) in the band of frequencies most likely to require innovative solutions to long-standing problems of noise and interference. The measurements include Near H-Field attenuation and field effects, Far Field shielding, and Backscatter. Minor variances in the thickness and layering of sputter deposition can have significant changes electromagnetic signature of devices which radiate energy through the material. The material properties presented in this research are H-Field attenuation, H-Field Flux Orientation, Far-Field Approximation, E Field Vector Directivity, H Field Vector Directivity, and Backscatter Magnitude. The results are presented, analyzed and explained using characterization techniques. Future work includes the effect of sputter deposition orientation, application to devices, and applicability in mitigating specific noise signals beyond the 5G band. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019
92

BagStack Classification for Data Imbalance Problems with Application to Defect Detection and Labeling in Semiconductor Units

January 2019 (has links)
abstract: Despite the fact that machine learning supports the development of computer vision applications by shortening the development cycle, finding a general learning algorithm that solves a wide range of applications is still bounded by the ”no free lunch theorem”. The search for the right algorithm to solve a specific problem is driven by the problem itself, the data availability and many other requirements. Automated visual inspection (AVI) systems represent a major part of these challenging computer vision applications. They are gaining growing interest in the manufacturing industry to detect defective products and keep these from reaching customers. The process of defect detection and classification in semiconductor units is challenging due to different acceptable variations that the manufacturing process introduces. Other variations are also typically introduced when using optical inspection systems due to changes in lighting conditions and misalignment of the imaged units, which makes the defect detection process more challenging. In this thesis, a BagStack classification framework is proposed, which makes use of stacking and bagging concepts to handle both variance and bias errors. The classifier is designed to handle the data imbalance and overfitting problems by adaptively transforming the multi-class classification problem into multiple binary classification problems, applying a bagging approach to train a set of base learners for each specific problem, adaptively specifying the number of base learners assigned to each problem, adaptively specifying the number of samples to use from each class, applying a novel data-imbalance aware cross-validation technique to generate the meta-data while taking into account the data imbalance problem at the meta-data level and, finally, using a multi-response random forest regression classifier as a meta-classifier. The BagStack classifier makes use of multiple features to solve the defect classification problem. In order to detect defects, a locally adaptive statistical background modeling is proposed. The proposed BagStack classifier outperforms state-of-the-art image classification techniques on our dataset in terms of overall classification accuracy and average per-class classification accuracy. The proposed detection method achieves high performance on the considered dataset in terms of recall and precision. / Dissertation/Thesis / Doctoral Dissertation Computer Engineering 2019
93

A Rationale for Furrow Irrigation System Design and Management

Hamad, Safa Noori 01 May 1976 (has links)
Mathematical and computerized models are developed to design and optimize furrow irrigation systems. The optimization process starts with land grading design, if any is needed, followed by a prediction of maximum non-erosive furrow stream size allowed on a given soil and the associated furrow-advance function. An average depth of application per irrigation is then assumed from which the wetting pattern along the furrow and the amounts of runoff water are predicted. A design of an Irrigation Runoff Recovery System, IRRS, is then executed, if desired, and system cost is determined. Using the predicted wetting pattern and the appropriate Crop Production Function, the gross return and the net farm profit associated with that particular average depth of application per irrigation are determined . The iterative procedure is continued by changing the average depth of application per irrigation and evaluating net farm profit until a depth and the associated system design and management program which yield the highest net profit are found. A Fortran IV detailed computer program is developed to perform the above procedure. The program is comprehensive and very flexible so that it can be used both for research and practical design purposes and can accommodate further improvements and expansion. The results of sensitivity analysis conducted to study the effect on net farm profit of ten major design and management factors are included. Numerous conclusions, suggestions, and recommendations to improve furrow irrigation system design and operation are presented.
94

