VictorJuiz/thesis huggingface dataset:
Surface-normal germanium quantum well modulators for free-space optical interconnects to silicon [electronic resource]
Keywords: Electrical Engineering.

Today's computer systems are constrained by the high power consumption and limited bandwidth of inter- and intra-chip electrical interconnections. Optical links could alleviate these problems, provided that the optical and electronic elements are tightly integrated. Most present optical modulators use materials systems that are incompatible with CMOS device fabrication, or rely on weak electrooptic effects that are difficult to utilize for vertical incidence devices. The extremely high communications bandwidth demands of future silicon chips may ultimately require massively parallel free-space optical links based on array integration of such vertical incidence modulators. We have investigated the suitability of surface-normal asymmetric Fabry-Perot electroabsorption modulators for short-distance optical interconnections between silicon chips. These modulators should be made as small as possible to minimize device capacitance; however, size-dependent optical properties impose constraints on the dimensions. We have thus performed simulations that demonstrate how the optical performance of the modulators depends on both the spot size of the incident beam and the dimensions of the device. We also discuss the tolerance to nonidealities such as surface roughness and beam misalignment. The particular modulators considered here are structures based upon the quantum-confined Stark effect in Ge/SiGe quantum wells. We present device designs that have predicted extinction ratios greater than 7 dB and switching energies as low as 10 fF/bit, which suggests that these CMOS-compatible devices can enable high interconnect bandwidths without the need for wavelength division multiplexing. Next, we present experimental results from these Ge/SiGe asymmetric Fabry-Perot modulators. Several approaches were investigated for forming resonant cavities using high-index-contrast Bragg mirrors around the Ge/SiGe quantum well active regions. These include fabrication on double-silicon-on-insulator reflecting substrates, a layer transfer and etch-back process using anodic bonding, and alkaline etching the backside of the Si substrate to leave suspended SiGe membranes. We present results from each of these modulator structures. The best performance is achieved from the SiGe membrane modulators, which are the first surface-normal resonant-cavity reflection modulators fabricated entirely on standard silicon substrates. Electroabsorption and electrorefraction both contribute to the reflectance modulation. The devices exhibit greater than 10 dB extinction ratio with low insertion loss of 1.3 dB. High-speed modulation with a 3 dB bandwidth of 4 GHz is demonstrated. The moderate-Q cavity (Q~600) yields an operating bandwidth of more than 1 nm and permits operation without active thermal stabilization.
Synchronization in rhythmic performance with delay [electronic resource]
Keywords: Music.

In the last few years, musicians have been exploring ways to perform with people in different parts of a city, a country or the world. New technologies for the Internet have been developed that are already high-quality in terms of audio experience. There is, however, a persistent problem: telecommunications delay. Even though these latencies are presently down to approximately 150 milliseconds from opposites sites of the globe, we know that delays of 20 milliseconds are already problematic for musical performance. This research presents an experimental analysis of the rhythmic strategies that humans use to stay synchronized with different delay conditions, similar to the ones encountered in present day networked music performance concerts. The vast majority of experimental studies of sensorimotor synchronization involve humans synchronizing to machines, usually some sort of tapping experiments. Likewise, rhythmic tracking has overwhelmingly focused on the analysis of one musical source, but not on the interaction of performing musicians. This research's focus is on the latter. The results show that performers are able to adapt to different delay conditions anticipating each other's beats. This anticipation is believed to be an intrinsic aspect of beat perception. The results are compared to earlier studies and new metrics are proposed that consider the alternating interaction between musicians. This approach also adopts phase dynamics using stroboscopic mapping. An integrated model for tracking and generating rhythmic interactions between two performers is also presented. This model uses coupled adaptive oscillators and includes an anticipation and reaction parameter that is shown to be critical to understand rhythmic synchronization with delay. We show how this model compares to the experimental data and use it to explain some common observations in rhythmic performance with delay.
Synthesis and organization of nanomaterials using biomolecules [electronic resource]
Keywords: Materials Science and Engineering.

Recent advances in materials synthesis have revealed unique properties that occur at the nanoscale; however, organization of nanomaterials into hierarchical three-dimensional structures remains an unmet challenge. In striking contrast, Nature exhibits control over precise nanoscale processing which leads to highly organized and complex three-dimensional structures. This control is achieved through the action of many molecules, especially a wide array of proteins, that direct the synthesis, morphology, and organization of the many organic and inorganic materials found in Nature. Understanding and applying insights from these natural processes offers a promising new way forward for the manipulation and organization of materials at the nanoscale. This thesis focuses on understanding the unique self-assembling protein clathrin and developing strategies to modify self-assembled clathrin scaffolds for the synthesis and organization of inorganic nanomaterials. I have studied clathrin as an example of a robustly self-assembling protein to gain insight into how self-assembly is achieved in natural systems. I have designed and used bi-functional peptides for functionalization of self-assembled clathrin cage scaffolds through site-specific molecular recognition to generate complexes for the synthesis of two classes of inorganic nanomaterials, metal oxides and noble metals. Additionally, I have demonstrated that a single clathrin-based biomolecular complex can be used to generate distinct arrangements of gold nanoparticles. I have extended the peptide design strategy to design components that will direct hierarchical organization and have demonstrated the importance of considering the effect of multivalent interactions in peptide-mediated assembly. Taken together, the results presented provide insight to aid in the design of novel biomimetic systems for the tunable control over nanoscale synthesis and organization.
Synthesis of microfluidic chips [electronic resource]
Keywords: Electrical Engineering.

