A characterisation of passive and active interactions and their influence on student's achievement using Moodle LMS Logs

During the last years, there has been much concern about learning management systems' (LMS) effectiveness when compared to traditional learning and about how to assess students' participation during the course. The tracking and monitoring capabilities of most recent LMS have made it possible to analyse every interaction in the system. The issues addressed on this study are: a) Is LMS student's interaction an indicator of academic performance?; b) Are different results in performance expected between distance and in-class LMS-supported education?; c) How can LMS interactions from logs be categorised?; d) May this categorisation detect 'learning witnesses'? To answer these questions, a set of interaction types from Moodle LMS activity record logs has been analysed during two years in online and in-class Master's degrees at the UPM. The results show partial or no evidence of influence between interaction indicators and academic performance, although the proposed categorisation may help detect learning witnesses.

Limiting properties in the characterisation of mixed recycled aggregates for use in the manufacture of concrete

El objetivo principal de este trabajo de investigación es estudiar las propiedades del árido reciclado mixto para la fabricación de hormigón reciclado en aplicaciones no estructurales. Se ha realizado la caracterización completa de 35 muestras de áridos reciclados mixtos gruesos de distinta calidad, procedentes de 13 plantas de tratamiento diferentes de la geografía española. Se han estudiado las correlaciones que existen entre las diferentes propiedades, en particular, con la absorción de agua, el contenido de sulfatos y la composición. Se propone una clasificación de los áridos reciclados y se limita de forma indicativa el contenido de yeso para que una muestra de árido reciclado mixto cumpla con la limitación del 0,8% de los sulfatos solubles en ácido de la Instrucción EHE-08. Recycling of construction and demolition waste (CDW) has become a widespread concern in Spain for the last years, as a way to preserve natural resources and achieve a better control of waste disposal sites.Specific applications which make use of mixed recycled aggregates are of great importance, as this types of aggregates constitute the majority of the total production. Structural and non-structural concrete is one of the possible applications, being this the main goal of our study. This paper presents a study on the physical and chemical characteristics of mixed recycled aggregates which have been obtained from different CDW treatment plants of Spain. Correlations between the different properties were investigated in order to find criterions of acceptance for recycled aggregates to be used in concrete. The comparison between the properties offers the possibility of pre-selecting a great quantity of mixed recycled aggregates, these being suitable for either structural and non-structural concrete. The determination of water absorption and the gypsum content are good indicators in order to evaluate the quality of the mixed recycled aggregates for its application in the production of concrete.

Operational characterisation of a Micro-SME producing farmhouse cheese in the south of Venezuela

A piece of research is presented that was conducted on the Guayanes Farmhouse Telita Cheese Producers Network located in the Piar and Padre Chien rural municipalities of Bolivar state in Venezuela. Guayanes telita cheese is a regional dairy product. The producers are to be found in a rural area with a high potential for marketing the label in the Southern Common Market (MERCOSUR). This market is the focal point of the strategic importance of this study for the Region and the Country. The research is of a descriptive scope conducted in the field. A questionnaire based on good food production practice was used as a data gathering technique. The final sample comprised 30 production units. Statistical processing was performed with version 15.2 of the STATGRAPHICS Centurion computational tool. The results would appear to confirm previous studies that point to the existence of factors that prevent these Micro-SMEs from guaranteeing the food safety of the product. The results indicate that new lines of research need to be opened up. These are oriented towards formulating strategies for the continuous improvement of these micro-SMEs, including quality control indicators.

