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Open Access Publications from the University of California

UC Santa Cruz Electronic Theses and Dissertations

Cover page of Searching for New Physics with the Fermi Large Area Telescope

Searching for New Physics with the Fermi Large Area Telescope

(2019)

Compelling astronomical evidence suggests that a majority of the matter in the Universe, known as dark matter, is not described by the Standard Model of paricle physics. A popular candidate for the identity of the dark matter is weakly interacting massive particles (WIMPs), which are well-motivated in part because they naturally reproduce the correct dark matter relic density in a standard thermal freeze-out scenario. Moreover, WIMP interactions with Standard Model particles can be used to detect WIMPs experimentally with a variety of complementary techniques. Primordial black holes (PBHs), which could have formed in the early Universe from the collapse of primordial overdensities, are another plausible candidate for dark matter. Detecting Hawking radiation from low-mass PBHs would be a monumental achievement in its own right, and the PBH light curve could be exploited as a probe of other physics beyond the Standard Model. The Fermi Large Area Telescope (Fermi-LAT), which is capable of detecting γ rays over a wide range of energies and across the entire sky, is an excellent instrument for studying both of these dark matter candidates. Techniques for detecting the Hawking radiation from evaporating PBHs are developed, and used to search the Fermi-LAT catalog of γ-ray point sources for PBH candidates.

The phenomenology of a WIMP model with a velocity-dependent annihilation cross-section is discussed, and an analysis of Fermi-LAT data at the Galactic Center is performed to search for the sharp kinematic features in the γ-ray spectrum predicted by the model. The searches return no significant indications of WIMPs or PBHs, and in both cases the nonobservation is used to place constraints on the presence of new physics.

Cover page of An exploration into adaptive methods for decreasing wear-leveling in SCM

An exploration into adaptive methods for decreasing wear-leveling in SCM

(2019)

Storage Class Memories (SCM) have recently emerged as promising technologies for use as system memory because of their advantages such as non-volatility, byte addressability and low idle power usage. Nevertheless, lower write endurance, higher asymmetric read/write latencies, and stronger consistency requirements pose new challenges for using SCM rather than DRAM as the next generation of memory. In this report, we focus on endurance challenges in SCM. More specifically, we challenge traditional simplified wear-leveling methods like Flip-N-Write by exploring the merits of adapting to data sets dynamically. In the process, we develop a novel method for improving wear leveling on SCM: Adaptive Bit Flip Pattern Learning (ABFPL). We show that our method works best in software rather than as a hardware implementation since it allows for more adaptability to changing workloads. We provide and demonstrate a preliminary configuration which can improve wear in a larger set of datasets than previous approaches. We evaluate our method and show it to have up to a improvement of 57% over Flip-N-Write.

New Perspectives on the Composition and Cycling of Dissolved Organic Carbon and Nitrogen in the Ocean

(2019)

Marine dissolved organic matter (DOM) is the largest pool of actively cycling organic carbon and nitrogen in the ocean. Despite the importance of DOM in biogeochemical cycles, understanding of its composition and cycling is limited, in part due to difficulty in isolating representative material. Here we present a new approach to DOM isolation via a sequential combination of ultrafiltration and solid phase extraction, which allowed the selective isolation of two fractions with different compositions and reactivities. By limiting the influence of reactivity mixtures, we were able to directly investigate the composition and cycling of both labile and refractory DOM. Measurements of bulk isotopic (Δ14C, δ13C, δ15N) and compositional (C/N ratio, 13C and 15N NMR) parameters confirmed the uniqueness of the two fractions. The ultrafiltered high molecular weight (HMW) fraction was younger and dominated by carbohydrate-like and protein-like molecules. In contrast, the low molecular weight (LMW) fraction was older and dominated by alicyclic carbon and heterocyclic nitrogen containing molecules.

Spectroscopic studies have shown that the nitrogen-containing fraction of DOM (DON) is dominated by labile proteinaceous material. Despite this, other evidence suggests that a large fraction of DON is resistant to degradation. However, the paradigm of DON composition is based on measurements of HMW DON alone. Measurements of isotopic (δ15N, AA-Δ14C) and compositional (15N NMR, AA-D/L ratios) parameters of LMW DON provided a new perspective on the composition and cycling of DON in the ocean. Amino acids in LMW DON had both old radiocarbon ages and high D/L ratios, suggesting a bacterial mechanism capable of preserving proteinaceous material on millennial timescales. NMR analysis and nitrogen isotopic ratios demonstrated that LMW DON is dominated by heterocyclic nitrogen-containing molecules likely with intrinsically refractory molecular structures. These observations present a new paradigm for marine DON composition and suggest a mechanism for its long-term persistence.

