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UC Riverside Electronic Theses and Dissertations

Cover page of Reimagining Transatlantic Iberian Conquests in Postcolonial Narratives and Rewriting Spaces of Resistance

Reimagining Transatlantic Iberian Conquests in Postcolonial Narratives and Rewriting Spaces of Resistance

(2020)

This dissertation analyzes the medieval and colonial imagery in three works which evoke a history of epistemic violence and erasures against indigenous, contemporaneous identities, communities, and traditions of knowledge in Al-Andalus and Latin America after 1492. Darren Aronofsky’s film, The Fountain, Radwa Ashour’s trilogy of Granada, and Laila Lalami’s The Moor’s Account, all show how fiction and film can both reinforce and subvert the mythology of conquest in the representation of transatlantic, sixteenth-century Iberian empire. Fiction offers a space of resistance to remember the voices of the subaltern, to deconstruct the silences of these histories, and to reflect on the perspectives and experiences of the colonized, occupied and displaced Others of colonial enterprise. Fiction can challenge the Orientalist tropes and imperial gaze which still color the contemporary imagination towards Amerindians, Muslims and Arabs. Reimagining the past speaks to the present, and redraws the blurred lines of historiography and storytelling.

Cover page of Measurement of the Casimir Effect in the Cylinder-Sphere Geometry

Measurement of the Casimir Effect in the Cylinder-Sphere Geometry

(2020)

The Casimir effect originates from the boundary effects on the quantum vacuum. The boundary modifies the allowed modes of zero-point, or virtual, photons. Current studies of the Casimir effect have taken place primarily between simple geometries such as the sphere-plate configuration. More complicated geometries will introduce modifications in the collective charge fluctuation anisotropy. In this work, we examine the Casimir force between a cylinder and a sphere in a UHV environment, examining the effects of the 1-D dimensionality of the cylinders. To reduce the ellipticity of the cylinders involved, we have used a glass optical fiber, coated with Au to provide a conductive surface. Co-location of the sphere and cylinder was achieved using a piezoelectric stage with a capacitive sensor controlled PID loop. To maintain cleanliness of the samples and minimize the effect of surface adsorbates, we utilize Ar ion bombardment and UV cleaning. We examine our results using the Proximity Force Approximation (PFA). The Casimir effect has broad implications for MEMS devices operating in the submicron regime.

Cover page of Characterization of Leaflet Inclination and LOB-Domain Genes in Vigna unguiculata (L.) Walp

Characterization of Leaflet Inclination and LOB-Domain Genes in Vigna unguiculata (L.) Walp

(2020)

ABSTRACT OF THE DISSERTATION

Characterization of LATERAL ORGAN BOUNDARIES (LOB) and leaflet inclination in Vigna unguiculata (L.) Walp (Cowpea)

By

Michael Frederick Schwartz

Plants undergo organogenesis throughout their lifetime by maintaining populations of pluripotent cells at their apices. The shoot apical meristem (SAM) produces lateral organs, such as leaves, which form at the periphery of the SAM. The SAM and the lateral organs are separated by the boundary region. The boundary region contains a population of cells which are smaller and divide infrequently and is a region of reduced growth. The boundary region plays an important role in regulating shoot architecture as it is the region of the plant that influences leaf inclination. The Arabidopsis transcription factor LATERAL ORGAN BOUNDARIES (LOB) is expressed in plant organ boundaries and functions to limit growth and separate the organs. This dissertation focuses on characterizing an ortholog of LOB, VuLOB, in cowpea, an economically important legume, and its role in regulating leaf inclination.

In chapter 1, I identify the LOB ortholog in cowpea, termed VuLOB, through the identification of the LOB-domain genes in cowpea and phylogenetic analysis. Characterization of the expression pattern of VuLOB shows transcript accumulation in the pulvini, structures at the base of the leaves and leaflets which incline the leaves under water-deficit. VuLOB is positively regulated by the phytohormone brassinosteroid (BR) which mimics LOB’s regulation, but functional analysis using Arabidopsis suggests that VuLOB may not form the boundary by restricting growth. VuLOB transcripts are not significantly changed in inclined pulvini. BRs have been shown to regulate leaf inclination in the grasses. When BRs are removed from cowpea using propiconazole they fail to incline. Propiconazole treatment changes the cellular morphology of the epidermis of the pulvinus which correlates with the failure to incline. This suggests that BRs are required to promote leaf inclination in cowpea

In chapter 2, I use genome-wide association studies (GWAS) to identify regions of the cowpea genome which correlate with the variation in the size of the pulvinus and leaflet inclination after water-deficit. Several significant peaks were identified which correlate to the variation in pulvinus size, but no peaks were identified with regards to leaflet angle. From the significant peaks a candidate gene, VuLBD41, was identified. VuLBD41 is a LOB-domain transcription factor that is orthologous to the Arabidopsis transcription factors LBD40 and LBD41. Transcripts of VuLBD41 accumulate in the pulvini of cowpea. However, functional analysis using Arabidopsis did not reveal any function in regard to development. Transgenic plants overexpressing VuLBD41 appear morphologically normal. This suggests that VuLBD41 has an unknown role in boundary formation.

