VictorJuiz/thesis huggingface dataset:
High-dimensional multivariate regression and reduced rank estimators [electronic resource]
Keywords: Computational and Mathematical Engineering.

In statistical learning and modeling, when the dimension of the data is higher than the number of samples, the estimation accuracy can be very poor and thus the model can be hard to interpret. One approach to reducing the dimension is based on the assumption that many variables are a nuisance and redundant; consequently, many variable selection methods have been proposed to identify only the most important variables. Another approach to reducing the dimension is factor extraction, which is based on the assumption that the high-dimensional data can be approximately projected on a lower-dimensional space. Factor extraction, such as principal component analysis (PCA) and canonical correlation analysis (CCA), provides a good interpretation of the data, but the dimension of the reduced space (the number of underlying features) is typically not easy to estimate. In the context of regression analysis, where we want to fit a linear model yt = BTxt + et given n observations xi 2 Rp and yi 2 Rq for i = 1; : : : ; n, several important variable selection methods, e.g. lasso-type shrinkage, forward stepwise selection and backward elimination, have been well studied for dimension reduction. However, there are not many theoretical results of these methods for multivariate regression models with stochastic regressors (also called 'stochastic regression models') found in the literature. In this dissertation, we present an effcient algorithm for solving high-dimensional multivariate linear stochastic regression. The motivation comes from modeling and prediction for multivariate time series models in macroeconomics and for linear MIMO (multiple-input and multiple-output) stochastic systems in control theory. By extending the 'orthogonal greedy algorithm' and 'high-dimensional information criterion' for 'weakly sparse' models in Ing and Lai (2011), we can choose a subset of xt and reduce the dimension p to o(n). We can then perform reduced-rank regression of yt on this reduced set of regressors and introduce an information criterion to choose the number of factors and estimate the factors. We provide theoretical results for our algorithm. We carry out simulation studies and an econometric data analysis to evaluate the algorithm.
High-efficiency thin-film crystalline solar cells [electronic resource]
Keywords: Electrical Engineering.

Thin-film high-efficiency crystalline solar cells are expected to play a significant role as a greener, renewable energy source of the future. Such cells have been extensively studied over the past 10 years. Most of this research focused on developing thinner cells to reduce material usage and improving the optical absorption within the thin absorber. Most recently, the active semiconductor layer can be 10 -- 100 times thinner than conventional solar cells by advanced light trapping. However, an improvement in efficiency in thin-film solar cells had not been previously appreciated and is an equally if not more important enhancement of the cells in addition to materials cost saving. This dissertation presents the device physics of thin-film crystalline solar cells and demonstrates the key design principle to achieve higher efficiency by improving two important parameters: open circuit voltage (Voc) and short circuit current (Jsc). The first part of this thesis focuses on achieving high Voc in thin-film c-Si solar cells and demonstrate the voltage enhancement in thin-film Si solar cells in both theoretical simulation and experimental demonstration. Theoretically, thin cells can significantly increase the carrier concentration by confining photo-carriers into a smaller active region and decrease the recombination by reducing the volume of the active region. This results in higher Voc and efficiency. Experimentally, the first Voc enhancement in thin-film solar cells is demonstrated. The 5 µm thick Si cell achieved a Voc of 649 mV, which is superior to the Voc of any other thin-film (sub-25-µm) Si solar cells reported to date. To further improve efficiency, a carrier selective contact of TiO2/Si was developed to reduce the high carrier recombination at the metal contacts associated with the high carrier centration in thin films. Such a contact demonstrates a contact recombination reduction of 33% and a Voc enhancement of 10 mV compared to a conventional metal contact. The second part mainly discusses high Jsc by applying nanoscale light trapping structures to thin-film c-Si and III-V solar cells. Given the challenges in obtaining low surface recombination and high efficiency in nanostructured solar cells, we demonstrated a nanowindow solar cell design with dielectric or wide bandgap semiconductor material that can overcome these challenges. A SiNx nanostructured dielectric layer can provide both light tapping and surface passivation for Si. A thin Si film with such SiNx layer exhibits < 5% reflection over a wide spectra and angular range. The last part focuses on absorption improvement in nanostructured GaAs thin-film solar cells. Applying front-side nanostructures significantly increases optical absorption in a 300 nm thick active region. This results in over 95% absorption from visible light to near infrared light, and enables GaAs solar cells with only 300 nm thick absorber.
High-energy lithium-sulfur batteries [electronic resource] : from theoretical understanding to materials design
Keywords: Materials Science and Engineering.

