Browsing by Author "Lear, Kevin, committee member"
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Item Open Access A direct D-bar reconstruction algorithm for complex admittivities in W2,∞(Ω) for the 2-D EIT problem(Colorado State University. Libraries, 2012) Hamilton, Sarah Jane, author; Mueller, Jennifer L., advisor; Duchateau, Paul, committee member; Tavener, Simon, committee member; Lear, Kevin, committee memberElectrical Impedance Tomography (EIT) is a fairly new, portable, relatively inexpensive, imaging system that requires no ionizing radiation. Electrodes are placed at the surface of a body and low frequency, low amplitude current is applied on the electrodes, and the resulting voltage value on each electrode is measured. By applying a basis of current patterns, one can obtain sufficient information to recover the complex admittivity distribution of the region in the plane of the electrodes. In 2000, Elisa Francini presented a nearly constructive proof that was the first approach using D-bar methods to solve the full nonlinear problem for twice-differentiable conductivities and permittivities. In this thesis the necessary formulas to turn her proof into a direct D-bar reconstruction algorithm that solves the full nonlinear admittivity problem in 2-D are described. Reconstructions for simulated Finite Element data for circular and non-circular domains are presented.Item Open Access Carbon-based electrodes for environmental health applications(Colorado State University. Libraries, 2019) Berg, Kathleen E., author; Henry, Charles, advisor; Ackerson, Christopher, committee member; Krummel, Amber, committee member; Lear, Kevin, committee memberEnvironmental risk factors of air pollution and unsafe water are leading contributors to human morbidity and mortality, causing millions of deaths and diseases annually worldwide. Fine particulate matter (PM2.5) air pollution is linked to millions of deaths worldwide annually along with millions of cardiovascular and respiratory diseases. Unsafe water can contain heavy metals, including manganese (Mn), which high doses are linked to a variety of neurological and developmental diseases in humans. Analytical methods for testing for environmental risk factors such as fine PM and Mn still need improving. The primary focus of the dissertation here was to use carbon-based electrodes for improvements on environmental risk factor applications. An electrochemical assay was developed and used to measure Mn(II) in aqueous samples with stencil printed carbon paste electrodes. Stencil printed carbon paste electrodes are a mixture of graphite and organic liquid; they are easy to fabricate, portable, and disposable. These electrodes also do not require modification before detecting Mn in aqueous samples, but 1,4-benzoquinone was added to the background electrolyte for improved precision. Mn was then detected in complex matrices of tea and yerba mate samples. The focus is shifted from Mn detection to air pollution applications. A commercially available stencil printed carbon electrode was used for the dithiothreitol (DTT) assay, which is an assay commonly used to estimate the health effects of air pollution samples. The presented, improved DTT assay reduces reagents and increases sample throughput, both of which will help enable larger scale air pollution studies to be executed in the future. The DTT assay was then further improved with a semi-automated system that further increases the sample throughput and reduces reagent volumes while reducing the required manual labor associated with liquid handling. The semi-automated system uses a custom carbon composite thermoplastic electrode (TPE). Changes were observed in the TPE response over time and are studied further. The dissertation shifts focus to a more fundamental electrode characterization of high performing TPEs that were previously used because TPEs have a vast array of potential analytical applications, including environmental risk factor applications. Atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM) were used for a thorough investigation of the local surface topography and electrochemistry of TPEs, which is needed to assess the cause of the excellent electrochemical properties. The evidence suggests that the TPEs behave as microelectrodes, which gives rise to their high electrochemical activity. The amount of potential applications from TPEs is then increased by modifying the surface. TPEs, while being high performing and easy to pattern, have previously been limited by their solvent compatibility to aqueous solvents. Presented here is an alternative fabrication, which makes TPEs polar organic solvent compatible, that greatly increases the number of applications. The TPEs were then modified and functionalized in acetonitrile as a proof of concept that TPEs can be used in non-aqueous solvents and can have modified surfaces, which can lead to more applications. The research here uses different carbon electrodes to advance method development of environmental risk factor quantification. Advances to Mn(II) detection and fine PM health impacts were made. Fundamental understandings were developed of carbon composite TPEs and then modified to show a large potential number of future applications for continual improvement of electrochemical sensing.Item Open Access Design and optimization of emerging interconnection and memory subsystems for future manycore architectures(Colorado State University. Libraries, 2018) Thakkar, Ishan G., author; Pasricha, Sudeep, advisor; Bohm, Wim, committee member; Jayasumana, Anura, committee