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Optical Response in Planar Heterostructures: From Artificial Magnetism to Angstrom-Scale Metamaterials
Get PDFThe idea of expanding the range of properties of natural substances with artificial matter was introduced by V. G. Veselago in 1967. Since then, the field of metamaterials has dramatically advanced. Man-made structures can now exhibit a plethora of extraordinary electromagnetic properties, such as negative refraction, optical magnetism, and super-resolution imaging. Typical metamaterial motifs include split ring resonators, dielectric and plasmonic particles, fishnet and wire arrays. The principle of operation of these elements is now well-understood, and they are being exploited for practical applications on a global scale, ranging from telecommunications to sensing and biomedicine, in the radio frequency and terahertz domains. Accessing and controlling optical and near-infrared phenomena requires scaling down the dimensions of meta- materials to the nanometer regime, pushing the limits of state-of-the-art nano- lithography and requiring structurally less complex geometries. Hence, within the last decade, research in metamaterials has revisited a simpler, lithography- free structure, particularly planar arrangements of alternating metal and dielectric layers, termed hyperbolic metamaterials. Such media are readily realizable with well-established thin-film deposition techniques. They support a rich canvas of properties ranging from surface plasmonic propagation to negative refraction, and they can enhance the photoluminescence properties of quantum emitters at any frequency range.
Here, we introduce a computational approach that allows tailoring the dielectric and magnetic effective properties of planar metamaterials. Previously, planar hyperbolic metamaterials have been considered non-magnetic. In contrast, we show theoretically and experimentally that planar arrangements com- posed of non-magnetic constituents can be engineered to exhibit a non-trivial magnetic response. This realization simplifies the structural requirements for tailoring optical magnetism up to very high frequencies. It also provides access to previously unexplored phenomena, for example artificially magnetic plasmons, for which we perform an analysis on the basis of available materials for achieving polarization-insensitive surface wave propagation. By combining the concept of metamaterials’ homogenization with previous transfer matrix approaches, we develop a general computational method for surface waves calculations that is free of previous assumptions, for example infinite or purely periodic media. Furthermore, we theoretically demonstrate that hyperbolic metamaterials can be dynamically tunable via carrier injection through external bias, using transparent conductive oxides and graphene, at visible and infrared frequencies, respectively. Lastly, we demonstrate that planar graphene-based van der Waals heterostructures behave effectively as supermetals, exhibiting reflective properties that surpass the reflectivity of gold and silver that are currently considered the state-of-the-art materials for mirroring applications in space applications. The (meta)materials we introduce exhibit an order-of-magnitude lower mass density, making them suitable candidates for future light-sail technologies intended for space exploration.</p
Towards a Theory of Quantum Gravity Through Geometrization of Quantum Mechanics
Get PDFIn this thesis, we adapt an approach by assuming quantum mechanics as a fundamental theory of nature and attempt to recover familiar concepts such as space-time geometry and gravity from quantum wavefunctions and their unitary evolutions. More specifically, we explore a number of approaches in "geometrizing" quantum systems using techniques such as tensor networks and manifold learning. We find that consistency conditions in quantum gravity can be used to put constraints on tensor network models that approximate the anti-de Sitter/Conformal Field Theory correspondence. Furthermore, quantum circuits and tensor networks can also be used to describe cosmological models and reproduce important features of space-time configurations such as de Sitter space. We find that a generic framework using quantum circuit to describe cosmology puts an upper bound on the number of e-folds during the inflationary phase of the Universe's expansion. In addition to tensor network models, we also propose a Bulk Entanglement Gravity framework that analyzes the entanglement data of a quantum state in a Hilbert space without any a priori assumptions on geometry, such as the likes of a boundary conformal field theory. We find that from an amorphous configuration, one can directly recover geometry of bulk space-time from a generic class of wavefunctions that is fully characterized in this thesis via quantum entropy cone techniques. We find that under a number of assumptions, it is possible to derive linearized Einstein's equation from a version of Jacobson's entanglement equilibrium conditions for an emergent spacetime geometry in the weak field limit near Minkowski space. We show that non-local entanglement perturbations display features of wormhole-like configurations. We also clarify connections between Bulk Entanglement Gravity and highly generic features in quantum error correction codes that can be used to derive gravity.</p
Design, Fabrication, and Characterization of 3D Nanolattice Photonic Crystals for Bandgap and Refractive Index Engineering
