36,941 research outputs found

    On the transport of alkali ions through polymeric mold compounds and polyelectrolyte membranes.

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    The aim of this work is the attempt in understanding ion transport properties across structured materials such as polyelectrolyte multilayers (PEMs) and highly filled epoxy resins used as an encapsulant, i.e. mold compounds. The ion transport properties are studied by means of the technique of charge attachment induced transport (CAIT), which was recently developed and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The mold compounds studied in this work are of four types (MCP1, MCP2, MCP3, MCP4) with a composition of 80% - 88% of silica filler and the rest of raw materials such as epoxy resin, hardener and flame retardant. The samples are analyzed by means of the CAIT technique, leading to the evaluation of values of ionic conductivity and activation energy related to the process of transport of potassium ions. The ionic conductivity of the mold compounds is on the order of 10-12/10-13 S/cm, while activation energy values are in a range of 1.3 eV - 2.7 eV. For a better understanding of the potassium diffusion process into the mold compounds, the diffusion of potassium through MCP3 sample is investigated via a combination of CAIT method and an ex-situ ToF-SIMS analysis. The ToF-SIMS analysis reveals a depth diffusion profile of the potassium into the material. A mathematical theory is established in order to evaluate the diffusion coefficients for the transport of potassium. According to the numerical procedure, a good fit between experimental and theoretical data is achieved assuming the presence of two different transport pathways operative inside the material: diffusion along the boundaries of grains, i.e. zones of accumulation of the inorganic component of the mold compound and diffusion through the bulk. Diffusion coefficients of DB = 1.8 x 10-21 cm2s-1 and DBG = 5.4 x 10-20 cm2s-1 are found for bulk and grain boundary diffusion, respectively. The PEM films studied in this work are prepared from the layer-by-layer assembly of ionic p-sulfonato-calix[8]arene (calix8) and cationic poly(allylamine hydrochloride) (PAH) onto functionalized gold substrates. Samples with n = 1, 3, 6, 9, 12, 15, 20, 30 bilayers are analyzed by means of the CAIT technique. The data lend support to the conclusion that conductivity, as well as activation energy measurements for (PAH/calix8)n, cannot be acquired under the conditions of the CAIT method, due to the low resistivity shown from the specific PEMs analyzed. Studies on the transport of Li+, K+ and Rb+ through (PAH/calix8)30 are performed by means of CAIT and ToF-SIMS. For each ion beam (Li+, K+, Rb+) two kind of experiments are performed: (PAH/calix8)30 samples are bombarded with the three different alkali ions varying the time for the bombardment, i.e. 5 seconds in one case and 100 seconds in the other. The evaluation of the concentration profiles gives qualitative information regarding the transport properties, whereas numerical analysis of the lithium and rubidium concentration profiles for 5 seconds long bombardment provides quantitative information on the diffusion process. The numerical calculation reveals that the lithium and rubidium transport across the membrane results in a combination of two diffusion pathways accounting for diffusion of slow ions and fast ions. For the lithium case, a good fit is achieved using diffusion coefficients of Dslow,Li+ = 0.4 x 10-16 cm2/s and Dfast,Li+ = 1.2 x 10-15 cm2/s and assuming that 40% of the incoming ions enter the slow pathway, whereas the rest of the ions is transported via a fast pathway. For the rubidium case, the numerical calculation reveals that the fast diffusion pathway is predominant: only the 0.01% of the rubidium ions enter the slow pathway, whereas the rest is dominated from the faster one, with a Dfast,Rb+ = 7 x 10-15 (± 1.5 x 10-15) cm2/s. The study of ion transport of alkali ions Li+ and Rb+ across calixarenes-based PEMs leads thus to the conclusion that the presence of the calixarenes units may influence the type of transport. Lastly, studies of voltage offset measured on current-voltage curves in a typical CAIT experiment are presented. This study aims to give a better understanding of the process beyond the measured voltage offset. In order to do that, a basic CAIT experiment is performed, where a metal plate is bombarded with an ion beam from a potassium emitter of the composition KAlSi2O6 : Mo (1:9). The registered current–voltage curves show finite offsets in the order of 0.5 eV. In order to investigate the detection process of the specific KAlSi2O6 : Mo (1:9) emitter, values of ionic and electronic work function are evaluated. By means of a theoretical model, the recombination of K+ ions from Leucite KAlSi2O6 : Mo (1:9) onto the metal detector is traced to a combination of the ionic work function of the emitter material, the electronic work function of the emitter material and the recombination energy of the elemental potassium I.E.K

    On the Smarandache Paradox

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    The Smarandache Paradox is a very interesting paradox of logic because it has a background common sense. However, at the same time, it gets in a contradiction with itself. Although it may appear well cohesive, a careful look on the science definition and some logic can break down this paradox showing that it exist only when we are trying to mix two different universes, where in one we have two possibilities and in the other we have only one. When we try to understand the second possibility in the universe which has only one possibility, we end in the Smarandache Paradox

    Economic Analysis and EC Merger Policy

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    political economy; regulation; competition policy

    Optimal Simple Monetary and Fiscal Rules under Limited Asset Market Participation

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    The combination of limited asset market participation and consumption habits generates indeterminacy for empirically plausible calibrations of a business cycle model characterized by price and nominal wage rigidities. Equilibrium determinacy is restored by demand management policies based on simple fiscal rules. In this regard, fiscal control of nominal income growth is particularly effective. In addition the complementarity between the Taylor rule and the fiscal feedback on nominal income growth produces relatively large welfare gains, limiting both aggregate and intragroup volatilities

    Solutions to the relativistic precession model

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    The relativistic precession model (RPM) can be used to obtain a precise measurement of the mass and spin of a black hole when the appropriate set of quasi periodic oscillations is detected in the power-density spectrum of an accreting black hole. However, in previous studies the solution of the RPM equations could be obtained only through numerical methods at a price of an intensive computational effort. Here we demonstrate that the RPM system of equations can be solved analytically, drastically reducing the computational load, now limited to the Monte-Carlo simulation necessary to estimate the uncertainties. The analytical method not only provides an easy solution to the RPM system when three oscillations are detected, but in all the cases where the detection of two simultaneous oscillations is coupled with an independent mass measurement. We also present a computationally inexpensive method to place limits on the black hole mass and spin when only two oscillations are observed.Comment: Accepted to MNRAS; 8 pages, 3 figure