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Articles 31 - 60 of 103
Full-Text Articles in Engineering
Dynamic Control Of Plasmonic Resonances With Graphene Based Nanostructures, Naresh Kumar Emani
Dynamic Control Of Plasmonic Resonances With Graphene Based Nanostructures, Naresh Kumar Emani
Open Access Dissertations
Light incident on a metallic structure excites collective oscillations of electrons termed as plasmons. These plasmons are useful in control and manipulation of information in nanoscale dimensions and at high operating frequencies. Hence, the field of plasmonics opens up the possibility of developing nanoscale optoelectronic circuitry for computing and sensing applications. One of the challenges in this effort is the lack of tunable plasmonic resonance. Currently, the resonant wavelength of plasmonic structure is fixed by the material and structural parameters. Post-fabrication dynamic control of a plasmonic resonance is rather limited.^ In this thesis we explore the combination of optoelectrical properties …
Application Of Integer Quadratic Programming In Detection Of High-Dimensional Wireless Systems, Ali Ahmed Elghariani
Application Of Integer Quadratic Programming In Detection Of High-Dimensional Wireless Systems, Ali Ahmed Elghariani
Open Access Dissertations
High-dimensional wireless systems have recently generated a great deal of interest due to their ability to accommodate increasing demands for high transmission data rates with high communication reliability. Examples of such large-scale systems include single-input, single-output symbol spread OFDM system, large-scale single-user multi-input multi-output (MIMO) OFDM systems, and large-scale multiuser MIMO systems. In these systems, the number of symbols required to be jointly detected at the receiver is relatively large. The challenge with the practical realization of these systems is to design a detection scheme that provides high communication reliability with reasonable computational complexity, even as the number of simultaneously …
Solid Oxide Fuel Cell Electrolytes Produced Via Very Low Pressure Suspension Plasma Spray And Electrophoretic Deposition, James D Fleetwood
Solid Oxide Fuel Cell Electrolytes Produced Via Very Low Pressure Suspension Plasma Spray And Electrophoretic Deposition, James D Fleetwood
Open Access Dissertations
Solid oxide fuel cells (SOFCs) are a promising element of comprehensive energy policies due to their direct mechanism for converting the oxidization of fuel, such as hydrogen, into electrical energy. Both very low pressure plasma spray and electrophoretic deposition allow working with high melting temperature SOFC suspension based feedstock on complex surfaces, such as in non-planar SOFC designs. Dense, thin electrolytes of ideal composition for SOFCs can be fabricated with each of these processes, while compositional control is achieved with dissolved dopant compounds that are incorporated into the coating during deposition. In the work reported, sub-micron 8 mole % Y …
Coupled Fluid-Thermal Analysis Of Low-Pressure Sublimation And Condensation With Application To Freeze-Drying, Arnab Ganguly
Coupled Fluid-Thermal Analysis Of Low-Pressure Sublimation And Condensation With Application To Freeze-Drying, Arnab Ganguly
Open Access Dissertations
Freeze-drying is a low-pressure, low-temperature condensation pumping process widely used in the manufacture of bio-pharmaceuticals for removal of solvents by sublimation. The goal of the process is to provide a stable dosage form by removing the solvent in such a way that the sensitive molecular structure of the active substance is least disturbed. The vacuum environment presents unique challenges for understanding and controlling heat and mass transfer in the process. As a result, the design of equipment and associated processes has been largely empirical, slow and inefficient.^ A comprehensive simulation framework to predict both, process and equipment performance is critical …
Analysis Of The Interaction Of Two Parallel Surface Cracks, Jeeyeon Hahn
Analysis Of The Interaction Of Two Parallel Surface Cracks, Jeeyeon Hahn
Open Access Dissertations
The objective of this research is to analyze and predict the interaction of surface cracks that occur in parallel planes. Multiple cracks may form in aging aircraft that forms at stress concentrations such as fastener holes and notched components by stress corrosion and fatigue cracking. The lifetime of the structures are significantly affected by the interaction between these cracks. Depending on relative positions and orientations of neighboring cracks, local stress fields and crack driving forces can be affected by the presence of adjacent cracks. Even small subcritical cracks may rapidly grow to a size that will cause failure in service …
