The first generation of stars in the Λ cold dark matter cosmology

We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics to study the formation of the first luminous objects in the Lambda cold dark matter cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from   z ∼ 10  to ∼50 and cover an order of magnitude in halo mass. We find that the physical properties of the central star-forming clouds are very similar in all of the simulated objects despite significant differences in formation redshift and environment. This suggests that the formation path of the first stars is largely independent of the collapse redshift; the physical properties of the clouds have little correlation with spin, mass or assembly history of the host halo. The collapse of protostellar objects at higher redshifts progresses much more rapidly due to the higher densities, which accelerates the formation of molecular hydrogen, enhances initial cooling and shortens the dynamical time-scales. The mass of the star-forming clouds cover a broad range, from a few hundred to a few thousand solar masses, and exhibit various morphologies: some have disc-like structures which are nearly rotational supported; others form flattened spheroids; still others form bars. All of them develop a single protostellar 'seed' which does not fragment into multiple objects up to the moment that the central gas becomes optically thick to H₂ cooling lines. At this time, the instantaneous mass accretion rate on to the centre varies significantly from object to object, with disc-like structures having the smallest mass accretion rates. The formation epoch and properties of the star-forming clouds are sensitive to the values of cosmological parameters.     

Interaction of Waves, Surface Currents, and Turbulence： the Application of Surface-Following Coordinate Systems

Surface waves comprise an important aspect of the interaction between the atmosphere and the ocean, so a dynamically consistent framework for modelling atmosphere-ocean interaction must take account of surface waves, either implicitly or explicitly. In order to calculate the effect of wind forcing on waves and currents, and vice versa, it is necessary to employ a consistent formula- tion of the energy and momentum balance within the airflow, wave field, and water column. It is very advantageous to apply sur- face-following coordinate systems, whereby the steep gradients in mean flow properties near the air-water interface in the cross-interface direction may be resolved over distances which are much smaller than the height of the waves themselves. We may account for the waves explicitly by employing a numerical spectral wave model, and applying a suitable theory of wave–mean flow interaction. If the mean flow is small compared with the wave phase speed, perturbation expansions of the hydrodynamic equations in a Lagrangian or generalized Lagrangian mean framework are useful: for stronger flows, such as for wind blowing over waves, the presence of critical levels where the mean flow velocity is equal to the wave phase speed necessitates the application of more general types of surface-following coordinate system. The interaction of the flow of air and water and associated differences in temperature and the concentration of various substances (such as gas species) gives rise to a complex boundary-layer structure at a wide range of vertical scales, from the sub-millimetre scales of gaseous diffusion, to several tens of metres for the turbulent Ekman layer. The bal- ance of momentum, heat, and mass is also affected significantly by breaking waves, which act to increase the effective area of the surface for mass transfer, and increase turbulent diffusive fluxes via the conversion of wave energy to turbulent kinetic energy.     

ISO Observations of Classical Novae

We describe the ISO programme to observe classical novae. The programme includes observations of novae during and shortly after eruption, and old novae. ISO observations of far infrared fine structure lines are providing us with information about physical conditions in nova ejecta which complement and extend knowledge obtained from ground-based observations. Surprisingly, we are getting little information about dust in nova systems, despite the fact that many novae are prolific dust-producers. This revised version was published online in August 2006 with corrections to the Cover Date.     

Constraints on σ8 from galaxy clustering in N-body simulations and semi-analytic models

We generate mock galaxy catalogues for a grid of different cosmologies, using rescaled N -body simulations in tandem with a semi-analytic model run using consistent parameters. Because we predict the galaxy bias, rather than fitting it as a nuisance parameter, we obtain an almost pure constraint on σ₈ by comparing the projected two-point correlation function we obtain to that from the Sloan Digital Sky Survey (SDSS). A systematic error arises because different semi-analytic modelling assumptions allow us to fit the r -band luminosity function equally well. Combining our estimate of the error from this source with the statistical error, we find  σ₈= 0.97 ± 0.06  . We obtain consistent results if we use galaxy samples with a different magnitude threshold, or if we select galaxies by b _J-band rather than r -band luminosity and compare to data from the 2dF Galaxy Redshift Survey (2dFGRS). Our estimate for σ₈ is higher than that obtained for other analyses of galaxy data alone, and we attempt to find the source of this difference. We note that in any case, galaxy clustering data provide a very stringent constraint on galaxy formation models.     

