Nucleated polymerization with secondary pathways. I. Time evolution of the principal moments.

Self-assembly processes resulting in linear structures are often observed in molecular biology, and include the formation of functional filaments such as actin and tubulin, as well as generally dysfunctional ones such as amyloid aggregates. Although the basic kinetic equations describing these phenomena are well-established, it has proved to be challenging, due to their non-linear nature, to derive solutions to these equations except for special cases. The availability of general analytical solutions provides a route for determining the rates of molecular level processes from the analysis of macroscopic experimental measurements of the growth kinetics, in addition to the phenomenological parameters, such as lag times and maximal growth rates that are already obtainable from standard fitting procedures. We describe here an analytical approach based on fixed-point analysis, which provides self-consistent solutions for the growth of filamentous structures that can, in addition to elongation, undergo internal fracturing and monomer-dependent nucleation as mechanisms for generating new free ends acting as growth sites. Our results generalise the analytical expression for sigmoidal growth kinetics from the Oosawa theory for nucleated polymerisation to the case of fragmenting filaments. We determine the corresponding growth laws in closed form and derive from first principles a number of relationships which have been empirically established for the kinetics of the self-assembly of amyloid fibrils.

Kinetics of the chemical looping oxidation of H2 by a co-precipitated mixture of CuO and Al2O3

Chemical-looping combustion (CLC) has the inherent property of separating CO2 from flue gases. Instead of air, it uses an oxygen-carrier, usually in the form of a metal oxide, to provide oxygen for combustion. When used for the combustion of gaseous fuels, such as natural gas, or synthesis gas from the gasification of coal, the technique gives a stream of CO2 which, on an industrial scale, would be sufficiently pure for geological sequestration. An important issue is the form of the metal oxide, since it must retain its reactivity through many cycles of complete reduction and oxidation. Here, we report on the rates of oxidation of one constituent of synthesis gas, H2, by co-precipitated mixtures of CuO+Al2O3 using a laboratory-scale fluidised bed. To minimise the influence of external mass transfer, and also of errors in the measurement of [H2], particles sized to 355-500μm were used at low [H2], with the temperature ranging from 450 to 900°C. Under such conditions, the reaction was slow enough for meaningful measurements of the intrinsic kinetics to be made. The reaction was found to be first order with respect to H2. Above ∼800°C, the reaction of CuO was fast and conformed to the shrinking core mechanism, proceeding via the intermediate, Cu2O, in: 2CuO+H2→Cu2O+H2O, ΔH1073 K0=- 116.8 kJ/mol; Cu2O+H2→2Cu+H2O, ΔH1073 K0-80.9 kJ/mol. After oxidation of the products Cu and Cu2O back to CuO, the kinetics in subsequent cycles of chemical looping oxidation of H2 could be approximated by those in the first. Interestingly, the carrier was found to react at temperatures as low as 300°C. The influence of the number of cycles of reduction and oxidation is explored. Comparisons are drawn with previous work using reduction by CO. Finally, these results indicate that the kinetics of reaction of the oxygen carrier with gasifier synthesis gases is very much faster than rates of gasification of the original fuel. © 2010 The Institution of Chemical Engineers.

Quantum Monte Carlo study of the CO interaction with a dimer model surface for Cr(110)

The chemisorption of CO on a Cr( 110) surface is investigated using the quantum Monte Carlo method in the diffusion Monte Carlo (DMC) variant and a model Cr2CO cluster. The present results are consistent with the earlier ab initio HF study with this model that showed the tilted/ near-parallel orientation as energetically favoured over the perpendicular arrangement. The DMC energy difference between the two orientations is larger (1.9 eV) than that computed in the previous study. The distribution and reorganization of electrons during CO adsorption on the model surface are analysed using the topological electron localization function method that yields electron populations, charge transfer and clear insight on the chemical bonding that occurs with CO adsorption and dissociation on the model surface.