In chapter 3, I characterize the genetic relationship between LOB and 2 putative targets, TREHALOSE-6-PHOSPHATE PHOSPHATASE I/J (TPPI and TPPJ). LOB directly regulates TPPJ, but not TPPI in yeast. However, higher order mutants don’t have an enhancement of the organ fusions found in lob mutant plants, but they do have a significant increase in the number of branches, which suggests that they have some role in the boundary. Further, I show that ectopic TPPJ accumulation in the boundary is sufficient to rescue the lob mutant phenotype. This suggests that LOB requires TPPJ to restrict growth at the boundary.

Cover page of Theranostic Window to the Brain for Multispectral Light Delivery and Microcirculation Imaging

Theranostic Window to the Brain for Multispectral Light Delivery and Microcirculation Imaging

(2020)

Interest in using optical methods in the development of noninvasive clinicaldiagnostic and therapeutic techniques for brain diseases has widely increased due to theirsimplicity, safety, and affordability. The main limitations of light-based techniques usedfor brain theranostics are the strong light scattering in the scalp and skull, which causedecrease of spatial resolution, low contrast, and small penetration depth. To address thischallenge, our group has previously introduced a transparent nanocrystallineyttria-stabilized-zirconia (nc-YSZ) cranial implant material which implant possesses themechanical strength and biocompatibility that are prerequisites for a clinically-viablepermanent cranial implant for patients.

This implant possesses the mechanical strength and biocompatibility that areprerequisites for a clinically-viable permanent cranial implant for patients. A potentialbenefit of this optical window is an improvement of light-based therapeutic techniquesthat rely on sufficient light penetration to a target embedded in tissue such asphotobiomodulation, photodynamic therapy, and optogenetics. Another application of thisoptical window is noninvasive visualization of brain blood vessels, hematomas, and smallpathologic structures (including cancerous growth) with high resolution. This isimportant for diagnosis and treatment of many diseases such as tumors of the brain,vascular pathologies, and so forth. In this dissertation, I investigated (1) characteristicsand durability of transparent nc-YSZ implants; (2) feasibility of chronic brain imagingthrough the implant; (3) multimodal imaging across the implant to generate anarteriovenous vascular map; (4) through-scalp VIS-NIR light delivery and microvascularimaging.

Cover page of Photodissociation Dynamics of Free Radicals Using High-n Rydberg Atom Time-of-Flight Spectroscopy

Photodissociation Dynamics of Free Radicals Using High-n Rydberg Atom Time-of-Flight Spectroscopy

(2020)

Free radicals are open-shell systems that have one or more unpaired valence electrons, and are thus short-lived and highly reactive. Free radicals can be found as important reactive intermediates in a wide range of chemical environments, for example, combustion, atmospheric chemistry, plasma, and interstellar chemistry. The photodissociation studies of free radicals can provide spectroscopic and electronic excited state information of free radicals, probe excited-state potential energy surfaces (PESs), their interactions, and their influence on reaction dynamics, and provide benchmarks for theoretical studies of the open-shell systems. The photodissociation dynamics of free radicals were studied using the high-n Rydberg H-atom time-of-flight technique. Several systems were investigated in the dissertation. The hydroxyl radical (OH), which is a prototypical diatomic radical, has been examined via several rovibrational levels in the A2Σ+ state. The H + O(3PJ) product branching ratios and angular distributions from the A2Σ+ state were obtained. Sequential two-photon excitations to the 22П and B2Σ+ repulsive states were observed, leading to the H + O(1D) and H + O(1S) products, respectively. Ultraviolet (UV) photodissociation of a series of alkyl radicals, ethyl (C2H5), n-butyl (n-C4H9), i-butyl (i-C4H9), t-butyl (t-C4H9), and 1-pentyl (1-C5H11), via their Rydberg states were observed to have two main dissociation channels: (i) direct dissociation from the electronic excited state, and (ii) unimolecular dissociation after internal conversion from the electronic excited state to the ground state. 2-Propenyl radical (CH2CCH3), in the alkenyl category, undergoes unimolecular dissociation on the ground electronic state following the UV photoexcitation and internal conversion from the excited state. Vinoxy radical (CH2CHO) is a prototypical unsaturated alkoxy radical. After photoexcitation to the B ̃2A" state, the vinoxy radical undergoes unimolecular dissociation following internal conversion to the ground state (X ̃2A") and the first excited state (A ̃2A'). The UV photodissociation of thiomethoxyl radical (CH3S), a sulfur system, is similar to that of the ethyl radical and has two main channels: (i) direct dissociation on the repulsive PES, and (ii) unimolecular dissociation after internal conversion from the electronic excited state to the ground electronic state.