Acoustic characterisation of cinema screens

As a consequence of cinema screens being placed in front of screen-speakers, a reduction in sound quality has been noticed. Cinema screens not only let the sound go through them, but also absorb a small amount of it and reflect the sound which impacts on the screen to the back, coming forward again in case it impacts on the loudspeaker. This backwards reflection in addition to the signal coming from the loudspeaker can lead to constructive or destructive interference at certain frequencies which usually results in comb filtering. In this project, this effect has been studied through researching amongst various data sheet provided by different manufacturers, acoustical measurements completed in the large anechoic chamber of the ISVR and some theoretical models developed with MatLab software. If results obtained with MatLab are accurate enough in comparison to the real measurements taken in the anechoic chamber this would lead to a good way to predict which would be the attenuation added to the system at each frequency, given that not all manufacturers provide an attenuation curve, but only an average attenuation. This average attenuation might be useless as sound waves have different wavelengths and its propagation through partitions varies. In fact, sound is composed by high and low frequencies, where high frequencies are characterised by a small wavelength which is usually easier to attenuate than low frequencies that characterised by bigger wavelengths. Furthermore, this information would be of great value to both screen manufacturers, who could offer a much more precise data in their data sheets; and customers, who would have a great amount of information to their disposal before purchasing and installing anything in their cinemas, being able to know by themselves which screen or loudspeaker should be best to meet their expectative. RESUMEN. La aparición de la digitalización de las bandas sonoras para las películas hace posible la mejora en la calidad de sonido de los cines. Sin embargo, un aspecto a tener en cuenta en esta calidad del sonido es la transmisión de éste a través de la pantalla, ya que normalmente tras ella se encuentran situados los altavoces. Las propiedades acústicas varían dependiendo del tipo de pantalla que se utilice, además de haber poca información a la que acceder para poder valorar su comportamiento. A lo largo de este proyecto, se analizan tres muestras de pantallas distintas donadas por distintos fabricantes para poder llegar a la conclusión de dependiendo del tipo de pantalla cuál es la distancia óptima a la que localizar la pantalla respecto al altavoz y con qué inclinación. Dicho análisis se realizó en la cámara anecoica del ISVR (University of Southampton) mediante la construcción de un marco de madera de 2x2 m en el que tensar las pantallas de cine, y un altavoz cuyo comportamiento sea el más similar al de los altavoces de pantalla reales. Los datos se captaron mediante cuatro micrófonos colocados en posiciones distintas y conectados al software Pulse de Brüel & Kjær, a través del cual se obtuvieron las respuestas en frecuencia del altavoz sin pantalla y con ella a diferentes distancias del altavoz. Posteriormente, los datos se analizaron con MatLab donde se calculó la atenuación, el factor de transmisión de la presión (PTF) y el análisis cepstrum. Finalmente, se realizó un modelo teórico del comportamiento de las pantallas perforadas basado en las placas perforadas utilizadas para atenuar el sonido entre distintas habitaciones. Como conclusión se llegó a que las pantallas curvadas son acústicamente más transparentes que las pantallas perforadas que a partir de 6 kHz son más acústicamente opacas. En las pantallas perforadas la atenuación depende del número de perforaciones por unidad de área y el diámetro de éstas. Dicha atenuación se reducirá si se reduce el diámetro de las perforaciones de la pantalla, o si se incrementa la cantidad de perforaciones. Acerca del efecto filtro peine, para obtener la mínima amplitud de éste la pantalla se deberá situar a una distancia entre 15 y 30 cm del altavoz, encontrando a la distancia de 30 cm que la última reflexión analizada a través de Cepstrum llega 5 ms más tarde que la señal directa, por lo cual no debería dañar el sonido ni la claridad del habla.

Non-destructive optical characterisation of fruits with time-resolved reflectance spectroscopy.

Increasing attention is being paid to the possible development of non-invasive tests for the assessment of the quality of fruits We propose a novel non-destructive method for the measurement of the internal optical properties of fruits and vegetables by means of time resolved reflectance spectroscopy in the visible and NIR range. A fully automated instrumentation for time-resolved reflectance measurements was developed It is based on mode-locked laser sources and electronics for time-correlated single photon counting, and provides a time-resolution of 120-160 ps The system was used to probe the optical properties of several species and varieties of fruits and vegetables in the red and NIR range (650-1000 nm). In most fruits, the absorption line shape is dominated by the absorption peak of water, centred around 970 nm Generally, the absorption spectra also show the spectral features typical of chlorophyll, with maximum at 675 nm In particular, for what concerns apples, variations in peak intensity are observed depending on the variety, the degree of ripeness as well as the position on the apple. For all the species and varieties considered, the transport scattering coefficient decreases progressively upon increasing the wavelength.

