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PROBING THE NATURE OF COMPACT OBJECTS: SCATTERING, TIDES AND QUASINORMAL MODES
No full textThe LIGO-VIRGO-KAGRA (LVK) collaboration has detected 90 confirmed gravitational-wave (GW) events and nearly 200 confident triggers across four observational runs. Coalescing black-hole (BH) and neutron-star (NS) binaries are primary GW sources, offering the unique possibility to probe the nature of compact objects and gravitational dynamics. This dissertation investigates how the intrinsic properties of compact objects affect their dynamics and GW emission, using worldline effective field theories (WEFTs) and BH perturbation theory (BHPT), with emphasis on selected scattering processes in General Relativity (GR).
Scattering of two BHs in the post-Minkowskian (PM) regime has proven valuable for extracting binary dynamics from gauge-invariant scattering observables. As a simpler analog, we study electromagnetic (EM) scattering of two charged particles in the post-Lorentzian (PL) expansion. We compute scattering observables to 3PL order and map them
to their bound-orbit counterparts, deriving new boundary-to-bound (B2B) relations. We verified these mappings for gravity at first post-Newtonian (PN) order.
Another key setup involves GWs scattering off compact objects i.e., gravitational Compton/Raman scattering. We compute the classical Compton amplitude at linear order in the mass of the scattering body, and to third order in spin, for generic parity-invariant compact objects, using a WEFT with spin-induced multipole couplings, finding agreement with expectations from amplitude-based methods in the Kerr BH case, while presenting new results for generic objects.
We extract the low-frequency tidal response of Kerr BHs by matching the tidal contribution to the Raman amplitude computed in BHPT to its WEFT counterpart, thereby constraining key tidal coefficients such as Love numbers and dissipation numbers. We then use the dissipation numbers to compute horizon-flux-induced mass and angular-momentum loss in Kerr-BH binaries, resolving longstanding discrepancies with the test-body limit and obtaining waveform corrections up to 4PN order. Additionally, we recover the vanishing of BH Love numbers and identify a nonlinear mixing of tidal and non-tidal effects, resulting in a scale-dependent tidal response via classical renormalization group flow.
We also extend this approach to NSs, and extract electric, quadrupolar, Love and dissipation numbers from the Raman amplitude as a function of the boundary conditions for the metric perturbations at the stellar surface, that are determined by numerically solving the metric- and matter-perturbation equations inside the NS. This allows us to roughly quantify the impact of tidal heating on the GW phase during the inspiral across different equations of state.
Finally, we study the interplay between quasinormal modes (QNMs) and reflectivity for generic compact objects modeled in the membrane paradigm --- a phenomenological framework that encodes interior structure via a fictitious surface fluid. We extend the phenomenological framework to linear order in spin, we analyze how membrane parameters influence the QNM spectrum and reflectivity
Quantum Codes, Transversal Gates, and Representation Theory
No full textRecently an algorithm has been constructed that shows the binary icosahedral group2I together with a T-like gate forms the most efficient single-qubit universal gate set [54].
To carry out the algorithm fault tolerantly requires a code that implements 2I transversally.
We fill this void by constructing a family of distance d = 3 codes that all implement 2I
transversally [39, 42]. To do this, we introduce twisted unitary t-groups, a generalization
of unitary t-groups under a twisting by an irreducible representation. We then apply
representation theoretic methods to the Knill-Laflamme error correction conditions to show
that twisted unitary t-groups automatically correspond to quantum codes with distance
d = t + 1.
Moreover, these methods produce many other quantum codes with interesting transver-
sal gates. In particular, we use our methods to construct families of d ≥ 2 quantum codes
realizing nearly all the possible transversal gate groups that are unitary 2-designs or better
[41].
We also classify certain groups of two qubit gates that may occur as the transversal
gate group of a quantum code with two logical qubits, describing the groups by their
entanglement structure [40].
