VictorJuiz/thesis huggingface dataset:
Intracardiac ultrasound imaging using Capacitive Micromachined Ultrasonic Transducer (CMUT) arrays [electronic resource]
Keywords: Electrical Engineering

Atrial fibrillation, the most common type of cardiac arrhythmia, now affects more than 2.2 million adults in the United States alone. Currently, electrophysiological interventions are performed under fluoroscopic guidance, which does not provide adequate soft-tissue resolution and exposes the patient and the operator to harmful ionizing radiation. Intracardiac echocardiography (ICE) provides real-time anatomical information that has proven valuable in reducing the fluoroscopy time and enhancing procedural success. This dissertation describes the design and implementation of two types of multi-functional, forward-looking ICE catheters developed using capacitive micromachined ultrasonic transducer (CMUT) technology: MicroLinear (ML) and Ring catheters. The ML catheter enables real-time, forward-looking 2D imaging using a 24-element, fine-pitch 1D CMUT phased array. The Ring catheter uses a 64-element, ring-shaped 2D CMUT array that enables real-time, forward-looking, volumetric imaging. Both of these catheters are equipped with custom-designed, front-end electronic circuits that are integrated with each transducer array at the catheter tip. The close integration of custom electronic circuits with the ML and Ring CMUT arrays improves the signal-to-noise ratio (SNR) in each case by 18 dB and 20dB, respectively. The integration process of the CMUT arrays with the electronics dice in the tight space available for full catheter construction shows 100% yield. The characterization of the fully-integrated CMUT arrays demonstrates excellent pulse-echo response with over 100% fractional bandwidth as well as surface transmit pressure levels in excess of 1 MPa (peak-to-peak). The first fully-functional 9F ML CMUT ICE catheter shows remarkable in vivo imaging performance using porcine animal models. A similar in vivo imaging experiment with the first fully-functional 12F Ring CMUT ICE catheter proves very promising. The volumetric imaging capability of the Ring ICE catheter and the versatility offered by its inner lumen make it an attractive interventional device. This dissertation also introduces a novel CMUT structure, called PCMUT. The preliminary simulation and experimental verification of the PCMUT structure show that it is possible to fabricate CMUTs that exhibit non-flexural piston-like plate motion with a significantly improved volume displacement and fill-factor.
Investigating structure property relations in compound semiconductors using single nanowire devices [electronic resource]
Keywords: Materials Science and Engineering

Semiconductor nanowires are an important class of materials. They have been used in a huge number of applications in the information, energy and medical sciences, and they also offer unique opportunities to study the large number of fundamental physical processes whose basic mechanisms operate on the nanoscale. Great progress has been made in the synthesis of these nanowires and the fabrication necessary to integrate them into top-down architectures; however, fully accounting for structural heterogeneity and understanding processing induced structural changes in these materials remains a challenge. A new approach to investigating structure property relationships combining in-situ transmission electron microscope (TEM) techniques with single nanowire devices and test structures fabricated on electron transparent membranes will be presented, and example studies on several metal chalcogenide materials for use in nonvolatile memory and thin film photovoltaics will be discussed. Several emerging strategies for nonvolatile information storage rely on systems in which an active element can be reversibly actuated between two structural states which can then be electronically distinguished. Gaining fundamental understanding of these systems requires an understanding of these different structural states, how they give rise to the required electronic properties, as well as the dynamics of the reversible process used to actuate the active element. In order to reach the high integration densities required to compete with existing technologies, these active elements must be on the nanoscale. To probe the materials science of two such candidate systems, silver selenide for pulsed electrochemical cell memory and germanium telluride for phase change memory, nanowires were synthesized and single nanowire memory devices were fabricated on electron transparent 50 nm thick silicon nitride substrates for ex-situ and in-situ experiments in the TEM. Currently, the world record power conversion efficiency, 20%, for a thin film photovoltaic device is held by the complicated quaternary material copper indium gallium selenide (CIGS). This excellent performance is not yet clearly understood, but may arise in large part due to the unique nature of the internal boundaries in CIGS materials. In order to understand the complicated relationship between processing and interface structure in this material, extensive TEM studies were undertaken using a variety of single nanowire test structures and in-situ heating. The fundamental understanding obtained by these studies was leveraged both to synthesize high quality p-type copper indium selenide (CIS) nanowires, and also to fabricate for the first time a single nanowire CIS solar cell, an achievement which will serve as a powerful platform for fundamental investigation into this important materials system.
Investigating the nucleation, growth and energy levels of organic semiconductors for high performance plastic electronics [electronic resource]
Keywords: Chemical Engineering

