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Full-Text Articles in Engineering

Towards Understanding Material Characteristics Through The Additive Manufacturing Arc, Alden Watts Jan 2019

Towards Understanding Material Characteristics Through The Additive Manufacturing Arc, Alden Watts

Graduate Theses and Dissertations

The directed energy powder feed additive manufacturing (AM) process fabricates components with good quality, accuracy, and efficiency. However, this is a complex process and without careful consideration can lead to discontinuities in the final product such as porosity, cracks, or unfavorable microstructure. These material discontinuities may occur due to the limited understanding of the relationship between AM source materials and the evolution of the composition and microstructure during the deposition process. This makes it vital to study and correlate the composition, morphology, and characteristics of both the source material and of the final printed parts. In this research the properties ...


Simulation Of Soil-To-Tool Interaction Using Discrete Element Method (Dem) And Multibody Dynamics (Mbd) Coupling, Sadaf Ghorbani Jan 2019

Simulation Of Soil-To-Tool Interaction Using Discrete Element Method (Dem) And Multibody Dynamics (Mbd) Coupling, Sadaf Ghorbani

Graduate Theses and Dissertations

Multi-physics simulation of soil-to-tool interaction using a coupled Discrete Element Method (DEM) and Multibody dynamics (MBD) techniques can support the design of off-road equipment. Quantitative prediction of the soil reaction forces on the equipment is essential to provide a reliable simulation-based design. DEM is a computational method for simulating the dynamic behavior of granular materials. In the coupling interface, DEM gives a high fidelity prediction of the forces for soil-to-soil and soil-to-tool interaction, which can be used in the MBD simulation workflow. Two laboratory tests were used to capture the bulk material behavior: the angle of repose test for calibration ...


Extending The Lag Parameter Approach Of Turbulence Modeling, Rajarshi Biswas Jan 2019

Extending The Lag Parameter Approach Of Turbulence Modeling, Rajarshi Biswas

Graduate Theses and Dissertations

The work presented in this dissertation extends upon the elliptic-blending lag parameter approach for linear eddy-viscosity model (LVM). The model aims at preserving the numerical simplicity of an LVM while incorporating important features of an underlying Reynolds Stress Model(RSM). One important phenomenon in a non-equilibrium turbulent flow that the proposed model attempts to represent is the stress-strain misalignment. To this end, the model includes an additional transport equation of a field variable φ ∗ (coined as a “lag” parameter) in addition to thconventional two equations (k & ω for the current formulation). φ∗ is then used to suitably scale the eddy ...


Investigation Of The Photophysical Properties Of Energy-Relevant Inorganic Nanocrystals, Brett Boote Jan 2019

Investigation Of The Photophysical Properties Of Energy-Relevant Inorganic Nanocrystals, Brett Boote

Graduate Theses and Dissertations

Environmental concerns over use of fossil fuels to generate power and the finite supply of these resources have driven major efforts for alternative energies. At the same time, the development of nanotechnology has blossomed to propose strategies and materials for renewable and less energy-intensive end-user devices, such as solar cells and LED lighting. Two examples of promising candidates for energy applications are germanium-based nanocrystals and lead halide perovskite nanocrystals.

Germanium-based materials have limited absorption efficiency due to their indirect band gap. To address this, germanium-tin alloy nanocrystals were synthesized to promote direct band gap character. A full characterization demonstrated tin ...


Design, Analysis, And Comparison Of Buffers For Online Multipoint Monitoring, Tao Chen Jan 2019

Design, Analysis, And Comparison Of Buffers For Online Multipoint Monitoring, Tao Chen

Graduate Theses and Dissertations

The increasing complexity of the System-on-Chips (SoCs) used in mission-critical systems such as autonomous cars or planes has led to the need for and various developments of online testing and monitoring methods to monitor circuit functionality and performance of these SoCs. However, the insertion of these monitoring circuits, especially when they are non-ideal, can negatively impact the normal operation or even basic function of the original circuits. For example, glitches generated by clocks or switches in the monitoring circuits can be coupled into the nodes under test (NUTs) through parasitic capacitors in the original circuits.

