In situ atomic force microscopy observations have been carried out of thin films under external compressive stress. Straight-sided buckling patterns arise perpendicular to the compression axis which tend to attract one another during propagation a few hundred nanometers apart. The mechanisms whereby these debonding patterns interact have been investigated taking into account the elastic energy of both the film and the substrate. The equilibrium distance between two straight-sided wrinkles has been determined; good agreement has been obtained between the experimental results and the mechanics involved.

After deposition, by evaporation under vacuum, of Al/Cu/Te. multilayer structures, annealing at 673 K or more for half an hour, under argon flow, allows CuAlTe2 films crystallised in the chalcopyrite structure to be obtained. The optical and electrical properties are interpreted by introducing the influence of impurity foreign phases present in the films. The optical properties are sensitive to the small Al2O3 domains randomly distributed into the CuAlTe2 polycrystalline matrix. The optical band gap is slightly increased (2.35 eV) by the presence of alumina. The conductivity measurements show that a short circuit effect can be induced by a binary Cu $_{2-x}$ Te degenerate phase present at the surface of the films. This effect can be suppressed by KCN etching of the samples that allows the superficial foreign phase to be dissolved.

HfV2O7 powders were prepared by means of thermal decomposition of a mixture of vanadyl and hafnyl oxalates in air at 973 K. The room temperature structure and its evolution with temperature was investigated using both electron microscopy (TEM and HREM) and powder diffraction (X-ray and neutron) techniques combined with DSC measurements. HfV2O7 exhibits two temperature-induced phase transitions between room temperature and 480 K. Over the highest transition (370 K), HfV2O7 crystallizes in a cubic system with a cell parameter of 8.75 Å and $Pa\bar{3}$ space group. A negative thermal expansion is observed in this high temperature phase and can be correlated to anisotropic oxygen atom displacements. On the other hand, the room temperature structure of HfV2O7 is also described in a cubic symmetry, but the existence of superstructure reflections leads to a cell parameter three times larger than for the high temperature structure (~ 26.25 Å). Moreover, HREM calculations have shown that the atomic positions, usually used to describe the superstructures of the ZrV2O7 compounds, cannot be used in the case of HfV2O7 at room temperature.

Excited state absorption of laser (≅ 1.3 µm, corresponding to the $^4{\rm F}_{3/2}\to {}^{4}I_{13/2}$ laser channel) and pump (790-860 nm) radiation have been investigated in Nd doped YAl3(BO3)4 non-linear laser crystal. Laser gain slope efficiency measurements as a function of pump wavelength have been used to estimate the excited state absorption of pump radiation. On the other hand, excited state absorption cross-section in the 1300−1400 nm wavelength range has been measured by using two beam spectroscopy. We have obtained that excited state absorption cross-section for pump radiation is negligible whereas around 1.3 µm it is comparable to the stimulated emission cross-section from 4F3/2 state, so that the net gain cross-section becomes negative for certain wavelengths.

Several novel field emission devices are analyzed in a unitary way. The devices involve the use of field emitter arrays in a special configuration where the emitted electrons are subject to crossed electric and magnetic fields. Due to the acting electric and (magnetic) Lorentz forces, the electrons are either deviated or have a cycloid-like confined motion. The angular deviation of the electron trajectory can be used for measuring magnetic fields. The pulsed electron current produced by a cold cathode can be used to generate electromagnetic radiation. Because the electrons have a confined motion with a long trajectory length, their chance of hitting a residual gas molecule is increased. They can either excite gas molecules, which in turn emit UV-radiation when relaxing back to the stable state, or ionize them, the ionic current being correlated with the gas pressure. Accordingly, devices for generating UV-radiation and vacuum gauges can be devised. Furthermore, if the ion generation takes place in a narrow and well-defined region, then their angular deviation can be correlated with their mass. A mass spectrometer (with miniaturized dimensions and field emission electron source) can be devised on this principle.

The Scanning Transmission Electron Beam Induced Current Technique (STEBIC) was adapted to allow the analysis of local electrical activity in semiconductor diodes. This technique enabled us to analyse the in situ properties of IMPATT junctions (IMPact Avalanche Transit Time: which are Si doped $p^+/p/n/n^+$ multijunctions). The samples were thinned down as cross-sections, to be observed and analysed in transmission electron microscopy. The current induced by the electron beam was collected by the depleted zone. By synchronising measurements with each scan of the electron beam, the electrical activity can be viewed at a very local scale. The STEBIC signal was simulated by using a model of drift-diffusion. The prevailing role of the recombination rate on the form of the STEBIC profile was evidenced. We found that the spatial resolution of this method depends on the thickness of the sample and on the zone where the measurement is taken. We show that the spatial resolution of this method is optimal when the electron beam is localised in the p/n depleted zone. In thin areas, the maximum spatial resolution is calculated to be $\le 20$ nm. Outside the electric field the transport phenomena are governed by the diffusion of carriers and the signal width is widened.

In this paper, the viscoplastic regularization method is used to simulate strain localization in a compressed prismatical sample of Fontainebleau sandstone. First of all, the limits of Rice's formalism concerning the prediction of the localization band width and the post-bifurcation treatment are recalled. Then the theoretical aspects of the viscoplastic regularization method is reviewed. The non-objectivity or mesh-sensitivity of the solution is pointed out when a simple plastic model without viscosity is used. Finally, a fictitious viscosity parameter in the form of relaxation time is introduced in the model and regularizes the problem.

Forward solution studies have been performed using a cellular automata computer model. This computational procedure has been applied to simulate cardiac tissue activation and its corresponding magnetic field generated has been calculated. The propagation pattern associated with different mechanisms of atrial flutter arrhythmia has been simulated. For each simulated pattern of propagation, one has investigated the effect on the magnetic field generated, produced by the introduction of a conduction inhomogeneity due to a slow-pathway. This latter represents the site of successful ablation in the treatment of atrial flutter. The analysis of different computational images obtained allowed one to characterize the possibility of identification of regions of slow conduction in the simulated cardiac tissues.

We have developed a new prototype of microwave radiometric imaging devoted to the measurement of the temperature inside a dissipative media. The main application we are looking for, is the non-invasive thermometry of human tissues. We obtain quite satisfactory results in the early characterisation of breast tumours in terms of malignancy or benignity. We have, at this moment in progress, a clinical evaluation of patients that gives good results at an intermediary stage. To improve the spatial resolution, we have developed an inversion process based on a regularisation method in the spatial frequency domain, associated with a Deriche filter for threshold extraction. We show that this process is well suited to our problem and can be applied to clinical images for a quantitative retrieval of the temperature.

The first aircraft experiment with the wide-angle airborne laser ranging system has been conducted in May 1998 over a small network of 1 km2, equipped with 64 cube-corner retroreflectors. The ranging system was operated from a research aircraft (ARAT, Fokker 27) at an altitude of 1 km. Data have been collected during two 4-hour flights. The paper describes the data processing methods and presents the first results from this experiment. A precision of 2 cm has been achieved on the difference of vertical coordinates from two sets of ~ 3000 distance measurements. Results are consistent with simulations and a posteriori covariance. A drastic data sorting for outliers, due to strong overlap of reflected echoes, has been necessary. Hence, the actual number of measurements and the positioning precision became relatively small. Higher precision is expected in future experiments, once the instrument's link budget will be improved.