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Spectroscopy and Kinetics of Reactive Intermediates in the Atmosphere of Venus: the Catalytic Role of Chlorine Atoms
Get PDFChlorine chemistry plays essential roles in both industrial and academic fields due to the special reactivity required to initiate or catalyze important reactions in our daily life. For example, Cl atoms are the most common oxidation agents in combustion and are famous for the catalyzed destruction of ozone that eventually leads to the ozone hole.
As terrestrial planets, Venus and Earth’s atmospheres have similar origins but very different evolutions. Compared to Earth, Venus suffers strong water loss in hydrodynamics escape due to its distinct distance from the Sun; as a result, high abundances of chlorine and sulfur species are not trapped in the sea and survive in Venus’ atmosphere. For example, a dense cloud, made with sulfuric acid, has been observed at the middle altitude (50 - 70 km) and the concentration profiles for distinct species (SO₂, CO, CO₂, O₂ ..., etc.) have been measured during the Venus Express mission operated by the European Space Agency. Digging into the discrepancy between the observations and model simulations, a few important questions arose, and further laboratory studies are needed to solve the puzzles, including (1) the unknown UV absorber, (2) the SO₂ concentration inversion at high altitude and (3) the extremely low O₂ and high CO₂ abundances, wherein a reactive chlorine atom is proposed for explaining these phenomena.
In this thesis, we performed the pulsed-laser photolysis experiments with a homemade time-resolved broadband UV-Vis transient-absorption spectroscopy coupled with a temperature- and pressure-controlled flow reactor to study the spectroscopic and kinetic
properties of key intermediates (ClSO, ClCO and ClCO₃) in the oxidation process of sulfur and carbon to ultimately form SO₂ and CO₂. The recorded spectra are analyzed, and highlevel ab initio calculations were performed to rationalize the electronic structures of target molecules to reveal the catalysis role of Cl atoms. In addition, key reaction rate coefficients
(ClSO + Cl, kClSO+Cl(292 K) = (1.48 ± 0.42)x10-11 cm³ molecule-1 s-1; ClCO + O₂,
kClCO+O₂(0) = (9.0 ± 2.3) × 10-32 cm⁶ s-1 a cm³ molecule-1 s-1, and thermodynamic property (Cl + CO ⇌ ClCO, Keq = 1.8 x10-18 molecules cm⁻³) have been measured to
further assist the model simulations.
This thesis not only offers essential data for model simulations to understand the complex chemistry in Venus' atmosphere but also provide new insights to guide future tasks to explore Venus, e.g. DAVINCI+ and VERITAS by NASA.</p
Progress Toward Precision Measurements Using Polyatomic Molecules
Get PDFSymmetry is a useful tool for solving problems and is a guide helping us to formulate new theories to better understand the universe. The violation of expected symmetries indicates a lack of full understanding and may point towards promising directions of inquiries. The combined Charge Parity (CP) symmetry is one such expected symmetry, and it's violated by a very minute amount in both theory and observations. Within the Standard Model, we don't know why it's here and we don't know its exact amount, though it is not enough to explain the observed asymmetry between matter and antimatter. Hence, studying CP-violating (CPV) physics is a great way to not only complete the Standard Model but also to find out new physics beyond it. We aim to measure CPV phenomena in polyatomic molecules. Specifically, we are going to measure the electron electric dipole moment and the nuclear magnetic quadrupole moment at a precision higher than ever before. Here I report the progress and developments we made towards achieving both
Customized and Modular Control of Gene Expression for Precision Gene Therapies
Get PDFGenetic disorders are caused by mutations in essential genes that disturb the abundance or function of proteins, tipping cells and tissues from homeostatic harmony into disorder. Developing treatment for genetic diseases involves precision approaches, as gene therapies target the root causes of highly specific pathologic processes at the level of gene replacement, editing, or downstream compensation for a harmful genetic change. Safe access to these cell populations, and the ability to control the behavior of therapeutic cargo after delivery to target tissues, will enable the field to develop safe and effective therapies with the potential to be curative. Systemically delivered AAVs can noninvasively target therapeutic genetic cargo to diverse disease loci throughout the body, but at high doses required for therapeutic penetrance of naturally occurring serotypes, these vectors can cause severe toxicity, emphasizing the need for both targeted, efficient gene delivery vectors, and other means of transgene expression control. This work describes three examples of AAV capsid and cargo design strategies that seek to control where, when, and at what level therapeutic transgene expression can be achieved in a preclinical context. First, we utilize native putative regulatory elements to encourage physiologic level of ectopic frataxin expression in a mouse model of Friedreich’s Ataxia, finding that when delivered to both the brain and peripheral nervous system, treatment prevents progression of motor and coordination deficits. Next, we utilize the genetic incoherent feedforward loop circuit motif at the RNA level to decouple vector delivery level from transgene expression level of MeCP2 in a mouse model of Rett Syndrome, finding that when regulated to near endogenous healthy levels of RNA, AAV-MeCP2-IFFL enables behavioral rescue without overexpression toxicity. Lastly, we employ the mechanism for AAV-genome stability in vivo to modulate expression using a post-hoc AAV administration. Together, these methods and applications demonstrate that modular and custom approaches can improve the precision, safety and efficacy problems that the gene therapy field needs in order to advance more treatments for rare disorders