Cover page of Two Degree of Freedom Optimal Control for Nonlinear Systems with Parameter Uncertainty

Two Degree of Freedom Optimal Control for Nonlinear Systems with Parameter Uncertainty

(2019)

This dissertation explores some of the ways that optimal control can be used to mitigate the effects of parametric uncertainty on the control's ability to achieve a desired endpoint condition on the state variables. Standard optimal control solutions rely on precise knowledge of parameter values which are difficult to measure in many practical applications. The result is that, when implementing the designed controls, there is likely to be some error between the desired state trajectories and the actual system outputs. Usually these errors are managed using feedback control using sensor measurements to correct the state deviations on the fly. However, recently there has been promising work done for generating controls which operate in the open-loop for generating state trajectories which are inherently robust to uncertainty in the parameters.

One avenue of applying optimal control for managing parameter uncertainty is unscented optimal control which borrows the low sample discretization of the Unscented Transform for approximating a Riemann-Stieltjes integral of an objective function. This method has proven effective for generating open-loop controls. In this dissertation we explore a family of sensitivity function based optimal control problems, which utilizes an approximation of the response to parameter deviations through a Taylor series, which can be used to likewise generate open-loop controls. We then use these sensitivity based problems as a lens for exploring the unscented control problem. Furthermore, we identify conditions for equivalence between the two optimal control problems. These inherently robust open-loop trajectories represent a single degree of freedom control.

In addition to generating the open-loop controls for a more robust state trajectory, this dissertation provides a problem formulation for generating a set of time-varying feedback gains. These gains use sensor measurement for both the sensitivity function based problem as well as the unscented problem frameworks. The unscented problem avoids linearizing the error dynamics which is shown to be advantageous for designing the feedback gains. The use of feedback gains represents a second degree of freedom when combined with a more robust open-loop control significantly improving the performance.

These concepts are demonstrated on a simulated nonlinear double gimbal mechanism with flexible effects where the unscented feedback control gives a nearly $100\%$ decrease in variance of the error of the trajectory endpoints and $82\%$ in the case of the purely open-loop. The mathematical model of the double gimbal as a second order set of differential equations represents a prevalent mechanical system in engineering. The controls generated by the neighboring unscented problem demonstrate a significant improvement in the robustness to the parameter uncertainty over the standard controls. The utility of these concepts is further illustrated experimentally using a nonlinear two link robotic arm with flexible joints.

Cover page of Larval dispersal of nearshore rockfishes

Larval dispersal of nearshore rockfishes

(2019)

Larval dispersal is consequential for the structure and dynamics of populations and the distribution of species. Most benthic marine species inhabit patchily distributed habitat and larval dispersal is often the primary means of population connectivity. Studies suggest that gene flow is the product of conduits and barriers to dispersal, including oceanic and geographic features and a combination of physical and behavioral mechanisms that effect the relationship between larval supply and settlement. Tracking larval dispersal in the ocean is considered one of the great logistical challenges in marine ecology, with a substantial history of using genetic markers to study dispersal. Although most studies apply indirect methods that integrate information across generations, in highly dispersive populations and across fine spatial scales, genetic parentage analysis has seen increasing use, but with limited examples from temperate environments or along open-coastlines where currents dominate and larvae may be advected offshore. Here, I describe larval dispersal of nearshore rockfishes across a network of marine reserves along the open-coastline of central California, a temper- ate current-driven ecosystem and the site of a network of marine protected areas (MPAs). Rockfishes of the genus Sebastes form a marine species flock of more than 100 species and are a prominent component of the ichthyofauna in temperate ecosystems. Kelp rockfish (S. atrovirens) are part of this species flock and one of >50 species present in the Monterey Bay, California region. In Chapter 1, I describe the development of a novel set of statistically powerful microhaplotype markers for efficiently performing pedigree relationship inference in the kelp rockfish and demonstrate that the false positive rates for single parent-offspring and full-sibling analyses are orders of magnitude lower than relying on the most informative single nucleotide polymorphism (SNP) in the same short-read sequence. In Chapter 2, I apply these new genetic markers to identify eight single parent-offspring pairs and 25 full siblings from thousands of samples of adult and juvenile rockfishes collected inside and outside of marine reserves. Dispersal between reserves and areas where fishing is allowed demonstrates the efficacy of the MPA network. Chapter 3 applies these microhaplotype markers to species identification of >50 rockfishes from the Northeast Pacific. Genetic assignment accuracy exceeds 99% and the species for which accuracy does not reach 100% are gopher (S. carnatus) and black-and-yellow (S. chrysomelas) rockfishes, sister species with evidence of ongoing gene flow. Phylogenetic analyses recovers relationships among species and subgenera concordant with previous studies. Finally, in Chapter 4, I analyze additional species of rockfishes obtained for the larval dispersal study and identify full siblings among juvenile gopher/black-and-yellow and copper rockfishes. Combining these data with results from Chapter 2, I compare the proportions of full sibling pairs among the species, finding the greatest proportion of full siblings sampled in the kelp rockfish. Collectively, these chapters provide valuable new genetic resources for studying rockfishes, describe the first direct observations of dispersal in rockfishes, and provide insight into the efficacy of a network of MPAs along an open-coastline.

