Browsing by Subject "Ensemble"
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Item Combining classifier and cluster ensembles for semi-supervised and transfer learning(2012-05) Acharya, Ayan; Ghosh, Joydeep; Mooney, Raymond J.Unsupervised models can provide supplementary soft constraints to help classify new, "target" data since similar instances in the target set are more likely to share the same class label. Such models can also help detect possible differences between training and target distributions, which is useful in applications where concept drift may take place, as in transfer learning settings. This contribution describes two general frameworks that take as input class membership estimates from existing classifiers learnt on previously encountered "source" data, as well as a set of cluster labels from a cluster ensemble operating solely on the target data to be classified, and yield a consensus labeling of the target data. One of the proposed frameworks admits a wide range of loss functions and classification/clustering methods and exploits properties of Bregman divergences in conjunction with Legendre duality to yield a principled and scalable approach. The other approach is built on probabilistic mixture models and provides additional flexibility of distributed computation that is useful when the target data cannot be gathered in a single place for privacy or security concerns. A variety of experiments show that the proposed frameworks can yield results substantially superior to those provided by popular transductive learning techniques or by naively applying classifiers learnt on the original task to the target data.Item Concerto for piano and wind ensemble(2012-05) Stanton, Zachary Kane, 1983-; Pinkston, Russell; Welcher, Dan; Grantham, Donald; Sharlat, Yevgeniy; O'Hare, ThomasConcerto for Piano and Wind Ensemble is a 16-minute work for piano and winds, brass, and percussion. Although piano is my primary instrument, I have written relatively little for it. With this piece I sought to write a work in the vein of the Romantic and early Twentieth Century piano concerto repertoire, which I listened to and absorbed as a young musician, but with a more contemporary harmonic language. Rather than using the traditional orchestra as the accompanying ensemble, I chose the wind ensemble, which has a limited concerto repertoire, giving me the opportunity to make a meaningful contribution to its literature.Item Ensemble sensitivity analysis applied to Southern Plains convection(2013-08) Bednarczyk, Christopher N.; Ancell, Brian A.; Weiss, Christopher C.; Kang, Song-LakThe recent increase in use of ensembles in numerical weather prediction has led to new information being available to forecasters, including uncertainty statistics and probabilistic guidance. Ensemble Sensitivity Analysis (ESA) offers additional information that describes the relationship between a forecast metric known as the response function and initial or early forecast errors, and it is capable of revealing features of the flow that are dynamically relevant to the chosen forecast. The applicability of ESA to a high resolution convection forecast of April 2012 is investigated with an Ensemble Kalman Filter based on the Weather Research and Forecasting model. It is shown that forecasts of convection are primarily sensitive to positional differences in the synoptic-scale flow. The selection of the response function is also explored to determine how to choose a convective forecast metric. Sensitivity does vary with the choice of response, but the same features tend to be highlighted in all cases. Sensitivity is also compared with a standardized form in which the raw value is weighted by the ensemble spread in order to determine the merit of each type. The standardized sensitivity provides information on expected forecast error, and it reveals features that are not highlighted in the raw sensitivity. In addition, a cross-grid approach to sensitivity is studied in order to determine if it shows similar results as the same-grid method. Results show them to have differences, but the cross-grid method still reveals realistic features in the context of the event.Item First-principles investigation of the surface reactivity of Pd-based alloys for fuel cell catalyst applications(2011-12) Ham, Hyung Chul; Hwang, Gyeong S.; Ekerdt, John G.; Mullins, Buddie C.; Arumugam, Manthiram; Ferreira, Paulo J.In recent years, palladium (Pd) has been extensively studied for a possible alternative for Pt that has been most commonly used as a catalyst in fuel cells. However, Pd shows lower activity than Pt towards the cathodic oxygen reduction reaction (ORR) and also exhibits poor tolerance toward carbon monoxide (CO) poisoning occurring in the anode process. To improve its performance, alloying Pd with other transition metals has been suggested as one of promising solutions as the Pd-based alloys have been found to boost the ORR activity and yield significant improvement in the CO tolerance. However, a detailed understanding of the alloying effects is still lacking, despite its importance in designing and developing new and more cost effective fuel cell catalysts. This is in large part due to the difficulty of direct characterization. Alternatively, computational approaches based on quantum mechanics have emerged as a powerful and flexible means to unravel the complex alloying effects in multimetallic catalysts; such first principles-based computational studies have provided many invaluable insights into the mechanisms of catalytic reactions occurring on the alloy surfaces. Using first-principles density-functional theory calculations, we have examined the surface reactivity of Pd-based bimetallic catalysts with the aim of better understanding the alloying effects in association with atomic arrangement, facet, local strain, ligand interaction, and effective atomic coordination number at the surface. More specifically, this thesis work has focused on examining the following topics: Role of Pd ensembles in selective H₂O₂ formation on AuPd alloys; Effect of local strain and low-coordination number at the surface on the performance of Pd monomer in selective H₂O₂ formation; Different facet effects on the activity of Pd ensembles towards ORR; Structure of ternary Pd-Ir-Co alloys and its reactivity towards ORR; Pd ensembles effects on CO oxidation on CO-precovered Pd ensembles; Role of ligand and ensembles in determining CO chemisorptions on AuPd and AuPt. Our first principles-based theoretical investigation of bimetallic alloys offers some insights into the rational design and development of alloyed catalysts.Item The Walk : holding space in the face of crisis, failure, and fear(2015-05) Hutchinson, Jessica Rae; Rasmussen, Sarah; Carlson, Andrew; Dietz, Steven; Engelman, ElizabethThis thesis is about fear, failure, and faith. The tools I have developed during my graduate study have enabled me first to tolerate and then to welcome the energy of these forces into my artistic process. By examining and establishing Structure, creating and empowering Ensembles, and insisting upon an Inquiry-driven process, I can encounter fear and failure as I seek out the unpredictable, unrepeatable transcendence of the living play. By cultivating and inviting uncertainty, I hold space for the emergence of grace.