Strong modification of the reflection from birefringent layers of semiconductor nanowires by nanoshells

The propagation of light in layers of vertically aligned nanowires is determined by their unique and extreme optical properties. Depending on the nanowire filling fraction and their diameter, layers of nanowires form strongly birefringent media. This large birefringence gives rise to sharp angle dependent peaks in polarized reflection. We demonstrate experimentally the tunability of the reflection by adding shells of SiO2 with thicknesses ranging from 10¿nm to 30¿nm around the nanowires. The strong modification of the reflection peaks renders nanowire layers as a promising candidate for sensing applications

Thermal diffusivity of ferrofluids as a function of particle size determined using the mode-mismatched dual-beam thermal lens technique

Ferrofluids are colloids of superparamagnetic nanoparticles that are envisaged for use in hyperthermia, which is based on nonradiative relaxation after interaction with a high-frequency magnetic field or light. For such applications, an important parameter is the thermal diffusivity. In this communication, we present an experimental study of the dependence of thermal diffusivity of ferrofluids on the size of the magnetite nanoparticles by employing the mode-mismatched thermal lens technique. The results show a huge enhancement of the thermal diffusivity by increasing the average size of the nanoparticles, while the number density of the nanoparticles is maintained as constant

Origin and timing of stratabound dolomitization in the Cretaceous carbonate ramp of Benicàssim

Hydrothermal dolomitization is one of the most important processes that may enhance or degrade carbonate porosity and permeability. Burial, high emperature or hydrothermal dolomite forms due to the interaction of one or more solutions, mainly seawater-derived or deep brines, with limestone. The Early Cretaceous Benicassim ramp (Maestrat Basin, E Spain) is an excellent outcrop analog for partially dolomitized petroleum reservoirs. In this area seismic-scale sub-stratiform dolomitized bodies extend for several kilometers, away from large-scale faults, in Aptian limestones (Fig. 1). In the present work the Benicassim ramp is used as a case study to characterize dolomite events and to evaluate controls on dolomitization via reactive transport simulations

Adaptive Mesh Refinement for Characteristic Grids

I consider techniques for Berger-Oliger adaptive mesh refinement (AMR) when numerically solving partial differential equations with wave-like solutions, using characteristic (double-null) grids. Such AMR algorithms are naturally recursive, and the best-known past Berger-Oliger characteristic AMR algorithm, that of Pretorius & Lehner (J. Comp. Phys. 198 (2004), 10), recurses on individual "diamond" characteristic grid cells. This leads to the use of fine-grained memory management, with individual grid cells kept in 2-dimensional linked lists at each refinement level. This complicates the implementation and adds overhead in both space and time. Here I describe a Berger-Oliger characteristic AMR algorithm which instead recurses on null \emph{slices}. This algorithm is very similar to the usual Cauchy Berger-Oliger algorithm, and uses relatively coarse-grained memory management, allowing entire null slices to be stored in contiguous arrays in memory. The algorithm is very efficient in both space and time. I describe discretizations yielding both 2nd and 4th order global accuracy. My code implementing the algorithm described here is included in the electronic supplementary materials accompanying this paper, and is freely available to other researchers under the terms of the GNU general public license.Comment: 37 pages, 15 figures (40 eps figure files, 8 of them color; all are viewable ok in black-and-white), 1 mpeg movie, uses Springer-Verlag svjour3 document class, includes C++ source code. Changes from v1: revised in response to referee comments: many references added, new figure added to better explain the algorithm, other small changes, C++ code updated to latest versio

Reactivity of dolomitizing fluids and Mg source evaluation of fault-controlled dolomitization at the Benicàssim outcrop analogue (Maestrat Basin, E Spain)

The mechanisms responsible for the formation of huge volumes of dolomitized rocks associated with faults are not well understood. We present a case study for high-temperature dolomitization of an Early Cretaceous (Aptian-Albian) ramp in Benicàssim (Maestrat basin, E Spain). In this area, seismic-scale fault-controlled stratabound dolostone bodies extend over several kilometres away from large-scale faults. This work aims at evaluating different Mg sources for dolomitization, estimating the reactivity of dolomitizing fluids at variable temperature and quantifying the required versus available fluid volumes to account for the Benicàssim dolostones. Field relationships, stable 13C and 18O isotopes, as well as radiogenic 87Sr/86Sr isotopes, indicate that dolomitization at Benicàssim was produced by a high temperature fluid (> 80ºC). 13C and 18O isotopic compositions for dolomite vary from +0.5 and +2.9 V-PDB and from +21.1 and +24.3 V-SMOW, respectively. A Mg source analysis reveals that the most likely dolomitizing fluid was seawater-derived brine that interacted with underlying Triassic red beds and Paleozoic basement. Geochemical models suggest that evolved seawater can be considerably more reactive than high-salinity brines, and that the maximum reactivity occurs at about 100ºC. Mass-balance calculations indicate that interstitial fluids with high pressure and/or high temperature relative to the normal geothermal gradient cannot account for the volume of dolomite at Benicàssim. Instead a pervasive fluid circulation mechanism, like thermal convection, is required to provide a sufficient volume of dolomitizing fluid, which most likely occurred during the Late Cretaceous post-rift stage of the Maestrat Basin. This study illustrates the importance of fluid budget quantification to critically evaluate genetic models for dolomitization and other diagenetic processes

Algoritmos de clasificación y redes neuronales en la observación automatizada de registros

El objetivo del presente estudio es analizar los datos obtenidos a través de una plataforma on-line, mediante diferentes técnicas de clasificación y aprendizaje orientadas al descubrimiento del conocimiento. Se aplican técnicas de minería de datos para obtener relaciones de habilidad que informen del interés de los usuarios por cumplimentar de manera rigurosa el cuestionario on-line atendiendo al modo de realizar el mismo. Aunque existen técnicas que nos permiten observar el comportamiento de los usuarios mientras realizan el cuestionario, en este caso se emplean Redes Neuronales Artificiales para predecir el comportamiento de aquellos, atendiendoa variables obtenidas al realizar el cuestionario. La muestra consta de 1.636 participantes de diferentes zonas geográficas y rangos de edad, obtenida al contestar de manera anónima o identi#cada al cuestionario Inventario Psicológico para el Seguimiento de Talentos Deportivos (IPSETA). Los resultados obtenidos mediante las diferentes técnicas de análisis informan que elgénero femenino prefiere realizar el registro en la plataforma para cumplimentar el cuestionario, alcanzando un alto porcentaje de fiabilidad (70%)

On the fraction of dark matter in charged massive particles (CHAMPs)

From various cosmological, astrophysical and terrestrial requirements, we derive conservative upper bounds on the present-day fraction of the mass of the Galactic dark matter (DM) halo in charged massive particles (CHAMPs). If dark matter particles are neutral but decay lately into CHAMPs, the lack of detection of heavy hydrogen in sea water and the vertical pressure equilibrium in the Galactic disc turn out to put the most stringent bounds. Adopting very conservative assumptions about the recoiling velocity of CHAMPs in the decay and on the decay energy deposited in baryonic gas, we find that the lifetime for decaying neutral DM must be > (0.9-3.4)x 10^3 Gyr. Even assuming the gyroradii of CHAMPs in the Galactic magnetic field are too small for halo CHAMPs to reach Earth, the present-day fraction of the mass of the Galactic halo in CHAMPs should be < (0.4-1.4)x 10^{-2}. We show that redistributing the DM through the coupling between CHAMPs and the ubiquitous magnetic fields cannot be a solution to the cuspy halo problem in dwarf galaxies.Comment: 21 pages, 2 figures. To appear in JCA