Students' Forms of Dialogue When Engaged with Contemporary Biological Research: Insights from University and High School Students' Group Discussions

Classroom dialogues have special educational value because they allow students to engage critically but constructively with each other’s ideas, solve scientific problems jointly and develop their scientific understanding. The present study focuses on how groups of twelfth-grade high school and university students communicate and co-operate through dialogue to solve a biological problem they have not encountered before. The specific research questions are as follows: (a) What are the dialogic structures that help students construct scientific explanations? (b) How does prior scientific knowledge support student dialogue in constructing explanations? A coding scheme was developed inductively for the analysis of participants’ utterances. We use illustrative exemplars from participants’ dialogues to discuss those aspects which might support explanatory reasoning. We focus on reasoned attention for contending opinions and striving for consensus that characterise cases of constructive dialogue. We also discuss observed objections and disagreements as triggering factors for constructive alternative explanations. Finally, we discuss the evidence showing that while prior knowledge supports student reasoning it can also hinder the ability of students to think in a creative way

Surface polaritons in magnetic metamaterials from perspective of effective-medium and circuit models

Surface waves are responsible for many phenomena occurring in metamaterials and have been studied extensively. At the same time, the effects of inter-element coupling on surface electromagnetic waves (polaritons) remain poorly understood. Using two models, one relying on the effective-medium approximation and the other on equivalent circuits, we studied theoretically surface polaritons propagating along an interface between air and a magnetic metamaterial. The metamaterial comprised split rings that could be uncoupled or coupled to each other in the longitudinal or transverse directions (along or perpendicular to the propagation direction). A metamaterial without inter-element coupling supported a single polariton. When a moderate longitudinal coupling was included, it changed the wave dispersion only quantitatively, and the results of the effective-medium and the circuit models were shown to agree at low wavenumbers. However, the presence of a transverse coupling changed the polariton dispersion dramatically. The effective-medium model yielded two branches of polariton dispersion at low values of the transverse coupling. As the coupling increased, both polaritons disappeared. The validity of the effective-medium model was further tested by employing the circuit model. In this model, surface polaritons could exist in the presence of a transverse coupling only if the boundary layer of the metamaterial included additional impedances, which could become non-Foster. The results reveal that the inter-element coupling is a major mechanism affecting the properties of the polaritons. They also highlight the limitations of using bulk effective-medium parameters for interface problems in metamaterials. I. INTRODUCTION </p

Surface polaritons in magnetic metamaterials from perspective of effective-medium and circuit models

Surface waves are responsible for many phenomena occurring in metamaterials and have been studied extensively. At the same time, the effects of inter-element coupling on surface electromagnetic waves (polaritons) remain poorly understood. Using two models, one relying on the effective-medium approximation and the other on equivalent circuits, we studied theoretically surface polaritons propagating along an interface between air and a magnetic metamaterial. The metamaterial comprised split rings that could be uncoupled or coupled to each other in the longitudinal or transverse directions (along or perpendicular to the propagation direction). A metamaterial without inter-element coupling supported a single polariton. When a moderate longitudinal coupling was included, it changed the wave dispersion only quantitatively, and the results of the effective-medium and the circuit models were shown to agree at low wavenumbers. However, the presence of a transverse coupling changed the polariton dispersion dramatically. The effective-medium model yielded two branches of polariton dispersion at low values of the transverse coupling. As the coupling increased, both polaritons disappeared. The validity of the effective-medium model was further tested by employing the circuit model. In this model, surface polaritons could exist in the presence of a transverse coupling only if the boundary layer of the metamaterial included additional impedances, which could become non-Foster. The results reveal that the inter-element coupling is a major mechanism affecting the properties of the polaritons. They also highlight the limitations of using bulk effective-medium parameters for interface problems in metamaterials. I. INTRODUCTION </p

Spectral enhancement in optical parametric amplifiers in the saturated regime

We present numerical and experimental studies on a front-end laser system for seeding a sub-picosecond multi-terawatt/petawatt light source based on two highly saturated optical parametric amplifiers. Numerical results showing energy gain, spectral gain, and stability as saturation is approached are presented. An experimental realisation of the system has been constructed, and its performance has been found to be in good agreement with the numerical simulations. The total gain is in excess of 105 over a few picosecond gain window, and the pulse energy is ∼100 μJ with 4 % root mean square stability. © 2013 Springer-Verlag Berlin Heidelberg