member; Lear, Kevin, committee memberWith ever-increasing core count and growing performance demand of modern data-centric applications (e.g., big data and internet-of-things (IoT) applications), energy-efficient and low-latency memory accesses and data communications (on and off the chip) are becoming essential for emerging manycore computing systems. But unfortunately, due to their poor scalability, the state-of-the-art electrical interconnects and DRAM based main memories are projected to exacerbate the latency and energy costs of memory accesses and data communications. Recent advances in silicon photonics, 3D stacking, and non-volatile memory technologies have enabled the use of cutting-edge interconnection and memory subsystems, such as photonic interconnects, 3D-stacked DRAM, and phase change memory. These innovations have the potential to enhance the performance and energy-efficiency of future manycore systems. However, despite the benefits in performance and energy-efficiency, these emerging interconnection and memory subsystems still face many technology-specific challenges along with process, environment, and workload variabilities, which negatively impact their reliability overheads and implementation feasibility. For instance, with recent advances in silicon photonics, photonic networks-on-chip (PNoCs) and core-to-memory photonic interfaces have emerged as scalable communication fabrics to enable high-bandwidth, energy-efficient, and low-latency data communications in emerging manycore systems. However, these interconnection subsystems still face many challenges due to thermal and process variations, crosstalk noise, aging, data-snooping Hardware Trojans (HTs), and high overheads of laser power generation, coupling, and distribution, all of which negatively impact reliability, security, and energy-efficiency. Along the same lines, with the advent of through-silicon via (TSV) technology, 3D-stacked DRAM architectures have emerged as small-footprint main memory solutions with relatively low per-access latency and energy costs. However, the full potential of the 3D-stacked DRAM technology remains untapped due to thermal- and scaling-induced data instability, high leakage, and high refresh rate problems along with other challenges related to 3D floorplanning and power integrity. Recent advances have also enabled Phase Change Memory (PCM) as a leading technology that can alleviate the leakage and scalability shortcomings of DRAM. But asymmetric write latency and low endurance of PCM are major challenges for its widespread adoption as main memory in future manycore systems. My research has contributed several solutions that overcome multitude of these challenges and improve the performance, energy-efficiency, security, and reliability of manycore systems integrating photonic interconnects and emerging memory (3D-stacked DRAM and phase change memory) subsystems. The main contribution of my thesis is a framework for the design and optimization of emerging interconnection and memory subsystems for future manycore computing systems. The proposed framework synergistically integrates layer-specific enhancements towards the design and optimization of emerging main memory, PNoC, and inter-chip photonic interface subsystems. In addition to subsystem-specific enhancements, we also combine enhancements across subsystems to more aggressively improve the performance, energy-efficiency, and reliability for future manycore architectures.Item Open Access Development of paper-based analytical devices for particulate metals in welding fume(Colorado State University. Libraries, 2015) Cate, David M., author; Henry, Charles S., advisor; Volckens, John, advisor; Dandy, David, committee member; Peel, Jennifer, committee member; Lear, Kevin, committee memberExposure to metal-containing particulate matter places a tremendous burden on human health. Studies show that exposures lead to cardiovascular disease, asthma, flu-like illnesses, other respiratory disorders, and to increased morbidity. Individuals who work in occupations such as metalworking, construction, transportation, and mining are especially susceptible to unsafe exposures because of their proximity to the source of particle generation. Despite the risk to worker health, relatively few are routinely monitored for their exposure due to the time-intensive and cost-prohibitive analytical methods currently employed. The current paradigm for chemical speciation of workplace pollution is outdated and inefficient. Paper-based microfluidic devices, a new type of sensor technology, are poised to overcome issues associated with chemical analysis of particulate matter, specifically the cost and timeliness of exposure assessment. Paper sensors are designed to manipulate microliter liquid volumes and because flow is passively driven by capillary action, analysis costs are very low. The objective of this work was to develop new technology for rapidly measuring Ni, Cu, Fe, and Cr in welding fume using easy-to-use paper devices. This dissertation covers the development of two techniques for quantifying metal concentration: spot integration and distance-based detection. Metal concentrations as low as 0.02 ppm are reported. A method for controlling reagent deposition as well as a new interface for multiplexed detection of metals, is discussed.Item Open Access Fiber optic enzymatic biosensors and biosensor arrays for measurement of chlorinated ethenes(Colorado State University. Libraries, 2011) Zhong, Zhong, author; Reardon, Kenneth F., advisor; Lear, Kevin, committee member; Dandy, David