Finally, inspired by unitary 2-design groups, we consider the problem of finding Lie
primitive subgroups of a simple Lie group
THE EFFECTS OF SHOOT THINNING AND POST-BLOOM LEAF REMOVAL ON FRUIT ROTS AND DOWNY MILDEW FUNGICIDE RESISTANCE IN MID ATLANTIC VINEYARDS
No full textThis thesis investigates integrated disease management strategies by evaluating essential canopy management practices and their effects on disease risk and development. Field trials were conducted across two vineyards in 2023 and 2024, involving three sites and five wine grape cultivars. Treatments included various combinations of high and low leaf removal and shoot density. Results demonstrated that low leaf removal significantly reduced ripe rot severity across trials and years, while low shoot density treatments lowered cluster powdery mildew and Botrytis severity. Disease severity varied by cultivar, with Merlot showing increased susceptibility to ripe rot and Vidal blanc to sour rot in 2024. Additionally, this research determined the fungicide resistance profiles of Plasmopara viticola, the causal agent of grapevine downy mildew. Between 2019 and 2023, 352 downy mildew samples were collected from 27 vineyards and 32 cultivars in Maryland and Pennsylvania. Resistance to common fungicides was assessed using whole-leaf bioassays, while amino acid mutations known for resistance development were confirmed via Sanger sequencing and PCR-RFLP. Overall, resistance was detected to azoxystrobin (69%), mandipropamid (39%), and phosphorous acids (33%) across all regions. Individual isolates, simultaneously displaying resistance to two or more chemical classes of fungicides, were frequently detected (20%). Notably, this study represents the first report of phosphorous acid resistance in North America, detected as early as 2020 and widespread across regions tested. These findings underscore the increasing threat posed by P. viticola to grape production in the Northeast, as rising resistance to multiple fungicide classes significantly limits control options for growers. Further, canopy management practices such as leaf removal and shoot thinning can be tailored to specific diseases by forming less conducive microclimates
All Talk, No Action? Evaluating Members of Congress’ Attention to Foreign Policy
No full textScholars agree that U.S. foreign policy is an issue which offers little distributive benefits to members of Congress and over which the executive branch exerts strong policy leadership. This raises the question of why legislators continue to spend considerable time and effort on foreign affairs. I argue that specific institutional and personal factors such as outparty membership, ideological lean, and constituent representation explain why members focus on foreign policy. In particular, I expect outparty members to use the president’s ownership of foreign affairs for costless position-taking through rhetorical statements, whereas lawmakers with strong ideological preferences or those who have constituent groups with an interest in foreign affairs invest in sponsoring legislation and building coalitions of support. I utilize a novel dictionary of foreign policy-related words to operationalize member-level rhetoric in e-newsletters sent by members of the U.S. House of Representatives from the 111th to the 117th Congress, combining it with bill sponsorship data to create a unique dataset of issue attention. The results reveal a previously unknown party asymmetry, with Republicans being more attentive to foreign affairs on both rhetoric and bill sponsorship. Importantly, this effect is only partly the result of their outparty status, suggesting instead a case of “issue ownership” in foreign affairs. In addition, I show that both constituency interests as well as member background influence members’ attentiveness to foreign policy and trade. On trade as a more distributive issue, members of Congress’ exhibit pragmatic constituency-driven attentiveness. This dissertation contributes to our understanding of the strategic calculations made by members of Congress in an executive-dominated policy area and builds on previous studies of asymmetric party politics and legislative representation
Characterizing Unsystematic Dispersion Of Misfit In Structural Equation Models
No full textStructural equation modeling relies on fit evaluation to assess how well models approximate theoretical relationships, with the goal of providing evidence for the validity of constituent hypotheses. While global fit indices offer convenient summaries of overall model adequacy (Jackson, 2009; McNeish & Wolf, 2023), they cannot guarantee the validity of individual hypotheses, potentially masking substantial localized misspecifications. This limitation becomes particularly problematic in larger models, where acceptable global fit may conceal severe localized misspecification. Current practice supplements global fit with local fit evaluation, but this approach lacks a formalized tolerance for approximation error, unlike global indices that explicitly define acceptable thresholds (Browne & Cudeck, 1993; Hu & Bentler, 1999; Steiger, 2016; Steiger & Lind, 1980). To address this, the current study makes three key contributions to SEM methodology. First, it introduces misfit dispersion as a new dimension of model fit evaluation. Second, it operationalizes the concept of evenly dispersed misfit through analysis of the statistical properties of local fit, yielding the misfit proportion test for assessing disproportionate local misfit. Third, through comprehensive simulation studies, it evaluates the empirical false positive rate and power of the misfit proportion test in finite samples, establishing guidelines for use in practice.
The novel framework presented here extends the principles of approximate global fit to local fit evaluation, unifying them within a consistent paradigm. By considering both the size of global misfit and its dispersion, this refined criteria better ensure that models and their constituent hypotheses provide acceptable approximations of the substantive processes they represent
Analysis of Pneumatic Artificial Muscles in Anchoring, Torsion, and Weight-Limited Robotic Applications
No full textPneumatic artificial muscles (PAMs) are studied in two novel actuation methods: radial expansion and torsional response. In addition, PAMs utilizing novel material for light weight scenarios are studied and applied to a sweeping wing mechanism in an unmanned aerial system (UAS).
For the radial expansion model, modeling was performed using a force balance approach to capture the effects that bladder strain and applied axial load have on the anchoring force. Radial expansion testing was performed to validate the model. Force due to anchoring was recorded using force transducers attached to sections of aluminum pipe using an MTS servo-hydraulic testing machine. Data from the test was compared to the predicted anchoring force. Radial expansion in large diameter (over 2 inches) PAMs were then used in worm-like robots to create anchoring forces that allow for a peristaltic wave which creates locomotion through tunnels and pipes. Modeling of the torsional response was also performed using a force balance approach, and multiple model variations were considered, such as St. Venant's torsion, bladder buckling, and asymmetrical braid loading. Torsional testing was performed to validate the model using a custom torsional testing system. Data from the tests was compared to the predicted torsional response.
