116964 research outputs found
Sort by
N-path filter architectures for radio frequency applications
Get PDFThis research focuses on the design and analysis of N-path filters for radio-frequency applications. A switched-based N-path filter circuit can be employed for filtering an RF signal, as well as a passive downconverter. A known limitation of this filter is that in addition to downconverting signals from around the desired center frequency, the circuit also downconverts signals located around harmonics of the LO frequency. This can degrade the desired signal in the presence of interferers located around these harmonics. Two solutions that address the above limitation are described in this dissertation. First, an N-path filter using a pulse-width modulated representation of a sinusoidal LO to mitigate harmonic downconversion is described. Pulse-width modulated clocks are used to drive the switches in the N-path filter. The potential for employing pulse-width modulation for providing gain control is also described. The architecture is simulated and analyzed in a 65-nm CMOS technology. Second, a downconversion receiver employing a switch-based N-path filter embedded inside a harmonic-selective negative feedback loop is described. A pulse-width-modulated local oscillator (PWM-LO) is used in a feedback-path upconverter to reduce the noise injected by the feedback path circuits around the fundamental frequency of the local oscillator (LO) at the input of the N-path downconverter. While both architectures are effective in reducing the harmonic response, the second approach allows for using lower PWM clock frequency. The feedback-based architecture is implemented, measured and analyzed in a 65-nm CMOS technology. The design is shown to reject the harmonic response of the N-path filter. The compression resulting from blockers around the 3rd and the 5th LO harmonics is also reduced, by 2.3 and 6.9 dB, respectively, while the noise figure is observed to degrade by 2.1 dB through use of the technique. Parasitic capacitance at the input of the N-path filter is known to reduce the gain of an N-path filter while shifting its passband center frequency to a lower value due to residual charge retention at the input node, from one clock phase of the Npath filter to the next. A technique is demonstrated to correct for this source of error. An auxiliary capacitor with alternating polarity is used at the output of the N-path filter to reset the residual charge in the parasitic capacitance in each phase of the N-path filter clock. The auxiliary capacitor is included in the above feedback-based architecture. An N-path architecture with harmonic response suppression which also compensates for the peak frequency shift of the N-path response is implemented, measured and analyzed in a 65-nm CMOS technology. At f [subscript LO] = 500 MHz, peak shift is observed to be 5.5 MHz without compensation, with 2.8 pF auxiliary capacitance, the peak shift reduces to 2.6 MHz, and the noise figure degrades by 1.6 dB. The peak-shift is reduced by 0.7-3.3 MHz depending on the LO frequency with 2.8 pF auxiliary capacitance, while the noise figure is observed to degrade by 0.7-1.7 dB though the use of the peak-compensation technique. Through the use of the above approaches, an N-path filter can be employed as a downconversion receiver with considerably relaxed requirement for harmonic attenuation at the input node.Electrical and Computer Engineerin
Moroccan reef ecosystems : evolution and extinction in the Early Jurassic
Get PDFExtinctions in the Jurassic (201.3-145 million years ago) were foundational to the development of modern marine communities. One of the most severe reef collapses of the Phanerozoic is associated with two consecutive extinctions in the Early Jurassic: the Pliensbachian/Toarcian (Pl/To) boundary event and the Toarcian Oceanic Anoxic Event (T-OAE). This dissertation uses fossil data from Pliensbachian and Toarcian reef sites to reconstruct the ecology of reefs from intervals surrounding these two events to identify variability in how taxa responded to each biotic crisis. These data were used to determine if those differences could be explained by differing extinction drivers in each event. These reefs grew in tropical carbonate settings in the Central Atlas Basin, Morocco; an interval uniquely expanded, enabling us to thoroughly sample reefal units from multiple locations, chronostratigraphic units, facies, and stages of reef growth, from across the Lower Jurassic. A quantitative analysis of more than 250 thin sections provides data for an assessment of the specific structural and ecological changes that occurred as reefs evolved across the Pl/To and the T-OAE. Occurrence and percent composition data were used to quantify the differences in reef facies between extinctions. During the Pliensbachian, lithiotid bivalve reefs grew in lagoonal environments and coral, sponge, and microbialite reefs grew on the platform edge. An influx of nutrients and siliciclastics just after the Pliensbachian/Toarcian boundary caused a collapse of reef ecosystems. In the earliest Toarcian, lithiotids recovered more rapidly than other reef builders, which led to a shift in reef type to predominantly lithiotid biostromes