In double white dwarf (WD) systems with sufficiently short initial orbital periods, angular momentum losses from gravitational wave radiation shrink the orbit and can lead to the merger of the WDs. Simulations of the merger show that the less massive WD is tidally disrupted, forming a disk around the more massive WD. Beginning with output from WD merger simulations, I study the subsequent viscous evolution using multi-dimensional hydrodynamical simulations. I find that the remnants evolve towards a spherical end-state, where the rotationally-supported disk has been converted into a hot, thermally-supported envelope. I then map these results into a stellar evolution code and evolve them over thermal and nuclear timescales. This is a necessary procedure to self-consistently study the long-term outcomes of WD mergers. I apply this to the merger of two carbon-oxygen WDs with a total mass in excess of the Chandrasekhar mass. My work follows the evolution of the remnants for longer than previous calculations and finds alternating episodes of fusion and contraction can lead to the formation and subsequent collapse of an iron core. I also characterize the observable properties of the remnant during this evolution. Additionally, I develop a framework to compute weak reaction rates that are essential in the evolution of massive, accreting WDs. I apply these results to understand the evolution of oxygen-neon WDs towards accretion-induced collapse to a neutron star.

The mirror neuron system is a fronto-parietal network of neurons that is activated both when a person performs an action and when he or she observes that action. The goal of this study was to investigate the semantic representation in this system during action language and gesture processing. This was done in a set of two behavioral experiments. Experiment 1 employed a simple priming paradigm—subjects viewed videos of symbolic gestures or landscapes, which served as the prime, followed by a word that was congruent or unrelated to the video prime, or a pseudo-word. The subject performed a lexical decision task on the target word. The study found a significant priming effect for semantically congruent target words, relative to semantically unrelated target words. However, this same priming effect was found for the video primes of landscapes.  In experiment 2 we aimed to determine whether the videos were primed through effector-specific means, that is, whether hand and arm gestures would activate mirror neurons somatotopically and lead to different priming results when comparing hand responses to foot responses. We used the same priming study as experiment 1 except that subjects made their lexical decision responses on a foot pedal rather than a keyboard. Results suggest that symbolic gestures prime in a very diffuse way, such that semantic priming occurs independent of the effector being used to respond.

Throughout the lifespan, the brain is sculpted by experience and by the developmental processes that prepare animals to face the challenges of each life stage. Adolescence and young adulthood represent critical times in which humans and other animals face the challenges associated with independence. During these times of exploration, specific learning experiences may shape neurodevelopmental trajectories and alter life outcomes. In Chapter 2, we focus on the idea that specific learning experiences in young adulthood may promote resilience in the face of environmental risk factors. We demonstrate that a cognitive training intervention in young adulthood can promote long-term resilience to cocaine-seeking behavior in mice. In Chapters 3 and 4, we shift to the role of developmental processes, particularly hormonal changes during puberty, in shaping frontal circuits and behaviors associated with these circuits. The frontal cortex matures during adolescence and is critical for the decision-making processes that shape life trajectories into adulthood. In Chapter 3, we show that pubertal hormones drive maturation of inhibitory neurotransmission in frontal cortex, which may have implications for the regulation of plasticity and learning across development. We also show that early exposure to pubertal hormones can induce an early reduction in flexible learning on a frontal cortex-dependent task, further supporting the idea that pubertal hormones may regulate developmental shifts in learning and decision-making. Chapter 4 extends these findings to affective behaviors, testing the role of pubertal hormones in the maturation of anxiety- and depression-related behavior, which both depend on interactions between frontal cortex and subcortical limbic structures. We find that gonadal hormones regulate anxiety-related behavior in a sex-specific manner during puberty in mice, while depression-related behavior increases with age regardless of gonadal hormone status. Our findings demonstrate that pubertal hormones regulate aspects of neural and behavioral maturation that may be critical for navigating this vulnerable life stage, indicating a need for further work on the implications of hormonal perturbation during puberty in humans. As we connect these results with the ideas presented in Chapter 2, we discuss adolescence as a critical time in which interventions may alter neurodevelopmental trajectories to promote emotional resilience and adaptive decision-making.

