VictorJuiz/thesis huggingface dataset:
Exploiting non-linear Arrhenius dependence of diode IV curves to determine Schottky barrier band diagrams [electronic resource]
Keywords: Electrical Engineering

Accurate extraction of Schottky barrier height is imperative to the development of low resistance contacts. An analytical model for current density is found that accurately accounts for conduction in the thermionic emission (TE), thermionic field emission (TFE), and field emission (FE) regimes. Use of this model in non-linear regression allows more information to be extracted from diode current-voltage-temperature (IVT) curves than previously possible. The proposed model uses the Arrhenius non-linear dependence experimental diode IV curves to regress the Schottky barrier height ([phi]B0), steepness factor (E00), and Fermi level ([xi]), enabling band diagrams of the measured interfaces to be determined. This model is tested against both simulated interfaces using the transmission matrix method (TMM) and experimental data. This complete picture of band information allows material interface behavior to be understood more completely, ultimately facilitating more efficient contact engineering.
Extracellular molecular interactions in celiac disease [electronic resource]
Keywords: Chemistry

This dissertation is aimed to explore two critical extracellular interactions in the pathogenesis of celiac disease: thioredoxin mediated extracellular tissue transglutaminase (TG2) activation and binding interaction between gluten peptides and HLA-DQ2. The mechanism of activation of TG2 in the extracellular matrix remained a fundamental mystery in biology as well as in celiac disease pathogenesis. Earlier investigations have highlighted the role of a disulfide bond formed by vicinal Cys residues in maintaining calcium-bound TG2 in an inactive state. We characterized the redox potential of this disulfide bond to be approximately -190 mV, which is very oxidative for a disulfide bond in proteins. We then identified a physiological factor human thioredoxin (Trx) for the activation of oxidized TG2. With a kcat/KM of 1.6 [mu]m-1min-1. Trx was a highly specific activator of oxidized human TG2. Both recombinant Trx and interferon-[gamma] stimulated Trx released from monocytes can activate extracellular TG2 around the fibroblasts. In addition to explaining how TG2 can be activated by dietary gluten in the small intestinal mucosa of celiac sprue patients, our findings reveal a new strategy for inhibiting the undesirable consequences of TG2 activity in this widespread and lifelong disease. Inspired by the finding of Trx mediated TG2 activation, we then sought to develop small molecule disulfide inhibitors targeting extracellular Trx. We performed a careful structural-activity relationship study based on an imidazolyl isobutyl disulfide compound. Two rounds of inhibitor screening suggested that aromatic ring part mainly contributes to ligand binding, and a new lead compound was identified with ~26 fold increased inhibition selectivity. Potential inhibitor binding site was also predicted near Cys73 by docking model and Trx mutant results. Our findings provide novel tools to study Trx-TG2 interaction in celiac disease as well as a promising therapeutic candidate. Understanding the binding interaction between HLA-DQ2 and antigenic peptides lies at the center of antigen presentation in celiac disease. We use capillary electrophoresis-fluorescence detection to investigate competition and displacement of endogenous peptides by an immunogenic gluten peptide (the 20-mer) for binding to HLA-DQ2. Remarkably, this immunogenic peptide could displace CLIP peptides from DQ2 binding site under neutral but not acidic pH condition. This unique property of gluten peptide supports a direct loading mechanism of antigen presentation in the extracellular environment.
Fabrication and characterization of nanoscale resistance change memory [electronic resource]
Keywords: Electrical Engineering

As the current charge-based memory technologies such as DRAM and Flash Memory are facing their fundamental scaling limits, new types of memory technologies such as spin-torque-transfer RAM (STTRAM), phase-change memory (PCM), and metal-oxide resistance change memory (RRAM) have been actively explored. Among these candidates, RRAM devices utilize the resistance change property of the metal-oxide films, and have shown promising results such as fast switching speed, low programming current, and good CMOS compatibility. Despite the potential advantages, they suffer from the critical issues that must be addressed for the high-density memory application, which includes existence of forming-process, large variation in switching characteristics, and cell selection issue in cross-point structures. In this thesis, first, the process and characterization methodology for RRAM devices is demonstrated to verify the characteristics and potential issues in the nanoscale regime down to 50x50-nm^2 size. Unipolar switching memory cells using NiO thin films were fabricated by ebeam lithography process. The fabricated device characteristics and the scaling trends will be discussed. Next, two novel RRAM structures are proposed for improved cell characteristics. In the first structure, both top and bottom electrodes are processed prior to the metal-oxide deposition, and therefore, contamination-less programming region is achieved in the memory cell. Moreover, the novel structure features more confined conduction path compared to the conventional structure, which results in narrower low-resistance distribution. The process flow and characteristics of the nanoscale NiO memory cells using this structure will be demonstrated. In the second structure, an oxide-to-oxide interface is incorporated inside the memory cell in order to utilize the initial leakage and eliminate the high-voltage forming process (OTO Cell Technology). Due to this initial leakage, the as-fabricated AlOx memory cells exhibit low-resistance sates, while the conventional AlOx devices show high-resistance initial states. The new memory cell does not require the high-voltage forming process since the as-fabricated cells can be switched to high-resistance states with a regular RESET voltage. Finally, application of the forming-free OTO cells to the complementary resistive switch (CRS) scheme will be discussed using the measured cell characteristics. The CRS scheme was proposed as a potential solution to the high-density cross-point memory arrays for resistive memory. The novel memory cells with forming-free property demonstrate promising results, which enables the CRS scheme for bipolar switching RRAM cells.
Factors that influence the open circuit voltage and stability of polymer [electronic resource] : fullerene bulk heterojunction solar cells
Keywords: Applied Physics