A multi‐century record of linked nearshore and coastal change

Using geographic information system (GIS) and field measurements the nearshore morphological variability of a headland bay beach at Tenby, West Wales (51·66 N; –4·71 W) was assessed over historical timeframes (1748–2007). Three areas chosen for detailed analysis were the area between mean low water (MLW) and lowest astronomical tide (LAT) contours; LAT and one fathom contours; and one and two fathom contours. Estuary closure c. 1855 has been suggested as the genesis for long‐term beach evolution and did have an initial effect, with northward dune migration and reduced flushing effects. However, this research suggests nearshore bank migration and retrogradation associated with spit collapse took place prior to closure and continued throughout the assessed timeframe. Historical data revealed patterns of shoreward migration demonstrated by changes in orientation, Giltar headland acting as a pivot. Variations in sandbank position correlated with areal reduction of both Giltar spit and White Bank. Temporal offshore areal loss was contrasted against variable gains inshore as offshore banks welded to the beachface. Annual volumetric change analyses represented by profiles that extend 1 km offshore, confirmed Giltar spit and White Bank erosion rates of 91 m³ yr^–1 and 458 m³ yr^–1 respectively, and 220 m³ yr^–1 beachface accretion. Diminution of sediment supply observed over historical timescales was supported by decadal evidence. Here, profile analysis revealed a trend of decreasing volumes both updrift and within the study area, and increasing downdrift volumes. This explained why proximal detachment and sediment redistribution had occurred. Distinct reversal's in shoreline trend (rotation) corresponded to nearshore change; therefore, variations in seabed configuration triggered shoreface dynamic change over century timescales. Five‐year cumulative average changes in North Atlantic Oscillation were further correlated to this reversal. As comparable scenarios are likely to exist at other worldwide coastal locations, similar analyses should be incorporated into shoreline monitoring programmes. Consequently, these assessments would inform shoreline trends and support coastal management decisions. Copyright © 2011 John Wiley & Sons, Ltd.     

The Ediacara member of the Rawnsley quartzite: The context of the Ediacara assemblage (late precambrian,flinders ranges)

The Ediacara fossil assemblage occurs widely in the Flinders Ranges, South Australia, in a single, readily mappable stratigraphic interval—the Ediacara Member of the Rawnsley Quartzite, which is part of the Pound Subgroup of the Wilpena Group. The Member occurs low in the Rawnsley Quartzite and consists of siltstones, medium‐ to thick‐bedded sandstones, and heterolithic units of intercalated siltstone and sandstone. Features such as rhythmical bedding and flaser bedding, interference and flat‐topped ripples, winnowed coarse sand residues, abundant clay galls, and rare desiccation cracks suggest that the heterolithic siltstone/sandstone units represent intertidal deposits. The rich body‐fossil assemblage occurs chiefly in these deposits of probable intertidal origin, and for the most part appears to represent organisms stranded by the tide away from their normal habitat. Associated bioturbation structures include horizontal, penetrative (post‐depositional) burrows, but vertical dwelling burrows have not been found; the Pound Subgroup evidently pre‐dates their widespread appearance.

The Rawnsley Quartzite appears to have been deposited during cycles of marine transgression, with the Ediacara Member inferred to have accumulated in environments varying from shallow shelf to tidally influenced lagoons sheltered by barrier bars.     

Indirect economic losses of drought under future projections of climate change: a case study for Spain

This study presents the results of numerical simulations of the 2004 Indian Ocean earthquake and tsunami in the Bay of Lhok Nga (northwestern coast of Sumatra, Indonesia) integrating sediment erosion and deposition. We investigate the transport of sediment both by suspension and by bedload under different scenarii of long breaking dispersive waves through a series of numerical experiments. The earthquake source model used by Koshimura et al. (Coast Eng J 51:243–273, 2008) with a 25-m dislocation better reproduces the wave travel time, flow depth and inundation area than the other models tested. The model reproduces realistically the pronounced coastal retreat in the northern part of Lhok Nga Bay (retreat ranging between 50 and 150 m), where Paris et al. (Geomorphology 104:59–72, 2009) estimated a mean retreat of 80 m. There is also a good agreement between the simulated area of coastal retreat (195,400 m²) and the field observations (203,200 m²). The simulation may underestimate the volume of tsunami deposits (611,700 m³ vs. 500,000–1,000,000 m³ estimated by Paris et al. (2009). The model fully reproduces the observed thickness of tsunami deposits when considering both bedload and suspension, even if bedload transport dominates. Limitations are due to micro-scale topographic, anthropic features (which are not always represented by the DEM) and the amount of debris which may influence flow dynamics and sediment transport.     

Solar influence on nuclear decay rates: constraints from the MESSENGER mission

We have analyzed ¹³⁷Cs decay data, obtained from a small sample onboard the MESSENGER spacecraft en route to Mercury, with the aim of setting limits on a possible correlation between nuclear decay rates and solar activity. Such a correlation has been suggested recently on the basis of data from ⁵⁴Mn decay during the solar flare of 13 December 2006, and by indications of an annual and other periodic variations in the decay rates of ³²Si, ³⁶Cl, and ²²⁶Ra. Data from five measurements of the ¹³⁷Cs count rate over a period of approximately 5.4 years have been fit to a formula which accounts for the usual exponential decrease in count rate over time, along with the addition of a theoretical solar contribution varying with MESSENGER-Sun separation. The indication of solar influence is then characterized by a non-zero value of the calculated parameter ξ, and we find ξ=(2.8±8.1)×10⁻³ for ¹³⁷Cs. A simulation of the increased data that can hypothetically be expected following Mercury orbit insertion on 18 March 2011 suggests that the anticipated improvement in the determination of ξ could reveal a non-zero value of ξ if present at a level consistent with other data.