UC Merced

Illumination systems have advanced significantly in the 21st century to develop more energy efficient lighting, however, many of the optical systems that direct the light from an illumination source remain archaic in their design principles. This leads to significant performance inefficiencies in lighting, even with a highly efficient energy source. With the advent of nonimaging optics, understanding of ideal light transfer has unlocked new opportunities to advance the field of illumination and deliver truly ideal optical systems, which minimize energy waste and light pollution while maximizing spatial illumination.

This dissertation will present novel work advancing the field of illumination by outlining a new figure of merit that characterizes the thermodynamic limits to geometric illumination. With this figure of merit, any optical design can be quantified by performing a ray tracing simulation. This figure of merit will help to inform illumination engineers whether their design is fully illuminating a space or wasting light to the environment.

Utilizing this novel figure of merit, two new optical systems are presented to improve on existing illumination designs. The first design, a new theatrical spotlight based on nonimaging optics, offers equivalent light output to existing commercial designs, while decreasing the energy requirement down to 10-fold. The second nonimaging design focuses on three-dimensional asymmetric off axis illumination. Building on the two-dimensional design principles of the nonimaging asymmetric compound parabolic concentrator (ACPC), a new 3D version was developed that preserves the asymmetry while maintaining ideal light transfer.

These two new designs were characterized by the novel figure of merit. Both the nonimaging theatrical spotlight and 3D ACPC showed significant optical performance benefits over existing designs in literature and commercial production. Future work will be proposed on how to enhance the usefulness of this novel figure of merit, as well as future applications, characterization, and production of the new illumination designs developed.

This thesis begins with the introduction of optomechanics, the study of the interaction between light (photons) and mechanical oscillations (phonons) using bulk 3-D cavities. The description of 3-D microwave cavities is introduced as the boundary of the electromagnetic field and the mathematics are developed for the interaction between the electromagnetic field and a fluctuating boundary (mechanical oscillator). This work was established in pursuit of observing optomechanical effects within macroscopic 3-D cavity systems.

Three main microwave 3-D cavity geometries were used for this work: cylindrical, re-entrant, and coaxial quarter-wave (λ/4) cavities. A large number of cavities were made by the author in a machine shop in an attempt to develop strongly-coupled optomechanical systems. The pursuit of this goal led to the first observation of strain engineering, or dissipation dilution, via the thermal Casimir effect and its exciting potential applications.

The noteworthy projects that saw success in this work were the development of tunable, superconducting microwave cavities using a lossless, non-contacting fashion in addition to the ground-up progression of re-entrant cavities that led to the first observation of the thermal Casimir spring and dilution effect at room temperature. The outcome of this work opens the doorway for the development of “in situ” arbitrary, topological resonators with the added benefit of an increased mechanical quality factor Qm due to heightened strain.

“Long Live the Arab Worker: A Transnational History of Labor and Empire in the Yemeni Diaspora,” examines how Yemeni workers and activists in their struggle to live and make a living highlighted the connections between local challenges in the diaspora with global politics of empire. By foregrounding experiences of Yemeni diasporic communities throughout the 20th century, this project interrogates the intersections of labor and empire while also highlighting the complicated, multifaceted, and often messy realities within histories of activism and community organizing. It analyzes how labor and labor activism in the diaspora became an ideological arena in which politics of empire were obscured, accommodated, exposed, and challenged.

In 1839, the establishment of the British Protectorate in Aden and the presence of the British East India Company in Yemen consolidated the colonial, political, and economic connections that would draw Yemeni labor and immigrants to Britain and later the United States. The ceaseless desire for cheap labor in both countries would lead to continued labor migration from Yemen throughout the 20th century. Classified as British subjects, some of the first Yemeni migrant workers were recruited from the ports of Aden to work on British ships. While some remained in the shipping industry as sailors, many eventually settled in cities in England and found work in the steel industry. By the 1960s and 1970s, more significant numbers of Yemenis immigrated to the United States and toiled in California’s fields as farm workers as well as auto workers in Detroit’s booming auto industry. Both British and U.S. imperialism in Yemen and the Middle East not only enforced labor migration, but continuously shaped the experiences of Yemeni workers and families in the diaspora.

Through an exploration of archival sources and original oral histories, this project tells the stories of these workers who provided labor throughout the “diaspora of empire.” Kobena Mercer theorized the “diaspora of empire” as a “reminder and a remainder of the nation’s historical past.” I borrow from Nadine Naber’s development of diaspora of empire which emphasizes how because of contemporary U.S. neocolonial and imperial formations, Arab diasporas cannot be understood simply within a postcolonial timeline in which people reside in the countries that formerly colonized them. Rather, diaspora of empire refers to the “moment in which empire and its subjects exist in a transnational and contemporaneous frame.” In other words, diaspora of empire points to the ongoing impacts of both formal and informal empire. This research explores how Yemeni workers and activists through their labor and activism experienced and resisted politics of empire in the diaspora throughout the 20th century. By unpacking these stories, we can come closer to understanding the current precarities facing Yemeni diasporic communities today.

