VictorJuiz/thesis huggingface dataset:
Lamb wave ultrasonic touchscreen [electronic resource]
Keywords: Mechanical Engineering.

Touchscreen sensors are widely used in many devices such as smart phones, tablets, laptops, etc., with diverse applications. This dissertation presents the design, analysis, and implementation of an ultrasonic touchscreen system that utilizes interaction of transient Lamb waves with objects in contact with the screen. It attempts to achieve an order of magnitude improvement on the existing ultrasound technologies, with the potential of addressing some of the weaknesses of the dominant technologies, such as the capacitive or resistive ones. Compared to the existing ultrasonic and acoustic modalities, among other advantages, it uniquely provides the capability of detecting several simultaneous touch points, and also a more robust performance. The localization algorithm, given the hardware design, can detect several touch points with a very limited number of measurements (one or two). This in turn significantly reduces the manufacturing cost. The basic governing principle revolves around the propagation of guided elastic waves in a bounded space. Wave propagation in enclosures can lead to mixing of the wave energy, ultimately leading to an incoherent spreading of information. This is the manifestation of a reverberant field, which makes the localization problem very challenging. Reverberant fields in enclosures can potentially carry useful information, however, in an incoherent way. Incoherency comes from consecutive reflections of the wave energy several times in the domain. This along with diffraction and dispersion effects can ultimately lead to mixing of the wave energy in a seemingly random way. However, spreading of the wave energy can lead to multiple interrogations of each point in the enclosure. Hence, any substructural changes in the enclosure can be sensed with sufficient information carried by the wave energy flow. Furthermore, the temporal information buried in the data makes it feasible to conduct only a few spatial measurements. I present localization schemes that benefit from the reverberant field and can reduce the required number of spatial measurements. I investigate two different approaches to address the localization problem in reverberant fields: (1) learning method and (2) the Waveform inversion (WI) approach. I show the application of the learning method to the experimental data and motivate the application of WI. Finally, I propose Lamb wave stylus designs based on three different physical mechanisms. Stylus as an input tool is used with touchscreen-enabled devices, such as Tablet PCs, to accurately navigate interface elements, send messages, etc. The main and desired features of a stylus are quiet different from a smooth touch contact such as human finger. Thus, almost all mainstream touch technologies have an accompanying stylus design with possibly a different interfacing mechanism. I propose stylus designs based on the Hertzian contact mechanics, photoacoustic, and thermoacoustic effects. The designs are conceptually motivated and demonstrated through a set of supporting measurements as the proof of concept.
Land, trade, and the law on the Sino-Tibetan border, 1723-1911 [electronic resource]
Keywords: History.

This study centers on the intersection of environment, society, and the law along the northwestern frontiers of the Qing Empire, particularly the area known as "Hehuang" straddling the modern-day Gansu-Qinghai border. Through an analysis of central and local legal case records, this work traces the ground-level changes that both bound Hehuang to the empire and triggered increasingly ethnicized explosions of violence that culminated in the Great Muslim Rebellion (1862-1873). In a region of altitudinal extremes and great ethnic diversity, I find that socio-demographic change occurred primarily in mid-altitude slope zones that were sites of overlapping jurisdictions and multiple landholding regimes. Concentrating on the lives of individual peddlers, smallholders, laborers, and herders, Part I shows how migration and the extraction of resources connected mid-slope settlements to regional networks. Over the course of the nineteenth century these changes eventually threatened both the environment and the village-level customary practices that had previously bound communities together. Behind the more proximate causes of violence and rebellion lies this deeper story of ecological crisis and growing communal struggle. Based on the local archives of Xunhua Subprefecture, Part II reveals how official reconstruction policies in the aftermath of the Great Rebellion froze in place resentments between Muslim, Tibetan, and Han Chinese populations. Despite occasional official orders to the contrary, reconstruction efforts did not return mid-slope communities to the status quo ante bellum. Rather, in a wave of post-rebellion disputes and fights over resources, Muslim cultivators often won official title for and recognition of their war-era gains. Official recovery efforts were ambitious. Implementation, however, was foiled by ground-level dynamics that officials did not fully understand. Beyond empowering local elites, reconstruction regulations, which centered primarily on rebuilding a tax base, demanded increased state intrusion into the village and the extraction of reconstruction expenses squeezed from war-torn populations. These policies bred resistance in mid-slope villages. Official efforts in the wake of the rebellion, therefore, froze ethno-religious hatreds in place, amplified the competition over land and resources, and increased tensions between local populations and the state. The legacy of these conflicts echoed in repeated rounds of strife over the course of the late nineteenth and early twentieth centuries. Though faded by the passage of time, memories of the inter-communal violence continue to haunt these villages.
Landmark Success or Colossal Failure? Exploring the Potential for Success of the Iran Nuclear Deal
Keywords: Center for International Security and Cooperation
Stanford University
Nuclear Arms Control
Joint Comprehensive Plan of Action
U.S.-Soviet Arms Control
Thesis

