Two physical characteristics of numerical apparent horizons

This article translates some recent results on quasilocal horizons into the language of $(3+1)$ general relativity so as to make them more useful to numerical relativists. In particular quantities are described which characterize how quickly an apparent horizon is evolving and how close it is to either equilibrium or extremality.Comment: 6 pages, 2 figures, conference proceedings loosely based on talk given at Theory Canada III (Edmonton, Alberta, 2007). V2: Minor changes in response to referees comments to improve clarity and fix typos. One reference adde

Quasilocal energy and naked black holes

We extend the Brown and York notion of quasilocal energy to include coupled electromagnetic and dilaton fields and also allow for spatial boundaries that are not orthogonal to the foliation of the spacetime. We investigate how the quasilocal quantities measured by sets of observers transform with respect to boosts. As a natural application of this work we investigate the naked black holes of Horowitz and Ross calculating the quasilocal energies measured by static versus infalling observers.Comment: 5 pages, 1 figure; submitted to the 8th Canadian Conference on General Relativity and Relativistic Astrophysics. This paper is a condensed version of gr-qc/990707

Tax Policy and Returns to Education

This paper considers how asymmetric tax treatment, where labour market earnings are taxed but household production is untaxed, aspects educational choice and labour supply. We show that taxes on labour market earnings can generate a large (non-marginal) switch to home production and the ensuing deadweight losses are large. Using a cross-country panel, we find that gender differences in labour supply responses to tax policy can explain differences in aggregate labour supply and years of education across countries.Increasing returns; tax policy; gender; labour supply; education

Glacier Physics of the Puget Lobe, Southwest Cordilleran Ice Sheet

The Puget lobe, the southwest-most extension of the Cordilleran ice sheet, provides an excellent opportunity to examine the connection between glacier physics and the resulting products of glaciation. The action of water, at and within the sediments of the glacier bed, is particularly significant for the geologic record of this ice sheet. Physical data and inferred mass balance relationships constrain lobe reconstruction and predict sliding velocities in excess of 500 m/a and water discharges of nearly 1 * 10" m3/a. This sub-glacial water produced a dendritic channel pattern well predicted by static analysis of sub-glacial hydrology. Near to the eastern ice margin, a much larger single channel drained subglacially and episodically, with tributary ice-dammed lakes releasing their water as jokulhlaups. Basal meltwater generated near-hydrostatic water pressures and very low till strengths at the base of the ice sheet. Water pressure dropped only close to the ice margin, allowing normal stresses to rise to significant fractions of the total ice overburden. Thus marginal and interior zones impose contrasting bed conditions. Although observation of sub-glacial deposits will reflect the late-stage passage of the marginal zone, conditions within the ice-sheet interior, far more significant to glacier history and behavior, may be substantially different.Le lobe de Puget, à la limite sud-ouest de l'Inlandsis de la Cordillère, permet d'étudier les liens entre la physique glaciaire et l'action glaciaire. L'action de l'eau à proximité et à l'intérieur des sédiments du lit glaciaire est un aspect particulièrement important de la géologie de l'inlandsis. Les données d'ordre physique et les calculs du bilan de masse permettent de faire une reconstitution assez fidèle du lobe et d'extrapoler les vitesses de glissement au delà de 500 m/a et les débits d'eau de près de 1 * 10" m3/a. L'écoulement de l'eau sous-glaciaire a créé un réseau de chenaux dentritiques que l'analyse statique de l'hydrologie sous-glaciaire a extrapolé avec justesse. Près de la marge glaciaire orientale, un important chenal isolé a assuré épisodiquement le drainage sous-glaciaire, alors que les lacs de barrage glaciaire emprisonnés dans les vallées adjacentes se déchargeaient par débâcles. L'eau de fonte basale a produit des pressions d'eau près de l'équilibre hydrostatique et de très faibles résistances du till à la base de l'inlandsis. La pression de l'eau ne diminuait que près de la marge glaciaire, laissant ainsi les taux de contrainte normaux s'élever jusqu'à des proportions importantes de la couverture totale de glace. Ainsi les conditions du lit sont très différentes selon qu'il se situe en zone interne ou en zone marginale. L'observation des dépôts sous-glaciaires révèle la phase finale en zone marginale, mais les conditions à l'intérieur même de l'inlandsis, d'une plus grande portée quant à l'évolution et au comportement du glacier, pourraient être très différentes.Der Puget-Lappen, die sûdwestliche Ausdehnung der Kordilleren-Eisdecke, bietet eine ausgezeichnete Gelegenheit, die Beziehung zwischen glazialer Physik und den daraus resultierenden Produkten der Vereisung zu untersuchen. Die Wirkung von Wasser in der Nàhe der Sedimente des Gletscherbettes und in ihnen ist besonders signifikant fur die geologische Dokumentierung der Eisdecke. Physikalische Daten und abgeleitete Massenbilanz-Beziehungen erlauben eine getreue Rekonstruktion des Lappens und Voraussagen ùber Rutschgeschwindigkeiten von ùber 500 m/a und Wasserfùhrungen von nahezu 1 * 1011 m3/a zu machen. Dies subglaziale Wasser bewirkte ein baumartiges Kanal-Muster, welches die statische Analyse der subglazialen Hydrologie richtig vorausgesagt hatte. In der Nàhe des ôstlichen Eisrands bewirkte ein sehr viel breiterer einzelner Kanal gelegentlich eine subglaziale Drânage, und tributàre, durch Eis eingeschlossene Seen entlieBen ihr Wasser in Gletscherlâufen. Basales Schmelzwasser bewirkte fast hydrostatische Wasserdruckwerte und sehr niedrige Widerstànde des Tills an der Basis der Eisdecke. Der Wasserdruck sank nur in der Nàhe des Eisrands, so daB normaler Druck bis zu bedeutenden Proportionen der totalen Eislast anstieg. So sind die bedingungen des Bettes sehr verschieden, je nachdem ob es sich in der Randzone oder der inneren Zone bef indet. Obgleich die Beobachtung der subglazialen Ablagerungen die Endphase der Randzone spiegelt, kônnten doch die Bedingungen im Innern der Eisdecke, die fur die Geschichte und das Verhalten des Gletschers viel wich-tiger sind, sehr verschieden sein