Rechargeable lithium-ion batteries have transformed the world of portable electronics and consumer devices today, but their specific energy and cycle life remain insufficient for many emerging, modern-day applications such as electric vehicles and grid energy storage. Lithium-sulfur (Li-S) batteries represent a very promising technology for these applications because their theoretical specific energy is about 7 times that of lithium-ion batteries today. However, the challenges of S and Li2S cathodes include: (1) the formation of intermediate lithium polysulfide species which dissolve into the electrolyte during cycling and (2) the low electronic conductivity of S and Li2S. Thus, there is an urgent need for novel encapsulation materials and morphologies for these cathodes that can effectively confine the polysulfide species and facilitate electronic conduction. In this thesis, I will present my work on developing high-energy Li-S batteries, from theoretical understanding to materials design. First, I will present results from theoretical ab initio simulations which enable the systematic screening of promising encapsulation materials. Next, I will present four different designs of S and Li2S cathodes. The first design is that of S-TiO2 yolk-shell nanostructures, which uses oxygen-rich TiO2 as the encapsulation material. The novelty of this yolk-shell cathode lies in the precise engineering of internal void space to accommodate the volumetric expansion of S during lithiation, enabling long cycle life of 1,000 cycles to be achieved. The second and third designs: Li2S-graphene oxide and Li2S-polypyrrole composite structures, use oxygen-rich and nitrogen-rich materials respectively to encapsulate fully-lithiated and fully-expanded Li2S cathodes. Using these cathodes, we demonstrate high specific capacity and stable cycling performance over hundreds of cycles. The fourth design: Li2S-TiS2 core-shell nanostructures, uses highly-conductive and sulfur-rich TiS2 as an effective 2D encapsulation material. This cathode not only exhibits high rate capability of 4C (fast charge/discharge in 15 min), but also high areal capacity of 3.0 mAh/cm2, both of which are on par with commercial standards today. These works pave the way for the future development of high-performance and long-lasting rechargeable batteries.
High-resolution SAR A/D converters with loop-embedded input buffer [electronic resource]
Keywords: Electrical Engineering.

Successive-approximation-register (SAR) analog-to-digital converters (ADCs) have generated a significant amount of interest in the past several years. While most of the recent literature focuses on low-to-moderate resolution designs (8-10 bits), we are now beginning to see significant advancements in the high-resolution space, targeting ≥14 bits at 10-100 MS/s. Traditionally, this performance range has been dominated by pipelined and delta-sigma architectures. However, several applications in high-speed control and interference cancellation require low laten-cy and this is where the SAR topology becomes attractive. While several SAR ADCs have demonstrated efficient digitization at high speed and resolution, the difficulty of driving a large sampling capacitor with high accuracy in a short sam-pling window is an important challenge in the System-on-a-Chip (SoC) integration of such ADCs that is often ignored in the literature. The work of this dissertation led to the design of a 14-bit 35 MS/s SAR ADC in 40 nm CMOS with a loop-embedded input buffer that consumes only 23% of the total ADC power. The buffer uses a source follower topology whose nonline-arities are cancelled by the SAR algorithm, allowing us to achieve 99 dB spurious-free dynamic range (SFDR) despite the small amount of invested power. That approach made it possible to reduce the input capacitance of the ADC by a factor of eighteen, easing the drive requirements substantially and resulting in the highest reported SFDR for SAR ADCs with a sampling speed greater than 20 MS/s. Additionally, a second SAR ADC design (30 MS/s) based on a noise filter gear-shifting concept is introduced. Using a comparator with time varying noise performance, this ADC achieves a state-of-the-art figure of merit (FOM) of 161.6 dB and a peak signal to noise-plus-distortion ratio (SNDR) of 77 dB, which is the highest reported value for SAR ADCs with a sampling frequency above 20 MHz.
High-sensitivity diaphragm-based fiber optic acoustic sensors and applications [electronic resource]
Keywords: Electrical Engineering.

