VictorJuiz/thesis huggingface dataset:
Patterns and determinants of landscape scale foliar functional variation in diverse tropical tree communities [electronic resource]
Keywords: Environmental Earth System Science.

More than half the species on the planet, and over 90% of all tree species, are found in tropical forests. However, the mechanisms that enable hundreds to thousands of competing tree species to co-exist in tropical forest communities remain poorly understood. Plant biodiversity is expressed not only in the taxonomic differences among species, but also in patterns among functional traits which contribute to their ecological success and among the phylogenetic and environmental determinants of functional trait variation. However, studies of plant functional diversity are rarely conducted with sufficient coverage or spatial scale to capture the influence of spatially-explicit environmental filters and derive patterns from highly heterogeneous tropical forest communities. This dissertation elucidates patterns of functional trait variation across spatial, phylogenetic, and environmental gradients in order to investigate how functional diversity may convey information on the community assembly mechanisms operating within tropical tree communities. Chapter 2 focuses on identifying patterns of functional trait co-variation among a community of tropical canopy trees on Barro Colorado Island, Panama (BCI). We find that two key axes relating to foliar resource allocation and anti-herbivore defense strategies describe over half the variation among 345 canopy trees across eleven functional traits. Chapter 3 explores the phylogenetic basis of variation among the foliar traits and spectral reflectance properties of tropical tree communities which span a range of environmental gradients. We find that the importance of phylogenetic relatedness in driving differences between species depends critically on environmentally-mediated trait variation. In Chapter 4, we evaluate the extent to which functional trait axes can be mapped using remotely-sensed imaging spectroscopy. We produce maps of functional variation for the tropical tree community of BCI, and evaluate the role for environmental gradients in generating patterns of strategic variation among canopy trees across the island. Through the identification of important dimensions of functional, phylogenetic, and environmental variation and the elucidation of relationships among these dimensions, this dissertation contributes to our understanding of the determinants of species co-existence in high diversity tropical plant communities at scales relevant to the expression and maintenance of tropical biodiversity.
Payment Schemes in Online Marketplaces: How Do Freelancers Respond to Monetary Incentives?
Keywords:  Department of Economics
Stanford Department of Economics
Upwork
Online Freelancing
Incentives for Employees
Hourly Wages
Performance-Based Bonuses
Reputation Scores
Job Success Scores
Thesis

The rise of online labor marketplaces has allowed employers to hire freelancers around the world to perform various tasks. Though effective incentive schemes are important in any labor market, they are particularly valuable in these marketplaces, as employers are unable to directly monitor their freelancers’ behavior to ensure that the freelancers are spending their time productively. This presents a challenge for all employers, but especially those who pay by the hour, as they do not want to pay freelancers for time spent working on other tasks or not working at all. I conduct an experiment on Upwork, the world’s largest online freelancing platform, to determine how freelancers respond to a simple monetary incentive that gives them the opportunity to earn a bonus for outperforming a benchmark. I examine how this incentive affects the quality and quantity of work, as well as how responses to the incentive differ based on a freelancer’s measurable characteristics. I find that for the group of freelancers as a whole, incentives do not have a significant effect on performance. However, it seems that this is due to the fact that different sub-groups of freelancers have opposite reactions to the incentive. Freelancers with low reputation scores respond by increasing the quantity of output and improving the accuracy of their work, while freelancers with high reputation scores respond by decreasing the quantity of output, with accuracy that does not significantly increase.
Peak
Keywords: feedback
performance management
feedback conversations
feedback at work
adult learning
goal setting
self-reflection
metacognition
self-assessment
feedback intervention theory
deliberate practice
protege effect
Thesis

Feedback is instrumental for improving performance. In professional environments, feedback has the potential to drive both organizational and individual development. Yet performance management processes are largely ineffectual. Extensive research demonstrates that individuals on both leadership and employee levels lack confidence in existing feedback processes. Peak is a mobile app for professional teams that seeks to transform the way we give, receive, and perceive feedback at work. Rooted in learning science theory, Peak teaches users to define goals that pave a clear pathway for growth, to self-assess performance and progress, and to construct feedback that is informative and conducive to learning. We integrated learnings from academic and user research to design an experience that is 1) mobile, 2) integrated, 3) collaborative, 4) scaffolded, 5) adaptive, 6) ongoing, and 7) personal. We have tested chunked segments of Peak and propose next steps to continue to increase its potential for impact. Our hope is that in putting Peak in the hands of all members of a team and integrating it into everyday work processes, it will push out an organizational culture of feedback and truly transform feedback at work.
Peons, prisons and probation [electronic resource] : the criminalization of the Mexican immigrant in Fresno County, 1880-1930
Keywords: History.

