Yttrium implanted and unimplanted various reference steels were oxidized at 700 °C, under controlled atmosphere (oxygen partial pressure: 0.04 Pa), for 24 h to observe the yttrium implantation and the addition element effects on steel high temperature oxidation behaviours. Yttrium implantation effects on reference steels were characterized using analytical and structural techniques such as Rutherford Backscattering Spectrometry (RBS), Reflection High Energy Electron Diffraction (RHEED), X-ray Diffraction (XRD) and Glancing Angle X-ray Diffraction (GAXRD). Yttrium implanted and unimplanted reference steel oxidation behaviours were observed by thermogravimetry and in situ high temperature X-ray diffraction. Our results clearly show that yttrium implantation and high temperature oxidation induced the formation of several yttrium mixed oxides which closely depend on the reference steel addition elements. Moreover, these yttrium mixed oxides seem to be responsible for the improved reference steel oxidation resistance at high temperature.

Measurements of the complex susceptibility, $\chi(\omega)=\chi'(\omega)-{\rm i}\chi''(\omega)$, as a function of the frequency (100 Hz–18 GHz) and polarizing field (0–90 kA m−1) at room temperature together with static magnetic measurements over the temperature range 4–300 K, are reported for a colloidal suspension of cobalt nanoparticles. The transition of the cobalt particles to the superparamagnetic state are supported by the temperature dependencies of field cooling (FC) and zero field cooling (ZFC) magnetization measurements. From these measurements, which show a typical blocking behaviour of an assembly of superparamagnetic particles with a wide distribution of blocking temperatures, the exponential pre-factor $\tau_0$ of Brown's equations for Néel relaxation, is found to be equal to 9.2 × 10−10 s. Measurement of the complex susceptibility $\chi(\omega)$ over this broad frequency range, with an upper frequency value corresponding to three times that previously reported in our measurements on cobalt, has enabled the presence of both resonance and Néel relaxation mechanisms to be identified. From the Néel component, a further value for $\tau_0$ was evaluated and shown to be in close agreement with that obtained from the ZFC data. Data on the after-effect function, realised by Fourier transformation of the $\chi''(\omega)$ component, is also presented.

The stability of compressed thin films on substrates is discussed in the frame of the Föppl-Von Karman theory of thin plate buckling. The destabilization from pre-existing straight-sided to worm-like patterns is investigated and a critical stress is determined, above which the morphological change of the film occurs. Experimental investigations by atomic force microscopy have been also conducted and the different stages of this evolution have been characterized.

Ultra thin film of Ag deposited using magnetron sputtering were found to be porous in nature and its porosity reduces with the increase in thickness. We present here some results on formation of periodic pattern having nano-size wire like structure on this porous film of Ag deposited on Si(001) substrate using the tip of the Atomic Force Microscope (AFM) cantilever. This pattern is induced by the interplay of tip-surface interaction and the adhesive force between the Ag particle and the substrate. The periodicity and growth direction of the wire like structure is mostly determined by the thickness of the deposited film. With the increase in thickness of the Ag film the growth direction of these wires changes from 45° angle to 90° angle to the scan direction. We have also observed that if the thickness of the deposited film is below a critical thickness then a carpet like growth occurs and beyond this critical thickness the film undergoes mound formation. The mound size increases as the thickness of the film increases. The onset of the mound growth inhibits the formation of the pattern induced by the tip of the AFM cantilever. This process of the pattern formation of the ultrathin films may have a wide application in the field of nanotechnology.

Thin films of Ge20Te80 and Cu6Ge14Te80 of different thicknesses are deposited on glass substrate by thermal evaporation under vacuum. The effect of incorporation of copper in Ge20Te80 film is studied by measuring the optical absorption. The mechanism of optical absorption follows the rule of direct transition. The films are annealed at different elevated temperatures from 370 to 520 K. The measurements were carried on as-deposited and annealed specimens. The optical energy gap (Eg) was found to decrease with increasing the annealing temperatures in the case of Ge20Te80 films. But in the case of Cu6Ge14Te80 films, Eg first increases with annealing temperature up to 410 K, then decreases sharply after further increasing the annealing temperature above the glass transition temperature. The decreases of Eg and the increase of the width of localized states Ee could be attributed to the amorphous - crystalline transformation. The values of optical energy gap Eg are also found to increase with thickness of both two-type films. The effect of films thickness on optical energy gap (Eg) of the films is interpreted in terms of the density of state model of Mott and Davis. The refractive index n, extinction coefficient k and dielectric constant $\varepsilon_{\rm i}$ and $\varepsilon_{\rm r}$ are also calculated for all samples.

