30,802 research outputs found

    The JCMT BISTRO Survey: Multi-wavelength polarimetry of bright regions in NGC 2071 in the far-infrared/submillimetre range, with POL-2 and HAWC+

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    Polarized dust emission is a key tracer in the study of interstellar medium and of star formation. The observed polarization, however, is a product of magnetic field structure, dust grain properties and grain alignment efficiency, as well as their variations in the line of sight, making it difficult to interpret polarization unambiguously. The comparison of polarimetry at multiple wavelengths is a possible way of mitigating this problem. We use data from HAWC+/SOFIA and from SCUBA-2/POL-2 (from the BISTRO survey) to analyse the NGC 2071 molecular cloud at 154, 214 and 850 Ī¼m. The polarization angle changes significantly with wavelength over part of NGC 2071, suggesting a change in magnetic field morphology on the line of sight as each wavelength best traces different dust populations. Other possible explanations are the existence of more than one polarization mechanism in the cloud or scattering from very large grains. The observed change of polarization fraction with wavelength, and the 214-to-154 Ī¼m polarization ratio in particular, are difficult to reproduce with current dust models under the assumption of uniform alignment efficiency. We also show that the standard procedure of using monochromatic intensity as a proxy for column density may produce spurious results at HAWC+ wavelengths. Using both long-wavelength (POL-2, 850 Ī¼m) and short-wavelength (HAWC+, ā‰²200Ī¼m) polarimetry is key in obtaining these results. This study clearly shows the importance of multi-wavelength polarimetry at submillimeter bands to understand the dust properties of molecular clouds and the relationship between magnetic field and star formation

    Strung pieces: on the aesthetics of television fiction series

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    As layered and long works, television fiction series have aesthetic properties that are built over time, bit by bit. This thesis develops a group of concepts that enable the study of these properties, It argues that a series is made of strung pieces, a system of related elements. The text begins by considering this sequential form within the fields of film and television. This opening chapter defines the object and methodology of research, arguing for a non-essentialist distinction between cinema and television and against the adequacy of textual and contextual analyses as approaches to the aesthetics of these shows. It proposes instead that these programmes should be described as televisual works that can be scrutinised through aesthetic analysis. The next chapters propose a sequence of interrelated concepts. The second chapter contends that series are composed of building blocks that can be either units into which series are divided or motifs that unify series and are dispersed across their pans. These blocks are patterned according to four kinds of relations or principles of composition. Repetition and variation are treated in tandem in the third chapter because of their close connection, given that variation emerges from established repetition. Exception and progression are also discussed together in the fourth chapter since they both require a long view of these serial works. The former, in order to be recognised as a deviation from the patterns of repetition and variation. The latter, In order to be understood in Its many dimensions as the series advances. Each of these concepts is further detailed with additional distinctions between types of units, motifs, repetitions, variations, and exceptions, using illustrative examples from numerous shows. In contrast, the section on progression uses a single series as case study, CarnivĆ le (2003-05), because this is the overarching principle that encompasses all the others. The conclusion considers the findings of the research and suggests avenues for their application

    In search of 'The people of La Manche': A comparative study of funerary practices in the Transmanche region during the late Neolithic and Early Bronze Age (250BC-1500BC)

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    This research project sets out to discover whether archaeological evidence dating between 2500 BC - 1500 BC from supposed funerary contexts in Kent, flanders and north-eastern Transmanche France is sufficient to make valid comparisons between social and cultural structures on either side of the short-sea Channel region. Evidence from the beginning of the period primarily comes in the form of the widespread Beaker phenomenon. Chapter 5 shows that this class of data is abundant in Kent but quite sparse in the Continental zones - most probably because it has not survived well. This problem also affects the human depositional evidence catalogued in Chapter 6, particularly in Fanders but also in north-eastern Transmanche France. This constricts comparative analysis, however, the abundant data from Kent means that general trends are still discernible. The quality and volume of data relating to the distribution, location, morphology and use of circular monuments in all three zones is far better - as demonstrated in Chapter 7 -mostly due to extensive aerial surveying over several decades. When the datasets are taken as a whole, it becomes possible to successfully apply various forms of comparative analyses. Most remarkably, this has revealed that some monuments apparently have encoded within them a sophisticated and potentially symbolically charged geometric shape. This, along with other less contentious evidence, demonstrates a level of conformity that strongly suggests a stratum of cultural homogeneity existed throughout the Transmanche region during the period 2500 BC - 1500 BC. The fact that such changes as are apparent seem to have developed simultaneously in each of the zones adds additional weight to the theory that contact throughout the Transmanche region was endemic. Even so, it may not have been continuous; there may actually have been times of relative isolation - the data is simply too course to eliminate such a possibility