Intranuclear Strain Measured By Iterative Warping In Cells Under Mechanical And Osmotic Stress, Jonathan T Henderson
Intranuclear Strain Measured By Iterative Warping In Cells Under Mechanical And Osmotic Stress, Jonathan T Henderson
Open Access Dissertations
The nucleus is a membrane bound organelle and regulation center for gene expression in the cell. Mechanical forces transfer to the nucleus directly and indirectly through specific cellular cytoskeletal structures and pathways. There is increasing evidence that the transferred forces to the nucleus orchestrate gene expression activity. Methods to characterize nuclear mechanics typically study isolated cells or cells embedded in 3D gel matrices. Often report only aspect ratio and volume changes, measures that oversimplify the inherent complexity of internal strain patterns. This presents technical challenges to simultaneously observe small scale nuclear mechanics and gene expression levels inside the nuclei of …
Quantifying Aesthetics Of Visual Design Applied To Automatic Design, Ali Jahanian
Quantifying Aesthetics Of Visual Design Applied To Automatic Design, Ali Jahanian
Open Access Dissertations
In today's "Instagram" world, with advances in ubiquitous computing and access to social networks, digital media is adopted by art and culture. In this dissertation, we study what makes a good design by investigating mechanisms to bring aesthetics of design from realm of subjection to objection. These mechanisms are a combination of three main approaches: learning theories and principles of design by collaborating with professional designers, mathematically and statistically modeling good designs from large scale datasets, and crowdscourcing to model perceived aesthetics of designs from general public responses. We then apply the knowledge gained in automatic design creation tools to …
Functional Programming Abstractions For Weakly Consistent Systems, Sivaramakrishnan Krishnamoorthy Chandrasekaran
Functional Programming Abstractions For Weakly Consistent Systems, Sivaramakrishnan Krishnamoorthy Chandrasekaran
Open Access Dissertations
In recent years, there has been a wide-spread adoption of both multicore and cloud computing. Traditionally, concurrent programmers have relied on the underlying system providing strong memory consistency, where there is a semblance of concurrent tasks operating over a shared global address space. However, providing scalable strong consistency guarantees as the scale of the system grows is an increasingly difficult endeavor. In a multicore setting, the increasing complexity and the lack of scalability of hardware mechanisms such as cache coherence deters scalable strong consistency. In geo-distributed compute clouds, the availability concerns in the presence of partial failures prohibit strong consistency. …
Understanding The Rhetorical Engineer, Zachery W Koppelmann
Understanding The Rhetorical Engineer, Zachery W Koppelmann
Open Access Dissertations
The purpose of this dissertation is to describe the development of the Purdue School of Mechanical Engineering Writing Enhancement Program and its definition of good engineering writing. Based on the work with the Mechanical Engineering Faculty and the Writing Enhancement Program, it was determined that good engineering writing is aware of its need to address specific rhetorical contexts and expectations. The Writing Enhancement Program was created to provide additional writing instruction to undergraduate mechanical engineering students Purdue University. Its development did not follow standard writing across the curriculum methods; it was developed following a modified writing center methodology. The modifications …
Investigation Of Optical Near Field Using Near Field Scanning Optical Microscopy, Yan Li
Investigation Of Optical Near Field Using Near Field Scanning Optical Microscopy, Yan Li
Open Access Dissertations
Conventional optical imaging techniques have a fundamental resolution limit due to the diffraction limit of light. The advances of science and technology on the nanoscale demand a new tool for characterization. The Near Field Scanning Optical Microscopy (NSOM) has been developed to tackle certain aspects of this problem. The work presented here applies different types of NSOM to explore the near field distribution of metal plasmonic nanostructures.^ Ridge apertures with shapes like bowtie and C can be used to focus light into sub-diffraction limit spot with enhancement. This localization of the field near the exit of a bowtie aperture is …
