VictorJuiz/thesis huggingface dataset:
Design, simulation, and fabrication of nanostructures for optoelectronic applications [electronic resource]

Improving the efficiency of semiconductor optoelectronic devices is a central pursuit on the path to affordable, universal access to solar power, energy-efficient lighting, sensitive photodetectors, and vibrant display technologies. In all of these applications, light must pass through an interface between the device and the outside world. Nanostructures on the scale of the wavelength of light offer a powerful way to control the flow of light through this interface, which could enable devices with new functionality and dramatically improved optical efficiency. However, nanostructured surfaces also present some interesting design challenges. Here, I will present three case studies illustrating the promise and challenges of nanostructured interfaces in optoelectronic applications. First, I will present a camera sensor architecture that is able to capture the full light field from a scene, enabling 3D image reconstruction and focusing after the photo is taken. By stacking polymer microspheres on silicon nanoshells, we can focus and confine light in a very small volume. Using this coupled system, we are able to resolve the angle of light incident at up to 40 degrees away from the normal. By contrast, microlenses on a planar substrate can only resolve angles up to 10 degrees away from the normal. Second, I will discuss vacuum photocathodes, which are currently used in low-light detectors and electron sources and have the potential to be used in solar energy generation systems. I will present a simulation suite that models the optical and electronic behavior of photocathodes, offering new insight into nanostructured architectures that should maximize electron yield. In particular, the anti-reflection properties of the surface must be carefully balanced against nanostructured profiles that block electron emission. I will also present measurements we made of photoemission from nanostructured photocathodes to highlight the importance of developing interfaces with low surface recombination and to motivate a study on the passivation of gallium arsenide using gallium nitride. Third, I will describe a new hybrid optoelectronic interface that offers both high light transmission and high electrical conductivity. We use metal-assisted chemical etching (MACE) to create a silicon substrate that is covered by a gold film with protruding silicon nanopillars. When coated with a silicon nitride anti-reflection layer, we observe up to 97% absorption in this structure, which is remarkable considering that metal covers 60% of the top surface. We use optical simulations to show that Mie-like resonances in the nanopillars funnel light around the metal layer and into the substrate, offering a general paradigm for creating ultra-transparent metal contacts for solar cells, displays, and more.

Keywords: Materials Science and Engineering.
Advisor: Cui Yi
Melosh Nicholas A. primary advisor. Thesis advisor
Brongersma Mark L. advisor. Thesis advisor
Detection and analysis of the electromagnetic pulse from hypervelocity impact plasma expansion [electronic resource]

Hypervelocity dust particles, including meteoroids and space debris, routinely impact spacecraft and produce plasmas that are initially dense (10^25/m^3), but rapidly expand into the surrounding vacuum. This research was the first to detect radio frequency (RF) emission associated with electromagnetic pulses (EMPs) from hypervelocity dust particle impacts in ground-based experiments. These micro particles that produced RF are 15 orders of magnitude less massive than previously observed. We find that one mechanism for EMP production is the result of the growth of the unstable Weibel mode in the plasma and that the EMP detection rate is strongly dependent on impact speed and on the electrical charge conditions at the impact surface. This mode grows from a plasma temperature anisotropy driven by the impact ionization process combined with the external electric field. Upon expansion, the Weibel mode grows, producing RF emission within nanoseconds. In particular, impacts of the fastest particles (speed > 15 km/s) occurring under spacecraft charging conditions representative of high geomagnetic activity are the most likely to produce RF emission. The sensor design and analysis that led to this discovery is discussed. This phenomenon may provide a source for unexplained RF measurements and satellite electrical anomalies.