Primitive Stellar Remnants and their Signatures as Probes to the Nascent Solar System
No full textThe confluence of eons of alteration, accretion, and a multitude of other planet-building processes present a tremendous challenge in studying the early Solar System through planetary materials. Mainly, pristine records of conditions in the nascent nebula are rare, and often pose significant analytical obstacles. Fine-grained (fg-) calcium-aluminum-rich inclusions (CAIs) offer a unique opportunity to investigate the earliest stages of nebular evolution, as these are (1) the most primitive condensates in the Solar System, and (2) have never seen melting unlike their coarse-grained counterparts. The main difficulty in working with these inclusions is their diminutive size. Central to the work presented here is the development of techniques that enable the analysis of ever-smaller extraterrestrial samples, mainly leachates from fine-grained CAIs, thereby allowing access to information often rendered unintelligable by bulk analysis.
First, I present a new software suite that optimizes mass-dependent isotope measurements on extraterrestrial materials (Chapter 1). This package, dubbed as COSMO, complements existing computational tools for optimizing the double spike technique (i.e., the double spike toolbox) by accounting for analytical artefacts from mass-independent effects (e.g., nucleosynthetic isotope anomalies). Specifically, the software aids in determining the ideal way to split a limited amount of materials between spiked and unspiked measurements. Such a tool should aid in extracting the most amount of information from rare and critical analytes (e.g., unique meteorites and returned samples).
Next, I discuss the nucleosynthetic barium isotope signatures in the various components of fine-grained CAIs (Chapter 3). These samples were derived via step-leaching of fine-grained CAIs from the Allende meteorite, which have previously been demonstrated to exhibit extreme nucleosynthetic 84Sr excesses. The barium isotope anomalies in these materials serve to potentially elucidate the stellar source(s) of these signatures, as Sr and Ba are documented to co-vary in known presolar materials and have similar geochemical behavior. However, our analyses revealed that these two elements are decoupled in these refractory leachates, pointing to nucleosynthetic sites that overproduce strontium such as electron-capture supernovae (ECSNe) and core-collapse (Type II) supernovae in massive rotating stars. In addition, the step-leaching procedure also reveals a strong congruence between L1-L3 isotopic variability and the anomalous signatures in presolar SiC grains.
Last, I demonstrate that the extreme strontium isotope anomalies in primitive condensates are hosted in oxides using a new protocol called intra-sample addition (ISA; Chapter 4). This experiment also reveals that 84Sr anomalies are heterogeneously distributed in these oxides, which is explained by the nugget effect via the presence of rare but highly anomalous grains. Such grains are interpreted here to be true presolar carriers, which we propose to have served as nucleation seeds of the earliest condensates in the nebula. These results are at-odds with the prevalent notion of a hot and homogeneous nebular gas from which early condensates form, and thus suggest an alternative mechanistic link between disk heterogeneity and the stellar building blocks of the Solar System.</p
Interferometric Millimeter Observations of the High Energy Universe
Get PDFThis thesis explores what can be accomplished in the ways of time-domain astrophysics with a variety of scales of millimeter interferometry. I touch upon techniques in instrumentation, theory, observation, and computation, showcasing the breadth and richness of the field.
The transient millimeter sky is largely comprised of synchrotron sources whose physical properties are just beginning to be revealed. We are entering an age where new wide-field surveys will exponentially increase the number of known transients, including the first wide-field millimeter survey capable of significant transient detections. As we approach this era, resources dedicated to monitoring and follow-up become increasingly more important.
A significant part of my work involves design and commissioning for a new single baseline millimeter interferometer at the Owens Valley Radio Observatory called SPRITE. Uniquely positioned as a dedicated transient follow-up telescope, SPRITE has the ability to observe nearby transients with a relatively high cadence. In this thesis, I also highlight two specific classes of sources for which millimeter observations may be particularly interesting. I present predictions for millimeter emission from supernovae interacting with dense circumstellar media and discuss their rates of detection in upcoming surveys. I additionally present lower frequency spatially-resolved radio observations of an X-ray binary in an active state.
