We report photoluminescence spectra of C60 single crystals grown by vapor phase transport method using either the sealed ampoule technique or the open tube technique. The spectra for both types of samples show similar features, but different line resolution related to the two different growth techniques. An analysis of temperature and excitation intensity dependencies of the luminescence spectra is reported. The main structures of the spectra have been interpreted according to a model involving intramolecular polaron-exciton recombinations. In particular, emissions due to purely electronic transitions of singlet and triplet or the exciton and related vibronic recombinations have been resolved. At low temperature, emission bands due to X-traps have been observed on the high-energy side of the excitonic singlet purely electronic transition.

In the last decades, many vector control techniques have been developed for induction machine to increase their dynamic performances. But they are based on an accurate estimation of flux variables, which are not measurable in conventional induction machines. So, observer strategies are used in induction machine controls. Complex algorithms have been developed, but their long calculation time does not allow a simple implementation in digital form. For this reason, reduced-order observers are often used when a real-time estimation is implemented. If these structures lead to better flux estimations than in the case of an open-loop model, their convergence gains have to be determined and they are sensitive to the parameters value. The authors present a new analytical method to elaborate a reduced-order observer. The influence of the sampling rate is taken into account and the paper investigates the optimal gain, which minimise the sensitivity to the parameters value. In order to measure the observer robustness, the authors define two criteria, which are computed in steady state: the orientation error and the modulus error of the rotor flux. Some examples illustrate the theory and their calculation results are presented.

This paper proposes an approach to determine the gain of closed loop flux observer for an induction machine with respect to robustness and stability criteria. In the companion paper, a sensitivity analysis of flux observer has pointed out the influence of the sampling rate and the parameters mismatch. From this study, an accurate observer can be deduced. The analytical results are checked experimentally, in steady state and during transients. For that aim, an experimental rig has been installed. This paper deals also with a new description of the induction machine drive thanks to Causal Informational Graph. This description is useful for the simulation and for the implementation of the experimental rig.

The scattering of waves by random rough surfaces has important applications in remote sensing of oceans and land. The problem of developing a model for rough surfaces is very difficult since, at best, the scattering coefficient σ0 is dependent upon (at least) radar frequency, geometrical and physical parameters, incident and observation angles, and polarization. The problem of electromagnetic scattering from a random rough surface is analyzed using the Kirchhoff approximation (stationary phase, scalar approximation), the small perturbation model and the two-scale model. The first major new consideration in this paper is the polarimetric signature calculation as a function of the transmitter location and receiver location for a bistatic radio- link. We calculate the like- and cross-polarized received power directly using the scattering coefficients, without calculating the Mueller matrix. Next, the study of the regions of validity of the Kirchhoff and small-perturbation rough surface scattering models (in the bistatic case) is presented. Comparisons between the numerical calculations and the models are made for various of the surface height rms and correlation length both normalized to the incident wave number (denoted by σ and L, respectively). By using these two parameters to form a two-dimensional space, the approximate regions of validity are then established. The second major new consideration is the development of a theoretical two-scale model describing bistatic reflectivity as well as the numerical results computed for the bistatic radar cross-section from rough surfaces especially from the sea and snow-covered surfaces. The results are used to show the Brewster angle effect on near-grazing angle scattering.

The 3D modeling of thin structures by the finite element method leads to a high number of elements or elements of bad quality, which yields to badly conditioned problems. For the thin plates, shell formulations have been used by several authors. In the case of thin wires, we use a model of unmeshed conductor in which the current is unknown. Physics characteristics: resistance, inductance are integrated in the circuit equation. This article presents a method that extracts the inductance computation which introduced a singularity in the case of thin wires.

This article presents a new experiment aiming at BEC of metastable helium atoms. It describes the design of a high flux discharge source of atoms and a robust laser system using a DBR diode coupled with a high power Yb doped fiber amplifier for manipulating the beam of metastable atoms. The atoms are trapped in a small quartz cell in an extreme high vacuum. The trapping design uses an additional laser (repumper) and allows the capture of a large number of metastable helium atoms (approximately 109) in a geometry favorable for loading a tight magnetostatic trap.