Solution processed organic photovoltaics offer the potential of providing solar energy at a significantly lower cost than conventional solar cells due to scalable manufacturing by roll-to-roll printing, low materials costs and facile installation of light-weight modules. Recently, power conversion efficiencies of over 10% have been achieved in small area multijunction devices, and stability lifetimes of several years have been demonstrated, though these are not yet sufficient for commercialization. The development of new materials that can produce high open circuit voltage devices is critically important for improving the efficiency of multijunction organic solar cells. Polymer:fullerene solar cells with power conversion efficiencies of over 7% are demonstrated with blends of the polymer PBDTTPD and the fullerene PCBM. These devices achieve an open circuit voltage of 0.94V and internal quantum efficiencies of 88% and thus are an ideal candidate for the large bandgap junction of tandem organic solar cells. The open circuit voltage is increased above 1V when the polymer is blended with multi-adduct fullerenes, but the current and fill factor are greatly reduced. Photoluminescence, electroluminescence and photocurrent measurements indicate that excitons undergo energy transfer to the fullerene rather than dissociate to form charges at the heterojunction interface due to the small difference in energy between the fullerene bandgap and charge transfer states. Consequently new non-fullerene electron acceptor materials with larger bandgaps may be required for devices to achieve both near unity internal quantum efficiencies and open circuit voltages exceeding 1.0V. The photodegradation of polymer:fullerene blend films exposed to ambient conditions for a variety of polymer and fullerene derivative combinations is also presented. The rate of irreversible polymer photobleaching in blend films was found to consistently and dramatically increase with decreasing electron affinity of the fullerene derivative. Furthermore, blends containing fullerenes with the smallest electron affinities photobleached at a faster rate than films of the pure polymer. These observations can be explained by a mechanism where both the polymer and fullerene donate photogenerated electrons to diatomic oxygen to form the superoxide radical anion which degrades the polymer.
Fast dynamics of aqueous biological molecules investigated with 2D IR spectroscopy [electronic resource]
Keywords: Chemistry

Proteins are dynamic structures that are in constant fluctuations, and their ability to undergo structural changes is critical to their function. However, their fastest dynamics in thermal equilibrium have remained largely unexplored. In this work, studies that examine the dynamics of aqueous proteins using two-dimensional infrared echo spectroscopy (2D IR) are presented. In particular, investigations of fast fluctuations in proteins and peptides within the context of structural changes upon denaturation are discussed. 2D IR is a nonlinear optical spectroscopic technique that can measure ultrafast dynamics of complex molecules in the picoseconds regime, timescales ~6-10 orders of magnitude faster than nuclear magnetic resonance. In addition, the relatively low energy mid-IR laser pulses used in this study probe the relevant nuclear degrees of freedom without significantly perturbing the protein structure or dynamics. Brief descriptions of the experimental setup and methods, as well as analysis and interpretation, are given.
Filtered floer and symplectic homology via Gromov-Witten theory [electronic resource]
Keywords: Mathematics

We describe a procedure for computing Floer and symplectic homology groups, with action filtration and algebraic operations, in a class of examples. Namely, we consider closed monotone symplectic manifolds with smooth symplectic divisors, Poincaré dual to a positive multiple of the symplectic form. We express the Floer homology of the manifold and the symplectic homology of the complement of the divisor, for a special class of Hamiltonians, in terms of absolute and relative Gromov--Witten invariants, and some additional Morse-theoretic information. As an application, we compute the symplectic homology rings of cotangent bundles of spheres, and compare our results with an earlier computation in string topology.
A finite element approach to the simulation of hydraulic fractures with lag [electronic resource]
Keywords: Mechanical Engineering

