Physical Sciences and Mathematics Commons^™

Plasmonic Devices Based On Transparent Conducting Oxides For Near Infrared Applications, Kim Jongbum

Open Access Dissertations

In the past decade, there have been many breakthroughs in the field of plasmonics and nanophotonics that have enabled optical devices with unprecedented functionalities. Even though remarkable demonstration of at photonic devices has been reported, constituent materials are limited to the noble metals such as gold (Au) and silver (Ag) due to their abundance of free electrons which enable the support of plasmon resonances in the visible range. With the strong demand for extension of the optical range of plasmonic applications, it is now a necessity to explore and develop alternative materials which can overcome intrinsic issues of noble metals …

Nanophotonics For Dark Materials, Filters, And Optical Magnetism, Mengren Man

Open Access Dissertations

Research on nanophotonic structures for three application areas is described, a near perfect optical absorber based on a graphene/dielectric stack, an ultraviolet bandpass filter formed with an aluminum/dielectric stack, and structures exhibiting homogenizable magnetic properties at infrared frequencies. The graphene stack can be treated as a effective, homogenized medium that can be designed to reflect little light and absorb an astoundingly high amount per unit thickness, making it an ideal dark material and providing a new avenue for photonic devices based on two-dimensional materials. Another material stack arrangement with thin layers of metal and insulator forms a multi-cavity filter that …

Exploring Spin-Transfer-Torque Devices And Memristors For Logic And Memory Applications, Zoha Pajouhi

Open Access Dissertations

As scaling CMOS devices is approaching its physical limits, researchers have begun exploring newer devices and architectures to replace CMOS.

Due to their non-volatility and high density, Spin Transfer Torque (STT) devices are among the most prominent candidates for logic and memory applications. In this research, we first considered a new logic style called All Spin Logic (ASL). Despite its advantages, ASL consumes a large amount of static power; thus, several optimizations can be performed to address this issue. We developed a systematic methodology to perform the optimizations to ensure stable operation of ASL.

Second, we investigated reliable design of …

Learning From Minimally Labeled Data With Accelerated Convolutional Neural Networks, Aysegul Dundar

Open Access Dissertations

The main objective of an Artificial Vision Algorithm is to design a mapping function that takes an image as an input and correctly classifies it into one of the user-determined categories. There are several important properties to be satisfied by the mapping function for visual understanding. First, the function should produce good representations of the visual world, which will be able to recognize images independently of pose, scale and illumination. Furthermore, the designed artificial vision system has to learn these representations by itself. Recent studies on Convolutional Neural Networks (ConvNets) produced promising advancements in visual understanding. These networks attain significant …

Effect Of Bioenergy Crops And Fast Growing Trees On Hydrology And Water Quality In The Little Vermilion River Watershed, Tian Guo

Open Access Dissertations

Energy security and sustainability require a suite of biomass crops, including woody species. Short rotation woody crops (SRWCs) such as Populus have great potential as biofuel feedstocks. Quantifying biomass yields of bioenergy crop and hydrologic and water quality responses to growth is important should it be widely planted in the Midwestern U.S. Subsurface tile drainage systems enable the Midwest area to become highly productive agricultural lands, but also create environmental problems like nitrate-N contamination of the water it drains. The Soil and Water Assessment Tool (SWAT) has been used to model watersheds with tile drainage, but the new tile drainage …

Optimal Monitoring And Mitigation Of Systemic Risk In Lending Networks, Zhang Li

Open Access Dissertations

This thesis proposes optimal policies to manage systemic risk in financial networks. Given a one-period borrower-lender network in which all debts are due at the same time and have the same seniority, we address the problem of allocating a fixed amount of cash among the nodes to minimize the weighted sum of unpaid liabilities. Assuming all the loan amounts and cash flows are fixed and that there are no bankruptcy costs, we show that this problem is equivalent to a linear program. We develop a duality-based distributed algorithm to solve it which is useful for applications where it is desirable …

On The 3d Point Cloud For Human-Pose Estimation, Kai-Chi Chan

Open Access Dissertations

This thesis aims at investigating methodologies for estimating a human pose from a 3D point cloud that is captured by a static depth sensor. Human-pose estimation (HPE) is important for a range of applications, such as human-robot interaction, healthcare, surveillance, and so forth. Yet, HPE is challenging because of the uncertainty in sensor measurements and the complexity of human poses. In this research, we focus on addressing challenges related to two crucial components in the estimation process, namely, human-pose feature extraction and human-pose modeling.

