Timescale of variation and the size of the accretion disc in active galactic nuclei

This paper sets out to measure the timescale of quasar variability with a view to new understanding of the size of accretion discs in active galactic nuclei. Previous attempts to measure such timescales have been based on sparsely sampled data covering small ranges of time. Here we combine data from two large scale monitoring programmes to obtain Fourier power spectra of light curves covering nearly three orders of magnitude in frequency in blue and red passbands. If the variations are interpreted as due to gravitational microlensing, then timescale measurements in the observer's frame imply a minimum mass for the microlensing bodies of around $0.4 M_{\odot}$. On the assumption that the variations are intrinsic to the quasars, a correction must be made for time dilation. In this case the power spectrum shows a break corresponding to a timescale of about 11 years. This timescale is used to measure the size of the accretion disc, which is found to be about $10^{-2}$ pc or 10 light days, in agreement with limits set by self-gravitation and coincident with the broad line region of the active galactic nucleus. It is suggested that the broad line region may be associated with the break up of the outer part of the accretion disc.Comment: 12 pages, 7 figures, accepted for publication in 'Astronomy and Astrophysics

High-Resolution Replication Profiles Define the Stochastic Nature of Genome Replication Initiation and Termination

Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.Peer reviewedPublisher PD

The affordances of an arts-based approach for building opportunities for young people's learning

This chapter sets out from the empirical basis of data collected in a digital storytelling activity implemented as part of the IEP! project, in which different creative practices and methods come into play. Considering the complex codependence of elements - mediational tools and artefacts, roles and identities, language/ s, histories, space, time, activities, etc. - that converge in and around a handicraft activity carried out in one session, we draw on the notion of ecology to consider the opportunities for young people's (language) learning that emerge therein. The analysis focuses on how: 1) life histories create a panoramicspace for learning; 2) the youth develop self- knowledge in the ways they manage their activity and their relationships; and 3) the youth harness the affordances of the context for managing their engagement and alignment in the activity and with others

Processing multiple non-adjacent dependencies: evidence from sequence learning

Processing non-adjacent dependencies is considered to be one of the hallmarks of human language. Assuming that sequence-learning tasks provide a useful way to tap natural-language-processing mechanisms, we cross-modally combined serial reaction time and artificial-grammar learning paradigms to investigate the processing of multiple nested (A(1)A(2)A(3)B(3)B(2)B(1)) and crossed dependencies (A(1)A(2)A(3)B(1)B(2)B(3)), containing either three or two dependencies. Both reaction times and prediction errors highlighted problems with processing the middle dependency in nested structures (A(1)A(2)A(3)B(3-)B(1)), reminiscent of the 'missing-verb effect' observed in English and French, but not with crossed structures (A(1)A(2)A(3)B(1-)B(3)). Prior linguistic experience did not play a major role: native speakers of German and Dutch-which permit nested and crossed dependencies, respectively-showed a similar pattern of results for sequences with three dependencies. As for sequences with two dependencies, reaction times and prediction errors were similar for both nested and crossed dependencies. The results suggest that constraints on the processing of multiple non-adjacent dependencies are determined by the specific ordering of the non-adjacent dependencies (i.e. nested or crossed), as well as the number of non-adjacent dependencies to be resolved (i. e. two or three). Furthermore, these constraints may not be specific to language but instead derive from limitations on structured sequence learning.Netherlands Organisation of Scientific Research (NWO) [446-08-014]; Max Planck Institute for Psycholinguistics; Donders Institute for Brain, Cognition and Behaviour; Fundacao para a Ciencia e Tecnologia (IBB/CBME, LA, FEDER/POCI) [PTDC/PSI-PCO/110734/2009]; Stockholm Brain Institute; Vetenskapsradet; Swedish Dyslexia Foundation; Hedlunds Stiftelse; Stockholm County Council (ALF, FoUU)info:eu-repo/semantics/publishedVersio

Robust future changes in temperature variability under greenhouse gas forcing and the relationship with thermal advection

Recent temperature extremes have highlighted the importance of assessing projected changes in the variability of temperature as well as the mean. A large fraction of present day temperature variance is associated with thermal advection, as anomalous winds blow across the land-sea temperature contrast for instance. Models project robust heterogeneity in the 21st century warming pattern under greenhouse gas forcing, resulting in land-sea temperature contrasts increasing in summer and decreasing in winter, and the pole-to-equator temperature gradient weakening in winter. In this study, future monthly variability changes in the 17 member ensemble ESSENCE are assessed. In winter, variability in midlatitudes decreases while in very high latitudes and the tropics it increases. In summer, variability increases over most land areas and in the tropics, with decreasing variability in high latitude oceans. Multiple regression analysis is used to determine the contributions to variability changes from changing temperature gradients and circulation patterns. Thermal advection is found to be of particular importance in the northern hemisphere winter midlatitudes, where the change in mean state temperature gradients alone could account for over half the projected changes. Changes in thermal advection are also found to be important in summer in Europe and coastal areas, although less so than in winter. Comparison with CMIP5 data shows that the midlatitude changes in variability are robust across large regions, particularly high northern latitudes in winter and mid northern latitudes in summer

A method of detecting radio transients

Radio transients are sporadic signals and their detection requires that the backends of radio telescopes be equipped with the appropriate hardware and software to undertake this. Observational programs to detect transients can be dedicated or they can piggy-back on observations made by other programs. It is the single-dish single-transient (non-periodical) mode which is considered in this paper. Because neither the width of a transient nor the time of its arrival is known, a sequential analysis in the form of a cumulative sum (cusum) algorithm is proposed here. Computer simulations and real observation data processing are included to demonstrate the performance of the cusum. The use of the Hough transform is here proposed for the purpose of non-coherent de-dispersion. It is possible that the detected transients could be radio frequency interferences (RFI) and a procedure is proposed here which can distinguish between celestial signals and man-made RFI. This procedure is based on an analysis of the statistical properties of the signals

The North Wyke Farm Platform: GreenFeed System Methane and Carbon Dioxide Data

The North Wyke Farm Platform (NWFP) was established in 2010 to study and improve grassland livestock production at the farm-scale. The NWFP uses a combination of environmental sensors, routine field and lab-based measurements, and detailed management records to monitor livestock and crop production, emissions to water, emissions to air, soil health, and biodiversity. The rich NWFP datasets help researchers to evaluate the effectiveness of different grassland (and arable) farming systems, which in turn, contributes to the development of sustainable, resilient and net zero land management strategies. This document serves as a user guide to the methane (CH4) and carbon dioxide (CO2) emission data, sampled from housed cattle and sheep using GreenFeed systems. This document is associated with other dedicated user guides that detail the collection, and quality control processing of all the datasets produced on the NWFP

Data sharing in genomics - re-shaping scientific practice

Author manuscript. Final version published by Nature. Available online at http://www.nature.com/Funding bodies have recently introduced a requirement that data sharing must be a consideration of all funding applications in genomics. As with all new developments this condition has had an impact on scientific practice, particularly in the area of publishing and in the conduct of research. We discuss the challenges that must be addressed if the full benefits of data sharing, as envisaged by funders, are to be realized