In this thesis, a finite-element-based algorithm is presented to simulate plane-strain hydraulic fractures in an impermeable elastic medium where the crack path is not known a priori. The algorithm accounts for the nonlinear coupling between the fluid pressure and the crack opening and separately tracks the evolution of the crack tip and the fluid front. It therefore allows the existence of a fluid lag. The fluid front is advanced explicitly in time, but the crack tip is determined implicitly by enforcing Griffith's criterion and maximum energy release rate. A spatial discretization is created that conforms to the crack path by perturbing the nodes of a background mesh. The coupling between the fluid and the rock is enforced by simultaneously solving for the fluid pressure and the crack opening at each time step. Verification of the algorithm is provided for straight hydraulic fractures by performing sample simulations and comparing them to two known similarity solutions. Also, sample simulations are carried out for the general case of curvilinear fractures for which the crack path is not known a priori.
Finite representation of an infinite molecular system [electronic resource] : algorithms and applications
Keywords: Chemistry

The utility of molecular simulation techniques relies on the ability to accurately and efficiently explore the appropriate distribution of configurations. For this reason, many simulation techniques use approximations that reduce the dimensionality of a system. The result is a molecular representation with fewer degrees of freedom than would otherwise be included. This dissertation explores a number of methods aimed at reducing the dimensionality for various molecular systems. The main focus of this work is the development of a new hybrid explicit/implicit solvent model capable of accurately reproducing solvation effects with significantly fewer explicitly represented molecules.
Flow separation control for robust conical diffuser design [electronic resource]
Keywords: Mechanical Engineering

In many practical applications of conical diffusers, the flow is fed by an annular flow passage formed by a center body. The annular inlet causes two possible regions of flow separation in the diffuser. The first is the separated wake of the center body and the second occurs if the boundary layer on the diffuser outer wall separates due to the adverse pressure gradient. The diffuser flow is further complicated by the strong coupling between the core flow and the outer wall boundary layer. The goal of this work was to optimize diffuser performance by controlling both separation regions. Magnetic resonance velocimetry was used to acquire three-dimensional three-component mean velocity measurements for an extensive array of diffuser configurations. The results show that a large separation bubble existed in the wake of the center body in the absence of flow control. Passive geometric perturbations were found to be ineffective in controlling the central separation bubble. An axisymmetric Coanda jet was shown to eliminate the bubble at a relatively low jet flow rate. The boundary layer separated asymmetrically when the Coanda jet was too strong. This mandates simultaneous control of both separation regions. A wavy-edge step-wall diffuser design was used to stabilize the outer wall boundary layer separation by fixing its location and allowing the separation bubbles to close quickly. The combination of Coanda blowing and the wavy-edge step-wall diffuser produced an outflow that was free of any flow separation. This configuration improved flow uniformity, increased pressure recovery, reduced loss, and reduced flow unsteadiness.
Follow the money [electronic resource] : representations of capital in Galdós
Keywords: Iberian and Latin American Cultures

Taking into account John Vernon's assertion in Money and Fiction that "money is perhaps the most common theme in nineteenth-century fiction" (7), it is not surprising that money is a recurrent theme in the novelas contemporáneas of nineteenth-century Spanish novelist, Benito Peréz Galdós. While literary economic criticism is blooming in literary studies, nineteenth-century Hispanists have not approached their work using this critical reading. This study attempts to answer the following question: What is Galdós revealing about his contemporary society through his representations of capital? This analysis literally follows the money in order to examine Galdós's scathing criticism of the Spanish middle class as an unproductive and adynamic social force. While there are many studies that link the disavowal of the Spanish bourgeoisie—high and low—in fulfilling the political role that its European counterparts had played in transforming the political and economic structures of the ancien régime, none have looked at the economic criticism Galdós makes in the "Contemporary Novels, " from La desheredada (1881) to Miau (1888), which I call the novels of capital. In order to have an adequate sense of Galdós's depiction of money, his views about money, his financial practices, his profits from his artistic labor, and his positioning within the marketplace becomes increasingly pertinent. Chapter one, "Galdós as an English Businessman in the Fabrication of a Novel Market, " explores our novelist's own relation to capital and the forces of the market. The careful examination of Galdós's artistic milieu and financial practices contextualizes the role of the market in his novelistic discourse. The following two chapters look at the representations of money through metaphors for capital and exchange—work and conspicuous consumption. Chapter two, "Señoritismo: The Anti-Work Ethic in Galdós, " examines both work and the lack of work in Galdós's "Contemporary Novels." Chapter three, "Conspicuous Consumption: The Transformation of Economic Capital into Symbolic Capital, " looks at the recurrent theme of conspicuous consumption of both male and female characters as a means of converting economic capital into symbolic capital in order maintain or attain a reputable position in society. Through the representations of capital Galdós reveals that values are shifting—moral and exchange values—and what once had been stable economic and societal tenets are no longer stable.
Force field parameterization techniques using genetic algorithm evolutionary strategies [electronic resource]
Keywords: Mechanical Engineering

