Self-consistent Gravitational Lens Reconstruction

We present a new method for directly determining accurate, self-consistent cluster lens mass and shear maps in the strong lensing regime from the magnification bias of background galaxies. The method relies upon pixellisation of the surface mass density distribution which allows us to write down a simple, solvable set of equations. We also show how pixellisation can be applied to methods of mass determination from measurements of shear and present a simplified method of application. The method is demonstrated with cluster models and applied to magnification data from the lensing cluster Abell 1689.Comment: 5 pages, 4 figures. References added to introduction. Accepted by MNRA

A new method to measure evolution of the galaxy luminosity function

We present a new efficient technique for measuring evolution of the galaxy luminosity function. The method reconstructs the evolution over the luminosity-redshift plane using any combination of three input dataset types: 1) number counts, 2) galaxy redshifts, 3) integrated background flux measurements. The evolution is reconstructed in adaptively sized regions of the plane according to the input data as determined by a Bayesian formalism. We demonstrate the performance of the method using a range of different synthetic input datasets. We also make predictions of the accuracy with which forthcoming surveys conducted with SCUBA2 and the Herschel Space Satellite will be able to measure evolution of the sub-millimetre luminosity function using the method.Comment: MNRAS in press. 14 pages, 7 figures

Discurso de la Dra. Nancy S. Dye Presidenta de Oberlin College

Discurso de agradecimiento por la distinción Abderramán III concedida por la Universidad de Córdoba a PRESCHO con motivo de los 25 años de esta entidad

Adaptive semi-linear inversion of strong gravitational lens imaging

We present a new pixelized method for the inversion of gravitationally lensed extended source images which we term adaptive semi-linear inversion (SLI). At the heart of the method is an h-means clustering algorithm which is used to derive a source plane pixelization that adapts to the lens model magnification. The distinguishing feature of adaptive SLI is that every pixelization is derived from a random initialization, ensuring that data discretization is performed in a completely different and unique way for every lens model parameter set. We compare standard SLI on a fixed source pixel grid with the new method and demonstrate the shortcomings of the former when modelling singular power-law ellipsoid (SPLE) lens profiles. In particular, we demonstrate the superior reliability and efficiency of adaptive SLI which, by design, fixes the number of degrees of freedom (NDOF) of the optimization and thereby removes biases present with other methods that allow the NDOF to vary. In addition, we highlight the importance of data discretization in pixel-based inversion methods, showing that adaptive SLI averages over significant systematics that are present when a fixed source pixel grid is used. In the case of the SPLE lens profile, we show how the method successfully samples its highly degenerate posterior probability distribution function with a single nonlinear search. The robustness of adaptive SLI provides a firm foundation for the development of a strong lens modelling pipeline, which will become necessary in the short-term future to cope with the increasing rate of discovery of new strong lens systems

Recovery and recruitment of the brown mussel, Perna perna (L.), in Transkei: implications for management

The brown mussel Perna perna, has been an important food resource for indigenous inhabitants of the Transkei coast for centuries. The impoverished state of mussel stocks in this region and major differences in lowshore community structure between exploited and protected areas, have been ascribed to the ever-increasing explOitation of this species. In spite of this there has been no effective management of this resource owing to political and logistical problems related to law-enforcement, and misconceptions concerning the resilience of P. perna and the interspecific interactions which govern its recovery. Our present understanding of the ecological impacts of exploitation, and of the potential for recovery, is based on a series of studies and observations made over the last 15 years. These studies have shown that algae usually replace mussels following disturbance and that recovery may take more than eight years. As mussels tend to recruit preferentially into existing mussel beds, exploitation not only affects reproductive output but also reduces the preferred habitat. Recruitment onto both natural and artificial substrata is extremely low, even in marine reserves where standing stock is considerably higher than in exploited areas. Under these conditions stock enhancement in conjunction with rotational cropping may be the best management strategy.S Afr. J. Zool. 1997,32(4

Geo-neutrinos and Earth Models

We present the current status of geo-neutrino measurements and their implications for radiogenic heating in the mantle. Earth models predict different levels of radiogenic heating and, therefore, different geo-neutrino fluxes from the mantle. Seismic tomography reveals features in the deep mantle possibly correlated with radiogenic heating and causing spatial variations in the mantle geo-neutrino flux at the Earth surface. An ocean-based observatory offers the greatest sensitivity to the mantle flux and potential for resolving Earth models and mantle features. Refinements to estimates of the geo-neutrino flux from continental crust reduce uncertainty in measurements of the mantle flux, especially measurements from land-based observatories. These refinements enable the resolution of Earth models using the combined measurements from multiple continental observatories.Comment: 9 pages, 4 figures; Contributed paper TAUP 201

What are the prospects for seasonal prediction of the marine environment of the North-west European Shelf?

Sustainable management and utilisation of the North-west European Shelf (NWS) seas could benefit from reliable forecasts of the marine environment on monthly to seasonal timescales. Recent advances in global seasonal forecast systems and regional marine reanalyses for the NWS allow us to investigate the potential for seasonal forecasts of the state of the NWS. We identify three possible approaches to address this issue: (A) basing NWS seasonal forecasts directly on output from the Met Office's GloSea5 global seasonal forecast system; (B) developing empirical downscaling relationships between large-scale climate drivers predicted by GloSea5 and the state of the NWS; and (C) dynamically downscaling GloSea5 using a regional model. We show that the GloSea5 system can be inadequate for simulating the NWS directly (approach A). We explore empirical relationships between the winter North Atlantic Oscillation (NAO) and NWS variables estimated using a regional reanalysis (approach B). We find some statistically significant relationships and present a skillful prototype seasonal forecast for English Channel sea surface temperature. We find large-scale relationships between inter-annual variability in the boundary conditions and inter-annual variability modelled on the shelf, suggesting that dynamic downscaling may be possible (approach C). We also show that for some variables there are opposing mechanisms correlated with the NAO, for which dynamic downscaling may improve on the skill possible with empirical forecasts. We conclude that there is potential for the development of reliable seasonal forecasts for the NWS and consider the research priorities for their development

Finite-element modelling of mechanobiological factors influencing sesamoid tissue morphology in the patellar tendon of an ostrich

The appearance and shape of sesamoid bones within a tendon or ligament wrapping around a joint are understood to be influenced by both genetic and epigenetic factors. Ostriches (Struthio camelus) possess two sesamoid patellae (kneecaps), one of which (the distal patella) is unique to their lineage, making them a good model for investigating sesamoid tissue development and evolution. Here we used finite-element modelling to test the hypothesis that specific mechanical cues in the ostrich patellar tendon favour the formation of multiple patellae. Using three-dimensional models that allow application of loading conditions in which all muscles, or only distal or only proximal muscles to be activated, we found that there were multiple regions within the tendon where transformation from soft tissue to fibrocartilage was favourable and therefore a potential for multiple patellae based solely upon mechanical stimuli. While more studies are needed to better understand universal mechanobiological principles as well as full developmental processes, our findings suggest that a tissue differentiation algorithm using shear strain and compressive strain as inputs may be a roughly effective predictor of the tissue differentiation required for sesamoid development