Acoustic sensors are used for applications in multiple disciplines, including oil and gas extraction, medical devices (magnetic resonance and acoustic/ultrasonic imaging), underwater communications, seismic research, monitoring large structures, and surveillance. Performance requirements vary greatly, but in general the sensors are expected to have a fairly low minimum detectable pressure (MDP), as low as 10 µPa/√Hz in some cases, a wide bandwidth (hundreds of Hz to a few kHz is typical), and a high dynamic range (60 dB in pressure is common). In the first half of this thesis, I present a highly sensitive fiber optic acoustic sensor that meets these requirements by utilizing a high-reflectivity photonic-crystal diaphragm 450 nm thick to convert the incident acoustic or ultrasonic pressure into a mechanical vibration. The diaphragm is placed ~30 µm from the reflective end of a single-mode fiber to form a miniature Fabry Perot (FP) interferometer, which converts this vibration into an optical readout. Thanks to the high compliance of the diaphragm, this sensor exhibits an extremely low MDP of ~2.6 µPa/√Hz over 1--30 kHz, the lowest value reported in the literature. This sensor has recently been used as a hydrophone to listen to the very weak sound generated by the beating of a small number of heart cells, of critical interest for cell sorting and stem-cell research. When used as a force sensor, this sensor was capable of detecting a force as low as 1.3 pN/√Hz in a laboratory environment. In a quieter environment, the minimum detectable force is predicted to be only ~76 fN/√Hz, which is lower than conventional room-temperature AFM-based force sensors. Additionally, a theoretical model based on a finite element analysis was developed to show that this sensor also operates at ultrasonic frequencies and predict its sensitivity dependence on frequency. Measurements of its sensitivity at 72 kHz and 1.025 MHz were perform to demonstrate this potential. In the second half of the thesis, I discuss a low-noise, compact fiber acoustic sensor that implements a novel transducer design, namely a microfabricated silicon diaphragm with a π/2 phase step combined to a single-mode fiber to form a simple two-wave interferometric sensor head. Compared to the FP sensor, this device has a similar strain resolution, it operates over a broad range of wavelengths (~±150 nm instead of ~±1 nm), and both its microfabrication and assembly are simpler. A prototype is reported with an average MDP as low as 5.4 µPa/√Hz between 1 kHz and 30 kHz, in agreement with a theoretical model.
High-throughput analysis and protein engineering using microcapillary arrays [electronic resource]
Keywords: Bioengineering.