In feature extraction, the main challenge involves reducing feature ambiguity. We propose a 3D-point-cloud feature called …

Supervised Learning-Based Explicit Nonlinear Model Predictive Control And Unknown Input Estimation In Biomedical Systems, Ankush Chakrabarty

Open Access Dissertations

Application of nonlinear control theory to biomedical systems involves tackling some unique and challenging problems. The mathematical models that describe biomedical systems are typically large and nonlinear. In addition, biological systems exhibit dynamics which are not reflected in the model (so-called 'un-modeled dynamics') and hard constraints on the states and control actions, which exacerbate the difficulties in designing model-based controllers or observers.

This thesis investigates the design of scalable fast explicit nonlinear model predictive controllers (ENMPCs). The design involves (i) the estimation of a feasible region using Lyapunov stability methods and support vector machines; and (ii) within the estimated feasible …

Modular Approach To Spintronics, Kerem Yunus Camsari

Open Access Dissertations

There has been enormous progress in the last two decades, effectively combining spintronics and magnetics into a powerful force that is shaping the field of memory devices. New materials and phenomena continue to be discovered at an impressive rate, providing an ever-increasing set of building blocks that could be exploited in designing transistor-like functional devices of the future. The objective of this thesis is to provide a quantitative foundation for this building block approach, so that new discoveries can be integrated into functional device concepts, quickly analyzed and critically evaluated. Through careful benchmarking against available theory and experiments we establish …

Computational Optical Imaging: Applications In Synthetic Aperture Imaging, Phase Retrieval, And Digital Holography, Dennis Joseph Lee

Open Access Dissertations

Computational imaging has become an important field, as a merger of both algorithms and physical experiments. In the realm of microscopy and optical imaging, an important application is the problem of improving resolution, which is bounded by wavelength and numerical aperture according to the classic diffraction limit. We will investigate the resolution enhancement of phase objects such as transparent biological cells. One key challenge is how to measure phase experimentally. Standard interferometric techniques have the drawback of being sensitive to environmental vibrations and temperature fluctuations, and they use a reference arm which requires more space and cost. Non-holographic methods provide …

Circular Bessel Field Statistics And The Pursuit Of Far-Subwavelength Resolution, Yulu Chen

Open Access Dissertations

The statistical description of wave propagation in random media is important for many applications. While polarized light in systems with weakly interacting scatterers and sufficient overall scatter has zero-mean circular Gaussian statistics, the underlying assumptions break down in the Anderson localization and weakly scattering regimes. Although probability density functions for wave intensity and amplitude exist beyond Gaussian statistics, suitable statistical descriptions for the field with strong and weak random scatter were unknown. The first analytical probability density function for the field that is effective in both the Anderson localization regime and the weakly scattering regime is derived by modeling the …

Fully Electronic Method Of Measuring Post-Release Gap And Gradient/Residual Stress Of A Mems Cantilever, Andrew Stephen Kovacs

Open Access Dissertations

Smartphones and other wireless devices have become ubiquitous over the past decade, and the RF front-end inside of them has become more complex and disproportionately consumes more power compared to other components. Micro-electromechanical systems (MEMS) have a huge potential to reduce these problems while simultaneously offering superior performance compared to current leading-edge technology. However, MEMS technology has difficulty transitioning from the lab to large-scale manufacturing due to the unpredictability of device lifetime and manufacturability issues. This can be mitigated by investigating how critical material or physical parameters (gap, stress, Young's modulus, material thickness, etc.) vary from manufacturing uncertainties and how …

Advanced Wireless Communications Using Large Numbers Of Transmit Antennas And Receive Nodes, Junil Choi

Open Access Dissertations

The concept of deploying a large number of antennas at the base station, often called massive multiple-input multiple-output (MIMO), has drawn considerable interest because of its potential ability to revolutionize current wireless communication systems. Most literature on massive MIMO systems assumes time division duplexing (TDD), although frequency division duplexing (FDD) dominates current cellular systems. Due to the large number of transmit antennas at the base station, currently standardized approaches would require a large percentage of the precious downlink and uplink resources in FDD massive MIMO be used for training signal transmissions and channel state information (CSI) feedback. First, we propose …

Advanced Iii-V / Si Nano-Scale Transistors And Contacts: Modeling And Analysis, Seung Hyun Park

Open Access Dissertations

The exponential miniaturization of Si CMOS technology has been a key to the electronics revolution. However, the continuous downscaling of the gate length becomes the biggest challenge to maintain higher speed, lower power, and better electrostatic integrity for each following generation. Hence, novel devices and better channel materials than Si are considered to improve the metal-oxide-semiconductor field-effect transistors (MOSFETs) device performance. III-V compound semiconductors and multi-gate structures are being considered as promising candidates in the next CMOS technology. III-V and Si nano-scale transistors in different architectures are investigated (1) to compare the performance between InGaAs of III-V compound semiconductors and …