Keywords: Aeronautics and Astronautics.
Advisor: Close Sigrid
Cantwell Brian advisor. Thesis advisor
Senesky Debbie advisor. Thesis advisor
Detection of atypical patterns of occupancy and mobility in smart homes and offices with a network of motion detectors [electronic resource]

Ambient sensors are a category of sensing technologies designed to be embedded in an environment for the purposes of monitoring changes to that environment from either internal or external sources, such as occupants or the weather, respectively. The goal of this dissertation is to study aspects of the behavior and wellbeing of occupants through unobtrusive and non-invasive ambient motion sensors. We focus on passive versions of motion sensors, such as Passive InfraRed (PIR) motion detectors, which have been utilized by researchers for the recognition of Activities of Daily Living (ADL) in homes. Motion sensors are also used in office settings, where they act as occupancy sensors to better control HVAC and lighting systems to save energy. We begin by discussing the types of information that can be extracted from a dense network of PIR sensors in a home, focusing on indicators of wellness. We then discuss methods for extracting occupancy based features from dense motion sensor deployments that represent an occupant's behavior. We demonstrate how these occupancy based features exhibit a strong correlation with features derived from human annotated activities for multiple long term smart home datasets. From this we reason that our derived features can be used as a proxy for human labeled activities for certain applications such as atypical behavior detection. We then present a method to use occupancy based features to find days that are atypical, and compare our results with a classifier based on human annotated activities. Lastly we discuss how low level mobility features can be extracted from a network of motion sensors to form a mobility graph, which can be used to summarize the aggregate mobility of the occupants of an environment. We show how this mobility graph can be visualized to represent how occupants move between sensors and how changes in the mobility graph over time can be quantified. In a home environment, we show how significant changes in this mobility graph correlate with changes in the occupant's underlying behaviors. In an office environment, we show how changes in the mobility graph can be related to global events, like fire alarms.

Keywords: Electrical Engineering.
Advisor: Law K. H. (Kincho H.) primary advisor. Thesis advisor
Aghajan Hamid K.
Poon Ada Shuk Yan
Rajagopal Ram advisor. Thesis advisor
Developed through Social Processes? Chinese Women’s Beliefs about Education, Family, and Career

In China, gender gaps in academic majors and career aspirations have persisted despite decades of institutional efforts to improve gender equality. While most studies attribute this phenomenon to external factors such as gender discrimination, others point to a need for exploring Chinese women’s beliefs towards education and career. Through 16 in-depth qualitative interviews conducted with women studying or staying in the United States, the present study looks into the possible proximate processes through which Chinese women internalize stereotypical gender beliefs. Two gender beliefs that emerged from the analysis are that boys perform better than girls in mathematics and science and that mothers should contribute more to their children’s education than fathers. By adopting a social psychological perspective, I explain those beliefs in terms of two corresponding social processes through which interviewees rationalized and internalized the beliefs. These beliefs and processes led many interviewees to lowered aspirations that might have contributed to the persistence of gender differences in academic major choices and career aspirations. This study contributes to the social psychological literature on the formation of gender beliefs, and informs the observed persistence of gender inequality in China through Chinese women’s narratives.

Keywords: gender beliefs
proximate processes
academic choices
women’s careers
education in China
mother’s family roles
social psychology
Stanford Graduate School of Education International Comparative Education
Thesis
Developing and testing a reconstitution model for RNA folding [electronic resource]

