Volcanic eruption frequency over the last 45 ky as recorded in Epica-Dome C ice core (East Antarctica) and its relationship with climatic changes

The sulphate glacio-chemical profiles constitute a reliable proxy marker for reconstruction of past volcanic history, assuming a reliable method to distinguish sulphate spikes and to evaluate the flux of individual events is set up. The resulting volcanic event profile is used to reconstruct past event frequencies, and to investigate possible links between volcanism and climatic changes. Volcanic event signatures are useful also in comparing time scales from ice cores drilled at different locations. In this paper, a new method to pick out volcanic signals is proposed. It improves on methods based on the calculation of a threshold using a general mean value plus a multiple of the standard deviation by adding: (1) quantification of nonvolcanic sulphate contributions; (2) sulphate fluxes, instead of concentrations, accounting for accumulation rate changes; (3) data treatment using a log-normal statistic, instead of a Gaussian-type distribution, to take into account the real sulphate distribution; (4) a smoothed curve (weighted fitting) to better understand the residual variability of the sulphate background.This method is used to detect volcanic events throughout the 45 ky time span of the EDC96 ice core, drilled at Dome C on the East Antarctic plateau. A total of 283 volcanic signatures are recovered, with a mean of 6.3 events per millennium. The temporal event frequencies indicate that the last 2000 years were probably characterized by the highest volcanic activity in the period covered by the core and that there is no clear link between number of events recorded and climatic changes.     

Galaxy evolution, cosmology and dark energy with the Square Kilometer Array

The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics – understanding how galaxies form – and astro-particle physics – inferring properties of the dark components.The Square Kilometer Array (SKA) will provide the only means of studying the cosmic evolution of neutral hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter over-densities and the rôles of gas accretion and galaxy merging.‘All hemisphere’ HI redshift surveys to z 1.5 are feasible with wide-field-of-view realizations of the SKA and, by measuring the galaxy power spectrum in exquisite detail, will allow the first precise studies of the equation-of-state of dark energy. The SKA will be capable of other uniquely powerful cosmological studies including the measurement of the dark-matter power spectrum using weak gravitational lensing, and the precise measurement of H₀ using extragalactic water masers.The SKA is likely to become the premier dark-energy-measuring machine, bringing breakthroughs in cosmology beyond those likely to be made possible by combining CMB (e.g. Planck), optical (e.g. LSST, SNAP) and other early-21st-century datasets.     

Global Bifurcations of Periodic Solutions of the Restricted Three Body Problem

We describe global bifurcations from the libration points of non-stationary periodic solutions of the restricted three body problem. We show that the only admissible continua of non-stationary periodic solutions of the planar restricted three body problem, bifurcating from the libration points, can be the short-period families bifurcating from the Lagrange equilibria L ₄, L ₅. We classify admissible continua and show that there are possible exactly six admissible continua of non-stationary periodic solutions of the planar restricted three body problem. We also characterize admissible continua of non-stationary periodic solutions of the spatial restricted three body problem. Moreover, we combine our results with the Déprit and Henrard conjectures (see [8]), concerning families of periodic solutions of the planar restricted three body problem, and show that they can be formulated in a stronger way. As the main tool we use degree theory for SO(2)-equivariant gradient maps defined by the second author in [25].This revised version was published online in October 2005 with corrections to the Cover Date.