immediately following the recovery of the carbonate factory. Coral, sponge, and microbial reefs were slower to recover from the Pl/To, but showed signs of reestablishment just before the onset of the T-OAE. The environmental changes associated with the T-OAE, such as siliciclastic influx and ocean acidification, resulted in the extinction of the lithiotids; in contrast, corals and microbialites recovered quickly, and coral and microbialite-dominated reefs returned to the platform within the interval of the T-OAE carbon isotopic excursion. This dissertation highlights the differential response of reef framework builders to Jurassic environmental changes and emphasizes that by understanding how past reefs responded to these changes, we can better protect modern and future reefs.Earth and Planetary Science
Worthy of safe haven : the politics of asylum in contemporary Brazil
Get PDFForced displacement worldwide has reached over 65 million for the first time in history. One in every 113 people on the planet is now an asylum seeker, refugee, or internally displaced. The current era demands our critical attention to forced migration in general, but also to asylum in particular. In 2015, two million people applied for asylum—more than any previous year on record. Under international law, asylum seekers are those who claim refugee status after migrating. Yet, as we know, refugee status is not freely chosen but decided by the state. Taking the case of Brazil, this dissertation asks: How does the state determine who qualifies for refugee status, and with what consequences? While there were 966 asylum applications in Brazil in 2010, this number reached almost 29,000 in 2015. Through 15 months of ethnographic fieldwork conducted inside the asylum apparatus, this study traced the perceptions, actions, and interactions—of and between state, civil society, and asylum-seeking actors—that lead to case decisions and constitute the refugee regime in Brazil. Research also entailed interviews, and analyses of asylum case documents and a case decision dataset. This dissertation investigates the logics of the refugee regime in Brazil. It argues that a series of thus-far-uncharted cognitive frames and epistemic practices are crucial to how asylum officials make sense of asylum seekers and evaluate their claims. Moreover, it asserts that the logics of refugee protection are racially configured and configuring by detailing the production of asylum seeker racial legibility and the racial inequalities that result. Finally, it contends that the confusing, piecemeal, and Janus-faced nature of the asylum process produces apathy about refugee status for those who seek and obtain it. In sum, this dissertation contributes to our understandings of the everyday workings of refugee status determination, and the consequences for those seeking safe haven.Sociolog
Exposure to little cigar/cigarillo marketing at the point-of-sale and use of little cigars/cigarillos and cigarettes among young adults
Get PDFIntroduction: There are little to no studies investigating the impact of objectively measured exposure to little cigar and cigarillo (LCC) point-of-sale (POS) marketing at tobacco retail outlets (TROs) on tobacco use. The aim of the present study was to examine the relationship between objectively measured exposure to LCC POS marketing and current and future use of LCCs and conventional cigarettes. Method: Data from the Marketing and Promotions Across College in Texas (Project M-PACT) study were used in the present study. Participants were 4,201 Texas young adults attending 24 Texas colleges. All LCC marketing at TROs within one mile of each of the 24 colleges was objectively documented and linked to the survey data. Separate multilevel logistic regression analyses examined the impact of LCC marketing at the POS on current and future (six months later) use of LCCs and cigarettes. All analyses controlled for age, sex, race/ethnicity, and type of college, and longitudinal models controlled for baseline use Results: Findings from cross-sectional analyses indicated that greater exposure to LCC POS marketing is associated with higher odds of current use of LCCs (AOR = 1.003, 95% CI = 1.0002, 1.0053) and cigarettes (AOR = 1.006, 95% CI = 1.0050, 1.0075). Specifically, for each additional piece of LCC marketing material observed, the odds of current LCC use increased by a factor of 1.003 and current use of cigarettes increased by a factor of 1.006. These findings did not hold in the longitudinal models. Exposure to LCC POS marketing at baseline predicted current cigarette use at 6-month follow-up, specifically, for each additional piece of LCC marketing material observed, the odds of current LCC use increased by a factor of 1.004. However, exposure to LCC POS marketing did not predict current LCC use at 6-month follow-up. Conclusion: Results demonstrated that exposure to LCC POS marketing is associated with higher odds of current LCC use as well as current and future cigarette use among young adults. This suggested a significant influence of LCC marketing exposure at the POS. Regulations on LCC POS marketing, especially around college campuses, should be considered.Kinesiology and Health Educatio