Microfluidic chips are devices that allow one to manipulate nano- and pico-liters of fluids and microscopic objects, such as cells and complex molecules, and are widely employed in bioengineering, molecular biology, chemistry and adjacent fields. We focus our work on soft lithography technology used to create microfluidic chips in a number of bio labs. The growing complexity of these chips increases the probability and the cost of a design mistake, thus making them harder to design and debug. In this thesis, we address these challenges by introducing appropriate design tools. First, we will present a robust compact modelling framework that enables rapid simulations of microfluidic chips via existing circuit simulators, such as SPICE, and validate these models on two simple devices, a long channel and a pump. Then, we frame our model as a geometric program, enabling us to perform fast and global optimizations of complete chip designs. Finally, we introduce a synthesis tool that conceives a design of a chip using parameterized building blocks and optimizes its performance.
Synthesizing patterns using factor graphs [electronic resource]
Keywords: Electrical Engineering.

In computer graphics, we are interested in recreating the richness and beauty of the world we see around us. We are also interested in helping artists create novel work. Even though the arrangement of design elements can vary greatly in patterns, we may still often characterize the relationships between design elements in the same kind of patterns. Previous pattern synthesis methods consist mainly of procedural and optimization techniques. Procedural techniques are good for generating a collection of models using a set of predefined rules and parameters. However, they are difficult to control. Optimization methods generate the best model given a cost function defined by a set of constraints. How do we combine the strength of the two methods such that we can generate a collection of models that satisfy both hard and soft constraints? That is, we want a system where preferred models are more likely to be generated. In this dissertation, we propose to use factor graphs, a type of graphical model, to encode the constraints present in patterns for computer graphics. We then model the design space for possible patterns as a generative probabilistic distribution. We also demonstrate how we can use factor graphs to set up the probabilistic distributions and develop synthesis algorithms for two classes of pattern synthesis problems: example- based tiled patterns and scene synthesis. In example-based tiled patterns, the patterns are grid-based and the size of a tiled pattern is fixed (i.e., a closed world). We learn the factor functions from the examples. Because of the hard constraints that the adjacent pairs of tiles must adjoin seamlessly, the distribution has high probability states that are isolated into disconnected regions. To address this challenge, we propose a search algorithm for tilings that is an extension of MC-SAT. Next, we consider the problem of scene synthesis. In scene synthesis, we relax the grid restriction and allow the number of objects to vary in the scene (i.e., an open world). The resulting distribution is transdimensional. Such a setting is useful when the number of objects is not known a priori. We propose a reversible jump Markov chain Monte Carlo method (LARJ-MCMC) that uses localized annealing. We also show through experimentation that the proposed MCMC sampler better adapts to the change in energy landscape when the dimensionality changes. Both algorithms exploit the factor graph formulation to synthesize layouts more efficiently.
Synthetic and mechanistic investigations of a diruthenium-catalyzed C-H amination reaction [electronic resource]
Keywords: Chemistry.

The development of efficient and selective rhodium-catalyzed C--H and [pi]-bond amination processes makes possible unprecedented C--N bond disconnections in the synthesis of complex molecules. The oxidizing conditions of the reaction, however, have limited a broad utilization of catalyst structures beyond the well-documented bimetallic tetracarboxylates. Our desire to uncover catalyst systems tolerant of a wider range of ligand architectures inspired an evaluation of a congeneric class of diruthenium complexes that feature higher oxidation potentials. These studies have culminated in the identification of a family of efficacious amination catalysts crafted from a diruthenium core. Empirical examinations have demonstrated exceptional performance for the strapped carboxylate catalyst [Ru2(esp)2]SbF6 in amination reactions, and a unique proclivity for allylic C--H bond oxidation exacted by the tetrakis-oxypyridinate complex [Ru2(hp)4Cl]. Density functional calculations on this latter catalyst have implicated a mechanism for C--H insertion that operates via an H-atom abstraction/radical rebound sequence, contrasting the body of work on intramolecular amination by dirhodium systems. Experimental studies were undertaken to corroborate the stepwise nature of the catalytic reaction and to dissect the details of the insertion event. Investigations of alternative pathways operating in parallel to productive turnover have unveiled a host of processes that effect substrate or product consumption, oxidant depletion, and global catalyst reorganization. With the assistance of desorption electrospray ionization mass spectrometry (DESI-MS), a wealth of mechanistic data has been amassed, including evidence of critical, short-lived reaction intermediates. The collective data provide a detailed mechanistic framework for diruthenium-mediated amination reactions that should assist the continued development of effective and varied C--H amination technologies.
Synthetic routes toward scalable, tunable carbon nanotube ensembles for use in devices [electronic resource]
Keywords: Electrical Engineering.

