Robust Machine Learning by Transforming and Augmenting Imperfect Training Data

Machine Learning (ML) is an expressive framework for turning data into computer programs. Across many problem domains -- both in industry and policy settings -- the types of computer programs needed for accurate prediction or optimal control are difficult to write by hand. On the other hand, collecting instances of desired system behavior may be relatively more feasible. This makes ML broadly appealing, but also induces data sensitivities that often manifest as unexpected failure modes during deployment. In this sense, the training data available tend to be imperfect for the task at hand. This thesis explores several data sensitivities of modern machine learning and how to address them. We begin by discussing how to prevent ML from codifying prior human discrimination measured in the training data, where we take a fair representation learning approach. We then discuss the problem of learning from data containing spurious features, which provide predictive fidelity during training but are unreliable upon deployment. Here we observe that insofar as standard training methods tend to learn such features, this propensity can be leveraged to search for partitions of training data that expose this inconsistency, ultimately promoting learning algorithms invariant to spurious features. Finally, we turn our attention to reinforcement learning from data with insufficient coverage over all possible states and actions. To address the coverage issue, we discuss how causal priors can be used to model the single-step dynamics of the setting where data are collected. This enables a new type of data augmentation where observed trajectories are stitched together to produce new but plausible counterfactual trajectories.Comment: A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy, Department of Computer Science, University of Toront

The volume elements intercepted by intersecting cylinders

Call number: LD2668 .T4 1935 H3

An improved approach for flight readiness assessment

An improved methodology for quantitatively evaluating failure risk for a spaceflight system in order to assess flight readiness is presented. This methodology is of particular value when information relevant to failure prediction, including test experience and knowledge of parameters used in engineering analyses of failure phenomena, is limited. In this approach, engineering analysis models that characterize specific failure modes based on the physics and mechanics of the failure phenomena are used in a prescribed probabilistic structure to generate a failure probability distribution that is modified by test and flight experience in a Bayesian statistical procedure. The probabilistic structure and statistical methodology are generally applicable to any failure mode for which quantitative engineering analysis can be employed to characterize the failure phenomenon and are particularly well suited for use under the constraints on information availability that are typical of such spaceflight systems as the Space Shuttle and planetary spacecraft

Gasification of liquid sprays in an entrained flow gasifier

In an advancing technological world, gasification is a relatively mature technology that can be refreshed to help achieve sustainable energy production. This thesis discusses the development of a pressurized gasification system that converts bio-oil from fast pyrolysis of red oak into producer gas. Focus will be given to the challenges of operating a pressurized system at high temperature while injecting a non-uniform liquid. Demonstration experiments using methanol resulted in development of experimental methods to show critical nozzle designs and their affects on gasification of liquid jets. Start up of the bio-oil gasification system was performed using methanol as a model fuel. Methanol provides a stable platform for proving the system\u27s capabilities and focused attention on areas that needed design improvements. The ideal fuel also made it easy to compare the system results directly with theoretical calculations of equilibrium. The methanol experiments highlighted a need to show the importance of volatility verses the importance of atomization. Due to this discovery, the experiments where adjusted to demonstrate the change in atomization within a fixed system. Producing the whole bio-oil that 1) could be readily pumped 2) would not clog the system and 3) have congruent properties throughout testing proved to be a challenge within itself. A list of lab experiments were conducted to show differences in bio-oils that had been filtered to three difference sizes; 500μm, 90μm and 40μm. To best show the importance in atomization, the 90μm bio-oil was selected. The bio-oil gasification tests were performed using 3 nozzle configurations. Each nozzle showed a unique result while further proving that atomization is critical to performing gasification of liquid jets

The aesthetics of metamorphosis: Ovidian poetics in the works of Maria Luisa Bombal and Elena Garro.

The study begins with an analysis of the Ovidian concept of metamorphosis and its effects on the body, identity, and the corpus of the text. Chapter Two addresses the notion of "literary myth, " and contextualizes Bombal's and Garro's work within a tradition that allows the authors to reinscribe and transform myths (both Western and Mesoamerican) in their texts. Chapter Three locates Bombal's Impressionistic aesthetic within French Symbolist and Post-Symbolist poetics, and establishes Bombal as one of the first novelists to translate its aesthetic for Latin America. Chapter Four provides an explication of Bombal's La ultima niebla through the interpretation of the myths of Narcissus, Orpheus, and Pygmalion---myths that illustrate her protagonist's psychic transformation and reveal a deconstruction of discourses on romantic love through parody and irony. Chapter Five both contextualizes Elena Garro within the avant-garde that characterized post-Revolutionary Mexico, and scrutinizes Garro's critical response to the ideology of liberation. Chapter Six explores textual and temporal transformations in Garro's Los recuerdos del porvenir, a work that reinterprets both the Surrealist myth of a golden age and the Mesoamerican myths of cosmic periodicity. The conclusion argues that, through the intertextual aesthetics of metamorphosis, these authors exploit the ambivalence of language in order to subvert essential notions of feminine identity and convey the paradoxes of Otherness, gender, and limitation.Maria Luisa Bombal's La ultima niebla and Elena Garro's Los recuerdos del porvenir represent two models of the evolving tradition of literary myth. Their novels offer examples of enigmatic female characters whose negations of reality are aesthetically rendered as transformations that end in either figurative stasis or literal petrification. Bombal and Garro revise some of Ovid's most fascinating myths in order to draw attention to the aesthetic dimension of their own complex texts, as well as to address fundamental questions concerning feminine subjectivity