To reduce the negative impact ...


Development Of Performance Models To Determine Effectiveness Of Flexible Pavement Preservation Using A Pavement Management System, Benjamin Claypool Jan 2019

Development Of Performance Models To Determine Effectiveness Of Flexible Pavement Preservation Using A Pavement Management System, Benjamin Claypool

Graduate Theses and Dissertations

More, now than ever, importance on saving materials, time, and money is at the forefront of infrastructure maintenance. Large strides have been made to achieve these goals through the use of pavement preservation. A properly applied preservation method will extend the service life of the pavement, use less materials than a typical overlay or reconstruction, and result in lower construction costs. The presented research evaluates a variety of analytical methods used to model the performance of four different flexible pavement preservation methods, including microsurfacing, slurry sealing, patching, and crack/joint sealing.

Best-fit curves were applied to performance data from the ...


Calcium Passivation And Properties Of Al/Ca Composite Conductors, Charles Czahor Jan 2019

Calcium Passivation And Properties Of Al/Ca Composite Conductors, Charles Czahor

Graduate Theses and Dissertations

Light, strong, high-conductivity materials are desirable for overhead power transmission and distribution conductors. An aluminum/calcium composite with nanofilamentary reinforcement was produced by powder metallurgy and deformation processing to fine wires. Upon achieving the desired dimension, the wires were heat treated to convert the calcium to Al2Ca intermetallic reinforcement filaments. Extended heat treatments were used to evaluate the upper operating temperature of the material. The processing steps, microstructure, conductivity, and tensile strength of Al/Ca composites were evaluated. The measured properties indicate that the number of support towers required for a HVDC transmission line can be reduced by more than ...


Data-Driven System Modeling And Optimal Control For Nonlinear Dynamical Systems, Apurba Kumar Das Jan 2019

Data-Driven System Modeling And Optimal Control For Nonlinear Dynamical Systems, Apurba Kumar Das

Graduate Theses and Dissertations

With the increasing complexity of modern industry processes, robotics, transportation, aerospace,

power grids, an exact model of the physical systems are extremely hard to obtain whereas abundant

of time-series data can be captured from these systems. This makes it a important and

demanding research area to investigate feasibility of using data to learn behaviours of systems and

design controllers where the end goal generally evolves around stabilization. Transfer operators

i.e. Perron-Frobenius and Koopman operators play an undeniable role in advanced research of

nonlinear dynamical system stabilization. These operators have been a alternate direction of how

we generally approach dynamical ...


An Investigation Of An Ionic Liquid Analog To The Conventional Metal-Oxide-Semiconductor Field-Effect Transistor, Richard Effler Jan 2019

An Investigation Of An Ionic Liquid Analog To The Conventional Metal-Oxide-Semiconductor Field-Effect Transistor, Richard Effler

Graduate Theses and Dissertations

An ionic circuit analogous to a traditional metal-oxide semiconductor was investigated, using 1-ethyl-3-methylimidazolium trifluoromethanesulfonate as the ionic liquid in the gating element. The circuit was observed to perform with comparatively high threshold and overdrive voltages in a region below the saturation current of the transistor. The concept of the design was successfully verified, although further improvements in electrode positioning and manufacturing precision are warranted.


Insights Into Performance Stability Of Lead-Free Piezoelectric Ceramics, Zhongming Fan Jan 2019

Insights Into Performance Stability Of Lead-Free Piezoelectric Ceramics, Zhongming Fan

Graduate Theses and Dissertations

Developing materials with superior functional properties is the primary goal of materials engineering. Nonetheless, the stability of performance during practical service should be of equal importance. This is, with no doubt, also true for piezoelectric materials.

The working conditions of piezoelectric materials can lead to either gradual or abrupt degradation in their functional properties. First, fatigue. In analogy to structural materials under cyclic stresses, the piezoelectric properties deteriorate during the electric field cycling. Second, aging. While the service is paused and the piezoelectric material is sitting idle, the piezoelectric properties will decay over time. Third, thermal depolarization. Electronic devices are ...


