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.

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.

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.

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.

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.

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.

An ultrasonic method using a large bandwidth transducer with a spherical lens and based on acoustic waves separation near the focal region is presented. The aim of this technique is to reduce the investigation size for non destructive mechanical properties evaluation. Compared to traditional acoustic microscopy (acoustic signature) the size of the analysed zone on the sample has been highly reduced. For instance, this technique has been applied on an aluminium sample with an acoustic frequency of 15 MHz. The Rayleigh wave velocity has been measured individually on grains smaller than one millimetre. Such local measurements would have required an acoustic lens working at higher frequency. All the efficiency of our experimental method and numerical signal processing has been proved by conclusive experiments on different materials such as glass, steel, silicon and uranium dioxide at different frequencies. This new method has also been tested at 100 MHz and we have demonstrated that its resolution was similar to performances of higher frequency acoustic microscopy working around 500 MHz. Furthermore our study shows that with this microdefocusing method, it is possible to assess directly from the same acquisition data Rayleigh, longitudinal and transverse velocities and consequently the elastic properties.