Monopole-vortex complex in a theta vacuum

We discuss aspects of the monopole-vortex complex soliton arising in a hierarchically broken gauge system, G to H to 1, in a theta vacuum of the underlying G theory. Here we focus our attention mainly on the simplest such system with G=SU(2) and H=U(1). A consistent picture of the effect of the theta parameter is found both in a macroscopic, dual picture and in a microscopic description of the monopole-vortex complex soliton.Comment: 18 pages 3 figure

Non-orthogonal Theory of Polarons and Application to Pyramidal Quantum Dots

We present a general theory for semiconductor polarons in the framework of the Froehlich interaction between electrons and phonons. The latter is investigated using non-commuting phonon creation/annihilation operators associated with a natural set of non-orthogonal modes. This setting proves effective for mathematical simplification and physical interpretation and reveals a nested coupling structure of the Froehlich interaction. The theory is non-perturbative and well adapted for strong electron-phonon coupling, such as found in quantum dot (QD) structures. For those particular structures we introduce a minimal model that allows the computation and qualitative prediction of the spectrum and geometry of polarons. The model uses a generic non-orthogonal polaron basis, baptized the "natural basis". Accidental and symmetry-related electronic degeneracies are studied in detail and are shown to generate unentangled zero-shift polarons, which we consistently eliminate. As a practical example, these developments are applied to realistic pyramidal GaAs QDs. The energy spectrum and the 3D-geometry of polarons are computed and analyzed, and prove that realistic pyramidal QDs clearly fall in the regime of strong coupling. Further investigation reveals an unexpected substructure of "weakly coupled strong coupling regimes", a concept originating from overlap considerations. Using Bennett's entanglement measure, we finally propose a heuristic quantification of the coupling strength in QDs.Comment: 17 pages, 11 figures, 3 table

Research-oriented training for Italian teachers involved in the European MOSEM Project

A study on the specific knots of electromagnetic induction and superconductivity for in-service teachers has been carried out within the PCK theoretical framework (Shulman L. S., Educ. Res., 15 (1986) 4). The main knots listed in the literature were the object of an analysis in terms of teachers’ pedagogic behaviour in planning intervention work to overcome the learning problems and organizing class activities

Un approccio fenomenologico alla superconduttivit\ue0 e i processi di apprendimento degli studenti

Superconductivity is an important part of modern physics. Its discussion in school connects with that of electromagnetism, allowing experimental exploration aimed at the construction of phenomenological laws, describing it. In the framework of the Model of Educational Reconstruction, an educational path in vertical perspective was designed. It pass from the exploration of Magnetic and Electric Properties of Materials, to the construction of phenomenological laws, describing the superconducting state. Research experiments, conducted with more than 300 students from High Schools and monitored with the use of tutorials and pre / post questionnaires, document positive learning paths, in which the peculiar properties of superconductors are more often correlate each Other in models based on electromagnetism, rather than remain separate descriptors of phenomena

Conceptual metaphor in teaching/learning electric circuits for student teachers of primary school and kindergarten

Integration between cognitive linguistic aspects and physics has been performed in the Physics Education course of the Master's Degree for prospective primary teachers at the University of Udine in Italy. Conceptual metaphors have been introduced to the students, who were then invited to apply the ideas to the electric circuits. In this contribution we present some relevant results of this activity pointing out how students have worked with metaphors, gaining better conceptual understanding on the disciplinary topic

Conservation of charge to understand potential using on line charge measurements

Electric potential turns out to be one of the most difficult concepts in students’ learning: its role is not recognized either in electrokinetics or in electrostatics. In this area the transfer of charge between conductors is explained according to Coulomb’s law and looking at the same amount of an entity on them as a balancing factor. Moreover, students’ ideas often imply a lack of awareness about the conservation of charge. The inclusion of the idea of potential as a magnitude running the transfer of charge was planned in a vertical path on electrostatics using a strategy based on simple experiments. The need for repeated quantitative measurements, with good sensitivity, makes the on-line measure a determining factor