5,757 research outputs found

    Technology for Low Resolution Space Based RSO Detection and Characterisation

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    Space Situational Awareness (SSA) refers to all activities to detect, identify and track objects in Earth orbit. SSA is critical to all current and future space activities and protect space assets by providing access control, conjunction warnings, and monitoring status of active satellites. Currently SSA methods and infrastructure are not sufficient to account for the proliferations of space debris. In response to the need for better SSA there has been many different areas of research looking to improve SSA most of the requiring dedicated ground or space-based infrastructure. In this thesis, a novel approach for the characterisation of RSO’s (Resident Space Objects) from passive low-resolution space-based sensors is presented with all the background work performed to enable this novel method. Low resolution space-based sensors are common on current satellites, with many of these sensors being in space using them passively to detect RSO’s can greatly augment SSA with out expensive infrastructure or long lead times. One of the largest hurtles to overcome with research in the area has to do with the lack of publicly available labelled data to test and confirm results with. To overcome this hurtle a simulation software, ORBITALS, was created. To verify and validate the ORBITALS simulator it was compared with the Fast Auroral Imager images, which is one of the only publicly available low-resolution space-based images found with auxiliary data. During the development of the ORBITALS simulator it was found that the generation of these simulated images are computationally intensive when propagating the entire space catalog. To overcome this an upgrade of the currently used propagation method, Specialised General Perturbation Method 4th order (SGP4), was performed to allow the algorithm to run in parallel reducing the computational time required to propagate entire catalogs of RSO’s. From the results it was found that the standard facet model with a particle swarm optimisation performed the best estimating an RSO’s attitude with a 0.66 degree RMSE accuracy across a sequence, and ~1% MAPE accuracy for the optical properties. This accomplished this thesis goal of demonstrating the feasibility of low-resolution passive RSO characterisation from space-based platforms in a simulated environment

    Decision-making with gaussian processes: sampling strategies and monte carlo methods

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    We study Gaussian processes and their application to decision-making in the real world. We begin by reviewing the foundations of Bayesian decision theory and show how these ideas give rise to methods such as Bayesian optimization. We investigate practical techniques for carrying out these strategies, with an emphasis on estimating and maximizing acquisition functions. Finally, we introduce pathwise approaches to conditioning Gaussian processes and demonstrate key benefits for representing random variables in this manner.Open Acces

    The generation, propagation, and mixing of oceanic lee waves

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    Lee waves are generated when oceanic flows interact with rough seafloor topography. They extract momentum and energy from the geostrophic flow, causing drag and enhancing turbulent mixing in the ocean interior when they break. Mixing across density surfaces (diapycnal mixing) driven by lee waves and other topographic interaction processes in the abyssal ocean plays an important role in upwelling the densest waters in the global ocean, thus sustaining the lower cell of the meridional overturning circulation. Lee waves are generated at spatial scales that are unresolved by global models, so their impact on the momentum and buoyancy budgets of the ocean through drag and diapycnal mixing must be parameterised. Linear theory is often used to estimate the generation rate of lee waves and to construct global maps of lee wave generation. However, this calculation and subsequent inferences of lee wave mixing rely on several restrictive assumptions. Furthermore, observations suggest that lee wave mixing in the deep ocean is significantly overestimated by this theory. In this thesis, we remove some common assumptions at each stage of the lee wave lifecycle to investigate the reasons for this discrepancy and to motivate and inform future climate model parameterisations. Firstly, we investigate the way that seafloor topography is represented in lee wave parameterisations, finding that typical spectral methods can lead to an overestimate of wave energy flux. Next, we make the case for considering lee waves as a full water column process by modelling the effect of vertically varying background flows and the ocean surface on lee wave propagation. Finally, we take a holistic view of topographic mixing in the abyssal ocean, finding that deep stratified water mass interfaces may modify the nature of the lee wave field, and themselves contribute to mixing and upwelling in the deep ocean through topographic interaction.Open Acces

