VictorJuiz/thesis huggingface dataset:
Impact of distributed PV generation on grid operation [electronic resource]

Distributed photovoltaic (PV) generation is growing rapidly due to renewable-energy policies, business innovation, and new technology. The variability and volatility of solar generation causes challenges when operating the grid. Given the current physical infrastructure and operational policies this results in limits on distributed PV generation. What the limit is to the penetration of PV is studied by analyzing the behavior of distributed PV generation and a model of the load. We investigate how to represent the power output from distributed PV generation. We propose a reduced-form approach for constructing maximum PV power curves, which describe the maximum power from a group of PV systems at any time instance. Unlike a structural approach used typically by PV providers, the reduced-form approach requires no information about configuration or specification of each PV system in the group. We show how a grid operator can use maximum power curves in various applications such as finding a simple limit to PV installation, defining volatility distinctly from variability, and constructing a short-term PV power forecast system. A key requirement is a model of the load. Analogous to the maximum power curve, a load reference curve is proposed with a simple definition and shown to improve the performance of a short-term load forecast. Lastly, a simulation of the grid operation using our forecast systems and a typical set of existing infrastructures is performed to measure the risk of demand-supply imbalance. The maximum level of distributed PV installation given an acceptable level of risk is established. Options of adding additional ancillary services and implementing PV curtailment to increase the maximum level of distributed PV installation are also investigated.

Advisor: Murray Walter primary advisor. Thesis advisor
Entriken Robert
Weyant John P. (John Peter) advisor. Thesis advisor
The impact of diurnal solar patterns on indoor air mixing [electronic resource]

Outdoor weather changes characterized by solar and windspeed patterns can affect indoor air mixing and ultimately pollutant distribution in indoor spaces. This research focuses on the spatial distribution and turbulence characterization of a continuous point source inside a residential home under both quiescent and human-perturbed conditions. Laser particle monitors were arranged in two different 3D arrays between both quiescent and human-perturbed conditions in order to capture spatial and temporal distributions of PM 2.5. Cigarette effluent was released at the center of the room after source and ambient temperature readings matched, revealing a neutrally-buoyant source. This resulted in roughly 2-hour experiments with 20 minute emission times and a 1 hour 40 minute decay period. Vertical temperature stratification was captured via real-time temperature monitors with resolutions of 0.1m/sensor and 0.5m/sensor in quiescent and human-perturbed experiment arrays, respectively. The air change rate, measured by a particle-size differentiating particle counter, read an average of 0.7 hr-1 ¬for quiescent settings, and 2.0 hr-1 for perturbed conditions. By using the volume of the space and source strength of the cigarette, a well-mixed concentration prediction was created for the room. A ratio of the measured concentrations to the well-mixed maximum readings (normalized concentration spikes) near the source height reached an average of 15× and 3.5× for quiescent and perturbed settings, respectively. In order to quantify the extent of mixing in each direction, an iterative solver for the turbulent diffusion coefficient (K) was written which accounted for particle removal, wall reflection, and assumed isotropic mixing based on Fick's 2nd law. Vertical and horizontal axes were isolated by only iterating through concentration readings along an x or y axis. A negative linear correlation was found between vertical K and vertical temperature slope (R2 = 0.72) in quiescent cases. In the cases of the perturbed experiments, horizontal K-- increased by outdoor windspeed from the opening of a door, was found to dominate over temperature stratification effects, and was found to create an exponential drop in normalized concentration spikes.

