The bandstructure of NiSb

The electronic bandstructure and the calculation of the density of states of NiSb using the APW-method have been performed. Some suggestions are given about d-like states and the position of the Fermi-energy. A new interpretation of the existing experimental data is made.     

MobileMath: exploring mathematics outside the classroom

Computer games seem to have a potential for engaging students in meaningful learning, inside as well as outside of school. With the growing availability of mobile handheld technology (HHT), a number of location-based games for handheld mobile phones with GPS have been designed for educational use. The exploitation of this potential for engaging students into meaningful learning, however, so far remains unexplored. In an explorative design research, we investigated whether a location-based game with HHT provides opportunities for engaging in mathematical activities through the design of a geometry game called MobileMath. Its usability and opportunities for learning were tested in a pilot on three different secondary schools with 60 12–14-year-old students. Data were gathered by means of participatory observation, online storage of game data, an online survey and interviews with students and teachers. The results suggest that students were highly motivated, and enjoyed playing the game. Students indicated they learned to use the GPS, to read a map and to construct quadrilaterals. The study suggests learning opportunities that MobileMath provides and that need further investigation.     

The bandstructure and optical properties of PtBi

By means of the APW-method the electronic bandstructure and the density of states of PtBi have been calculated. The spatial behaviour of the d-states has been investigated and the Fermi-level calculated. Experimental data, e.g. XPS, were used to test the results. Also a comparison was made with two closely related compounds PdSb and PtSn. Finally the optical properties of PtBi have been calculated from the collected numerical data, using the joint density of states and density—density correlation formalism.     

Optics of embedded semiconductor nano-objects using a hybrid model: bare versus dressed polarizabilities

The influence of the surrounding semiconducting matrix upon the optical response of embedded nano-objects (quantum dots) has been investigated. This system can be described by means of a hybrid model, where the full response is a combination of a macroscopic electrostatic response term and a dynamic response term, obtained quantum mechanically. The result is a modified discrete dipole model, where excess discrete dipoles having an excess polarizability with respect to a uniform background identical to the dielectric host material represent the response. In this model all electrodynamic interactions are screened by the host material. The electrostatic response is obtained by approximating the quantum dots by embedded dielectric oblate ellipsoids. Closed expressions for the electrostatic response of these ellipsoids have been derived. The electrodynamic nature of the dynamic quantum mechanical polarizability term however is unclear. It is not certain whether this polarizability is dressed or bare. Therefore we have investigated in detail the consequences of both options. Although there is no real qualitative difference between them, the difference is so large that experiment can easily discriminate between both. Results should be easily measurable anyhow.     

A one-wavelength,in situ alignment method for rotating analyser ellipsometers

The mathematical background and method of an in situ alignment method for rotating analyser ellipsometers, that requests only one wavelength, is described. The method is especially useful in combination with a microcomputer. As a further consequence a balancing technique is obtained that confines the error to the pure statistical fluctuations.     

Problem solving as a challenge for mathematics education in The Netherlands

This paper deals with the challenge to establish problem solving as a living domain in mathematics education in The Netherlands. While serious attempts are made to implement a problem-oriented curriculum based on principles of realistic mathematics education with room for modelling and with integrated use of technology, the PISA 2003 results suggest that this has been successful in educational practice only to a limited extent. The main difficulties encountered include institutional factors such as national examinations and textbooks, and issues concerning design and training. One of the main challenges is the design of good problem solving tasks that are original, non-routine and new to the students. It is recommended to pay attention to problem solving in primary education and in textbook series, to exploit the benefits of technology for problem solving activities and to use the schools’ freedom to organize school-based examinations for types of assessment that are more appropriate for problem solving.     

Mathematics standards and curricula in the Netherlands

This paper addresses the question of what mathematics Dutch students should learn according to the standards as established by the Dutch Ministry of Education. The focus is on primary school and the foundation phase of secondary school. This means that the paper covers the range from kindergarten to grade 8 (4~14 years olds). Apart from giving an overview of the standards, we also discuss the standards' nature and history Furthermore, we look at textbooks and examination programs that in the Netherlands both have a key role in determining the intended mathematics curriculum. In addition to addressing the mathematical content, we also pay attention to the way mathematics is taught. The domain-specific education theory that forms the basis for the Dutch approach to teaching mathematics is called “Realistic Mathematics Education” Achievement scores of Dutch students from national and international tests complete this paper. These scores reveal what the standards bring us in terms of students' mathematical understanding. In addition to informing an international audience about the Dutch standards and curricula, we include some critical reflections on them.     

Membrane modification to avoid wettability changes due to protein adsorption in an emulsion/membrane bioreactor

This study addresses problems encountered with an emulsion/membrane bioreactor. In this reactor, enzyme- (lipase) catalyzed hydrolysis in an emulsion was combined with two in-line separation steps. One is carried out with a hydrophilic membrane, to separate the water phase, the other with a hydrophobic membrane, to separate the oil phase. In the absence of enzyme, sunflower oil/water emulsions with an oil fraction between 0.3 and 0.7 could be separated with both membranes operating simultaneously. However, two problems arose with emulsions containing lipase. First, the flux through both the hydrophilic and the hydrophobic membranes decreased with exposure to the enzyme. Second, the hydrophobic membrane showed a loss of selectivity demonstrated by permeation of both the oil phase and the water phase through the hydrophobic membrane at low transmembrane pressure. These phenomena can be explained by protein (i.e. lipase) adsorption to the polymer surface within the pores of the membrane. It was proven that lipase was present at the hydrophilic membrane and that this, in part, explains the flux decrease of the hydrophilic membrane. To prevent the observed loss of selectivity with exposure to protein, the hydrophobic polypropylene membrane (Enka) was modified with block copolymers of propylene oxide (PO) and ethylene oxide (EO). These block copolymers act as a steric hindrance for proteins that come near the surface. The modification was successful: After 10 days of continuous operation the minimum transmembrane pressure at which water could permeate through an F 108-modified membrane was 0.5 bar, the same value as that observed in the beginning of the experiment. This indicates that loss of selectivity due to protein adsorption is prevented by the modification of the membrane.