Extended From What?: Tracing the Construction, Flexible Meaning, and Cultural Discourses of "Extended Vocal Techniques"

(2019)

This study traces the usage and development of the concept of “extended vocal techniques,” [EVT] from its early appearances in musical discourse in the 1970s to the present. Though many authors suggest a long lineage for EVT, the actual term is relatively new. In fact, this term is virtually absent from scholarly or journalistic literature before the 1970s. Vocal pedagogues and music scholars have contributed substantially to the discussion concerning which vocal practices, artists, and performance literature might be considered part of the EVT tradition. Musicological work more specifically focused on EVT has profiled individual performer-composers working experimentally with their voices, and many have woven critical theory into their analyses of these artists’ vocal practices. Curiously, few of these musicological studies have attended to their own acceptance of the EVT label, commonly applied to artists such as Meredith Monk, Joan La Barbara, and Pamela Z, among others. The oversight of the historical and critical issues underpinning the term itself has allowed EVT's definition to be tacitly shaped by each author’s cultural assumptions. These unacknowledged assumptions drive various definitions and responses to EVT, forming a hidden transcript that this project seeks to unearth.

By locating the appearances of the term EVT in musical discourse from earliest to latest, this work specifies the time period, social context, institutional affiliations, and musical background for each contributor to the EVT record and profiles representative artists from different social-historical contexts who have been frequently associated with EVT. Through an investigation of EVT’s various historical definitions, cultural implications, and power dynamics, I formulate a rhizomatic account of the development of EVT as a concept. Moreover, I examine how its differences and similarities over the years indicate our shifting perspectives on voices, bodies, music, and identity. Recasting EVT as a culturally-situated mode of listening holds the potential to move conservatory singing toward a more flexible, inclusive understanding of vocal practice that celebrates different bodies, abilities, and backgrounds.

Cover page of Restraining Mayors: Local Councils as Agents of Horizontal Accountability

Restraining Mayors: Local Councils as Agents of Horizontal Accountability

(2019)

Local councils in Latin America often fail to hold mayors accountable, even where they are legally required and empowered to do so. These failures are particularly significant, considering that decentralization has given greater power to mayors throughout the region. The dissertation aims to improve our understanding of local horizontal accountability by analyzing the influence of mayors and constituencies on local councils’ disposition for horizontal accountability, and by conceiving these actors as embedded in systems of local relationships. Following an inductive and theory building strategy, the research compares five municipalities in Santiago de Chile with diverse socioeconomic and political features using original qualitative evidence.

The results challenge explanations of accountability based on administrative capacity, socioeconomic characteristics, and partisan alignments. They show, instead, that the configuration of local systems of relationships—comprising relationships between councils, executives (i.e., the mayor and the municipal bureaucracy) and constituencies (i.e., the local voters)—have significant effects over a critical factor determining Municipal Councils’ disposition for horizontal accountability: their autonomy from the mayor.

According to the cases analyzed, local councils’ dependence on the mayor is a significant factor for inhibiting their disposition to hold these mayors accountable. This dependence has a critical electoral component, thus making the triangular relations between council members, local executives and constituencies a determinant factor going beyond their party affiliation. Specifically, and as a general proposition, when council members are unable to generate and maintain sufficient constituent support, local executives can use their resources and influence to reduce or increase council members’ electoral chances. This influence on council members’ electoral performance can be used to induce their loyalty to the mayors, thus discouraging them from holding these mayors accountable.

