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Strategies for the Mechanically Triggered Release of Small Molecules
Get PDFThe development of force-responsive molecules called mechanophores is a central component of the field of polymer mechanochemistry. Mechanophores enable the design and fabrication of polymers for a variety of applications ranging from sensing to self-healing materials. Nevertheless, an insufficient understanding of structure–activity relationships limits experimental development, and thus computation is necessary to guide structural design. Herein, we use the constrained geometries simulate external force (CoGEF) method to evaluate a library of covalent mechanophores using density functional theory (DFT). We use these results to identify key parameters that accurately predict experimentally determined mechanochemical reactivity.
Polymers that release small molecules upon external stimulation are promising for a wide range of applications, including sensing, catalysis, and drug delivery. Mechanophores are uniquely suited to enable molecular release with excellent selectivity and control. We have designed a general platform for mechanically gated small molecule release that leverages a latent 2-furylcarbinol species masked as a mechanically labile Diels–Alder adduct. Here, we describe the computationally guided design of metastable 2-furylcarbinol derivatives through the prediction of activation energy values and construction of structure–activity relationships. These results enable a molecular release platform suitable for a wide scope of cargo molecules across a broad range of chemical environments.</p
Strategic Applications of Electrochemistry in Ammonia Oxidation and Alkyl Halide Reduction
Get PDFThis thesis describes the strategic application of electrochemistry in the development of catalytic systems for two challenging processes: alkyl halide reduction and ammonia oxidation. In the case of alkyl halide reduction, the ability to precisely tune electrochemical potential favored the use of electrochemistry as compared to chemical reagents. By contrast, for ammonia oxidation, electrochemistry was specifically targeted due to motivations in the eventual development of ammonia fuel cell technology. The first chapter introduces these and other advantages of electrochemistry, as well as details regarding the thermodynamic potentials and kinetic barriers associated with alkyl halide reduction or ammonia oxidation. The second chapter details our development of photoelectrochemical methodology to employ a strongly luminescent dicopper system for outer-sphere, single-electron transfer reduction of benzyl chlorides. The third chapter marks the beginning of our work in molecular iron-mediated ammonia oxidation catalysis, in which we develop our hypothesis that catalyst structures featuring cis-labile coordination sites should mediate ammonia oxidation. We disclose the first iron electrocatalyst ([(TPA)Fe(MeCN)₂]²⁺) as well as a framework for the analysis of metrics such as overpotential, catalytic rate, and catalyst stability. The fourth chapter introduces a hypothesis for catalyst improvement—favoring low-spin electronic structures—and a model system for testing: ([(BPM)Fe(MeCN)₂]²⁺). Using this second-generation catalyst, improved stability, enhanced activity, and lowered overpotential were observed. The fifth chapter explores the validity of the cis-labile and low-spin hypotheses via Hammett-type substituent studies on both the [(TPA)Fe(MeCN)₂]²⁺ and the [(BPM)Fe(MeCN)₂]²⁺ platforms. This study resulted in the development of a further enhanced molecular electrocatalyst for ammonia oxidation and revealed mechanistic information pertinent to the development of future catalytic systems
On the Categorical Approach to the Frobenius Trace
Get PDFMotivated by the study of the local and global Langlands correspondence from a geometric prespective, we establish two results of a general nature regarding categories of sheaves in algebraic geometry. The first result, motivated by the work of Drinfeld and Lafforgue on the Langlsnds correspondence over function fields, establishes a categorical enhancement of the Künneth formula for categories of Weil sheaves, generalizing a famous result of Drinfeld. In the second part, motivated by the geometric approach to the study of representations of reductive groups over local fields, we develop a method to calculate the categorical trace of monoidal categories arising from convolution pattern in algebraic geometry
Planet Host Star Properties as Probes of Planet Formation and Evolution
Get PDFOver the past three decades, we have discovered over 5000 exoplanets that exhibit sizes, orbital architectures, and other properties that are often dramatically different from those of planets in our own Solar System. To understand the various processes that sculpted this diversity of planets, we can examine the stars they orbit. In the first project of my thesis, I modified a machine learning framework that models stellar spectra (The Cannon, Ness et al. 2015) to measure iron abundances for M dwarfs - small, cool stars that dominate the stellar population of our galaxy. Next, I combined Bayesian statistical methods and astrometric data that tracks the movements of stars to examine orbital alignment between planet host stars and their stellar companions. I discovered that close-in gas giant planet systems tend to be misaligned, which suggests that their dynamical histories include obliquity excitation through interactions with e.g., the protoplanetary disk and/or nearby stars. I then used Keck-HIRES spectroscopic observations and MESA stellar evolution models to uncover planet formation signatures encoded in host star elemental abundance patterns. I found that abundance differences between stars in binary systems may increase as a function of their separation, which has important implications for studies that rely on binary star chemistry. Most recently, I extended my abundance methodology to large spectroscopic samples to examine abundance patterns in planet host versus non-planet host stars, and thus explore planet formation signatures on a galactic scale