Plastic or organic electronics offer several advantages over conventional inorganic technologies. Firstly, the molecular structure of organic semiconductors and conductors can be tuned for various applications using synthetic chemistry. In addition organic thin films are flexible, and can be processed and patterned inexpensively. However, improving the thin film conductivity of organic semiconductors and conductors is necessary for widespread application and adoption. The overall goal of this thesis is to investigate and control organic small molecule growth at surfaces in order to improve the performance of organic electronic devices. In first part of the thesis, improving the charge carrier mobility of organic thin film transistors (OTFTs), the building block for plastic electronics, is discussed. The nucleation, stability and thin film growth of model organic semiconductors such as pentacene and C60 are described with focus on correlating thin film structure to charge carrier mobility. More specifically, pentacene nucleation and growth on the most common substrate for OTFTs, an octadecylsilane (OTS) monolayer modified silicon oxide surface, is investigated. The role of the density of the OTS was determined to be a critical device parameter that impacts organic semiconductor nucleation and growth, and the charge carrier mobility, as the OTS transitions from an amorphous monolayer into a crystalline one. Dense OTS monolayers were fabricated using the well known ultrathin film Langmuir Blodgett (LB) technique, as well as a new spin-coating technique developed in our lab. The crystalline OTS monolayer serves as an excellent template for promoting desirable organic semiconductor thin film growth leading to high performance transistors. Therefore a crystalline OTS dielectric surface modification layer, which greatly improves organic semiconductor performance, may be important for the future success of OTFTs and organic circuits. In the second part of the thesis, lessons learned from studying organic semiconductor nucleation and growth are applied to improving the conductivity of carbon nanotube (CNT) networks for transparent electrode applications. Selective growth of organic small molecules with low molecular orbital energies was used to greatly reduce the sheet resistance of CNT films by both decreasing junction resistances and stable doping of the semiconducting CNTs. The result is a material which has the highest value (in terms of transparency and sheet conductivity) of any carbon based transparent electrode.
Investigation of a plasma deflagration gun and magnetohydrodynamic Rankine-Hugoniot model to support a unifying theory for electromagnetic plasma guns [electronic resource]
Keywords: Mechanical Engineering

Electromagnetic Plasma Guns generally operate by pulsing a large current through a gas, thereby ionizing it, and then using the Lorentz force from the self-induced magnetic field to accelerate the generated plasma. In most cases, plasma gun operation is characterized by the formation of a current sheet which forms at the gun breech and is then accelerated downstream. Therefore, these devices are often described using a snowplow model, which describes the observed luminous front as a moving piston that has a certain sweeping efficiency associated with it. In plasma guns where the snowplow model does not apply, a complete set of magnetohydrodynamic (MHD) equations often has to be solved numerically. As an alternative to these approaches, this dissertation explores an underutilized concept that is based on an MHD extension of the Rankine-Hugoniot model from combustion theory. This approach treats the snowplow as an MHD detonation rather than as a piston and suggests that a plasma deflagration should also be possible. A plasma gun was then designed and constructed based on this concept and investigated through a series of experiments. It was determined that the constructed gun does operate in a plasma deflagration mode. In addition, the extent of the MHD Rankine-Hugoniot analogy to the combustion case and the breadth of its applicability to different types of plasma guns were briefly explored. Finally, an interesting effect was observed when operating in deflagration mode and at high energy. An intense, inductively amplified current loop forms near the exit plane of the gun. It is believed that this effect may also cast new light on the so-far unexplained origin of energetic ion beams emitted from Dense Plasma Focus devices.
The investigation of online consumer reviews as intentional social actions [electronic resource]
Keywords: Business.

Online reviews play an increasingly important role in consumers' purchase decisions. Such internet-enabled Word-of-Mouth communication offers society a tremendous potential to reduce information asymmetries and in this way, increase the efficiency of electronic and traditional markets (Dellarocas, 2005). Voluntary reporting, however, introduces the potential for reporting biases. In this dissertation, I argue that consumers' willingness to post a review on an online forum is conditioned on the social normative landscape of this public space. I conducted four exploratory investigations of the social dynamics involved in review posting behavior. Given the broadness of the research agenda, these studies focus on different aspects of the research question and, as a result, vary in their levels of analysis and methods. As evidence, I found that review posting behavior was motivated by social obligations and regulated by social norms. Furthermore, these social motives produced systematic biases in review valence distributions. The implications of these findings are clear: Biased distribution of online product reviews can lead to inefficiencies in consumer choice and erroneous conclusions about consumer product preferences.
Investigations of magmatic end-members [electronic resource] : silicic magma chambers and mafic dikes
Keywords: Geological and Environmental Sciences.