Over the past decade, high-throughput technologies have allowed researchers to gain unprecedented insights into intrinsically complex and interconnected biological systems. As examples, whole-genome sequencing has enabled the identification of crucial genes and mutations underlying disease pathophysiology, DNA microarrays have been used to elucidate transcription patterns involved in healthy and diseased states, and large-scale proteomics methods have helped map the connectivity of cell signaling networks that orchestrate responses to growth factors and other external stimuli. In contrast, analogously powerful approaches for rapidly and deeply interrogating the sequence-structure-activity relationship of proteins, with functional read-outs that span a range of biophysical and biochemical measurements, have lagged because of technical challenges. In this dissertation, I describe the development of a new technology platform, termed µSCALE (microcapillary single-cell analysis and laser extraction), that aims to improve high-throughput protein characterization and engineering. The µSCALE platform is built around a microcapillary array, automated fluorescence imaging, and a novel laser-based sample recovery method. The platform spatially segregates millions of cells or their protein products in a microcapillary array and interrogates the dense array within minutes. µSCALE also enables recovery of target sample from the microcapillary array using a precise laser-based extraction technique. To showcase capabilities and breadth of µSCALE, I applied it to three distinct protein-analysis and engineering applications, using libraries expressed in yeast or bacteria. In each case, I demonstrated feasibility and then engineered a novel protein variant, identifying new binders against a clinical target, creating a novel fluorescent protein biosensor, or reducing inhibition of an enzyme. Compared to conventional screening techniques, such as FACS and plate-based screens, the µSCALE affords several distinctions advantages, including a five orders of magnitude improvement in throughput, direct cell imaging, and high sorting purity and yield. Collectively, these benefits present µSCALE as an exciting, novel technology to the field of protein engineering and beyond.
Holography of de sitter space and disordered systems [electronic resource]
Keywords: Physics.

This dissertation is devoted to the study of models that capture the intricate dynamics of two different physical setups: exponentially expanding universes and disordered systems. We explore late time divergences in the perturbative corrections of wavefunctions of interacting light fields on a fixed de Sitter background. The divergences are holographically interpreted as shifts in the conformal weights of dual CFT operators. We then compute functional determinants in a Euclidean CFT for various non-perturbative deformations. According to the dS/CFT correspondence, these functional determinants calculate the late time Hartle-Hawking wavefunctional of asymptotically de Sitter space in higher spin gravity as a function of the profile of the fields in the bulk. Numerical experiments suggest that upon fixing the average of the bulk scalar profile, the wavefunction becomes normalizable in all the other (infinite) directions of the deformations we study. For disordered systems, we investigate the extent to which quiver quantum mechanics models encode the complex dynamics of multicentered black holes in string theory. In a certain limit of the quiver system we display the emergence of a conformal symmetry, which mimics the emergence of conformal symmetry in the near-horizon geometries of extremal black holes. Finally, we take a Newtonian multiparticle limit of the quiver system away from the conformal regime. We study the dynamics of the system numerically to look for signs of ergodicity breaking, cages, and transitions to chaos.
Host-centric proteomics of stool [electronic resource] : monitoring global host responses to the gut microbiota
Keywords: Chemical and Systems Biology.

The diverse community of microbes that inhabits the human bowel, known as the gut microbiota, is vitally important to human health. While the identity and abundance of the microbes has been widely studied, little is known about the ways in which they interact with their host. The breakdown of the host-microbiota symbiosis has been linked to numerous diseases, including inflammatory bowel diseases, autoimmune diseases and even autism. Host-expressed proteins are essential for maintaining this mutualistic relationship and serve as reporters on the status of host-microbiota interactions. Previously, a global means for non-invasively monitoring the expression of proteins by the host in the gastrointestinal tract has not been described. In this thesis, I elucidate the need for an unbiased method to monitor host responses to the microbiota and describe a mass spectrometry-based method we developed, called host-centric proteomics of stool, which can simultaneously measure hundreds of host secreted proteins. I then illustrate how this method can be used to study host protein secretions in various regions of the gastrointestinal tract and the host responses to antibiotic-associated pathogens.
How does politics affect central banking? [electronic resource] : evidence from the Federal Reserve
Keywords: Political Science.

My dissertation investigates the ways in which political dynamics influence decision-making at central banks. I address this question by looking at the different mechanisms through which political influence occurs. I devote a chapter to examining this topic in each of the following contexts: the evolution of the structure of the Federal Reserve, the preferences of monetary policymakers around elections, and the Federal Reserve's lending during the 2008 financial crisis. Through this series of chapters, I find that politicians designed the American central bank in such a way that political considerations are able to consistently affect monetary policymakers. However, stemming from the partial compromises inherent in its design, this influence is constrained in such a way to ensure its stability, as too much would lead to a new equilibrium in which the central bank is more apolitical.
Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes as an In Vitro Model of Doxorubicin-Induced Cardiotoxicity
Keywords:  Department of Biology
Biology
induced pluripotent stem cell
cardiomyocyte
cardiotoxicity
doxorubicin
iron
Thesis