Drinking Water plays an important role in human society and its consumption is increasing significantly due to growth in population and living standards. More than 97% of the water on earth is saline and undrinkable. Desalination is an engineering solution to produce drinking water from saline water. Although desalination is a prac- tical solution that could solve the water scarcity challenge around world, there are two major challenges associated with desalination: energy-intensity and brine disposal. Desalination is an energy-intensive process that requires large amounts of electricity and/or heat. Therefore, desalination plants prefer to use cheap energy sources mostly powered by fossil fuels. However, solving the water scarcity challenge should not ex- acerbate global warming, which will have catastrophic effects on our planet. Also, desalination produces a concentrated brine which must be discharged back to the en- vironment. Brine disposal from inland desalination is very problematic. Brine is also often discharged to the ocean, which can threaten the health of marine ecosystems. In this thesis, I present research on two solar collector systems that can be used as an energy source to drive desalination, and one desalination system that can reduce brine discharge to the environment. The first system is a novel medium-temperature solar collector with pentagon absorber called the External Compounds Parabolic Concentrated (XCPC). The collector, with 6 evacuated tubes, CPC reflector and manifold, is designed in SolidWorks. Then the collector is simulated using the finite element method implemented in COMSOL Multiphysics with coupled optical-thermal multiphysics to predict optical and thermal efficiency of the system. The proposed medium-temperature collector is tested with a selective-coated pentagon absorber un- der real-world conditions at the University of California, Merced. The experimental and numerical results show close similarity; the optical efficiency of 64% and thermal efficiency of 50% at working temperature of 200 ◦C are achieved both numerically and experimentally. Secondly, a low-cost concentrated hybrid Photovoltaic-Thermal (PV/T) collector is designed, simulated, and experimentally tested. The proposed PV/T collector simultaneously generates both electricity and thermal energy for low temperature application (60-90 ◦C) such as residential and/or commercial hot wa- ter and small-scale desalination. The collector itself consists of a glass tube with a reflective coating applied on the bottom half which directs incoming rays to strings of solar cells applied over a flat minichannel absorber. Performance is simulated us- ing COMSOL Multiphysics to guide the collector design. Afterwards, multiple tubes are manufactured and tested in both direct-flow minichannel and heat pipe absorber configurations. The assembled PVT collector demonstrated a thermal, electrical and combined efficiency of 60% and 10-15% , 70-75%. The third system presented uses a novel zero liquid discharge desalination approach called Immiscible Liquid Medi- ated Humidification Dehumidification (ILM-HDH). This system introduces a second liquid, mineral oil, to provide heat for evaporation to separate the salt and contam- ination from fresh water in a feedwater stream. ILM-HDH reuses the condensation energy of water which makes it potentially 3-4 times more efficient than state-of-art evaporators while still achieving maximum water recovery. In addition, ILM-HDH address the issue of corrosion in thermal desalination systems since it uses mineral oil instead of saline water as the Heat transfer Fluid(HTF). This feature also makes ILM-HDH highly compatible with the two solar collectors proposed in this study, since the HTF can be directly pumped into the solar collectors with no corrosion issues or need for a heat exchanger.

This project examines the ways Taiwan’s contested sovereignty pokes holes in dominant understandings of what it means to be a sovereign nation based on the discourses of Taiwan that appear in transnational popular culture and media. As a result of Taiwan’s role as a global economic center, the traces Taiwan leaves behind in transnational media, and the scandals they garner, reflect the larger dynamic of Taiwan as a constant problem and yet a valuable commodity for powerful nation-states. Taiwan is simultaneously a site of transnational profit for states like China, as well as a rhetorical threat to a One China Policy. This liminality represents a kind of impossible sovereignty—one that is politically illegible, but functional nonetheless. This form of sovereign absurdity for Taiwan is perhaps best encapsulated by the Hokkien term ku-mo. Ku-mo is a transliteration of a 台語 colloquialism 龜毛, which describes someone who is slow or high maintenance to the point of inconveniencing others. There is a second definition to龜毛, one grounded in a Buddhist idiom that represents an absurdity—something that does not and ought not to exist. I argue that Taiwan’s impossible sovereignty can be described as ku-mo in the sense that it is conceptualized both as an impossibility and an inconvenience that disrupts otherwise uniform and smooth processes of international trade and media production.