Approximately 10% of the global population, some 550 million people, live within 100 km of an active volcano, making it imperative that the causes of magma accumulation in the crust and the factors affecting the scale of subsequent volcanic eruptions are investigated and modeled. This PhD dissertation examines magmatic processes at two scales: silicic calderas represent the large but infrequent end of the continuum, whereas mafic dikes are small in scale but common. Many previous authors have presented hypotheses for how large silicic systems develop. In order to test and refine these hypotheses, I undertook a global compilation that empirically examines how the characteristics of 140 young silicic calderas reflect their crustal-tectonic setting. Results indicate that the size and geochemistry of silicic calderas are affected by the nature of the underlying crust, the tectonic setting, and the local stress regime. For example, large, rhyolitic calderas tend to occur in continental settings under extension. There are, however, few true "rules, " and exceptions may prove useful in analyzing how silicic magma chambers form. Based on this compilation, I present a probabilistic method for determining the tectonic-crustal setting of a given caldera from its diameter, and eruption geochemistry. Focusing specifically on arc settings, this study demonstrates that (1) the abundance of silicic calderas in a given arc is proportional to the trench-normal convergence rate, except in arcs with back-arc spreading; and (2) silicic calderas in continental arcs tend to occur farther behind the volcanic front than do more typical arc volcanoes, possibly because of the abundance of pre-existing structures in continental margins. At the opposite end of the volcanic spectrum, this dissertation examines the intrusion of two mafic dikes. The first lies beneath Mammoth Mountain, California, and was associated with a 1989 seismic swarm. Based on an inversion of leveling data constrained by relocated earthquakes, I propose that a dike 2 km long, 8 km high, with 1 m of opening was intruded at 9 km depth beneath the south side of Mammoth Mountain. The second dike investigation focused on the eruption of Miyakejima, Japan, in 2000, associated with more than 10,000 earthquakes, several small eruptions and progressive caldera collapse. Displacements recorded by GPS stations and pre- and syn- event seismicity were used to determine a geological explanation of the event. In the proposed model, a shallow dike propagated ~30 km away from Miyakejima for one week, stopped propagating laterally after intersecting a pre-existing fault zone, and then continued to open and grow vertically for nearly two months.
In-vitro experimental validation of finite element analysis of blood flow and vessel wall dynamics [electronic resource]
Keywords: Bioengineering.

Biomechanical forces such as hemodynamic parameters and stress and strain in blood vessel walls have significant effects on the initiation and development of cardiovascular diseases, as well as on the operations of implantable medical devices. Computational fluid dynamics is an emerging powerful numerical tool capable of providing fine temporal and spatial resolutions in the quantifications of these cardiovascular biomechanical forces. The overall goal of this research is to develop tools and methods for conducting in-vitro experiments, and to acquire experimental data for the validation of the computational methods. We first developed a physical Windkessel module which can provide realistic vascular impedances at the outlets of flow phantoms in order to enable in-vitro experiments that mimic in-vivo conditions. We also defined a corresponding analytical model of the Windkessel module, and showed that upon proper characterization, the analytical model can accurately predict the pressure and flow relationships produced by the physical Windkessel module. The precise analytical model can then be prescribed as a boundary condition for the finite element domain, resulting in a direct parallel between the computational description of the physical model and the physical reality. We then performed validation of the numerical method using the Windkessel module, and a rigid, two outlet, patient-derived abdominal aortic aneurysm phantom under resting and light exercise flow and pressure conditions. Physiological pressures within the phantom, and flow waveforms through the two phantom outlets were achieved. Finally, we performed validation of the numerical method incorporating deformable vessel walls, using two compliant flow phantoms under physiological flow, pressure, and deformation conditions. The compliant phantoms mimicked a patent thoracic aorta, and one with an 84% coarctation (by area). The computational predictions of pressure, flow, and velocity patterns compared favorably with experimental measurements in both of the validation studies. The accurate prediction of wave propagation behaviors in the deformable phantom study indicated a faithful prediction of the vessel wall motion. In addition to numerical methods validation, the experimental techniques we have developed can also be used in direct in-vitro evaluations of medical devices.
Ion-beam texturing at nucleation [electronic resource] : investigation of the fundamental mechanism of biaxial texture development in ion beam assisted deposition and applications
Keywords: Materials Science and Engineering