Cover page of The Role of Data Quality and Heterogeneity on the Calibration of Neural Networks

The Role of Data Quality and Heterogeneity on the Calibration of Neural Networks

(2020)

Neural networks have been widely studied and used in recent years due to its high

classification accuracy and training efficiency. With the increase of network depth, however,

the models become worse calibrated, meaning they cannot reflect the true probabilities. On

the other hand, in many applications such as medical diagnosis, facial recognition and selfdriving cars, the calibrated output probabilities are of critical importance. Therefore, the

understanding of the cause of deep neural network uncalibration is of much concern.

The influence of model structures on the output calibration has been explored.

However, the impact of the training dataset quality and heterogeneity, such as dataset size

and label noise remains unclear. In this thesis, the impact of data quality and heterogeneity

on the output calibration is investigated theoretically and experimentally. Afterwards, the

defect of calibration methods using single global parameter are discussed. To overcome

the calibration issues resulting from the dataset heterogeneity, we propose an improved

calibration technique that can give better performance.

Cover page of Chicano Science Fiction and the Shattering of Colonized Reality: The Resurgence of the Alien Sublime

Chicano Science Fiction and the Shattering of Colonized Reality: The Resurgence of the Alien Sublime

(2020)

In this project I explore the uncharted domains of Chicana/o science fiction. Expanding on the interdisciplinary body of scholarship generated within the Chicana/o Studies tradition, which has generally focused on investigating the past as method to express the diverse Chicana/o experience, I deploy science fiction as method to theorize on a new consciousness of empowerment and liberation for Chicanas/os. I examine the ways in which Chicana/o science fiction not solely engages with speculative futures, but of greater magnitude, the ways in which Chicana/o science fiction dimensionalizes space and time to expose colonized reality as artificial. My project, therefore, in addition to extending upon conventional Chicana/o scholarship, engages with science fiction as an existential phenomenon by locating the experience of genuine empowerment and liberation on the resurgence of the alien sublime. The alien sublime is re-discovering the true self as the creative and vibrant essence of science fiction itself…cosmic consciousness as timeless, formless, boundless life-energy, which may also be understood as primordial awareness that experiences space-time-reality in material form. I contend that true liberation cannot be accessed through an imagined political identity that originates from the colonial form, but by experiencing liberation as a science-fictional practice of self-realization. Liberation, in other words, cannot be achieved within the colonized dominion of space and time, but rather, by discovering liberation as the fundamental essence of the alien sublime. Featuring several Chicana/o science fiction novels, I demonstrate how the alien sublime is expressed using a myriad of techniques. In its entirety, this project offers a vastly alternative approach to empowerment and liberation, thereby encouraging a re-evaluation that contextualizes the Chicana/o experience as an ontological activity.

Cover page of A Combined Molecular and Morphological Revision of Cirrospilini LaSalle (Hymenoptera: Eulophidae) with a Focus on Zagrammosoma Ashmead and Cirrospilus Westwood

A Combined Molecular and Morphological Revision of Cirrospilini LaSalle (Hymenoptera: Eulophidae) with a Focus on Zagrammosoma Ashmead and Cirrospilus Westwood

(2020)

The tribe Cirrospilini (Hymenoptera: Chalcidodea: Eulophidae) is revised in a combined molecular and morphological phylogenetic context, using ribosomal (18S, 28S, ITS2) and mitochondrial (COI) data, and scoring specimens for morphological characters. Twenty genera are now recognized in the tribe. Colpoclypeus Lucchese and Trichospilus Ferrière are included in Cirrospilini, while Cirrospiloidelleus Girault is removed. Melittobiopsis Timberlake is also removed from Cirrospilini, and raised to Melittobiopsini Perry n. tribe., sister to Eulophini Ashmead. Cirrospilus Westwood is revised and is split into 6 morphologically distinct genera: Atoposoma Masi stat. rev., Burkseus Perry, Cirrospilus str. s., Gyrolasella Girault stat. rev., Pseudozagramma Perry n. gen., and Vagus Perry n. gen. The new synonymy of Semielacher Bouček under Cirrospilus is proposed. The first worldwide key to all genera is presented, as well as distribution maps, and extensive specimen, host, and host plant records. Zagrammosoma Ashmead is molecularly revised using ribosomal (28S, ITS2) and mitochondrial (COI) data, with 24 species now recognized, including descriptions of 9 new species. A worldwide key, distribution maps, and image plates of all species are provided.