Get PDFThree-dimensional (3D) photonic crystals (PhCs) have been the focus of ever-increasing interest in the scientific community given their potential to impact areas spanning energy conversion to analyte sensing. These architected materials are defined by a refractive index that is spatially modulated with a period comparable to that of the electromagnetic wavelength. As a result, constructive and destructive interference due to multiple scattering gives rise to a band structure for photons which may contain gaps. Both bands and bandgaps can be engineered to specifically manipulate light propagation by 3D PhCs. In this work we explore the effect of lattice architecture, finite-size effects, and material constraints on stopband position and emergence of band dispersion phenomena like negative refraction. We show that uniaxial mechanical compression can be used to stably and reversibly tune stopband position in 3D polymer nanolattice PhCs with octahedron unit-cell geometry. We then explore how lattice architecture, namely the differences in 3D cubic space group and finite size effects impact experimentally observable stopbands, and assess the degree to which the stopband behavior of real PhCs can be adequately described by the photonic band structure for an infinite, ideal PhC. Finally, we discuss the design, fabrication, and characterization of a core-shell 3D nanolattice PhC which exhibits an effective negative refractive index in the mid-infrared range.</p
Harnessing Biological Tools of Protein Transport and Catalysis
Get PDFThis work covers two projects related to protein structure and function. The first focuses on studies of chloroplast signal recognition particle 43 (cpSRP43), its interaction with substrate (the light-harvesting, chlorophyll-binding proteins, or LHCP), the role of conformational change in its activity, and the use of cpSRP43 as a tool for handling nonnative proteins. This work utilizes a variety of biochemical and biophysical approaches including light scattering and electron paramagnetic resonance to probe the structure-function relationship of cpSRP43. The second project entails the study of the C-C bond formation mechanism of nitrogenase, a biological nitrogen fixer found in soil microorganisms. Together these projects make for an interesting story of the medicinal and agricultural applications of basic biochemistry.</p
Information and Strategic Decision-Making in the Oil and Gas Industry: An Empirical Assessment
Get PDFThis dissertation comprises three essays addressing questions from Industrial Organization Economics concerning the oil and gas industry. The essays offer substantive contributions to the study of joint decision-making (Chapter 2), extrapolative beliefs (Chapter 3), and auctions (Chapter 4).
Chapter 2 investigates the quality of joint operations, where multiple oil and gas companies explore a piece of land together. By developing a discrete-choice model which can be matched to actual drilling data, I show that joint operators consisting of only large companies have the least accurate signals. Further counterfactual analyses show that the best policy governing joint operations depends on government priority: to maximize revenue or to avoid damage to the environment.
Chapter 3, co-authored with Lawrence Jin and Matthew Shum, presents a model of dynamic investment and production in which producers over-extrapolate recent demand conditions into the future. We show theoretically and empirically that, in a volatile industry, these biased beliefs can be beneficial in the long-run by counteracting the general trend in the industry. Calibration of our model to Alaska oil exploration shows that the cushioning effect can be large in reducing price decline and accelerating price recovery.
Chapter 4 examines whether common value or private value auction model best describes the bidding decisions made by oil and gas companies. The common value model suggests that more competition can lead to lower equilibrium bids from bidders and lower revenue. By analyzing tract auction data from Alaska, I find that common value components play a slightly larger role when observable heterogeneity is removed. However, expected revenue still increases with competition and plateaus when competition becomes sufficiently high.</p
The Evolutionary Construction of Sleep
Get PDFTo understand the biological basis of sleep we need to understand its neuronal and genetic regulation. In this thesis, I explore how individual behaviors serve as building blocks to construct the sleep state where a block is defined as a set of measurable behaviors. These behavioral blocks are shaped by evolutionary forces. From one animal to the next, blocks may remain or change. If a block remains across all the sleep states in the metazoan lineage then it must have an important and conserved role in sleep regulation. For example, reduced locomotion is a behavior that is often observed during sleep. There are two possible explanations for the changing of a block: either the block was vestigial or the block was easily replaceable with another block that fulfills the same function. Consider sleep duration: some animals may require five hours of sleep, while others only require one hour. The changing of a block is one way that the sleep state could evolve. Blocks may also be added during the evolution of the sleep state, increasing the dimensions and number of tasks that are accomplished during sleep. Here, I discuss the origin of sleep, as well as its conserved neuronal and genetic regulation. I report the following: the discovery of sleep in jellyfish which are among the first animals to evolve neurons and the identification of novel sleep regulators in the roundworm Nematode Caenorhabiditis elegans (C. elegans). The sleep regulators discovered in C. elegans may have conserved functions in vertebrates. These studies show that some sleep behaviors and various sleep molecules change or remain homologous across metazoans. The studies are united by our simple block hypothesis of sleep construction.</p
Regional Structural Geology of Earth and Mars