Advisor: Hildemann Lynn M. (Lynn Mary) primary advisor. Thesis advisor
Cheng Kai-Chung (Research Associate) advisor. Thesis advisor
Monismith Stephen Gene advisor. Thesis advisor
Implications of grazing for the internal distribution of Macrocystis pyrifera chemical defense compounds

Grazing organisms can negatively affect giant kelp (Macrocystis pyrifera) individuals and ecosystems by consuming large amounts of biomass. M. pyrifera, however, serves important ecosystem functions, providing food, habitat, shelter, and nursing grounds for a suite of organisms. Thus, it is crucial to understand M. pyrifera’s mechanisms of defense in order to predict how M. pyrifera responds to heavy grazing events and how M. pyrifera protects itself on a day-to-day basis. Little is known about the distribution of M. pyrifera’s chemical defense compounds (polyphenols) across life stages and within a blade. To test this, M. pyrifera blades were subjected to grazing by Chlorostoma brunnea. This was repeated for juvenile, adult, and apical blades. Polyphenol levels of each blade were tested and compared. Polyphenol concentrations were found to be highest in apical blades, lowest in juvenile blades, and moderate in adult blades. Within juvenile blades, the tip contained the lowest concentration of polyphenols, whereas the base contained the highest. Polyphenol distributions were found to align with distributions of compounds and biological processes that may enhance the individual’s fitness.

Keywords:  Department of Biology
grazer
chemical defense compounds
polyphenols
life stage
Macrocystis pyrifera
blade
Thesis
Advisor: Micheli Fiorenza
Denny Mark
Improving evidence from administrative data to better inform the practice of cardiac surgery [electronic resource]

Success in cardiac surgery is no longer defined by a patient's vital status at hospital discharge, but rather by his/her survival a decade—or more—later. Low early-event rates complicate randomized clinical trial design and make them prohibitively expensive or infeasible. As a result, practice recommendations from cardiovascular societies are seldom supported by strong evidence. Administrative databases contain a wealth of longitudinal patient information, but their lack of granularity and observational nature limit the conclusions drawn from such "big data" research. Herein lies a major opportunity for improvement; rather than dismiss data that chronicles the "real world" care of millions of patients, perhaps we can use this data more effectively to understand and inform clinical practice. In this dissertation, we apply rigorous causal inference methods to statewide and national claims databases to better guide care for patients with valvular heart disease, coronary artery disease, and aortic dissection. We found that: 1) despite an increasing use of biological prostheses, the long-term survival benefit of a mechanical prosthesis persists until 70 years of age in patients undergoing mitral valve replacement, but disappears by age 55 years in those undergoing aortic valve replacement; 2) second arterial conduit use is low and declining, but arterial grafts significantly improve survival and reduce cardiovascular events in patients undergoing multi-vessel coronary bypass; and 3) the majority of patients with an acute type A aortic dissection are treated at low-volume hospitals, yet directed transfer of patients to high-volume hospitals is safe, feasible, and substantially improves survival. Our methods may be broadly applied to improve claims database research in a variety of healthcare fields, and our results have the potential to inform the care of hundreds of thousands of patients undergoing heart surgery annually in the United States.

Advisor: Nelson Lorene M.
Baiocchi Michael advisor. Thesis advisor
Sainani Kristin
Woo Joseph advisor. Thesis advisor
Improving functions of redox proteins for hydrogen production [electronic resource]

