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From Venus to Mars: Spectroscopy and Kinetics of Reactive Intermediates in Planetary Atmospheres
Get PDFThe spectroscopy and kinetics of reactive intermediates in the atmospheres of Venus, Earth, and Mars were investigated through a combination of experimental and theoretical methods. Vibrational progressions in the A- and B-bands of ClSO were assigned, and predicted spectra matched well with experiment. A new unimolecular mechanism for 3-hydroxy-substituted Criegee intermediates was proposed, and predicted to be competitive with known isomerization pathways. The kinetic isotope effect and temperature dependence of the H + HO₂ reaction was calculated using high-level ab initio methods, with implications for the understanding of water loss on Mars
Nonaqueous Electrolyte Design for Energy Storage and Electrosynthesis
No full textElectrochemically driven metal redox has enabled advances in both academic and industrial processes, including production of metals from their ores, storage of renewable energy in batteries and fuel cells, and greener chemical synthesis conditions. While many electrochemical reactions are performed in aqueous solutions, applications in energy storage and organic synthesis often require extreme applied potentials that lie outside the electrochemical stability window of water or necessitate water-free conditions to prevent undesirable side reactions. Herein, we develop tailored non-aqueous electrolytes for applications in both energy storage and organic electrosynthesis and analyze the effects of electrolyte composition on interfacial and electrochemical reactions. First, a series of highly concentrated solvate electrolytes is developed for Li-S batteries, and interfacial reactivity between the solvate electrolytes and the Li anode is investigated in detail. The addition of a fluoroether cosolvent limits electrolyte decomposition at the Li surface, improving cycling stability and enabling new high-temperature applications. Next, samarium(III)/(II) redox is investigated in a variety of non-aqueous electrolytes to support an electrocatalytic cycle for samarium-mediated carbon-carbon bond formation. The coordination environment of the samarium salt, which can be tuned through anion exchange between the electrolyte and the samarium precursor, strongly affects the reversibility and reducing power of the samarium redox couple. Third, electrolyte additives are studied to increase the desolvation barrier of Zn²⁺. When Zn sacrificial anodes are used in organic electrosynthesis, such additives may prevent deleterious cross-plating of Zn²⁺ at the cathode. Finally, a detailed guide to troubleshooting metal sacrificial anodes is presented with special attention to issues commonly encountered in reductive electrosynthesis
Fates of Carbon
Get PDFThis thesis investigates the organic matter relevant to the oldest rocks on the Earth and in the Solar System, along with novel methods for exploring the composition of that organic matter. Chapter II describes a novel method for using a gas chromatography-Orbitrap mass spectrometer system to simultaneously analyze multiple isotopic properties from multiple compounds within a complex mixture. This method is ideal for the study of environmental or extraterrestrial samples and was integral to the study described in Chapter III. Chapters III and IV highlight new isotopic properties that can be measured in extraterrestrial samples to constrain processes of abiotic organic molecule formation: These processes have direct implications for where the carbon on Earth comes from. Chapter III details the measurement of ¹³C, D, and double-¹³C contents of five polycyclic aromatic hydrocarbons in samples returned by the Hayabusa2 spacecraft mission to the Ryugu asteroid. The findings of this study support the formation of aromatic hydrocarbons---arguably the most abundant molecules in the Milky Way galaxy and other galaxies---through low-temperature reactions within molecular clouds in the interstellar medium. Chapter IV characterizes the position-specific carbon isotopic compositions of three structurally-distinct amino acids-- α-alanine, β-alanine and aspartic acid--from the Murchison meteorite, which provide constraints for how they were synthesized abiotically within the meteorite parent body. Chapters V-VI of this thesis relate to organic molecules on the early Earth. Chapter V is a scholarly review of prior data documenting the carbon isotope contents of organic carbon in Archean rocks. It also includes a model for the evolution of the carbon isotopic composition of organic matter as it goes through the rock cycle (i.e., diagenesis, catagenesis, metagenesis and metamorphism), which is then used to re-interpret carbon isotope data based on extant biology and models of metabolic evolution. Chapter VI uses sedimentological experiments to demonstrate that water-soluble organic compounds may have led to the rise of mud deposition concurrent with the evolution of land plants
Entanglement-Enhanced Bioimaging and Sensing
