Microstructure and photocatalytic activity of APS coatings obtained from different TiO2 nanopowders

In recent years, intense research has shown that thermal spray techniques, especially atmospheric plasma spraying (APS), can be used to obtain nanostructured TiO2 coatings with effective photocatalytic activity. This study compares the photocatalytic activity of APS coatings obtained from different powders: two nanostructured TiO2 powders produced by spray-drying of two TiO2 nanosuspensions with different solids contents, one spray-dried powder obtained from a suspension comprising a mixture of submicronic and nanometric TiO2 particles and finally one commercial, nanostructured, TiO2 spray-dried powder. All powders were characterised by XRD, FEG-ESEM, granule size distribution, and a flowability evaluation. Feedstock powders were then deposited on austenitic stainless steel coupons using APS. Hydrogen or helium was used as secondary plasma gas. Coating microstructure and phase composition were characterised using FEG-ESEM and XRD techniques; coating anatase content was quantified by the Rietveld method. A significant amount of anatase to rutile transformation was found to take place during the plasma spraying process. In general, the coatings had a bimodal microstructure characterised by the presence of completely fused areas in addition to non-molten areas consisting of agglomerates of anatase nanoparticles. Results also showed that anatase content and porosity of the coatings largely depend on the secondary plasma gas nature, as well as on the characteristics of the feedstock. Finally the photocatalytic activity of the coatings was determined by measuring the degradation of methylene blue dye in an aqueous solution. A reasonably good fit of a first-order kinetic model to the experimental data was found for all coatings. The values of the kinetic constant were related to feedstock characteristics as well as to plasma spraying conditions. (C) 2012 Elsevier B.V. All rights reserved.Bordes, MC.; Vicent, M.; Moreno, A.; Moreno, R.; Borrell Tomás, MA.; Salvador Moya, MD.; Sanchez, E. (2013). Microstructure and photocatalytic activity of APS coatings obtained from different TiO2 nanopowders. Surface and Coatings Technology. 220:179-186. doi:10.1016/j.surfcoat.2012.08.059S17918622

Conducción de Calor en Placas Matalicas Perforadas. Parte 1: Modelo y Solución Debil en un Paso de Tiempo

Proponemos una formulaci6n dl!bil de un modelo de conducci6n de calor para Ia detecci6n de perforaciones en placas metalicas. Una discretizaci6n impHcita en tiempo produce un sistema leneal acoplado de ecuaciones diferenciales parciales. En cada paso de tiempo, el sistema se reduce a un problema de Helmholtz con condiciones de frontera tipo Robin y demostramos que su formulaci6n debil equivalente es un problema bien planteado.We propose a weak formulation of a heat conduction model for the detection of holes in metallic plates. An implicit discretization in time leads to a cou p l ed , linear system of partial differential equations. At each time step, the system reduces to a Helmholtz problem with Robin boundary conditions and we show that its equivalent weak formulation is a well-posedness problem

Modelo numérico de elementos finitos para la simulación de conducción de calor en placas perforadas de metal y materiales compuestos tipo carbono-carbono

In this work is presented a numerical model based on finite element method (FEM) for the simulation of heat conduction in perforated plates of metal and material composed of carbon fibers. For this, a mathematical model based on a type Robin boundary problem for the Helmholtz operator is proposed for demonstrating that it is a well-posed problem in the distributions sense. The numerical model was obtained through the equivalent variational problem and its discretization using the Courant finite element for a finite element mesh of size h. The numerical approach was of order h with respect to H1 norm and order h2 with respect to norm L2. Numerical simulations through a designed and implemented code in Matlab were done and thus, the profiles of temperatures were visualized for some test problems assuming a regular perforation in metal plates and carbon fiber materials. En este trabajo se presenta un modelo numérico basado en el método de los elementos finitos (FEM) para la simulación de la conducción de calor en placas perforadas de metal y de material compuesto de fibras de carbono. Para esto, se propone un modelo matemático que consistió en un problema de frontera tipo Robín para el operador de Helmholtz y se demuestra que está bien planteado en el sentido de distribuciones. El modelo numérico se obtuvo por medio del problema variacional equivalente y su discretización usando el elemento finito de Courant para un tamaño h de la malla de elementos finitos. La aproximación numérica fue del orden h respecto a la norma H1 y de orden h2 respecto a la norma L2. Se realizaron simulaciones numéricas mediante un código numérico en MATLAB y acá, se visualizaron los perfiles de temperaturas de algunos problemas de prueba en los que se supone una perforación regular en placas de metal y materiales de fibras de carbono

Education should be a fundamental right in colombia, analysis of program Ser Pilo Paga

