Optimizing a Simple Natural Dye Production Method for Dye-Sensitized Solar Cells: Examples for Betalain (Bougainvillea and Beetroot Extracts) and Anthocyanin Dyes

We present a study about the sensitizers extracted from natural resources. This paper focuses on how to select, extract and characterize natural dyes, giving some guides to establish a protocol for the whole process of fabricating and using these dyes. The influence of the extraction solvent and method, and of parameters such as pH are analyzed. Also, dye precursor and dye extract stability have been studied, as well as how the dye adsorbs onto substrates and the effect of mixing or concentrating the extracts. Results concerning betalain pigments present in bougainvillea and beetroot extracts, and anthocyanins in eggplant extracts, analyzed by using UV-Vis spectrometry, are included. As an example of application, we report procedures intended to test and enhance the dye potential as a main component of dye-sensitized solar cells (DSSCs). DSSCs mimic nature’s photosynthesis and have some advantages like an easy and low-cost fabrication procedure. Their efficiency depends on its design and fabrication process and also on the different components involved. Hence, optimizing each component is essential to achieve the best performance, and thus the dye used as a sensitizer is crucial. We fabricate cells by using a simple procedure: As the interest is focused on the sensitizer, the same consecutive steps are followed, varying only the dye extract. Among all the natural-dyes tested, beetroot extract reaches up to 0.47% cell efficiency, which is near the highest values found in literature for this pigment

Análisis numérico de problemas tridimensionales de mecánica de la fractura

XII Congreso Nacional de Ingeniería Mecánica, celebrado en Bilbao en 1997El Método de los Elementos de Contorno se ha revelado en los últimos quince años como una de las herramientas más eficaces ( quizás la que más) para la resolución de problemas de Mecánica de la Fractura Elástica Lineal. Se presenta aquí un elemento de contorno singular con nodo a un cuarto que permite evaluar de manera muy sencilla y precisa Factores de Intensidad de Tensión en problemas tridimensionales de Mecánica de la Fractura. Para poder formular este elemento se ha desarrollado un procedimiento específico de integración que evita de una manera natural las singularidades de los núcleos de integración resultando muy sencillo y fiable el proceso de evaluación numérica de las integrales. Se han resuelto varios problemas tridimensionales a modo de ejemplo y se comprueba que los valores de los Factores de Intensidad de Tensión calculados son muy precisos

A Direct Approach for Hypersingular Integral Evaluation in 3-D B.E.M.

Ministerio de Ciencia y Tecnología PB96-1380Ministerio de Ciencia y Tecnología PB96-1322-C03-0

Una solución numérica eficiente para problemas dinámicos de mecánica de la fractura

XIV Congreso nacional de Ingeniería Mecánica, celebrado en Leganés en 2000Los problemas de Mecánica de la Fractura pueden estudiarse usando la formulación clásica de elementos de contorno combinada con la subdivisión del dominio por medio de contornos internos artificiales que no están únicamente definidos. La necesidad de emplear subregiones desaparece cuando se combinan la ecuación integral clásica y la ecuación integral en tracciones. Una de las principales dificultades que se derivan del uso de la representación integral de las tracciones es la evaluación de las integrales hipersingulares. En este trabajo las integrales hipersingulares se transforn1an analíticamente en integrales regulares que pueden evaluarse numéricamente. Se presenta la formulación e implementación efectiva de esta formulación mixta para problemas dinámicos armónicos tridimensionales de Mecánica de la Fractura. Se utiliza por primera vez la representación integral tridimensional de las tracciones para problemas de este tipo. Los ejemplos numéricos muestran la eficacia del modelo propuesto. Los resultados se comparan con los obtenidos por otros autores utilizando diferentes procedimientos.Ministerio de Educación y Cultura PB96-l 380Ministerio de Educación y Cultura PB96-l 322-C03-0

Anthracological analysis of the Cruz del Negro necropolis (Carmona, Sevilla)