Fracture And Toughening Of Soft Elastic Composites, Xiangchao Feng Jan 2019

Fracture And Toughening Of Soft Elastic Composites, Xiangchao Feng

Graduate Theses and Dissertations

Characterized by their low moduli and high stretchability, soft composites have recently attracted great interest from researchers in related areas. The main objective of the present study is on the fracture property and toughening mechanisms of soft composites. Three types of soft composites will be studied: soft elastic foams, double-network (DN) composites and magnetic DN composites. A theoretical/numerical study is carried out over soft elastic foams. By using the analogy between the cellular structure of foams and the network of rubbery polymers, a scaling law for the fracture energy is proposed for soft elastic foams. A phase-field model for ...


Development, Installation And Preliminary Data Collection Of An Environmental Sensor System For Freeze–Thaw Monitoring Under Granular-Surfaced Roadways, Derya Genc Jan 2019

Development, Installation And Preliminary Data Collection Of An Environmental Sensor System For Freeze–Thaw Monitoring Under Granular-Surfaced Roadways, Derya Genc

Graduate Theses and Dissertations

Granular-surfaced roadways, one of the most significant public road systems in the U.S., are highly vulnerable to be severely affected by the seasonal freeze-thaw cycles in cold regions. The state of Iowa is located in a cold region and experiences severe winter weather each year. To minimize the damage, seasonal load restrictions (SLRs) are applied, for typically 8 to 9 weeks from February to May. In addition, the Road Weather Information System is used to monitor the winter weather conditions, which consists of equipment to collect and transfer observations from roads. To help local transportation agencies with the organization ...


Coded Caching: Information Theoretic Bounds And Asynchronism, Hooshang Ghasemi Jan 2019

Coded Caching: Information Theoretic Bounds And Asynchronism, Hooshang Ghasemi

Graduate Theses and Dissertations

Caching is often used in content delivery networks as a mechanism for reducing network traffic. Recently, the technique of coded caching was introduced whereby coding in the caches and coded transmission signals from the central server were considered. Prior results in this area demonstrate that carefully designing the placement of content in the caches and designing appropriate coded delivery signals from the server allow for a system where the delivery rates can be significantly smaller than conventional schemes.

However, matching upper and lower bounds on the transmission rate have not yet been obtained. In the first part of this thesis ...


An Offset Auto-Calibration Technique With Cost-Effective Implementation For Comparator And Operational Amplifier, Xinyu Gong Jan 2019

An Offset Auto-Calibration Technique With Cost-Effective Implementation For Comparator And Operational Amplifier, Xinyu Gong

Graduate Theses and Dissertations

Comparators are one of the most fundamental building blocks in all electronic systems involving analog and digital information. A comparator’s performance, or the accuracy of its output, is determined by the comparator’s offset voltage, which includes random offset and systematic offset. To guarantee the overall performance of an entire electronic system, offset-trimming techniques are often necessary to reduce inaccuracy. This study analyzes the offset errors in a representative comparator structure and describes an auto-calibration technique to systematically and significantly reducing the offset. The auto-calibration technique involves trimming of the comparator input transistor pair. Various trimming-switch structures are considered ...


Evaluation Of Work Zone Safety Using The Shrp2 Naturalistic Driving Study Data, Amrita Goswamy Jan 2019

Evaluation Of Work Zone Safety Using The Shrp2 Naturalistic Driving Study Data, Amrita Goswamy

Graduate Theses and Dissertations

Work zones provide challenging and hazardous conditions not only for vehicle drivers, but also for highway workers who are injured or killed by errant vehicles. Over, 96,000 work zone crashes occurred in 2015 which equates to a work zone crash every 5.4 minutes. Several factors have been noted as contributing to work zone crashes. Driver factors have not been as well studied as other factors. The main objective of this study was to evaluate safety in work zones utilizing the SHRP2, Roadway Information Database (511 data) to identify potential work-zones. The study looked into the effectiveness of each ...


