VictorJuiz/thesis huggingface dataset:
Miniaturized, high-frequency DC-DC power conversion for embedded applications [electronic resource]
Keywords: Electrical Engineering.

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.
Mitochondrial association [electronic resource] : a new window of opportunity for toxoplasma gondii?
Keywords: Microbiology and Immunology.

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.
Modeling and measurement of the modal properties of hollow core photonic-bandgap fibers [electronic resource]
Keywords: Electrical Engineering.

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.
Modeling consumer choice of non-networked water supply options in Maputo, Mozambique [electronic resource]
Keywords: Civil and Environmental Engineering.

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.
Modeling of Piezo-induced ultrasonic wave propagation for structural health monitoring [electronic resource]
Keywords: Aeronautics and Astronautics.

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.
Mode-locked thulium-doped fiber lasers for supercontinuum generation in the mid-infrared [electronic resource]
Keywords: Electrical Engineering.

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].
Modifications to flux balance analysis to enable large scale integrated modeling [electronic resource]
Keywords: Chemical Engineering.

Metabolism is the cellular system that converts surrounding material and energy gradients into the molecules needed to sustain life. All the processes of cell maintenance and replication rely on metabolic products to function. For this reason, quantitative metabolic models contribute greatly to our understanding of biological systems, and underlie many of our predictive capabilities for microbial cells. Therefore, to increase understanding and expand predictions, we must advance quantitative models of metabolism and how cell processes use metabolic products. The metabolic modeling method Flux Balance Analysis (FBA) facilitated the first genome-scale microbial models. FBA consists of a detailed stoichiometric mass balance over hundreds of small molecule reactions. Classic FBA presents a cell-as-metabolism perspective so far as the interface with and function of all other cellular processes are contained in a single summary biomass reaction. A screen for host-dependencies of bacteriophage --- bacterial virus --- prompted my investigation of how infecting pathogens exploit host metabolic resources. Viruses lack metabolic infrastructure, so new viral particles are necessarily built using macromolecular precursors and energy from the host cell. To computationally model viral use of host metabolites, a previously developed model of bacteriophage T7 macromolecular replication was combined with an FBA model of host E. coli metabolism. To enable solution of the combined system, I developed an algorithm to simulate the differential equation and linear optimization models simultaneously with mutual constraint. However, difficulties with FBA in integrated models arise from the biomass reaction. Previously the biomass reaction gave FBA power by abstracting cell process interaction and regulation detail, but in order to do so it assumed a long-time, steady-state, and population average function of metabolism. These assumptions are inconsistent with dynamic and single-cell applications. By relaxing the rigid biomass reaction and its assumptions, I developed FBA methods suited to integrated and whole-cell modeling applications. The first component of this solution was my introduction of a flexible (flexFBA) objective to encourage, rather than require, proportional production of cell process reactants. The second update is to link the processes' use of reactants and return of byproducts across simulation time steps (tFBA). In combination, these modifications make FBA relevant on a much shorter timescale. For example, flexFBA and tFBA can simulate transitions between metabolic steady states, and avoid FBA artifacts due to small copy number enzymes.
The moduli space of real curves and a Z/2-equivariant Madsen-Weiss theorem [electronic resource]
Keywords: Mathematics.

Galatius, Madsen, Tillmann, and Weiss proved that the classifying space of the category of 2-cobordisms is equivalent to the loopspace of a particular Thom spectrum. We show that this is in fact a Z/2-equivariant equivalence, where we equip all spaces with a Z/2-action which is motivated by complex conjugation of complex curves. In order to do this, we prove an equivariant delooping theorem which shows that grouplike topological monoids with Z/2-action are Z/2-equivalent to loopspaces. Furthermore, we motivate our choice of Z/2-action by showing that it determines a Z/2-space BDiff_g whose fixed points classify real curves.
Molecular and stable isotopic analyses of the fatty acyl components of the pottery of Çatalhöyük, Turkey [electronic resource] : understanding the relationships between animal domestication, ceramic technology, environmental variation and their roles in the secondary products revolution
Keywords: Environmental Earth System Science.

