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Modeling and Parameterization of Basin Effects for Engineering Design Applications
Get PDFThe term "Basin effects" refers to trapped and reverberating earthquake waves in soft sedimentary deposits overlying convex depressions of the basement bedrock, which significantly alter the frequency content, amplitude, and duration of seismic waves. This has played an important role in shaking duration and intensity in past earthquakes such as the Mw 8.0 1985 Michoácan, Mexico, Mw 6.9 1995 Kobe, Japan, and Mw 7.8 2015 Gorkha, Nepal earthquakes. While the standard practice is to perform a 1D analysis of a soil column, edge-effect and surface waves are among the key contributors to the surface ground motion within a basin. This thesis studies basin effects in a 2D medium to help better understand the phenomena, better parameterize them, and suggest a path to appropriately incorporate them in ground motion prediction equations and building design codes. After the introduction in Chapter 1, I present the results in three main parts as follows:
In Chapter 2, we perform an extensive parametric study on the characteristics of surface ground motion associated with basin effects. We use an elastic idealized-shaped medium subjected to vertically propagating SV plane waves and examine the effects of basin geometry and material properties. We specifically study the effects of four dimensionless parameters, the width-to-depth (aspect) ratio, the rock-to-soil material contrast, a dimensionless frequency that quantifies the depth of the basin relative to the dominant incident wavelength, and a dimensionless distance that quantifies the distance of the basin edges relative to the dominant wavelength. Our results show that basin effects can be reasonably characterized using at least three independent parameters, each of which can significantly alter the resultant ground motion. To demonstrate the application of dimensional analysis applied here, we investigate the response of the Kathmandu Valley during the 2015 Mw 7.8 Gorkha Earthquake in Nepal using an idealized basin geometry and soil properties. Our results show that a simplified model can capture notable ground motion characteristics associated with basin effects.
Chapter 3 uses the identified parameters from the previous chapter to estimate surface acceleration time-series given earthquake frequency content, basin geometry and material properties, and location inside a basin. This is of practical use when the amount of available data is limited or the fast estimation of time-series is desirable. For that, we train a neural network to estimate surface ground acceleration time-series across a basin. Three input parameters are needed for the estimation: basin-to-bedrock shear wave velocity ratio, aspect ratio of the basin, and dimensionless location. These parameters define an idealized-shaped basin and the location at which the time-series are to be computed. It will be shown that the model performs with high accuracy in comparison to the result of a full-fidelity Finite Element (FE) simulation (ground truth) and generalizes reasonably well for input parameters outside of the training set. Moreover, we will also use the model for the case of Kathmandu Valley, Nepal during the 2015 Mw 7.8 Gorkha earthquake and compare the results of NN versus recordings of the mainshock, similarly to Chapter 2.
Once we have studied basin behavior in a homogeneous case in previous chapters, we focus on material representation inside a basin in Chapter 4. Here, we study basin effects for the cases where high-frequency response and realistic material representation are desirable. However, the lack of sufficient information about the material properties and stratigraphy of a basin prevents accurate simulation of the phenomena. To do that, we perform a stochastic analysis using the Monte Carlo technique, where a random field represents basin material. Similarly to the previous chapters, we use a 2D FE model with an idealized basin subjected to vertically propagating SV plane waves and investigate the spatial variation of surface ground motion (SGM) associated with basin effects by assuming different realizations of the correlated random field. We then study various correlation lengths, coefficients of variations, and autocorrelation functions to evaluate their contribution to SGM. We show that the coefficient of variation is the most influential parameter on SGM, followed by correlation lengths and type of autocorrelation function. Increasing the coefficient of variation not only affects the mean surface amplification, but also results in a dramatic change in the standard deviation. Correlation lengths and autocorrelation functions, on the other hand, are of less importance for the cases we examine in this study.</p
New Methods for the Detection and Characterization of Exoplanets
Get PDFAdvancements in detection technologies have allowed the discovery of thousands of exoplanets. These discoveries have revolutionized our understanding of the Universe; not only are planets ubiquitous, but the planetary systems they populate are as diverse as the complex processes that govern their formation allow. This thesis compiles several studies on the development and application of exoplanet detection and characterization methods, in particular for direct imaging and spectroscopy. From all the planets discovered to date, only a marginal portion have been imaged. This is due to the limited access of high contrast instruments into the parameter space where most exoplanets habitate. Developments in high contrast are key to reaching a full understanding of the exoplanet population. In particular, direct methods allow for an effective characterization of the atmospheric compositions, making it possible to probe exoplanet atmospheres in search of biosignatures.