The usage of hydrogen as an alternative energy carrier has become increasingly important to support environmental sustainability. A portion of this hydrogen could be produced from renewable biomass sources, particularly from the sugar components of cellulosic feedstocks. The electrons extracted from the sugars would be delivered to one of the best hydrogen producing catalysts available in nature, an [FeFe] hydrogenase from Clostridium pasteurianum, through a synthetic pathway involving NADPH and two other proteins: Ferredoxin-NADP+ Reductase (FNR) and the Clostridium pasteurianum ferredoxin (CpFd) as an electron carrier protein. This electron transfer pathway enables in vitro hydrogen production and, when coupled with unpurified cell extracts containing native E. coli metabolic pathway enzymes, will provide an economical advantage. We sought to improve the electron transfer efficiency between the proteins for more efficient hydrogen generation from biomass sugars. We focused on improving the electron transfer rate of the downstream NADPH to hydrogen pathway, because it has been shown to limit the overall productivity. We initially hypothesized that the rate-limiting step in the pathway lies in the FNR-catalyzed electron transfer, but also evaluated the CpFd-mediated electron transfer from FNR. Several mutagenesis strategies were employed to change the inherent properties of the two redox proteins, FNR and CpFd, to increase their electron transfer rates. First, two different FNR mutant libraries from Anabaena PCC 7119 and rice root were mutated and evaluated. Subsequently, a mutant library of CpFd was explored. Mutagenesis of both redox proteins has enabled a final ~2.3-fold improvement in hydrogen productivity compared to the wild-type proteins, with an FNR turnover rate of 0.9 s-1. Beneficial mutations consist of S154H in rice root FNR and S17V in CpFd, and significantly lower the KM of the rice root FNR mutant and the CpFd mutant. Electron transfer from NADPH to the FAD cofactor of FNR occurs by a hydride transfer, but the CpFd can only accept two electrons. The improved ability of the new histidine (in S154H mutant) to accept the un-transferred proton may be improving FNR functionality in our pathway. Since the interaction between rice root FNR and CpFd has been improved, future work will employ similar mutagenesis strategies to search for an [FeFe] hydrogenase variant that can improve the hydrogen production rate even further. Ultimately, the electron transfer between proteins is a complex process that needs to be optimized for hydrogen production. This study provides further understanding of how redox protein interactions influence electron transfer.

Keywords: Bioengineering.
Advisor: Swartz James R. primary advisor. Thesis advisor
Lin Michael
Smolke Christina D. advisor. Thesis advisor
Improving heterologous expression in yeast through a selective assay [electronic resource]

Heterologous expression of valuable proteins and biosynthetic pathways is a worthwhile endeavor of modern biotechnology, with pharmaceutical, industrial, and agricultural applications. But the process of expressing heterologous protein often requires significant optimization. Here, I have sought to express several proteins of bacterial, fungal, and human origin. In Chapter 2, I demonstrate the successful expression of two genes from the disorazole biosynthetic pathway from Sorangium cellulosum ce12: the first module (dszM1) and the trans-acting acyltransferase (dszD). I developed a growth-based reporter for protein expression by fusing the yeast URA3 gene to the C-terminus of dszM1 and explored the role of codon optimization in improving protein expression. In Chapter 3, I describe an assay for host improvement by screening the yeast homozygous deletion collection for strains that improve the heterologous expression of proteins fused to selectable markers. I performed this screen for three genes: dszM1; the core enzyme of the cytochalasin biosynthetic cluster (ccsA); and an isoform of human fibrinogen (FGA). I identified two (Δtif2 and Δecm25) strains that improve the heterologous expression of a fungal (ccsA) and a bacterial (dszM1) biosynthetic gene and proceeded to test these strains under alternate promoters. These results demonstrate the utility of unbiased screens coupled to selectable reporters and may be useful for researchers seeking to express large, complex pathways in yeast.

Keywords: Biology.
Advisor: Davis Ronald W. (Ronald Wayne)
Khosla Chaitan
Stearns Tim advisor. Thesis advisor
Improving lanthanide-based upconversion by overcoming the parity selection rule [electronic resource]