On the other extreme, this thesis also explores the use of very long baseline interferometry to investigate how high resolution images of supermassive black holes vary over the timescale of a year. In 2017, the Event Horizon Telescope Collaboration (EHTC) observed the supermassive black hole in nearby galaxy M87, producing the first resolved image of the shadow of a black hole and potentially revealing intra-day variability of the observed synchrotron emission around the shadow. I present work on the imaging and preliminary analysis of the 2018 epoch of EHT observations of the black hole in M87, and discuss the EHTC’s conclusions of intra-day and year-long variations in the images.</p
Design, Realization, and Applications of 3D Multifunctional Nanophotonics
No full textMetaoptics leverages electromagnetic phenomena and the advanced abilities of modern nanofabrication to replicate traditional optical devices in a fraction of the thickness and to realize novel, compact, multifunctional devices with no known bulk equivalent. Motivated by the expanding role of optics in modern technologies, this field has seen a rise in design techniques for realizing increasingly powerful photonic structures. Three-dimensional (3D) devices, with refractive index distributions patterned at subwavelength scales, represent an enormous design space capable of achieving highly efficient, free space, multifunctional structures. By utilizing a gradient-based, iterative optimization algorithm, a technique for nanophotonic inverse design, we demonstrate scattering structures with unique responses to all the fundamental properties of light. The algorithm is constrained such that resulting devices can be made with realistic multilayer fabrication processes. We present dielectric structures that can be placed directly on top of image sensor arrays and sort light to different pixels based on its wavelength, polarization, and angular momentum, thus enabling efficient and exotic camera technologies. The following work contains fabrication and measurement of 3D devices in the mid-infrared, practical evaluations of devices for visible light imaging applications, and visualizations of underlying structure of photonic design optimization problems.</p
The Birth of PICL: New Laboratory Experiments for Understanding Ocean Worlds
Get PDFA laboratory set up was built analogous to that of the environment of the Galilean system. Previous work has focused on vapor deposition and shied away from bulk samples which more closely resemble the surface of Europa. The focus of this research has been the relationship between laboratory data to observational spectra collected. Data from various telescopes has given an indication of the species which exist on the surface of Europa. Linear spectral modeling has not been effective in identifying these species due to a lack of viable candidates.
Chapter II focuses on the instrumentation and sample preparation for the laboratory set up. In Chapter III data is presented on the irradiation of sodium chloride at Europa like conditions and the features that arise with cryogenic irradiation. This data is compared to observational data from HST and provides strong evidence for the presences of sodium chloride (NaCl) on Europa's leading hemisphere. Chapter IV presents FTIR and UV/VIS data for the irradiation of sulfate salts suspected to be present on Europa. This presents one of the first instances of cyrogenic electron irradiation of sulfates compared to new data from JWST. Mechanisms for the trapping of carbon dioxide at both Europa and Ganymede have also been investigated. These experiments are paramount for understanding the composition of Europa’s ocean and can be utilized by the Europa Clipper team. Future experiments involving laboratory spectroscopy of carbon dioxide trapping are also highlighted. The use of cyrogenic gamma irradiation experiments and their feasibility are explored
Masked 2-Furylcarbinol Derivatives: A Modular and General Platform for Mechanically Triggered Molecular Release
No full textStimuli-responsive polymers that undergo chemical transformations when exposed to external stimuli are attractive materials for a wide range of applications, such as targeted drug delivery, sensing, and catalysis. Within the emerging field of polymer mechanochemistry, mechanical force is harnessed to promote productive chemical transformations in stress-responsive molecules known as mechanophores. My research over the past several years has focused on the development of a modular and general mechanophore platform capable of releasing covalently-bound payloads in response to mechanical force. I envision that the further advancement of this design will not only aid in a deeper understanding of the design principles of mechanophores, but also enable new technologies, including non-invasive spatiotemporal delivery of bioactivate small molecules and self-healing materials.
Chapter 1 reviews the recent process of the development of small molecule-releasing mechanophores and provide an overview of the masked 2-furylcarbinol derivatives we developed that enables a mechanically gated release cascade. Chapter 2 describes our initial demonstration of mechanically gated small molecule release from our mechanophore and the subsequent structural-property investigation to optimize for faster release rates. In Chapter 3, an alternative mechanophore design is introduced that has a shortened synthetic sequence while maintaining a fast release kinetics. In Chapter 4, we address the challenge of low release capacity from previous designs with a novel mechanophore that can be incorporated into multimechanophore polymers. Finally, Chapter 5 demonstrates the use of our modular and general release platform to trigger the depolymerization of a self-immolative polymer.</p
Ultrasound Control and Imaging of Cellular Immunotherapy
Get PDFBiomedical ultrasound-based therapeutics and diagnostics are becoming an increasingly important clinical tool. Techniques like focused ultrasound tissue heating and microbubble-enhanced ultrasound imaging have enabled new ways to noninvasively treat and detect diseases cost-effectively and safely. While these are great leaps forward in ultrasound technology, leveraging synthetic biology tools to engineer cells with the capabilities to interact with ultrasound in novel ways may enable even more avenues for ultrasound to address important clinical challenges.