Studies on two-phase co-current air/non-Newtonian shear-thinning fluid flows in inclined smooth pipes

In this work. co-current flow characteristics of air/non-Newtonian liquid systems in inclined smooth pipes are studied experimentally and theoretically using transparent tubes of 20, 40 and 60 turn in diameter. Each tube includes two 10 m lone pipe branches connected by a U-bend that is capable of being inclined to any angle, from a completely horizontal to a fully vertical position. The flow rate of each phase is varied over a wide range. The studied flow phenomena are bubbly, plug flow, slug flow, churn flow and annular flow. These are observed and recorded by a high flow. stratified flow. -speed camera over a wide range of operating conditions. The effects of the liquid phase properties, the inclination angle and the pipe diameter on two-phase flow characteristics are systematically studied. The Heywood-Charles model for horizontal flow was modified to accommodate stratified flow in inclined pipes, taking into account the average void fraction and pressure drop of the mixture flow of a gas/non-Newtonian liquid. The pressure drop gradient model of Taitel and Barnea for a gas/Newtonian liquid slug flow was extended to include liquids possessing shear-thinning flow behaviour in inclined pipes. The comparison of the predicted values with the experimental data shows that the models presented here provide a reasonable estimate of the average void fraction and the corresponding pressure drop for the mixture flow of a gas/ non-Newtonian liquid. (C) 2007 Elsevier Ltd. All rights reserved.

Reseña bibliográfica : Rodrik, Dani (2011) The globalization paradox. Democracy and the future of the world economy. W. W. Norton & Co. New York, USA

Dani Rodrik es un conocido economista, nacido en Turquía, Profesor de Economía Política Internacional en la John F. Kennedy School of Government, de Harvard University. Su trabajo se ha destacando en temas de economía internacional, desarrollo económico y economía política. Su área central de investigación se centra en la explicación de que constituye una buena política económica y por qué algunos gobiernos son mejores que otros al adoptar distintas políticas, logrando distintos resultados en materia de desarrollo económico. En este sentido, es un defensor de la estrategia “productivista” del Este de Asia, asignando al Estado y a determinada política económica activa un rol central.

黑体泵浦CO_2-CO,N_2O-CO,CO_2-H_2O和N_2O-H_2O激光的研究

本文对黑体辐射泵浦CO_2激光和N_2O激光由于CO和H_2O的加入所引起的激光功率变化进行了理论和实验研究.CO的加入可使的N_2O激光功率增加28%.

稳态CO激光的解析理论

为了分析CO激光的特性,通常需要对上百个方程进行数值计算,因而解析的分析就成为一个很值得探讨的方面。本文从分布函数方程和辐射强度谱分量传输方程出发,导出稳态CO激光在级联跃迁发射时的增益饱和特性,得到的强度谱分量与增益的关系式适用于均匀和非均匀加宽同时起作用的一般情况。文中所使用的振动分布函数由一个非线性积分方程求得。对两能级特例,本文结果与文献[9]一致。对均匀加宽极限的特例,本文给出的强度和强度谱分量的关系式与文献[4]的结果一致。

半焦在流化床燃烧中Cl元素影响CO氧化的试验

在非均匀布风的流化床燃烧系统中进行了半焦中添加PVC/NaCl的混烧试验,研究了Cl元素对燃烧中CO氧化的影响以及混烧时SO_x等污染物的生成规律.试验结果表明,半焦与PVC/NaCl混烧在技术上可行,添加Cl元素抑制CO氧化,加入PVC增加SO_2排放,而加入NaCl则减少SO_2排放.

Aplicación de la Lógica Dominante del servicio (LDS) en el sector turístico: el marketing interno como antecedente de la cultura de co-creación de innovaciones con clientes y empleados

[ES] Este trabajo trata de profundizar en la comprensión del concepto de marketing interno (MI), considerado como un recurso operante desde la óptica de la Lógica Dominante del Servicio (LDS), así como en su influencia en la obtención de resultados empresariales superiores a los de la competencia. Para ello, se examina el efecto del MI en la predisposición de las empresas analizadas a que sus clientes y empleados de primera línea participen en el desarrollo de innovaciones de servicio, ampliando de este modo, de acuerdo con la LDS, las oportunidades de co-creación de valor disponibles para las organizaciones. Para contrastar las hipótesis planteadas se aplica un análisis de ecuaciones estructurales a la información facilitada por los gerentes de 240 hoteles de una muestra de ámbito nacional.