Embodied Interaction With Visualization And Spatial Navigation In Time-Sensitive Scenarios, Yu-Ting Li
Embodied Interaction With Visualization And Spatial Navigation In Time-Sensitive Scenarios, Yu-Ting Li
Open Access Dissertations
Paraphrasing the theory of embodied cognition, all aspects of our cognition are determined primarily by the contextual information and the means of physical interaction with data and information. In hybrid human-machine systems involving complex decision making, continuously maintaining a high level of attention while employing a deep understanding concerning the task performed as well as its context are essential. Utilizing embodied interaction to interact with machines has the potential to promote thinking and learning according to the theory of embodied cognition proposed by Lakoff. Additionally, the hybrid human-machine system utilizing natural and intuitive communication channels (e.g., gestures, speech, and body …
Material And Device Aspects Of Semiconducting Two-Dimensional Crystals, Han Liu
Material And Device Aspects Of Semiconducting Two-Dimensional Crystals, Han Liu
Open Access Dissertations
Two-dimensional (2D) crystals have attracted much attention in recent years due to their unique physical, chemical, and mechanical properties. Semiconducting 2D crystals with van der Waals structures, such as transition metal dichalcogenides, are considered promising candidates for future device applications, as many have large band gaps, high carrier mobilities, and enable devices with immunity to short channel effects in addition to compatibility with silicon CMOS processes.^ In this thesis, the fundamental device implications of using semiconducting 2D crystals are investigated. This includes: 1) the optimization of device fabrication processing for better device performance, 2) comparing the device physics in 2D …
Nearly Orthogonal, Doppler Tolerant Waveforms And Signal Processing For Multi-Mode Radar Applications, Uttam Kumar Majumder
Nearly Orthogonal, Doppler Tolerant Waveforms And Signal Processing For Multi-Mode Radar Applications, Uttam Kumar Majumder
Open Access Dissertations
In this research, we investigate the design and analysis of nearly orthogonal, Doppler tolerant waveforms for diversity waveform radar applications. We then present a signal processing framework for joint synthetic aperture radar (SAR) and ground moving target indication (GMTI) processing that is built upon our proposed waveforms. ^ To design nearly orthogonal and Doppler tolerant waveforms, we applied direct sequence spread spectrum (DSSS) coding techniques to linear frequency modulated (LFM) signals. The resulting transmitted waveforms are rendered orthogonal using a unique spread spectrum code. At the receiver, the echo signal can be decoded using its spreading code. In this manner, …
Ultrasound Assisted Low-Temperature Synthesis Of Tib2 And Al3ti Particulates In Molten Aluminum, Zhiwei Liu
Ultrasound Assisted Low-Temperature Synthesis Of Tib2 And Al3ti Particulates In Molten Aluminum, Zhiwei Liu
Open Access Dissertations
In situ formed TiB2 and Al3Ti are two typical representatives of ceramic and intermetallic reinforcements in the in situ particulate reinforced Al composites. TiB2 particulates can be synthesized in molten Al via the mixed-salts reaction by adding mixed K2TiF6 and KBF4 salts into the Al melt at high temperatures. Al3 Ti particulates can be produced by the direct-melt reaction between solid Ti powders and liquid Al at high temperatures. Generally, a high reaction temperature is always needed to obtain both reinforcements. Some issues, however, such as high cost and burning loss …
The Role Of Microstructure On The Combustion And Impact Behavior Of Mechanically Activated Nickel/Aluminum Reactive Composites, Benjamin Aaron Mason
The Role Of Microstructure On The Combustion And Impact Behavior Of Mechanically Activated Nickel/Aluminum Reactive Composites, Benjamin Aaron Mason
Open Access Dissertations
Metal-based reactive composites are a class of materials that consist of at least one metals, such as Ni/Al, that have high-energy densities and can produce significant energy output during exothermic reaction after thermal or mechanical initiation. However, conventionally these materials typically have slow reaction rates and are difficult to ignite at typical micron particle size ranges limiting their application. Therefore, mechanical activation techniques have been used to create materials with high surface areas and smaller characteristic dimensions in order to increase combustion velocity and ignition sensitivity. Their combustion and mechanical impact behavior is being studied to develop the understanding needed …