Automated characterisation of intergrowth textures in mineral particles. A case study

The characterisation of mineral texture has been a major concern for process mineralogists, as liberation characteristics of the ores are intimately related to the mineralogical texture. While a great effort has been done to automatically characterise texture in unbroken ores, the characterisation of textural attributes in mineral particles is usually descriptive. However, the quantitative characterisation of texture in mineral particles is essential to improve and predict the performance of minerallurgical processes (i.e. all the processes involved in the liberation and separation of the mineral of interest) and to achieve a more accurate geometallurgical model. Driven by this necessity of achieving a more complete characterisation of textural attributes in mineral particles, a methodology has been recently developed to automatically characterise the type of intergrowth between mineral phases within particles by means of digital image analysis. In this methodology, a set ofminerallurgical indices has been developed to quantify different mineralogical features and to identify the intergrowth pattern by discriminant analysis. The paper shows the application of the methodology to the textural characterisation of chalcopyrite in the rougher concentrate of the Kansanshi copper mine (Zambia). In this sample, the variety of intergrowth patterns of chalcopyrite with the other minerals has been used to illustrate the methodology. The results obtained show that the method identifies the intergrowth type and provides quantitative information to achieve a complete and detailed mineralogical characterisation. Therefore, the use of this methodology as a routinely tool in automated mineralogy would contribute to a better understanding of the ore behaviour during liberation and separation processes.

Characterisation of laser hybrid welded dissimilar joints

The investigation addresses the over-all performance of dissimilar joints of low carbon steel and stainless steel thin sheets achieved by laser hybrid welding. First, the technological de-velopment of dissimilar laser hybrid welding of thin sheets is briefly pre-sented. Joint characterisation by means of macro and microstructural examination and hardness tests is fur-ther described. Microhardness testing was used as an alternative and effi-cient mean of assessing the changes in mechanical properties of difficult to characterize areas, like HAZ and fu-sion zone of these thin sheets Laser-GMA dissimilar welded joints. The overall tensile performance of the joint is discussed together with the weld metal strength overmatching. The ten-sile tests results indicate that in case of transversally loaded joints, the po-sitive difference in yield strength between the weld metal and the base materials (overmatching welds) may reduce the weight of the structure, without diminishing its strength.

Optical characterisation of semi-transparent PV modules for building integration

A complete characterisation of PV modules for building integration is needed in order to know their influence on the building’s global energy balance. Specifically, certain characteristic parameters should be obtained for each different PV module suitable for building integrated photovoltaics (BIPV), some by direct or indirect measurements at the laboratory, and others by monitoring the element performance mounted in real operating conditions. In the case of transparent building envelopes it is particularly important to perform an optical and thermal characterization of the PV modules that would be integrated in them. This paper addresses the optical characterization of some commercial thin-film PV modules having different degrees of transparency, suitable for building integration in façades. The approach is based on the measurement of the spectral UV/Vis/NIR reflectance and transmittance of the different considered samples, both at normal incidence and as a function of the angle of incidence. With the obtained results, the total and zoned UV, visible and NIR transmission and reflection values are calculated, enabling the correct characterization of the PV modules integrated in façades and the subsequent evaluation of their impact over the electrical, thermal and lighting performance in a building.

Mechanical characterisation of tungsten-1wt.% yttrium oxide as a function of temperature and atmosphere

This study evaluates the mechanical behaviour of an Y2O3-dispersed tungsten (W) alloy and compares it to a pure W reference material. Both materials were processed via mechanical alloying (MA) and subsequent hot isostatic pressing (HIP). We performed non-standard three-point bending (TPB) tests in both an oxidising atmosphere and vacuum across a temperature range from 77 K, obtained via immersion in liquid nitrogen, to 1473 K to determine the mechanical strength, yield strength and fracture toughness. This research aims to evaluate how the mechanical behaviour of the alloy is affected by oxides formed within the material at high temperatures, primarily from 873 K, when the materials undergo a massive thermal degradation. The results indicate that the alloy is brittle to a high temperature (1473 K) under both atmospheres and that the mechanical properties degrade significantly above 873 K. We also used Vickers microhardness tests and the dynamic modulus by impulse excitation technique (IET) to determine the elastic modulus at room temperature. Moreover, we performed nanoindentation tests to determine the effect of size on the hardness and elastic modulus; however, no significant differences were found. Additionally, we calculated the relative density of the samples to assess the porosity of the alloy. Finally, we analysed the microstructure and fracture surfaces of the tested materials via field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In this way, the relationship between the macroscopic mechanical properties and micromechanisms of failure could be determined based on the temperature and oxides formed

Short communication. Collection and characterisation of a population of Triticum boeoticum Boiss., a wild wheat species not previously found in the Mediterranean western region