Between the years 1910 and 1930 Fresno County, situated in California's Central Valley, witnessed a tremendous upsurge in the number of Mexican immigrants seeking opportunity and employment in the rich agricultural zone enclosed by the Sierra Nevada and Coastal mountain ranges. Fresno attracted a great number of Mexicans during the years of the Mexican Revolution, and experienced the greatest percentage increase of Mexicans per capita than any other California county in the same period. Although farmers throughout the county welcomed them for their cheap labor, they were otherwise perceived as a problem by a White culture predicated on a racial hierarchy. Indeed, once Mexican immigrants stepped away from fields and out of the role as workers they became a nuisance and even a menace—a menace unfit for citizenship, and rather incarceration. In the aftermath of the American Civil War, southern Whites trekked into the Fresno area to make a new home, establishing a "new south." Beginning in the late 1860s migration from the southern states into Fresno County continued well into the early twentieth century. These southern migrants were essential in creating a culture in early Fresno founded on notions of White superiority. They built and worked the land where only deserts and swamps once thrived; they harnessed the waters of the mountains and created a veritable agricultural paradise—a White paradise with defined niches and little room for what they perceived as lesser, darker races. In the dynamics of power in Fresno County the ability to inflict legal punishment was wholly vested in the hands of White gatekeepers. Unlike other immigrant destinations in California such as Los Angeles, Santa Barbara, San Diego and the Monterey area, Fresno County did not have a substantial Spanish and Mexican past. Before the advent of irrigation in the late nineteenth century there was no reason to settle the Central desert region. Fresno was not founded on the site of a Mexican town with the typical Spanish plaza centered between the main church and municipal buildings. This meant that Mexican immigrants that came into the County in the early twentieth century came into an area that was totally foreign -- they came as strangers into an alien land. Without a local history to reference, the vast majority lacking education, and without the support of Californios to at least engage with the anti-Mexican discourse of the day, Mexicans lacked the power to combat their demonization and harsh treatment by the Fresno County justice system. This dissertation is concerned with the Mexican immigrant at the periphery of society who, for various reasons, committed a crime and was dealt with by an early twentieth-century justice system in Fresno, California. Of particular interests are how Mexicans were treated by the criminal court and how their sentences compare with similar cases involving Whites. Over seven hundred criminal court cases from the Fresno Superior Court archives provide the foundation for this examination.
Performative modernity [electronic resource] : Shanghai style Peking opera in pre-war Shanghai, 1872-1937
Keywords: East Asian Languages and Cultures.

My dissertation explores the dynamic relationship between Chinese theater and the city of Shanghai between 1872 and 1937, and its wider effects on Chinese modernity. Peking opera, a hybrid art form of singing, dancing, acrobatics, and storytelling, is generally thought as having two characteristics: a traditional art form and an art that is closely tied to the city of Beijing. However, such an understanding fails to take into account a series of exciting developments that occurred to Peking opera in Shanghai. During 1872 and 1937 in Shanghai, the constant negotiations about the form, the content, and the purpose of Peking opera—along with the changing mechanisms of cooperative authorship, the emergence of a mass-media based critical community, an expansion of thematic subjects treated, and the audience's new multi-faceted engagement with the opera—all point to a complicated epistemology that emerged concurrently with Shanghai's urban transformation. My study argues that Peking opera in its current form was fundamentally created in the cosmopolitan and concession-based city of Shanghai at the turn of the twentieth century, motivated by the emergence of Chinese modernity. Moreover, Peking opera in turn shaped Chinese modernity and helped form the cultural and political identity of Shanghai.
Phase change optical antennas [electronic resource] : applications of germanium antimony telluride for the dynamic control of light
Keywords: Electrical Engineering.

As materials are reduced from bulk quantities to micron or sub-micron dimensions, remarkable changes in the optical properties of these materials appear. Over the past several decades, the physics of these small structures has been studied, leading to a host of novel ways to control light. The devices which achieve this control are referred to as optical antennas, in analogy with their radio-frequency counterparts. In this thesis, we illustrate a model for understanding the optical properties of antennas fabricated out of dielectric materials using conventional semiconductor processing methods, such as etching or lift-off. This model, which operates faster than standard brute-force full-field simulation methods, reveals the existence of two classes of Fabry-Perot type resonances in such structures. Knowledge of these separate modes enables us to manipulate them using the properties of adjacent materials, including the substrate on which the antenna is placed. After developing this theory, the intuition is applied to the design of antennas using so-called phase change chalcogenide materials - that is, the alloys of germanium, antimony, and tellurium. These materials show uniquely large refractive index contrasts in the near- to mid-infrared bands of the electromagnetic spectrum. While previous studies have applied films of these materials near established optical device designs, our project demonstrates the first individual, patterned phase change optical antennas. The antennas perform remarkably well, allowing the post-fabrication tuning of an optical resonance over a free spectral range, from 3.2 to 4.5 um. Finally, from our experience developing these antennas, we propose and fabricate a second generation of phase change optical antennas. The newer design is based on coupled metallic nanorods, and enables independent optimization of the phase change and optical behavior of the antenna device. We show a proof-of-principle experiment in which the resonances of such antennas are also tunable post-fabrication, and we suggest a path towards measurements on individual, electrically-controlled devices.
Photoinactivation of bacteria [electronic resource] : effects of physiology, water conditions, and sunlight intensity
Keywords: Civil and Environmental Engineering.