Low-energy ion-beam irradiation (< 1 keV) during the concurrent deposition of cubic oxide materials results in the growth of crystallographically textured thin films. A model system, magnesium oxide (MgO), has been successfully used as a biaxially textured template fillm for the heteroepitaxial deposition of many materials with texture dependent properties like high temperature superconductors, tunable microwave materials, and ferroelectrics. The ion beam assisted deposition of MgO is unique in that it requires only a few nanometers (< 10nm) at room temperature to develop texture very near that of a single crystal substrate and is substrate independent (glass, metal, etc.). Here, I present data on the nucleation of biaxial crystallographic texture in this model system using a novel in situ quartz crystal microbalance (QCM) substrate combined with in situ reflected high-energy electron diffraction (RHEED). Correlation of mass uptake with the RHEED images of the growing surface shows that the development of crystallographic biaxial texture in this material system occurs suddenly as the initially polycrystalline MgO films reaches a critical film thickness of 2 nm. This texture continues to improve during subsequent growth. I use a combination of in-situ RHEED and ex situ transmission electron microscopy to elucidate the mechanism of this sudden texture formation. I have also investigated these ultra-thin films using synchrotron radiation and report some of the most complete analysis of their in-plane orientation. I present a model to describe this behavior and further explain the role of ion-to-molecule arrival ratio and underlying nucleation surface on texture development. In addition, I will present some empirical rules for selecting new materials for IBAD processing. I will discuss the use of IBAD materials as template layers for several applications. Among these, I have recently developed a new template layer, CaF2, for use in photovoltaic applications. I present my recent effort to develop this system for the deposition of biaxially textured polycrystalline Si and Ge thin films.
It goes without saying [electronic resource] : the importance of creating space for writing talk with African American students
Keywords: Education.

Writing research, primarily done in the 1980s, led to better understanding of writing as a recursive social process and affected change in many language arts classrooms. However, more research is needed to determine what instructional practices around writing are effective in supporting students who struggle with writing, particularly African American students. The achievement gap in American schools is widely documented; this gap is especially wide with regard the writing achievement of African American students. As a group, African Americans scored in the lowest percentile across all grades tested on the 2002 National Assessment of Educational Progress (NAEP) writing exam and the 2007 NAEP writing exam scores continue to show a drop in the percentage of African American students at proficient between eighth and twelfth grade. This is a case study of two middle school English/Language Arts teachers chosen from a larger pool of effective teachers based on value-added measures, and observational data from a prior study. The author investigated the instructional practices of these teachers in one predominantly African American middle school and their impact on the development of students' writing skills and identities as writers. Data included classroom observations, student and teacher interviews, class sets of student writing from the beginning and end of the academic year, and artifacts such as graphic organizers and rubrics. The aim of this study was not to pinpoint one best way of teaching writing, but to develop a better understanding of the ways we can support struggling writers, particularly African American students, to develop their writing skills and a writer's identity. From this work, certain facets of teaching seem particularly supportive during the teaching of writing with African American students: namely, the use of writing talk as a mechanism to bridge between students' and the academic writing required in schools today. This talk creates opportunities for students to engage with models and their peers in ways that support engagement and persistence, and approximate the practice of experienced writers.
Keyhole diffraction microscopy for semiconductor circuit inspection [electronic resource]
Keywords: Applied Physics

Non-destructive inspection of integrated circuits requires a microscope that features high resolution (< 20 nm) and high penetration (> 0.07mm of silicon substrate), thus suggesting the use of x-ray microscopy. The advent of intense coherent sources of hard (< 1nm wavelength) x-rays has led to the study of x-ray diffraction microscopy in which the image is reconstructed from the far-field diffraction pattern. Atomic resolution is possible with this lensless approach. Because this pattern records only intensity information, additional information, e.g. the phase distribution, is needed for image reconstruction. Here this information is provided by illuminating the sample with a collimated beam of well-defined shape and thus is a form of "keyhole diffraction microscopy". The research featured computer simulations, scaled optical experiments, soft (1.4 nm) x-ray experiments and one hard x-ray experiment. Different reconstruction algorithms were compared. The hybrid input-out (HIO) algorithm followed by a few iterations using the error reduction (ER) algorithm proved to be e±cient. Dynamic support was used to improve the convergence of computation. Samples with complex-valued transmission functions were more difficult to reconstruct. The geometry and periodicity of the sample itself were found to affect the reconstruction. Illumination with asymmetric shapes (such as a triangle) sharply bounded gave the best reconstruction. The results of scaled optical experiment conducted under blind conditions (no a priori knowledge of the sample) suggest that a resolution of 10 nm should be readily achievable at an x-ray wavelength of 0.18 nm.