Optimization of Energy Transfer during Active Balancing of Lithium-Ion Batteries

Unknown Date (has links)
Balancing is one of the most important function of any battery management system (BMS). We need it to adjust all the batteries in the system for them to work efficiently, based on battery voltage or state-of-charge (SOC). One of the most common and easier ways to achieve cell balancing is by using active or passive cell balancing techniques. Active balancing is when you equalize a battery or a cell with another battery with higher potential. Active balancing is widely implemented method as it is cheap, but it is not as optimum and efficient as compared to the new methods like pulse charging. In this proposed study, we have a dynamic topology for active balancing method that would give us optimized results, with faster balancing and an expandable system for ‘n’ number of batteries or cells. We have reduced the charge and discharge time, removing the delays that many existing systems faces. We achieved it in both simulations and experimental testing. It also, enables in improved charging that does not allow the stack to fail. The use of microcontrollers has proved to reduce the switching time and optimize the results. These switches are precisely controlled hence saving the amount of time needed in charge and discharge cycles. This topology uses an inductor, which is the main component for charge transfer. When charge is transferred from one battery to the other we use inductor as the medium. This inductor basically stores the charge in the first cycle and then dumps it onto the battery in the second cycle. This topology also includes an external charger that keeps charging the stack while equalization takes place. This improves the charging and balancing time for the entire stack. / A Thesis submitted to the Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2019. / April 4, 2019. / Includes bibliographical references. / Pedro L. Moss, Professor Directing Thesis; Mark H. Weatherspoon, Committee Member; Simon Foo, Committee Member.
95

Smart In Situ Fibers And Their Applications

Kim, Sundong 01 January 2018 (has links)
This study describes an innovative fiber technology with various applications, such as fiber-reinforced concrete (FRC), fiber-reinforced plastic (FRP), and plastic foaming. Unlike incumbent passive fiber reinforcing technology, in situ shrinking fibers that respond to an external stimulus such as heat, pH, or moisture variations can induce pre-compression to the matrix and create additional resistance from external loads, creating stronger composite structures. This new technology includes the design and fabrication of in situ shrinking fibers to improve performances in each application. Shrinking ratios and tensile strengths of fibers used in each application were measured. Specimens with active shrinking fibers, passive non shrinking fibers, as well as control samples have been made, and their performances have been compared. The first part describes the application of shrinking fibers in cementitious composite structures to provide supplemental strength-enhancing compressive stresses. Mechanical properties of the samples are compared with compression and three-point bending tests, using heat activated shrinking (HAS) fibers pH activated shrinking (pHAS) fibers. The second part describes the applications of through-thickness fiber reinforcement technology for polymeric laminate to provide supplemental strength-enhancing interlaminar stresses. To prove this concept, peel strengths of epoxy/glass fiber composite layers are measured. Also, in-plane tensile tests are conducted to investigate whether the through-thickness shrinking fibers affect in-plane properties. The third part demonstrates the application of shrinking fiber in improving foaming ability of linear polymers. The smart fiber blending technology would be able to tune the optimum degree of strain hardening behavior cost efficiently. The modification of the rheological properties by the fiber shrinkage is discussed. The extensional viscosity measurements are described in terms of strain-hardening behaviors in polymer composites containing shrinking fibers. Final foam properties resulting from these structures are also presented.
96

Crystallization Study Of Polymers Under High Pressure Gas / Supercritical Fluid

Romero, Sandra 01 January 2018 (has links)
The global demand for polymers especially Polypropylene (PP) foams is increasing rapidly. Foam structures can be very beneficial for producing structural components which can be significantly larger than the raw material formed by volume expansion. In this context, the objective of this work is to develop uniform fine-cell and low-density polymer foams with improved mechanical properties. In order to promote a deeper understanding of the low-density (<0.1 g/cc) and microcellular structure (10^8 cells/cm^3), a novel foaming-visualization system was developed. This novel custom-made system captures in situ crystallization-induced foaming behaviors of polymers. The shear effect on bubble and crystal growth processes were investigated independently in an isolated manner. Based on data observed from the visualization system, a two-dimensional model of the foam nucleation process was developed. The model was extended to account for the simultaneous cell nucleation, growth, and collapse processes of the foaming bubbles. By means of connection among neighboring bubbles, secondary nucleation behaviors emerged from multi-bubble interactions were attempted in simulations. Finally, the effects of gas pressure, temperature, additive content, and shear stress were thoroughly investigated for the sake of optimizing the processing conditions and foamed products. Potential applications from these researches lie in the analysis of the resulting micro-/nano-cellular structures and the development of innovative plastic foaming technologies and foams.
97

