VictorJuiz/thesis huggingface dataset:
The effect of teacher qualifications on student achievement gains: evidence from the fundesola schools in Brazil, 1999-2003
Keywords: teachers
teacher effectiveness
teacher qualifications
learning outcomes
student achievement
Brazil
Fundo de Fortalecimento da Escola
Stanford Graduate School of Education International Comparative Education
Thesis

It is recognized that teachers have a crucial role in improving learning outcomes. Because quality differs by teacher, their potential impact on student outcomes may also differ. However, measuring teacher quality and its influence on learning has been challenging in educational research. In this paper I explore the effect of teacher qualifications on the rate of learning in Mathematics and Portuguese in Brazil. Drawing on longitudinal data from the Fundo de Fortalecimento da Escola (FUNDESCOLA) program from 1999 to 2003 and using a dose-response analysis and a latent trait model, I conclude that teacher qualifications positively influence the pace of learning in Mathematics. However, results for Portuguese were not significant, which may indicate that subjects require different models of teacher effectiveness. Also, I find that students’ socioeconomic status does not enhance the effect of teacher qualifications on the pace of learning in Mathematics and Portuguese.
The Effects of Relative Age on Early Childhood Academic Achievement: How They Differ Between Gender and Change Across Time
Keywords:  Department of Economics
Stanford Department of Economics
human capital investment
relative age effects
kindergarten entrance cutoff age policy
redshirting practice
early childhood academic achievement
Thesis

Gary Becker argues that a person should make investments in human capital as early as possible because he will thereby maximize the period over which the investment pays out. Also, the pay out period will be less discounted, and a person's opportunity cost of time is lowest when he is young. However, this theory does not provide much guidance on what is the optimal age to enroll children in formal education. At that point, there are two concerns: (i) whether the child is learning more at home than he would at school and (ii) whether his age relative to his peers is such that he would learn more given his aptitude. Relative age has recently become a controversial issue because some parents now deliberately enrolled their children a year after they are eligible to start school, in the hope of giving them a permanent learning advantage. This is known as redshirting. There is little robust quantitative evidence on how relative age affects learning and whether the effects differ by gender or parents' education. I examine how relative age affects achievement using the nationally representative ECLS-K longitudinal survey. Because relative age could be endogenous to parents' observations of their child's maturity, I construct instrumental variables for relative age based on state-level policies of kindergarten entrance age cut-off dates. I find that the relative age has a positive effect from kindergarten through grade five in reading and from kindergarten through grade eight in math. I find little evidence of the permanent effect for which redshirting families hope. The relative age effect is greater for females and for children whose parents are more educated. The latter result suggests that children with more educated parents learn more at home than do other children.
The Efficacy of Booster Seat Laws in Reducing Injury and Mortality: Estimating the Effects on Children and Testing for Compensating Behavior
Keywords:  Department of Economics
Stanford Department of Economics
Peltzman effect
child safety restraint
KABCO scale
Thesis

Motor vehicle accidents have been the leading cause of death for children and youth for decades. Booster seats are designed to better protect children four to eight years old in the event of an accident, and over the past decade, forty-seven states and the District of Columbia have passed laws mandating their use. In this paper I estimate the effect that booster seat laws have on reducing injury and mortality among five- to eight year-old children, using data from the WISQARS cause of death database for the years 1999 to 2007 as well as from FARS fatal crashes database from 1994 to 2009. In addition to estimating the direct effect on children, I also test for compensating behavior among older age groups, who may change their behavior due to the perception of diminished risk to their children while driving. My findings indicate that there is a nearly 25% decrease in mortality among six-year-olds covered by booster seat laws, but that there is no statistically significant effect on five-, seven-, or eight-year-old mortalities. I also find that there is evidence of compensating behavior among older drivers, and that the estimated total increase in deaths among older drivers exceeds the number of lives saved among children.
The Veil of Communism: An Analysis of Lifespan, GDP per Capita, Human Capital, and Agricultural Productivity in Eastern Europe
Keywords:  Department of Economics
communism
economic growth
GDP per capita
human capital
labor to land ratio
ratio of unskilled to skilled workers
lifespan
expenditure per student
Stanford Department of Economics
Thesis

