3,366 research outputs found
Modelling the redshift-space distortion of galaxy clustering
We use a set of large, high-resolution cosmological N-body simulations to
examine the redshift-space distortions of galaxy clustering on scales of order
10-200h^{-1} Mpc. Galaxy redshift surveys currently in progress will, on
completion, allow us to measure the quadrupole distortion in the 2-point
correlation function, \xi(\sigma,\pi), or its Fourier transform, the power
spectrum, P(k,\mu), to a high degree of accuracy. On these scales we typically
find a positive quadrupole, as expected for coherent infall onto overdense
regions and outflow from underdense regions, but the distortion is
substantially weaker than that predicted by pure linear theory. We assess two
models that may be regarded as refinements to linear theory, the Zel'dovich
approximation and a dispersion model in which the non-linear velocities
generated by the formation of virialized groups and clusters are treated as
random perturbations to the velocities predicted by linear theory. We find that
neither provides an adequate physical description of the clustering pattern. If
used to model redshift spacedistortions on scales for 10<\lambda <200 h^{-1}Mpc
the estimated value of \beta (\beta=f(\Omega_0)/b where f(\Omega_0) ~
\Omega_0^{0.6} and b is the galaxy bias parameter) is liable to systematic
errors of order ten per cent or more. We discuss how such systematics can be
avoided by i) development of a more complete model of redshift distortions and
ii) the direct use of galaxy catalogues generated from non-linear N-body
simulations.Comment: 13 pages, Latex, uses mn.sty and mnextra.sty (mnextra.sty included
here
The stability of the ways of coping (revised) questionnaire over time in parents of children with Downs-Syndrome:a research note
The stability of the Ways of Coping (Revised) Questionnaire over time was assessed by comparing the scores of 68 mothers and 53 fathers of school-aged children with Down's syndrome over a 3-year time interval on the five coping strategy subscales described by Knussen et al. (1992). For this analysis, mothers' and fathers' scores were analysed separately. It was shown by t tests that mothers' and fathers' scores on the coping strategy subscales had not significantly changed over the three-year period. Time 1 and Time 2 scores on all of the coping subscales were strongly positively associated, with the exception of fathers' scores on the Stoicism subscale. Test-retest reliability was adequate for all subscales except mothers' scores on the Passive Acceptance subscale and fathers' scores on the Stoicism subscale. These results, by demonstrating the stability of the Ways of Coping (Revised) Questionnaire over a 3-year time period, further illustrate the utility of this instrument for investigating coping in families with special problems
First phylogenetic analyses of galaxy evolution
The Hubble tuning fork diagram, based on morphology, has always been the
preferred scheme for classification of galaxies and is still the only one
originally built from historical/evolutionary relationships. At the opposite,
biologists have long taken into account the parenthood links of living entities
for classification purposes. Assuming branching evolution of galaxies as a
"descent with modification", we show that the concepts and tools of
phylogenetic systematics widely used in biology can be heuristically transposed
to the case of galaxies. This approach that we call "astrocladistics" has been
first applied to Dwarf Galaxies of the Local Group and provides the first
evolutionary galaxy tree. The cladogram is sufficiently solid to support the
existence of a hierarchical organization in the diversity of galaxies, making
it possible to track ancestral types of galaxies. We also find that morphology
is a summary of more fundamental properties. Astrocladistics applied to
cosmology simulated galaxies can, unsurprisingly, reconstruct the correct
"genealogy". It reveals evolutionary lineages, divergences from common
ancestors, character evolution behaviours and shows how mergers organize galaxy
diversity. Application to real normal galaxies is in progress. Astrocladistics
opens a new way to analyse galaxy evolution and a path towards a new
systematics of galaxies
Research into anxiety of childhood: playing catch-up (to Olympic standard)
This special issue is the culmination of an ESRC seminar series grant awarded to the authors of this editorial. We named the seminar series CATTS (Child Anxiety, Theory and Treatment Seminars) and it took the form of six highly stimulating, one-day seminars on the subject of child anxiety, with participants from clinical and academic backgrounds and from Great Britain, Europe, the USA and Australia. Most of the authors in this publication, and a sister special issue in Cognitions and Emotion (2008), participated in the CATTS series
Path Planning of an Autonomous Surface Vehicle based on Artificial Potential Fields in a Real Time Marine Environment
With growing advances in technology and the everyday dependence on oceans for resources, the role of unmanned marine vehicles has increased many a fold. Extensive operations having naval, civil and scientific applications are being undertaken and demands are being placed on them to increase their flexibility and adaptability. A key factor for such vehicles is the requirement for them to possess a path planning subsystem. Most path planning techniques are implemented in self-simulated environments. This study accounts for use of artificial potential field in path planning of an autonomous surface vehicle (ASV) in a real time marine environment. Path cost, path length and computational time are described to ensure the effectiveness of the motion planning
High-performance silver window electrodes for top-illuminated organic photovoltaics using an organo-molybdenum oxide bronze interlayer
We report an organo-molybdenumn oxide bronze that enables the fabrication of high-performance silver window electrodes for top-illuminated solution processed organic photovoltaics without complicating the process of device fabrication. This hybrid material combines the function of wide-band-gap interlayer for efficient hole extraction with the role of metal electrode seed layer, enabling the fabrication of highly transparent, low-sheet-resistance silver window electrodes. Additionally it is also processed from ethanol, which ensures orthogonality with a large range of solution processed organic semiconductors. The key organic component is the low cost small molecule 3-mercaptopropionic acid, which (i) promotes metal film formation and imparts robustness at low metal thickness, (ii) reduces the contact resistance at the Ag/molybdenumn oxide bronze interface, (iii) and greatly improves the film forming properties. Silver electrodes with a thickness of 8 nm deposited by simple vacuum evaporation onto this hybrid interlayer have a sheet resistance as low as 9.7 Ohms per square and mean transparency âŒ80% over the wavelength range 400â900 nm without the aid of an antireflecting layer, which makes them well-matched to the needs of organic photovoltaics and applicable to perovskite photovoltaics. The application of this hybrid material is demonstrated in two types of top-illuminated organic photovoltaic devices
Towards use of Dijkstra Algorithm for Optimal Navigation of an Unmanned Surface Vehicle in a Real-Time Marine Environment with Results from Artificial Potential Field
The growing need of ocean surveying and exploration for scientific and industrial application has led to the requirement of routing strategies for ocean vehicles which are optimal in nature. Most of the optimal path planning for marine vehicles had been conducted offline in a selfâmade environment. This paper takes into account a practical marine environment, i.e. Portsmouth Harbour, for finding an optimal path in terms of computational time between source and end points on a real time map for an USV. The current study makes use of a grid map generated from original and uses a Dijkstra algorithm to find the shortest path for a single USV. In order to benchmark the study, a path planning study using a wellâknown local path planning method artificial path planning (APF) has been conducted in a real time marine environment and effectiveness is measured in terms of path length and computational time
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