3,604 research outputs found
Krylov subspace methods for approximating functions of symmetric positive definite matrices with applications to applied statistics and anomalous diffusion
No full textMatrix function approximation is a current focus of worldwide interest and finds application in a variety of areas of applied mathematics and statistics. In this thesis we focus on the approximation of A^(-α/2)b, where A ∈ ℝ^(n×n) is a large, sparse symmetric positive definite matrix and b ∈ ℝ^n is a vector. In particular, we will focus on matrix function techniques for sampling from Gaussian Markov random fields in applied statistics and the solution of fractional-in-space partial differential equations. \ud
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Gaussian Markov random fields (GMRFs) are multivariate normal random variables characterised by a sparse precision (inverse covariance) matrix. GMRFs are popular models in computational spatial statistics as the sparse structure can be exploited, typically through the use of the sparse Cholesky decomposition, to construct fast sampling methods. It is well known, however, that for sufficiently large problems, iterative methods for solving linear systems outperform direct methods. \ud
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Fractional-in-space partial differential equations arise in models of processes undergoing anomalous diffusion. Unfortunately, as the fractional Laplacian is a non-local operator, numerical methods based on the direct discretisation of these equations typically requires the solution of dense linear systems, which is impractical for fine discretisations. \ud
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In this thesis, novel applications of Krylov subspace approximations to matrix functions for both of these problems are investigated. Matrix functions arise when sampling from a GMRF by noting that the Cholesky decomposition A = LL^T is, essentially, a `square root' of the precision matrix A. Therefore, we can replace the usual sampling method, which forms x = L^(-T)z, with x = A^(-1/2)z, where z is a vector of independent and identically distributed standard normal random variables. Similarly, the matrix transfer technique can be used to build solutions to the fractional Poisson equation of the form ϕn = A^(-α/2)b, where A is the finite difference approximation to the Laplacian. Hence both applications require the approximation of f(A)b, where f(t) = t^(-α/2) and A is sparse. In this thesis we will compare the Lanczos approximation, the shift-and-invert Lanczos approximation, the extended Krylov subspace method, rational approximations and the restarted Lanczos approximation for approximating matrix functions of this form. \ud
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A number of new and novel results are presented in this thesis. Firstly, we prove the convergence of the matrix transfer technique for the solution of the fractional Poisson equation and we give conditions by which the finite difference discretisation can be replaced by other methods for discretising the Laplacian. We then investigate a number of methods for approximating matrix functions of the form A^(-α/2)b and investigate stopping criteria for these methods. In particular, we derive a new method for restarting the Lanczos approximation to f(A)b. We then apply these techniques to the problem of sampling from a GMRF and construct a full suite of methods for sampling conditioned on linear constraints and approximating the likelihood. Finally, we consider the problem of sampling from a generalised Matern random field, which combines our techniques for solving fractional-in-space partial differential equations with our method for sampling from GMRFs
Simpson Filled Sinkholes in Eastern Kansas
No full textSix sinkholes involving rocks of Simpson age (Ordovician) were found from examination of logs of wells drilled in eastern Kansas. These sinks contain abnormally thick Simpson sediments, chiefly St. Peter sandstone, which is interpreted as having been deposited as fill in sinkholes developed on an eroded surface of dolomite and limestone of the Arbuckle group. Chert conglomerate and green shale are present in the bottom of the sinks. The shale consists mainly of an illitic clay and quartz, which may be residual weathering products formed in place or washed into the sinks. It is believed that these subsurface features are similar to the Otterville structure in Cooper County, Missouri
Author correction: obesity and ethnicity alter gene expression in skin
No full textDaniel Butler was omitted from the author list in the original version of this Article. The Author contributions section now reads: “J.M.W. designed, conducted, and contributed to the writing of the manuscript, prepared Fig. 1. S.G. evaluated and did statistical analysis on the skin and fat samples, prepared Figs. 2–9. J.O.A. evaluated and contributed to writing the manuscript. D.B prepared and sequenced DNA libraries for the skin microbiota data, and wrote the applicable parts of the methods section. C.M. analyzed and wrote up the skin microbiota data, prepared Fig. 10. All authors have read the manuscript and approved its contents. D.D. analyzed and wrote up the skin microbiota data. S.Z. ran and analyzed the skin metabolite data. J.S. assisted in design, analysis and wrote up the skin metabolite data. J.K. assisted in analysis write up of skin and fat data. J.L.B. assisted in analysis, interpretation and writing of the manuscript. P.R.H. designed, analyzed, interpreted the data, and was the primary author of the manuscript.” This has been corrected in the PDF and HTML versions of the Article, and in the accompanying Supplementary Information file.</p
Florida Historical Quarterly Podcast Episode 07: Fall 2010
No full textWe interviewed the three authors that contributed to this special issue, all of whom are graduate students finishing their Ph.D.s on Florida history topics. We asked the authors about their experiences researching a Florida topic while early in their scholarly careers. Our guests on this podcast were Deborah L. Bauer, author of “. . . in a strange place”: The Experiences of British Women during the Colonization of East & West Florida,” Nicole C. Cox, author of “Selling Seduction: Women and Feminine Nature in 1920s Florida,” and Peter Ferdinando, author of “A Translation History of Florida.”https://stars.library.ucf.edu/fhq-podcast/1006/thumbnail.jp
Bursting Bubbles with Dan McQuillan
No full textIs the rise of AI inevitable or just the latest cycle of hype for a sector that thrives on the vibes? The author of “Resisting AI’, Professor Dan McQuillan, joins the show to argue for a more fundamental response to Big Tech.