    From a Duty to a Right: The Political Development of the Second Amendment

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    Thesis advisor: Marc LandyThis dissertation addresses the question of how the issue of gun rights is debated and resolved in American politics. While the Supreme Court’s landmark ruling in District of Columbia v. Heller (2008) has often been described as a distinct political win for gun rights advocates, it left open crucial political and regulatory questions that remain unsettled, including the constitutional permissibility of gun control measures and the proper balance between state and federal authority in establishing those parameters. This dissertation provides an account of the Second Amendment’s political development and its interpretation as a civic, state, collective, and individual right, and how shifts in interpreting the right to keep and bear arms have changed the way competing claims of gun rights and gun control are reconciled through the political process. Doing so aligns the Second Amendment with other major changes in American politics – outside of the courts – including the growing role of the federal government, the increase in polarization and the importance of cultural issues to partisan politics, and the rise of the gun rights movement as a pivotal political force. Using the lens of American political development, this dissertation is structured to identify critical junctures over time when changing interpretations of the Second Amendment transformed the politics of gun control, which include policy changes, partisan realignment, and broader patterns of federalism. Detailed historical and legal research of primary sources was conducted, including analysis of newspapers, journals, correspondence, as well as early state constitutions, records from the Constitutional Convention, briefs from state legislatures regarding gun regulation, and relevant court cases. Based on this research, the evidence is sufficiently compelling to support the collectivist reading of the Second Amendment rather than the individual rights interpretation. In other words, the Second Amendment was intended to protect the states from federal encroachment by guaranteeing their right to arm their militias – not to grant an individual right – a position that was subsequently maintained by the courts until District of Columbia v. Heller (2008) overturned decades of precedent, further complicating the already contentious issue of gun rights in American politics. Chapter One focuses on the historical and intellectual origins of the right to bear arms that influenced early state constitutions and gun regulations. Chapters Two through Four discuss the nature of arms-bearing during the Revolutionary era; the debates surrounding the drafting and ratification of the Second Amendment; and the crucial role of the state militia system to early notions of republican government. Subsequent chapters provide an account of the changing nature of the state militia system, ultimately resulting in the formation of the National Guard; early legal interpretations of the right to bear arms, including whether the Second Amendment applied to the states; and a comprehensive account of federal gun legislation. From there, Chapter Seven discusses the development of collective rights theory and the Supreme Court’s traditional position on the Second Amendment. Chapters Eight and Nine turn to the rise of the gun rights movement; the establishment of the National Rifle Organization as an influential political actor and how the Second Amendment was politicized to advance its cause; changes to federal gun legislation; and the development of individual rights theory and its influence on the partisan debate about gun control, including a literature review to account for the “New Standard Model” of Second Amendment scholarship. Chapter Ten analyzes the milestone decisions District of Columbia v. Heller (2008) and McDonald v. Chicago (2010) and also provides a detailed account of the process of incorporating the Second Amendment against the states, arguing that even though the Supreme Court established the individual right to keep and bear arms, its traditional interpretation as a states’ right must be maintained in the interest of federalism. The Conclusion further advances this assertation, contending that the intense debate about gun rights in American politics could be tempered by allowing the states greater latitude to regulate both gun control and gun rights. Under a federalized system of well-regulated liberty that emphasizes state autonomy, the states would be free to either limit or expand the right to keep and bear arms based on the demands of their constituents, which balances the politics of gun control with the constitutional protections of the Second Amendment.Thesis (PhD) — Boston College, 2023.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Political Science

    The Anti-Fascism Of Ernest Hemingway

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    Despite complicated political views, Ernest Hemingway remained a staunch opponent to fascism throughout his life. Writing as a newspaperman, lifestyle writer, naturalist, and frequently a novelist, the Hemingway oeuvre is robust and teeming with political thought. This thesis dives deep into Hemingway’s political thinking during the interwar period. From the end of World War I to the defeat of Republican forces in the Spanish Civil War, the paper tracks Hemingway’s antifascism through letters, novels, short stories, public appearances, essays, and journalism. Hemingway was fascinated with proletarian masses and aspired to advocate for their needs in his writing. His leftist inclinations can be found throughout his work in varying degrees of obviousness that fluctuate with pressures both outside and within. The same can be said for his serious criticisms of war. Once present on the Italian Front in 1918, Hemingway became hugely critical of war. These consistent motivations, advocacy for proletarian concerns and antiwar sentiment, were driven by his disdain for fascism and the despots he’d criticize from the early twenties on. Tracking the matrix of these motivations through Hemingway’s interwar work produces a complicated but politically impassioned interpretation of Ernest Hemingway

    Magma Chemical Evolution in the Lesser Antilles Arc Crust: Insights from Plutonic Xenoliths

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    Magmas generated beneath volcanic arcs at subduction zones must traverse the crust of the overriding plate, via “magma plumbing systems” prior to eruption. Magma plumbing systems are predominantly composed of crystal mush, where low volumes of melt are distributed throughout higher volumes of crystals. To understand processes controlling the chemical compositions of arc lavas, it is essential to constrain how magmas are chemically modified within mushy plumbing systems during storage and transit through the upper plate crust. Arc lavas often carry fragments of crystal mush, known as plutonic xenoliths, to the surface, which can be used to study the influence of crustal processes on arc magma chemical compositions. This thesis investigates plutonic xenoliths from the islands of Martinique and St Vincent in the active intra-oceanic Lesser Antilles arc. These samples are used to determine whether the majority of the trace element and isotopic variation in Lesser Antilles arc lavas can be produced by crustal processes. Strontium isotopic compositions of plagioclase, in plutonic xenoliths derived from different crustal depths, are used to demonstrate that isotopic variation and highly radiogenic isotopic compositions observed in Martinique lavas are acquired via assimilation of upper crustal sediments. Textural features and mineral trace element compositions in St Vincent plutonic xenoliths record polybaric fractional crystallization and melt-mush reaction processes. These two processes control magma chemical evolution in mushes beneath the island and consequently influence the trace element compositions of St Vincent lavas. These findings suggest that majority of trace element and radiogenic isotopic variation in Lesser Antilles arc lavas is generated within mushy magma plumbing systems in the arc crust. An important wider implication is that contributions from crustal processes must be well constrained before using trace element and isotopic compositions of arc lavas to assess subduction recycling processes and mantle source heterogeneity

    Anime Studies: media-specific approaches to neon genesis evangelion

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    Anime Studies: Media-Specific Approaches to Neon Genesis Evangelion aims at advancing the study of anime, understood as largely TV-based genre fiction rendered in cel, or cel-look, animation with a strong affinity to participatory cultures and media convergence. Making Neon Genesis Evangelion (Shin Seiki Evangerion, 1995-96) its central case and nodal point, this volumen forground anime as a media with clearly recognizable aesthetic properties, (sub)cultural affordances and situated discourses
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