VictorJuiz/thesis huggingface dataset:
Microstructure and charge transport in conjugated polymers [electronic resource]

Conjugated polymers have attracted broad interest in the past few decades due to their potential applications in organic light emitting diodes, low-cost flexible circuits, biosensors and photovoltaics. Because of their semicrystalline nature, the spatial arrangement of the crystallites and the disordered regions would have strong impact on the charge transport properties of conjugated polymer thin films. Therefore, in this presentation, I will focus on understanding the relationship between the film's morphology, microstructure and electronic properties, and how to fabricate desired structure to achieve devices with novel electronic performance. In the first part of the presentation, I will show that the device's electronic performance can be greatly improved by engineering its structure in solution based fabrication process. The binary blends of regioregular (rr) and regiorandom (RRa) P3HT are used to form desired FET structures. X-ray diffraction of the blended films is consistent with a vertically-separated structure, with rr-P3HT preferentially crystallizing at the semiconductor/dielectric interface. Because of the ultra-thin rr-P3HT active layer at the interface, these devices not only preserve high mobility in rr-P3HT, but also eliminate the short channel effects due to bulk currents, suggesting a new route to fabricate high performance, short-channel and reliable organic electronic devices. After that, I will discuss the microstructural origin of high mobility in poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophenes) (PBTTT) thin-film transistors (TFTs). Charge transport in PBTTT TFTs is analyzed with a mobility edge (ME) model and compared to these in poly(3-hexylthiophene) (P3HT) TFTs. With TEM characterization of delaminated films, we conclude that the improved performance of PBTTT compared to P3HT is not due to a low trap density but rather to a high mobility in the crystallites. Finally, the third part of the presentation will focus on optical characterization of doping in conjugated polymers. UV-vis and IR absorption spectra of 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) doped P3HT at different doping concentration are measured and analyzed. Absorption peaks from P3HT, F4TCNQ, F4TCNQ anion and P3HT polaron/bipolarons are identified and decomposed. The P3HT polaron/bipolarons cross sections in UV-vis region are estimated, which can be used to evaluate doping efficiency in this material.

Keywords: Applied Physics.
Advisor: Fisher Ian R. (Ian Randal) primary advisor. Thesis advisor
Salleo Alberto
Lindenberg Aaron Michael advisor. Thesis advisor
Microsystems for studying single heart cell mechanobiology [electronic resource]

With each heart contraction, blood rushes throughout the expansive circulatory system providing oxygen and other nutrients to the body. Cardiomyocytes are the contractile units responsible for these contractions. In the event of ischemia, the heart reduces its contractile output and loses a significant number of cardiomyocytes. In the ischemic region of the heart, the tissue remodels and the mechanical properties differ significantly from healthy tissue. Due to the limited regeneration capabilities of the heart, recent focus has been on understanding how the reintegration of pluripotent-derived cardiomyocytes can help restore contractile function. These pluripotent-derived cardiomyocytes will need to survive in mechanically active environments and contribute to the contractile output of the heart. However, even before these cardiomyocytes can be used, we need to develop an understanding for how primary immature cardiomyocytes should respond to mechanical forces in vitro. This work explores cardiomyocyte contractile ability in the presence of mechanical forces. For this work, we investigate neonatal murine cardiomyocytes. We begin by developing a protein patterning technique suitable for polyacrylamide. With this technique, we achieve repeatable arrays of neonatal cardiomyocytes and control their shape and size. We found this technique improves sarcomere distribution, making them look more mature and like adult cardiomyocytes. Using micro-tools, we then investigate cardiomyocyte contractility in the presence of mechanical forces. These findings suggest that the Frank-Starling law that governs the heart is also applicable to neonatal cardiomyocytes. Later in this work, we introduce the MEMS tool developed to better understand cardiomyocyte contractile forces. We describe the design goals and fabrication process of the micro-device. In addition, we present the calibration and testing results, and demonstrate that this device provides a reliable and alternative way to calibrate substrates used to study contractile forces. In the closing section of this work, we introduce ideas for future studies building on this work, and the work of others.