An Online Algorithm For Separating Sparse And Low-Dimensional Signal Sequences From Their Sum, And Its Applications In Video Processing, Han Guo Jan 2019

An Online Algorithm For Separating Sparse And Low-Dimensional Signal Sequences From Their Sum, And Its Applications In Video Processing, Han Guo

Graduate Theses and Dissertations

In signal processing, ``low-rank + sparse'' is an important assumption when separating two signals from their sum. Many applications, e.g., video foreground/background separation are well-formulated by this assumption. In this work, with the ``low-rank + sparse'' assumption, we design and evaluate an online algorithm, called practical recursive projected compressive sensing (prac-ReProCS) for recovering a time sequence of sparse vectors St and a time sequence of dense vectors Lt from their sum, Mt = St + Lt, when the Lt's lie in a slowly changing low-dimensional subspace of the full space.

In the first part of this work (Chapter 1-5), we study ...


Optimizing Bioprosthetic Heart Valves Using Isogeometric Analysis And Surrogate Modeling, Jung Hyun Ha Jan 2019

Optimizing Bioprosthetic Heart Valves Using Isogeometric Analysis And Surrogate Modeling, Jung Hyun Ha

Graduate Theses and Dissertations

Various studies in the biomechanics field have been conducted to analyze the aortic valvular disease and develop prosthetic heart valves. Optimization is an efficient solution to improve prosthetic heart valve performance. This thesis aims to optimize the bioprosthetic heart valve design to increase the coaptation area during the diastole and the orifice area during the systole. Large coaptation area prevents some possibilities of aortic regurgitation, and large orifice area increases the blood flow efficiency from the left ventricle to the aorta. The proposed solution for optimizing aortic heart valve design includes the surrogate management framework, which is a derivative-free pattern ...


Oleds: Light Extraction And Deep Blue Emission, Chamika Manoj Dulanja Hippola Jan 2019

Oleds: Light Extraction And Deep Blue Emission, Chamika Manoj Dulanja Hippola

Graduate Theses and Dissertations

OLEDs have emerged in the market over the last decade mainly in display applications due to their unique and attractive properties, such as lightweight, high brightness with strong color contrast, thin and flexible designs as well as potentially of low cost. OLEDs for lighting applications are under extensive research and development. Though promising for solid-state lighting, there are critical aspects that need to be addressed to increase their efficiency, which will lead to commercialization.

One major issue is the ~20% OLEDs’ limited forward outcoupling efficiency. This is due to several loss processes. More specifically, light generated in the emissive layer ...


Two-Dimensional Early Transition Metal Carbides As Supports For Platinum Catalysts, Zhe Li Jan 2019

Two-Dimensional Early Transition Metal Carbides As Supports For Platinum Catalysts, Zhe Li

Graduate Theses and Dissertations

Tuning catalytic active sites through metal-support interactions (MSIs) has emerged as an effective strategy to design supported metal catalysts. The development and selection of supports are paramount for achieving the desired catalytic performance, which are however, great challenges. This dissertation involves elucidating the MSIs between platinum and two-dimensional early transition metal carbides (MXenes) and harnessing the MSIs for several industrial catalytic processes and electrocatalytic reactions.

This work discovered the reactive metal support interactions (RMSI) in MXenes supported Pt catalysts. RMSI refers to a chemical reaction between a metal and the support that induces the formation of bimetallic structures. By utilizing ...


Low Moisture Anhydrous Ammonia (Lmaa) Pretreatment Of Lignocellulosic Biomass And Assessments For Biobutanol Production, Nazira Binti Mahmud Jan 2019

Low Moisture Anhydrous Ammonia (Lmaa) Pretreatment Of Lignocellulosic Biomass And Assessments For Biobutanol Production, Nazira Binti Mahmud

Graduate Theses and Dissertations

Low-value biomass materials such as processing co-products and agricultural wastes possess abundant potential in value-added products production. The effort for utilization of these materials, especially as the substrate for fermentation process was limited by the low availability of fermentable sugar. This is due to the presence of lignin and hemicellulose in biomass structure, which entails appropriate pretreatment procedure to be conducted to expose the cellulose for the enzymatic reaction. Alkali-based pretreatments offer the attractive benefit of low inhibitor compound production. In this study, low moisture anhydrous ammonia (LMAA) pretreatment was conducted on selected biomass. Anhydrous ammonia, which is a gaseous ...


