Abstract. The growing awareness of serious difficulties in the learning of energy issues has produced a great deal of research, most of which is focused on specific conceptual aspects. In our opinion, the difficulties pointed out in the literature are interrelated and connected to other aspects (conceptual as well as procedural and axiological), which are not sufficiently taken into account in previous research. This paper aims to carry out a global analysis in order to avoid the more limited approaches that deal only with individual aspects. From this global analysis we have outlined 24 propositions that are put forward for debate to lay the foundations for a profound reorientation of the teaching of energy topics in upper high school courses, in order to facilitate a better scientific understanding of these topics, avoid many students' misconceptions and enhance awareness of the current situation of planetary emergency.

This study examined university engineering and physical science students' misconceptions of the nature of magnetic field. It is assumed that a significant knowledge of the sources of magnetic field is a basic prerequisite when students have to think about electromagnetic phenomena. To analyze students' conceptions, we have taken into account the fact that individuals build mental representations to help them understand the functioning of a physical system. These mental representations include different explanatory categories of reality in one same individual, depending on the context and the contents concerned. Therefore, we have designed an interview and an open-question questionnaire with an emphasis on explanations, so as to analyze the students' reasoning. We found that most of the students failed to identify the source of the magnetic field and they confuse magnetic force and magnetic field. It is concluded that although the questionnaire and interviews involved a wide range of phenomena, the misconceptions identified fall into four main categories of explanations which can inform curriculum development by identifying the strengths and weaknesses of the students' conceptions.

High Si contents in nodular cast irons lead to a significant volume fraction of retained austenite in the material after the austempering treatment. In the present work, the influence of the amount and morphology of this phase on the mechanical properties (proof stress, ultimate tensile strength (UTS), elongation, and toughness) has been analyzed for different austempering conditions. After 300 ЊC isothermal treatments at intermediate times, the austenite is plastically stable at room temperature and contributes, together with the bainitic ferrite, to the proof stress and the toughness of the material. For austenite volume fractions higher than 25 pct, the proof stress is controlled by this phase and the toughness depends mainly on the stability of ␥. In these conditions (370 ЊC and 410 ЊC treatments), the present material exhibits a transformation-induced plasticity (TRIP) effect, which leads to an improvement in ductility. It is shown that the strain level necessary to initiate the martensitic transformation induced by deformation depends on the carbon content of the austenite. The martensite formed under TRIP conditions can be of two different types: ''autotempered'' plate martensite, which forms at room temperature from an austenite with a quasi-coherent epsilon carbide precipitation, and lath martensite nucleated at twin boundaries and twin intersections.

The importance of the concepts of 'amount of substance' and 'mole' is supported by the abundance in the last decade of research papers on the problem of the teaching and learning of these concepts. The present study attempts a review of the relevant bibliography, including recent investigations on both the difficulties of learning these concepts and the didactic alternatives that are provided from different perspectives. The literature reviewed shows that students have great difficulty in handling the above concepts. In addition, a clear discrepancy exists between what is assumed as correct by the scientific community and the thinking of educators. Finally, strategies for the teaching of these concepts emerge.

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In this study the origin and evolution of the meanings of the concepts 'amount of substance' and 'mole' are described. Serious disagreements about these concepts amongst chemistry teachers and the recommendations of the international scientific community are identified. Attention is also drawn to the didactic implications that these epistemological difficulties may have for the teaching of chemistry.

The goal of this study is to identify students' difficulties with learning the concepts of electromotive force (emf) and potential difference in the context of transitory currents and resistive direct-current circuits. To investigate these difficulties, we developed a questionnaire based on an analysis of the theoretical and epistemological framework of physics, which was then administered to first-year engineering and physics students at universities in Spain, Colombia, and Belgium. The results of the study show that student difficulties seem to be strongly linked to the absence of an analysis of the energy balance within the circuit and that most university students do not clearly understand the usefulness of and the difference between the concepts of potential difference and emf.

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