Interfacial Mechanical Behavior Between Nacreous Tablets Under Normal And Shear Stresses

Alghamdi, Saleh Jaman 01 January 2019 (has links)
Nacre, a natural composite consisting of biogenic aragonite and protein, possesses superior strength and toughness compared to its brittle aragonite components. In this work, we first show that dry nacreous sections exhibit complete brittle fracture along the tablet interfaces at the proportional limit under pure shear of torsion. We quantitatively separate the initial tablet sliding primarily resisted by nanoscale aragonite pillars from the following sliding resisted by various microscale toughening mechanisms. In addition, we use the pure shear of torsion to demonstrate how hydrated nacre resists the initial tablet sliding by tuning its nanoscale toughening mechanisms. In hydrated nacre, hydrogen bonds between water molecules and organic matrices provide temporal paths for stress redistributions, through which the shear resistance is gradually transferred from mineral bridges to contacted nanoasperities. In the subsequent sliding, dynamical interactions between nacreous tablets enable substantial plasticity before the catastrophic failure of hydrated nacre. Microscale growth layers between nacreous tables possess distinctive aragonite structures, including columns, spherulites and organic matrices. High temporal resolution experiments were performed to elucidate the tensile and shear behavior of growth layers under dry and hydrated conditions. Hydrated growth layers exhibited lower strengths and larger failure strain than hydrated nacre under both shear and tensile loadings. However, they successfully confined or deflected cracks within themselves when failure happened.
98

Production of Synthetic Spider Silk Fibers

Copeland, Cameron G. 01 May 2016 (has links)
Orb-weaving spiders produce six different types of silks, each with unique mechanical properties. The mechanical properties of many of these silks, in particular the dragline silk, are of interest for various biomedical applications. Spider silk does not elicit an immune response, making it an ideal material for several applications in the medical field. However, spiders cannot be farmed for their silk as they are cannibalistic and territorial. The most reasonable alternative for producing spider silk fibers is to utilize genetic engineering to produce the proteins in a foreign host and then spin fibers from the synthetic protein. Spider silk-like proteins have been expressed in transgenic goats on a scale sufficient to spin synthetic fibers. To spin it, the protein is dissolved in a solvent to create a viscous spin dope. This spin dope is extruded into a coagulation bath where it forms a fiber. Fibers spun in this manner have poor mechanical properties and are water soluble, unlike natural spider silk. By applying a post-spin draw, the mechanical properties of the fibers improve and they are no longer water soluble. This increase occurs because β-sheets, important secondary structures, form and begin to align parallel to the fiber axis. In previous work, post-spin draw has been applied by hand to the fibers after initial spinning. This is not a viable method for the commercial production of synthetic spider silk. The first aim of this research was to design, test, and optimize a mechanical system that can create consistent, synthetic spider silk fibers. The second aim of this research was to discover how parameters such as solvents, temperature, spinning speed, additives, and post-spin draw, among other variables, affect the properties of synthetic spider-silk proteins purified from goat milk. As part of this research, a mechanical system that can perform these treatments while the fiber is being made was designed, built and tested. This system was built with the intent to inform the creation of a process for the creation of a synthetic on an industrial level.
99