There is a clear economic difference between the more economically-developed Western Europe and their poorer counterparts in Eastern Europe and central Asia. But what caused this economic divergence? How big of a role did communism play? If communism is responsible, through what economic mechanisms did it manage to hinder growth? This paper will look at GDP/capita, growth in GDP/capita, human capital, labor to land ratio, ratio of unskilled to skilled workers, growth in lifespan, average expenditure per student and variations in these outcomes in order to determine a more specific impact of communism. This paper finds not only that communism had a huge negative impact on growth, but that even though communism was completely gone from Europe by 1991; it still impacts the growth of former communist countries. Moreover, there seem to be 2 blocks of countries within the communist bloc: non-Soviet Central and Eastern Europe and Soviet Eastern Europe and Central Asia and these two regions behave very differently.
The War on Whooping Cough: The Impact of Prevalence Elasticity and State Policies on Vaccination Behavior
Keywords:  Department of Economics
Prevalence elasticity
pertussis
vaccination
immunization
rational disease dynamics
Stanford Department of Economics
Thesis

According the theory of prevalence elasticity of disease, the demand for preventative care (e.g. vaccination) against a disease increases with the prevalence of that disease. In light of this theory, I will look at pertussis incidence over the past three decades within the United States. Over this time period pertussis (also known as whooping cough) has increased in prevalence among certain age cohorts, particularly the adolescent cohort. This prevalence increase has been attributed by many to an antivaccine movement which created holes in vaccination coverage. In an attempt to curb these epidemics, states have instituted mandatory vaccination policies for school children entering preschool and kindergarten, and some states are also beginning to require a booster vaccine for entry to middle school. Since these policies target specific age cohorts, I look at pertussis prevalence and vaccination behavior amongst both the adolescent and infant age groups. Using three econometric methods, I identify the effects of prevalence elasticity, mandates, and the anti-vaccine movement on vaccination behavior, and draw policy recommendations from these empirical findings. I observe low prevalence elasticity, likely the result of the anti-vaccine movement, and therefore recommend a larger role for mandated vaccination.
Thermal and mechanical phenomena in aligned carbon nanotube films [electronic resource]
Keywords: Mechanical Engineering

Efficient heat conduction is critical to the performance and reliability of a variety of devices. To ensure efficient heat removal from electronic devices, thermal interface materials (TIMs) are used to enhance heat conduction between two contacting surfaces. Ideal TIMs have high thermal conductivity, conform to the microscale roughness of the surfaces in contact, and accommodate stresses due to mismatch in thermal expansion coefficients. Commercial TIMs exhibit a tradeoff between these desired thermal and mechanical properties. Vertically aligned carbon nanotube (VACNT) films have great promise as TIMs because they have high through-plane thermal conductance and mechanical compliance. VACNT films are typically composed of a complex, entangled network of CNTs and the density and alignment of CNTs within a film affect its mechanical and thermal properties. Given the variety of growth techniques and variations in film morphology, it is important to understand how these factors influence film behavior. The present work combines three major aspects of VACNT film characterization: mechanical and thermal characterization, analysis of the film microstructure, and modeling of the film properties. The inhomogeneous VACNT film morphology is investigated by using image analysis to quantify CNT alignment and density and by measuring the elastic modulus at the top and bottom film surfaces using nanoindentation. The alignment and density information is input into a model of the mechanical response of the VACNT film, which is compared to measured data. The through-plane thermal properties of VACNT films are measured using thermoreflectance techniques. Multiwall VACNT films are grown directly on a thermoelectric material and the thermal properties of the films are characterized using nanosecond thermoreflectance. A set of eight single-wall VACNT films are measured using frequency domain thermoreflectance to extract four relevant thermal properties: thermal conductivity, heat capacity, and the upper and lower boundary resistances.
Thermal phenomena in nanostructured materials & devices [electronic resource]
Keywords: Mechanical Engineering

Nanostructuring leads to unique material properties and combinations of properties not naturally available in bulk materials. The study of these properties is critical to improving the device performance and reliability for a range of applications including electronics, thermoelectrics, and nanophotonics. This work focuses on efforts to push the thermal conductivity of nanostructured materials to the extremes: the thermal conductivity of carbon nanotubes (CNT) and nanotube-based materials can exceed that of metals, while the introduction of nanoscale boundaries (e.g. nanoscale pores in silicon nanowires) yields extremely low thermal conductivity materials. Furthermore, this nanostructuring also leads to unique combinations of properties. Porous silicon nanowires are a step towards the desired electron-crystal, phonon-glass combination ideal for thermoelectric applications, while thermally-conductive, mechanically-compliant carbon nanotube films for promising for electronics packaging. This work first explores how the high axial thermal conductivity of carbon nanotubes can be leveraged effectively in thin film and composites through detailed understanding of the phonon transport and measurements of CNT-based films. This work then investigates how nanostructuring silicon significantly reduces the thermal conductivity through enhanced boundary scattering and the possibility of phononic crystal effects. Specifically, measurements of individual, porous silicon nanowires and arrays of silicon nanowires show significant reduction in the thermal conductivity compared to bulk silicon. A detailed model for reduced thermal conductivity due to phonon boundary scattering is developed in conjunction with measurements. Finally, this work also examines how the composition and annealing conditions impact both thermal transport and photoluminescence in silicon-rich silicon nitride films.
Tie-simplex method for thermal-compositional simulation [electronic resource]
Keywords: Energy Resources Engineering