Temperature Dependence of Gas Physisorption Energy: Experimental and Computational Studies of Krypton on Porous Carbon
Get PDFThis work comprehensively investigated the temperature dependence of physical adsorption energy, combining theoretical, computational, and experimental approaches. A thermodynamic analysis of the 2D ideal gas and the slit-pore models highlighted the role of van der Waal potentials in the adsorption energy and isotherm fitting methods, especially Henry's law. Experimental data of krypton adsorption on CNS-201 and MSC-30 porous carbon materials revealed a significant weakening in the isosteric adsorption energy with temperatures from 250 K to 330 K. Using the zero-coverage Henry's constants and Clausius–Clapeyron equation, the adsorption energies weaken for 13% and 15% for CNS-201 and MSC-30. The corresponding changing rates are 4.35k_B for CNS-201 and 3.65k_B for MSC-30.
The DFT-based computational study with the slit-pore model showed the van der Waal potentials of different-sized pores. Then it showed how the structures of the pores significantly influence the surface dynamics and the internal energies of the adsorbates at different temperatures. Gas molecules adsorbed in pores of different sizes have different heat capacities larger than the gas phase, leading to a temperature dependence of adsorption energy. Monte Carlo calculation indicated that displacements of adsorbent atoms caused by thermal vibration slightly weaken the van der Waal potentials but have a negligible effect on the temperature dependence of the adsorption energy.
The distribution of pore sizes plays a crucial role in the temperature dependence of the overall adsorption energy. With increasing temperature, the pores with higher energy states become more accessible due to the Boltzmann distribution, weakening the statistically averaged internal energy. Adsorption energy weakening of 5% and 15% for CNS-201 and MSC-30 are given by combining the computational van der Waal potentials and experimentally measured pore sizes. The changing rates are 0.62k_B and 2.03k_B.</p
Topics in Gravitational Wave Physics: Black-Hole Spectroscopy, Neutron Star Dynamical Tides, and Numerical Relativity
Get PDFIn this thesis, we explore various topics in gravitational wave physics, including black hole spectroscopy, dynamical tides of neutron stars, numerical relativity, and modified theories of gravity.
In our study of black hole spectroscopy, we develop a novel framework for identifying quasinormal modes in ringdown signals. We apply this method to numerical-relativity waveforms of binary black hole systems and find second-order and retrograde quasinormal modes in the ringdown regime. We also apply this method to GW150915, resulting in new insights into the existence of the first overtone. On the other hand, we explore how the excitation of quasinormal modes encodes information about binaries’ parameters. Focusing on superkick configurations, we find universal dependence of the mode amplitudes and phases on the binary’s configurations.
Tidal effects have significant imprints on gravitational waves emitted during the final stage of the coalescence of binaries involving neutron stars. We examine how dynamical tides can be significant when neutron stars’ characteristic oscillations become resonant with orbital motion, and we investigate their impact on measuring neutron-star parameters with gravitational waves. Specifically, we conduct systematic studies on the tidal excitation of fundamental and Rossby modes of spinning neutron stars and find that their effects may be significant and detectable in the era of third-generation gravitational-wave detectors, which in turn could lead to more stringent constraints on the properties of neutron stars.
Regarding numerical relativity, we implement a fully relativistic three-dimensional Cauchy-characteristic matching algorithm to establish a more accurate boundary condition for numerical-relativity simulations. We justify the correctness of the algorithm by nonlinearly propagating gravitational-wave pluses and find that the new boundary condition does reduce spurious numerical reflection at outer boundaries and improves the accuracy of the generated waveforms. The second part focuses on the initial data of binary black holes for numerical simulations. We extend the superposed harmonic initial data, which breaks down for high-spin black holes, to higher spins by introducing a new spatial coordinate system: superposed modified harmonic. We find that the new initial data preserves a nice property of the superposed harmonic system: the suppression of junk radiation. Furthermore, we find that the volume-weighted constraint violations for the new initial data converge with numerical resolution during the junk stage, which means there are fewer high-frequency components at outer spacetime regions.