Bombs, Bots, and the Principle of Distinction: The Law of Armed Conflict and Contemporary Warfare
Get PDFCritics of autonomous weapons systems (AWS) argue that these weapons cannot reliably distinguish between legitimate targets and those protected from attack. As a result, the use of AWS seems to violate the principle of distinction under international humanitarian law (IHL), which requires that combatants “not make civilians the object of attack” and not carry out attacks that are “indiscriminate in nature.” This criticism, however, misunderstands the principle of distinction and ignores important aspects of how AWS are being developed and deployed. Critics rely on an overly broad definition of AWS, and hold these systems to a standard that is inconsistent with the principle of distinction as it is actually formulated under IHL. Despite their very real limitations, the characteristics of modern AWS in fact highlight an impressive feat of technological design, and mark a further step on our long and fitful road to making warfare a less brutal and bloody enterprise.LBJ School of Public Affair
Engineering polymers for advanced technologies
Get PDFPolymer science began in 1920’s with the work of Staudinger, coworkers and others who convinced the world of the existence of macromolecules and their value. Since that beginning, polymers have played an ever-increasing role in the advancement of society. Polymeric materials have had an important role in commodity applications and in high technology. These applications invariably require the design and optimization of new polymer materials and processes. The work in this dissertation focuses on the design of polymers for three important applications: characterization of oil reservoirs, enhanced oil recovery and efficient production of microelectronic devices. Magnetic nanoparticles are expected to have a major impact in subsurface crude oil exploration as contrast enhancing agents. However, the harsh subsurface conditions often lead to nanoparticle aggregation and retention in porous media. Polyelectrolytes are often used as stabilizers to nanoparticles against colloidal aggregation in such conditions. In chapters 2 and 3, the mobility of polyelectrolyte functionalized nanoparticles has been investigated. The effect of size and polymer architecture on transport was studied. The growing demand for oil has necessitated the need for advanced extraction techniques. Polymers are often used as viscosity modifiers in oil recovery to stabilize waterflood front and increase recovery. Incumbent synthetic polymers are however limited to low salinity and low temperature sandstone reservoirs owing to their weak polyelectrolyte nature. In chapter 4, synthesis and solution properties of high molecular weight non-ionic polyethers have been explored for flooding applications. Collapse of high aspect ratio (HAR) nanostructures (found in NAND devices, Capacitors and transistors) has been a high value problem in semiconductor industry. During fabrication steps such as cleaning, liquid environments are often encountered which result in surface tension forces, pulling them towards each other once the structural/material strength of the structures is overcome. In chapter 5, stimuli responsive depolymerizable materials are explored as bracing materials to prevent collapse of HAR structures.Chemical Engineerin
Structural behavior of reinforced concrete members with cold joints : characterization and modeling in disturbed regions
Get PDFThis dissertation investigates the structural behavior of reinforced concrete (RC) members with cold joints through a combination of analytical and experimental studies. The research comprises material-level and structural-level experiments, nonlinear finite element analyses, database evaluation, and development of STM-based analytical model and design recommendation. The major achievements of this work include identifying and quantifying influential parameters governing cold joint behavior, developing design recommendations for RC structures with cold joints in disturbed regions (D-regions), and formulating a mechanics-based constitutive model for cold joints suitable for implementation in advanced numerical analysis.
The study began with an extensive literature review and an industrial survey to identify critical variables and common design practices. An experimental program was subsequently developed, including both material-level and structural-level experiments. 54 slant shear specimens were tested to quantify the effects of six key parameters on cold joint behavior. Based on these findings, two full-scale experimental programs were conducted to evaluate cold joint behavior in two- and three-dimensional structural elements, including ten deep beams and one drilled-shaft footing cap. These experiments provided detailed information about the shear capacity, stiffness, stress distribution, and failure mechanisms.
Building on the experimental results, a mechanics-based numerical model for cold joints was developed, grounded in principles of equilibrium, constitutive relationships and compatibility of interface slip. The model was integrated into a nonlinear finite element analysis software, and its accuracy was validated against experimental observations.
