Reducing the dimensionality effect in importance sampling simulations

The dimensionality effect is avoided by the use of sufficient statistics in event probability estimators realised by importance sampling. If the system function is not a sufficient statistic, an approach is proposed to reduce the dimensionality effect in the estimators. Simulation results of false-alarm probability estimations, applied to radar detection, confirm a clear concordance with the theoretical result

Fischer-Tropsch synthesis in microchannels

Different metallic supports (aluminum foams of 40ppi, honeycomb monolith and micromonolith of 350 and 1180cpsi, respectively) have been loaded with a 20%Co-0.5%Re/γ-Al2O3 catalyst by the washcoating method. Layers of different thicknesses have been deposited onto the metallic supports. The catalytic coatings were characterized measuring their textural properties, adhesion and morphology. These structured catalysts have been tested in the Fischer-Tropsch synthesis (FTS) and compared with a microchannel block presenting perpendicular channels for reaction and cooling. The selectivity depends on the type of support used and mainly on the thickness of the layer deposited. In general, the C5+ selectivity decreased at increasing CO conversion for all of the systems (powder, monoliths, foams and microchannels block). On the other hand, the selectivity to methane increased with the thickness of the catalytic layer due to the higher effective H2/CO ratio over the active sites resulting from the higher diffusivity of H2 compared with CO in the liquid products filling the pores. The C5+ selectivity of the microchannels reactor is higher than that of the structured supports and the powder catalyst.Ministerio de Ciencia e Innovación MAT2006-12386-C05, ENE2009-14522-C0

An Analysis of Scripting Languages for Research in Applied Computing

There are several scripting languages that exist today. However, some are used more frequently and popular than others. This is due to certain characteristics and features that they possess. Particularly in applied computing fields like software engineering, bioinformatics and computational biology, scripting languages are gaining popularity. This paper presents a comparative study of ten popular scripting languages that are used in the above mentioned fields/area. For making comparison, we have identified the factors against which these languages are evaluated. Accordingly, based on selected criteria we determine their suitability in the fields of software engineering, bioinformatics and computational biology research. This will serve as a guide to researchers to choose the appropriate scripting language in the various fields

Los productos petrolíferos en Hispanoamérica: Noticias anteriores al siglo XIX

Las sustancias petrolíferas han sido conocidas desde tiempos muy antiguos. Las aplicaciones que de ellas se hicieron se orientaron en un principio hacia fines arquitectónicos, artesanales y medicinales. Fueron los denominados en Geoquímica como Indicios Superficiales o filtraciones los que llamaron la atención de nuestros antepasados, sobre todo por su aspecto físico, ya fuera el color, el olor o el tacto. Los Indicios Superficiales son las diferentes manifestaciones de propiedades químicas de gases, aguas, rocas y suelos que están relacionadas en su origen con depósitos petrolíferos cercanos, o que señalan condiciones favorables a la existencia de los mismos

Geothermometrical modelling applied to the CO2-rich thermal waters of the Lanjarón hydrothermal system (Granada, Spain)

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Experimental and numerical study of wind flow behind windbreaks

The shelter effect of a windbreak protects aggregate piles and provides a reduction of particle emissions in harbours. RANS (Reynolds-averaged Navier–Stokes equations) simulations using three variants of k–ε (standard k–ε, RNG k–ε and realizable k–ε) turbulence closure models have been performed to analyse wind flow characteristics behind an isolated fence located on a flat surface without roughness elements. The performance of the three turbulence models has been assessed by wind tunnel experiments. Cases of fences with different porosities (φ) have been evaluated using wind tunnel experiments as well as numerical simulations. The aim is to determine an optimum porosity for sheltering effect of an isolated windbreak. A value of 0.35 was found as the optimum value among the studied porosities (φ=0, 0.1, 0.24, 0.35, 0.4, 0.5)

Effect of pressure on the behavior of copper-, iron-, and nickel-based oxygen carriers for chemical-looping combustion