A sure pathway to enhance exoplanet characterization capabilities is by taking full advantage of synergies between detection methods. In Chapter 2 these synergies are explored in the context of ε Eridani's elusive companion: three different methods are combined to constrain its mass and orbital parameters. Combining astrometry, radial velocity, and direct imaging data offers a complementarity that enhances the overall constraining power. In Chapter 3, the α Centauri system is reviewed regarding the possibility of imaging an exoplanet with the JWST observatory in the infrared. The following chapters deal with technological development for high contrast imaging and spectroscopy instruments. In Chapter 4 a coronagraph design study is presented in which new design tools are discussed and evaluated, demonstrating better coronagraph performance. In this chapter the case study is the Nancy Grace Roman Space Telescope Coronagraph Instrument, in which its heavily obstructed pupil constitutes a huge challenge for coronagraph design. Along the same lines, Chapter 5 presents the technology demonstration of the apodized vortex coronagraph (AVC). The AVC is a coronagraph concept that effectively deals with the telescope pupil discontinuities. Chapters 6 and 7 introduce a novel wavefront sensing and control algorithm for the high contrast concept of a fiber injection unit in the image plane of a coronagraph. A single mode fiber (SMF) is placed in the position of the planet to extract its light and feed it into a spectrograph. Our algorithm leverages the synergies of the coronagraph and the mode selectivity of the SMF to maximize the signal-to-noise ratio of the planet.</p
Targeting Fusion Proteins of HIV-1 and SARS-CoV-2
Get PDFViruses are disease-causing pathogenic agents that require host cells to replicate. Fusion of host and viral membranes is critical for the lifecycle of enveloped viruses. Studying viral fusion proteins can allow us to better understand how they shape immune responses and inform the design of therapeutics such as drugs, monoclonal antibodies, and vaccines. This thesis discusses two approaches to targeting two fusion proteins: Env from HIV-1 and S from SARS-CoV-2. The first chapter of this thesis is an introduction to viruses with a specific focus on HIV-1 CD4 mimetic drugs and antibodies against SARS-CoV-2. It discusses the architecture of these viruses and fusion proteins and how small molecules, peptides, and antibodies can target these proteins successfully to treat and prevent disease. In addition, a brief overview is included of the techniques involved in structural biology and how it has informed the study of viruses. For the interested reader, chapter 2 contains a review article that serves as a more in-depth introduction for both viruses as well as how the use of structural biology has informed the study of viral surface proteins and neutralizing antibody responses to them. The subsequent chapters provide a body of work divided into two parts. The first part in chapter 3 involves a study on conformational changes induced in the HIV-1 Env protein by CD4-mimemtic drugs using single particle cryo-EM. The second part encompassing chapters 4 and 5 includes two studies on antibodies isolated from convalescent COVID-19 donors. The former involves classification of antibody responses to the SARS-CoV-2 S receptor-binding domain (RBD). The latter discusses an anti-RBD antibody class that binds to a conserved epitope on the RBD and shows cross-binding and cross-neutralization to other coronaviruses in the sarbecovirus subgenus.</p
Inhibition is the Hallmark of CA3 Intracellular Dynamics Around Awake Ripples
Get PDFHippocampal ripples are transient population bursts that structure cortico-hippocampal communication and play a central role in memory processing. However, the mechanisms controlling ripple initiation in behaving animals remain poorly understood. Here we combine multisite extracellular and whole cell recordings in awake mice to contrast the brain state and ripple modulation of subthreshold dynamics across hippocampal subfields. We find that entorhinal input to DG exhibits UP and DOWN dynamics with ripples occurring exclusively in UP states. While elevated cortical input in UP states generates depolarization in DG and CA1, it produces persistent hyperpolarization in CA3 neurons. Furthermore, growing inhibition is evident in CA3 throughout the course of the ripple buildup, while DG and CA1 neurons exhibit depolarization transients 100 ms before and during ripples. These observations highlight the importance of CA3 inhibition for ripple generation, while pre-ripple responses indicate a long and orchestrated ripple initiation process in the awake state.</p