En julio del 2010 se recolectó una población de trigo silvestre en una zona abandonada cerca de Madrid, España. Esta zona posee una biodiversidad botánica elevada y un tipo de suelo muy peculiar denominado “arcillas verdes”. Se recogió una muestra de trigo y se multiplicó y caracterizó para varios caracteres agro-morfológicos y subunidades de gluteninas. El número cromosómico 2n de las semillas demostró que es una especie diploide de trigo y los datos de caracterización indicaron que es Triticum boeoticum Boiss. Esta especie llegó probablemente como mala hierba del cultivo de escaña que se producía en la zona hasta al menos la primera mitad del s. xix. Las características edáficas y climáticas del lugar y el hecho de que no haya referencias hasta ahora de esta especie en la zona oeste de la región Mediterránea aumentan el valor de esta adquisición para la mejora del trigo. La nueva accesión se conserva en el Centro Nacional de Recursos Fitogenéticos y se ha depositado una hoja de herbario en el Real Jardín Botánico de Madrid

Advanced Characterisation of a Coffee Fermenting Tank by Multi-distributed Wireless Sensors: Spatial Interpolation and Phase Space Graphs

The fermentation stage is considered to be one of the critical steps in coffee processing due to its impact on the final quality of the product. The objective of this work is to characterise the temperature gradients in a fermentation tank by multi-distributed, low-cost and autonomous wireless sensors (23 semi-passive TurboTag® radio-frequency identifier (RFID) temperature loggers). Spatial interpolation in polar coordinates and an innovative methodology based on phase space diagrams are used. A real coffee fermentation process was supervised in the Cauca region (Colombia) with sensors submerged directly in the fermenting mass, leading to a 4.6 °C temperature range within the fermentation process. Spatial interpolation shows a maximum instant radial temperature gradient of 0.1 °C/cm from the centre to the perimeter of the tank and a vertical temperature gradient of 0.25 °C/cm for sensors with equal polar coordinates. The combination of spatial interpolation and phase space graphs consistently enables the identification of five local behaviours during fermentation (hot and cold spots).

Characterisation of the operation & maintenance phase in PV rural electrification programmes