8 pages, 8 figures, 2 tables.The combustion process integrated by coal gasification and chemical-looping combustion (CLC) could be used in power plants with a low energy penalty for CO2 capture. This work analyzes the main characteristics related to the CLC process necessary to use the syngas obtained in an integrated gasification combined cycle (IGCC) power plant. The kinetics of reduction with H2 and CO and oxidation with O2 of three high-reactivity oxygen carriers used in the CLC system have been determined in a thermogravimetric analyzer at atmospheric pressure. The iron- and nickel-based oxygen carriers were prepared by freeze-granulation, and the copper-based oxygen carrier was prepared by impregnation. The changing grain size model (CGSM) was used for the kinetic determination, assuming spherical grains for the freeze-granulated particles containing iron and nickel and a platelike geometry for the reacting surface of the copper-based impregnated particles. The dependence of the reaction rates on temperature was low, with the activation energy values varying from 14 to 33 kJ mol-1 for the reduction and 7 to 15 kJ mol-1 for the oxidation. The reaction order depended on the reacting gas and oxygen carrier, with values ranging from 0.25 to 1. However, an increase in the operating pressure for the IGCC + CLC system increases the thermal efficiency of the process, and the CO2 is recovered as a high pressure gas, decreasing the energy demand for further compression. The effect of pressure on the behavior of the oxygen carriers has been analyzed in a pressurized thermogravimetric analyzer at 1073 K and pressures up to 30 atm. It has been found that an increase in total pressure has a negative effect on the reaction rates of all the oxygen carriers. Moreover, the use of the CGSM with the kinetic parameters obtained at atmospheric pressure predicted higher reaction rates than those experimentally obtained at higher pressures, and therefore, the kinetic parameters necessary to design pressurized CLC plants must be determined at the operating pressure. © 2006 American Chemical Society.This work was carried out with financial support from the European Coal and Steel Community Project (7220-PR125) and the Spanish Ministry of Education and Science (Project CTQ 2004-04034). The authors thank Dr. Anders Lyngfelt and Dr. Tobias Mattisson for the preparation of the freeze-granulated particles.Peer Reviewe

Calcination of calcium-based sorbents at pressure in a broad range of CO2 concentrations

11 figures, 3 tablesThe calcination reaction of two limestones and a dolomite with different porous structures was studied by thermogravimetric analysis. The effects of calcination temperature (1048-1173 K), particle size (0.4 2.0 mm), CO2 concentration (0 80%) and total pressure (0.1 1.5 MPa) were investigated. SEM analysis indicated the existence of two different particle calcination models depending on the sorbent type: a shrinking core model with a sharp limit between the uncalcined and calcined parts of the particle and a grain model with changing calcination conversion at the particle radial position. The appropriate reaction model was used to determine the calcination kinetic parameters of each sorbent. Chemical reaction and mass transport in the particle porous system were the main limiting factors of the calcination reaction at the experimental conditions. A Langmuir-Hinshelwood-type kinetic model using the Freundlich isotherm was proposed to account for the effect of the CO2 during sorbent calcination. This allowed us to predict the calcination conversion of very different sorbents in a broad range of CO2 partial pressures. Total pressure also inhibited the sorbent calcination. This fact was accounted for by an additional decrease in the molecular diffusion coefficient with increasing total pressure with respect to that indicated by Fuller's equation.This research was carried out with the financial support from the Comisión Interministerial de Ciencia y Tecnología (CICYT) (Project No. AMB 98-0883). The authors thank Dr. Diego Alvárez for his assistance with the SEM technique.Peer Reviewe

Liquid-liquid equilibria for the systems 2-ethoxy-benzenamine + CH3(CH2) CH3 (n = 6,8,10,12) and 4-ethoxy-benzenamine + CH3(CH2) CH3 (n = 5,6)

Liquid-liquid equilibria (LLE) phase diagrams have been determined for the systems: 2-ethoxy-benzenamine + octane, or +decane, or +dodecane, or +tetradecane and for 4-ethoxy-benzenamine + heptane, or +octane. The experimental method used is based on the observation, by mean of a laser scattering technique, of the turbidity produced on cooling when a second phase takes place. All the mixtures show an upper critical solution temperature, which increases with the alkane size. Dipolar interactions between like molecules become stronger in the sequence: 2-ethoxy-benzenamine < aniline < 4-ethoxy-benzenamine. Data available in the literature suggest that this relative variation is also valid for alkane mixtures containing other substituted anilines or phenols, characterized by having a second polar group. The dependence of the UCST values with the molecular structure of the polar aromatic compound involved is shortly discussed in terms of intramolecular and steric effects