The Impact Of National Science Foundation Investments In Undergraduate Engineering Education Research: A Comparative, Mixed Methods Study, Jeremi Shavonda London
The Impact Of National Science Foundation Investments In Undergraduate Engineering Education Research: A Comparative, Mixed Methods Study, Jeremi Shavonda London
Open Access Dissertations
The U.S. invests billions of taxpayers' dollars in research tied to the national priorities that contribute to its competitiveness in a global economy. As the federal funding agency with an explicit focus on engineering education, the National Science Foundation (NSF) contains a portfolio of projects focused on improving the quantity of engineering graduates and the quality of engineering programs. Within the agency, the Division of Undergraduate Education invests approximately $190 million (FY 2012) annually on science, technology, engineering and mathematics (STEM) education projects. Although the DUE portfolio includes a suite a projects with different foci supporting national initiatives and Principal …
Application Of Integer Quadratic Programming To Detection Of High-Dimensional Wireless Systems, Jamal Yousuf Alsawalhi
Application Of Integer Quadratic Programming To Detection Of High-Dimensional Wireless Systems, Jamal Yousuf Alsawalhi
Open Access Dissertations
This work introduces a novel permanent-magnet synchronous machine (PMSM) architecture that employs rotational asymmetry to increase the torque density output in constant power variable speed applications. A population based multi-objective design optimization algorithm is used to design and analyze the new machine topology. A number of design studies are presented to show that the proposed machine structure outperforms a conventional PMSM machine. Validation of the analytical machine design model using a three dimensional finite element analyses is performed and the results are presented. Finally, a case study in which a hybrid electric bus traction motor is designed is presented.
A Nonlinear Interface Formulation For Frictional Contact, Layla K Amaireh
A Nonlinear Interface Formulation For Frictional Contact, Layla K Amaireh
Open Access Dissertations
Finite element simulations of contact problems often involve modeling the interaction of multiple bodies across a non-confirming interface. Non-Confirming Meshes (NCM) are typically associated with large sliding or adaptive refinement on one side of the interface to capture localized nonlinear behavior due to large deformations, damage and inelasticity. The use of NCMs, however, presents a number of numerical issues; the main challenge with such discretizations is to ensure compatibility of the kinematic and traction fields along the non-conforming interface. ^ The Enriched Discontinuous Galerkin Approach (EDGA) (Haikal and Hjelmstad,2010)addresses this challenge by implementing a local enrichment along with an interface …
Unsteady Flamelet Progress Variable Modeling Of Reacting Diesel Jets, Muhsin Mohammed Ameen
Unsteady Flamelet Progress Variable Modeling Of Reacting Diesel Jets, Muhsin Mohammed Ameen
Open Access Dissertations
Accurate modeling of turbulence/chemistry interactions in turbulent reacting diesel jets is critical to the development of predictive computational tools for diesel engines. The models should be able to predict the transient physical and chemical processes in the jets such as ignition and flame lift-off. In the first part of this work, an existing unsteady flamelet progress variable (UFPV) model is employed in Reynolds-averaged Navier-Stokes (RANS) simulations and large-eddy simulations (LES) to assess its accuracy. The RANS simulations predict that ignition occurs toward the leading tip of the jet, followed by ignition front propagation toward the stoichiometric surface, and flame propagation …
Assessment Of Irrigation Use On Crop Yield And Water Supplies In The Midwestern U.S., Wei-Chih Chen
Assessment Of Irrigation Use On Crop Yield And Water Supplies In The Midwestern U.S., Wei-Chih Chen
Open Access Dissertations
Climate plays an important role in many aspects of hydrological and agricultural systems. Temperature and precipitation are usually the main forcing inputs for hydrological and agricultural simulations, while wind effect has generally been neglected in previous research. Wind speed is, however, an important factor for many physical processes, including evaporation from soil, and transpiration from plants. In order to investigate how climate variability impacts agricultural production, there are three hypotheses addressed in this dissertation. Hypothesis 1 is that the representation of changing wind speed will play an important role in the simulation of hydrological processes, and that the effect of …