Constituencies, therefore, also play a significant role in local horizontal accountability, by giving council members a chance to be autonomous from their mayors despite their disposition to hold the mayor accountable (or lack thereof). This autonomy, however, disappears if council members rely on the help of the local executives to obtain constituents’ support.

Cover page of Lead Concentrations Within The Condor Skeleton: Advancing Biomarkers Of Lead Exposure History And Poisoning

Lead Concentrations Within The Condor Skeleton: Advancing Biomarkers Of Lead Exposure History And Poisoning

(2019)

Lead (Pb) poisoning is a global problem among avian species, including the endangered California Condor (Gymnogyps californianus). Condors are highly monitored and frequently lead poisoned and may serve as a model species to investigate Pb exposure biomarkers. Bone Pb levels are a well-recognized biomarker of Pb exposure and related health effects in humans but have not been used widely in avian species. My overarching objective is to further establish biomarkers of lead exposure history and poisoning in avian species using bone Pb concentrations. In chapter 1, I investigated whether bone Pb differed between and within condor bones, depending on Pb exposure history between epiphyses, mostly composed of trabecular bone type, and diaphysis, mostly composed of compact bone type. In chapter 2, I determined if Pb levels in different bones can be used as biomarkers of recent and cumulative Pb exposure history and examined the effects of Pb exposure on bone mineral density and potential risk for bone fracture. In chapter 3, I used Pb stable isotopic composition to inform about Pb uptake into multiple bones and bone regions. My results showed that Pb concentrations were ~3-fold higher in epiphysis than diaphysis of tibiotarsus in condors that died of Pb toxicosis but less than 2-fold in condors that died of other causes. A discriminant analysis using bone Pb concentrations correctly classified 17 out of 18 birds as to whether they were Pb poisoned at the time of death, suggesting that bone Pb, particularly tibiotarsus epiphysis proximal, can be used as an additional piece of information to inform recent Pb exposure. Bone Pb levels, particularly in tibiotarsus diaphysis, were associated with time in the wild, consistent with prior studies in humans showing that bone Pb levels in long bones reflect long term cumulative Pb exposure. I also found a modest negative association between bone Pb and bone mineral contents in epiphyses of long bones, suggesting that bone Pb may be associated with a reduction in bone mineral. Finally, using stable lead isotopes, I found that there was ~10-fold difference in the rate of Pb incorporation between the tibiotarsus proximal epiphysis and diaphysis following a Pb exposure event. In conclusion, bone Pb levels in condors, and by extension other large avian species, appear to be a valuable biomarker of both recent acute and cumulative Pb exposure, and may help inform Pb poisoning status at the time of death.

Cover page of Asking and Answering Questions: Discourse Strategies in Japanese

Asking and Answering Questions: Discourse Strategies in Japanese

(2019)

This dissertation explores a subset of lexical items in Japanese (contrastive wa, outer negation, and no(da)), which are strategically used in asking and answering questions in discourse. The results reveal what conventionalized discourse effects each of these items has and also how those effects work at the interface between semantics and pragmatics. Based on the discourse effects of a particle across sentence types (declarative/interrogative) and the discourse effects of questions with multiple particles, throughout the dissertation, I argue that the discourse effects of the whole sentence can be attained compositionally by putting together the discourse effects of each expression and those of sentence types.

This dissertation also aims at integrating experimental methods into semantic and pragmatic analyses of the language; Psycholinguistic experiments provide valuable clues to understanding how people use and understand utterances, with certain linguistic expressions. The formal account of contrastive wa is specifically based on the results of the experiments, which revealed that the lexical item is particularly sensitive to whether there could be contrastive questions to be pursued in the discourse. This aspect forms a part of the analysis of contrastive wa, as a language-specific conventional effect tied to this lexical item, and it interacts with its function as a contrastive topic. The analysis has broader empirical coverage than previous ones, in that it provides a way to unify the contribution of wa in declarative and interrogative sentences.

Overall, the behavior of these unique items in Japanese suggests that the discourse effects encoded into lexical items and sentence types can be compositionally derived. This is not trivial, given that not all languages allow to combine different sentence types and (multiple) discourse particles, to begin with. The exploration carried out in this dissertation implies also that this compositionality could be extended to cover other discourse management tools that languages are equipped with.