Hydromechanical analysis in geotechnical engineering using the material point method

The explicit version of the Material Point Method [1] has been extended in order to model coupled hydromechanical saturated problems. MPM discretizes the continuum, which is considered as a saturated soilfluid mixture, by dividing it into particles or material points. The discrete movement equations are not solved at the material points. Instead a support mesh, built to cover the domain of the problem, is used. In this paper it is assumed that particles carry all the variables needed to represent the state of the continuum including the pore pressure as a variable associated with each particle. The particle pore pressure increment is calculated explicitly using the equation of fluid mass balance, from the particle volumetric deformation and the fluid velocity relative to the soil skeleton, at the particle location. The shape functions used for the mesh elements are usually the same bilinear functions of the Finite Element Method and therefore the background mesh elements suffer the same drawbacks. These drawbacks include: volumetric locking for quasiincompressible materials when four particles per cell are used, which is equivalent to four integration points in the finite element method, pressure instability for quasiincompressible and low permeability materials and the generation of zero energy modes when one particle per cell is used, which corresponds to reduced integration in the finite element method. The MPM original version has also the disadvantage of generating "noise" in the solution [2] when a particle pass from one cell to another. A simple procedure that can be used to reduce instabilities is to consider constant stress at each cell equal to the stress average of the particles which are in the cell at the instant k. In this case the internal forces are obtained in the same way as in the finite element method when one point of integration is used, using the gradient of the shape functions calculated in the cell center. In this work, to avoid volumetric locking and simultaneously achieve a stable behavior, internal forces and pressure increments at the nodes are calculated using the gradients calculated at the cell center. The procedure is completely explicit and has proved to be stable for the low permeability values used to model the foundation of Aznalcollar dam. The simulation of Aznalcollar dam progressive failure is presented as an example [3]

Self-organization of ultrasound in viscous fluids

We report the theoretical and experimental demonstration of pattern formation in acoustics. The system is an acoustic resonator containing a viscous fluid. When the system is driven by an external periodic force, the ultrasonic field inside the cavity experiences different pattern-forming instabilities leading to the emergence of periodic structures. The system is also shown to possess bistable regimes, in which localized states of the ultrasonic field develop. The thermal nonlinearity in the viscous fluid, together with the far-from-equilibrium conditions, are is the responsible of the observed effects

Decoherence in an accelerated universe

In this paper we study the decoherence processes of the semiclassical branches of an accelerated universe due to their interaction with a scalar field with given mass. We use a third quantization formalism to analyze the decoherence between two branches of a parent universe caused by their interaction with the vaccum fluctuations of the space-time, and with other parent unverses in a multiverse scenario.Comment: 11 pages, 2 figure

Does the Pulvinar-Lp Complex Contribute to Motor Programming?

[Abstract] Extracellular unit recording studies in the pulvinar lateral posterior complex (Pui-LP) of behaving monkeys have shown a response property not previously reported. In monkeys performing aimed arm reaching movements towards frontally located targets some cells showed a change in activity beginning 495 ± 84 ms before the onset of the reaching movement. This change in frequency precedes that observed in primary motor and parietal posterior cortex for reaching movements. These findings seem to indicate the involvement of the Pul-LP in motor functions and suggest its possible contribution to motor programming.Comisión Asesora de Investigacion Cientifica y Tecnica (España); PR83-210