A Qualitative Study of Fatal Intersection Crashes in the State of Florida

Unknown Date (has links)
One of the most primary requirements of any efficient transportation system is safety of the users. The national highways should provide the required mobility and accessibility accompanied with safety for its smooth functioning. Efforts are being made to improve the safety of our highways, which are still exposed to a significant number of fatalities due to traffic crashes. An intersection is, at its core, a planned point of conflict in the roadway system. With different crossing and entering movements by both drivers and pedestrians, an intersection is one of the most complex traffic situations that motorists encounter. Add the element of speeding motorists who disregard traffic controls and the dangers are compounded. At-grade intersections are one of the highest frequency accident-prone locations. Studies reveal that almost 40 % of the total crashes occur at the intersections. Left turn collisions and Red Light Running crashes are found to be common types of accidents occurring at intersections. Most of the crashes at un-signalized intersections are right angle collisions. Such high frequency of crashes at a particular kind of location makes it obvious that there are more factors that need to be studied in addition to the traffic volume and traffic characteristics. This research thesis aims at analyzing the Statewide Traffic Crash data for crashes at intersections in the State of Florida and to determine the contributing causes of the crash which are not only driver errors, as are generally accepted. The analysis shall look into the type of the crash, Roadway Geometrics and other Transportation Engineers' concerns, which could have added to the probability of the crash and thereby suggesting relevant countermeasures. The source data used for analysis was obtained from the Florida Department of Transportation (FDOT) and the scope of the research is restricted to the State of Florida. Failure to yield the right of way due to inattention or misjudging of safe gap is the most frequently observed contributing factor to the crashes at intersections, which may be a result of inadequate sight distance, improper stop signs or higher posted speeds, which are a cause of concern for a Transportation Engineer. In an attempt to make the roads safer for the users, suitable generic and site-specific countermeasures are suggested in this research. / A Thesis submitted to the Department of Civil Engineering in partial fulfillment of the Requirements for the degree of Master of Science. / Degree Awarded: Spring Semester, 2005. / Date of Defense: April 8, 2005. / Crash Study, Intersection Safety, Traffic Safety, Fatal Intersection Crashes / Includes bibliographical references. / John O. Sobanjo, Professor Directing Thesis; Lisa K. Spainhour, Committee Member; Renatus N. Mussa, Committee Member.
100

Biobased Epoxy Asphalt Binder (BEAB) for Pavement Asphalt Mixtures

Al Fuhaid, Abdulrahman Fahad 27 March 2018 (has links)
In recent years, there have been significant concerns about environmental issues, sustainability of infrastructure, and depletion of nonrenewable resources for pavement construction. These concerns have led to substituting petroleum-based paving materials with their biobased counterparts. Research efforts have attempted to produce asphalt from renewable bio-resources. As a special modifier for asphalt, petroleum-based epoxy resin has been used in a few asphalt paving projects that require superior performance of asphalt mixtures. This study attempts to develop a biobased epoxy modifier for asphalt, which may improve asphalt performance at lower economic and environmental costs. Based on the findings from research in the chemistry industry, an epoxidized soybean oil (ESO) and a biobased curing agent, maleic anhydride (MA), were selected to develop the epoxy modifier for asphalt. The proper proportions of ESO, MA, and a base asphalt (PG 67-22) were determined to achieve a homogenous biobased epoxy asphalt binder (BEAB) with the desired properties evaluated by a rotational viscosity test, a penetration test, and a dynamic shear rheometer test. Pavement performance related properties of asphalt mixtures using such a BEAB were also evaluated using a Marshall stability test. It was found that the optimum ratio of MA:ESO:Asphalt in the BEAB is 0.45:1:8, and the asphalt mixture containing such a binder has a higher Marshall stability and higher rutting and fatigue cracking resistance indicators than the mixture using a neat asphalt (PG 67-22). In addition, the BEAB with the optimum formula has a curing time (i.e., the time when the binder viscosity increases to 1 Pa·s) of at least 50 minutes, which is sufficient for construction of typical epoxy asphalt pavements.

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