Cover page of Noncuring Graphene Thermal Interface Materials for Advanced Electronics

Noncuring Graphene Thermal Interface Materials for Advanced Electronics

(2020)

As transistors continue to decrease in size and packing densities increase, thermal management becomes a critical bottleneck for development of the next generation of compact and flexible electronics. The increase in computer usage and ever-growing dependence on cloud systems require better methods for dissipating heat away from electronic components. The important ingredients of thermal management are the thermal interface materials. The discovery of excellent heat conduction properties of graphene and few-layer graphene stimulated research on practical applications of graphene fillers in thermal interface materials. The initial studies of graphene fillers in thermal interface materials were focused almost exclusively on curing epoxy-based composites. However, many thermal management applications require specifically noncuring thermal paste type materials. This dissertation reports on the synthesis and thermal conductivity measurements of noncuring thermal paste based on mineral oil with the mixture of graphene and few-layer graphene flakes as the fillers. The relatively simple composition has been selected in order to systematically compare the performance and understand the mechanisms governing heat conduction. It was found that graphene thermal paste exhibits a distinctive thermal percolation threshold with the thermal conductivity revealing a sublinear dependence on the filler loading. This behavior contrasts with the thermal conductivity of curing graphene thermal interface materials, based on epoxy, where super-linear dependence on the filler loading is observed. The performance of graphene thermal paste was benchmarked against top-of-the-line commercial thermal pastes. The obtained results show that noncuring graphene thermal interface materials outperforms the best commercial pastes in terms of thermal conductivity, at substantially lower filler concentration. The results of this dissertation research shed light on the thermal percolation mechanism in noncuring polymeric matrices laden with quasi-two-dimensional fillers. Considering recent progress in graphene production via liquid phase exfoliation and oxide reduction, it is possible that the undertaken approach will open a pathway for large-scale industrial application of graphene in thermal management of electronics.

Cover page of Longitudinal Loneliness and Cognitive Aging in Mid and Late Life: Patterns of Associations and Epigenetic Pathways

Longitudinal Loneliness and Cognitive Aging in Mid and Late Life: Patterns of Associations and Epigenetic Pathways

(2020)

The aims of this dissertation were to compare associations between baseline and longitudinal loneliness and performance and change in four specific cognitive abilities and to explore whether DNA methylation at specific locations in blood leukocytes may play a role in the association between loneliness and cognition. In Study 1, we assessed effects of baseline loneliness and two measures of longitudinal loneliness (time-varying loneliness and geometric means for loneliness across waves) on cognitive performance and change across up to 28 years of follow-up in a large pooled sample from the Consortium on Interplay of Genes and Environment Across Multiple Studies (IGEMS). Results showed small effects of loneliness on cognition that varied across cognitive domains, with faster processing speed at age 65 and faster decline in processing speed and spatial ability. In Study 2, we evaluated loneliness and longitudinal methylation and cognitive data in a subsample from the Swedish Adoption/Twin Study of Aging (SATSA) to evaluate associations between loneliness and methylation at 1,586 CpG sites within genes linked with the conserved transcriptional response to adversity (CTRA) using both phenotypic and co-twin control approaches. For sites with associations between loneliness and methylation, regression models were used to explore relations between loneliness, methylation, and cognition. Results showed associations between loneliness and methylation level at age 70 at cg00403457 in PTPN12 and change in methylation with age at cg00619097 in CPT1B and cg26661481 in IL10RA, with partial confounding of these relations by genetic or common environmental factors indicated by co-twin control results. Although direct effects of loneliness on cognition were not significant, indirect associations of perceived loneliness to methylation of cg00403457 in PTPN12 to change in processing speed were observed, indicative of a potential role of methylation at this site in the loneliness—cognition relation. Overall, across study1 and study 2, results indicate that feelings of loneliness predict faster cognitive decline with small albeit meaningful effects that play out across age with hints of indirect mediation via methylation pathways that may be partly genetically moderated. Additional work is needed to further clarify how loneliness relates to cognition change.

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