A study on the influence of tabletting pressure upon the internal morphology of Fe2O3-Cr2O3 catalytic system shows the behaviour of that system at crystallite level or even below it. On increasing tabletting pressure of catalytic powder, remanent stresses are left in the tablets formed which can be calculated in terms of the remanent strain. The macrostresses are constant and small at tabletting pressures ranging within 108 − 5 × 108 Pa and increase linearly between 6 × 108 and 14 × 108 Pa. The microstresses take measurable values only in samples tabletted at pressures higher than 7 × 108 Pa. Besides the formation of remanent stresses, the increase of tabletting pressure brings about the overall change of porous structure and mechanical resistance of the catalytic system. The remanent stresses that appeared at tabletting result in cracks along some planes which, in most instances, are parallel to the planar faces of tablets. The maximum acceptable tabletting pressure of the catalytic system studied amounts to 5 × 108 Pa.

The martensitic transition of a Cu-Al-Ni single crystal has been studied by isothermal mechanical spectroscopy and in situ transmission electron microscopy (TEM) observations. A damping instability (with time) has been found at low frequency at the beginning of the transition. At the same time, TEM study has evidenced the presence of thin martensite plates which appear just at the beginning of the (massive) martensite formation and growth. The martensite plate growth rate is quite low and non continuous. While high internal friction in the transition domain is usually associated with the mobility between martensite/austenite interfaces, the present internal friction anomaly has been ascribed to the unstable motions of the first martensite plates.

Hf70Cu25Rh5 and Hf70Cu25Ir5 amorphous alloys were prepared by a single roller melt-spinning method and the crystallization processes were studied by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. For both of the two alloys, the crystallization proceeds through the reactions of Am${\to}$I-phase${\to}$Hf2Cu+α-Hf, where Am and I-phase represent the amorphous and icosahedral quasicrystalline phases, respectively. Under optimum annealing conditions, the particle size of the I-phase is 10−25 and 10−20 nm for Rh- and Ir-containing alloys, respectively. Considering the fact that the crystallization process of Hf70Cu30 amorphous alloy does not accompany the precipitation of an I-phase, the present result demonstrates that the addition of Rh or Ir is significant. It is suggested that icosahedron-like atomic clusters exist in the amorphous state of Hf70Cu25Rh5 and Hf70Cu25Ir5 alloys, which serve as the seeds for the precipitation of the I-phase in the initial crystallization process.

Ga2Te3 has been prepared in bulk and thin film forms. The composition of films has been checked using energy dispersive X-ray (EDX) spectroscopy technique. X-ray diffraction (XRD) measurements have showed that the Ga2Te3 films evaporated at room temperature substrates were amorphous. Investigation of the I-V characteristics in amorphous Ga2Te3 films reveals that it is typical for a memory switch. The thickness dependence of the mean value of the switching voltage Vth is linear in the investigated range and Vth decreases exponentially with temperature in the range (298−393 K). The switching voltage activation energy (ε) calculated from the temperature dependence of Vth is found to be 0.277 eV. Electrical conduction activation energy ($E_{\sigma}$) is found to be (0.564 eV). The agreement between the obtained value of the ratio $\varepsilon/E_{\sigma}$ (0.49) and its value derived theoretically (0.5) suggests that the switching phenomenon in amorphous Ga2Te3 films is explained according to an electrothermal model for the switching process. The transmittance (T) of Ga2Te3 thin films, has been measured over the wavelength range 400−2500 nm. From an analysis of the transmittance data, the optical constants, the refractive index (n) and the extinction coefficient (k), have been determined. Similarly the absorption coefficient (α) measurements, have been evaluated. Allowed nondirect transitions with optical energy gap ($E_{\rm g}^{\rm opt}$) of 1.15 eV have been obtained.

Fuzzy logic offers nowadays an interesting alternative to the designers of non linear control laws for electrical or electromechanical systems. However, due to the huge number of tuning parameters, this kind of control is only used in a few industrial applications. This paper proposes a new, very simple, on-site tuning strategy for a PID-like fuzzy logic controller. Thanks to the experimental designs methodology, we will propose sets of optimized pre-established settings for this kind of fuzzy controllers. The proposed parameters are only depending on one on-site open-loop identification test. In this way, this on-site tuning methodology has to be compared to the Ziegler-Nichols one's for conventional controllers. Experimental results (on a permanent magnets synchronous motor and on a DC/DC converter) will underline all the efficiency of this tuning methodology. Finally, the field of validity of the proposed pre-established settings will be given.

The following calculation method permits the evaluation of the transverse distribution of the field amplitude Ψ(x,y,z) propagating in a waveguide. This method is based on a standard method for propagation in free space, which is using the Fast Fourier Transform (FFT). It is very simple in practice, and it does not require a mode decomposition for the waveguide propagation. It uses the properties of periodicity and symmetry of the FFT in the transverse plane in order to take into account the influence of the waveguide. The advantage of this calculation method is the full compatibility with the case of a guided wave (waveguide propagation), an unguided wave (free space propagation) and any intermediate regime where the guiding occurs softly or only in a limited part of the waveguide; for example when an input wave is not guided at the entrance of the waveguide, and becomes guided at the end. In practice, these conditions are observed experimentally for example in the infrared “Free Electron Lasers”, which are broadband tunable lasers, and some of them are using a waveguide, in the center of the optical cavity, coupled with free space areas. The calculation method presented here works in this special configuration. On the other hand, although not using a mode decomposition, this method allows also a rapid decomposition in eigenmodes TEpq and TMpq. Using only one symmetry operator and one FFT, it gives the whole set of mode amplitudes.

The goal of this study is a better understanding of the interaction between cells and a solidification front during a cryopreservation process. This technique of freezing is commonly used to conserve biological material for long periods at low temperatures. However the biophysical mechanisms of cell injuries during freezing are difficult to understand because a cell is a very sophisticated microstructure interacting with its environment. We have developed a finite element model to simulate the response of cells to an advancing solidification front. A special front-tracking technique is used to compute the motion of the cell membrane and the ice front during freezing. The model solves the conductive heat transfer equation and the diffusion equation of a solute on a domain containing three phases: one or more cells, the extra-cellular solution and the growing ice. This solid phase growing from a binary salt solution rejects the solute in the liquid phase and increases the solute gradient around the cell. This induces the shrinkage of the cell. The model is used to simulate the engulfment of one cell modelling a red blood cell by an advancing solidification front initially planar or not is computed. We compare the incorporation of a cell with that of a solid particle.

This paper presents the principle of an air wavelength standard for high accuracy length metrology. According to the definition of the Mètre, nanometric accuracy by interferometric measurement techniques can be reached only for measurements made under vacuum or by taking into account the fluctuations of the refractive index of air. We have developed a new type of laser source whose wavelength is insensitive to slow fluctuations of the refractive index of air. The sensitivity of our air wavelength standard to some characteristics (such as temperature, pressure, ageing behaviour...) has been measured. Results show that the relative uncertainty level of the wavelength of our source is below 10−8.

The same typographical error crept in the last term on the right sides of equations (19), (21) and (23) referred of the paper above. Please replace −1 by −δ (t). All other equations as well as our results are not affected. We regret any inconvenience caused by this error.

A transcription error crept in the last term on the right sides of equations (10), (12) and (14) of the referred paper above. Please replace −1 by $-\delta (t)$. All other equations as well as our results are not affected. We regret any inconvenience caused by this error.