Keywords: Mechanical Engineering.
Advisor: Pruitt Beth primary advisor. Thesis advisor
Kenny Thomas William advisor. Thesis advisor
Levenston Marc Elliot advisor. Thesis advisor
Mid-infrared laser diagnostics for chemical kinetics study of oxygenates [electronic resource]

Biofuels are classified as renewable because the carbon present in the vegetable oil or animal fat feedstocks originates from carbon dioxide already present in the atmosphere. One of the current focuses on biofuel-based combustion research is the design of advanced energy conversion devices using complex reaction mechanisms. The development of these mechanisms requires a large experimental database to ensure accuracy of computational predictions. Infrared laser-absorption diagnostics are widely used in combustion research for fast, sensitive, and non-intrusive measurements of species concentration, temperature, and pressure. This thesis explores three new areas of laser diagnostic research: (a) mid-infrared diagnostics, (b) sensing in multiphase flows, and (c) applications to shock tube chemical kinetics. A novel distributed-feedback quantum-cascade laser (DFB-QCL) near 4.7 um was investigated to develop a new mid-infrared absorption sensor for in situ measurements of carbon monoxide (CO) and temperature in combustion gases. The laser provides convenient access to the stronger vibrational bands of CO than was possible previously, enabling ppm-level detectivity with an optical path length of 10 cm at high temperatures between 1000-2000 K. Wavelength modulation spectroscopy with 1f-normalized 2f detection (WMS-2f/1f) of CO2 was developed for accurate temperature sensing in multiphase combustion flows. In this method, two tunable diode lasers with wavelengths near 2.7 um were used to measure time-varying gas temperature during the evaporation of shock-heated fuel aerosols. These recently developed mid-IR laser absorption diagnostics were then applied in studying the thermal decomposition of oxygenates (biofuel surrogates) by measuring species concentration time-histories behind reflected shock waves. In a particular study of methyl formate (the simplest biodiesel surrogate), the reaction rate constants of methyl formate unimolecular decomposition were measured using the mid-IR CO absorption behind reflected shock waves. Detailed comparisons of the measured methanol and CO time-histories with the model predictions were made. Sensitivity and reaction pathway analyses for these oxygenated fuel components were performed, leading to rate recommendations with improved model performance.

Keywords: Mechanical Engineering.
Advisor: Hanson Ronald primary advisor. Thesis advisor
Bowman Craig T. (Craig Thomas)
Davidson David advisor. Thesis advisor
Miniaturized, high-frequency DC-DC power conversion for embedded applications [electronic resource]

In order to achieve high power density in battery-powered systems, as well as accommodate the reduced breakdown voltages in scaled CMOS technologies, systems-on-a-chip (SoCs) typically employ one or more supply voltages generated using dc-dc converters. Dc-dc converters are commonly implemented as inductive switching converters because of their high efficiency. However, inductive converters typically have a large footprint that is dominated by the size of bulky off-chip inductors and capacitors. In order to reduce the size of an inductive converter, its switching frequency can be increased by orders of magnitude above the existing practice. However, the use of a high switching frequency leads to increased switching power losses that in turn decrease the power conversion efficiency. To address this challenge, techniques for designing a high-efficiency buck converter while using miniaturized external components are investigated in this research. Design techniques, such as using a high switching frequency that is tunable with the load current and the segmentation and cascoding of power transistors are employed to achieve high power efficiency across a wide range of load currents. While in SoC applications multiple voltages are typically derived from battery by connecting converters in parallel, this work introduces a cascaded, dual-output buck converter topology. Cascading buck converters reduces the input supply voltage of the second converter, thus reducing the switching and ripple-conduction losses that severely affect the efficiency of buck converters using small inductors and operating at high switching frequencies. The use of high-frequency, cascaded conversion presents two significant challenges to the design of the controller for a buck converter. First is the need for adjustability of the switching frequency with varying load currents, and second is the possibility of cross regulation between the outputs of the converter. A digital constant-off-time controller is proposed to address these challenges. The controller enables tuning of the converter's switching frequency. The controller has a fast transient response and good line regulation that help to suppress cross regulation between the two outputs of the buck converter. To demonstrate the proposed multiple-output, cascaded, high-frequency converter, an experimental prototype has been integrated in a 90-nm CMOS technology. This prototype provides two output voltages using a cascade of two buck converters, each employing a small output capacitor on the order of 100 picofarads and a small inductor on the order of nanohenries, thereby reducing the overall size of the converter compared to conventional alternatives.

Keywords: Electrical Engineering.
Advisor: Arbabian Amin primary advisor. Thesis advisor
Wooley Bruce A.
Su David
Mitochondrial association [electronic resource] : a new window of opportunity for toxoplasma gondii?