Get PDFStudies of entangled light-matter interactions have been gaining momentum because of their potential applications in bioimaging and sensing. Entangled photons are predicted to linearize nonlinear optical processes and offer orders of magnitude of enhancement to the interaction cross sections. To investigate the validity of entanglement-enhanced bioimaging techniques, a continuous wave (CW)-powered, on-chip, broadband entangled light source based on periodically poled lithium tantalate (ppLT) was designed and characterized. This light source achieved femtosecond entangled correlation times comparable to classical ultrafast lasers with an unprecedented power of ~100 nW in near-infrared (NIR), which is a crucial first step toward fully integrated, thin-film lithium niobate (TFLN)-based, visible to NIR entangled photon sources. This light source was then used for subsequent spectroscopy/microscopy experiments to systematically investigate the feasibility of entanglement-enabled microscopy techniques such as entangled two-photon absorption (ETPA) microscopy and entangled fluorescence lifetime measurements. A novel method was developed to measure fluorescence from ETPA using a spectrotemporally resolved Michelson interferometer which is good at eliminating false signals due to one-photon absorption and scattering. Careful experimental attempts at detecting virtual-state mediated ETPA from rhodamine 6G (R6G) and resonance-enhanced ETPA from indocyanine green (ICG) were made, and the ETPA signals were found to be below the instrument detection limits and often masked by one-photon effects such as scattering and linear absorption. Instead, experimental upper bounds were placed on the ETPA cross sections of the studied molecules, with an emphasis on continued improvement of the light source and instrument detection limits. On-chip entangled fluorescence lifetime imaging microscopy (entangled-FLIM) has also been identified as a new future development focus. The feasibility of the technique was demonstrated via a proof-of-principle experiment which measured the fluorescence lifetime of ICG in various solvents. Using entangled photons produced from a CW laser, the lifetime measurement scheme achieved a temporal resolution of 50 ps and a minimum measurable lifetime of 365 ps, which can be used to distinguish most biologically relevant fluorophores in the corresponding wavelength range. This experiment is a critical first step toward scalable, high-throughput, wavelength-multiplexed, and on-chip FLIM or lifetime measurements which could be used in label-free health monitoring technologies
Limning Asian American Literature with Social Generationality: Violence and Subversion
Get PDFThe existence and identity of the Asian American literary canon have been contentious, and thus so have the methods to study it. Operating with a capacious definition of the Asian American literary canon, I argue the canon exists as a vast heterogeneous one encapsulating the diverse experiences of Asian Americans over generations. I apply a longitudinal study of selected works of the Asian American literary canon and adapt a queer reading hermeneutic to identify forms of literary dissent. Applying social generationality (generational identity) and the hermeneutic in reading the canon illuminates a pattern of socially imposed violences and quasi-queer acts of literary subversion. Ultimately, reading the canon vis-à-vis social generationality illustrates the evolution of Asian American experiences via the evolution of their perceived violences and modes of persistence
Nonlinear Enhancement of Optical Spectroscopy in the Mid-infrared
Get PDFOptical spectroscopy has long been a cornerstone in studying material properties, playing a pivotal role in the advancement of science and technology. It remains crucial in both research and industry, particularly in the mid-infrared (MIR) region, known for its unique molecular fingerprint capabilities. The emergence of optical frequency comb technology has set the stage for dual-comb spectroscopy (DCS) to revolutionize optical spectroscopy with its potential superiority in speed, resolution, sensitivity, precision, and compactness. However, practical implementation of DCS in the MIR region faces challenges due to its demanding requirements for sources, inefficient photodetection, and dynamic range
limitations, despite an exciting prospect.
This dissertation explores the use of quadratic optical nonlinearity to tackle these challenges. By manipulating energy and information flows between photons of different
frequencies through nonlinear optics, we leverage well-developed near-infrared (NIR) sources, detectors, and optics to address difficulties in the MIR region. We first
demonstrate optical parametric oscillators in the regime of simulton (quadratic soliton pair), achieving a high-power broadband MIR frequency comb with a remarkably high NIR-to-MIR power conversion efficiency. We also introduce cross-comb spectroscopy (CCS), which upconverts the MIR frequency comb to the NIR region and allows MIR spectral analysis with NIR photodetection. This novel approach can offer superior signal-to-noise ratio (SNR), dynamic range, and detection efficiency compared to conventional DCS, while providing wavelength flexibility. Additionally, we present a new method to facilitate the detection of trace samples with short-pulse optical parametric amplifiers, which can significantly enhance SNR and limit of detection of existing methods.
