By using solid state ceramic synthesis technique, we have produced high-Tc superconducting ceramics with a fixed nominal composition of Bi1.7Pb0.3Sr2Ca2Cu3Oy (BSCCO). Annealing treatments in air at 800 °C for different time periods from 6 to 30 h were carried out for the BSCCO samples. The influence of annealing time on the superconducting and mechanical properties were examined by measurements of thermoelectric power (TEP), X-ray diffraction, surface morphology, bulk density and Vickers microhardness (V H N). The results reveal that the most appropriate annealing time to obtain the highest peak intensity of high-Tc phase (2223), highest and sharpest transition temperature ($T^0_{\rm c}$), maximum value of density and maximum of V H N is 18 h. Prolongation of the annealing time was associated with a reduction of all these parameters. These observations show that the annealing treatment plays an important role for producing consolidate superconducting compounds with improved mechanical properties.

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.

Some electrostrictive ceramics like 0.9 PMN-0.1 PT show large reduction of the apparent Young's modulus (more than 50%) as a function of the electric field. In the literature, this result is always obtained in the direction of the applied electric field. We performed some measurements of the elastic modulus in the direction perpendicular to the electric field and we found an unexpected small variation (less than 6%). This result shows that the apparent mechanical properties are much more dependent of the direction of the electrical field than known previously.

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.

A model is developed to describe the formation of metallic foams in which liquid drainage acts to collapse the foam before it can freeze. Numerical solution of the foam drainage equation, combined with the equations of heat conduction, provides new insight into the competition between these two processes. It also stimulates and confirms a theoretical analysis which leads to criteria for creating uniform samples of frozen metal foam. The analysis suggests new experiments to clarify the role of the various processes leading to foam formation.

The present study reviews the techniques suitable for twin characterisation in TSMTG-processed ceramics: Conventional Transmission Electron Microscopy, Scanning Electron Microscopy (backscattered electrons images), and X-ray diffraction (pole figures). Optical microscopy can not be used because twin spacing in the studied ceramics are smaller than this technique resolution. A difference between SEM looking like twins average spacing and TEM twins average spacing is pointed out and some explanations are envisaged. Concerning X-ray diffraction, rocking curves can not be used to characterise twins in textured ceramics, but pole figures allow qualitative measurements.

An interesting method based on a variable splitting into two time-scales, the “transient time harmonic method” is proposed allowing to compute transient phasor solutions of problems involving slow, close to quasi-static and fast dynamics simultaneously, yielding stiff properties. The time-step of the dynamic problem can be chosen larger than the fundamental time interval, resulting in an “envelope” model for the problem with the small time constant. The derivation of the FEM matrices is discussed. Examples, including a transformer operating a slow varying load and a transient coupled electromagnetic-thermal problem, are discussed.

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.

We present simulations of the transmission and reflection of narrow-extent pulses incident upon a chiral sculptured thin film (STF) along its axis of spirality, when the circular Bragg phenomenon is excited. Even though the frequency-domain reflection and transmission spectrums of a sufficiently thick chiral STF slab acquire final shapes within the Bragg regime, the shape and the duration of the transmitted pulse change with slab thickness over the entire range of our simulations. The emergence of a multiple-hump structure in the transmitted pulse is relevant to the use of chiral STFs in digital optics communication.

In this paper the dependence of the effective secondary emission coefficient-effective electron yield γeff in nitrogen on the reduced field (the ratio of the electric field and the gas density E/N) for various cathode surfaces is determined. Two different methods are applied: swarm measurements (from breakdown voltage) and time delay measurements. In the latter technique, first the breakdown probability is determined as a function of voltage and then γeff is derived from it. The results of applying both methods are in good agreement for the γeffversusE/N dependence. The measurements were made for copper cathode, untreated and treated by gas discharge and also several thousand electrical breakdowns, gold-plated copper and steel cathodes. Secondary electron yield γeff is of the order of a few percent at moderate and high E/N, and slightly increases with increasing E/N up to several kTd. At low E/N, a characteristic peak appears (at about 600 Td for copper). The γeff value increases when copper cathode is treated by gas discharges and becomes stable after several thousand breakdowns, agreeing well with other breakdown results in the literature. The chosen values for the Townsend primary ionization coefficient, obtained from best fits to available experimental data in the literature and the choice of the equilibration distance from the cathode significantly influence determination of γeff. Finally, our results are compared with the results of other authors for different cathode materials and a good agreement is found.

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.