Droplet Behavior On Superhydrophobic Surfaces: Interfaces, Interactions, And Transport, Susmita Dash
Droplet Behavior On Superhydrophobic Surfaces: Interfaces, Interactions, And Transport, Susmita Dash
Open Access Dissertations
The primary objective of the present work is to study droplet dynamics on smooth hydrophobic and textured superhydrophobic surfaces, and to understand the dependence of interfacial interaction mechanisms on surface morphology. ^ A detailed understanding of the dynamics of droplet response to an applied electric field is essential for implementation of electrowetting techniques in various devices. In the first part of the thesis, a systematic study of the transient response in terms of contact angle and contact radius of a sessile droplet on a smooth hydrophobic surface under electrical actuation is presented. A scaling analysis predicts the response time of …
Applications Of Femtosecond Coherent Anti-Stokes Raman Scattering In Combustion, Claresta Nicole Dennis
Applications Of Femtosecond Coherent Anti-Stokes Raman Scattering In Combustion, Claresta Nicole Dennis
Open Access Dissertations
The dissertation deals with the further development of chirped-probe-pulse femtosecond coherent anti-Stokes Raman spectroscopy (CPP fs-CARS) for applications of gas phase thermometry and extension to methane concentration measurements. The main effort has been to assess the usefulness and robustness of the technique in turbulent combustors of practical interest. A primary aim has been to evaluate the use of CPP fs-CARS for vibrational N2 thermometry in a highly turbulent environment. It has been suggested that due to the laser beam temporal overlap required for fs-CARS signal generation, the technique would be unsuccessful due to beam propagation retardation effects from density …
Thermal Efficiency And Emission Analysis Of Advanced Thermodynamic Strategies In A Multi-Cylinder Diesel Engine Utilizing Valve-Train Flexibility, Chuan Ding
Open Access Dissertations
Stringent emission regulations and a growing demand for fossil fuel drive the development of new technologies for internal combustion engines. Diesel engines are thermally efficient but require complex aftertreatment systems to reduce tailpipe emissions of unburned hydrocarbons (UHC), particulate matter (PM), and nitrogen oxides (NOx). These challenges require research into advanced thermodynamic strategies to improve thermal efficiency, control emission formation and manage exhaust temperature for downstream aftertreatment. The optimal performance for different on-road conditions is analyzed using a fully flexible valve-train on a modern diesel engine. The experimental investigation focuses on thermal management during idling and high-way cruise conditions. In …
Investigation Of Condensed And Early Stage Gas Phase Hypergolic Reactions, Jacob Daniel Dennis
Investigation Of Condensed And Early Stage Gas Phase Hypergolic Reactions, Jacob Daniel Dennis
Open Access Dissertations
Traditional hypergolic propellant combinations, such as those used on the space shuttle orbital maneuvering system first flown in 1981, feature hydrazine based fuels and nitrogen tetroxide (NTO) based oxidizers. Despite the long history of hypergolic propellant implementation, the processes that govern hypergolic ignition are not well understood. In order to achieve ignition, condensed phase fuel and oxidizer must undergo simultaneous physical mixing and chemical reaction. This process generates heat, intermediate condensed phase species, and gas phase species, which then may continue to react and generate more heat until ignition is achieved. The process is not well understood because condensed and …
A Stochastic Multi-Criteria Assessment Of Security Of Transportation Assets, Michelle Sophie Dojutrek
A Stochastic Multi-Criteria Assessment Of Security Of Transportation Assets, Michelle Sophie Dojutrek
Open Access Dissertations
Transportation project evaluation and prioritization use traditional performance measures including travel time, safety, user costs, economic efficiency, and environmental quality. The project impacts in terms of enhancing the infrastructure resilience or mitigating the consequences of infrastructure damage in the event of disaster occurrence are rarely considered in project evaluation. This dissertation presents a methodology to address this issue so that in evaluating and prioritizing investments, infrastructure with low security can receive the attention they deserve. Secondly, the methodology can be used for evaluating and prioritizing candidate investments dedicated specifically to security enhancement. In defining security as a function of threat …
