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Search Results: 1 - 10 of 12689 matches for " Christopher Wyatt "
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Missing Data Estimation in FMRI Dynamic Causal Modeling
Shaza Zaghlool,Christopher Wyatt
Frontiers in Neuroscience , 2014, DOI: 10.3389/fnins.2014.00191
Abstract: Dynamic Causal Modeling (DCM) can be used to quantify cognitive function in individuals as effective connectivity. However, ambiguity among subjects in the number and location of discernible active regions prevents all candidate models from being compared in all subjects, preventing the use of DCM as an individual cognitive phenotyping tool. This paper proposes a solution to this problem by treating missing regions in the first-level analysis as missing data, and performing estimation of the time course associated with any missing region using one of four candidate methods: zero-filling, average-filling, noise-filling using a fixed stochastic process, or one estimated using expectation-maximization. The effect of this estimation scheme was analyzed by treating it as a preprocessing step to DCM and observing the resulting effects on model evidence. Simulation studies show that estimation using expectation-maximization yields the highest classification accuracy using a simple loss function and highest model evidence, relative to other methods. This result held for various dataset sizes and varying numbers of model choice. In real data, application to Go/No-Go and Simon tasks allowed computation of signals from the missing nodes and the consequent computation of model evidence in all subjects compared to 62 and 48 percent respectively if no preprocessing was performed. These results demonstrate the face validity of the preprocessing scheme and open the possibility of using single-subject DCM as an individual cognitive phenotyping tool.
X-Ray Phase-Contrast Imaging with Three 2D Gratings
Ming Jiang,Christopher Lee Wyatt,Ge Wang
International Journal of Biomedical Imaging , 2008, DOI: 10.1155/2008/827152
Abstract: X-ray imaging is of paramount importance for clinical and preclinical imaging but it is fundamentally restricted by the attenuation-based contrast mechanism, which has remained essentially the same since Roentgen's discovery a century ago. Recently, based on the Talbot effect, groundbreaking work was reported using 1D gratings for X-ray phase-contrast imaging with a hospital-grade X-ray tube instead of a synchrotron or microfocused source. In this paper, we report an extension using 2D gratings that reduces the imaging time and increases the accuracy and robustness of phase retrieval compared to current grating-based phase-contrast techniques. Feasibility is demonstrated via numerical simulation.
Inexact Solves in Interpolatory Model Reduction
Christopher A. Beattie,Serkan Gugercin,Sarah Wyatt
Mathematics , 2010, DOI: 10.1016/j.laa.2011.07.015
Abstract: We investigate the use of inexact solves for interpolatory model reduction and consider associated perturbation effects on the underlying model reduction problem. We give bounds on system perturbations induced by inexact solves and relate this to termination criteria for iterative solution methods. We show that when a Petrov-Galerkin framework is employed for the inexact solves, the associated reduced order model is an exact interpolatory model for a nearby full-order system; thus demonstrating backward stability. We also give evidence that for $\h2$-optimal interpolation points, interpolatory model reduction is robust with respect to perturbations due to inexact solves. Finally, we demonstrate the effecitveness of direct use of inexact solves in optimal ${\mathcal H}_2$ approximation. The result is an effective model reduction strategy that is applicable in realistically large-scale settings.
The Great Escape III: Placing post-main-sequence evolution of planetary and binary systems in a Galactic context
Dimitri Veras,N. Wyn Evans,Mark C. Wyatt,Christopher A. Tout
Physics , 2013, DOI: 10.1093/mnras/stt1905
Abstract: Our improving understanding of the life cycle of planetary systems prompts investigations of the role of the Galactic environment before, during and after Asymptotic Giant Branch (AGB) stellar evolution. Here, we investigate the interplay between stellar mass loss, Galactic tidal perturbations, and stellar flybys for evolving stars which host one planet, smaller body or stellar binary companion and reside in the Milky Way's bulge or disc. We find that the potential evolutionary pathways from a main sequence (MS) to a white dwarf (WD) planetary system are a strong function of Galactocentric distance only with respect to the prevalence of stellar flybys. Planetary ejection and collision with the parent star should be more common towards the bulge. At a given location anywhere in the Galaxy, if the mass loss is adiabatic, then the secondary is likely to avoid close flybys during AGB evolution, and cannot eventually escape the resulting WD because of Galactic tides alone. Partly because AGB mass loss will shrink a planetary system's Hill ellipsoid axes by about 20 to 40 per cent, Oort clouds orbiting WDs are likely to be more depleted and dynamically excited than on the MS.
Asymmetric Heating of the HR 4796A Dust Ring Due to Pericenter Glow
Margaret Moerchen,Laura Churcher,Charles Telesco,Mark Wyatt,R. Scott Fisher,Christopher Packham
Physics , 2010, DOI: 10.1051/0004-6361/201014881
Abstract: We have obtained new resolved images of the well-studied HR 4796A dust ring at 18 and 25 microns with the 8-meter Gemini telescopes. These images confirm the previously observed spatial extent seen in mid-IR, near-IR, and optical images of the source. We detect brightness and temperature asymmetries such that dust on the NE side is both brighter and warmer than dust in the SW. We show that models of so-called pericenter glow account for these asymmetries, thus both confirming and extending our previous analyses. In this scenario, the center of the dust ring is offset from the star due to gravitational perturbations of a body with an eccentric orbit that has induced a forced eccentricity on the dust particle orbits. Models with 2-micron silicate dust particles and a forced eccentricity of 0.06 simultaneously fit the observations at both wavelengths. We also show that parameters used to characterize the thermal-emission properties of the disk can also account for the disk asymmetry observed in shorter-wavelength scattered-light images.