Get PDFThis thesis explores the geologic context around several key environmental transitions on Earth and Mars which are expressed at continental margins. Regional mapping techniques are applied to build links between methodologies used to explore rock samples and units — stratigraphy, structural geology, remote sensing, geochemistry, petrology, and geodynamic modeling. Four research projects are presented: Chapter 2 explores the tectonic context of xenoliths beneath the western margin of North America and illuminates the structural history of the lithospheric underpinnings of the California coast. In Chapter 3, we undertake a structural study of the southern Naukluft Mountains, Namibia, and re-interpret its tectonic context and age. Chapter 4 builds a new method for applying statistical errors to remotely measured planar orientations, and Chapter 5 applies this method to mapping the 3D structure of a globally significant stratigraphy on Mars. We find a long history of interaction with water at the margin of Isidis Basin. Together, these projects demonstrate the application of structural techniques to continental margins on Earth and Mars, and the creation of new techniques to support geological analysis from remotely-sensed data, where structural measurements may be poorly resolved
Lurking in the Shadows: Wide-Separation Gas Giants as Tracers of Planet Formation
Get PDFOver the past two decades, thousands of planets with an extraordinary diversity of properties have been discovered orbiting nearby stars. Many of these exoplanetary systems challenge our narrative for how planets form and evolve, motivating the search for observational clues to the underlying mechanisms that led to this diversity. In this quest, gas giant analogs to our own Jupiter and Saturn immediately stand out as the most visible relics of the planet formation process. They are products of their birth environment, with properties such as atmospheric and interior compositions, masses, and formation locations sculpted by protoplanetary disk and host star properties. They also actively shape their surroundings; early in their lifetimes, gas giants can alter the structure of the gas disk from which additional planetary bodies may coalesce and affect the transport of rocky and icy materials to the inner disk. After the gas has dissipated these same behemoths can push smaller planets around, causing them to migrate or even ejecting them from the system. Thus to explain the observed diversity of exoplanet systems, we must first understand how gas giant planets form and evolve. This thesis presents four studies that harness multiple observational techniques to explore this question of how gas giant planets outside our solar system form and evolve
Dynamics of Resolved Polar Clouds
Get PDFThe polar regions have been experiencing rapid warming and ice loss as greenhouse gas concentrations have risen. The projected warming in the Arctic varies significantly across climate models, part of which is attributed to polar cloud feedbacks. This thesis addresses the question of what drives the changes in polar clouds as the climate warms, using a large eddy simulation (LES) model. LES is a powerful high-resolution model that resolves the most energetic turbulence relevant for clouds. First, we focus on the Arctic boundary layer clouds through three observation based case studies. The cloud and boundary layer characteristics simulated by the LES agree reasonably well with observations and model intercomparisons. We found that during polar night over sea ice, cloud water path increases with temperature and free-tropospheric relative humidity, but it decreases with inversion strength across the cloud top. Most of these changes can be explained by a mixed-layer model. The strength of the estimated positive cloud longwave feedback largely depends on the cloud top inversion strength. Next, we extend the LES domain to cover the entire polar troposphere, and use output from an idealized GCM as forcing to drive the LES. This novel framework allows changes in the large-scale circulation to be parameterized in the LES. The simulated seasonal cycle of liquid clouds resembles observations. In a warmer climate, there is a significant decrease of the low-level liquid clouds during summer and autumn. In spring and winter, liquid clouds increase at all levels. Both the liquid and ice cloud tops rise as the climate warms. Offline radiative transfer calculations estimate a positive cloud feedback that is dominated by longwave feedback
Theoretical and Experimental Study of Pressure Hysteresis in the Palladium Hydride Phase Transformation
Get PDFA unique phenomenon occurring with metal hydride systems that presents a loss in hydrogen storage efficiency and has received little scientific attention is the hysteresis behavior observed during H2 absorption and desorption. As an ambient H2 pressure is introduced into a metal hydride, the material undergoes a phase transformation from a hydrogen-poor phase to a hydrogen-rich phase during absorption and the reverse during desorption. However, the phase transformation is hysteretic as it occurs at a much higher H2 pressure for absorption than for desorption.
In this work, the thermodynamics of the metal hydride phase transformation with hydrogen uptake are experimentally studied using the palladium-hydride system with in-situ x-ray diffraction. The in-situ x-ray diffraction has enabled the study of the thermodynamic evolution of the microstructure of the palladium through lattice parameters, phase fractions, strain analyses and other information. The diffraction data has then been compared to the predictions from existing theories on hysteresis in metal hydrides, such as the Schwarz-Khachaturyan and Flanagan-Clewley theories. Finally, these theories are extended and combined to form a new general theory of metal hydride phase transformation thermodynamics that incorporates new attributes of importance for practical metal hydride systems, such as phase interface coherency and changes in dislocation formation energies due to work hardening. This new theory is very effective in explaining the prominent trends in the experimental data and provides a highly general approach for the analysis of phase transformations from hydriding in real metals.</p