According to the experimental and analytical results, a load-transfer model for cold joints in D-regions was developed by incorporating the interface shear mechanics into the Strut-and-Tie Method, effectively capturing the influence of critical design parameters on cold joint behavior. The proposed model was ultimately refined into a step-by-step design recommendation, providing a practical and reliable framework for evaluating RC structures in D-regions with cold joints.Civil, Architectural, and Environmental Engineerin
Multi-threaded attracting manifold adaptive control for aerospace systems
Get PDFAdaptive control has been used to provide closed-loop tracking guarantees for dynamic systems with unknown parameters. In such cases, estimates of unknown parameters are adapted over time and these estimates are used within a judiciously prescribed control law. As part of the adaptation, adaptation gains can be increased to accelerate the rate of convergence of these estimates to their true values. In practice, however, it is not prudent to simply increase learning gains as this can have the adverse effect of amplifying any unmodeled dynamics in a true system. As such, it has been the goal of adaptive control practitioners to design adaptive control structures which provide better performance for equivalent control gains. The Multi-Thread Attracting Manifold (MTAM) adaptive control methodology developed in this work seeks to provide an improved adaptive control framework through multiple design features. The first feature is the utilization of multiple threads. This allows for the unknown parameter space to be robustly sampled, rather than relying on a single estimate. Secondly, the adaptation of each individual thread is designed with an attracting manifold design which provides desirable "no-regret" learning. These features combine to provide an adaptive controller which outperforms existing single thread adaptive controllers with identical learning gains. In this work, the baseline methodology behind MTAM is presented first for classical adaptive control and parameter identification scenarios. Secondly, forms of MTAM which accommodate uncertainties attached to the control input in both direct adaptive control and indirect adaptive control cases are presented and shown to retain performance benefits through numerical simulation. Finally, a methodology for adding and removing threads is presented which decreases the marginal computational cost of the MTAM algorithm while still providing performance benefits over existing single thread architectures.Aerospace Engineerin
Race to equity : leadership, politics, and school disciplinary policies
Get PDFThis research addresses sociological questions aimed at enhancing our understanding of the sociopolitical contexts among macro-, meso-, and micro-levels that shape high school principals school discipline policies in the racial neoliberal state. This study is informed by three bodies of theory to guide research questions and the analysis of the data. Embedded with a concept of racial neoliberalism and its connection to discipline and punishment, as the foundation of the context of this research, this research uses Foucault’s (1977) notion of docile bodies as a fruitful theoretical lens for grounding the discussion of how institutionalized power works through punishment in shaping school discipline practices, and how high school principals negotiate their disciplinary practices under the pressure of the current accountability education system in an era of neoliberal market-based reforms. The structure of this research extends the ideas of sensemaking theory to provide a novel view on the interactions of various elements of institutionalized political constraints that shape high school principals’ disciplinary practices. Using convergent mixed methods in a single case study, I investigate the following: (a) how principals make sense of pressures, constraints, and incentives that shape disciplinary practices; (b) how principals negotiate competing pressures and expectations as they implement disciplinary practices; and (c) how principals’ sociocultural identities, principals’ belief systems and sociocultural contexts inform variations in both perceptions and implementation behaviors. The findings reveal that gentrification and immigration policies bring great concerns about students’ enrollment trends and students’ social-emotional well-being. Students’ enrollment trends not only shape demographic compositions in schools but also lead to different patterns of the use of discretionary disciplinary policies. Other factors, such as statewide disciplinary policies, accountability systems, and school finance policy also put pressures and constraints on high schools’ disciplinary practices. High school principals in Austin have experienced especially strong financial constraints and use different strategies to practice the most current alternative disciplinary practices with limited budgets, yet some strategies reinforced racial biases in the school system. Findings also show that regardless of the diverse beliefs about students’ behaviors, sociopolitical views, or religion, as long as school leaders have an awareness of racial biases in the school disciplinary system and have campus administrators and teachers support to changes in disciplinary practices, schools can effectively decrease unequal disciplinary decisions to students of color. This analysis offers several directions for educational leadership practices, education policy, and research.Educational Leadership and Polic
Exploring a language-modeling approach to jargon in genre-specific instructional texts
Get PDFThe use of jargon is far-reaching not only in technical domains such as medical or engineering, but also in non-technical ones targeting a broad audience. This work introduces a dataset and an investigation of jargon in 1,014 instructions for the Free Application for Federal Student Aid (FAFSA) across 341 post-secondary institutions in the US. These instructions are crucial for students in need of financial aid for higher education, thus require both precision and low barrier of entry. Using large scale pre-trained language models, we confirm the common-sense hypothesis that jargon tends tend to be less predictable than non-jargon in language models.Linguistic