1,959 research outputs found
The Axis-Ratio Distribution of Galaxy Clusters in the SDSS-C4 Catalog as a New Cosmological Probe
We analyze the C4 catalog of galaxy clusters from the Sloan Digital Sky
Survey (SDSS) to investigate the axis-ratio distribution of the projected two
dimensional cluster profiles. We consider only those objects in the catalog
whose virial mass is close to 10^{14}h^{-1}M_{sun}, with member galaxies within
the scale radius 1000 kpc. The total number of such objects turns out to be
336. We also derive a theoretical distribution by incorporating the effect of
projection onto the sky into the analytic formalism proposed recently by Lee,
Jing, & Suto. The theoretical distribution of the cluster axis-ratios is shown
to depend on the amplitude of the linear power spectrum (sigma_8) as well as
the density parameter (Omega_{m}). Finally, fitting the observational data to
the analytic distribution with Omega_{m} and sigma_{8} as two adjustable free
parameters, we find the best-fitting value of sigma_{8}=(1.01 +/-
0.09)(Omega_{m}/0.6)^{(0.07 +/- 0.02) +0.1 Omega_{m}}$. It is a new
sigma_{8}-Omega_{m} relation, different from the previous one derived from the
local abundance of X-ray clusters. We expect that the axis-ratio distribution
of galaxy clusters, if combined with the local abundance of clusters, may put
simultaneous constraints on sigma_{8} and Omega_{m}.Comment: accepted for publication in ApJ, 17 pages, 3 figures, improved
analysis, more discussion on the validity and the caveats of the mode
Megacrystals track magma convection between reservoir and surface
Active volcanoes are typically fed by magmatic reservoirs situated within the upper crust. The development of thermal and/or compositional gradients in such magma chambers may lead to vigorous convection as inferred from theoretical models and evidence for magma mixing recorded in volcanic rocks. Bi-directional flow is also inferred to prevail in the conduits of numerous persistently-active volcanoes based on observed gas and thermal emissions at the surface, as well as experiments with analogue models. However, more direct evidence for such exchange flows has hitherto been lacking. Here, we analyse the remarkable oscillatory zoning of anorthoclase feldspar megacrystals erupted from the lava lake of Erebus volcano, Antarctica. A comprehensive approach, combining phase equilibria, solubility experiments and melt inclusion and textural analyses shows that the chemical profiles are best explained as a result of multiple episodes of magma transport between a deeper reservoir and the lava lake at the surface. Individual crystals have repeatedly travelled up-and-down the plumbing system, over distances of up to several kilometers, presumably as a consequence of entrainment in the bulk magma flow. Our findings thus corroborate the model of bi-directional flow in magmatic conduits. They also imply contrasting flow regimes in reservoir and conduit, with vigorous convection in the former (regular convective cycles of âŒ150 days at a speed of âŒ0.5 mmâsâ1) and more complex cycles of exchange flow and re-entrainment in the latter. We estimate that typical, 1-cm-wide crystals should be at least 14 years old, and can record several (from 1 to 3) complete cycles between the reservoir and the lava lake via the conduit. This persistent recycling of phonolitic magma is likely sustained by CO2 fluxing, suggesting that accumulation of mafic magma in the lower crust is volumetrically more significant than that of evolved magma within the edifice.The work reported here has been partially supported by the National Science Foundation (Division of Polar Programs) under grant ANT1142083. The authors thank the Natural Environment Research Council (NERC) for access to the NERC Ion Microprobe Facility (Grant IMF453/1011) and Richard Hinton for invaluable help with SIMS analyses. Y.M. acknowledges support from the Cambridge Philosophical Society, the University of Cambridge Home and EU Scholarship Scheme, and the Philip Lake and William Vaughan Lewis funds from the Department of Geography, University of Cambridge. Y.M. also acknowledges support from ERC grant #279790.This is the final published version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0012821X14007833#
The Low-Level Control System for the CERN PS Multi-Turn Extraction Kickers
To reduce the beam losses when preparing high intensity proton beam for the CERN Neutrino to Gran Sasso (CNGS) facility, a new Multi-Turn extraction (MTE) scheme has been implemented in the PS, to replace the present Continuous Transfer (CT) to the SPS. Industrial off-the-shelf components have been used for the low-level part of the MTE kicker control system. National Instruments PXI systems are used to control the high voltage pulse generators and a SIEMENS programmable logic controller (PLC) handles the centralised oil cooling and gas insulation sub-system
The impact of constructive operating lease capitalisation on key accounting ratios