Taiwan’s contemporary liminal sovereignty presents a profound problem for the very nation-states that attempt to erase it, and as a result of Taiwan’s role as a center of transnational capital, the debate over Taiwanese sovereignty is contested and mediated transnationally through culture and the culture industry of multiple nation-states. The relevant question of Taiwan’s sovereignty for us is not, “Is Taiwan sovereign?” but rather “What does the discourse surrounding the question of Taiwanese sovereignty accomplish and how does it function?” Examining sovereignty as a discourse and a practice allows us to explore the ways conceptions of sovereignty are defined by documentation, institutions, and bureaucracy that are perpetually attempting to contain that which cannot be contained.

The biomimetic structures of carbon nanotube porins and lipid membranes provide a membrane coating to isolate biosensor surface from potential foulants present in biological fouling solution. The lipid membranes mimic cellular membrane while the ultrashort carbon nanotube porins mimic the structure and functionalities of membrane protein channels. This versatile biosensor platform enables the ion sensing at nano-bio interfaces and opens up the potential for intracellular and multimodal sensing.

In this dissertation, I will review the properties and advantages of carbon nanotubes in the nanofluidics field. I will report the optimization of high-yield synthesis of carbon nanotube porins, the biomimetic nanochannels in membranes. I will also discuss the fully synthetic membrane with incorporation of carbon nanotube porins into a block-copolymer matrix. In addition, I will present a biomimetic approach for creating fouling-resistant pH sensors by integrating silicon nanoribbon transistor sensors with an antifouling lipid bilayer coating that contains proton-permeable carbon nanotube porin channels and demonstrate robust pH detection in a variety of complex biological fluids. And lastly I will describe potential applications of the carbon nanotube porin based biosensor platform.

Quantum dots (QDs) are semiconductor nanoparticles that trap electrons and holes in all three dimensions, resulting in discrete energy levels with strong optical transitions. InAs/GaAs QDs are grown by molecular beam epitaxy of lattice-mismatched InAs on a GaAs substrate, resulting in strain-induced island formation on a two-dimensional wetting layer. In addition to optoelectronic applications such as lasing, infrared detection, and photovoltaics, QDs are capable of hosting optically-controlled spin qubits and emitting photonic qubits for quantum communication and quantum computation.

This dissertation focuses on InAs/GaAs coupled quantum dot pairs (CQDs) formed by strain-induced alignment of QDs in nearby layers, resulting in interdot charge tunneling that can be controlled with an applied electric field. We use a combination of theoretical modeling and optical spectroscopy to understand dynamical processes of bound photoexcited charges, aiming to enhance their usefulness for quantum information and sensing technologies and help overcome difficulties preventing their implementation.

We develop a model of electron and hole confinement in CQDs, including Coulomb and spin interactions, phonon coupling, and optical transitions. This model is used to simulate relaxation dynamics during neutral molecular biexciton cascades, identifying parameter regimes where two-photon polarization entanglement can be expected. While this process has been demonstrated in single QDs, we find that charge separation in interdot states of CQDs allows for tunable emission energies and a higher tolerance to anisotropic electron-hole exchange splitting.

Using low-temperature optical photoluminescence spectrosopy, we identify charge and spin states in single CQDs and investigate their interactions. Two-laser photoluminescence excitation spectroscopy demonstrates two-photon excitation into the molecular biexciton state via a stepwise process, while calculations identify conditions required for efficient simultaneous two-photon absorption. Further investigations find decoherence by electric field fluctuations from charged lattice defects, and identify a novel enhancement of acoustic phonon coupling at hole tunneling resonances from piezoelectric interactions.

Background and Objective: Sugar-sweetened beverage (SSB) taxes have been increasing in popularity across the United States and have been implemented in some California cities. Studies have shown SSB taxes reduce the consumption of SSB but also increase the consumption of juice, milk and sugary sweets. Support for an SSB tax is influenced by various factors, including the proposed amount of the tax, how the tax is used and the demographics of the population. The purpose of this study is to examine attitudes towards SSB taxes among a predominantly young, Latino population in California.

Method: Discrete Choice Experiment (DCE). Attributes and levels were defined according to the findings of a literature review and focus groups. The DCE included five attributes and within each attribute were separate related choices. Data was analyzed using a conditional logistic regression model. Separate analyses were performed for low and high SSB consumers to determine if participants took into consideration different attributes when making decisions about what to drink.

Results: A total of n= 315 participated in the DCE survey. Overall, participants expressed a preference for water and juice compared to regular soda. The time it takes to get the beverage and price were important attributes which influence their beverage consumption decisions; they want convenience when getting their drinks and to pay less for them.

Conclusion: These data show that for those who are not yet replacing soda with water or juice they would convert easily. The high value these participants place on water may result in a higher reduction in caloric intake if the price to SSB is increased.

