a direct encoding for nnc polyhedra

We present an alternative Double Description representation for the domain of NNC (not necessarily closed) polyhedra, together with the corresponding Chernikova-like conversion procedure. The representation uses no slack variable at all and provides a solution to a few technical issues caused by the encoding of an NNC polyhedron as a closed polyhedron in a higher dimension space. A preliminary experimental evaluation shows that the new conversion algorithm is able to achieve significant efficiency improvements

The model of educational reconstruction – a powerful strategy to teach for conceptual development in physical geography: the case of water springs

Springs are an important hydrological concept because springs form an interface between underground and surface sub-systems of the hydrological cycle. Furthermore, springs are important suppliers of drinking water but are at risk today due to numerous anthropogenic interferences. The general knowledge of springs and their formation is usually rudimental and characterised by personal conceptions, which view springs as the release of water from large subsurface cavities. These conceptions are based on intuitive knowledge, and are tenacious and difficult to change. Based on the model of educational reconstruction (MER), a constructivist approach for the design of teaching–learning sequences aimed at changing the students’ intuitive conceptions, a learning environment about springs in mountain areas was developed. This paper describes the design process of the learning environment and the analysis of its efficacy with regard to persistent knowledge gains of 73 12-year-old students from lower secondary schools in Central Switzerland. Data gained from questionnaires, student drawings and texts were analyzed quantitatively in a repeated measure design using a pre-, post- and follow-up test. The gain in knowledge proved to be significant and remained stable on a high level during a period of two months