In this thesis, we explore the potential in engineering immune cells with various genetic elements which interact with either therapeutic or diagnostic ultrasound in novel ways. In Chapter 2, we engineer T-cells capable of sensing increases in temperature and responding by activating expression of therapeutic proteins to potentially increase safety of cell-based immunotherapies by controlling their spatiotemporal activation. In Chapters 3 and 4, we develop monocytes as ultrasound reporter cells for cancer detection by engineering them to express gas vesicles (GVs), a class of air-filled protein nanostructures natively found in certain aquatic microbes, which have been demonstrated to produce ultrasound contrast. We demonstrate the potential to confine GV expression to certain disease related signals to create ultrasound reporter cells. Together, these findings highlight the potential of engineering cells to activate in certain locations in response to ultrasound heating or serve as sentinel cells for disease detection.</p
Electron-Phonon Interactions and Charge Transport in Organic Crystals and Transition Metal Oxides from First-Principles Calculations
Get PDFElectron-phonon (e-ph) interactions play a critical role in determining material properties, such as charge and heat transport, optical response, and superconductivity. Recent advances in first-principles calculations based on density functional theory (DFT) enable quantitatively predictive studies of e-ph interactions and charge transport in a wide range of simple semiconductors and metals. However, certain technologically important materials, such as organic crystals and transition metal oxides (TMOs), remain less explored. Organic molecular crystals, known for their versatile electronic and mechanical properties, typically require high charge carrier mobility for practical applications. Yet accurately predicting the mobility and engineering approaches to improve it are challenging in organic crystals, because of their complex crystal structures with large unit cells and various charge transport regimes induced by e-ph interactions. Similarly, TMOs, both conventional and strongly correlated, are materials with broad applications and unique physics. A notable example are copper oxides (cuprate) superconductors, which are central to the study of high-temperature superconductivity and other exotic physical phenomena. Extensive experimental studies, particularly using photoemission techniques, have been employed to indirectly probe the e-ph interactions in TMOs. Nevertheless, many results are not fully understood, and calculations of e-ph coupling in TMOs are still scarce. This is mainly due to the strong correlation induced by d- and f-electrons posing a significant challenge to modeling.
This thesis aims to develop state-of-the-art first-principles calculations to accurately describe e-ph interactions and the associated physical properties in organic crystals and TMOs. We focus on three research topics. First, we investigate the high-mobility bandlike transport regime in organic crystals. Using the formalism of the Boltzmann transport equation with electronic collisions computed from first principles, we study the mobility and its temperature dependence in benzene, anthracene, tetracene, pentacene, and biphenyl. Our results are in excellent agreement with experiments in all cases, and our pentacene calculation (72 atoms per unit cell) sets the record for the largest first-principles e-ph calculation to date. We find that the mobility is mainly regulated by e-ph scattering from low-frequency intermolecular phonons. Our analysis evidences the effectiveness of strain-based engineering to improve the mobility of organic crystals. Second, we propose a computational approach to study the intermediate polaronic transport regime in organic crystals. This method combines a finite-temperature cumulant-expansion approach for calculating electron spectral functions with the Kubo formula to compute the electronic conductivity and mobility. We show calculations of electron mobility in a naphthalene crystal in excellent agreement with experiments, and find that polaron effects, encoded in the satellites of the spectral functions, are induced by strong e-ph coupling of intramolecular hydrogen-atom vibrations. In the third and final topic, we study quantitatively the e-ph interactions in cuprate superconducting materials. Using the framework of Hubbard-corrected DFT, we focus on the prototypical parent (undoped) cuprate compound La2CuO4, which becomes superconducting upon doping. We show the first quantitative evidence of strong Fröhlich-type e-ph interactions between holes and oxygen atomic vibrations, as well as polaron effects in hole spectral functions. Our findings explain a range of observations in photoemission experiments on both undoped and doped cuprates, suggesting the strong e-ph coupling is an intrinsic feature of the parent compounds rather than being induced by doping. The computational workflow presented in this work can be easily extended to a broad class of strongly-correlated oxides and insulators more generally. In summary, this thesis pushes the boundaries of first-principles calculations of e-ph interactions and transport, paving the way for a microscopic understanding of materials with large and complex unit cells, strong electronic correlations, and strong e-ph interactions.</p