Con 1.300 millones de personas en el mundo sin acceso a la electricidad (la mayoría en entornos rurales de países empobrecidos), la energía solar fotovoltaica constituye una solución viable técnica y económicamente para electrificar las zonas más remotas del planeta donde las redes eléctricas convencionales no llegan. Casi todos los países en el mundo han desarrollado algún tipo de programa de electrificación fotovoltaica rural durante los últimos 40 años, principalmente los países más pobres, donde a través de diferentes modelos de financiación, se han instalado millones de sistemas solares domiciliarios (pequeños sistemas fotovoltaicos para uso doméstico). Durante este largo período, se han ido superando muchas barreras, como la mejora de la calidad de los sistemas fotovoltaicos, la reducción de costes, la optimización del diseño y del dimensionado de los sistemas, la disponibilidad financiera para implantar programas de electrificación rural, etc. Gracias a esto, la electrificación rural descentralizada ha experimentado recientemente un salto de escala caracterizada por la implantación de grandes programas con miles de sistemas solares domiciliarios e integrando largos períodos de mantenimiento. Muchos de estos grandes programas se están llevando a cabo con limitado éxito, ya que generalmente parten de supuestos e hipótesis poco contrastadas con la realidad, comprometiendo así un retorno económico que permita el desarrollo de esta actividad a largo plazo. En este escenario surge un nuevo reto: el de cómo garantizar la sostenibilidad de los grandes programas de electrificación rural fotovoltaica. Se argumenta que la principal causa de esta falta de rentabilidad es el imprevisto alto coste de la fase de operación y mantenimiento. Cuestiones clave tales como la estructura de costes de operación y mantenimiento o la fiabilidad de los componentes del sistema fotovoltaico no están bien caracterizados hoy en día. Esta situación limita la capacidad de diseñar estructuras de mantenimiento capaces de asegurar la sostenibilidad y la rentabilidad del servicio de operación y mantenimiento en estos programas. Esta tesis doctoral tiene como objetivo responder a estas cuestiones. Se ha realizado varios estudios sobre la base de un gran programa de electrificación rural fotovoltaica real llevado a cabo en Marruecos con más de 13.000 sistemas solares domiciliarios instalados. Sobre la base de este programa se ha hecho una evaluación en profundidad de la fiabilidad de los sistemas solares a partir de los datos de mantenimiento recogidos durante 5 años con más de 80.000 inputs. Los resultados han permitido establecer las funciones de fiabilidad de los equipos tal y como se comportan en condiciones reales de operación, las tasas de fallos y los tiempos medios hasta el fallo para los principales componentes del sistema, siendo este el primer caso de divulgación de resultados de este tipo en el campo de la electrificación rural fotovoltaica. Los dos principales componentes del sistema solar domiciliario, la batería y el módulo fotovoltaico, han sido analizados en campo a través de una muestra de 41 sistemas trabajando en condiciones reales pertenecientes al programa solar marroquí. Por un lado se ha estudiado la degradación de la capacidad de las baterías y por otro la degradación de potencia de los módulos fotovoltaicos. En el caso de las baterías, los resultados nos han permitido caracterizar la curva de degradación en capacidad llegando a obtener una propuesta de nueva definición del umbral de vida útil de las baterías en electrificación rural. También sobre la base del programa solar de Marruecos se ha llevado a cabo un estudio de caracterización de los costes reales de operación y mantenimiento a partir de la base de datos de contabilidad del programa registrados durante 5 años. Los resultados del estudio han permitido definir cuáles son costes que más incidencia tienen en el coste global. Se han obtenido los costes unitarios por sistema instalado y se han calculado los montantes de las cuotas de mantenimiento de los usuarios para garantizar la rentabilidad de la operación y mantenimiento. Finalmente, se propone un modelo de optimización matemática para diseñar estructuras de mantenimiento basado en los resultados de los estudios anteriores. La herramienta, elaborada mediante programación lineal entera mixta, se ha aplicado al programa marroquí con el fin de validar el modelo propuesto. ABSTRACT With 1,300 million people worldwide deprived of access to electricity (mostly in rural environments), photovoltaic solar energy has proven to be a cost‐effective solution and the only hope for electrifying the most remote inhabitants of the planet, where conventional electric grids do not reach because they are unaffordable. Almost all countries in the world have had some kind of rural photovoltaic electrification programme during the past 40 years, mainly the poorer countries, where through different organizational models, millions of solar home systems (small photovoltaic systems for domestic use) have been installed. During this long period, many barriers have been overcome, such as quality enhancement, cost reduction, the optimization of designing and sizing, financial availability, etc. Thanks to this, decentralized rural electrification has recently experienced a change of scale characterized by new programmes with thousands of solar home systems and long maintenance periods. Many of these large programmes are being developed with limited success, as they have generally been based on assumptions that do not correspond to reality, compromising the economic return that allows long term activity. In this scenario a new challenge emerges, which approaches the sustainability of large programmes. It is argued that the main cause of unprofitability is the unexpected high cost of the operation and maintenance of the solar systems. In fact, the lack of a paradigm in decentralized rural services has led to many private companies to carry out decentralized electrification programmes blindly. Issues such as the operation and maintenance cost structure or the reliability of the solar home system components have still not been characterized. This situation does not allow optimized maintenance structure to be designed to assure the sustainability and profitability of the operation and maintenance service. This PhD thesis aims to respond to these needs. Several studies have been carried out based on a real and large photovoltaic rural electrification programme carried out in Morocco with more than 13,000 solar home systems. An in‐depth reliability assessment has been made from a 5‐year maintenance database with more than 80,000 maintenance inputs. The results have allowed us to establish the real reliability functions, the failure rate and the main time to failure of the main components of the system, reporting these findings for the first time in the field of rural electrification. Both in‐field experiments on the capacity degradation of batteries and power degradation of photovoltaic modules have been carried out. During the experiments both samples of batteries and modules were operating under real conditions integrated into the solar home systems of the Moroccan programme. In the case of the batteries, the results have enabled us to obtain a proposal of definition of death of batteries in rural electrification. A cost assessment of the Moroccan experience based on a 5‐year accounting database has been carried out to characterize the cost structure of the programme. The results have allowed the major costs of the photovoltaic electrification to be defined. The overall cost ratio per installed system has been calculated together with the necessary fees that users would have to pay to make the operation and maintenance affordable. Finally, a mathematical optimization model has been proposed to design maintenance structures based on the previous study results. The tool has been applied to the Moroccan programme with the aim of validating the model.