Doxorubicin (DOX; trade name Adriamycin) is an anthracycline antibiotic and widely used chemotherapeutic agent. Despite its powerful and wide-spectrum anticancer effects, its clinical utility is limited by its cardiotoxicity, which increases the risk of dilated cardiomyopathy and subsequent heart failure among DOX-treated cancer patients and survivors. Recent animal-based studies have suggested that DOX-induced cardiotoxicity (DIC) is due, at least in part, to iron accumulation and resulting oxidative stress, and that this is mediated by the downregulation of ABCB8, which encodes a mitochondrial iron transporter protein called ATP-binding cassette subfamily B member 8 (ABCB8). Circumventing the challenges of validating these findings in primary human heart tissue, this study applies human iPSC-derived cardiomyocytes (hiPSC-CMs) as a surrogate human platform to probe the pathogenic processes of DIC. I hypothesized that DOX causes dose-dependent ABCB8 downregulation and mitochondrial iron accumulation in hiPSC-CMs, consistent with studies performed on animal-based in vitro models. Patient-specific hiPSC-CMs, generated from DOX-treated breast cancer patients who experienced cardiotoxicity (DOX TOX) and those who did not (DOX CONTROL), were utilized to investigate whether patient-specific differences in the pattern and severity of ABCB8 expression and mitochondrial accumulation of iron could predict susceptibility to DIC. I found that, while high concentrations of DOX caused significant reduction of ABCB8 in hiPSC-CMs, modest and non-cytotoxic concentrations did not. Further, while no robust difference was observed between the baseline expression of ABCB8 in DOX CONTROL and DOX TOX cells, these two cancer patient-derived hiPSC-CM populations both expressed significantly lower levels of ABCB8 than their HEALTHY CONTROL counterparts. Finally, preliminary data suggested that DOX does not induce consistent dose-dependent trends in mitochondrial iron accumulation in hiPSC-CMs. As the first humanized model of DIC in the specific context of iron metabolism, this work represents a key step toward improving the clinical utility of DOX, by elucidating the molecular basis of both its cardiotoxic effects and patient-specific susceptibility to this condition.
Humor in fascist Italy [electronic resource]
Keywords: French and Italian.

In this dissertation I trace a cultural history of humor in fascist Italy by looking at novels, vignettes and articles through the lens of the humorous philosophies of Giacomo Leopardi, Luigi Pirandello, and Aldo Palazzeschi, and the political and cultural context of fascism. The Introduction lays the philosophical foundations of humor in Italian literature and finds Leopardian, Pirandellian and Palazzezchian influences in the works of Massimo Bontempelli and Achille Campanile. Chapter One finds similar echos of literary humor in editions of Il corriere della sera and Il popolo d'Italia printed around the March on Rome and during Mussolini's first months in power. Chapter Two delves into the more overt convergence of politics and humor in the humorous and politically engaged newspapers Il becco giallo and La libertà. It follows the two starkly antifascist publications through the assassination of Matteotti, Mussolini's famous January 3, 1925 speech to parliament, and comments upon the goal of creating political change through humor. Chapter Three looks at the fascinating and extremely perplexing strapaesista magazine Il selvaggio, whose irreverence and critique of fascism leaves the reader wondering how it thwarted regime-sanctioned censorship. Chapter Four returns to Il corriere della sera and Il popolo d'Italia to find the transformation of humor into traditional propaganda, and at times, irrelevant nonsense. The Conclusion looks at the humorous magazines Il bertoldo and the Marc'Aurelio and their biting critique of the failure of humor to effectively fight fascism, ultimately finding that humor unmasks, subverts and criticizes fascism, but remains a passive observer of reality.