    Anytime algorithms for ROBDD symmetry detection and approximation

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    Reduced Ordered Binary Decision Diagrams (ROBDDs) provide a dense and memory efficient representation of Boolean functions. When ROBDDs are applied in logic synthesis, the problem arises of detecting both classical and generalised symmetries. State-of-the-art in symmetry detection is represented by Mishchenko's algorithm. Mishchenko showed how to detect symmetries in ROBDDs without the need for checking equivalence of all co-factor pairs. This work resulted in a practical algorithm for detecting all classical symmetries in an ROBDD in O(|G|Ā³) set operations where |G| is the number of nodes in the ROBDD. Mishchenko and his colleagues subsequently extended the algorithm to find generalised symmetries. The extended algorithm retains the same asymptotic complexity for each type of generalised symmetry. Both the classical and generalised symmetry detection algorithms are monolithic in the sense that they only return a meaningful answer when they are left to run to completion. In this thesis we present efficient anytime algorithms for detecting both classical and generalised symmetries, that output pairs of symmetric variables until a prescribed time bound is exceeded. These anytime algorithms are complete in that given sufficient time they are guaranteed to find all symmetric pairs. Theoretically these algorithms reside in O(nĀ³+n|G|+|G|Ā³) and O(nĀ³+nĀ²|G|+|G|Ā³) respectively, where n is the number of variables, so that in practice the advantage of anytime generality is not gained at the expense of efficiency. In fact, the anytime approach requires only very modest data structure support and offers unique opportunities for optimisation so the resulting algorithms are very efficient. The thesis continues by considering another class of anytime algorithms for ROBDDs that is motivated by the dearth of work on approximating ROBDDs. The need for approximation arises because many ROBDD operations result in an ROBDD whose size is quadratic in the size of the inputs. Furthermore, if ROBDDs are used in abstract interpretation, the running time of the analysis is related not only to the complexity of the individual ROBDD operations but also the number of operations applied. The number of operations is, in turn, constrained by the number of times a Boolean function can be weakened before stability is achieved. This thesis proposes a widening that can be used to both constrain the size of an ROBDD and also ensure that the number of times that it is weakened is bounded by some given constant. The widening can be used to either systematically approximate an ROBDD from above (i.e. derive a weaker function) or below (i.e. infer a stronger function). The thesis also considers how randomised techniques may be deployed to improve the speed of computing an approximation by avoiding potentially expensive ROBDD manipulation

    Magnetized accretion disks around compact objects

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    Los recientes avances observacionales logrados por la colaboracioĢn LIGO-Virgo- KAGRA ā€“ con las primeras detecciones histoĢricas de ondas gravitacionales de fusiones de sistemas binarios de objetos compactos ā€“ junto con la colaboracioĢn Event Horizon Telescope - con la imagen del agujero negro supermasivo que reside en el centro de la galaxia M87 - han brindado una oportunidad sin precedentes para investigar la fiĢsica de la gravedad en el regimen de campo intenso e incluso analizar la TeoriĢa General de la Relatividad de Einstein en esta situacioĢn tan extrema. En esta tesis se discute un caso particular de sistema astrofiĢsico relativista que suele considerarse como el ejemplo paradigmaĢtico de sistema en el reĢgimen de campo intenso ā€“ un agujero negro rodeado de un disco grueso de acrecioĢn (o toro). Se presentan nuevas prescripciones para construir datos iniciales de discos de acrecioĢn magnetizados alrededor de objetos compactos, extendiendo el estado actual del tema en varias direcciones, a saber, acomodando diferentes configuraciones de campo magneĢtico, distribuciones de momento angular, y tipos de espacio-tiempo (incluyendo agujeros negros de Kerr, agujeros negros con pelo escalar y agujeros negros de Yukawa) sobre los que evoluciona el fluido. Los resultados obtenidos en esta tesis nos proporcionan valiosa informacioĢn sobre los efectos que tiene anĢƒadir diferentes fenoĢmenos fiĢsicos en las propiedades morfoloĢgicas y fiĢsicas del sistema. AdemaĢs, los resultados de esta investigacioĢn tambieĢn proporcionan una amplia muestra de datos iniciales de dominio puĢblico para que puedan ser usados en simulaciones evolutivas del sistema toro de acrecioĢn-agujero negro, gobernado por las ecuaciones de la magnetohidrodinaĢmica relativista .The recent observational breakthroughs accomplished by the LIGO-Virgo-KAGRA Collaboration ā€“ with the historical first detections of gravitational waves from mergers of compact binaries ā€“ and by the Event Horizon Telescope Collaboration ā€“ with the image of the supermassive black hole lurking in the centre of the M87 galaxy ā€“ have provided an unprecedented opportunity to investigate the physics of strong gravity and to even test Einsteinā€™s General Theory of Relativity in such a extreme situation. This thesis discusses one particular relativistic astrophysical system which is often invoked as a paradigmatic example of such strong-gravity realm ā€“ a black hole surrounded by a geometrically thick accretion disk (or torus). New prescriptions to build initial data of magnetized accretion disks around compact objects are presented, extending the current state-of-the-art in several directions, namely accommodating diverse magnetic field configurations, angular momentum distributions, and types of spacetimes (including Kerr black holes, black holes with scalar hair, and Yukawa black holes) where the fluid evolves. The results reported in this thesis provide insight on the eff ects that adding diff erent physics has in the systemā€™s morphological and physical properties. In addition, this research o ers large new samples of open-source initial data to conduct time-dependent general-relativistic, magneto-hydrodynamical simulations of black hole-torus systems

    The application of Evidence-Based Medicine methodologies in sports science: problems and solutions

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    This thesis analyses the use of 'Evidence-Based' methodologies of evidence assessment and intervention and policy design from medicine, and their use in sport and exercise science. It argues that problems exist with the application of Evidence-Based methodologies in sports science, meaning that the quality of evidence used to inform decision-making is lower than is often assumed. This thesis also offers realistic solutions to these problems, broadly arguing for the importance of taking evidence from mechanistic studies seriously, in addition to evidence from RCTs

    Social identity theory and group diversity : an analysis of functions of group identification

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    This thesis examines differences between social groups and the relationship between ingroupidentification and ingroup bias within the framework of Social Identity Theory. The main goalof our investigation is that of understanding the reason of the variation encountered in studiestesting the identification-bias association. While one of the solutions proposed by previousresearch (Hinkle and Brown, 1990) focuses on group differences on the dimensions ofcollectivism and relational orientation, our suggestion is that of considering group differences inthe functions that drive their group identification. Two functions of group identificationemerged ā€” between the others ā€” as meaningful in differentiating between the four groups wetested (Psychology students, football supporters, and trade unionists): A materialistic and self-interested motivation
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