One of the most fascinating phenomena in biology is the folding of macromolecules into complex three-dimensional shapes that carry out all biological functions. Critical to the efficacy of these molecules is their capacity to fold on timescales relevant to biology and form specific and stable (but not too stable) structures. For decades, scientists have been studying how the physical properties of each macromolecule are utilized to combat the entropy of countless alternative conformations to form a native state. The function of structured RNAs is critical at every level of gene-expression regulation, thus developing a predictive model for how these molecules fold is of fundamental importance as it holds the promise of therapeutic design and control. Previous studies of RNA structure have determined that the architecture of RNA is structurally modular, therefore we posit that we can harness this feature of RNA to simplify the folding process into separate energetic contributions that are additive to predict the kinetic and thermodynamic behavior of structure RNA, i.e. energetic "Reconstitution". These energetic contributions are the conformational entropy due to the dynamics of the helices and junctions that connect them, the electrostatic penalty for bringing these RNA elements together, and the free energy of formation of tertiary contacts. Using, smFRET I provide support for energetic independence of these contributions from comparisons of measurements of rate and equilibrium constants for the effects of mutations in the tertiary contacts of the P4-P6 RNA, which found these energetics were the same over a range of conditions and structural contexts. To further test this reconstitution hypothesis and determine other simplifying and predictive rules for RNA building blocks, we utilized a simple RNA tertiary system, the tectoRNA, in concert with RNA-array technology to assess variations in ~ 100,000 variants. The number of variants provided by this approach and the simplicity of this system allowed us to address multiple open questions in the field of RNA folding regarding the conformational preferences of RNA helical sequences, junctions, and tertiary contacts. This thesis represents a step towards testing and developing a quantitative and predictive model for RNA folding.

Keywords: Biochemistry.
Advisor: Herschlag Daniel primary advisor. Thesis advisor
Das Rhiju
Straight Aaron
Developing code [electronic resource] : aspiration and exclusion in the making of 'Silicon Savannah'

On a 2013 tour across Africa, Google's Executive Chairman Eric Schmidt proclaimed that Kenya's capital city of Nairobi "has emerged as a serious tech hub and may become the African leader." Echoing this statement, local and international press outlets have dubbed Nairobi "Silicon Savannah." They celebrate its burgeoning technology sector for spurring democracy and development, and for precipitating Africa's political and economic "rise." Based on twenty-five months of ethnographic fieldwork in Nairobi, my research addresses both these grandiose claims and the disparate places in which they find empirical traction: the elite spaces of software's production and the impoverished informal settlements in which such software is implemented and used. By putting into conversation theoretical approaches from anthropology, science and technology studies, African studies, and urban geography, this dissertation examines how diverse political and ethical claims become enmeshed in and expressed through digital technologies, which in turn shape understandings and experiences of development, citizenship, and governance in Nairobi.

Keywords: Anthropology.
Advisor: Yanagisako Sylvia Junko
Ebron Paulla A.
Ferguson James
Smith James advisor. Thesis advisor
Developing gold-based electrocatalysts for the production of fuels from CO2 and water [electronic resource]

Carbon dioxide electroreduction is presented as a way to convert CO2 into commodity chemicals. This thesis starts with an overview of CO2 electroreduction, the methods used to study CO2 electroreduction catalysts and analysis of a specific application of CO2RR: the conversion of CO2 emissions from the fermentation of corn. Subsequently, a thorough analysis of gold as a catalyst for CO2 electroreduction is presented, followed by analysis of four novel gold-based materials for CO2 electroreduction. For these materials, electrochemical analysis and characterization is discussed as well as some mechanistic implications. The thesis is concluded with a combination of theory and experimental hydrogen partial current densities to generate a relationship between surface CO-binding and HER during CO2 electroreduction.

Keywords: Mechanical Engineering.
Advisor: Jaramillo Thomas Francisco primary advisor. Thesis advisor
Mitchell Reginald primary advisor. Thesis advisor
Nørskov Jens K.
Developing maximum-efficiency architectures for steady-flow chemical engines [electronic resource]

Improving the efficiency of natural gas-based power plants is essential for significantly curtailing future greenhouse gas emissions. Historically, improvements to power plant thermodynamics have been implemented as incremental changes from existing systems. Only recently has work been done to systematically develop optimally-efficient combustion engines using existing technologies without artificial constraints on the system's size, components, or shape. This systematic process was used to optimize steady-flow combustion engines for work and heat transfer. This dissertation builds off of this recent work by additionally optimizing systems for matter transfer. The best flow paths for air and fuel are determined, as well as the flow path for an additional environmental (non-exergetic) fluid: water. As an alternative to the highly-entropic combustion process, a solid-oxide fuel cell is also incorporated into the design scope. Both numerical and analytical approaches to optimizing these architectures are examined. Through a systematic expansion in the scope of candidate systems, this thesis develops optimal thermodynamic schematics that achieve efficiencies more than 15 percentage points better than those for the most efficient existing power plants.

