Las rocas encajantes de la mineralización aurífera en el yacimiento de La Zarza (Huelva)

La mina La Zarza (Strauss et a1.1981) está situada en la zona central del Cinturón Pirítico Ibérico, cerca del pueblo de Silos de Calañas, unos 30 Km al Nordeste de Tharsis y 20 Km al Oeste de Riotint

Coupled microbial and geochemical reactive transport models in porous media: Formulation and Application to Synthetic and In Situ Experiments

El estudio de la calidad natural y la contaminación de las aguas subterráneas así como la evaluación de la seguridad de las instala¬ciones subterráneas de almacenamiento de residuos radiactivos requiere utilizar modelos acoplados de flujo subterráneo, transporte de calor y solutos, reacciones químicas y procesos biológicos. Este artículo presenta la formulación matemática y numérica del modelo acoplado de flujo y transporte reactivo con procesos biológicos para medios porosos que ha sido implementada en el código BIO CORE2D© mediante la adición de los procesos microbiológicos en el código de transporte reactivo no isotermo CORE2D©. BIO-CORE2D© incorpora algoritmos numéricos eficientes para resolver la versión cuasi implícita del método de iteración secuencial y determinar de forma automática los intervalos de tiempo óptimos. Se presentan modelos hidrobiogeoquímicos para una columna sintética y para el experimento in situ CERBERUS realizado en el laboratorio subterráneo de Mol en Bélgica para evaluar el efecto del calor y la radiación en la arcilla de Boom

DIA: A complexity-effective decoding architecture

Fast instruction decoding is a true challenge for the design of CISC microprocessors implementing variable-length instructions. A well-known solution to overcome this problem is caching decoded instructions in a hardware buffer. Fetching already decoded instructions avoids the need for decoding them again, improving processor performance. However, introducing such special--purpose storage in the processor design involves an important increase in the fetch architecture complexity. In this paper, we propose a novel decoding architecture that reduces the fetch engine implementation cost. Instead of using a special-purpose hardware buffer, our proposal stores frequently decoded instructions in the memory hierarchy. The address where the decoded instructions are stored is kept in the branch prediction mechanism, enabling it to guide our decoding architecture. This makes it possible for the processor front end to fetch already decoded instructions from the memory instead of the original nondecoded instructions. Our results show that using our decoding architecture, a state-of-the-art superscalar processor achieves competitive performance improvements, while requiring less chip area and energy consumption in the fetch architecture than a hardware code caching mechanism.Peer ReviewedPostprint (published version

Very Low Temperature Tunnelling Spectroscopy in the heavy fermion superconductor PrOs4_4Sb12_{12}

We present scanning tunnelling spectroscopy measurements on the heavy fermion superconductor PrOs$_4$Sb$_{12}$. Our results show that the superconducting gap opens over a large part of the Fermi surface. The deviations from isotropic BCS s-wave behavior are discussed in terms of a finite distribution of values of the superconducting gap.Comment: 4 pages, 4 figure

A global method for coupling transport with chemistry in heterogeneous porous media

Modeling reactive transport in porous media, using a local chemical equilibrium assumption, leads to a system of advection-diffusion PDE's coupled with algebraic equations. When solving this coupled system, the algebraic equations have to be solved at each grid point for each chemical species and at each time step. This leads to a coupled non-linear system. In this paper a global solution approach that enables to keep the software codes for transport and chemistry distinct is proposed. The method applies the Newton-Krylov framework to the formulation for reactive transport used in operator splitting. The method is formulated in terms of total mobile and total fixed concentrations and uses the chemical solver as a black box, as it only requires that on be able to solve chemical equilibrium problems (and compute derivatives), without having to know the solution method. An additional advantage of the Newton-Krylov method is that the Jacobian is only needed as an operator in a Jacobian matrix times vector product. The proposed method is tested on the MoMaS reactive transport benchmark.Comment: Computational Geosciences (2009) http://www.springerlink.com/content/933p55085742m203/?p=db14bb8c399b49979ba8389a3cae1b0f&pi=1

Maximizing multithreaded multicore architectures through thread migrations

Heterogeneity in general-purpose workloads often end up in non optimal per-thread hardware resource usage. The current trend towards multicore architectures, containing several multithreaded cores, increases the need of a complexity-effective way to expose the heterogeneity in general-purpose workloads to the underlying hardware, in order to obtain all the potential performance of these architectures. In this paper we present the Heterogeneity-Aware Dynamic Thread Migrator (hDTM), a novel complexity-effective hardware mechanism that exposes the heterogeneity in software to the hardware, also enabling the hardware to react to the dynamic behavior variations in the running applications. By means of core-to-core thread migrations, the hDTM mechanism strives to perform the desired behavior transparently to the Operating System. As an example of the general-purpose hDTM concept presented in this paper, we describe a naive hDTM implementation for a Power5-like processor and provide results on the benefits of the proposed mechanism. Our results indicate that even this simple hDTM implementation is able to get close to hDTM’s goal, not only avoiding losses due to bad thread-to-core assignments (up to a 25%) but also going beyond the best static thread-to-core assignment upper limit.Postprint (published version

Spatial and temporal variability of seagrass at Lizard Island, Great Barrier Reef

Increasing threats to natural ecosystems from local and global stressors are reinforcing the need for baseline data on the distribution and abundance of organisms. We quantified spatial and/or temporal patterns of seagrass distribution, shoot density, leaf area index, biomass, productivity, and sediment carbon content in shallow water (0-5 m) at Lizard Island, Great Barrier Reef, Australia, in field surveys conducted in December 2011 and October 2012. Seagrass meadows were mapped using satellite imagery and field validation. A total of 18.3 ha of seagrass, composed primarily of Thalassia hemprichii and Halodule uninervis, was mapped in shallow water. This was 46% less than the area of seagrass in the same region reported in 1995, although variations in mapping methods may have influenced the magnitude of change detected. There was inter-annual variability in shoot density and length, with values for both higher in 2011 than in 2012. Seagrass properties and sediment carbon content were representative of shallow-water seagrass meadows on a mid-shelf Great Barrier Reef island. The data can be used to evaluate change, to parameterize models of the impact of anthropogenic or environmental variability on seagrass distribution and abundance, and to assess the success of management actions

Magnetic field dependence of superconducting energy gaps in YNi2B2C: Evidence of multiband superconductivity

We present results of in field directional point contact spectroscopy (DPCS) study in the quaternary borocarbide superconductor YNi2B2C, which is characterized by a highly anisotropic superconducting gap function. For I||a, the superconducting energy gap (D), decreases linearly with magnetic field and vanishes around 3.25T which is well below the upper critical field (Hc2~6T) measured at the same temperature (2.2K). For I||c, on the other hand, D decreases weakly with magnetic field but the broadening parameter (G) increases rapidly with magnetic field with the absence of any resolvable feature above 3.5T. From an analysis of the field variation of energy gaps and the zero bias density of states we show that the unconventional gap function observed in this material could originate from multiband superconductivity.Comment: 19 pages including figures (final version