Overall, this research demonstrates the capabilities of quadratic nonlinearity in enabling high-performance optical sensing in spectral regions where sources, detectors, and optics are less developed
Measuring Charge Carrier and Structural Photodynamics at Solar Energy Material Surfaces Using Transient Extreme Ultraviolet Reflection Spectroscopy
Get PDFElectronic and vibrational degrees of freedom, and their interactions, control the chemical and physical properties of solids. Core-level spectroscopies, such as transient extreme ultraviolet (XUV) spectroscopy, provide detailed information on the electronic structure and local coordination environment of a material. In this work, we employ transient XUV reflection spectroscopy to measure surface carrier and structural dynamics in solar energy materials. To interpret experimental spectra, excited state valence effects are incorporated into the OCEAN code (Obtaining core excitations from ab initio electronic structure and the NIST Bethe-Salpeter equation solver). The modeling of core-level spectra from first principles enables the extraction of carrier kinetics via the robust assignment of spectral features. Moreover, this thesis explores experimental and theoretical methods for understanding carrier-structural coupling in solids relevant to solar energy applications.
Specifically, we explore the chemical and physical information contained in core-level spectra for various solar energy material systems and present guiding principles for designing a core-level electronic spectroscopy experiments to determine photoexcited carrier and structural dynamics. We report on experimental measurements of ultrafast surface carrier and structural dynamics in photocathodes zinc telluride and copper iron oxide. Further, complementary excited state theory is presented to extract excited state valence dynamics from experimental core-level spectra based on ground state implementations of the Bethe-Salpeter equation.</p
Asymptotics with Numerical Relativity: Gravitational Memory, BMS Frames, and Nonlinearities
Get PDFWith the recent commencement of the LIGO-Virgo-KAGRA (LVK) Collaboration's fourth observing run, the field of gravitational-wave physics is uniquely poised to collect even more accurate data from compact binary coalescences. Consequently, we will soon be able to perform more stringent tests of general relativity (GR). Because GR must, in some regime, be violated---either because the Universe is described by an alternative theory or because of the emergence of quantum effects---these tests of GR are crucial for unveiling new physics. Performing such tests, however, requires that our understanding of GR and gravitational waves is reliable. And, while there are many tools for unraveling Einstein's equations, the only one that is robust in every regime of GR is numerical relativity (NR): a means for computing accurate solutions to Einstein's equations with supercomputers.
In this thesis, I highlight some recent and impactful advancements that have been incorporated into NR simulations of binary black holes. In particular, I show how a more robust procedure for calculating the radiative data at future null infinity from NR simulations, called Cauchy-characteristic evolution (CCE), produces waveforms that exhibit a not-yet observed prediction of GR colloquially referred to as memory. This phenomenon corresponds to the permanent net displacement that two observers will experience due to the passage of transient gravitational radiation. Memory is of particular interest in the testing GR and theory communities because of its relation to asymptotic symmetries and scattering amplitude calculations in particle physics. With these contemporary CCE waveforms, I provide explicit methods to calculate the various memory effects and I also comment on their relative magnitudes and detectability in the near future. Apart from this, I also demonstrate the importance of controlling the BMS freedoms of these waveforms, i.e., their frame freedom at future null infinity, for building waveform models as well as for extracting physics, such as GR's nonlinearities, from the ringdown phase of binary black hole mergers.
As we start to enter the next phase of high-precision gravitational-wave astronomy, correctly modeling gravitational waves with NR simulations will play a crucial role in pushing Einstein's theory of relativity to its limits. It is the aim of this thesis to illustrate the importance of combining gravitational-wave theory and NR to not only improve our understanding of black holes and gravitational waves, but also further our prospects for unveiling the true nature of gravity within our universe.</p
Carbon Currencies: Isotopic Constraints on the Biogeochemistry of Organic Acids
Get PDFOn both human and geologic timescales, the microbial degradation of organic carbon in anoxic environments significantly influences the Earth’s climate. The rate-limiting step of this process is the initial breakdown of complex organic polymers (e.g. cellulose) into small organic acids (e.g. acetate), which are then rapidly converted into either carbon dioxide or methane. While the steady-state concentration of organic acids is kept low by microbial turnover, the flux of reactions producing and consuming them is large. In my doctoral work, I leveraged this dynamic pool of metabolites as a window into the broader carbon cycle. Specifically, I developed novel analytical and computational tools that quantify and interpret the isotope composition of organic acids. These techniques provide new information about the mechanism and rates of organic acid turnover in nature.