Declining water quality along the world's coastlines threatens ecosystems and human health. Exposure to coastal waters polluted with pathogens from wastewater causes in excess of 120 million gastrointestinal and 50 million severe respiratory illnesses globally each year. In those coastal environments, field observations suggest sunlight is one of the most important factors modulating pathogen concentrations; however, there is an imperfect understanding of the extent to and the manner in which sunlight damage the pathogens. This dissertation aimed to link several physical and biological factors to the decay efficacy of bacteria by sunlight. The findings from this dissertation will improve our ability to forecast fecal indicator bacteria concentrations, design proper mitigation strategies for pathogenic bacteria, and overall reduce risk to public health. The work for the dissertation was organized into five research chapters. The first research chapter focused on the potential of the yellow carotenoid pigment in Enterococcus to provide protection from sunlight, first through field observations then through direct laboratory measurements. The second research chapter further explored the biological factors affecting photoinactivation, where it was found that the physiological state of the Enterococcus faecalis cells upon the application of the solar irradiation affected the photoinactivation kinetics. The work presented in the third and fourth research chapters began to link some biological factors with the physical factors of the water, specifically the presence of exogenous photosensitizers. These two chapters use a wide range of health relevant bacteria (8), photosensitizers (5), and types of sunlight (2), which allowed for a greater breadth of analysis. Through this greater breadth, it was found that the bacterial membrane, photosensitizer properties, and degree of UVB light intensity determined the contribution of the exogenous mechanism to the overall bacterial photoinactivation. The last research chapter started to bridge the gap between the laboratory and the field, finding that a simple linear regression model based on UVB light intensity could largely predict inactivation rate constants in natural waters of any depth and absorbance. Taken together, the results form this work provide insight into the mechanisms of photoinactivation, potential applications of models to predict photoinactivation kinetics, and design factors for engineered systems utilizing sunlight.
Physical and biogeochemical constraints on hexavalent chromium generation within soils and sediments [electronic resource]
Keywords: Environmental Earth System Science.

Hexavalent chromium (Cr(VI)) is an emerging contaminant of the twenty-first century of critical importance for human and ecosystem health. As our understanding of known Cr(VI) sources expands from industrial point sources to include pristine soils and sediments throughout the globe, this contaminant poses a dramatic threat to Earth's surface and groundwaters. Given the potential for naturally occurring Cr(III)- minerals to transform into toxic and highly mobile Cr(VI) within unperturbed aquifers, determining the processes responsible for Cr(VI) concentrations is critical to predict release and assess future human health risk. Within this thesis, I first evaluate Cr(VI) groundwater concentrations throughout California to investigate how industrial activity and shifts in land/water use patterns enhance Cr(VI) generation relative to native rates. Next, I explore the mechanism of Cr(VI) oxidation within physically-structured soils and sediments and examine the competitive microbial and geochemical processes that govern Cr(VI) generation and transport. Finally, I show how Cr(VI) groundwater concentrations are ultimately constrained by the physical heterogeneity in soils and sediments and fluctuations in hydrologic conditions. This research combines geospatial analysis, dynamic laboratory microcosms, and reactive transport modeling to investigate the controls on Cr cycling within the environment. Together, this multi-scale investigation of Cr(VI) generation and transport enhances our understanding of geogenically-sourced hexavalent chromium and shifts our understanding of contaminant release within aggregated soils and sediments. I provide the first direct evidence of Cr(VI) production within physically structured sediments and constrain how changes in physical and hydrologic conditions govern Cr(VI) groundwater concentrations. This knowledge not only allows us to better predict regions susceptible to hazardous Cr(VI) concentrations, but also transforms the way we interpret the release of redox active contaminants and nutrients within the subsurface environment.
Physical and chemical tuning of electrocatalysts for renewable energy applications [electronic resource]
Keywords: Applied Physics.

