The linear rms-flux relation in an Ultraluminous X-ray Source

We report the first detection of a linear correlation between rms variability amplitude and flux in the Ultraluminous X-ray source NGC 5408 X-1. The rms-flux relation has previously been observed in several Galactic black hole X-ray binaries (BHBs), several Active Galactic Nuclei (AGN) and at least one neutron star X-ray binary. This result supports the hypothesis that a linear rms-flux relation is common to all luminous black hole accretion and perhaps even a fundamental property of accretion flows about compact objects. We also show for the first time the cross-spectral properties of the variability of this ULX, comparing variations below and above 1 keV. The coherence and time delays are poorly constrained but consistent with high coherence between the two bands, over most of the observable frequency range, and a significant time delay (with hard leading soft variations). The magnitude and frequency dependence of the lags are broadly consistent with those commonly observed in BHBs, but the direction of the lag is reversed. These results indicate that ULX variability studies, using long X-ray observations, hold great promise for constraining the processes driving ULXs behaviour, and the position of ULXs in the scheme of black hole accretion from BHBs to AGN.Comment: 4 Pages, 3 figures, accepted for publication by MNRAS

Visualising London's Suburbs

2 - 4 April 200

Space and exclusion: does urban morphology play a part in social deprivation?

There is currently a growing interest in the spatial causes of poverty, particularly its persistence. This paper presents methodological innovations that have been developed for investigating the relationship between physical segregation and economic marginalization in the urban environment. Using GIS to layer historical poverty data, contemporary deprivation indexes and space syntax measures of spatial segregation, a multivariate system has been created to enable the understanding of the spatial process involved in the creation and stagnation of poverty areas as well as to analyse the street segment scale of configuration

Do the suburbs exist? Discovering complexity and specificity in suburban built form

In human geography cities are routinely acknowledged as complex and dynamic built environments. This description is rarely extended to the suburbs, which are generally regarded as epiphenomena of the urbs and therefore of little intrinsic theoretical interest in themselves. This article presents a detailed critique of this widely held assumption by showing how the idea of 'the suburban' as an essentially non-problematic domain has been perpetuated from a range of contrasting disciplinary perspectives, including those that directly address suburban subject matter. The result has been that attempts to articulate the complex social possibilities of suburban space are easily caught between theories of urbanisation that are insensitive to suburban specificity and competing representations of the suburb that rarely move beyond the culturally specific to consider their generic significance. This article proposes that the development of a distinctively suburban theory would help to undermine one-dimensional approaches to the built environment by focusing on the relationship between social organisation and the dynamics of emergent built form

A multi-disciplinary perspective on the built environment: Space Syntax and cartography – the communication challenge

8-11 June 2009

Observations of stratospheric aerosols associated with the El Chichon eruption

Lidar observations of aerosols were carried out at Aberystwyth between Nov. 1982 and Dec. 1985 using a frequency doubled and frequency tripled Nd/Yag laser and a receiver incorporating a 1 m diameter in a Newtonian telescope configuration. In analyses of the experimental data attention is paid to the magnitude of the coefficient relating extinction and backscatter, the choice being related to the possible presence of aerosols in the upper troposphere and the atmospheric densities employed in the normalisation procedure. The aerosol loading showed marked day to day changes in early months and an overall decay was apparent only after April 1983, this decay being consistent with an e sup -1 time of about 7 months. The general decay was accompanied by a lowering of the layer but layers of aerosols were shown intermittently at heights above the main layer in winter months. The height variations of photon counts corrected for range, or of aerosol backscatter ratio, showed clear signatures of the tropopause. A strong correlation was found between the heights of the tropopause identified from the lidar measurements and from radiosonde-borne temperature measurements. A notable feature of the observations is the appearance of very sharp height gradients of backscatter ratio which seem to be produced by differential advection

Search engine coverage bias: Evidence and possible causes

Commercial search engines are now playing an increasingly important role in Web information dissemination and access. Of particular interest to business and national governments is whether the big engines have coverage biased towards the US or other countries. In our study we tested for national biases in three major search engines and found significant differences in their coverage of commercial Web sites. The US sites were much better covered than the others in the study: sites from China, Taiwan and Singapore. We then examined the possible technical causes of the differences and found that the language of a site does not affect its coverage by search engines. However, the visibility of a site, measured by the number of links to it, affects its chance to be covered by search engines. We conclude that the coverage bias does exist but this is due not to deliberate choices of the search engines but occurs as a natural result of cumulative advantage effects of US sites on the Web. Nevertheless, the bias remains a cause for international concern. © 2003 Elsevier Ltd. All rights reserved

Why are hyperlinks to business Websites created? A content analysis

Motivations for the creation of hyperlinks to business sites were analyzed through a content analysis approach. Links to 280 North American IT companies (71 Canadian companies and 209 U.S. companies) were searched through Yahoo!. Then a random sample of 808 links was taken from the links retrieved. The content as well as the context of each link was manually examined to determine why the link was created. The country location and the type of the site where the link came from were also identified. The study found that most links were created for business purposes confirming findings from early quantitative studies that links contain useful business information. Links to competitors were extremely rare but competitors were often co-linked, suggesting that co-link analysis is the direction to pursue for information on competitive intelligence. Copyright © 2006 Akadémiai Kiadó, Budapest. All rights reserved

Ozone and NO2 measurements from Aberystwyth and Lerwick

Measurements of the total column of ozone and NO2 were obtained by a SAOZ UV/Visible spectrometer at Aberystwyth (52.4 deg N, 4.1 deg W) and Lerwick (60.1 deg N, 1.2 deg W) during the period March 1991 - April 1992. NO2 measurements show a marked decrease in 1992 compared with 1991, due to the effect of aerosols from Mt. Pinatubo. Ozone measurements appear to have been affected by the aerosols - comparisons with both Dobson and TOMS measurements are presented