Image Analysis Using Visual Saliency With Applications In Hazmat Sign Detection And Recognition, Bin Zhao

Open Access Dissertations

Visual saliency is the perceptual process that makes attractive objects "stand out" from their surroundings in the low-level human visual system. Visual saliency has been modeled as a preprocessing step of the human visual system for selecting the important visual information from a scene. We investigate bottom-up visual saliency using spectral analysis approaches. We present separate and composite model families that generalize existing frequency domain visual saliency models. We propose several frequency domain visual saliency models to generate saliency maps using new spectrum processing methods and an entropy-based saliency map selection approach. A group of saliency map candidates are then …

Tunable Impedance Matching Network Fundamental Limits And Pracitical Considerations, Wesley N. Allen

Open Access Dissertations

As wireless devices continue to increase in utility while decreasing in dimension, design of the RF front-end becomes more complex. It is common for a single handheld device to operate on a plethora of frequency bands, utilize multiple antennae, and be subjected to a variety of environments. One complexity in particular which arises from these factors is that of impedance mismatch. Recently, tunable impedance matching networks have begun to be implemented to address this problem. ^ This dissertation presents the first in-depth study on the frequency tuning range of tunable impedance matching networks. Both the fundamental limitations of ideal networks …

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 …

Theory Of Topological Insulators And Its Applications, Parijat Sengupta

Open Access Dissertations

An important pursuit in semiconductor physics is to discover new materials to sustain the continuous progress and improvements in the current electronic devices. Traditionally, three material types are in use: 1) Metals 2) Semiconductors 3) Insulators. All the three material types are classified according to the energy gap between conduction and valence bands derived from band theory of solids. Recent theoretical predictions and confirmed by experimental observations have provided evidence that there exists materials which behave as insulators in the bulk but possess gapless conducting states on the surface. These new class of materials are called topological insulators (TI). In …

Energy Efficient Hybrid Computing Systems Using Spin Devices, Mrigank Sharad

Open Access Dissertations

Emerging spin-devices like magnetic tunnel junctions (MTJ's), spin-valves and domain wall magnets (DWM) have opened new avenues for spin-based logic design. This work explored potential computing applications which can exploit such devices for higher energy-efficiency and performance. The proposed applications involve hybrid design schemes, where charge-based devices supplement the spin-devices, to gain large benefits at the system level. As an example, lateral spin valves (LSV) involve switching of nanomagnets using spin-polarized current injection through a metallic channel such as Cu. Such spin-torque based devices possess several interesting properties that can be exploited for ultra-low power computation. Analog characteristic of spin …

Electric Machine Differential For Vehicle Traction Control And Stability Control, Sandun Shivantha Kuruppu

Open Access Dissertations

Evolving requirements in energy efficiency and tightening regulations for reliable electric drivetrains drive the advancement of the hybrid electric (HEV) and full electric vehicle (EV) technology. Different configurations of EV and HEV architectures are evaluated for their performance. The future technology is trending towards utilizing distinctive properties in electric machines to not only to improve efficiency but also to realize advanced road adhesion controls and vehicle stability controls. Electric machine differential (EMD) is such a concept under current investigation for applications in the near future. Reliability of a power train is critical. Therefore, sophisticated fault detection schemes are essential in …

Modeling The Atomic And Electronic Structure Of Metal-Metal, Metal-Semiconductor And Semiconductor-Oxide Interfaces, Ganesh Krishna Hegde

Open Access Dissertations

The continuous downward scaling of electronic devices has renewed attention on the importance of the role of material interfaces in the functioning of key components in electronic technology in recent times. It has also brought into focus the utility of

atomistic modeling in providing insights from a materials design perspective. In this thesis, a combination of Semi Empirical Tight-Binding (TB), first-principles Density

Functional Theory and Reactive Molecular Dynamics (MD) modeling is used to study aspects of the electronic and atomic structure of three such 'canonical' material interfaces - Metal-Metal, Metal-Semiconductor and Semiconductor oxide interfaces.

An important contribution of this thesis …

Mispronunciation Detection For Language Learning And Speech Recognition Adaptation, Zhenhao Ge

Open Access Dissertations

The areas of "mispronunciation detection" (or "accent detection" more specifically) within the speech recognition community are receiving increased attention now. Two application areas, namely language learning and speech recognition adaptation, are largely driving this research interest and are the focal points of this work.