An analytical model for the effective magnetic properties of a thin film consisting of a few layers of particles with arbitrary permeability and the stochastical initial magnetization is presented. The model is magnetostatic and implies the explicit averaging of the true field. It is shown that it works for all possible thicknesses of the film (arbitrary number of particles across the film) and there is no need for surface-to-bulk transition. The surface effect leading to the change of the reflective properties of the thin film compared to the prediction of the traditional theory is significant for a sparse arrangement of the grains and vanishes when these are touching. The method is verified by comparison with the model of the lattice of magnetic scattering centers.

The reflection and transmission of optical videopulses incident axially upon a slab of a chiral sculptured thin film (STF) is studied using a finite-difference simulation in the time domain. Videopulse bleeding is shown to occur when the handedness of the carrier plane wave matches the structural handedness of the chiral STF and the carrier wavelength lies in the Bragg regime.

In the present work, the stress-impedance and the stress-resistance for Co68.5Fe4.5Si12B15 amorphous ribbon are reported. The stress-impedance decreases with increasing tensile stress. In contrast, the large stress-resistance appears at high frequency. The value of $(R(0)-R(F))/R(0)$ with F = 20g can reach 31.4% at 5 MHz. The mechanism of the stress-impedance effect is also discussed.

This article proposes a methodology of design adapted to the optimal dimensioning of piezoelectric actuators. The study relates to a heterogeneous bimorph bar working in bending quasi-static mode. First an analytical model of the bimorph is established on the basis of classically allowed assumptions in theory of the beams and piezoelectricity. The field of validity of this model is then specified by comparison with a computer code by finite elements. Moreover the results obtained are validated and refined using measurements realised on a model of bimorph. The developed model is then exploited within a procedure of automated dimensioning founded on the implementation of a new method of Global Optimization. The possibilities of the developed method are finally illustrated through the dimensioning of a particular piezoelectric actuator intended for a vibratory magnetometric equipment.

The eddy current sensor method is widely used to evaluate conductive parts. The eddy current measurements are very sensitive to the variations of the sensor positioning relatively to the part under evaluation, which can disturb consequently such evaluation. The effect of the variation of the positioning of a sensor having an U-shaped magnetic core has been studied by 3-D finite element computations. The results show that the tilt and the lift-off of the sensor relatively to the part under evaluation induce similar straight lines in the normalized impedance plane. Consequently their effect can be corrected fairly thanks to a single processing. This notably allows to reduce the sensor handling during its calibration as well as the calibration time.

Triglycine sulphate, $(\rm NH_2CH_2CO_2H)_3\cdot H_2SO_4$ (TGS), is a ferroelectric crystal widely used in optical properties studies, phase transitions theory as well as test for experimental techniques. Lead monohydrogen phosphate, PbHPO4 (LHP), is a typical representative of the family of ferroelectric schultenites, suitable in testing microscopic theories of ferroelectricity. In this work the so-called high-accuracy universal polarimeter (HAUP) has been used to determine the natural anisotropy in the birefringent crystalline sections (010), obtaining the temperature dependence of optical anisotropy magnitudes of the crystal: gyrotropy, birefringence and optical indicatrix rotation. Our HAUP technique also permits to investigate the electro-optic (EO) coefficients associated to the phases above and below phase transition temperatures.

This paper is the third of a trilogy [16,75] devoted to polystyrene thin film treatment under DC pulsed discharges conditions. In order to study the wettability variations ($\Delta \theta/\theta_i$) of the surface, N2-Ar or O2-Ar mixtures are used. The experimental conditions are close to the best running conditions deduced from [16,75]. The pressure is varied from 1 mbar to 10 mbar and the mixture proportion from 0% to 100%. The importance of metastable states is pointed out. Reaction processes in the plasma and on the polystyrene surface are proposed in order to explain the surface activation and the formation of chemical bonds with nitrogen or oxygen. The best running conditions are reached when the generator frequency equals 500 Hz for a pressure about 4 mbar in nitrogen and 10 mbar in oxygen, whatever the gas mixture composition is. The wettability is better with oxygen than with nitrogen and the best value is reached for a duration time shorter in oxygen than in nitrogen. The minimum of treatment time necessary to reach the $\Delta \theta/\theta_i$ plateau value depends on the mixture composition.

The magneto-thermo-mechanical behavior of metals in inductive heating devices is investigated by means of numerical calculations. The goal of this paper is to attract attention to necessity of mechanical problems solution for inductive heating technology and to develop three-dimensional and two-dimensional (axisymmetrical) mathematical models, coupling algorithm and software for such computations. The paper presents a finite element formulation, based on an indirect coupling model of electromagnetic, thermal and static elastic-plastic mechanical processes in treated workpieces in inductive heating devices. The effect of electromagnetic, thermal and mechanical material properties depending on temperature is taken into account. The presented numerical technique is applied for technological problems of practical interest.