Enhanced Oil Recovery (EOR) processes usually involve complex phase behaviors between the injected fluid (e.g., steam, hydrocarbon gas, CO2) and the in-situ rock-fluid system. Equation-of-State (EoS) computations for complex mixtures than can form three, or more, phases at equilibrium pose significant challenges. In addition, issues related to proper coupling of the thermodynamic phase-behavior with multi-component transport across multiple fluid phases must be resolved in order to model the behaviors of large-scale EOR processes accurately and efficiently. Here, we propose an EoS-based tie-simplex framework to deal with the thermodynamic phase behavior, in which an arbitrary number of phases can form. It is shown that our generalized negative-flash method yields the unique tie-simplex parameterization of the compositional space. Specifically, we show that the tie-simplexes change continuously as a function of temperature, pressure, and composition. In the course of a thermal-compositional simulation, the compositional space is tabulated adaptively using tie-simplexes. We also prove that the Gibbs free-energy analysis of this tie-simplex space is equivalent to conventional methods for equilibrium phase calculations. This multiphase tie-simplex method is integrated into Stanford's General-Purpose Research Simulator (GPRS), and its application to thermal-compositional simulation is demonstrated here using several challenging thermal-compositional flows with complex phase behaviors.
Topics in sparse multivariate statistics [electronic resource]
Keywords: Statistics

In this thesis, we visit three topics in modern sparse multivariate analysis that has received and still continues to receive significant interest in applied statistics in recent years: (a) Sparse high dimensional regression (This work appears in our paper Mazumder et al 2010.); (b) Low-rank matrix completion \& collaborative filtering (This work appears in our paper Mazumder et al 2011) and (c) Sparse undirected gaussian graphical models. (This work appears in our papers Mazumder and Hastie 2012 and Mazumder and Hastie 2011). A main challenge in high dimensional multivariate analysis is in developing scalable and efficient algorithms for large scale problems that naturally arise in scientific and industrial applications. This thesis explores the computational challenges that arise in these problems. We develop and analyze statistically motivated algorithms for various models arising in the aforementioned areas. This enhances our understanding of algorithms, sheds novel insights on the statistical problems and leads to computational strategies that appear to outperform state of the art. A salient feature of this work lies in the exchange of ideas and machinery across the fields of statistics, machine learning, (convex) optimization and numerical linear algebra.
The topology of spaces of J-holomorphic maps to CP² [electronic resource]
Keywords: Mathematics

In [Seg79], Graeme Segal proved that the space of holomorphic maps from a Riemann surface to a complex projective space is homology equivalent to the corresponding continuous mapping space through a range of dimensions increasing with degree. I will address if a similar result holds when other almost complex structures are put on projective space. For any compatible almost complex structure J on CP^2, I prove that the inclusion map from the space of J-holomorphic maps to the space of continuous maps induces a homology surjection through a range of dimensions tending to infinity with degree. The proof involves comparing the scanning map of topological chiral homology ([Sal01], [Lur09], [And10]) with gluing of J-holomorphic curves ([MS94], [Sik03]).
Towards a holographic framework for cosmology [electronic resource]
Keywords: Physics

Studies on black hole physics have lead to the holographic principle, which states that a quantum gravitational system can be captured by a theory living in fewer dimensions. Given the observed accelerating expansion of our universe, it has been a major challenge to understand the realization of the holographic principle in cosmology. In this dissertation we review our progress in building such a framework. Starting from concrete AdS/CFT dual pairs, we obtain de Sitter and other general FRW solutions by adding branes and other ingredients from string theory. In the de Sitter case, our brane construction gives a microscopic realization of the dS/dS correspondence. The degrees of freedom in the semi-holographic dual theory provide a parametric interpretation of the Gibbons-Harking entropy of the bulk de Sitter space. In the FRW case, we focus on a family of simple FRW solutions sourced by magnetic flavor branes. These solutions have a holographic dual interpretation which decouples from gravity at late time, opening up the possibility of a precise duality. Time-dependent effects play a crucial role in these dual theories. In particular, we find that time-dependent couplings in a quantum field theory can strongly affect long-distance physics, effectively shifting the infrared operator dimensions and generalizing known unitarity bounds.
Towards a precise theory of cosmology [electronic resource]
Keywords: Physics