The Joint Comprehensive Plan of Action (JCPOA), a nuclear arms control agreement between six world powers and Iran, has led to an enormous amount of controversy around the world. The deal is the result of more than a decade of informal diplomacy and two years of formal negotiations, and it marks the first diplomatic engagement between the United States and Iran since the 1979 Iranian Revolution. Skeptics of the deal argue that the agreement includes neither proper verification nor incentives for an untrustworthy Iran to cooperate, and is thereby doomed to fail.
This thesis investigates why countries comply with agreements that involve reducing the nuclear capabilities that safeguard national security. By analyzing factors that influence cooperation with nuclear arms control agreements, this thesis explores the potential for success of the JCPOA. Three factors in particular, are relevant to predicting cooperation with an agreement: (1) verification measures focused on technological capabilities and dispute resolution mechanisms, (2) negotiations and the development of personal relationships between leaders, and (3) domestic political context. This thesis studies three agreements between the U.S. and the Soviet Union, along with the JCPOA. Using the above factors as analytical prisms to understand the case studies, this thesis evaluates the contribution of each factor to the potential for success of the deal. Ultimately, this thesis suggests that verification is necessary in agreements, but not sufficient in predicting their success. Domestic political context does not make or break a deal. Negotiations, while hardest to quantify, appear most important; particularly, personal relationships that develop through informal channels are salient in determining the potential for success of a nuclear arms control agreement.
Large deviations approximation to normalizing constants in exponential models [electronic resource]
Keywords: Electrical Engineering.

Exponential families are a class of probability distributions that contain many common distributions and thus have been a subject of considerable study by statisticians. A basic problem in statistics is the estimation of the normalizing constant of these models. In many cases, this constant is not available in closed form, and direct numerical computation is infeasible. This thesis studies techniques for numerically approximating the normalizing constant with application to maximum likelihood estimation through the use of some recent results from large deviations theory. Three examples are explored in this thesis: the Curie-Weiss model from statistical physics, exponential random graph models, and a model for relatedness in the California condor. Methods for approximately computing the normalizing constant are carried out in all three examples, and a new technique for performing maximum likelihood estimation is developed in the last example. This new technique appears to be a reasonable alternative to exisitng methods for maximum likelihood estimation in models with unknown normalizing constants.
Large-scale two-photon microscopy studies of sensory neural coding [electronic resource]
Keywords: Applied Physics.

Understanding the functions of the brain has been a subject of intensive scientific interest for centuries. At the level of individual neurons, there is a relatively detailed understanding of the mechanisms of spiking, signaling between individual cells and extensive categorization of neuron types. Similarly, at the large scale, many studies advanced our knowledge about the organization of brain regions by their function. However, the fundamental principles of neural coding at the scale of hundreds up to thousands of neurons remain largely unknown. One of the main obstacles to studying neural networks in the living brain has been a lack of technologies allowing simultaneous recording of activity across large populations of cells. In this dissertation, I first present a two-photon microscope capable of imaging the calcium dynamics of more than 2000 neurons simultaneously in awake mice. I then present an experiment that uses this new microscope to address longstanding questions in neuroscience regarding the extent to which correlated variability of neuronal responses affects the accuracy of the neural population code. I show that in the mouse visual cortex, noise correlations lead to a substantial decrease and saturation of information capacity with growing population size. I further demonstrate evidence for the presence of information-limiting 'differential' correlations. Finally, I present a theoretical model that shows how the connectivity in a hierarchical neural network may define the structure of such correlations.
Large-scale video retrieval using image queries [electronic resource]
Keywords: Electrical Engineering.