Finally, we investigate the features of gravitational waves within theories beyond general relativity, focusing on two specific aspects. First, we present a numerical-relativity simulation of a black hole-neutron star merger in scalar-tensor gravity with binary parameters consistent with the gravitational wave event GW200115. We consider the Damour-Esposito-Farèse extension to Brans-Dicke theory and find that the scalar-tensor system evolves faster than its general-relativity counterpart due to dipole radiation, merging a full gravitational-wave cycle before the GR counterpart. We also compare the numerical waveforms with post-Newtonian theory and find good agreement during the inspiral. Second, we propose a new approach, based on numerical-relativity waveforms, for reconstructing the late-time near-horizon geometry of merging binary black holes and computing gravitational-wave echoes from exotic compact objects. We use a physically-motivated way to impose boundary conditions near the horizon and apply the Boltzmann reflectivity to compute the quasinormal modes of non-rotating ECOs, as well as gravitational-wave echoes. Additionally, we investigate the detectability of these echoes in current and future detectors and prospects for parameter estimation.</p
Genetically Encoded Biosensors for Ketamine and Other Rapidly Acting Antidepressants in Zebrafish and Cell Culture
Get PDFOver the past century, the development and use of treatments for depression has been one of the most important projects in both neuroscience and medicine. Not only is relatively little known about the underlying pathophysiology of major depressive disorder (MDD), a mechanistic understanding of the ways in which common antidepressants — such as selective serotonin reuptake inhibitors (SSRIs) — contribute to symptomatic relief remains elusive. Furthermore, the delay until typical antidepressant treatments take effect (a 'therapeutic lag' of weeks to months) presents a series of challenges to researchers in chemistry, neuroscience, pharmacology, and medicine, as the connection between apparent physiological changes and clinical benefit has yet to be established. The recent advent of a new class of drugs — rapidly acting antidepressants (RAADs), including the multi-purpose compound ketamine — which ameliorate symptoms within hours to days provides a crucial (if perplexing) perspective on the treatment of MDD and neuropsychiatric disorders more broadly. To answer questions concerning how various kinds of antidepressants might exert their effects, where those interactions take place, and what sorts of physiological changes drive clinical response, we have designed genetically encoded drug-specific intensity-based sensing fluorescent reporters (iDrugSnFRs) which are engineered to detect drugs of interest in both in vitro and in vivo applications. We have successfully evolved iDrugSnFRs for an array of RAADs (iRAADSnFRs) which detect pharmacologically relevant concentrations of their target drugs sensitively and specifically in both cell culture as well as in the nervous tissue of larval zebrafish. Another set of iDrugSnFRs for SSRIs has provided novel insights into the potential reasons for the aforementioned 'therapeutic lag' as well as side effects, while yet another set has provided a pharmacokinetic basis for the evaluation of smoking cessation drugs. In all, our findings lead us to posit that iDrugSnFRs can aid in the elucidation of mechanisms by which a wide variety of orally active pharmaceutical compounds operate as well as provide a crucial basis for the development of better medicines.</p
Search for Supersymmetry Using Higgs Boson to Diphoton Decays and Search for Long-Lived Particles Using Out-of-Time Trackless Jets at √s = 13 TeV
Get PDFThe thesis describes two searches conducted at the Large Hadron Collider with a center-of-mass energy of 13 TeV, using proton-proton collison data collected by the CMS experiment. The supersymmetry (SUSY) search focus on the production of at least one Higgs boson that decays into two photons in the decay chains of pair-produced SUSY particles. The data used has an integrated luminosity of 77.5 fb⁻¹. The events are classified into different search regions based on charged leptons, Higgs boson candidates, and kinematic variables to make them sensitive to different SUSY scenarios. The results reveal no statistically significant excess of events compared to the standard model predictions. The searches exclude bottom squark pair production for bottom squark masses below 510 GeV and a lightest SUSY particle mass of 1 GeV. The wino-like chargino-neutralino production in gauge-mediated SUSY breaking (GMSB) is excluded for chargino and neutralino masses below 235 GeV, with a gravitino mass of 1 GeV. Furthermore, the higgsino-like chargino-neutralino production in GMSB, where the neutralino decays exclusively to a Higgs boson and a gravitino, is excluded for neutralino masses below 290 GeV. The thesis also reports a search for long-lived particles that decay in the outer regions of the CMS silicon tracker or in the calorimeters. The search uses data with an integrated luminosity of 138 fb⁻¹. The identification of long-lived particle decays utilizes a novel technique that combines nearly trackless and out-of-time jet information into a deep neural network discriminator. The results are interpreted using a simplified GMSB model of chargino-neutralino production, where the neutralino is the next-to-lightest supersymmetric particle that decays to a gravitino and either a Higgs or Z boson. The search achieves the highest sensitivity for neutralino proper decay lengths of approximately 0.5 meters and excludes masses up to 1.18 TeV at a 95\% confidence level. This search represents the most stringent constraint to date in the mass range from the kinematic limit imposed by the Higgs boson mass up to 1.8 TeV.</p