Keywords: Mechanical Engineering.
Advisor: Edwards C. F. (Christopher Francis) primary advisor. Thesis advisor
Mitchell Reginald primary advisor. Thesis advisor
Brandt Adam (Adam R.) advisor. Thesis advisor
Developing subtype-specific stochastic simulation models of breast cancer incidence and mortality [electronic resource]

Breast cancer is the second leading cause of death among women in the United States. Several advances have been made in early detection and treatment of breast cancer in the last few decades, in particular with the widespread adoption of screening mammography and the identification of molecular targets that have enabled the development of therapies for specific subtypes. In light of the changing landscape of available interventions, there is an urgent need to develop approaches that integrate molecular and population-level data to evaluate the efficacy of current and emerging screening and treatment technologies in order to support the development of clinical guidelines that reduce the burden of breast cancer. Population modeling is a comparative effectiveness paradigm capable of linking the complex dynamics of adopting new interventions and their net effects on breast cancer incidence and mortality. Although several population-level models of breast cancer have been constructed, there are several challenges that must be addressed in order to construct estrogen receptor (ER) and human growth epidermal factor 2 (HER2) subtype-specific models. In this dissertation, I present several methodologies developed to enable the construction of molecular-specific population models of breast cancer progression, screening and treatment. I propose to achieve this goal through the following specific aims: 1) develop a framework to model breast cancer incidence in the U.S from 1975 to 2010, explicitly accounting for the effects of screening and menopausal hormonal therapy (MHT), 2) develop an approach to estimate parameters that characterize progression and baseline survival by estrogen receptor (ER) and human epidermal growth factor 2 (HER2) status in the absence of any intervention, and 3) use these results to construct an ER and HER2-specific breast cancer population model to evaluate the effects of screening and treatment on breast cancer incidence and mortality trends. Finally, I will also discuss an implementation of our model to characterize breast and ovarian cancer among women with a BRCA1 or BRCA2 mutation, and how it was used to quantify the benefits of risk-reducing interventions, such as prophylactic surgery and screening, to support women choosing to undergo these procedures at different ages.

Keywords: Biomedical Informatics.
Advisor: Plevritis Sylvia primary advisor. Thesis advisor
Kurian Allison advisor. Thesis advisor
Shah Nigam
Development and evaluation of two novel instruments for X-ray imaging [electronic resource]

The evolution of x-ray equipment has been stagnant because of its demanding design requirements, but clinical need for an advanced imaging technique has been continually growing. To contribute to hardware advances in the x-ray imaging devices, we designed and implemented innovative instruments by applying both mechanical and electrical principles. Herein, we explore two essential novel instruments for x-ray imaging: (1) a new electric motor for an MR-compatible x-ray tube and (2) a testing system for a high-energy x-ray detector. Because each imaging modality has different strengths and limitations, we are able to obtain more accurate medical images by combining at least two modalities. A hybrid x-ray/MR imaging system, leveraging the complementary advantages of both x-ray and MR imaging, is ideal for image guidance of catheters, guide wires, and prosthetic devices in real time. However, the performance of conventional x-ray tube motors is degraded when exposed to an external magnetic field, thus we developed and evaluated a new x-ray tube motor that can operate in the presence of the strong magnetic fields of an MRI machine. We further explored simulation models to improve the performance and dynamic characteristics of the new motor. High-energy x-ray imaging used in concert with low-energy x-ray imaging creates clearer and more accurate images. It is necessary to have a thicker scintillating phosphor layer to improve quantum efficiency for high-energy x-rays, but the spreading becomes more severe in that case. To resolve this issue, we can use a thick scintillating layer segmented by other thin layers (a.k.a. pixelated detector). Even though the pixelated detector prototype based on Sawant's design demonstrates relatively high detective quantum efficiency (DQE), both measured DQE and spatial resolution differ from corresponding expectations from theory and simulations. In order for the Monte Carlo method to accurately simulate the imaging performances, the characteristics of the basic pixelated unit must be understood. Therefore, we developed a new instrument to measure both light reflection and transmission distribution within the basic detector unit as a function of material, surface, and angle of incidence. Based on manufacturing procedures and the light distributions of the candidate samples, we also made valuable suggestions for a better, more profitable detector. We expect that our instruments will lead the next generation of diagnostic and therapeutic equipment to produce accurate diagnoses and efficient treatments for various disease states.