There are a number of Computer Aided Language Learning (CALL) systems with Computer Aided Pronunciation Training (CAPT) techniques that have been developed. In this thesis, a new HMM-based text-dependent mispronunciation system is introduced using text Adaptive Frequency Cepstral Coefficients (AFCCs). It is shown that this system outperforms the conventional HMM method based on Mel Frequency Cepstral …

Redefining The Operation And Design Considerations Of Organic Solar Cells: Role Of Morphology And Defect States, Biswajit Ray

Open Access Dissertations

Organic photovoltaic (OPV) technology is currently a topic of great interest for potentially low cost solar energy conversion and possibility of many novel PV applications (e.g., building-integrated PV, portable solar cells). Successful commercialization of this technology, however, will require significant improvement in efficiency and lifetime. In the last few years, innovation in novel polymer synthesis has raised the efficiency of OPV above 10%, at par with a-Si and earth-abundant solar cells. Further improvement in performance relies on breakthroughs in device design, which requires profound understanding of the physics of device operation. A major challenge in the design of the state …

Altered Cholesterol Metabolism In Human Cancers Unraveled By Label-Free Spectroscopic Imaging, Shuhua Yue

Open Access Dissertations

Despite tremendous scientific achievements, cancer remains the second leading cause of death in the United States. Metabolic reprogramming has been increasingly recognized as a core hallmark of cancer. My dissertation work identified novel diagnostic markers and therapeutic targets for human cancers through the study of cholesterol in cancer cells.

Enabled by label-free Raman spectromicroscopy, we performed the first quantitative analysis of lipogenesis at single cell level in human patient cancerous tissues. Our imaging data revealed an unexpected, aberrant accumulation of esterified cholesterol in lipid droplets of high-grade prostate cancer and metastases, but not in normal prostate, benign prostatic hyperplasia, or …

Solar Cell Temperature Dependent Efficiency And Very High Temperature Efficiency Limits, John Robert Wilcox

Open Access Dissertations

Clean renewable solar energy is and will continue to be a critically important source of electrical energy. Solar energy has the potential of meeting all of the world's energy needs, and has seen substantial growth in recent years. Solar cells can convert sun light directly into electrical energy, and much progress has been made in making them less expensive and more efficient. Solar cells are often characterized and modeled at 25 °C, which is significantly lower than their peak operating temperature. In some thermal concentrating systems, solar cells operate above 300 °C. Since increasing the temperature drastically affects the terminal …

Technology Agnostic Analysis And Design For Improved Performance, Variability, And Reliability In Thin Film Photovoltaics, Sourabh Dongaonkar

Open Access Dissertations

Thin film photovoltaics (TFPV) offer low cost alternatives to conventional crystalline Silicon (c-Si) PV, and can enable novel applications of PV technology. Their large scale adoption however, requires significant improvements in process yield, and operational reliability. In order to address these challenges, comprehensive understanding of factors affecting panel yield, and predictive models of performance reliability are needed. This has proved to be especially challenging for TFPV for two reasons in particular. First, TFPV technologies encompass a wide variety of materials, processes, and structures, which fragments the research effort. Moreover, the monolithic manufacturing of TFPV modules differs significantly from that of …

Reconfigurable Technologies For Next Generation Internet And Cluster Computing, Deepak C. Unnikrishnan

Open Access Dissertations

Modern web applications are marked by distinct networking and computing characteristics. As applications evolve, they continue to operate over a large monolithic framework of networking and computing equipment built from general-purpose microprocessors and Application Specific Integrated Circuits (ASICs) that offers few architectural choices. This dissertation presents techniques to diversify the next-generation Internet infrastructure by integrating Field-programmable Gate Arrays (FPGAs), a class of reconfigurable integrated circuits, with general-purpose microprocessor-based techniques. Specifically, our solutions are demonstrated in the context of two applications - network virtualization and distributed cluster computing.

Network virtualization enables the physical network infrastructure to be shared among several …

Information Measures For Statistical Orbit Determination, Alinda Kenyana Mashiku

Open Access Dissertations

The current Situational Space Awareness (SSA) is faced with a huge task of tracking the increasing number of space objects. The tracking of space objects requires frequent and accurate monitoring for orbit maintenance and collision avoidance using methods for statistical orbit determination. Statistical orbit determination enables us to obtain estimates of the state and the statistical information of its region of uncertainty given by the probability density function (PDF). As even collision events with very low probability are important, accurate prediction of collisions require the representation of the full PDF of the random orbit state. Through representing the full PDF …