The NAIAD experiment for WIMP searches at Boulby mine and recent results

The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented.     

Galaxy formation: Warm dark matter, missing satellites, and the angular momentum problem

We present warm dark matter (WDM) as a possible solution to the missing satellites and angular momentum problem in galaxy formation and introduce improved initial conditions for numerical simulations of WDM models, which avoid the formation of unphysical haloes found in earlier simulations. There is a hint, that because of that the mass function of satellite haloes has been overestimated so far, pointing to higher values for the WDM particle mass. This revised version was published online in August 2006 with corrections to the Cover Date.     

Circular Polarisation Observations of SS433

We present four epochs of observations of the Galactic X-ray binarySS433 using the Australian Telescope Compact Array (ATCA). These observations, taken on 4 February, 29 February, 23 March and 27 June 2000, at four frequencies ranging from 1–9 Ghz, are used to monitor the circular polarised emission from the source. We obtain circular polarisation spectra for the first three epochs with spectralindices α, (m _c ∝ν ^α), equal to 0.07±0.10, –1.07±0.09 and –0.18±0.05 and also observe a sign change in Stokes V. This change of handedness may indicate along-term restructuring of the magnetic field.     

Rare earth, major and trace elements in Jurassic manganese shales of the Northern Calcareous Alps: hydrothermal versus hydrogenous origin of stratiform manganese deposits

Summary ?The rare earth, major and trace element geochemistry of Jurassic deep marine manganese shales allow insight into their environment of deposition. We present data of 24 samples from the Northern Calcareous Alps (Eastern Alps), collected from Late Jurassic strata of the Tennengebirge and from Early Jurassic strata of the Karwendel Mts. Whereas major and trace element geochemistry is controlled by the detrital input, rare earth element data and the relationship between total organic carbon and (pyritic) sulfur can be used to constrain the origin of the manganese accumulation. The data of this study are compatible with a hydrogenous precipitation of manganese by strongly varying redox-conditions at the sediment–water interface of a slope basin. Received December 21, 2001; revised version accepted February 18, 2002     

Tephrochronology and tephrostratigraphy of two Pleistocene continental fossiliferous successions from central Italy

The stratigraphical context of two Middle Pleistocene fossiliferous palaeosols from Central Italy (Abruzzo and Tuscany) have been studied. Small mammals and molluscs occur in both palaeosols, which are covered by tephra layers that were analysed using an interdisciplinary approach. Application of fission‐track dating to apatites separated from the Case Picconetto tephra (Pescara, Abruzzo), yielded an age of 0.48 ± 0.04 Ma, indistinguishable from those previously determined for the Campani Quarry (Lower Valdarno, Tuscany) (0.46 ± 0.05 Ma and 0.48 ± 0.05 Ma). Geochemical and petrographic investigations indicate that these tephra originated from different volcanoes, the Alban Hills Volcanic Complex and the Vico Volcano (Latium) respectively. Small mammal and mollusc assemblages indicate different palaeoclimatic and palaeoenvironmental conditions for the Case Picconetto and Campani Quarry palaeosols. Warm and humid conditions can be inferred for the Campani Quarry site, whereas open and cold conditions can be inferred for Case Picconetto. On the basis of faunal data, fission‐track dates and attribution of tephra to specific volcanic eruptions, we suggest a correlation of these faunas with marine oxygen isotope stage 14 (Case Picconetto) and with marine oxygen isotope stage 11 (Campani Quarry), respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

Reliability assessment of granular filters in embankment dams

Empirical criteria have been used successfully to design filters of most embankment large dam projects throughout the world. However, these empirical rules are only applicable to a particular range of soils tested in laboratory and do not take into account the variability of the base material and filter particle sizes. In addition, it is widely accepted that the safety of fill dams is mainly dependent on the reliability of their filter performance. The work herein presented consists in a new general method for assessing the probability of fulfilling any empirical filter design criteria accounting for base and filter heterogeneity by means of first‐order reliability methods (FORM), so that reliability indexes and probabilities of fulfilling any particular criteria are obtained. This method will allow engineers to estimate the safety of existing filters in terms of probability of fulfilling their design criteria and might also be used as a decision tool on sampling needs and material size tolerances during construction. In addition, sensitivity analysis makes possible to analyse how reliabilities are influenced by different sources of input data. Finally, in case of a portfolio risk assessment, this method will allow engineers to compare the safety of several existing dams in order to prioritize safety investments and it is expected to be a very useful tool to evaluate probabilities of failure due to internal erosion. Copyright © 2006 John Wiley & Sons, Ltd.     

The Electron Energy Spectrum from Large Solar Flares

We report on the differential electron spectrum for intense transient events seen at one AU by the EPAM instrument on the Advanced Composition Explorer (ACE) spacecraft. Over an observing period from September 1997 to September 2005, there were 45 major events that could be reliably identified with a source flare on the Sun. In the ∼40 – 300 keV energy range, the electron spectral index was between one and three for all but two of the events. Twenty-five of the events were associated with Geostationary Operational Environmental Satellites (GOES) X-ray class X flares. We compare this result with the spectral index measured from electron pulse events, lasting approx. one hour or less, where the spectral index is typically much softer than three. This suggests that the measured spectral index of near-relativistic electrons at one AU may be a reliable indicator of the source. We also examine the likelihood that fast coronal mass ejections (CMEs) are responsible in themselves for accelerating near-relativistic electrons and conclude that they do not.     

A major sulphur isotope event at c. 510 Ma: a possible anoxia–extinction–volcanism connection during the Early–Middle Cambrian transition?

A new approach to constraining seawater δ³⁴S and sulphate concentration using francolite‐bound sulphate reveals an abrupt increase in δ³⁴S to +50‰ around the Early–Middle Cambrian boundary. Such high δ³⁴S values are best explained by increased rates of pyrite burial due to ocean anoxia coupled with an increased sensitivity of the ocean sulphate reservoir to perturbations due to low sulphate concentrations of 500–700 μgL^?1. We argue that the spread of anoxic waters at this time was partly the result of greenhouse warming related to the eruption of the Kalkarindji Large Igneous Province of northern Australia and that it triggered the collapse of early metazoan reef ecosystems during the latest Early Cambrian. Mass extinctions of the last 260 Myr have all coincided with enhanced volcanic activity, while several are also associated with positive shifts in seawater δ³⁴S. Extending this correlation back in time further implicates volcanically induced climate change as a major determining factor in biosphere evolution. Terra Nova, 18, 257–263, 2006     

An HLLC Riemann solver for relativistic flows – II. Magnetohydrodynamics

An approximate Riemann solver for the equations of relativistic magnetohydrodynamics (RMHD) is derived. The Harten–Lax–van Leer contact wave (HLLC) solver, originally developed by Toro, Spruce and Spears, generalizes the algorithm described in a previous paper to the case where magnetic fields are present. The solution to the Riemann problem is approximated by two constant states bounded by two fast shocks and separated by a tangential wave. The scheme is Jacobian-free, in the sense that it avoids the expensive characteristic decomposition of the RMHD equations and it improves over the HLL scheme by restoring the missing contact wave.
Multidimensional integration proceeds via the single step, corner transport upwind (CTU) method of Colella, combined with the constrained transport (CT) algorithm to preserve divergence-free magnetic fields. The resulting numerical scheme is simple to implement, efficient and suitable for a general equation of state. The robustness of the new algorithm is validated against one- and two-dimensional numerical test problems.