An extensive study of the organic residue associated with the Neolithic pottery of Çatalhöyük has further confirmed the timing of dairy production on-site after following the methods of a previous study (Evershed et al. 2008). By utilizing gas chromatography (GC) on 313 potsherds, and high temperature-GC/mass spectrometry (HT-GC/MS), GC-combustion-IRMS (GC-C-IRMS) and GC-thermal conversion-IRMS (GC-TC-IRMS) on subsets of that pottery collection from the Neolithic site of Çatalhöyük in central Turkey, the first well-dated stratigraphic record of both compound-specific [delta] 13C and [delta] D values of C16:0 and C18:0 fatty acids has now been established. The combination of this new information with the faunal and stable isotope records of the same site has provided a more detailed account of changes in animal management strategy over time. This study provides an in-depth look at some of the oldest dairy residues found to date as well as environmental and social factors that may have contributed or resulted from the transition to secondary product use during the Neolithic. In addition, a newly developed palaeoenvironmental proxy may provide a direct link between changes in local precipitation levels and changes in subsistence practices by assessing stable hydrogen isotope ([delta] D) values of fatty acids extracted from pottery residues. The origins of the fatty acids were determined based on their [delta] 13C values as arising largely from ruminant adipose and dairy fats. A [delta] D record was constructed, based on a subset of ruminant adipose fats only, which showed most negative isotopic values from ~6900 to 6600 cal BC indicative of wet conditions, followed by a drying trend which reached a maximum at or just after 6280 cal BC, coincident with the 8.2 ka (~6200 cal BC) cold, dry climate event. The drying trend is consistent with that observed in the [delta] 18O record from the nearby lake Eski Acıgöl carbonates. Thus, [delta] D analysis of archaeological residues may be useful in assessing broader environmental and climatic changes directly from cultural residues.
Moments of automorphic L-functions and related problems [electronic resource]
Keywords: Mathematics.

We present in this dissertation several theorems on the subject of moments of automorphic L-functions. In chapter 1 we give an overview of this area of research and summarize our results. In chapter 2 we give asymptotic main term estimates for several different moments of central values of L-functions of a fixed GL_2 holomorphic cusp form f twisted by quadratic characters. When the sign of the functional equation of the twist L(s, f \otimes \chi_d) is -1, the central value vanishes and one instead studies the derivative L'(1/2, f \otimes \chi_d). We prove two theorems in the root number -1 case which are completely out of reach when the root number is +1. In chapter 3 we turn to an average of GL_2 objects. We study the family of cusp forms of level q^2 which are given by f \otimes \chi, where f is a modular form of prime level q and \chi is the quadratic character modulo q. We prove a precise asymptotic estimate uniform in shifts for the second moment with the purpose of understanding the off-diagonal main terms which arise in this family. In chapter 4 we prove an precise asymptotic estimate for averages of shifted convolution sums of Fourier coefficients of full-level GL_2 cusp forms over shifts. We find that there is a transition region which occurs when the square of the average over shifts is proportional to the length of the shifted sum. The asymptotic in this range depends very delicately on the constant of proportionality: its second derivative seems to be a continuous but nowhere differentiable function. We relate this phenomenon to periods of automorphic forms, multiple Dirichlet series, automorphic distributions, and moments of Rankin-Selberg L-functions.
Monitoring matrix cracking in composite laminates using built-in piezoelectric sensors [electronic resource]
Keywords: Aeronautics and Astronautics.

Fiber reinforced composite materials use has increased tremendously in many applications from aerospace structures to sporting goods. These materials have many advantages, but the major challenge in composites design is their damage mechanics. Matrix cracking develops first, decreasing structural performance and promotion of other damage development. The state-of-the-art inspection techniques cannot quantify crack density and they require the component to be off-service. For better design, safety, and maintenance of composite structures it is desirable to monitor the increase of cracks in-service. The objective of this investigation is to determine the quantity of matrix cracks in a composite laminate rapidly and in-service using built-in piezoelectric actuators and sensors. A diagnostic method was proposed which compared the sensed signal before and after the presence of matrix cracks and related these signal changes to crack density. It was found that change in the signal's Power Spectral Density can be used to quantify crack density, and its sensitivity was dependent on the actuator to sensor orientation. This orientation dependence was found to be the same as that of the laminate's stiffness degradation. A crack density quantification model was developed that uses signal changes and theoretical laminate stiffness parameters. The model was tested on two layup configurations, and its crack density estimates matched experimental crack density values within established error bounds.