Multilayers ceramic capacitors (MLCC) presenting non linear behaviours of their C(V) characteristics may have interesting applications in power electronics. Most of them have already been described. Nevertheless, the choice of a particular type instead of another one is all the more so difficult since, on one hand the physical mechanisms able to explain this behaviour is far from being understood. On the other hand, C(V) characteristics are in general obtained for low voltage values different from the ones they are going to be involved in. In this paper, direct in situ characterisations of different BaTiO3 based capacitors commercially available are achieved. The role of the capacitors' type (X7R,Z5U), of the temperature and of the voltage waveform (and more particularly its polarity) is demonstrated. Temperature values up to 200 °C are measured during normal operations in a RCD dissipative snubber without any alterations of the C(V) characteristics. All these results are discussed as regards the main physical properties of the constitutive materials in order to reach an optimisation of their use through an appropriate dimensioning.

Results on the deposition of aluminum nitride thin films on silicon (111) substrates by pulsed laser deposition are reported. A KrF excimer laser was used to ablate in vacuum an AlN target. The intensity and the repetition rate of the laser as well as the substrate temperature were varied and their effects on film properties were determined. The AlN films were characterized by several techniques such as in situ laser interferometry, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and transmission electron microscopy. At a deposition temperature of 500 °C and a laser intensity of 1 × 108 W/cm2, highly oriented AlN layers are deposited. Increasing the laser intensity leads to the presence of metallic Al in the films. As temperature is increased from 500 to 920 °C, the growth rate is found to decrease but the crystalline structure as well as the smoothness of the films are both significantly improved. It is also found that a reduction of the growth rate by varying the repetition rate from 30 to 10 Hz leads to a further improvement of the crystalline quality of the AlN layers.

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.

The evolution of initial perturbations in a plasma-filled system with a high current relativistic electron beam is considered. The beam current is assumed to be comparable or higher than the limiting vacuum current. The approach is based on equation for slowly varying amplitude of the induced waveform, which enable us to separate out the most intrinsic peculiarities of the overlimiting electron beam instabilities. An equation for slowly varying amplitude is derived and solved. An analytical expression describing space structure and development dynamics of the fields is obtained and analyzed. The well-known maximal growth rate of beam instability is actually the growth rate in the peak of induced wave train. Results are valid both for instability due to aperiodic modulation of the beam density in medium with negative dielectric constant and for instability due to excitation of beam wave with negative energy. Comparison with the case of a sublimiting beam is carried out.

It is necessary for the optimum design of arc quenching chamber in the molded case circuit breakers to analyze magnetic force acting on the arc in the chamber. The magnetic blowout forces and the distribution of magnetic field induced by arc current depend on the shape, arrangement, and kinds of material of grids in the chamber. The effective method to design V-slotted iron grid in the arc quenching chamber is discussed in this paper. The magnetic blowout force and flux density were obtained by using the 3-D finite element method considering non-linearity of iron grids. The grid model designed optimally was also verified by means of the interruption performances test. It is shown that our design method is a useful tool for design of arc quenching chamber in the circuit breakers.

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.

Metal-Insulator-Semiconductor Field-Effect-Transistors based on Dihexyl- quaterthiophene (DH4T), has been realized. Unlike conventional MISFET, these devices work through the modulation of an accumulation layer at the semiconductor-insulator interface. An analytical model that describes the operation of organic thin-film-transistors based on a simple trap distribution, with a single shallow trap level located between the valence-band edge and the Fermi level, has been used to determine some microscopic parameters such as the mobility, the density of traps and the corresponding level of traps.

We use a full quantum model of MOS (metal oxide semiconductor) structure to study the influence of a non-uniform doping profile of the substrate on the capacitance-voltage (C−V) behavior of the structure. For different “realistic” doping profiles, simulations are performed and compared to simulations with an uniform doping and to C−V measurements for samples with oxide thickness in the range [2−5 nm] [1]. In each case, we have extracted the oxide thickness that is found to be independent of the doping and the flat-band voltage which can be shifted up to 200 mV regarding the different profiles tested here. Moreover, below about 3 nm, the shape of the C−V simulation is more affected, which shows that the doping profile of the substrate has a great importance for an accurate C−V modeling of ultra-thin MOS structures.

The generation and the behavior of amorphous hydrogenated carbon particulates in a pure methane rf discharge have been studied for different methane flow rates (2−14 sccm) and different incident rf powers (40−120 W). Laser light scattering provides informations on their localization in the discharge. The 90° laser light scattered is used to determine the appearance times. The higher the incident rf power, the shorter the particulate appearance time: conversely the higher the methane flow rate, the higher the appearance time. The appearance times have been correlated to the inverse of the residence times of CH4 molecules. Good correlations have been observed between the particulate generation and the time evolutions of both laser beam extinction and dc self bias voltage. Whatever our experimental conditions, the influence of the methane flow rate seems lower than the rf power one. An increase of the rf power leads to a more important generation of particulates in the plasma.