Efficient State Estimation Via Inference On A Probabilistic Graphical Model, Luke David Myers Jan 2019

Efficient State Estimation Via Inference On A Probabilistic Graphical Model, Luke David Myers

Graduate Theses and Dissertations

This thesis presents a unique and efficient solver to the state estimation (SE) problem for the power grid, based on probabilistic graphical models (PGMs). SE is a method of estimating the varying state values of voltage magnitude and phase at every bus within a power grid based on meter measurements. However, existing SE solvers are notorious for their computational inefficiency to calculate the matrix inverse, and hence slow convergence to produce the final state estimates. The proposed PGM-based solver estimates the state values from a different perspective. Instead of calculating the matrix inverse directly, it models the power grid as ...


Nondestructive Evaluation Of Layered Ceramic Materials Using Terahertz Imaging, John Nagel Jan 2019

Nondestructive Evaluation Of Layered Ceramic Materials Using Terahertz Imaging, John Nagel

Graduate Theses and Dissertations

As the combustion temperature of modern turbine engines climbs higher and higher for greater fuel efficiency, new materials are needed to survive the increased temperature. As a result, there is much research interest in the areas of ceramic coatings, such as environmental barrier coatings (EBC) along with its abradable top coat and ceramic matrix composites (CMC’s), as these advanced materials can withstand the higher operating temperature of new generation turbines and offer significant weight savings as well. As such, it is essential to be able to evaluate the integrity of these materials as manufactured and in service. It is ...


Head Impact Simulation Using Coupled Eulerian-Lagrangian Approach, Miao Na Jan 2019

Head Impact Simulation Using Coupled Eulerian-Lagrangian Approach, Miao Na

Graduate Theses and Dissertations

As a major cause of death and disability, traumatic brain injury (TBI) creates considerable burdens to society due to high economic costs. Accordingly, investigation into the common causes of TBI such as dynamic head impact problems is of great importance in order to further understand the injury mechanisms, precisely diagnose the level of the injuries, and develop effective prevention methods. Finite element (FE) method has been widely used for gaining insights into the mechanical response of brain tissue during impacts, yet there are still computational challenges to be addressed and severe mesh distortion effect in the cerebrospinal fluid (CSF) is ...


Solution Phase Synthesis Of Lead-Free Perovskite And Perovskite-Inspired Materials, Rainie Dean Nelson Jan 2019

Solution Phase Synthesis Of Lead-Free Perovskite And Perovskite-Inspired Materials, Rainie Dean Nelson

Graduate Theses and Dissertations

This dissertation is a broad overview of research in the field of lead-free perovskite

inspired materials. While lead halide perovskites have promising properties, we sought to

investigate non-toxic alternatives – typically ones containing bismuth halides. We looked

into the flexibility of this element to be produced on different length scales, fabricating films

from bulk material, synthesizing nanocrystals, and growing crystals of 2D layered double

perovskites. We discovered that due to complexation with a solvent, bismuth iodide films can

be morphology controlled through use of solvent additives. During our synthesis of Cs3Bi2X9

nanocrystals, we found that BiX3 precursors possessed photoluminescence and that ...


Optimization Of Multi-Injection Diesel Combustion Through Direct Application Of Abc And Pso Variant Algorithms, Ryan Michael Ogren Jan 2019

Optimization Of Multi-Injection Diesel Combustion Through Direct Application Of Abc And Pso Variant Algorithms, Ryan Michael Ogren

Graduate Theses and Dissertations

In this study a modified artificial bee colony algorithm and the cooperative-swarm variant of particle swarm optimization were applied to minimize diesel engine emissions and fuel consumption in the laboratory at medium load conditions. Tests were conducted using No. 2 diesel fuel in a four-cylinder, production diesel engine with series turbochargers and a high-pressure exhaust gas recirculation loop. Emissions were recorded at steady-state conditions and input into custom scripts in Matlab.