Current UK lease accounting regulation does not require operating leases to be capitalised in the accounts of lessees, although this is likely to change with the publication of FRS 5. This study conducts a prospective analysis of the effects of such a change. The potential magnitude of the impact of lease capitalisation upon individual users' decisions, market valuations, company cash flows, and managers' behaviour can be indicated by the effect on key accounting ratios, which are employed in decision-making and in financial contracts. The capitalised value of operating leases is estimated using a method similar to that suggested by Imhoff, Lipe and Wright (1991), adapted for the UK accounting and tax environment, and developed to incorporate company-specific assumptions. Results for 1994 for a random sample of 300 listed UK companies show that, on average, the unrecorded long-term liability represented 39% of reported long-term debt, while the unrecorded asset represented 6% of total assets. Capitalisation had a significant impact (at the 1% level) on six of the nine selected ratios (profit margin, return on assets, asset turnover, and three measures of gearing). Moreover, the Spearman rank correlation between each ratio before and after capitalisation revealed that the ranking of companies changed markedly for gearing measures in particular. There were significant inter-industry variations, with the services sector experiencing the greatest impact. An analysis of the impact of capitalisation over the five-year period from 1990 to 1994 showed that capitalisation had the greatest impact during the trough of the recession. Results were shown to be robust with respect to key assumptions of the capitalisation method. These findings contribute to the assessment of the economic consequences of a policy change requiring operating lease capitalisation. Significant changes in the magnitude of key accounting ratios and a major shift in company performance rankings suggest that interested parties' decisions and company cash flows are likely to be affected
Einfluss rĂ€umlicher HeterogenitĂ€t von Phosphor auf die mikrobielle PâAufnahme und die Zusammensetzung der mikrobiellen Gemeinschaft in Waldböden
Neben Stickstoff ist Phosphor (P) das wichtigste wachstumslimitierende NĂ€hrelement in Böden. Dennoch gibt es wenig Information ĂŒber die rĂ€umliche HeterogenitĂ€t des P-Gehaltes in Waldböden. DarĂŒber hinaus ist der Effekt einer homogenen versus heterogenen PâVerteilung im Boden auf die mikrobielle PâAkquirierung und Zusammensetzung der mikrobiellen Gemeinschaft weitgehend unbekannt. Ein Rhizotronexperiment mit P-armem Waldboden wurde durchgefĂŒhrt um konkurrierende PâAufnahmestrategien von Mikroorganismen zu untersuchen. Um den Effekt rĂ€umlicher PâHeterogenitĂ€t auf pflanzliche und mikrobielle PâAufnahme zu eruieren wurden mit F.sylvatica bepflanzte Rhizotrone mit Pâ33âEisen(III)phosphat, einer relativ immobilen P Quelle, in verschiedenen rĂ€umlichen Verteilungen markiert. Die PâMobilisierung durch Mikroorganismen wurde mittels einer verbesserten P-33-PLFA-Methode verfolgt, welche die Pâ33âInkorporierung in Mikroorganismen mit Ănderungen in der Zusammensetzung mikrobieller Gemeinschaften in situ verbindet.
Die mikrobielle P-Aufnahme war erhöht in Rhizotronen mit hoher PâVerfĂŒgbarkeit, sowie in solchen mit heterogener PâVerteilung. Charakteristische PLFA weisen auf eine Akkumulation von Ektomykorrhizapilzen, typischerweise assoziiert mit Buchenwurzeln, in Pâreichen Arealen hin. Diese Ektomykorrhizzapilze fĂŒhren wahrscheinlich zu einer starken Zunahme der PâMobilisierung des ausgebrachten Pâ33âEisen(III)phosphats in stark P-haltigen Habitaten. Im Gegensatz hierzu benötigen Habitate mit niedriger P-VerfĂŒgbarkeit eine komplexer zusammengesetzte mikrobielle Gemeinschaft um unzugĂ€ngliche P-Quellen zu mobilisieren. Entsprechend fördern hohe PâVorkommen die Bildung von Pilzhyphen zur P-Mobilisierung â ein Effekt, der mit sinkendem P-Gehalt abnimmt. Des Weiteren zeigen grampositive und ânegative Bakterien eine massiv erhöhte PâAufnahme unter zunehmend heterogenen P-Verteilungen. Sie stellen jedoch einen kleineren Anteil der mikrobiellen Gemeinschaft als in homogen Pâangereicherten Rhizotronen, was auf einen Vorteil filamentöser Organismen bei heterogener P-Verteilung hindeutet. Entsprechend fördert eine heterogene P-Verteilung in Waldböden die P-Aufnahme mikrobieller Gemeinschaften aus mineralischen P-Quellen mit geringer biologischer VerfĂŒgbarkeit in Waldböden
Reduced haemodynamic response in the ageing visual cortex measured by absolute fNIRS
The effect of healthy ageing on visual cortical activation is still to be fully explored. This study aimed to elucidate whether the haemodynamic response (HDR) of the visual cortex altered as a result of ageing. Visually normal (healthy) participants were presented with a simple visual stimulus (reversing checkerboard). Full optometric screening was implemented to identify two age groups: younger adults (n = 12, mean age 21) and older adults (n = 13, mean age 71). Frequency-domain Multi-distance (FD-MD) functional Near-Infrared Spectroscopy (fNIRS) was used to measure absolute changes in oxygenated [HbO] and deoxygenated [HbR] haemoglobin concentrations in the occipital cortices. Utilising a slow event-related design, subjects viewed a full field reversing checkerboard with contrast and check size manipulations (15 and 30 minutes of arc, 50% and 100% contrast). Both groups showed the characteristic response of increased [HbO] and decreased [HbR] during stimulus presentation. However, older adults produced a more varied HDR and often had comparable levels of [HbO] and [HbR] during both stimulus presentation and baseline resting state. Younger adults had significantly greater concentrations of both [HbO] and [HbR] in every investigation regardless of the type of stimulus displayed (p<0.05). The average variance associated with this age-related effect for [HbO] was 88% and [HbR] 91%. Passive viewing of a visual stimulus, without any cognitive input, showed a marked age-related decline in the cortical HDR. Moreover, regardless of stimulus parameters such as check size, the HDR was characterised by age. In concurrence with present neuroimaging literature, we conclude that the visual HDR decreases as healthy ageing proceeds
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