This dissertation addresses the problem of retrieving videos from large repositories using image queries. Such technology is important for numerous applications, such as brand monitoring or content linking. This work introduces a new retrieval architecture, where the image query can be directly compared to database videos -- significantly improving retrieval scalability, compared to a baseline system that searches the database on a video frame level. Comparing an image to a video is an asymmetric problem, as only videos present a temporal component. Our first contribution is an asymmetric comparison technique for Fisher vector descriptors. We explore problems where query or database items contain varying amounts of clutter, showing the benefits of the proposed technique. Our second and third main contributions consider the design of video descriptors that can be compared directly to image descriptors. We start by constructing Fisher vectors for video segments, by exploring different aggregation techniques. For a database of lecture videos, such methods obtain two orders of magnitude compression gain with respect to a frame-based scheme, with no loss in retrieval accuracy. Then, we consider the design of video descriptors which combine Fisher embedding with hashing techniques, in a flexible framework based on Bloom filters. We investigate different spatio-temporal aggregation configurations, hash functions and scoring approaches. Large-scale experiments using three datasets show that this technique enables faster and more memory-efficient retrieval, compared to a frame-based method, with similar accuracy.
Laser acceleration and deflection of sub-100 keV electrons with silicon dielectric laser accelerator structures [electronic resource]
Keywords: Electrical Engineering.

Particle accelerators are ubiquitous in modern research, industrial, and medical facilities, but they are often large, prohibitively expensive, and have limited accessibility. This size and expense is due in large part to the low accelerating gradients achievable in radio-frequency accelerators, limited by high-field breakdown to ~30 MeV/m. Leveraging nanofabrication techniques developed by the electronics industry and ultrafast laser technology, Dielectric Laser Accelerators (DLAs) have the potential to provide one-to-two orders of magnitude higher accelerating gradients than radio frequency accelerators, allowing compact and accessible accelerators to be produced. This thesis describes the demonstration of laser acceleration and deflection of sub-relativistic 65-96.3 keV electrons using silicon-based Inverse Smith-Purcell structures and silicon coupled mode dual pillar structures. This marked the first successful demonstration of silicon-based dielectric laser acceleration, first measurement of electron deflection using DLAs, and the first demonstration of a uniform field coupled-mode accelerator at sub-relativistic energies. Electrons synchronously interacting with the optical near-field of the silicon grating structures are accelerated with gradients of up to 370 MeV/m and deflected with gradients up to 255 MeV/m, more than one order of magnitude higher gradients than used in typical radio-frequency accelerators. The organization of this thesis is as follows: first, we describe the principles behind dielectric laser accelerators and present the design of the dielectric laser accelerators used in this thesis. Then we describe the 100 keV modular electron optics column built as a test platform for rapidly prototyping DLA devices. We then describe the first measurement of dielectric laser acceleration and deflection of electrons using silicon Inverse Smith-Purcell gratings with accelerating gradients up to 220 MeV/m. Next, acceleration and deflection of electrons with dual pillar silicon gratings using both Inverse Smith-Purcell modes and coupled modes with a uniform accelerating gradient are presented. Finally, the prospect of a future "Accelerator on a Chip" is explored, including scalability and integration of DLA devices with on-chip electron sources and laser power delivery.
Laser-based diagnostics of electronically excited oxygen atoms at extreme temperatures [electronic resource]
Keywords: Mechanical Engineering.

Tunable diode laser absorption spectroscopy (TDLAS) sensors were developed for in situ detection of electronically excited oxygen atoms (O*) in high-temperature environments. Near-infrared absorption sensing techniques, utilizing electronic transitions near 777.2 nm and 844.6 nm, were implemented to enable sensitive measurements of important thermodynamic flow properties, such as kinetic temperature and excited-state populations. In particular, this work discusses the development and deployment of O* TDLAS sensors for (1) a large-scale arc-heated-plasma wind tunnel and (2) shock tube kinetic studies of O-atom electronic excitation. Collaborative research with NASA's Ames Research Center Thermophysics Facilities Branch was performed to investigate tunable diode laser sensing of gas temperature in the arc-heater plenum of the 60 MW Interaction Heating arcjet Facility (IHF). An external cavity diode laser was used to generate light near 777.2 nm and laser absorption used to monitor the population of electronically excited oxygen atoms in an air plasma flow. Under the assumption of thermochemical equilibrium, time-resolved and spatially-resolved measurements of temperature were obtained at multiple lines-of-sight. Differences between inferred temperatures for distinct lines-of-sight revealed important details regarding the degree of flowfield uniformity in the arcjet plenum. These results led to the design, fabrication, and testing of an extension to the arc-heater column of the IHF to improve gas mixing and overall arcjet performance. In addition to the work performed at NASA Ames, the present work discusses shock tube studies of nonequilibrium electronic excitation processes conducted at Stanford University. Cavity-enhanced absorption spectroscopy (CEAS) was utilized to improve the detection sensitivity of O* laser-based sensors by nearly two orders of magnitude over conventional single-pass schemes. Mixtures of 1% O2/Ar were shock-heated to temperatures up to 8000 K and two distributed-feedback diode lasers near 777.2 nm and 844.6 nm were employed to measure time-resolved populations of two O-atom electronic states. Measurements were compared with simulated population time-histories obtained using two distinct kinetic models that accounted for thermal nonequilibrium effects: (1) a multi-temperature model and (2) a reduced collisional-radiative model. The former assumed a Boltzmann distribution of electronic energy whereas the latter allowed for non-Boltzmann populations by treating the probed electronic states as pseudo-species and accounting for dominant electronic excitation/de-excitation processes. The effects of heavy-particle collisions were investigated and found to play a major role in the kinetics of O-atom electronic excitation at the conditions studied.
A laser-driven fiber optic gyroscope for inertial navigation of aircraft [electronic resource]
Keywords: Applied Physics.