Do-it-yourself-Design von Lehrmaterialien für den Englisch-Unterricht Becoming a Do-it-yourself Designer of English Language Teaching Materials Convertirse en un dise ador "hágalo usted mismo" de materiales para la ense anza del idioma inglés
Mark Wyatt
Forum : Qualitative Social Research , 2010,
Abstract: Sehr viele Lehrer/innen, die Sprachen unterrichten, erstellen selbst Materialien zus tzlich zu denen, die sie im Haus erhalten, um den Bedarf von Lernenden in den je spezifischen Kontexten bestm glich zu adressieren. Dies erfordert Praxiswissen unterschiedlichster Art, die die Person der Lernenden, Fragen des Spracherwerbs, des Unterrichtens und des Designs von Materialien betreffen. Obwohl vermehrt Forschung zu Sprachunterricht stattfindet, wird der Frage, wie Lehrer/innen ihr Material entwerfen, bisher wenig Beachtung geschenkt, und es fehlen insbesondere l ngsschnittliche Perspektiven. In diesem Beitrag geht es mir um Entwicklungsprozesse eines Lehrers als "Do-it-yourself-Designer" von Materialien für den Englischunterricht im Rahmen des "BA TESOL"-Programms, ein Programm für den Englisch-Unterricht mit Nicht-Muttersprachler/innen im Mittleren Osten. Im Rahmen einer qualitativen Einzelfallstudie, die ich im Folgenden vorstelle, habe ich mich über drei Jahre mit den Konzepten dieser Lehrers und der Umsetzung in der Unterrichtspraxis befasst. Implikationen für den Sprachunterricht werden am Ende diskutiert. URN: http://nbn-resolving.de/urn:nbn:de:0114-fqs1101334 Many language teachers around the world design materials to supplement those they are provided with to address the needs of the learners in their particular context. This is a task which requires practical knowledge of various kinds relating to learners and language learning, teaching and materials design. However, while there is a growing body of research into the practical knowledge of language teachers, little of this is longitudinal and there is a lack of research into how teachers develop as materials designers. This article focuses on one teacher's growth as a DIY (do-it-yourself) designer of English language teaching materials during an in-service BA TESOL (teaching English to speakers of other languages) programme in the Middle East. Using qualitative case study methodology, I follow the teacher's development over three years, exploring changes in ideas and teaching practices. Implications for in-service language teacher education are discussed. URN: http://nbn-resolving.de/urn:nbn:de:0114-fqs1101334 Muchos profesores de idiomas alrededor de mundo dise an materiales para complementar aquellos que se proporcionan para satisfacer las necesidades de los alumnos en su contexto particular. Esta es una tarea que requiere conocimiento práctico de varios tipos, relacionado a los alumnos y al aprendizaje de idiomas, a la ense anza y al dise o de materiales. Sin embargo, si bien existe un cuerpo
E-Publishing Today
Wyatt, Deborah
Australian Journal of Emerging Technologies and Society , 2003,
Abstract: Publishers traditionally draw on a number of services and skills to create books and journals, including: (i) commissioning and (in the case of academic texts) peer review; (ii) editing and proofreading; (iii) design and typesetting; (iv) printing; (v) sales and marketing; and (vi) warehousing and distribution. The aim of the present study was to analyse the impact that e-publishing technology has already had on each of these areas and the extent to which traditional approaches to publishing may change in the future. This includes an overview of hypertext both fictional and non-fictional and a broad historical analysis of the reaction that publishers and booksellers have had to e-publishing to date. Drawing on this overview, the main section of this review consists of a tour through the publishing process, balancing the merits and pitfalls of e-publishing s effect on each of the aforementioned stages. The concluding section offers some conclusions and recommendations, based on the results of this study. For the purposes of this study, the term e-publishing was used to describe the provision of any text in an electronic format from hyperlinked websites to CD ROMs to read-only PDF files although it was most often used to describe e-books (read through PDAs) and websites. based services.
Discourse Coalitions and Consumer Understanding of Organic and Pesticide Free Vegetables in Chiang Mai, Thailand
Brett Wyatt
Asian Social Science , 2010, DOI: 10.5539/ass.v6n3p92
Abstract: This paper will demonstrate how discourse coalitions promote and institutionalize regulations, communicating the meanings of certified, alternative agricultural production processes through the labeling of vegetable produce. This analysis introduces the concepts of discourse coalitions as a way to evaluate the power and linkages constituting an alternative agricultural commodity network. The actors constituting these networks will be shown to work as coalitions of actors promoting complementary and competing discursive strategies explains the role of consumer understanding in completing the commodity network. Data for this analysis was derived from a survey instrument used to determine the attitudes and propensities toward the purchase of conventional and alternative vegetables of 324 consumers in the city of Chiang Mai, Thailand Discourse coalitions are responsible for enacting the relationship between regulatory practice, method of certification, and labeling practices. Effective communication of regulatory practices used in certification can be seen by the level of trust consumers have in the marketplaces and labeling.
South African National Wetlands Awareness Campaign
Wyatt J.
IUCN Otter Specialist Group Bulletin , 1992,
Science and technology: socialising what for whom?
Sally Wyatt
JCOM : Journal of Science Communication , 2009,
Abstract: In the Handbook on the socialisation of scientific and technological research, edited by Wiebe Bijker and Luciano d’Andrea, ‘socialisation’ is used to both describe and prescribe the ways in which science and technology are used in society. In this comment, ‘socialisation’ is discussed from two other points of view. First, the ways in which science and technology are sometimes used to organize, structure and dominate the social are identified. Second, drawing on Merton’s norms of science, an argument is made against over-socialising science and in favour of acknowledging and preserving the ‘special’ nature of science, for its own sake and because, at its best, science can offer an alternative model for other social activities.
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