In addition to alternative forms of actuation, alternative materials for end fittings were also tested. Two materials were tested, stand alone Acrylonitrile Butadiene Styrene (ABS-R) and ABS embedded with carbon fiber. These materials were chosen to reduce the overall weight of the PAM and increase the specific axial force output. Multiple iterations were designed and tested to achieve an operable pressure range of zero to one hundred psi with a minimum safety factor of 1.5. The PAMs also underwent endurance testing to determine the number of cycles before fatigue failure. The final iteration of the PAM design for both materials were compared to traditional metallic end fitting PAMs in specific force production as well as fatigue life.
Once design work was complete, the 3D-printed end fitting PAM was utilized in a sweeping wing mechanism for a UAS. Due to their small size, UAS possess the ability to fly through confined areas that full-sized aircraft would not be able to. This, however, presents the challenge of an increased risk of collisions with obstacles present in these areas. An active wing sweeping mechanism was proposed to both mitigate the possibility of, and damage associated with, collisions. The mechanism was capable of sweeping the wings of an E-flite V900 BNF Basic remote controlled plane by 45 degrees. Multiple bench top tests were performed on the system, such as a simple actuation test, a response time test, and a hardware-in-the-loop (HITL) test. The gear system was found to be fully capable of sweeping the wings from the default 35.4 inch wingspan to a 24 inch wingspan and clearing a 30 inch gap at speeds up to 55 mph in the HITL tests
MULTIMODAL OPTICAL COHERENCE ELASTOGRAPHY AND BRILLOUIN MICROSCOPY TO EVALUATE IN VIVO LENS BIOMECHANICS IN PRESBYOPIA
No full textPresbyopia is a loss of the dynamic accommodation response of our visual system to adjust to near and far stimuli and affects everyone as they age. Unlike static visual defects such as myopia, presbyopia affects the ability of the eye to adjust it’s focusing power since the lens must change both size and shape. Despite this, current therapies such as spectacles are static corrections of vision and do not treat the underlying cause of presbyopia. Growing evidence suggests that lens stiffening is critical to the inability of the eye to adjust focus, and that spatial varying mechanical properties of the lens are changing with age, and thus the structure-function relationship of these properties is of clinical importance. However, the major barrier to innovation in this space is the lack of clinical characterization and monitoring of accommodation biomechanics, which would aid both diagnostic monitoring and therapeutic planning. Optical coherence elastography (OCE) and Brillouin microscopy are promising technologies with synergistic strengths that can quantitatively assess lens elastography in vivo. To address this unmet need, we developed a clinical multimodal OCE/Brillouin system capable of measuring co-located Brillouin spectra and OCE information to map the depth-dependent elastic moduli. First, the multimodal OCE/Brillouin instrument was developed, and performance specifications were quantified. Next, the relationship between spatial-varying mechanical properties and overall mechanical properties were validated using porcine lenses and clinical OCE/Brillouin datasets to characterize the human lens. Finally, improvements to the Brillouin spectrometer acquisition time were made to reduce motion artifacts and improve translation into the clinical pipeline. This research will ultimately result in enabling patient-specific predictive models of accommodation changes from lens softening procedures for presbyopia treatment
BROADBAND INTEGRATED OPTICAL DEVICES ON THE SILICON-NITRIDE PLATFORM
No full textThe silicon nitride (Si3N4) photonic integrated platform is a low-loss and compact optical platform that has many applications. To further increase its wide applicability, we improve the performances of several optical devices in terms of their bandwidths and polarization dependence. For the first part of this thesis, we increase the bandwidths of multi-mode interference coupler (MMI) couplers, Mach-Zehnder interferometers (MZIs) and fiber-to-chip edge couplers, both theoretically and experimentally. In the second part, we demonstrate polarization independent arrayed waveguide gratings (AWGs) using three different methods, each one with its own advantages and disadvantages.We combine sub-wavelength grating (SWG) and MMI to achieve a significantly enhanced bandwidth, compared to a conventional MMI. The optimized SWG MMI exhibits a 1 dB bandwidth of 300 nm for both the insertion loss and power imbalance, which was verified experimentally. We propose a π-phase shift MMI MZI (πPS MMI-MZI) which serves as a broadband nulling interferometer. This new design uses a novel low phase shift error (PSE) broadband taper-sections phase shifter (TSPS). Our simulations predict an extraordinary low PSE, falling below 1°/0.02° in the wavelength range of 1450 nm to 1650nm for two and three-section TSPS respectively. Our experimental results demonstrate a PSE of 1^o within a 190 nm bandwidth for the two section TSPS. We also study the problem of achieving high coupling efficiency in chip-to-fiber edge couplers. With an innovative double-tip coupler design, we demonstrate a high coupling efficiency of 97.1%. The coupling efficiency remains above 90% within the measurement range (1450-1640 nm) for both TE and TM polarizations.