Studies of carbon nanotube forests, carbon nanotube transistors and wire bundles, and carbon nanotube doping are carried out. A synthesis technique called "synergetic carbon nanotube growth" is developed in which enhanced growth rates are induced in catalyst areas of micron-scale feature size using asymmetric catalyst designs. This technique is used to fabricate carbon nanotube wire bundles with fair alignment which have resistivities of 1.4-2.2 Ohm*cm. Control of the chirality distribution in carbon nanotube growths is attained using alcohol chemical vapor deposition. Spectroscopic measurements and statistical analysis of transistor device measurements show that the semiconducting fraction in carbon nanotube ensembles can be tuned from 69% to 85% by varying growth temperature. The use of a precursor, triethylamine, is demonstrated to achieve in situ nitrogen doping in carbon nanotube growth at levels of approximately 0.2%, measured by X-ray photoelectron spectroscopy measurements and corroborated by Raman spectroscopy measurements. This work shows that mechanistic explanations ascribing to a surface-mediated process of carbon nanotube growth are correct.
Systematic effects in cosmic shear measurements for future ground-based optical surveys [electronic resource]
Keywords: Physics.

Cosmic shear measurements with large optical surveys have the largest potential power in the near future for revealing the nature of dark energy -- the greatest mystery in modern cosmology. This is one of the main science goals for the Large Synoptic Survey Telescope (LSST) project. The 10-year survey from LSST will image $\sim$ 20,000 square degrees of sky in six filter bands to a final survey depth of $-band magnitude $\sim27.5$ and median redshift $\sim1.2$. To take full advantage of this unprecedented statistical power, however, the systematic errors associated with cosmic shear measurements need to be controlled to a level similar to the statistical errors. In this thesis, I estimate the statistical and systematic errors in the cosmic shear dataset expected for LSST and investigate methods to mitigate some of the major systematic errors. The analyses are based on high-fidelity simulated images generated by a fast Monte Carlo ray-tracing code. The code models the interactions of the photons including major physical effects from the top of the atmosphere down to the charge-coupled devices, or CCDs. I first calculate the number density of % detectors? galaxies expected for a cosmic shear analysis with LSST, which provides a quantitative measure of the statistical power of the survey for these topics of investigation. Accounting for the realistic measurement errors for shear and blending/masking effects, I show that $\sim26$ arcmin$^{-2}$ well-measured galaxies is expected using conventional algorithms, but the number can increase by as much as
Systems for real-time image-guided therapy [electronic resource]
Keywords: Electrical Engineering.

Image-guided therapy is a recently developed field that combines the use of computer technology with tracked surgical tools and pre-operative or intra-operative images for planning, guiding, and performing diagnoses and surgical interventions in a minimally invasive manner. It has been used in neurosurgery, orthopaedics, otolaryngology, and plastic and cranio-facial surgeries to improve patient safety and health-care outcomes. This technology relies upon a set of complex subsystems to perform tasks such as optical and electromagnetic 3D tracking, ultrasound imaging, endoscopy, and overall navigation, yet they have not been well characterised in this regard. This work presents methods and results for calibration and error analysis of these subsystems, and presents solutions to issues that impede their use for practical and intuitive real-time navigation and guidance in the operating room. Keywords: 3D, accuracy, calibration, computer graphics, distortion correction, electromagnetic tracking system, error analysis, freehand, graphics processing unit, image-enhanced endoscopy, image-guided surgery, jitter, lens distortion, minimally invasive surgery, optical tracking system, real-time, texture mapping, ultrasound, virtual endoscopy, visualization, volume rendering.
Taking the "history" out of historical thinking to teach adolescents to evaluate informational text [electronic resource]
Keywords: Education.