Dual-stage actuation is an important technology enabler for advancing hard disk drive capacity and performance. This thesis describes the ongoing trend of decreasing track pitches required for areal density growth and increasing disturbances arising from rising spindle speeds, demonstrating that future dual-stage actuators will need to overcome the bandwidth limitations faced by the current suspension-based devices. First, the state of the art for dual-stage actuation is presented in the form of a literature review. This is followed by an overview of a new servo-mechanical design and analysis technique which is a hybrid of Galerkin beam elements and optimal linear quadratic Gaussian control analysis. This new technique is used to demonstrate the potential performance benefits of head-based actuation over suspension-based actuation. With the driving goal of designing a new head-based actuator, the constraints posed by industry are presented and discussed in detail. This is followed by an overview of the various actuation mechanisms evaluated, including several electrostatic and piezoelectric devices. The two most significant challenges identified through this analysis are the introduction of a gap at the trailing edge of the air-bearing and the necessity to actuate traces with sufficiently high actuation force.

A quasi-shear mode piezoelectric actuator is proposed as a cost-effective head-based actuator which meets the given criteria and can be implemented at the wafer-scale. A new prototype was fabricated at the Berkeley Nanofabrication Laboratory with a measured bandwidth above 50 kHz. Since the proposed head-based actuation scheme requires a gap in the air-bearing surface, a second actuation mode is also presented. It is shown that the gap width between the slider body and read/write head can be controlled independently of track-following displacement in order to minimize pressure loss at the air-bearing surface. It is also shown that the directionality along each actuation mode of this device is greater that 1:10, although the resolution of measurement tools makes it difficult to determine how much greater the directionality is.

The two key figures of merit for this project are microactuator bandwidth and static displacement gain. For the prototype presented herein, the bandwidth is shown to be greater than 50 kHz, which is the highest frequency measurable by the available equipment. The static gain is measured to be approximately 1 nm/V. With sol-gel based stacking methods, however, the static gain could be scaled as high as 20 nm/V or more, although this will require further investigation by industry to develop. The intellectual merits of this project include a newly developed servo-mechanical design tool, modified beam equations with piezoelectric energy taken into account, and several new fabrication methods. The new fabrication methods include chemical mechanical polishing of PMN-PT, eutectic bonding of PMN-PT to silicon, scribing high aspect-ratio geometry in PMN-PT with a dicing blade, epoxy drop deposition with flipchip bonding, and fabrication of tall MEMS structures with sacrificial copper plating with a wet etch release.

Negative childhood experiences are associated with poor health and psychosocial outcomes throughout one’s lifespan. We examine associations between specific adverse childhood events, recent negative life events, and several adulthood outcomes: psychological distress, functional impairment, general worries about the future, and physician-diagnosed mental and physical health ailments. Data were gathered from multiple waves of an online survey initially administered to a nationally representative sample of U.S. adults between 4/29/13-5/13/13. Over the next two years, respondents (n = 2908) completed detailed measures of exposure to multiple negative childhood experiences as well as physician-diagnosed mental and physical health ailments; over time, respondents also completed measures assessing exposure to negative life events occurring in the past year. All analyses were weighted to adjust for attrition and sampling design. Overall, 24.86% (n = 723) of the sample reported bullying during childhood, 14.65% (n =426) reported physical abuse, 14.43% (n = 420) reported witnessing parental violence, 10.24% (n = 298) reported sexual abuse, and 7.94% (n = 231) indicated parental neglect. Respondents who reported experiencing childhood bullying, physical abuse, and sexual abuse reported greater distress, functional impairment, and worry about future negative events as mediated through recent negative life events compared to those who did not. Those who experienced bullying, neglect, and sexual abuse reported more mental health ailments compared to those who did not while those reporting bullying and sexual abuse reported more physical health ailments. Negative childhood experiences are linked to ongoing exposure to stressful events, which are associated with poorer outcomes in adulthood.

