A multi‐level parallelized substructuring‐frontal solution for coupled thermo/hydro/mechanical problems in unsaturated soil

This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd.     

On the most general accurate solutions for Buchdahl's fluid spheres

The most general accurate solutions for the Buchdhal fluid sphere were obtained and matched with the Schwarzchild's exterior solution at the pressure free interface. Various parameters of the solutions were so adjusted that the energy density, pressure and temperature were positive and decreasing away from the centre, and the velocity of sound was less than unity throughout the spheroid model. Using this procedure, the maximum mass of the fluid sphere with a surface density of2 × 10¹⁴gm cm^-3 was determined to be 3.82MΘ and 4.57 MΘ for strong and weak energy conditions respectively. PACS number: 0402, 0402J, 0440D, 95301 This revised version was published online in July 2006 with corrections to the Cover Date.     

Microtextures and crystal chemistry in P21/c pigeonites

Summary ?A single-crystal X-ray investigation was performed on crystals of P2₁/c natural pigeonite with varying Ca and Fe^* ( = Fe²⁺ + Mn²⁺) contents, in order to verify the effect of microtextural disorder on structure refinements and to constrain the crystal chemistry of pigeonite. Antiphase domains and exsolution lamellae affect differently the refinement results. In a crystal free of exsolution the structure obtained after refinement with all reflections is an average of that of the antiphase domains and of their boundaries, whereas in an exsolved crystal it represents only the structure of the prevailing pigeonite lamellae. The refinement using only h + k odd reflections seems to give the structure of the Ca-free pigeonite characteristic of the antiphase domains rather than that of Ca-rich domain walls. The ratio of the scale factors in refinements with all reflections and with only h + k odd reflections allows the ratios of the exsolved augite and pigeonite phases to be estimated. The crystal chemistry of the investigated samples follows the trends outlined by data on Ca-free and Fe-free synthetic samples. In particular, it is shown that Ca and Fe^* substitution for Mg induce similar changes in the average structure, i.e. both induce an expansion in the M1 polyhedron and decrease the difference between the M2–O3 distances. Received October 18, 2001; revised version accepted February 15, 2002     

Ionprobe U-Pb zircon ages from the high-pressure/low-temperature mélange of Syros, Greece: age diversity and the importance of pre-Eocene subduction

The Cycladic blueschist belt in the central Aegean Sea has experienced high‐pressure (HP) metamorphism during collisional processes between the Apulian microplate and Eurasia. The general geological and tectonometamorphic framework is well documented, but one aspect which is yet not sufficiently explored is the importance of HP mélanges which occur within volcano‐sedimentary successions. Unresolved issues concern the range in magmatic and metamorphic ages recorded by mélange blocks and the significance of eventual pre‐Eocene HP metamorphism. These aspects are here addressed in a U‐Pb zircon study focusing on the block–matrix association exposed on the island of Syros. Two gneisses from a tectonic slab of this mélange, consisting of an interlayered felsic gneiss‐glaucophanite sequence, yielded zircon ²⁰⁶Pb/²³⁸U ages of 240.1 ± 4.1 and 245.3 ± 4.9 Ma, respectively, similar to Triassic ages determined on zircon in meta‐volcanic rocks from structurally coherent sequences elsewhere in the Cyclades. This strongly suggests that parts of these successions have been incorporated in the mélanges and provides the first geochronological evidence that the provenance of mélange blocks/slabs is neither restricted to a single source nor confined to fragments of oceanic lithosphere. Zircon from a jadeitite and associated alteration zones (omphacitite, glaucophanite and chlorite‐actinolite rock) all yielded identical ²⁰⁶Pb/²³⁸U ages of c. 80 Ma. Similar Cretaceous U‐Pb zircon ages previously reported for mélange blocks have been interpreted by different authors to reflect magmatic or metamorphic ages. The present study adds a further argument in favour of the view that zircon formed newly in some rock types at c. 80 Ma, due to hydrothermal or metasomatic processes in a subduction zone environment, and supports the interpretation that the Cycladic blueschist belt records both Cretaceous and Eocene HP episodes and not only a single Tertiary HP event.     

Size and shape evolution of pores in a viscoplastic matrix under compression

The frequent use of soils and earth materials for hydraulic capping and for geo‐environmental waste containment motivated our interest in detailed modelling of changes in size and shape of macro‐pores to establish links between soil mechanical behaviour and concurrent changes in hydraulic and transport properties. The objective of this study was to use finite element analysis (FEA) to test and extend previous analytical solutions proposed by the authors describing deformation of a single macro‐pore embedded in linear viscoplastic soil material subjected to anisotropic remote stress. The FEA enables to consider more complex pore geometries and provides a detailed picture of matrix yield behaviour to explain shortcomings of approximate analytical solutions. Finite element and analytical calculations agreed very well for linear viscous as well as for viscoplastic materials, only limited for the case of isotropic remote stress due to the simplifications of the analytical model related to patterns and onset of matrix‐yielding behaviour. FEA calculations were compared with experimental data obtained from a compaction experiment in which pore deformation within a uniform modelling clay sample was monitored using CAT scanning. FEA predictions based on independently measured material properties and initial pore geometry provided an excellent match with experimentally determined evolution of pore size and shape hence lending credence to the potential use of FEA for more complex pore geometries and eventually connect macro‐pore deformation with hydraulic properties. Copyright © 2006 John Wiley & Sons, Ltd.     

Laboratory studies of the interaction of carbon monoxide with water ice

The interaction of carbon monoxide (CO) with vapour-deposited water(H₂O) ices has been studied using temperature programmed desorption (TPD) and Fourier transform reflection-absorption infrared spectroscopy (FT-RAIRS) over a range of astrophysically relevant temperatures. Such measurements have shown that CO desorption from amorphous H₂Oices is a much more complex process than current astrochemical models suggest. Re-visiting previously reported laboratory experiments (Collings et al., 2003), a rate model has been constructed to explain, in a phenomenological manner, the desorption of CO over astronomically relevant time scales. The model presented here can be widely applied to a range of astronomical environments where depletion of CO from the gas phase is relevant. The model accounts for the two competing processes of CO desorption and migration, and also enables the entrapment of some of the CO in the ice matrix and its subsequent release as the water ice crystallises and then desorbs. The astronomical implications of this model are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.