Twenty-four eighth-grade students in an urban public school participated in a classroom-based design experiment for four months. The purpose of the study was to discover how an established high school history curriculum featuring multiple documents and historical thinking strategies can be modified for use with younger students of average reading ability and applied to nonhistorical topics in a classroom setting. Classroom studies about historical thinking, whether large-scale interventions (De La Paz, 2005; Nokes, Dole, & Hacker, 2007; Reisman, 2012) or exploratory stories (Stahl, Hynd, Britton, McNish, & Bosquet, 1996; Wolfe & Goldman, 2005; VanSledright, 2002; Wineburg, 1991a) have focused understandably on the discipline of history. Most research about multiple documents reading has been primarily postsecondary psychological studies that explored what students already know how to do (Bråten, Strømsø, & Britt, 2009; Strømsø, Bråten, & Samuelstuen, 2003). Training studies for school age students evaluating multiple documents have been of short duration and have sought primarily cognitive explanations (Macedo-Rouet, Braasch, Britt, & Rouet, 2013). The present study attempted to discover how to teach these skills in an authentic, long-term classroom setting; how historical thinking strategies can be applied to nonhistorical text; how young adolescents develop such skills over time and in a social setting; and how teachers can apply these principles without relying solely on professionally developed curricula. In accordance with the principles of a design experiment, curriculum and instructional methods were modified regularly throughout the intervention. Findings included insights into how written responses to historical thinking questions do not adequately reflect the complexity of thinking students are able to communicate in small-group discussions; the importance of social interactions in developing these critical reading skills; and a framework of instructional design for teachers who wish to use historical thinking strategies to promote critical reading of contemporary informational texts. In particular, one of the more successful modifications was the reconfiguration of the sourcing task from its traditional presentation in a historical thinking curriculum as a reading task featuring six constant factors to consider. An informal assessment of historical thinking conducted prior to and after the intervention showed a significant increase in students' ability to think historically.
The Ambiguity of Nuclear Commitments
Keywords: CISAC
Center for International Security and Cooperation
Stanford University
nonproliferation
North Atlantic Treaty Organization
nuclear sharing
Firestone Medal Award
Thesis

Since the 1950’s, the United States has engaged in nuclear sharing with its NATO allies. However, the Nuclear Nonproliferation Treaty (NPT) prohibits the transfer of nuclear weapons to non-nuclear weapon states. Thus, there has been a debate over the effect of nuclear sharing on the NPT. This thesis finds that nuclear sharing originally strengthened the NPT by discouraging proliferation by West Germany. However, U.S. efforts to preserve NATO’s pre-existing arrangements produced ambiguity in Articles I and II. This ambiguity has since limited the scope of debates over the legality of nuclear sharing at NPT Review Conferences. However, the potential release of U.S. tactical nuclear weapons to NATO allies constitutes the main source of contention between NATO and the NAM in these debates. Security reasons for keeping the weapons are tenuous: their presence is not necessary to discourage Turkey from developing nuclear weapons if Iran acquires them and their role in reassuring Eastern European NATO allies and deterring Russia is limited. Moreover, there are major flaws in relying on the weapons for reassurance and extended deterrence against Russian threats to cyber security, energy security, and political stability. The implication of this thesis is that NATO’s nuclear sharing arrangements undermine the NPT by setting a precedent for other countries to engage in similar practices and hindering Turkey’s goal of building a Nuclear Weapons Free Zone in the Middle East. Projecting forward, the U.S. could explore alternative avenues for reassuring its NATO allies and negotiate reciprocal reductions in tactical nuclear weapons with Russia.
The British Aren’t Coming: Why the French Intervene in their Former African Colonies and the British Do Not
Keywords: Center for International Security and Cooperation
British history
French history
British foreign policy
French foreign policy
Africa
post-colonial
military intervention
Thesis

Despite close parallels throughout their imperial histories, Britain and France have diverged greatly in how often they have intervened in former African colonies since independence. In this thesis, I explore how the nature and frequency of military interventions is directly rooted in the histories of the empires themselves, including imperial governance, decolonization, and post-colonial regimes. Through case studies of some of the most recent and prominent interventions for each country (Sierra Leone in 2000 for Great Britain; Côte d’Ivoire in 2002 and 2011 for France), as well as instances of non-interventions, I show how colonial legacies play a direct role in determining intervention. Although neo-colonial links and legacies have a significant and expected impact for France through its network of “Françafrique,” their influence on the British is subtler. History shows us that Britain did not value its African empire as much as France did, and consequently it intervened there less. Nonetheless, Prime Minister Tony Blair’s Doctrine of the International Community, under which the Sierra Leone and other interventions took place, had subtle neo- imperial undertones, suggesting a different kind of colonial legacy. This legacy has been indirectly continued across party lines by the government of Prime Minister David Cameron. Additionally, I find that interventions to protect certain postcolonial interests, such as significant expatriate populations, might elicit a swift, but limited, response that then evolves into a more robust mission. Other legacies, like regional military presence, facilitate interventions once decided or preclude their possibility. Finally, I conclude that assumptions that the international community can rely on former colonial powers to shoulder the military burden in Africa is inaccurate, having never been the case for Britain and decreasingly so for France, as it shifts to a less neo-imperial attitude toward Francophone Africa.