A novel evolutionary strategy in the form of a steady-state genetic algorithm (GA) is presented for the derivation of an accurate parameterization of the shell model potential as applied to a metal oxide perovskite. Using barium titanate, (BaTiO$_3$ or BTO), as a testbed material, the GA technique is implemented by fitting to a density functional theory (DFT) rendered landscape of the four phases of the material, representing a wide range of unit cell configurations. Using the stochastic processes of recombination and mutation which are fundamental to the GA approach, a parameter set of the shell model potential has been identified that not only matches the energetics of the reference database accurately, but is also able to directly capture the implicit elasto-mechanical characterization of the material that is embedded in the DFT analysis. The evolutionary strategy is described in detail, and it is noted that in its current form it is directly applicable to a diverse number of other metal oxides for which similar analysis is entirely compatible. The method is then compared to the conjugate gradient technique whereby it is seen that while the gradient-based method faces significant challenges in identifying globally optimal parameterizations despite repeated initiations at distinct starting points for the search, the GA method is able to continuously explore the rugged parametric solution space to identify those regions which produce the greatest fidelity to the DFT energies. The validation of the technique includes renditions of equilibrium lattice lengths, unit cell volume and bulk modulus for the four phases of BTO using static energetic calculations. In addition, using molecular dynamics (MD) in both the canonical and isobaric-isothermal ensembles, the elastic stiffness constants, coefficient of thermal expansion, bulk modulus, and average electronic polarization for the cubic phase have been derived. These results are in excellent agreement with empirical analysis presented in the literature.
Foreign exchange policies in small open economies [electronic resource]
Keywords: Economics

Over the past two decades, New Keynesian Dynamic Stochastic General Equilibrium (DSGE) model has become a major macroeconomics tool for the purpose of policy analysis. However, the majority of literature has ignored emerging market countries which typically present more difficulties in modeling. Among those challenges, one of the most important is to model the exchange rate policy in developing countries. Typically, there are two different actions which central banks in developing countries adopt with respect to the exchange rate. The first one is exchange rate targeting, where the central bank manipulates its instruments, i.e. operational targets such as the policy interest rate, to achieve some intermediate target of the exchange rate. The second action is exchange rate intervention where the exchange rate is now an operational target instead of an intermediate one. Chapter 1 considers the question: `Does the State Bank of Vietnam respond to exchange rate movements when it sets the interest rate in the co-existence of multiple exchange rates?' To answer this, chapter 1 uses Bayesian methods to estimate a structural New Keynesian DSGE model for a small open economy where there are different exchange rates co-existing. The result shows strong evidence for the alternative hypothesis that Vietnamese central bank strongly reacts to exchange rate movements in its monetary policy formulation. The result is robust to various prior choices on structural parameters as well as to different specifications of the monetary policy rule. Furthermore, this result also holds when the Bayesian VAR-DSGE method is used instead of a simple Bayesian estimation technique. Chapter 2 considers exchange rate intervention as most central banks in emerging markets have directly and actively intervened in the FX market to stabilize the exchange rate (among other claimed objectives) and chapter 3 adds an extra layer of sterilization as central bank aims to mitigate negative impacts of capital inflow. The model introduces FX intervention as an independent central bank instrument in a New Keynesian DSGE small open economy model with a full-fledged banking sector. Central bank participates in the foreign exchange market to meet its objectives on reserve coverage and exchange rate. Main findings validate that the model dynamics under different exchange rate regimes are consistent with common thoughts about impacts of FX intervention and sterilization. In addition, it shows that an FX intervention policy tends to lower volatilities of key macro variables and stabilize them much faster than an FX targeting policy. Besides, full sterilization stabilizes the economy faster than no sterilization does, leading to lower volatilities for most macro variables and the difference in impacts between full and zero sterilization is more significant under a fixed crawling peg. Finally, welfare analysis shows that the `optimal' sterilization level decreases as consumption habit persistence falls.
Forest dynamics across temporal and spatial scales [electronic resource]
Keywords: Biology

The research conducted in this dissertation is focused on understanding different aspects of forest degradation and regeneration in the tropics. Similar to the multiple spatial and temporal scales this topic encompasses, the studies described in this dissertation encompass spatial scales ranging from as large as the Brazilian Amazon to as small as an individual leaf and temporal scales ranging from one-minute micro-climate measurements to multi-decadal remote sensing analyses. The causes and effects of forest degradation are numerous and require methods and concepts crossing traditional disciplinary boundaries. Likewise, this dissertation incorporates varied methods and concepts as required to understand forest dynamics within different study systems. The core of this dissertation is the development and integration of new remote sensing methods. In this theme, I use a variety of remote sensors, including satellite based Landsat and Quickbird sensors and the Carnegie Airborne Observatory (CAO) -- which integrates airborne LiDAR with hyperspectral imagery. I also include a study (chapter 5) focusing specifically on issues related to forest dynamics following swidden agricultural abandonment.