S., committee member; Henry, Charles S., committee memberChlorinated ethenes such as trichloroethylene (TCE), tetrachloroethylene (PCE), three isomers of dichloroethylene (DCEs) and vinyl chloride (VC) are used as solvents and cleaners in a variety of industrial and commercial areas. Chlorinated ethenes have become one of the most common environmental pollutants in groundwater contamination sites due to their widespread usage, moderate solubility compared with other organic pollutants and recalcitrance to natural attenuation. Fiber optic enzymatic biosensor was developed in this study as a continuous, real time and in situ measurement principle. TOM biosensor, first reported enzymatic biosensor, was initiated with toluene measurement in aqueous solution as proof-of-concept experiments. The subsequent success of TOM and TOM-Green in TCE analysis showed great potential of biosensor measurement for chlorinated ethenes, despite the ubiquitous problem for monooxygenase-based biosensor with NADH consumption overtime and after usage. In addition, epoxide toxicity also increased the difficulty of biosensor application for measurement of chlorinated ethenes, although several TOM-Green transformants could mitigate the toxicity with rapid epxoide degradation. Plasmid transformation with was introduced to manipulate the construction of new TOM and TOM-Green transformants with capability of intracellular NADH regeneration. FDH regeneration system was studied for both TOM and TOM-Green cells, while TOM+FDH showed great activity retention and regeneration ability and TOM-Green+FDH was able to retain activity over prolonged storage but failed on regeneration after repeated usage due to the toxicity of TCE epoxide. Biosensor array was built with pH-based biosensor to measure a group of haloalkanes. The design concept of biosensor array and detection instrumentation was successful. Linear approach in array data analysis was simple and fast but lacked of accuracy, while nonlinear approach increased the complexity of data analysis to a new level with precision in sacrifice of efficiency. Multivariable chemometric approach was also introduced in array data analysis, providing a high-throughput alternative and a means of quantitatively assessing matrix effects. This project demonstrates the potential of fiber optic enzymatic biosensor and biosensor array as measurements for different analyte are described. This is also one of the first comprehensive studies in oxygen-based biosensor and its application and great potential in food, clinical, and environmental monitoring, industrial process control and other related areas.Item Open Access Functional nanostructured ionic liquid-based block copolymer systems for energy applications(Colorado State University. Libraries, 2021) May, Alyssa Winter, author; Bailey, Travis S., advisor; Reynolds, Melissa, committee member; Sambur, Justin, committee member; Lear, Kevin, committee memberRoom-temperature ionic liquids (RTILs) are pure molten salts that have zero vapor pressure, a wide range of thermal stability, negligible flammability, and high ionic conductivity. These qualities make them desirable as electrolyte replacements for the more common lithium salt-doped carbonate solvents which are ubiquitous in current battery technology despite being exceptionally flammable. Use of liquid electrolytes, even non-flammable ones, has its drawbacks and challenges, like preventing leakage of the electrolyte and maintaining good contact with electrode surfaces, particularly when the battery electrodes or container become physically warped. With the emergence of flexible electronics technologies like foldable phones, bendable displays, and "wearables," interest has grown in developing solid electrolytes that are mechanically robust and sufficiently good ionic conductors, as they greatly expand the design possibilities for batteries. Block copolymers (BCPs) are an ideal platform from which to develop solid electrolyte materials as the variety of polymerizable blocks and physical properties that can be derived from them are nearly limitless. In this dissertation, we explore two methods for incorporating ionic liquid components into solid BCP materials, and thoroughly delve into their interesting chemical, physical, and mechanical properties to demonstrate their potential as functional materials. The first method is the direct, sequential polymerization of both ionic liquid-based and traditional monomers to create poly(ionic liquid) (PIL) BCPs that can microphase separate to form ordered nanostructures. We report on the synthesis of both cobalt-containing and imidazolium-based PIL BCPs and provide a comprehensive examination of their melt-state phase behavior, including the observation of all four equilibrium morphologies available to diblock copolymers: lamellae (Lam), bicontinuous gyroid (Gyr), hexagonally packed cylinders (Hex), and spheres (S). From the morphological phase behavior, we were able to build two phase diagrams and extract critical information about the materials, such as block density of the methyl-imidazolium PIL block. This is an essential parameter for BCP design that enables researchers to target specific morphologies when creating similar materials in the future. The morphology of solid-state conductive materials like PIL BCPs has direct implications on their transport properties, as only certain morphologies (Gyr, S) can have fully continuous domains in which ions can flow, so fully understanding the spectrum of phase behavior in a BCP material is incredibly important for creating truly functional