Regular panellists Digital Rights Watch Chair Lizzie O’Shea, Health Engine CEO Dan Stinton and Per Capita’s Peter Lewis also discuss:
- the launch of AI’s new Sora video product
- the push to sell advertising inside GPTs
- and how consultants are embracing work slo
Ethnic identity, political identity and ethnic conflict: simulating the effect of congruence between the two identities on ethnic violence and conflict
No full textThis thesis outlines and presents an alternative hypothetical process to the emergence of ethnic conflict. Ethnic conflicts, rather than being dependent upon pre-existing 'ancient hatreds', are instead the result of a congruence between ethnic and political identity which grants individuals the ability to use ethnicity to identify and eliminate political threats. This hypothesis is formed by the examination of three case studies of ethnic conflict: Lebanon, Northern Ireland and Croatia. This hypothesis is then formalised and tested using an agent based simulation in which agent interactions are dependent upon ethnic and political identity and the congruence between the two. As predicted there was a strong positive correlation between how accurately ethnic identity reflected political identity and the level of ethnically motivated violence in the simulation, although the relationship was not linear. Furthermore the effect of a shift in congruence was found to be roughly comparable to the effect of initialising agents with a moderate level of pre-existing ethnic antagonism
An Assay System For Point-of-Care Diagnosis Of Tuberculosis using Commercially Manufactured PCB Technology
No full textThe data included in this file is provided in an excel format and provides the supporting data for the graphs in Figures 2 -6 in the paper: An Assay System of Point-of-care Diagnosis of Tuberculosis using commercially manufactured PCB Technology. Corresponding author Daniel Evans- University of Southampton.
Accepted Manuscript 13/3/2017 by Scientific Reports - Nature.com</span
Manganese
No full textA Toxicological Profile for Manganese, Draft for Public Comment was released in September 2008. This edition supersedes any previously released draft or final profile.Chemical manager(s)/author(s): Malcolm Williams, G. Daniel Todd, Nickolette Roney, Jewell Crawford, Charleton Coles, ATSDR, Division of Toxicology and Human Health Sciences (proposed), Atlanta, GA; Peter R. McClure, Joan D. Garey, Kimberly Zaccaria, Mario Citra, SRC Inc. (formerly known as Syracuse Research Corporation), North Syracuse, NY.Includes bibliographical references (p. 443-499) and index
Music for classical guitar by South African composers : a historical survey, notes on selected works and a general catalogue
No full textIncludes abstract.Includes bibliographical references (leaves 296-309).This is the first comprehensive investigation of music for, or including, the classical guitar by South African composers. The focus of this research has been, firstly, to uncover as much of the repertoire as possible, and, secondly, to collate, study, catalogue and report on the information. A brief historical survey of the guitar in South Africa provides the context within which this study was conducted. The primary sources of quantitative data collection were through the archival catalogues of the South African Music Rights Organisation and through personal contact with guitarists, composers and guitar teachers. Other sources consulted were publishers, broadcasting corporations, recording companies, libraries and the internet. The body of the dissertation comprises biographical sketches, background notes, analyses and technical notes on 17 selected solo and chamber works dating from 1947 to 2007 by some of South Africa's most prominent composers and guitaristcomposers. The repertoire ranges in style from the traditional and ethnically inspired to the experimental and abstract. As this is an empirical survey, each selected entry includes details on instrumentation, duration, level of difficulty, number of pages, scordatura, commissions or requests, sources or publishers, premières and recordings. A biography of each composer is provided as well as background notes which offer an overview of the selected work. The notes discuss historical, cultural, musical and extra-musical influences, and frequently include references to interview material. The commentaries on the selected works, with musical examples, include an analytical component describing structure, form, stylistic and compositional elements, while the technical observations include performance suggestions and a grading for each work
Through Her Eyes: Celebrating Women in Photography through the Peter Palmquist Collection
No full textDr. Matthew Daniel Mason, Archivist, Beinecke Rare Book and Manuscript Library, Yale University, New Haven, Conn., U.S.A.
Through Her Eyes: Celebrating Women in Photography through the Peter Palmquist Collection
The presentation focuses on the Peter Palmquist Collection of Women in Photography at Yale University’s Beinecke Rare Book and Manuscript Library. This collection offers a unique and invaluable perspective on the contributions of women to the field of photography, spanning from the early days of the medium to contemporary practices.
The presentation outlines how the collection serves as a critical resource for understanding the historical and contemporary achievements of women photographers, providing insight into the gender dynamics that have shaped photographic practice and representation. The presentation also explores how the collection highlights the significant, yet often overlooked, accomplishments of women in photography across diverse cultural and geographic contexts.
Matthew Daniel Mason is an archivist responsible for processing photographs and other visual resources at the Beinecke Rare Book and Manuscript Library at Yale University. He also worked with archival collections at the Wisconsin Historical Society and Montana State University. He also earned a Ph.D. in history from the University of Memphis (2008), and a Master of Arts in Library and Information Studies from the University of Wisconsin-Madison School of Library and Information Studies (2003). In addition to his more than two decades of archival work, Dr. Mason teaches courses in American history and history of photography at Quinnipiac University in Hamden, Connecticut. He is also a co-author of People of the Big Voice: Photographs of Ho-Chunk Families by Charles Van Schaick, 1879-1942 (Wisconsin Historical Society Press, 2011) and Through a Woman’s Eye: The Early 20th Century Photography of Alabama’s Edith Morgan (New South Books, 2015)
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