The 26S proteasome is responsible for selective protein degradation in eukaryotic cells. Polyubiquitin chains mark proteins for degradation by the proteasome, but before degradation can occur, ubiquitin chains must be removed by the intrinsic proteasomal deubiquitinase Rpn11. My graduate work primarily focused on understanding how Rpn11 is regulated so it only removes ubiquitin chains from substrates that have been committed to degradation. To answer this question, I developed an Rpn11 purification strategy and solved the crystal structure of Rpn11 alone and in complex with ubiquitin. These structures revealed several features that control the activity of Rpn11 toward ubiquitin substrates. I showed that Rpn11 is promiscuous in its activity toward different ubiquitin substrates, which explained how the enzyme is able to remove ubiquitin molecules from the wide range of proteasome substrate proteins. Comparison of our ubiquitin-bound and ubiquitin-free structures revealed that a critical loop changes conformation when ubiquitin binds to Rpn11 to form a catalytically active state and that substrate translocation may accelerate this transition, thereby activating the enzyme.

Rpn11 is part of a proteasome sub-complex called the lid. In the isolated lid Rpn11 is inhibited to reduce off pathway deubiquitination prior to proteasome assembly, but the mechanism of Rpn11 inhibition in the lid was not understood. We used cryo-EM to determine the atomic structure of the isolated lid which explained how Rpn11 is inhibited and how it becomes activated when incorporated into the proteasome. Our structure revealed that Rpn11 is held in a conformation that fully occludes its active site and prevents the enzyme from accessing ubiquitin substrates. Mutagenesis of inhibitory residues in the lid release Rpn11 from its inhibited state and activate the enzyme. Similarly, when the lid incorporates into the proteasome, Rpn11 is released from its inhibited state and adopts a fully extended, open conformation seen in the 26S proteasome.

The Philippines contains a highly diverse musical history rich in avant-garde compositional practices. Composers such as José Maceda and Jonas Baes have been significant contributors composing pieces for several decades that have progressed their praxis specific to this region. These Filipino avant-garde practices were first developed by Maceda while he worked as an ethnomusicologist, leading him to search for non-Western “musical truths” through the discovery and development in his own compositions by incorporating elements from indigenous Philippine and Southeast Asian cultures. Filipino composers in the generations after Maceda, such as Jonas Baes, would follow this path and help further the practice of avant-garde composers in the Philippines. This dissertation investigates and analyzes this traditions in two representative compositions: Basbasan (1983) by Jonas Baes, and Colors Without Rhythm (1999) by José Maceda. These pieces are placed in perspective with the cultural and historical elements that lead to their inceptions, while analyzing compositional techniques that are unique to these composers and the region of the world that they are from.

Learning to lead by example and to lead with positivity creates a world of opportunity. Voice work with Ursula Meyer showed me that I had a wide range to work with when I was using very little before. Movement work with Stephen Buescher reminded me that I love to play and full commitment is easier than achieving perfection. Text work with Marco Barricelli made me realize how important it is to put in the hours and understand not just the words, but the life behind them. All of this and more helped me to stay on top of my craft and allowed me to come prepared and ready to play for every day of rehearsal. When I was in Preston Choi’s 900 Years, I was thrust into a leadership position as I became an anchor in production because people started to drop out. Everyone started to get worried, and I felt a need to make sure everyone who was there was being looked after. Though it was a very stressful environment, I lead by example with my work and did my best to stay positive in the uncertain times. In the end, we were able to tell a beautiful story about the love of family. More recently, I was a part of Shakespeare’s The Comedy of Errors and continued to stay on top of my work and outputted positivity to keep the ensemble moving in a forward direction. We came together and made a fun experience with many laughs. A world filled with positivity is a world filled with opportunities.