The Relationship Intimacy Model of Couple Adaptation to Cancer (RIM; Manne & Badr, 2008) theorizes that relationship-enhancing behaviors increase couples’ intimacy and, in turn, improves psychological and relationship adaptation to cancer. In contrast, relationship-compromising behaviors reduce intimacy, which in turn negatively impacts outcomes. This model has been applied to examine the relationship experiences of couples along the cancer survivorship spectrum. Yet, it is unknown if the model accounts for relationship dynamics in situations outside the cancer context. The primary goal of this study is to test the validity of the RIM framework within general relationship dynamics and during a health event. Participants were asked to draw upon their interactions with their romantic partners, relationship intimacy, relationship satisfaction, and psychological adaptation in general daily life as well as during a recent health event. Participants (N = 505) were on average 20.1 (SD = 1.94) years old, female (75%), Hispanic/Latino (66.3%), and in committed relationships. Stepwise linear regression analyses revealed that in the context of general daily life: (1) partner responsiveness was positively associated with intimacy, positive affect, and relationship satisfaction, and negatively associated with negative affect; (2) perceived self-disclosure was positively associated with intimacy, positive affect, and relationship satisfaction; (3) both emotional suppression and self-demand/partner-withdraw were positively associated with intimacy, negative affect, and depression, and negatively associated with relationship satisfaction; and (4) partner-demand/self-withdraw was positively associated with intimacy and positive affect. In the context of a health event: (1) partner responsiveness was positively associated with intimacy, positive affect, and relationship satisfaction; (2) emotional suppression was negatively associated with positive affect and couples relationship satisfaction, and positively associated with negative affect and intrusiveness and avoidance; (3) criticism was negatively associated with relationship satisfaction; (4) partner-demand/self-withdraw was positively associated with negative affect and intrusiveness and avoidance; (5) self-demand/partner-withdraw was positively associated with intimacy. Mediational analyses revealed that in general daily life, intimacy mediated the relationships between: (1) partner responsiveness, emotional suppression, self-demand/partner-withdraw, partner-demand/self-withdraw and positive affect (2) partner responsiveness, partner-demand/self-withdraw and negative affect; and (3) relationship satisfaction and partner responsiveness, emotional suppression, self-demand/partner-withdraw, partner-demand/self-withdraw. During a health event, intimacy mediated the relationships between: (1) positive affect and partner’s responsiveness, self-demand/partner-withdraw, and (2) negative affect and partner responsiveness. This study highlights important components of relationship behaviors that may predict relationship satisfaction and adaptation to health events and in general relationship dynamics. These findings can improve efforts to tailor couples-based interventions to promote adaptive coping and adjustment to different illness experiences and for relationship satisfaction in everyday life.

In SOFCs, we observe that the porous electrodes tend to agglomerate and thus decrease the cell performance over time. The agglomeration (or sintering) of a porous oxide can be understood as the diffusion of the oxide atoms along the surface of a material to minimize the surface energy of the structure. Therefore, even an ultrathin overcoat is expected to deter the sintering process and thus maintain the porous geometry for longer period of time. In this thesis, the actual role of YSZ overcoat in the ORR process is presented through a series of electrochemical analyses. Without an overcoat, a nanoporous Pt is significantly agglomerated during a high-temperature operation, and ORR kinetics becomes limited by the availability of TPB. An ultrathin YSZ overcoat significantly suppressed the sintering kinetics and preserved the morphology of its underlying Pt layer. More importantly, the overcoat acts as an excellent facilitator of the atomic oxygen species-mediated chemical process(es), which used to be rate-limiting in the ORR of a non-coated Pt/YSZ system.

In the next step, to understand the impact of spincoated layer on the interface of cathode/electrolyte, EIS data obtained at different temperatures and oxygen partial pressures. Beside SEM imaging and XRD, to support the hypothesis of ORR kinetics, infiltration and ALD coating also performed on different samples. We found out that spin-coated layer has smaller nanoparticle sizes and 3~4 times smaller nanocrystalinity that increase the active cites for dissosiative adsorption on the cathode side, comparing to the available cites on bare LNF. EIS data along with ALD coating also strongly support the hypothesis that ion conducting pass through the LNFGDC FL playes an important role in decreasing the polarization resistance comparing the bare LNF cathode as well. It helps the available cites not limited to the vicinity of GDC interlayer but be available in entire FL and the ion transport to the GDC interlayer through GDC nanoparticles paths.

To sum up, a combination of nanoscale treatments including cathode infiltration, metal oxide ALD coating, and cathode-electrolyte interface spin-coating pursued to achieve a significantly enhanced performance and durability by addressing the issues. In addition, I also performed a systematic studies on the change in electrochemical kinetics and a possible shift of bottleneck process by the treatments to better understand the effect of each of this nano-functionalization on oxygen reduction catalysis process in SOFCs.