A Qualitative Study Of Problematic Reasonings Of Undergraduate Electrical Engineering Students In Continuous Time Signals And Systems Courses, Farrah Fayyaz
Open Access Dissertations
Continuous Time Signals and Systems is a core course in the undergraduate electrical engineering curriculum. The topics covered in this course are difficult to learn conceptually because a significant number of topics are abstract, disconnected from a student's daily life, and make extensive use of mathematical modeling and formulas. Engineering educators have put in significant effort to design effective educational strategies for this course; however, there remained a gap in qualitative understanding of students' reasonings associated with difficulties in conceptual learning of the course content. This study aims to fill this gap by identifying problematic reasonings of undergraduate electrical engineering …
Hierarchical Cell Fluid Extracellular Matrix Interaction In Cell Microenvironment, Soham Ghosh
Hierarchical Cell Fluid Extracellular Matrix Interaction In Cell Microenvironment, Soham Ghosh
Open Access Dissertations
Hierarchical structural interactions between components of cell microenvironment, the extracellular matrix (ECM), cytoplasm, nucleus and fluid, are important phenomena that decide cell level physiological process and tissue engineering applications. One of those tissue engineering modalities is freezing of biomaterials, important in a wide variety of biomedical applications including cryopreservation and cryosurgeries. In order to design these applications, freezing-induced changes of the cells and tissues and corresponding biophysical mechanisms need to be well understood. Although the effects of freezing on cells in suspension have been extensively studied, the intracellular mechanics of cells embedded in the extracellular matrix (ECM) during freezing are …
Measurements Of Entropy-Layer Instabilities Over Cone-Ogive-Cylinders At Mach 6, Roger T Greenwood
Measurements Of Entropy-Layer Instabilities Over Cone-Ogive-Cylinders At Mach 6, Roger T Greenwood
Open Access Dissertations
Predicting the onset of boundary layer transition is critical in hypersonic flight. To improve transition prediction methods, it is necessary to understand the underlying instability mechanisms that cause transition. Entropy-layer instabilities are of particular interest in the design of blunt reentry vehicles and other blunt supersonic and hypersonic vehicles. Entropy-layer instabilities from outside the boundary layer may enter the boundary layer and have a significant effect on transition. There is little experimental data for entropy-layer instabilities. ^ Experimental measurements of what appear to be entropy-layer instabilities have been made in the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) using surface pressure transducers …
Modeling The Dynamics And Stresses Of Elongated Particles In Vertical Axis Mixers, Xia Hua
Modeling The Dynamics And Stresses Of Elongated Particles In Vertical Axis Mixers, Xia Hua
Open Access Dissertations
Vertical axis mixers, such as high shear granulators and agitated filter dryers (AFDs), are commonly used in the processing of particulate materials. For example, AFDs are regularly used in the pharmaceutical industry to dry the wet active pharmaceutical ingredient (API) particles. During the drying process, an impeller blade agitates the bed to increase the drying rate and enhance drying uniformity. Unfortunately, the needle-shaped API particles tend to flow poorly, are frequently damaged, and can sometimes form undesirable agglomerates, causing manufacturing inefficiencies, flow stoppages, and unpredictable product quality. Therefore, it is important to gain an improved understanding of the system's particle …
Tools For Efficient Design Of Multicomponent Separation Processes, Joshua Lee Huff
Tools For Efficient Design Of Multicomponent Separation Processes, Joshua Lee Huff
Open Access Dissertations
Separations account for as much as 85% of plant operating costs in chemical production; it is therefore important that they be designed with energy efficiency in mind. This can only be achieved if two things are achieved: the complete space of design options is known, and an accurate way is developed to compare all possible design options. For both membrane separation cascades and multicomponent distillation configurations, this dissertation explores methods for designing energy efficient separations.^ The operating cost of membranes used in production of nitrogen gas from air is largely driven by the compressors required to maintain a pressure differential. …