materials from them. The second method is the integration of RTIL into amphiphilic, non-ionic BCPs as a selective swelling solvent to create ion gels, or gel polymer electrolytes (GPEs). We have designed these BCPs, based on melt-state phase separating blends of polystyrene-b-poly(ethylene oxide) (SO) and polystyrene-b-poly(ethylene oxide)-polystyrene (SOS) in which the hydrophilic O block is the majority component, to form hydrophobic spherical domains of S that form a tethered, physically crosslinked networked that acts like an elastic solid when swollen. We demonstrate that SOS BCPs swollen in the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, or [EMIM][TFSI], have exceptional ionic conductivity, elasticity, distensibility, recovery rates, bulk toughness, and fracture toughness. This rare combination of multiple excellent mechanical properties and high ionic conductivity makes SOS GPEs auspicious candidates as solid electrolytes in energy transport and storage applications.Item Open Access Measurement of the total flux averaged neutrino induced neutral current elastic scattering cross section with the T2K Pi-Zero detector(Colorado State University. Libraries, 2014) Ruterbories, Daniel, author; Berger, Bruce E., advisor; Buchanan, Norman, committee member; Lear, Kevin, committee member; Wilson, Robert, committee memberTokai-to-Kamioka (T2K) is a second generation accelerator neutrino oscillation experiment. T2K uses a high intensity proton beam produced at the Japan Proton Accelerator Research Complex (J-PARC) incident on a carbon target and focused with three magnetic horns to produce a high intensity and nearly pure muon neutrino beam with a peak energy of 600 MeV at a 2.5º axis angle. The muon neutrino beam travels 295 km across Japan to the Super Kamiokande (SK) water Cherenkov detector in the Kamioka mine. The neutrino beam is also sampled by a complex of near detectors 280 m downstream of the carbon target located both on and off the beam axis. These detectors measure the neutrino beam before neutrino oscillations occur to provide input constraints to oscillation searches using SK. The off-axis near detector, ND280, is a composite detector made up of a tracker section and a Pi-Zero detector (PØD), all surrounded by an electromagnetic calorimeter. The entire detector is enclosed in a dipole magnet with a field of 0.2 T. The primary purpose of the tracker section is to measure neutrino induced charged current events characterized by the production of muons. The PØD is primarily designed to detect electromagnetic showers and to measure interactions on water through the use of a removable water target. In addition to these measurements, the ND280 detector is also used to study the cross sections of neutrino interactions on the various materials in the detectors. Limited knowledge of the cross sections in this neutrino energy regime are an important source of systematic error in neutrino oscillation measurements. This thesis presents a measurement of one neutrino interaction channel in the PØD, neutral current elastic scattering (NCE). In this process a neutrino elastically scatters off a proton or neutron in the target nucleus producing a proton or neutron with higher energy. The signature of this process is a single proton track. A particle identification algorithm (PID) was developed to suppress the dominant muon background. Using this algorithm in conjunction with a Michel electron veto the flux averaged absolute cross section is measured to be <σ>flux =2.24×10-39 cm2,nucleon ±0.07(stat.) +0.53,-0.63 (sys.).Item Open Access Sensing via signal analysis, analytics, and cyberbiometric patterns(Colorado State University. Libraries, 2022) Anderson, Wesley, author; Simske, Steve, advisor; Lear, Kevin, committee member; Volckens, John, committee member; Carter, Ellison, committee memberInternet-connected, or Internet of Things (IoT), sensor technologies have been increasingly incorporated into everyday technology and processes. Their functions are situationally dependent and have been used for vital recordings such as electrocardiograms, gait analysis and step counting, fall detection, and environmental analysis. For instance, environmental sensors, which exist through various technologies, are used to monitor numerous domains, including but not limited to pollution, water quality, and the presence of biota, among others. Past research into IoT sensors has varied depending on the technology. For instance, previous environmental gas sensor IoT research has focused on (i) the development of these sensors for increased sensitivity and increased lifetimes, (ii) integration of these sensors into sensor arrays to combat cross-sensitivity and background interferences, and (iii) sensor network development, including communication between widely dispersed sensors in a large-scale environment. IoT inertial measurement units (IMU's), such as accelerometers and gyroscopes, have been previously researched for gait analysis, movement detection, and gesture recognition, which are often related to human-computer interface (HCI). Methods of IoT Device feature-based pattern recognition for machine learning (ML) and artificial intelligence (AI) are frequently investigated as well, including primitive classification methods and deep learning techniques. The result of this research gives insight into each of these topics individually, i.e., using a specific sensor technology to detect carbon monoxide in an indoor environment, or using accelerometer readings for gesture recognition. Less research has been performed on analyzing