Protozoan and prokaryotic pathogens are able to recruit mitochondria to the vacuoles in which they grow (Friis, 1972; Horwitz, 1983), in mammalian and protozoan cells. The functional significance of the recruitment and association of this phenomenon in Toxoplasma-infected cells has been a subject of speculation since it was first described in the early 1970s (Jones et al., 1972). Previous work has proposed Toxoplasma gondii rhoptry protein 2 (Sinai and Joiner, 2001) as the physical link that tethers host mitochondria to the parasitophorous vacuole and conventional wisdom since has suggested that mitochondrial recruitment served a nutritional function supplementary to the parasite. A recent analysis of the ROP2 structure raised questions about this model ((Labesse et al., 2009; Reese and Boothroyd, 2009). Chapter II describes the effect of deleting ROP2 on mitochondrial association while Chapter III describes the identification of a novel mediator of mitochondrial association, Mitochondrial association factor I (MAF1) and experiments that attempt to answer the role of this remarkable phenomenon in the host-pathogen interaction. Chapter IV describes a project undertaken to determine the impact of Toxoplasma gondii infection in humans acutely and chronically infected in different geographical regions. Chapter V concludes with a discussion of future directions for further characterization of host mitochondrial association in the host response to microbial infection.

Keywords: Microbiology and Immunology.
Advisor: Boothroyd John C. primary advisor. Thesis advisor
Cyert Martha S.
Davis Mark M. advisor. Thesis advisor
Singh Upinder (Physician) advisor. Thesis advisor
Modeling and measurement of the modal properties of hollow core photonic-bandgap fibers [electronic resource]

Hollow-core photonic-bandgap fibers (PBFs), which consist of an air core surrounded by a photonic-crystal array of air holes, have attracted significant attention due to their unique optical properties, and they have found interesting applications in sensing, nonlinear optics, and microscopy. The design and understanding of these fibers depend critically on our ability to model their optical properties accurately, a task made difficult by the complexity and very fine features (< 100 nm) of their internal structures. In this thesis, we developed two advanced codes to model several key modal properties of PBFs. The first one utilizes the finite-difference frequency-domain method to predict the modal dispersion diagram of the fiber, as well as the intensity profile, group-index spectrum, and group-velocity dispersion spectrum of the fundamental mode. This code implements two major innovations. First, it samples the fiber's index profile on a hexagonal grid to match the symmetry of the fiber and avoid digitization errors. Second, it uses as an input a realistic index profile of the fiber carefully constructed from SEM photographs to incorporate all observable structural deformations in the core and in the first two rows of cladding holes of the fiber (NKT Photonics' HC-1550-02 fiber). We demonstrate that the properties of the fundamental mode predicted by this code are in good agreement with their experimental counterparts measured in the laboratory. In a PBF the propagation loss and backscattering coefficient are dominated by random geometrical fluctuations of the fiber cross-section, which couple the fundamental mode to higher order modes. Modeling these two properties required first applying a strong perturbation theory to predict the amount of couplings induced by these perturbations, since the index difference between the two fiber materials (air and silica) is too high for a weak-perturbation approach. It also required developing a new physical and mathematical model of the core wall's surface roughness statistics. This model recognizes for the first time that the very small thickness of the core wall increases the wall roughness quite significantly, with the implication that the loss and backscattering are significantly higher than predicted by existing models. We show again good agreements between the predicted and measured values of loss and backscattering.

Keywords: Electrical Engineering.
Advisor: Digonnet Michel J. F. primary advisor. Thesis advisor
Fan Shanhui
Solgaard Olav advisor. Thesis advisor
Modeling consumer choice of non-networked water supply options in Maputo, Mozambique [electronic resource]

In cities of Sub-Saharan Africa (SSA), only 34% of the urban population had access to a piped water connection in their home or compound in 2010. Unconnected households in SSA instead typically rely on shared water points furnished by the public water utility, or small-scale, private providers (SSPs), yet little attention has been afforded to understanding how households choose among different off-plot water service options. Accordingly, little is known about the service attributes of a shared water supply option that matter most to users, and thus should receive the attention of practitioners and policy makers. Applying a revealed preference, discrete choice model, we investigate household preferences for shared water supply service options in peri-urban neighborhoods of Maputo, Mozambique, where service provision by small-scale water entrepreneurs is prevalent. In addition to service attributes typically measured in the water sector--such as time and money costs, reliability and perceived water quality-- we consider several measures of service quality and provider-client relationships that are not typically considered in the water planning framework. We find that several of these attributes are indeed significantly associated with households' water supply choices. Current efforts to define policy that supports SSPs in the water sector would benefit from considering a broader set of service-quality attributes that are particularly relevant to the urban and peri-urban poor.