First, in Chapter 2, I adapted electrospray ionization (ESI) Orbitrap mass spectrometry (MS) to simultaneously measure the carbon and hydrogen isotope compositions of acetate. This approach is 50 to 1000-fold more sensitive than established techniques, making measurements of environmental samples feasible for the first time. This technique clearly distinguishes the metabolic sources of acetate (fermentation and acetogenesis). In Chapter 3, I developed a complementary computational tool to interpret this new isotopic information. Quantifying Isotopologue Reaction Networks (QIRN) builds numerical models of complex reaction networks, including metabolic pathways, and predicts the isotope composition of molecules produced by these networks. In Chapter 4, I combined my analytical and computational approaches to investigate the isotopic fractionations of the microbial metabolism that generate organic acids in nature, fermentation. I found that fermentation imposes a significant isotopic fractionation during the degradation of organic matter. By coupling flux-balance analysis and QIRN, I isolated the enzymes responsible for these fractionations. These results suggested that fermentation may have imprinted a carbon isotope trophic enrichment that is observable in the compound-specific carbon isotope composition of Proterozoic biomarkers. In Chapter 5, I used my Orbitrap method to quantify in situ acetate turnover rates based on the exchange of hydrogen atoms between water and acetate's methyl group. I took this tool to the environment, where I studied the biogeochemical drivers of carbon cycling in the deep continental subsurface. In Kidd Creek mine, which has subsurface fracture fluids that have been isolated for over a billion years, I found that acetate is being actively produced and consumed in the subsurface. My analyses of acetate's isotope composition suggested that turnover may be driven by low-temperature water-rock reactions with implications for the habitability of subsurface environments elsewhere in the Solar System. Chapter 6 is a second application of the Orbitrap and QIRN in natural systems. This time I expanded the Orbitrap technique to include not only acetate but also the organic acids propionate and butyrate. I investigated carbon turnover in the rumen fluid of cows, where microbial fermentation breaks down cellulose and transfers organic acids to the animal host. I found clear trends in the carbon and hydrogen isotope composition of acetate and propionate that may hold information about the metabolic strategies of fermenters in the rumen. Finally, in Chapter 7, I highlight the challenges and opportunities of transitioning Orbitrap MS isotopic applications from pure standards to compelx samples. These studies demonstrate bespoke strategies for isolating organic acids, and possibly other ESI-Orbitrap analytes, from environmental samples without fractionating their isotope ratios. Together, these chapters use a combination of novel analytical and computational tools to study the rate and mechanism of organic acid cycling in nature. Elucidating these drivers is necessary to understand the modern and ancient carbon cycle and to predict its response to climate change.</p
Institutional Design of Criminal Justice Processes
Get PDFThis dissertation contains three essays that contribute to ongoing debates about the design of institutions and procedures related to criminal justice.
Chapter 1 investigates how peremptory challenges in the jury selection process affect the diversity of and outcomes from juries. A game-theoretic model of attorneys’ decisions to strike potential jurors finds that the process 1) can lead selected jurors from a majority group to be a skewed sample and 2) can increase minority representation, contrary to common intuition. The first theoretical finding about the skew is supported by empirical analysis of data from jury selection transcripts: a novel measure of the pro-defense lean of jury pool members is developed, and selected White jurors are found to be more pro-defense than the average White pool member.
Chapter 2 develops a game-theoretic model of decisions about the verdict and sentence in a criminal trial, considering both single-actor and two-actor versions of this two-step process. Restrictions on sentencing discretion can lead to nullification where an actor with acquits who would have convicted under full discretion. When actors care about the lawfulness of their own actions, a two-actor process may lead to additional convictions, as the convicting actor can free ride off of a separate sentencing actor who will pay the cost of sentencing away from the lawful sentence. The model also leads to non-monotonic effects on the verdict when lawfulness or the expected sentence change.
Chapter 3 (joint work with Alexander V. Hirsch) uses mechanism design to examine single-threshold information escrows in a workplace setting. In this setting, reports of misconduct by a manager are kept secret until the number of reports exceeds a threshold and the manager is fired. When the firm designing the system wishes to minimize misconduct, a single-threshold mechanism leads to optimal results when misconduct reports are costless. In contrast, costly misconduct reports can make truthful reporting impossible under certain threshold values, raising the threshold above the firm’s ideal or even eliminating the possibility of any truthful mechanism. We find that single-threshold mechanisms are generally worse for the firm than mechanisms that mix two thresholds and can be worse than choosing whether to fire the manager without eliciting any information about misconduct.</p