Extremality conditions for isolated and dynamical horizons

A maximally rotating Kerr black hole is said to be extremal. In this paper we introduce the corresponding restrictions for isolated and dynamical horizons. These reduce to the standard notions for Kerr but in general do not require the horizon to be either stationary or rotationally symmetric. We consider physical implications and applications of these results. In particular we introduce a parameter e which characterizes how close a horizon is to extremality and should be calculable in numerical simulations.Comment: 13 pages, 4 figures, added reference; v3 appendix added with proof of result from section IIID, some discussion and references added. Version to appear in PR

Free Space Optical Link Utilizing a Modulated Retro-Reflector Intended for Planetary Duplex Communication Links Between an Orbiter and Surface Unit

Presented are simulation and experimental results that provide duplex optical-free space communication links with minimal power and pointing requirements by using a modulated retro-reflector (MRR) for planetary communications. The design is the MRR resides on the surface of a planet or moon, where energy is scarce, while the source of the communication laser resides on an orbiter to achieve satellite-to-ground communications. Also, a simulated scenario using the Mars Reconnaissance Orbiter (MRO) is provided for real world potential results. The information sent through this communication path can range from raw scientific data to multimedia files such as videos and pictures. Bidirectional communications is established with the MRR by using a nested pulse position modulation (PPM) structure. This modulation scheme is then evaluated for its validity in a proof-of-concept experiment. Initial results indicate a promising return-link performance of at least 300 kbps in the nested arrangement

‘Don’t talk about the gay character’: Barriers to queer young adult fiction and authors in schools and libraries

© 2018, AATE - Australian Association Teaching English. All rights reserved. This article explores findings from an investigation into the publishing experiences of Australian authors of inclusive Young Adult (YA) fiction. A total of seven authors, each publicly identifying as part of a marginalised community in Australia, were interviewed. This paper concentrates on the findings of semi-structured interviews with two authors of Lesbian, Gay, Bisexual, Transgender, Intersex, Asexual, Pansexual, and Other (LGBTQIAP+) fiction, and their experience of promoting their books in school and library environments. Findings were analysed using Critical Discourse Analysis to understand their interactions with publishers, audiences, and school staff. The research was carried out in 2016 but highlights longstanding issues regarding the inclusion of queer literature for young people in educational spaces, including school libraries and high school English curriculums. More broadly, it contributes to the understanding of how diversity and inclusion within YA Fiction is viewed in Australia, and the role of gatekeepers in providing or denying access