Coherent absorption and enhanced photoluminescence in thin layers of nanorods

We demonstrate a large light absorptance (80%) in a nanometric layer of quantum dots in rods (QRs) with a thickness of 23 nm. This behavior is explained in terms of the coherent absorption by interference of the light incident at a certain angle onto the very thin QR layer. We exploit this coherent light absorption to enhance the photoluminescent emission from the QRs. Up to a seven- and fivefold enhancement of the photoluminescence is observed for p- and s-polarized incident light, respectively.Comment: Physical Review B 201

Estimating stellar oscillation-related parameters and their uncertainties with the moment method

The moment method is a well known mode identification technique in asteroseismology (where `mode' is to be understood in an astronomical rather than in a statistical sense), which uses a time series of the first 3 moments of a spectral line to estimate the discrete oscillation mode parameters l and m. The method, contrary to many other mode identification techniques, also provides estimates of other important continuous parameters such as the inclination angle alpha, and the rotational velocity v_e. We developed a statistical formalism for the moment method based on so-called generalized estimating equations (GEE). This formalism allows the estimation of the uncertainty of the continuous parameters taking into account that the different moments of a line profile are correlated and that the uncertainty of the observed moments also depends on the model parameters. Furthermore, we set up a procedure to take into account the mode uncertainty, i.e., the fact that often several modes (l,m) can adequately describe the data. We also introduce a new lack of fit function which works at least as well as a previous discriminant function, and which in addition allows us to identify the sign of the azimuthal order m. We applied our method to the star HD181558, using several numerical methods, from which we learned that numerically solving the estimating equations is an intensive task. We report on the numerical results, from which we gain insight in the statistical uncertainties of the physical parameters involved in the moment method.Comment: The electronic online version from the publisher can be found at http://www.blackwell-synergy.com/doi/abs/10.1111/j.1467-9876.2005.00487.

Towards mobile-centered authentic, personalized and collaborative assignments in engineering education

The last decade has seen a significant rise in the use of mobiles devices, such as smartphones, tablets, or laptops in all areas of society. Professionally, engineers collaborate with partners all over the world and this is made possible by mobile technology. In tertiary education, students learn in different settings, in and out of campus, in the train or at a café. Researchers have identified new possibilities for teaching and learning, afforded by the use of mobile technologies (and termed 'mobile learning'; ML). They claim that ML may (1) facilitate learning, formally or informally, in a place, at a time, and in a way preferred by students, (2) help students to become engaged in tasks that resemble authentic tasks in the workplace, and (3) facilitate student cooperation and collaboration. In this paper we present the first results of an ongoing project which aims to design and evaluate - for different engineering disciplines - prototypical ML assignments. We report on the results of a survey carried out at a Dutch University on the current use of and attitudes towards ML from both the instructors' and the students' perspectives. The results show that in various faculties at the university ML initiatives have been introduced in education and that there is a basis to create further opportunities for active student learning. We also present an outlook on the next stage of the project: the design of prototypical student activities from the respective engineering disciplines of the project partners: Mathematics, Physics and Built-Environment.</p