La presente investigación se ha organizado en cuatro capítulos de la siguiente forma: al comienzo se presenta la contextualización de los fenómenos internacionales que han impactado en forma significativo en el tema de la educación en Colombia y al mismo tiempo, busca establecer cuál es el enfoque ideal para establecer que la educación sea un derecho. En seguida, muestra que la implementación de un modelo neoliberal en Colombia, logró transformar considerablemente el sistema de gobierno y en consecuencia, la educación. Acto seguido, incluye el análisis del programa Ser Pilo Paga, con sus beneficios y falencias. Por último, se incluye el desarrollo de una posible política pública efectiva cuyo objetivo es mejorar las temáticas que no fueron incluidas en el programa Ser pilo paga.Resumen…………………………………………………………………………………………..4 Introducción…………………………………………………………………………………….…5 1. La educación como un derecho fundamental…….…………………..…………………….…...6 1.1 Planteamiento del problema……….…………………………………………………….…….6 1.2 Formulación de la pregunta……………………………………………………………….…..9 1.3 Justificación…………………………………………………………………………………...9 1.4 Antecedentes……………………………………………………………………………..……9 1.5 Estado del arte………………………………………………………………………………..10 1.6 Objetivos……………………………………………………………………………………..13 1.7 Marco teórico………………………………………………………………………………...13 2. Fenómenos internacionales que direccionan el derecho a la educación………………………19 2.1 La globalización……………………………………………………………………………...19 2.2 La mundialización……………………………………………………………………………22 2.3 La educación como un derecho………………………………………………………………25 2.4 El derecho a la educación en Colombia……………………………………………….……..27 2.5 La globalización y el modelo neoliberal en Colombia..……………………………….…….28 2.5.1 Implementación del modelo neoliberal: ¿El fin de la educación como derecho?................31 2.5.2 La educación superior en Bogotá…………………………………………………………..33 3. La política pública del programa Ser pilo paga……………………………………………….35 3.1 Descripción del programa Ser pilo paga……………………………………………………..36 3.2 Problemática del programa Ser pilo paga……………………………………………………38 3.3 La cobertura………………………………………………………………………………….38 3.4 La calidad…………………………………………………………………………………….40 3.5 La equidad……………………………………………………………………………………44 4. Propuesta de una política pública en educación………………………………………………46 5. Conclusiones………………………………………………………………………………….49 Referencias………………………………………………………………………………………52 Listado de tablas…………………………………………………………………………………54This research has been organized in four chapters as follows: at the beginning, the contextualization of international phenomena that have a significant impact on the issue of education in Colombia is presented and, at the same time, seeks to establish the ideal approach to establish that education is a right. Then, it shows that the implementation of a neoliberal model in Colombia, managed to significantly transform the system of government and, consequently, education. Then, it includes the analysis of the Ser Pilo Paga program, with its benefits and shortcomings. Finally, it includes the development of a possible effective public policy whose objective is to improve the issues that were not included in the program Ser pilo paga.Pregrad

Role of process type and process conditions on phase content and physical properties of thermal sprayed TiO2 coatings

Thermal spray represents an advantageous technique for depositing large-area titanium dioxide coat- ings that are of interest for both traditional wear-resistant coatings as well as functional applications such as photo- induced decontamination surfaces. Numerous past studies have examined the phase evolution and properties of TiO2 coatings using different thermal spray processes or parameters. In this paper, an integrated study of thermal sprayed TiO2 was conducted with different thermal spray devices and process parameters for a single feedstock powder comprising the metastable anatase phase. The aforementioned variables are correlated with in-flight par- ticle state (particle temperature and velocity), phase evolution, and coating physical properties. The results are represented through the framework of process maps which connect process parameters with material properties. Based on the phase characterization, an initial exploration of the metastable phase evolution during thermal spray deposition of TiO2 is proposed. Furthermore, the sprayed TiO2 coat- ings show varying degrees of electrical conductivity associated with process-induced stoichiometric changes (vacancy generation) in the TiO2. The effects of these stoichiometric changes as well as extrinsic microstructural attributes (pores, cracks, interfaces), contribute to the complex electrical response of the coatings. This integrated study provides insights into the process–microstructure– property relationship with the ultimate goal of tailoring the functionality of spray deposited oxide thick films

Design and evaluation of a continuous flow, integrated nebulizer-hydride generator for flame atomic absorption spectrometry

An evaluation of the performance of a continuous flow hydride generator-nebulizer for flame atomic absorption spectrometry was carried out. Optimization of nebulizer gas flow rate, sample acid concentration, sample and tetrahydroborate uptake rates and reductant concentration, on the As and Se absorbance signals was carried out. A hydrogen-argon flame was used. An improvement of the analytical sensitivity relative to the conventional bead nebulizer used in flame AA was obtained (2 (As) and 4.8 (Se) µg L-1). Detection limits (3σb) of 1 (As) and 1.3 (Se) µg L-1 were obtained. Accuracy of the method was checked by analyzing an oyster tissue reference material

Between algorithm and model: different Molecular Surface definitions for the Poisson-Boltzmann based electrostatic characterization of biomolecules in solution.

The definition of a molecular surface which is physically sound and computationally efficient is a very interesting and long standing problem in the implicit solvent continuum modeling of biomolecular systems as well as in the molecular graphics field. In this work, two molecular surfaces are evaluated with respect to their suitability for electrostatic computation as alternatives to the widely used Connolly-Richards surface: the blobby surface, an implicit Gaussian atom centered surface, and the skin surface. As figures of merit, we considered surface differentiability and surface area continuity with respect to atom positions, and the agreement with explicit solvent simulations. Geometric analysis seems to privilege the skin to the blobby surface, and points to an unexpected relationship between the non connectedness of the surface, caused by interstices in the solute volume, and the surface area dependence on atomic centers. In order to assess the ability to reproduce explicit solvent results, specific software tools have been developed to enable the use of the skin surface in Poisson-Boltzmann calculations with the DelPhi solver. Results indicate that the skin and Connolly surfaces have a comparable performance from this last point of view