Keywords: Civil and Environmental Engineering.
Advisor: Davis Jenna (Professor)
Modeling of Piezo-induced ultrasonic wave propagation for structural health monitoring [electronic resource]

The process of implementing a damage detection and characterization strategy for engineering structures is referred to as structural health monitoring (SHM). Recently, damage detection using piezoelectric actuators and sensors has gained extensive attraction. Piezoelectric actuators are used to induce elastic stress waves that can propagate for long distances in thin-walled structures with very little amplitude loss enabling inspection of large areas of a structure. These waves interact with damage and provide information on location, size, and type of damage; this information is extracted from sensor signals by diagnostic algorithms. However, these signals are sensitive to the operating conditions. Change in ambient temperature or loading conditions may affect the wave propagation and the sensor response leading to inaccurate diagnostics. Hence, fundamental understanding of the physics of wave propagation, their interaction with the structure, and the influence of varying operating conditions is crucial for developing appropriate diagnostic algorithms. Therefore, the prime objectives of this investigation are: (i) develop an efficient and accurate numerical model to simulate the sensor signals and the piezo-induced acoustoelastic wave propagation in prestressed homogeneous and layered media, (ii) study the effect of load on wave propagation (acoustoelastic effect) and varying ambient temperature on the sensor signals. A numerical model called Piezo-Enabled Spectral Element Analysis (PESEA), based on spectral element method is developed. PESEA can accurately and efficiently simulate ultrasonic wave propagation in complex structures with built-in piezoelectric sensor network. Experiments and simulations are performed on metallic and composite structures to verify and validate the accuracy of PESEA. Fatigue cracks in metallic structures and debond/delamination is laminated composite structures are modeled by separating the nodes to create volume split. Simulations are carried out to show the wave-damage interaction and the scatter in the sensor signals due to damage. These simulation results show that PESEA can be used as a powerful tool to gain physical insights into the effect of different types of damage on wave propagation and sensor response. The influence of loading on ultrasonic waves actuated and sensed by piezoelectric sensors in aluminum plate is studied. A numerical and experimental study of axially stressed aluminum plates with surface-mounted piezoelectric sensors is carried out to investigate the dependence of wave velocity on applied load. Similarly, simulations and experiments are presented to understand how the piezoelectric sensor signal amplitude changes with adhesives of different thickness and material when the structure is exposed to elevated temperature.

Keywords: Aeronautics and Astronautics.
Advisor: Chang Fu-Kuo primary advisor. Thesis advisor
Christensen R. M. (Richard M.) advisor. Thesis advisor
Law K. H. (Kincho H.) advisor. Thesis advisor
Mode-locked thulium-doped fiber lasers for supercontinuum generation in the mid-infrared [electronic resource]

In recent years, there has been significant interest in the "eye-safer" 2-[micrometer] wavelength range for applications varying from laser-driven particle acceleration to remote sensing to mid-infrared spectroscopy. Trivalent thulium has shown promise as a viable dopant to fulfill several requirements of these applications through its wide gain bandwidth, from ~1.8 to 2.1 [micrometers], and its ability to efficiently power scale. By further broadening the output spectrum of an ultrafast Tm-doped fiber source through supercontinuum generation (SCG), an instantaneously broadband mid-IR spectrum can be produced, which is particularly useful for mid-IR spectroscopy. In this dissertation, I demonstrate thulium's ability to generate ultrafast pulses in a mode-locked all-fiber laser, the figure-eight laser (F8L). Through the various operating regimes of the F8L, pulse widths ranging from 1.5 ps to 20 ns could be generated. Amplification of the F8L output allowed for temporal pulse compression to less than 400 fs with ~100 kW of peak power. In addition to the F8L, a subharmonic optical parametric oscillator (OPO) was explored as a possible 2-[micrometer] oscillator. The sync-pumped doubly-resonant OPO converted pulses from a 1-[micrometer] mode-locked fiber laser to 2 [micrometers], utilizing a PPLN crystal as the nonlinear gain medium. The subharmonic OPO generated less than 50-fs pulses, shorter than any reported Tm-doped oscillator to date. To utilize these sources for mid-IR spectroscopy, the spectral bandwidth can be significantly broadened through SCG. With a tapered chalcogenide fiber pumped by a Tm-doped fiber laser, the output spectrum was broadened from ~227 nm centered at 2.04 [micrometers] to span from 1 to 3.7 [micrometers].

Keywords: Electrical Engineering.
Advisor: Byer R. L. (Robert L.)
Digonnet Michel J. F. advisor. Thesis advisor
Solgaard Olav advisor. Thesis advisor