Upconverting materials generate high-energy photons from two or more lower-energy photons. By virtue of this ability, they have the potential to allow solar cells to utilize sub-band gap photons and to enable inherently background-free biological imaging. Lanthanide-based upconverters, which convert near-infrared light to visible light, are particularly well-suited to these applications but remain hindered by poor efficiencies, typically below 1% in nanoparticles. Primarily responsible are their low radiative rates, which stem from the parity-forbidden nature of the constituent transitions. Here, I demonstrate three successful methods of overcoming the parity selection rule, thereby enhancing radiative rates and increasing performance in lanthanide-based upconverting nanoparticles. First, I show how we use mechanical strain to increase orbital mixing and relax the parity selection rule in NaYF4 nanoparticles doped with Yb and Er. Upconversion emission spectra and lifetimes are monitored as the NaYF4:Yb, Er nanoparticles are compressed hydrostatically with a diamond anvil cell. A 1% compressive strain diminishes upconversion emission in the hexagonal-phase nanoparticles but yields nearly a twofold emission enhancement in the cubic-phase particles. I then describe how we use synthetic strain to induce local symmetry distortions. Hexagonal-phase NaYF4:Yb, Er nanoparticles are codoped with Gd and Lu, which have slightly larger and smaller ionic radii than does Y, respectively. Using this approach, a 1.6x upconversion quantum yield enhancement as well as a record efficiency value are achieved. A broad suite of characterization techniques is used to confirm that the particle morphology, global structure, and Yb/Er concentrations are constant throughout the sample series, confirming symmetry distortion to be the source of the quantum yield improvement. Finally, I discuss a method we demonstrate in which energy is shuttled to a fluorescent dye rather than being emitted directly from the upconverter. Here, NaYF4:Yb, Er nanoparticles are decorated with a dye capable of achieving radiative efficiencies above 90%. This sensitization yields size-dependent upconversion quantum yield enhancements as high as 10x. These three broadly implementable approaches for improving upconversion are among the first to successfully overcome the parity selection rule in lanthanides. In conjunction with alternative methods of efficiency enhancement, this work provides a clear path toward realizing the transformative potential of upconversion for photovoltaic and bioimaging applications.

Keywords: Materials Science and Engineering.
Advisor: Dionne Jennifer Anne primary advisor. Thesis advisor
Salleo Alberto
Mao Wendy (Wendy Li-wen) advisor. Thesis advisor
Improving life cycle assessment as a decision support tool using empirical data for multicriteria prioritization [electronic resource]

Energy systems are essential to society and play major roles in two of the greatest global challenges of our time: climate change and social inequity. Advancing environmentally sustainable and socially responsible energy transitions around the world will require solutions for complex interdisciplinary challenges. Additionally, multicriteria analysis methods are needed given the diverse set of social goals and expectations for energy projects. My dissertation addresses life cycle assessment (LCA) as an engineering decision support tool, using rigorous social science methods to derive and implement an approach to multicriteria optimization founded on empirical data about societal priorities. I argue that rigorous, transparent approaches to prioritizing across noncomparable impact categories in LCA is fundamental to making LCA an engineering method that is useful and robust enough to play a role in policy processes where life cycle evaluation is demanded by decision makers. Further, I argue that prioritization of impacts in multicriteria assessment is ultimately a question of values and, as such, should privilege society's values over those of individual decision makers or the expert community. My research shows that nontransparent prioritization in LCA exists and uses a case study of a community experiencing energy development to argue that value systems are extremely important to decision making. I argue that LCA can benefit from use of transparent intercategory weighting factors that reflect societal values, specifically by use of a set of empirical priority archetypes that can be used to test a decision's robustness under different value conditions.

Advisor: Algee-Hewitt Mark primary advisor. Thesis advisor
Brandt Adam (Adam R.) primary advisor. Thesis advisor
Freyberg David L. advisor. Thesis advisor
Lepech Michael advisor. Thesis advisor
Improving prussian blue electrodes for salinity and organic energy recovery from wastewater [electronic resource]