The Claytons
No full text[Prologue] To the North, tucked beside the Adirondack Mountains, lay the suburban town of Bethlehem, an average town filled with ordinary people. The nearest city, Albany, was a small city with few attractions, so that natives who saw the tourist stand at the airport would wonder why tourists would ever visit. Indeed, few did. Despite the mediocrity that existed in the place, the people of Bethlehem held for it a fierce pride – they bragged about its boredom rather than renounced it.</p
Searching for Persistent Radio Sources
Get PDFWe present a sample of 27 sources from the Very Large Array Sky Survey (VLASS) associated with dwarf galaxies as possible persistent radio sources (PRS). This thesis presents a novel approach of high offset associations between radio sources and optical counterparts from the Galaxy List for the Advanced Detector Era+ (GLADE+) through the use of the Bayesian association algorithm Probabilistic Association of Transients to their Hosts (PATH). We follow up on this sample with SED fitting through UV, optical, and IR photometry to garner accurate star formation and stellar masses for the sample. We use this data to search for high luminosity (excess Lν ≥ 10²⁹ ergs⁻¹ Hz-1), high offset (> 2"), and high association probability (P(O|x) ≥ 0.93) sources for follow up. Our goal for further follow up is to eliminate possible astrophysical foreground such as AGN, SNe, and star formation as explanation for these sources. We follow up with Keck Low Resolution Imaging Spectrometer (LRIS) optical spectra of 2 sources and find no evidence of AGN activity. We also discuss our VLBA proposal for 11 of our sources to search for compactness of source radio emission, a feature of PRS. Additional follow-up spectroscopy and radio observations are necessary to confirm any of these candidates and PRS due to the large number of foregrounds and this thesis presents a possible list of 27 candidates within VLASS in order to do so.</p
Automorphic L-Functions, Geometric Invariants, and Dynamics
Get PDFWe address three different problems in analytic number theory.
In the first part, we show that the completed L-function of a modular form has Ω(Tδ) simple zeros with imaginary part in [-T, T], for any δ < 2⁄27. This is the first power bound for forms with non-trivial level in this problem, where previously the best result was Ω(log log log T). Along the way, we also improve the corresponding bound in the case of trivial level, and sharpen a certain zero-density result.
In the second part, we study the variance for the distribution of closed geodesics in random balls on the modular surface. A probabilistic model in which closed geodesics are modeled using random geodesic segments is proposed, and we rigorously analyze this model using mixing of the geodesic flow. This leads to a conjecture for the asymptotic behavior of the variance, and we prove this conjecture for sufficiently small balls.
In the third part, we prove Sarnak's Möbius disjointness conjecture for C1+ε skew products on the 2-torus over a rotation of the circle.</p
Traveling Wave Parametric Amplifiers and Other Nonlinear Kinetic Inductance Devices
Get PDFThe microwave frequency range is home to a large amount of cosmologically crucial signals including the cosmic microwave background, emission from high redshift galaxies, and spectral absorption from interstellar dust. In addition to this wealth of scientifically interesting signals, various cutting-edge detector technologies such as microwave kinetic inductance detectors also operate at those frequencies. Both of these areas would greatly benefit from improved readout electronics, which would ideally include broadband, high gain, and low noise amplification. These conditions are generally quite difficult to achieve simultaneously, and have driven the development of a large number of innovative technological solutions. Recently, superconducting traveling wave parametric amplifiers have emerged as a promising candidate for simultaneously meeting the amplification requirements in the microwave regime.