With rising concerns over the environment and the need for sustainable energy sources, the development of highly efficient electrocatalysts for renewable energy conversion processes, such as in water splitting electrocatalysis and fuel cells, is becoming increasingly important. Instead of discovering different types of new catalysts as in traditional approaches, my PhD study was focused on developing novel methods to systematically tune the morphologies and electronic structures of existing catalysts, and thus significantly improve their catalytic activities. The first chapter gives a brief introduction of renewable energy technologies including clean H2 generation via water splitting and fuel cell catalysis. Basic principles in H2O-H2-O2 electrocatalysis system, including the reaction mechanisms, design principles of catalysts, as well as the characterization methods, are presented. In the second chapter I demonstrate the morphology tuning of two-dimensional (2D) MoS2 for hydrogen evolution reaction (HER). Instead of synthesizing MoS2 with layers lying flat on the substrate as most previous studies presented, I used rapid sulfurization method to kinetically force the 2D layers to vertically stand on the substrate, which maximally exposes the HER active edge sites on the surface. This unique structure presents no change when synthesized on curved surfaces in high surface area substrates. In addition, the S-edge sites were further activated by doping with transition metals, which successfully doubles the MoS2 HER activity. The tuning of MoS2 layer orientation also provides great inspirations in designing high-performance Li-ion batteries. Chapter three includes the electrochemical tuning of electronic structures and morphologies of catalysts for improved water-splitting catalysis. The unique crystal structure of 2D materials allows guest ions to be intercalated or extracted between the molecular layers, opens up great opportunities to continuously tune the electronic structure of catalysts for optimized activities. Combining with Li-ion battery technologies, I intercalated Li ions into MoS2 catalyst, reducing the oxidation states of Mo and also inducing the 2H to 1T phase transition, which dramatically improves its HER activities. Inspired by this successful demonstration, Li ions were extracted out of LiCoO2 to tune up the oxidation state of Co and thus greatly improves its oxygen evolution reaction (OER) activities. In addition, a highly active bifunctional catalyst for overall water splitting was obtained by treating transition metal oxide (TMO) catalysts with Li-ion battery cycling process which transforms monocrystalline particles into interconnected ultra-small nanoparticles.
Physical modeling of particle and chromosome dynamics in living cells [electronic resource]
Keywords: Chemical Engineering.

The cellular cytoplasm is a complex, viscoelastic medium whose properties result in a rich spectrum of transport behaviors for the biomolecules moving within it. Disrupting the organization of this medium can lead to a wide variety of disease states or even the death of the cell, thus a fundamental physical understanding of these effects could guide novel strategies for the treatment of infection and disease. Our work develops physical models to better predict the consequences of the intracellular medium on biomolecular motion and interpret the results from experimental particle tracking data of RNA-protein particles and chromosome loci in living cells. We employ Brownian dynamics simulations to investigate the effects of macromolecular crowding and finite sample sizes on the observed particle trajectories. We find that RNA-protein particles inside cells exhibit non-Gaussian behavior in addition to subdiffusive dynamics. We also show that relatively simple dynamic polymer models can describe the motion of chromosomal DNA inside bacterial cells during segregation and use this same framework to predict the dynamic correlations between two connected loci.
Pick up the pieces [electronic resource] : combining information from multiple genetic loci
Keywords: Biology.

In this dissertation, I consider problems related to the accumulation of information from many genetic loci. The first chapter gives mathematical bounds on Wright's fixation index, a statistic used to measure the degree of genetic differentiation between populations at a genetic locus, in terms of two statistics that measure the degree of genetic variability at a locus: the frequency of the most frequent allele and the homozygosity in the total population. In the second and third chapters, I develop a model for understanding the relationship between neutral genetic divergence and differentiation between populations on neutral quantitative traits, finding, in agreement with previous work using different models, that the degree of differentiation on a neutral quantitative trait is expected to reflect the degree of differentiation at a single neutral locus. The second chapter uses a model based on the simple model for allele-frequency difference of Edwards (2003), and the third chapter extends the model to consider arbitrary allele-frequency distributions and arbitrary ploidy. Chapter four contains a review of some choice results from population genetics relevant to the design and interpretation of genetic association studies, in which one seeks to uncover genetic loci statistically associated with a disease or trait. The fifth and six chapters consider population-genetic properties of the CODIS (Combined DNA Index System) markers, which are used for forensic identification in the United States. In the fifth chapter, we consider the degree of information about population membership available at the CODIS loci. We find that the degree of population information at the CODIS loci is typical for tetranucleotide-repeat microsatellite markers and that across a broad sample of markers, population-membership information is correlated with the degree of heterozygosity at the loci considered. In the sixth chapter, I propose a method for linking genetic datasets when individual identifiers are unavailable and apply the method to a set of CODIS genotypes from a worldwide sample.