We describe a home made small angle light scattering apparatus. The detection is based on a high sensitivity 16 bits CCD camera placed in the focal plane of a lens. The apparatus is calibrated in such a way that it allows measurements of the scattered intensity in absolute values as a function of the scattering vector. Carefully characterized latex particle suspensions (determined size distribution and particle density number) are used to test the validity of calibrations. Particle scattering patterns in absolute units show good agreement with computed intensities using Mie theory. The apparatus performances are finally discussed.

Weakly nonlinear coupling comes from deterministic noises due to fixed boundaries and mean stochastic motion of molecular gases inside interior domains is investigated. The effect of deterministic surface wavy-roughness on molecular flows inside annuli with microfabricated solid walls was presented. The continuum-limit equations are being solved using perturbation methods with incorporated microscopic slip conditions along the small wavy-wall. The volume flow rate thus obtained, considering fully-developed parallel flow cases, contains terms which are related to the Knudsen number (Kn) of the fluid; the ratio of the inner to outer radius ($r_1/r_2$); roughness ratio (ϵ), phase shift (β) and wave number (k) of the small wavy-roughness elements. There are critical pairs (k,β) which tell us under certain Kn and larger $r_1/r_2$ cases, the trend for the second order volume flow rate is increasing or decreasing.

We have simulated the experimental spectroscopic charge pumping technique by the implementation of a model in the electrical simulator SPICE3F4. This model takes into account the temperature effect on the geometrical and electrical parameters of the studied transistor. The simulated results are in a good agreement with recent and different experimental results.

The correlation of deposition parameters with output functions when using a novel rotating cryostat (RC) system to produce magnetic materials has been investigated here. In order to do this, an orthogonal design technique was applied for magnetic material production using a resistively heated furnace. The results of orthogonal analysis indicate that the thickness uniformity across the film was not greatly improved, due to the large standard deviation, but an optimum deposition rate was obtained by appropriate choice of control parameters. Furthermore, the orthogonal design process was applied to systematically optimise the production of low coercivity in iron films. The results indicate that the process can be easily optimised.

The present work is aimed at studying both the entry length and the wall shear stress in a laminar steady flow of an incompressible Newtonian fluid. The fluid is conveyed through rigid straight tubes with axially uniform cross sections which correspond to the characteristic collapsed states. The cross section shapes have been defined from the collapse of an infinitely long elastic tube subjected to an uniform transmural pressure on its lateral surface. For each tube configuration, the Navier-Stokes equations are solved by using the finite element method for three Reynolds numbers. The numerical tests are performed with the same value of the volume flow-rate whatever the tube configuration. The maximum axial fluid velocity is used to define an index which aims to estimate the entry length. The results are described and analyzed in order to exhibit the link between the cross section shape, the velocity field and the wall shear stress in vessel configurations which mimic collapsed veins, especially when the opposite walls are in contact.

Biomaterials used in some bioreactors are porous and exposed to normal and tangential flow of physiological fluid. Flow-induced forces may influence the morphological and biochemical responses of cells adhering to these materials. The objective of this work is to examine the capacity of mechanical stress to cause changes in cell morphology via the cAMP pathway (cyclic adenosine monophosphate). This second messenger is known to modulate cell morphology in static conditions. In classical flow devices, cells are submitted to only tangential stresses. We designed a new flow system, a Hele-Shaw cell with a porous bottom wall, in order to take into account the influence of a transmural pressure. This flow chamber allows to follow up continuously the shape changes of cells that are adherent to a porous biomaterial (polyacrylonitrile) and are exposed to controlled levels of shear stress or transmural pressure. Mouse Swiss 3T3 fibroblasts exposed to a 1.1-Pa shear stress, as well as those exposed to a 84-mm Hg transmural pressure, round up (up to 50%) in a few minutes. If the cAMP pathway is inhibited when a mechanical stress is applied, cell rounding is significantly prevented. These observations suggest that flow-induced cell shape changes are cAMP-dependent. This conclusion is supported by an increased cAMP accumulation measured in cells under mechanical stress when compared to static experiments. Our in vitro flow system is thus useful to study the influence of transmural pressure or shear stress on the early morphological and biochemical responses of cells in contact with a biomaterial.

In this paper the finite-difference time-domain (FDTD) method is reviewed and then used to model and predict the geometric parameters used for the design of the device. The waveguide consists of a periodic array of air gap etched into a silicon (Si) strip on a silicon dioxide (SiO2) layer. The width and the depth of the grooves of the air gap (n = 1) as well as the length of the silicon layer (n = 3.4) are investigated. Using FDTD, the optical parameters are characterized. The effect of the air gap on the field profile distribution of the whole structure is calculated and performed in the range 0.09687 μm –1.55 μm. The field profile, and the response of the microcavity against frequency are calculated from sinusoidal sources. The spectral behavior of the structure is performed and its validity is verified by calculation of the reflectance spectra.