In the second part of the thesis, we reduce the polarization dependence of AWGs by managing the light beam’s polarization state in-line (in the fiber system) or on-chip. For the in-line approach, the two orthogonal polarizations are separated using a prism. After polarization control in the fiber, the beams are injected into the chip and processed by a multi-input AWG. The on-chip approach processes the polarization using on-chip integrated optical devices including the polarization splitter and rotator. Finally, we propose a Bragg grating AWG to address the polarization dependence. The AWG is folded by reflecting the power using Bragg gratings placed on the arrayed waveguides. Both TE and TM Bragg gratings are designed so that we can control and align these two polarizations separately. As a result, we match the TE and TM responses and achieve polarization independence
Love and Other Emotions Across Time
No full textIn A Grief Observed, C.S. Lewis notes the typical arc of most long-term romantic relationships: “[F]or all pairs of lovers without exception, bereavement is a universal and integral part of our experience of love. It follows marriage as normally as marriage follows courtship or as autumn follows summer. It is not a truncation of the process but one of its phases; not the interruption of the dance, but the next figure” (Lewis, 1994, p. 50). This dissertation consists of three essays, each of which thematizes a general phase of romantic love over time: courtship, partnership, and bereavement. Upon close inspection, each phase is fraught with normative problems. What follows is a brief sketch of the problems and my proposed resolutions.
The first essay of my dissertation examines an aspect of romantic courtship. In “Ethical Seduction,” I take up the worry that seduction belongs in the category of sexual wrongdoing alongside coercion and rape. I claim that those with this worry tend to play down our ambivalence towards seduction. Despite our discomfort, we sometimes desire to be seduced. Many romantic clichés reflect this desire: we want other people to sweep us off our feet, carry us away, make us fall in love with them, woo us. This tension makes clear that seduction has some appeal and implies that it is not a straightforward moral problem. I argue that seduction is not wholly bad and suggest that ethical seduction is possible. Though “ethical seduction” may sound like an oxymoron, I propose criteria to mark the good-making features of seduction, which include the indirect, non-rational engagement of people’s latent desires and interests in ways that (i) amplify any positive emotions with which people are not in tune, and/or (ii) deactivate the problematic inhibitions that lead people to resist what they freely desire.
The second essay, “Love and Evaluative Conflict,” concerns long-term romantic partnership. I take it as a fact that lovers often disagree. We may reject the specific goals our loved ones pursue or the broad values they hold. Some philosophers suggest that such evaluative conflict makes romantic love in its ideal form deficient. But I argue that this is mistaken. On the contrary, our ideal of love holds that we can love people for ‘who they are’ (as we say), even as we profoundly disagree with them. My argument draws on intuitive cases from screwball comedy about love amid conflict, love across political party lines, as well as ‘forbidden’ love across religions and cultures. At a deeper level, I sketch an ideal of love I call intimate independence and argue that this ideal is (i) fully compatible with any evaluative conflict, (ii) embedded in our ordinary attitudes towards mature love between equals, and (iii) an ideal worth achieving. As long as intimate independence is a compelling ideal, deep conflict will not seem like an obstacle to true love. The ideal reminds us that love can bring together people with radically different points of view, and that to insist on shared ends or values is thus to miss a part of the meaning and power of love.
Finally, if a couple doesn’t split over their disagreements, their partnership ends in death. This dissertation is no different. In the last chapter of this dissertation, “Grief Rekindles,” I examine something often repeated in editorials, blogs, and popular books about the deaths of loved ones: grief is forever. I present a qualified defense of this folk insight. We don’t feel the impact of loss maximally all the time. Rather, we continue to feel it for the rest of our lives, because grief doesn’t simply diminish but rekindles like fire. As I put it, grief is an intermittent emotion, capable of going out of existence, then existing again as the same thing. I argue that this trajectory is fitting. Intermittent emotions have a rational status; their distinct temporal pattern gets something right about their objects. This proposal dissolves a recent philosophical worry that grief diminishes over a short time despite the persistence of its eliciting loss. Moreover, it provides a sophisticated sketch of the fittingness of emotions over time: intermittence is a norm to evaluate emotional fittingness alongside character and intensity
Archivists Leading the Reckoning: Confronting Slavery and its Legacies at the University of Maryland
No full textCase study of The 1856 Project, the University of Maryland’s chapter of the Universities Studying Slavery consortium. Provides practical strategies for social justice workers who seek scalable project models for addressing legacies of racialized harm at their institutions