Keywords: Mechanical Engineering.
Advisor: Cutkosky Mark R. primary advisor. Thesis advisor
Fahrig Rebecca primary advisor. Thesis advisor
Pelc Norbert J. advisor. Thesis advisor
Development of a molecular tension sensor to visualize force production by nonmuscle myosin IIB in living cells [electronic resource]

Mechanical forces exert a strong influence over biological form and function. For example, during the transition of a fertilized egg cell into a complete multicellular organism, an embryo experiences growth, but also movements that deform and rearrange its cells. These movements ultimately shape tissues and sculpt functional organs. Cellular movement originates in molecular events that generate, resist, and transduce mechanical force, and work with chemical signaling to direct individual and collective cellular functions. As such, improved insight into the fundamental aspects of cellular biophysics would dramatically enhance our understanding of cell motility, cell division, and embryonic development, with potentially transformative consequences for the fields of tissue engineering and medicine. In my thesis research I designed tools to explore the mechanical state of molecular motors and crosslinkers, and investigated the role that mechanical forces play in cellular motility and mechanotransduction. I first describe the development of a FRET-based molecular tension sensor specific for nonmuscle myosin IIB, and show that the sensor localizes similarly to endogenous myosin IIB, responds to strain and relaxation, and provides the first force measurement of myosin II in a living cell. Next, I examine the role of ion gradients and nonmuscle myosin II dynamics in the formation of membrane blebs, a cellular protrusion required for some forms of three-dimensional cell motility. Our results suggest that that blebbing M2 cells exhibit a constitutive alkaline pH beneath the membrane, and that distinct organizational patterns for nonmuscle myosin IIA and IIB occur during bleb retraction. Finally, I test the hypothesis that the crosslinker ezrin transduces tension between the cytoskeleton and the sodium proton exchanger 1 (NHE1). pH measurements to monitor NHE1 activity reveal that epithelial cells do not show a substantial proton flux response to applied touch, and FRET measurements on an ezrin tension sensor do not support its role as a tension-sensing cytoskeletal element.

Advisor: Dunn Alexander Robert primary advisor. Thesis advisor
Goodman Miriam Beth advisor. Thesis advisor
Theriot Julie advisor. Thesis advisor
Diffraction of elastic waves by edges [electronic resource]

The purpose of this thesis is to investigate the diffraction of singularities of solutions to the linear elastic equation on manifolds with edge singularities. Such manifolds are modeled on the product of a smooth manifold and a cone over a compact fiber. For the fundamental solution, the initial pole generates a pressure wave (p-wave), and a secondary, slower shear wave (s-wave). If the initial pole is appropriately situated near the edge, we show that when a p-wave strikes the edge, the diffracted p-waves and s-waves (i.e. loosely speaking, are not limits of p-rays which just miss the edge) generated from such an interaction are weaker in a Sobolev sense than the incident p-wave. More generally, we show that subject to a "coinvolutivity" hypothesis, if a p-singularity (or s-singularity) of any solution strikes the edge, the diffracted p and s wavefronts are smoother that the incident singularity.

Keywords: Mathematics.
Advisor: Vasy András primary advisor. Thesis advisor
Mazzeo Rafe advisor. Thesis advisor
Ryzhik Leonid advisor. Thesis advisor