Despite longstanding success as the world's most commercially successful fiber optic sensor, the fiber optic gyroscope (FOG) suffers from relatively poor scale factor stability compared to its competitors in the market for inertial navigation of aircraft. One way to improve the stability is to replace the broadband superfluorescent fiber source (SFS) used to interrogate the FOG with a laser, though this choice reintroduces coherent backscattering, polarization coupling, and other coherent errors into the FOG output. In this thesis we develop a new analytical model of the polarization coupling errors, the first to include the effects of dynamic phase biasing, which is used in essentially all FOGs. We also develop a new model of the backscattering errors which can be used to provide quantitative estimates of the backscattering noise and drift far faster than existing models. Combining these calculations of the backscattering and polarization coupling errors with experimental measurements, we show that navigation-grade noise and drift performance is possible for a laser with a linewidth in the 10's of GHz range. We propose and test several methods of broadening the linewidth of a single mode laser to this level. Ultimately the most successful method uses an electro-optic phase modulator driven by either a pseudo-random bit sequence (PRBS) or a Gaussian white noise (GWN) to scramble the phase of a single mode laser and thereby broaden its linewidth. Using a PRBS-modulated laser as a source for a FOG we demonstrate the first laser-driven FOG with noise below the requirement for inertial navigation of aircraft (0.001 deg/h^1/2). Through calculations and experiments we show that the width and carrier suppression in the modulated laser spectrum can be improved by replacing the PRBS modulation with a GWN modulation. In a FOG driven by a laser with GWN modulation we measure an ARW of 0.00055 deg/h^1/2, a drift of 0.0068 deg/h, and a light source mean wavelength stability below 0.15 ppm. This performance represents the first time that the noise, drift, and scale factor stability requirements for inertial navigation of aircraft are met in a laser-driven FOG. Possibilities for further improvements to a laser-driven FOG are discussed.
Leadership Decapitation and Strategic Trajectories of Jihadi Terrorist Groups
Keywords: Center for International Security and Cooperation
terrorism
jihadi terrorism
leadership decapitation
targeted killing
terrorist leaders
Thesis

Counterterrorism policies often incorporate leadership decapitation, which refers to the removal of a militant organization’s leaders through capture or targeted killing. Previous studies of leadership decapitation measure its effects on a limited set of quantifiable variables, especially a terrorist group’s lifespan and attack frequency. Despite the resources and attention devoted to using and studying the tactic, its effects are not well understood.
This thesis explores leadership decapitation of jihadi terrorist groups in relation to strategic trajectory, the combination of a group’s goals and the methods employed in pursuit of those goals. After a jihadi terrorist group’s founding leader is killed by a government, what happens to the group’s strategic trajectory?
This thesis finds that jihadi terrorist groups demonstrate one of three strategic trajectory trends after losing their founders: resilient continuity, relational shifts, or major change. The strategic trajectories of resilient groups are generally unchanged after leadership decapitation, while relational-shift groups change the ways in which they interact with target audiences and other militant organizations. Major-change groups shift their goals or strategic emphasis.
This thesis concludes that killing the founders of jihadi terrorist groups does not produce a single type of strategic trajectory change across organizations. Further, the thesis does not find strong trends or shared characteristics across groups within the same category of strategic trajectory change, meaning that the outcome of leadership decapitation is unpredictable. The thesis asserts that further study and debate must define what constitutes success in the context of strategic trajectory change in terrorist groups.