Suction-controlled experiments on Boom clay

The understanding of the thermo-hydro-mechanical behaviour of a clay barrier is needed for the prediction of its final in situ properties after the hydration and thermal transient in a radioactive waste repository. As part of the CEC 1990-1994 R&D programme on radioactive waste management and storage, the CEA (Fr), CIEMAT (Sp). ENRESA (Sp). SCK CEN (B). UPC (Sp) and UWCC (UK) have carried out a joint project on unsaturated clay behaviour (Volckaert et al.. 1996). The aim of the study is to analyse and model the behaviour of a clay-based engineered barrier during its hydration phase under real repository conditions. The hydro-mechanical and thermo-hydraulic models developed in this project have been coupled to describe stress/strain behaviour, moisture migration and heat transfer. A thermo-hydraulic model has also been coupled to a geochemical code to describe the migration and formation of chemical species. In this project. suction-controlled experiments have been performed on Boom clay (B), FoCa clay (Fr) and Almeria bentonite (Sp). The aim of these experiments is to test the validity of the interpretive model developed by Alonso and Gens (Alonso et al., 1990). and to build a database of unsaturated clay thermo-hydro-mechanical parameters. Such a database can then be used for validation exercises in which in situ experiments are simulated. The Boom clay is a moderately swelling clay of Rupellian age. It is studied at the SCK. CEN in Belgium as a potential host rock for a radioactive waste repository. In this paper, suction-controlled experiments carried out on Boom clay by SCK CEN are described. SCK CEN has performed experiments to measure the relation between suction, water content and temperature and the relation between suction, stress and deformation. The applied suctioncontrol techniques and experimental setups are detailed. The results of these experiments are discussed in the perspective of the model of Alonso and Gens. The influence of temperature on water uptake was rather small. The measured swelling-collapse behaviour can be explained by the Alonso and Gens model.Peer Reviewe

Seasonal contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system (Ría de Vigo, NW Spain)

The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365mgm-2d-1, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (Cphyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546mgm-2d-1 and 22mgchl am-2d-1, respectively) and minimum values during winter (22mgm-2d-1 and 0.1mgchl am-2d-1, respectively). The contribution of Cphyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of Cphyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, Cphyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal Cphyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension.Financial support came from CICYT projectREN 2003-04458 and EU projectEVK3-19 CT-2002-00071. D.Z. is funded by a postdoctoral fellowship (Jae-Doc) from the CSIC.Peer reviewe

Contribución a la determinación de los contenidos de yeso y hemihidrato en los cementos portland

Not availableLa mayoría de los técnicos de cemento eceptan que las anormalidades del fraguado, conocidas como "falso fraguado" en el cemento portland, se deben primordialmente a la presencia de yeso parcialmente deshidratado (SO4Ca 1/2H2O). Si el clinker que se muele está enriquecido en cal libre, o la temperatura del molino es elevada (superior a los 110 ºC) o hay escasa ventilación de éste, se llega a originar una parcial deshidratación del yeso, que se mantiene durante el proceso de ensilado y origina las anormalidades del fraguado anteriormente referidas. Por esta razón creemos muy importante el poder conocer el grado de deshidratación en que se encuentra el yeso en un cemento

Hybrid Monte Carlo algorithm for the double exchange model

The Hybrid Monte Carlo algorithm is adapted to the simulation of a system of classical degrees of freedom coupled to non self-interacting lattices fermions. The diagonalization of the Hamiltonian matrix is avoided by introducing a path-integral formulation of the problem, in d + 1 Euclidean space–time. A perfect action formulation allows to work on the continuum Euclidean time, without need for a Trotter–Suzuki extrapolation. To demonstrate the feasibility of the method we study the Double Exchange Model in three dimensions. The complexity of the algorithm grows only as the system volume, allowing to simulate in lattices as large as 163 on a personal computer. We conclude that the second order paramagnetic–ferromagnetic phase transition of Double Exchange Materials close to half-filling belongs to the Universality Class of the three-dimensional classical Heisenberg model

Monte Carlo determination of the phase diagram of the double-exchange model

We study the phase diagram of the double exchange model, with antiferromagnetic interactions, in a cubic lattice both at zero and finite temperature. There is a rich variety of magnetic phases, combined with regions where phase separation takes place. We identify phases, intrinsic to the cubic lattice, which are stable for realistic values of the interactions and dopings. Some of these phases break chiral symmetry, leading to unusual features