Time-Dependent Failure of Thin-Ply Composite Laminates
Get PDFThe demand for larger and lighter structures for next-generation space designs necessitates the use of deployable structures. Among the materials that hold promise for such applications, thin-laminate fiber composites with thicknesses less than 200 μm stand out due to their strength-to-weight ratio, packaging efficiency, and ability to deploy using stored strain energy. However, designing deployable structures with thin-laminate composites is challenging as they need to be stiff enough to withstand loads during deployment while also having a small volume in the packaged configuration. Complicating matters further, stress relaxation of the polymer matrix within the composite during long-term stowage in response to an imposed curvature can drastically impact both the deployment process and the performance of the structure in its deployed state, even leading to catastrophic failure in the stowed configuration.
This thesis presents a comprehensive study of the time-dependent failure behavior of thin-laminate fiber composites under bending, with a focus on a fundamental material-level understanding. The work is divided into three main parts. First, a novel test method called Flattening to Rupture (FTR) test was developed to effectively load composite coupons under long-term bending, enabling the measurement of time-dependent rupture and identification of the underlying failure mechanisms. Second, numerical simulations using the Abaqus/Standard finite element software were developed to understand the sequence of rupture events and the influence of several parameters that affect time-dependent rupture. Finally, a statistical approach was proposed to model the stochastic nature of the failure of thin composite laminates.
The contributions of this thesis extend the understanding of the microscale failure mechanisms involved in the time-dependent failure of fiber composites. These new insights pave the way for the efficient design of tightly and safely packaged deployable structures under long-term loading. The findings of this research can be utilized to optimize the design and performance of deployable space structures made of fiber composites, leading to new technologies that can advance space exploration.</p
Fractonic Orders from Lattice Models and Field Theories
Get PDFFracton models are characterized by exotic features such as point-like excitations with restricted mobility, sub-extensive ground state degeneracy and UV/IR mixing. They have been studied previously using exactly solvable lattice models, higher rank gauge theories, etc. In an effort to classify fracton models into phases (i.e., fractonic orders), the so-called foliation structure has been introduced and shown to exist in many previously known models. A natural question then arises concerning the feasibility of the foliation paradigm in general. In this thesis, I study fracton models beyond the foliation paradigm and give simple diagnostics for the absence of a foliation structure. New notions of fractonic orders therefore need to be conceived, and I present such a conception which is a generalization of the foliation RG.
In Chapters 2 - 4, I introduce new fracton models obtained from infinite-component Chern-Simons (CS∞) theories. By calculating observables such as ground state degeneracy and planon braiding statistics, I prove that most CS∞ theories are not foliated. A CS∞ theory can also be gapless with certain choices of parameters, and I show that such a theory is a stable gapless fracton model. Furthermore, I discuss topological features of a large subclass of gapless CS∞ theories and present fully continuous effective field theories for this subclass.
In Chapters 5 - 6, I discuss a new notion of fractonic orders by studying the example of the Ising cage-net model. I begin by calculating the ground state degeneracy of the model, which shows that the model is not foliated. The calculation uses an operator algebra approach which relies only on intrinsic physical properties of the model rather than microscopic details, and I establish the framework of this approach conceptually and via examples. I then argue why this intrinsic approach, despite being a tool for calculation initially, may be a useful characterization of a fractonic order. Finally, I present a generalized foliation RG scheme, apply it to the Ising cage-net model, and discuss its limitations.</p