In current wastewater treatment plants, dissolved organics and salt gradients are vast untapped energy resources. Microbial batteries (MBs) operate with a bio-anode to oxidize organic matter in wastewater, with a solid-state cathode as an electron receiver. Mixing entropy batteries (MEBs) are redox systems that capture salinity gradient energy; applicable for systems such as treated wastewater being discharged to coastal waters. For coastal treatment plants that adopt both kinds of recovery technologies, this energy could power the plant. This study aims to improve the Prussian blue (PB) cathodes of these batteries to prepare for their future scale-up. This work focuses on a method to protect PB electrodes and stabilize long-term performance using a thin layer of cation exchange polymer on the electrode surface. Results indicated that the polymer improved the performance of PB electrodes in several ways. First, there was no detachment of PB due to mechanical abrasion, demonstrating a reasonably practical mechanical strength. Second, the capacity retention, an important characteristic for long-term use of a battery, improved to ~97% for 190 cycles (around 16 days). By comparison, uncoated PB electrodes had 90% retention over 50 cycles. Third, results indicated that the sulfosuccinic acid (SSA) component of the polymer reduced electrode overpotential by 40 to 51% depending on the proportion of SSA in the polymer, electrolyte concentration, and current density. The coating layer enabled use of a stainless steel wire mesh as a current collector instead of expensive and fragile carbon cloth. The coulombic efficiency and capacity of the stainless steel mesh electrode were nearly constant over 150 charge/discharge cycles. The stainless steel mesh required ~60% less PB than the carbon mesh for recovery of the same amount of net energy per cycle. Coated PB was evaluated as a cathode material in an 800-ml automatic-operated microbial battery. Results demonstrated that the coated PB can be applied for use in microbial batteries with short-term performance that is similar to that of an uncoated electrode. Long-term experiments are needed to understand the performance and biofouling behavior of the PB coated electrode.

Advisor: Criddle Craig advisor. Thesis advisor
In Vivo Characterization of Murine Inner Ear Hair Cell Progenitors

The most common cause of hearing loss and balance disorders is loss of inner ear sensory hair cells. While sensory organs from non-mammalian species robustly regenerate, previous studies have found no regeneration in the mature mammalian cochlea and only limited regeneration in the mammalian vestibular system. It has recently been found that a subset of non-sensory supporting cells, marked by the protein Lgr5 (leucine rich repeat containing G protein-coupled receptor 5), is capable of spontaneously regenerating lost hair cells in the neonatal mouse cochlea and utricle. However, knowledge of the time-course of cell fate change, differentiation, and proliferation by these hair cell progenitors is lacking. Here we probed the genetic signature of hair cell progenitors to understand the molecular mechanisms that guide hair cell regeneration after damage. A mouse model that allowed for selective ablation of hair cells was used, and immunohistochemical staining of early hair cell markers (Gfi1, Atoh1) and a proliferation marker (Ki67) allowed us to map the transition of supporting cells into hair cells in the neonatal mouse cochlea and utricle after damage. The findings demonstrated that the neonatal utricle and cochlea have an upregulation of early hair cell markers before proliferative markers. These data suggested that regenerating cells in the neonatal mouse inner ear sensory organs follow a similar temporal pattern of regeneration to the inner ear organs from non-mammalian species.

Keywords:  Department of Biology
Atoh1
Gfi1
Ki67
proliferation
differentiation
regeneration
Thesis
Advisor: Cheng Alan
McConnell Susan
Income Segregation and Intergenerational Mobility: Evidence from U.S. Highways

In recent decades, racial segregation has declined while income segregation has increased and continues to intensify, but past studies have failed to estimate the effects of income segregation through causal methods. I measure the intergenerational mobility gap between children with low income and high income parents by gender in response to higher levels of income segregation at the county-level. A causal estimate is approached through an original instrumental variables strategy that uses income sorting of census tracts following the construction of the interstate highway system. Neighborhoods in close proximity to a highway experience a negative disamenity effect from the noise and pollution generated from the highway but also receive access benefits from using the faster transportation network. I find that income segregation leads to less upward mobility for children from both low income and high income backgrounds, and in particular exacerbates income disparity among boys. These results show that the correlational estimates of previous studies have underestimated the effects of income segregation and shed light on the impacts of transportation infrastructure on the shape of the income distribution.

Keywords: Department of Economics
Stanford University
Undergraduate Honors Thesis Program
Thesis