the systems aspects of the IoT sensors themselves. However, an important part of attaining overall situational awareness is authenticating the surroundings, which in the case of IoT means the individual sensors, humans interacting with the sensors, and other elements of the surroundings. There is a clear opportunity for the systematic evaluation of the identity and performance of an IoT sensor/sensor array within a system that is to be utilized for "full situational awareness". This awareness may include (i) non-invasive diagnostics (i.e., what is occurring inside the body), (ii) exposure analysis (i.e., what has gone into the body through both respiratory and eating/drinking pathways), and (iii) potential risk of exposure (i.e., what the body is exposed to environmentally). Simultaneously, the system has the capability to harbor security measures through the same situational assessment in the form of multiple levels of biometrics. Through the interconnective abilities of the IoT sensors, it is possible to integrate these capabilities into one portable, hand-held system. The system will exist within a "magic wand", which will be used to collect the various data needed to assess the environment of the user, both inside and outside of their bodies. The device can also be used to authenticate the user, as well as the system components, to discover potential deception within the system. This research introduces levels of biometrics for various scenarios through the investigation of challenge-based biometrics; that is, biometrics based upon how the sensor, user, or subject of study responds to a challenge. These will be applied to multiple facets surrounding "situational awareness" for living beings, non-human beings, and non-living items or objects (which we have termed "abiometrics"). Gesture recognition for intent of sensing was first investigated as a means of deliberate activation of sensors/sensor arrays for situational awareness while providing a level of user authentication through biometrics. Equine gait analysis was examined next, and the level of injury in the lame limbs of the horse was quantitatively measured and classified using data from IoT sensors. Finally, a method of evaluating the identity and health of a sensor/sensory array was examined through different challenges to their environments.Item Open Access The active complex electrode (ACE1) electrical impedance tomography system & anatomically inspired modeling of electrode-skin contact impedance(Colorado State University. Libraries, 2016) Mellenthin, Michelle M., author; Mueller, Jennifer L., advisor; Lear, Kevin, committee member; Krapf, Diego, committee member; Pezeshki, Ali, committee memberElectrical Impedance Tomography (EIT) is a technique used to image the varying electrical properties of biological tissues or tissue conductivity and permittivity. There are many clinical uses of EIT, but as a newer imaging modality, there is interest in improving hardware to acquire EIT data, creating models of the system and generating high quality images. The two main contributions of this work include: (1) EIT hardware advancements and (2) software modeling to simulate measured human subject data. Specifically, this dissertation includes the design and testing of Colorado State University's first EIT system, the pairwise current injection active complex electrode (ACE1) system for phasic voltage measurement. The ACE1 system was primarily designed for thoracic EIT applications, and its performance and limitations were tested through a variety of experiments. Additionally, the EIT forward problem was used to investigate electrode-skin contact impedance.Item Open Access Thin film integrated optical waveguides for biosensing using local evanescent field detection(Colorado State University. Libraries, 2010) Stephens, Matthew David, author; Dandy, David, advisor; Lear, Kevin, committee member; Reardon, Kenneth, committee member; Belfiore, Laurence, committee memberA waveguide is a high refractive index material that is surrounded by lower refractive index cladding. This waveguide structure can be used to carry light confined to the high refractive index core. Surrounding the core of the waveguide is a decaying evanescent light field that extends into the cladding layers. The intensity profile of the evanescent field is dependent on the refractive index of the cladding. The changes in the local intensity of the evanescent field can be used to detect refractive index changes near the core of the waveguide. A high refractive index film deposited on a flat, low refractive index .substrate can be used to form a waveguide with a planar geometry. The planar design allows the upper cladding refractive index to be modified by attaching proteins or patterning organic films. This design also allows the evanescent field intensity to be measured using near field scanning optical microscopy or a silicon photo detector array. The fabrication and characterization of a waveguide device with a coupled light source was accomplished. The evanescent field response to thin films of patterned photoresist was found using NSOM. Light intensity measured at the surface of the .sample showed significant response to the presence of the photoresist features. Light response to a protein affinity assay was found and results indicated that protein concentration could be inferred from local evanescent field measurements. A buried silicon photo detector was fabricated and characterized. The results show the field responds in a significant matter to uniform and pattered features on the waveguide core.