Student perspectives on the relationship between a curve and its tangent in the transition from Euclidean Geometry to Analysis

The tangent line is a central concept in many mathematics and science courses. In this paper we describe a model of students’ thinking – concept images as well as ability in symbolic manipulation – about the tangent line of a curve as it has developed through students’ experiences in Euclidean Geometry and Analysis courses. Data was collected through a questionnaire administered to 196 Year 12 students. Through Latent Class Analysis, the participants were classified in three hierarchical groups representing the transition from a Geometrical Global perspective on the tangent line to an Analytical Local perspective. In the light of this classification, and through qualitative explanations of the students’ responses, we describe students’ thinking about tangents in terms of seven factors. We confirm the model constituted by these seven factors through Confirmatory Factor Analysis

Etude comparative de protocoles de vaccination contre la maladie de Newcastle dans les élevages modernes de poules pondeuses au Sénégal

Plusieurs protocoles de vaccination contre la maladie de Newcastle sont utilisés au Sénégal sur les poulettes futures pondeuses en élevage moderne. Cependant, chaque année, cette virose se manifeste par des mortalités ou des chutes de ponte qui grèvent le budget des exploitants de la filière. Afin de déterminer l'efficacité de la prophylaxie médicale mise en oeuvre, il a donc été procédé à une comparaison des différents schémas de vaccination dans les conditions réelles de production. Il s'avère que les programmes vaccinaux comportant essentiellement des vaccins vivants fournissent une moins bonne protection que ceux qui ont recours aux vaccins inactivés huileux injectables, sans doute à cause du manque de technicité dans l'administration des vaccins vivants. Une primo vaccination associant un vaccin vivant administré individuellement par trempage du bec et une injection de vaccin inactivé huileux procure une bonne protection pendant les dix premières semaines de la vie. Une nouvelle injection à cette période permet d'assurer une couverture pendant toute la durée de l'élevage de la poulette et améliore l'effet de la vaccination par injection à l'entrée en ponte. Dès lors, aucun rappel n'est nécessaire jusqu'à la réforme des pondeuses. (Résumé d'auteur

Training Agricultural Research & Extension Staff to Produce and Communicate Agro-Climatic Information, to Enhance the Resilience and Food Security of Farmers and Pastoralists in Kiteto, Tanzania: Preliminary Findings from the GFCS Adaptation Programme in Africa

National Agricultural Extension Systems in ten districts in Tanzania and Malawi are receiving training in the production and use of climate services as part of a WFP-CCAFS joint activity within the GFCS Adaptation Programme in Africa. This document reports on the first training of intermediaries, conducted for 30 agricultural extension and NGO staff from Kiteto District, Tanzania, 13-17th October 2014 and draws lessons from this to feed forward into preparation and training in the remaining districts in 2015. Preparation for the course included analysis of historical climate information, as well as training of staff from the Tanzania Meteorological Agency in downscaling using the Climate Prediction Tool (CPT). The ensuing training course for intermediaries covered the Participatory Integrated Climate Services for Agriculture (PICSA) approach. This aimed to equip agricultural extension field staff to provide local historical climate information, seasonal and sub-seasonal forecasts (seamless forecasts) together with crop and livelihood information and to facilitate use of participatory decision making tools by smallholder farmers, in order to enhance farm and field-level decision making for resilience and food security. Training included a strong practical component. At the end of the training course agricultural extension officers and NGO staff developed plans for implementation in the locations that they work. Formal and informal feedback from participants was very positive. From this first training several improvements to feed into subsequent training in Tanzania and Malawi were identified and recommendations are made. These include: how to ensure that climate information for districts is analysed well in advance; appropriate crop and livestock management options are identified to cover variation within each district; climatic variability is adequately addressed within districts; and the potential benefits of CPT downscaled forecasting are fully explored

An experimental and modelling study of dual fuel aqueous ammonia and diesel combustion in a single cylinder compression ignition engine

The ability of ammonia to act as a hydrogen carrier, without the drawbacks of hydrogen gas-storage costs and low stability-renders it a potential solution to the decarbonisation of transport. This study combines both modelling and experimental techniques to determine the effect of varying the degree of aspiration of ammonium hydroxide (NH4OH) solution, at different engine loads, in the combustion of a compression ignition engine. Ignition delay was extended as ammonia injection increased, causing an increase in peak in-cylinder temperature, but generally lower combustion quality-increasing incomplete combustion products, while decreasing particle size. The higher peak in-cylinder temperatures generally correlated with a higher nitrous oxide (NOx) emissions in the exhaust, though fuel-bound nitrogen effect was apparent. Chemical kinetic modelling at equivalent conditions found increasing levels of unburnt ammonia with greater aspiration. Moreover, the ignitability of NH4OH was found to improve in simulations substituting diesel with hydrogen peroxide direct injection