1,296 research outputs found

    Are Montana\u27s Price Fixing Statutes Valid?

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    Are Montana\u27s Price Fixing Statutes Valid

    A response-adaptive randomization procedure for multi-armed clinical trials with normally distributed outcomes.

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    We propose a novel response-adaptive randomization procedure for multi-armed trials with continuous outcomes that are assumed to be normally distributed. Our proposed rule is non-myopic, and oriented toward a patient benefit objective, yet maintains computational feasibility. We derive our response-adaptive algorithm based on the Gittins index for the multi-armed bandit problem, as a modification of the method first introduced in Villar et al. (Biometrics, 71, pp. 969-978). The resulting procedure can be implemented under the assumption of both known or unknown variance. We illustrate the proposed procedure by simulations in the context of phase II cancer trials. Our results show that, in a multi-armed setting, there are efficiency and patient benefit gains of using a response-adaptive allocation procedure with a continuous endpoint instead of a binary one. These gains persist even if an anticipated low rate of missing data due to deaths, dropouts, or complete responses is imputed online through a procedure first introduced in this paper. Additionally, we discuss how there are response-adaptive designs that outperform the traditional equal randomized design both in terms of efficiency and patient benefit measures in the multi-armed trial context

    Material migration and fuel retention studies during the JET carbon divertor campaigns

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    The first divertor was installed in the JET machine between 1992 and 1994 and was operated with carbon tiles and then beryllium tiles in 1994–5. Post-mortem studies after these first experiments demonstrated that most of the impurities deposited in the divertor originate in the main chamber, and that asymmetric deposition patterns generally favouring the inner divertor region result from drift in the scrape-off layer. A new monolithic divertor structure was installed in 1996 which produced heavy deposition at shadowed areas in the inner divertor corner, which is where the majority of the tritium was trapped by co-deposition during the deuterium-tritium experiment in 1997. Different divertor geometries have been tested since such as the Gas-Box and High-Delta divertors; a principle objective has been to predict plasma behaviour, transport and tritium retention in ITER. Transport modelling experiments were carried out at the end of four campaigns by puffing 13C-labelled methane, and a range of diagnostics such as quartz-microbalance and rotating collectors have been installed to add time resolution to the post-mortem analyses. The study of material migration after D-D and D-T campaigns clearly revealed important consequences of fuel retention in the presence of carbon walls. They gave a strong impulse to make a fundamental change of wall materials. In 2010 the carbon divertor and wall tiles were removed and replaced with tiles with Be or W surfaces for the ITER-Like Wall Project

    An assessment of threats to terrestrial protected areas

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    Protected areas (PAs) represent a cornerstone of efforts to safeguard biodiversity, and if effective should reduce threats to biodiversity. We present the most comprehensive assessment of threats to terrestrial PAs, based on in-situ data from 1,961 PAs across 149 countries, assessed by PA managers and local stakeholders. Unsustainable hunting was the most commonly reported threat and occurred in 61% of all PAs, followed by disturbance from recreational activities occurring in 55%, and natural system modifications from fire or its suppression in 49%. The number of reported threats was lower in PAs with greater remoteness, higher control of corruption and lower human development scores. The main reported threats in developing countries were linked to overexploitation for resource extraction, while negative impacts from recreational activities dominated in developed countries. Our results show that many of the most serious threats to PAs are difficult to monitor with remote sensing, and highlight the importance of in situ threat data to inform the implementation of more effective biodiversity conservation in the global protected area estate

    Kompetenznetz E-Learning Hessen

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    Mit dem Kompetenznetz e-learning-hessen.de vernetzen sich die hessischen Hochschulen mit Hilfe der Koordination und Unterstützung durch das httc und Förderung durch das Hessische Ministerium für Wissenschaft und Kunst rund um das Thema E-Learning. Dieser Beitrag beschreibt die Ziele des Netzwerks, dessen Maßnahmen und Elemente und die bisherigen Erfahrungen und seine Entwicklung seit dem Jahr 2000. Mit der abschließenden Bewertung werden Anhaltspunkte für eine erfolgreiche Vernetzung von Hochschulen und ein Ausblick auf die geplanten Aktivitäten des hessischen Netzwerkes in den nächsten Jahren gegeben. (DIPF/ Orig.

    Business experience and start-up size: buying more lottery tickets next time around?

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    This paper explores the determinants of start-up size by focusing on a cohort of 6247 businesses that started trading in 2004, using a unique dataset on customer records at Barclays Bank. Quantile regressions show that prior business experience is significantly related with start-up size, as are a number of other variables such as age, education and bank account activity. Quantile treatment effects (QTE) estimates show similar results, with the effect of business experience on (log) start-up size being roughly constant across the quantiles. Prior personal business experience leads to an increase in expected start-up size of about 50%. Instrumental variable QTE estimates are even higher, although there are concerns about the validity of the instrument
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