In this thesis I discuss progress towards a precise mathematical description of cosmology and in particular of eternal inflation. I present a conjecture for a necessary condition for a spacetime to have a precise dual description, discuss how the dictionary of dS/CFT is more sophisticated than that of AdS/CFT, present a soluble model of eternal inflation that has a conformal boundary theory at future infinity, and discuss the implications of this model for a conjectured precise dual theory based on observers in bubbles with zero cosmological constant. The work described was done in collaboration with Leonard Susskind, Douglas Stanford, and Stephen Shenker.
Towards clinically relevant neural prostheses [electronic resource]
Keywords: Bioengineering.

Neural prostheses translate signals from the brain into useful control signals, manipulating end-effectors such as computer cursors or robotic arms. Their aim is to offer greater interaction with the world for patients suffering from limb dysfunction due to spinal cord injury, neurodegenerative disease, and other conditions leading to limb paralysis. Prior intracortical electrode neural prosthesis studies have demonstrated compelling proof-of-concept systems, but barriers to successful clinical translation still remain, such as performance and robustness. Measures of performance include the speed, accuracy, and bitrate of the system. Robustness refers to the sustained performance of the system within a day and across days. The work presented here demonstrates algorithms and advances for neural prostheses that increase both performance and robustness. The recalibrated feedback intention trained Kalman filter (ReFIT-KF) increased performance by at least twofold compared to previously reported decoders, approaching the speed of natural arm movements. It achieved bitrates of up to 4.5 bits per second (bps) and communication rates of up to 10 words per minute (wpm) when used on a typing task. These results were reliable and repeatable for hours at a time across 4 array-years between two subjects. Utilizing neural spike threshold crossings as a signal source, the ReFIT-KF algorithm also demonstrated sustainable performance without any changes to decoder weights for one year with a degradation rate of 0.05 bps per month. Performance further increased when the ReFIT-KF was combined with an HMM state decoder for the detection of clicks, eliminating the need for hold periods. This combined ReFIT-KF and HMM decoder achieved bitrates of up to 6.5 bps and 15 wpm. Taken together, these findings may help advance neural prostheses closer to clinical viability.
Towards monolithic semiconductor photonic crystal passively mode locked laser for two-photon microscopy [electronic resource]
Keywords: Electrical Engineering

Semiconductor Monolithic Passively Mode Locked Lasers (MMLLs) have been demonstrated and have a variety of applications including sensing, in optical communications and optical clock generation. The major advantage that these semiconductor light sources possess is their compact size, high efficiency, low cost and robustness. Also the ability to access different wavelengths using various semiconductor materials is a big advantage. The inability to get these lasers to operate at low repetition rates and the limited peak output power of the pulses are the two major limitations of these lasers. The repetition rate is inversely proportional to the semiconductor laser cavity length. The lowest repetition rate in current MMLLs is around 1GHz. This rate is limited by the complexity involved in the fabrication of centimeter long semiconductor laser cavities. The material loss, dispersion and carrier radiative recombination lifetime also limit the output repetition rate. Lower repetition rate lasers can be used in low frequency integrated optical circuits and also for imaging especially for Two-Photon Microscopy (TPM). TPM works by exciting florescence dyes using two photons instead of one. This requires pulsed lasers with high peak power and high energy per pulse. TPM is currently done by using expensive and bulky Ti:Sapphire mode locked lasers that can produce subpicosecond pulses at a repetition rate of order of 100 MHz. The possible use of semiconductor lasers for this application can transform this field by dramatically reducing the cost of imaging and allowing for dramatically smaller sized and more mobile imaging solutions. One potential way to reduce the repetition rate of the lasers without increasing the physical cavity length is to incorporate a slow light photonic crystal structure inside the lasers cavity. Such a laser cavity will have a group index that is much larger than the material refractive index thereby giving a longer optical path length for the same physical length of the device. The incorporation of the photonic crystal will also allow the possibility to do dispersion engineering within the laser cavity and to enable pulse compression. Both these effects can increase the two-photon excitation efficiency for TPM. In this work we highlight the design and progress towards the development of a monolithic semiconductor photonic crystal passively mode locked laser for two-photon microscopy.