In this thesis, we present further developments of traveling wave parametric amplifiers and other devices based on the nonlinear kinetic inductance of NbTiN transmission lines. The design techniques used for dispersion engineering and impedance matching are very robust, allowing for straightforward alterations to produce amplifiers with bandwidths centered at vastly different frequencies. The majority of our designs focus on the low frequency region from 2 to 12 GHz, where we demonstrate broadband amplifiers with 20 to 30 dB gain, quantum-limited noise, and minimal losses enabling vacuum noise squeezing. The excellent gain and noise performance of one such amplifier is further demonstrated by its use in the readout of a hidden photon dark matter search that sets new limits on the allowable kinetic mixing coupling. One such device was also operated in an up-conversion mode to demonstrate nearly perfect photon conversion efficiency of a narrowband signal near 1.75 GHz to a 12.55 GHz output. At higher frequencies, similar devices are shown to produce gain across over three octaves of bandwidth extending up to 34 GHz and a parametric amplifier operating in the W band. Utilizing the change in phase velocity in our transmission lines with applied current, we build and test a Fourier transform interferometer. We further present a smaller, optimized design that could someday enable the construction of a single-wafer kilopixel array of spectrometers for spatially resolved measurements of the spectral distortions in the cosmic microwave background.</p
Direct Detection of Light Dark Matter with Electrons, Phonons, and Magnons
Get PDFDiscovering the nature of dark matter (DM) remains one of the most important outstanding questions in particle physics. While the astrophysical evidence for its existence continues to accumulate, we know very little about its fundamental constituents, and how it connects to the Standard Model. Terrestrial direct detection experiments offer a unique experimental perspective. Detection of a signal would be the first evidence for non-gravitational interactions between DM and ordinary matter, a crucial clue in understanding the particle nature of DM. Moreover detection in a laboratory is less susceptible to astrophysical uncertainties which accompany indirect detection strategies, and offer a wider vantage than colliders with the ability to swap target materials and search for modulation effects. In this dissertation I will discuss searching for DM with the current state-of-the-art direct detection experiments based on electronic excitations, as well as a potential direction for future experiments based on phonon and magnon excitations.
Previous generations of direct detection experiments utilized nuclear recoil to search for DM particles. While this process is well suited for DM candidates with masses above typical nuclear masses, ℴ(GeV), sensitivity drops precipitously for lighter DM. New physical processes must be utilized to facilitate the search for well-motivated light, sub-GeV, DM candidates. Electronic excitations are one such process which can probe DM candidates which have enough energy to excite electrons across the band gap. I will discuss many aspects of this DM-induced excitation rate which were developed in this work: the most advanced first-principles calculations of DM scattering and absorption signals using density functional theory (DFT) input, daily modulation effects in anisotropic crystal targets, comparisons of a wide variety of potential detector targets, theoretical development of a non-relativistic effective field theory (NR EFT) to aid in the calculation of DM absorption rates, as well as a study of interactions in cutting edge small gap, spin-orbit coupled targets.