Resultados que fueron presentados en el IV International Symposium on Computing and Archaeology, celebrado en Bilbao en 1998.Se analizan los carbones recuperados en 68 estructuras de combustión de la necrópolis de incineración de Cruz del Negro. Los resultados obtenidos se han sometido a varios análisis clúster para intentar descubrir, en primer lugar, si la aparición de las distintas especies esta condicionada por factores postdeposicionales y, en segundo, si la aparición de estas responden a la recogida y utilización selectiva de las mismas. A nivel paleoetnobotánico se han descubierto: conjuntos de estructuras que han utilizado las mismas especies vegetales como combustible para realizar la cremación de los cadáveres o ritos funerarios, asociaciones vegetales que pueden tener una distribución diferenciada en el entorno de la necrópolis y a nivel espacial zonas de la necrópolis caracterizadas por la aparición de varios taxones. A nivel paleoecológico se han determinado varias zonas con vegetación natural que parecen denotar unos parámetros bioclimáticos muy parecidos a los actuales, aunque quizás con un poco mas de humedad, posiblemente un ombroclima subhúmedo frente al seco actual.The carbon recovered at 68 combustion structures at the cremation necropolis of Cruz del Negro (Carmona, Spain) has been analysed. The results have been submitted to several cluster analyses to establish, firstly, whether the appearance of the different plant species is determined by postdepositional factors and, secondly, whether the appearance of these species relates to the gathering and selective use of them. In palaeobotanical terms, groups of structures were found to have used the same plant species as fuel in order to perform either cremations or funerary rites, and these plant associations may have had a differentiated distribution in the surroundings of the necropolis. In spatial terms, zones of the necropolis were characterized by the presence of various taxa. In terms of palaeoecology, various zones were determined to have had natural vegetation, apparently denoting bioclimatic parameters very similar to those of today, although perhaps with somewhat more humidity, possibly an subhumid umbroclimate as opposed to the present-day dry one

Evaluación y medición: Comparación de cuatro maneras de medición asistidas por ordenador. Un estudio estadístico

Este artículo describe un programa informático que genera y corrige pruebas de tipo test. Se constituye como un entorno abierto y flexible que puede ser actualizado y modificado a través de las bases de datos que contienen las preguntas de los diferentes temas. Posee distintos criterios de corrección que son analizados para comprobar su adecuación en la medición de los aprendizajes de un grupo de alumnos.This article describes software that generates and grades multiple choice tests. It consists of an open and flexible environment that can be updated and modified by means of databases containing discrete item questions for different units. It has different grading standards that are - analysed to check its accuracy measuring the uptake of a group of students

Analysis of the tensile fracture properties of ultra-high-strength fiber-reinforced concrete with different types of steel fibers by X-ray tomography

This study is concerned with the analysis of the tensile properties of an ultra-high-strength fiber-reinforced concrete manufactured with short and long steel fibers. The analysis involve using different techniques - from mechanical tests to X-ray computed tomography - to relate the observed variation of the mechanical properties of the mixes with their porosity. A comprehensive study of the porosity distribution was conducted on the basis of the analysis of X-ray computed tomography images and porosimetry. The study shows the influence of the type of fiber used in the reinforcement on the pore size and distribution of the concrete matrix and consequently on its tensile properties. The tensile properties are obtained with an inverse analysis method available in the literature that yielded the first-cracking tensile strength (f t ) and the ultimate tensile strength (f tu ) and related with the inner structure of the concrete matrix. Our results prove that the tensile properties, especially the first-cracking strength, vary depending on the fibers used. These findings help mix designers make a decision about the type of fibers that should be used when a high first-cracking tensile strength is needed and make it possible to quantify the effect of the fiber.Ministerio de Economía y competitividad BIA2016-75431-RMinisterio de Economía y Competitividad DPI2015-66534-RAcademia de Ciencias de la República Checa 16-18702

Teachers’ teleworking job satisfaction during the COVID-19 pandemic in Europe

This research takes insights from the job demand resource model to examine the teleworking job satisfaction of teachers for the period of COVID-19 pandemic. This study evidenced that teachers’ satisfaction with teleworking has been reduced as a consequence of the job demand increase. In contrast, access to adequate resources has allowed them to confront the challenges of teleworking, thus increasing their job satisfaction. The adverse efect of job demands on teleworking job satisfaction is bufered by job resources as teachers’ required extra means to confront unexpected and increased job demands. The technological gap between younger and older teachers was uncovered

Time harmonic and static crack problems in 3-D transversely isotropic bodies

Boundary Elements XXVI, ISBN 1-85312-708-6Three dimensional crack problems in transversely isotropic solids under static and time harmonic dynamic loading conditions are studied in this paper using a mixed BE approach. Hypersingular and strongly singular kernels appearing in the formulation are regularized prior to any discretization. Two different crack geometries are studied. Stress Intensity Factors are computed from the crack opening displacements at quarter-point quadratic elements. The results obtained in this paper show a good agreement with other results. The number of elements required is rather small.Ministerio de Ciencia y Tecnología DPI2000-1217-C02-01Ministerio de Ciencia y Tecnología DPI2001-2377-C02-0