Both triple-injection strategies, consisting of a pilot-main-post injection scheme, and quadruple-injection strategies, using two pilots, were investigated for a high exhaust gas recirculation rate of 38%. A two-factor design ...


Persistence In Aerospace Engineering: Why Students Choose And Leave Aerospace Engineering, Sara Oliveira Pedro Dos Santos Jan 2019

Persistence In Aerospace Engineering: Why Students Choose And Leave Aerospace Engineering, Sara Oliveira Pedro Dos Santos

Graduate Theses and Dissertations

Technological development, research and progress are one of the boosters of the US economy. Preparing students is important for the advance of the US economy and quality of life. STEM (science, technology, engineering and mathematics) degrees prepare students for the technological and economic challenges by providing them with tools to advance in these areas. However, the decline in enrollment in engineering degrees and a low retention rate may be hindering the US’s ability to respond to their technological and economic challenges. It is then important to increase the retention of students in STEM and engineering.

Despite several studies on ...


Behavior, Welfare, Production And Bioenergetics Of Laying Hens In Alternative Housing Systems, Jofran Luiz De Oliveira Jan 2019

Behavior, Welfare, Production And Bioenergetics Of Laying Hens In Alternative Housing Systems, Jofran Luiz De Oliveira

Graduate Theses and Dissertations

Transitioning of egg production systems from conventional cage to alternative housing (e.g., enriched colony, aviary cage-free) is increasingly occurring in various parts of the world, especially in Europe and the United States, to meet animal welfare requirements or legislations. This dissertation had the central goal of providing scientific knowledge or discoveries related to behavior, welfare, production, and bioenergetics of laying hens in alternative housing systems. It covers five experiments that were conducted in controlled environment and commercial settings with the following specific objectives: 1) Develop and validate a UHF RFID system able to evaluate nesting and feeding behaviors of ...


Analyzing And Advancing Maize And Sugarcane Biorefinery Systems, Maria C. T. B. Oliveira Jan 2019

Analyzing And Advancing Maize And Sugarcane Biorefinery Systems, Maria C. T. B. Oliveira

Graduate Theses and Dissertations

Fossil fuels are considered one of the most significant contributors to anthropogenic greenhouse gas (GHG) emissions, and renewable energy derived from biomass has potential to displace fossil fuels and to significantly reduce the CO2 emissions. One example of the conversion of biomass into renewable energy is the production of biofuels such as ethanol and biodiesel. Nowadays, producing a green product with lower cost is challenging because of production cost and environmental impacts of the manufacturing process that involve expensive technologies and significant amounts of emission. While much research in this area has been published over the last few decades, gaps ...


Dynamic Analysis Of Composite Wind Turbine Blade, Divya Teja Pinnamaneni Jan 2019

Dynamic Analysis Of Composite Wind Turbine Blade, Divya Teja Pinnamaneni

Graduate Theses and Dissertations

The purpose of this paper is to establish a basis for determining the accuracy level required in load prediction models by comparing fatigue results of a composite material wind turbine blade for a set of experimental wind loads. Wind data for two successive years is considered separately as two load cases to calculate aerodynamic loads. These loads are used in monthly and yearly cycles to perform fatigue analysis and the difference in safety life and damage for successive years is calculated, to check, if faithful prediction of hourly or daily wind speeds for a wind forecast model is required. Thus ...


Process Intensification Of Biomass Fast Pyrolysis Via Autothermal Operation, Joseph Patrick Polin Jan 2019

Process Intensification Of Biomass Fast Pyrolysis Via Autothermal Operation, Joseph Patrick Polin

Graduate Theses and Dissertations

Heat transfer is the bottleneck to fast pyrolysis of biomass. Although the enthalpy for pyrolysis of biomass is relatively small, operation at temperatures around 500°C constrains heat carrier selection to inert gases and granular media that can sustain only modest thermal fluxes in practical pyrolysis systems. With heat transfer controlling the rate of pyrolysis, reactor capacity only scales as the square of reactor diameter and does not benefit from economies of scale in building larger reactors. We have eliminated this heat transfer bottleneck by replacing it with partial oxidation of pyrolysis products to provide the enthalpy for pyrolysis in ...