While direct detection experiments using electronic excitations are currently underway, to reach even lower DM masses, which do not carry enough energy to excite states across the band gap, new ideas must be explored. Collective excitations, such as phonons and magnons, exist below the electronic band gap and offer an exciting future for direct detection experiments. Detectors searching for single phonon excitations are currently in development, whereas those based on magnons are in their infancy. Similar to the electronic excitations we will discuss a myriad of topics involving single phonon and magnon excitations: an EFT of DM-collective excitation scattering for general UV theories, potential uses for detection of axion DM, as well as advanced first-principles calculations, detailed study of the directional detectability in anisotropic crystal targets, and comparisons across a variety of candidate target materials.</p
The Chemistry of Europa and Venus, and Characterization of Earth-Like Exoplanets
Get PDFThis thesis contains three parts of work, including oxidant sources on Europa, sulfur chemistry on Venus, and the characterization of Earth-like exoplanets. In the first part, we build two chemical-transport models to study the various oxidant-generation processes that occur in both Europa’s atmosphere and surface ice. The atmospheric model focuses on the role that water plumes play in the formation of Europa’s ionosphere. The simulation results, which show that the ionization reactions are initiated by electron-impact ionization and photoionization of water and continued by charge transfer between water and oxygen molecules, have successfully reproduced the observations. This model has also been used to study the dissociation processes of water molecules from the plumes, which can be regarded as an alternative source for the oxygen in the atmosphere. The chemical-transport model on Europa’s surface ice is built to simulate chemical processes occurring in the ice during irradiation by electrons and to describe how the chemical species of interest (oxidants) are formed, transported, and distributed in the ice. This model also has implications for the chemical composition of Europa’s subsurface ocean. Since the availability of oxidants could be the limiting factor for biologically useful chemical energy on Europa, the proposed research may give us insight into Europa’s habitability.
The second part of this thesis focuses on the unknown ultraviolet (UV) absorber(s) in the atmosphere of Venus. Ever since the detection of the enigmatic ultraviolet absorption in the upper atmosphere of Venus, questions have been raised about the identity of the unknown UV-visible absorber(s) and how it is formed on Venus. Our recent photochemical modelling study suggests that SO dimers may not be the major UV absorber(s) in Venus’ upper atmosphere. However, SO dimers are important intermediaries in the formation of more complex S species (e.g., Sn (n = 1 to 7)). Polysulfur aerosol, which is formed from the nucleation process of Sn (n = 1 to 7), is a possible candidate for the unknown UV absorber(s). In this work, we compute that the mixing ratio of polysulfur aerosol is ~1.76×10-14 in the upper atmosphere. By putting the polysulfur aerosol into the Spectral Mapping Atmospheric Radiative Transfer model (SMART), we find that the simulated spectrum of Venus agrees well with the observations. This result provides useful constraints for unraveling the identity(ies) of the unknown UV-visible absorber(s) on Venus.
The third part of this thesis is devoted to the characterization of Earth-like exoplanets. In this part, we study the glints, a possible phenomenon on Earth-like exoplanets and the rotation period detection for Earth-like exoplanets. Small flashes of reflected light—called glints—are found in images taken by spacecraft observing the Earth and occur due to specularly reflected solar radiation. These glints have been found over both ocean and land. Using Deep Space Climate Observatory observations, we show that glints over land are due to specular reflection off horizontally oriented ice platelets floating in the air, while glints over ocean have contributions from reflection off either platelets floating above the ocean or a relatively smooth ocean surface. We use a radiative transfer model to simulate different kinds of glints and to explore their properties. This technique of comparing observations of terrestrial glints with model simulations may provide new information relevant to atmospheric dynamics and the search for habitable exoplanets. A terrestrial planet’s rotation period is one of the key parameters that determines its climate and habitability. Here we demonstrate that, under certain conditions, the rotation period of an Earth-like exoplanet will be detectable using direct-imaging techniques. We use a global climate model that includes clouds to simulate reflected starlight from an Earth-like exoplanet and show that the rotation period of an Earth-like exoplanet is detectable using visible-wavelength channels with time-series monitoring at a signal-to-noise ratio (S/N) >20 with ∼5–15 rotation periods of data, while the rotation period of a planet with full ocean coverage is unlikely to be detectable. To better detect the rotation period, one needs to plan the observation so that each individual integration would yield a S/N >10, while keeping the integration time shorter than 1/6 to 1/4 of the rotation period of the planet. Our results provide important guidance for rotation period detection of Earth-like exoplanets in reflected light using future space telescopes.</p