Synthesis,dielectric and magnetic properties of Mn-Ge substituted Co2Y hexaferrites

The substituted strontium Y-type hexaferrites Sr₂Co₂Ge_xMn_xFe_12−2xO₂₂ (X = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) was synthesized by sol–gel auto-combustion method. The crystal structures of the present materials were identified using X-ray diffraction analysis. The XRD patterns of the prepared samples pointed out the successful formation of Y-type hexagonal phase. The dielectric and magnetic properties have been studied for Ge-Mn substituted Y-type hexaferrites. The results showed that the dielectric parameters decrease with increasing frequencies. The values of magnetic parameters such as saturation magnetization, remanent magnetization and magnetic moment were found to decrease which are attributed to the weakening of super-exchange interactions. The values of Squareness ratio are found to be 0.48–0.56, which shows that the fabricated materials are multi domain. With decreasing dielectric parameters and increasing coercivity support these investigated samples have appealing applications in micro-wave devices, and Multilayer chip inductors.     

Coulomb bare interactions in inhomogeneous 4-layer graphene structures

We investigate Coulomb bare interactions in 4-layer graphene systems, taking into account the inhomogeneity of dielectric environment. By solving Poisson equation in momentum space, 16 elements of Coulomb potential tensor have been formed with analytical expressions. The formulae illustrate that Coulomb bare interactions in inhomogeneous 4-layer graphene system differ noticeably from those in homogeneous one. Nevertheless, both intra- and interlayer Coulomb potentials become independent with dielectric constants of contacting media, but they are decided by those of dielectric layer surrounding the system in long wavelength approximation. Besides, numerical results demonstrate that Coulomb bare interactions decrease considerably with the increase in carrier density in graphene sheets as well as their separated distance. In all investigations, the inhomogeneity of dielectric background should not be neglected for improvement in the model.     

On the thermal anisotropy affecting transfers in a multilayer porous mediumSur l'effet de l'anisotropie thermique sur les transferts dans un milieu poreux multicouches

An analytical model for studying double-diffusive natural convection within a multilayer anisotropic porous medium is developed and validated with respect to a direct numerical silmulation. The studied domain is composed of two horizontal porous layers where the lower one is thermally anisotropic and is submitted to a uniform horizontal heat flux and a vertical mass flux. The assumption of parallel flow is validated and the effect of anisotropy on dynamic transitions is investigated. To cite this article: R. Bennacer et al., C. R. Mecanique 332 (2004).     

Laser heating of multilayer assembly and stress levels: elasto-plastic consideration

Laser heating of multilayer assembly results in temperature profiles, which differ in each layer. Depending upon the material and laser pulse properties, high temperature gradients can occur. This, in turn, results in excessive stress levels in the region irradiated by a laser beam. When the magnitude of stress level exceeds the yield stress of the material, plastic deformation is resulted. In this case, elasto-plastic analysis should be applied when modeling the thermal stresses due to a laser heating pulse. In the present study, time exponentially varying pulse laser heating of four and two layer assemblies is considered. The four layer assembly composes of gold, chromium, gold and silicon while two layer assembly is formed from gold and silicon. The resulting temperature field is obtained numerically using a control volume approach. The elasto-plastic analysis employed to compute the stress levels in the substrate material. It is found that stress levels higher than the yield stress of the substrate material occurs in the surface region. This, in turn, results in plastic zone in this region. The size of the plastic region extends towards the solid bulk as the heating progresses.     

Combined action of anticonvection and thermocapillarity in two- and three-layer systemsAction simultanée d'anticonvection et de thermocapillarité dans des systèmes multi-couches

Anticonvection generated by the joint action of the external heating and heat sources (sinks) on the interface in the layers with finite thicknesses is studied. Anticonvective structures in fluid systems subject to the anticonvective instability only in the presence of heat sources (sinks) on the interface have been obtained. The nonlinear regimes of anticonvection in the system of three immiscible viscous fluids heated from above are investigated. The specific phenomena caused by direct and indirect interaction of anticonvective and thermocapillary mechanisms of instability are considered. In particular, different oscillatory configurations where anticonvection arises mainly near the upper interface and thermocapillary convection appears mainly near the lower interface, have been studied. To cite this article: I.B. Simanovskii, C. R. Mecanique 332 (2004).     

One-step synthesis and stabilization of gold nanoparticles and multilayer film assembly

Au nanoparticles (NPs) were synthesized in the one-pot procedure in water at room temperature with the wheel-shaped V^V-V^IV mixed-valence tungstovanadate [P₈W₄₈O₁₈₄{V₄^VV₂^IVO₁₂(H₂O)₂}₂]³²⁻ (V12) acting as both reducing and stabilizing agents. The V12 stabilized Au NPs (Au@V12 NPs) were characterized by SEM, TEM, DLS, UV-vis spectroscopy, XPS, and XRD analyses and the negatively charged surface of the Au@V12 NPs was proved by the zeta potential analysis. Based on the layer-by-layer assembly (LbL), the Au@V12 NPs-containing multilayer films have been fabricated on ITO-coated glass slide and quartz substrates with poly(ethyleneimine) (PEI). The regular growth of the multilayer films was monitored by UV-vis spectroscopy and cyclic voltammetry, the composition was characterized by XPS. The Au@V12 NPs based composite films showed electrocatalytic activities towards the reduction of dioxygen and the oxidation of methanol. This approach is expected to open the way towards procedures aimed at the one-step fabrication of Au NPs and polyoxometalates (POMs) into the multilayer films.     

Void fraction prediction in two-phase flows independent of the liquid phase density changes

Gamma-ray densitometry is a frequently used non-invasive method to determine void fraction in two-phase gas liquid pipe flows. Performance of flow meters using gamma-ray attenuation depends strongly on the fluid properties. Variations of the fluid properties such as density in situations where temperature and pressure fluctuate would cause significant errors in determination of the void fraction in two-phase flows. A conventional solution overcoming such an obstacle is periodical recalibration which is a difficult task. This paper presents a method based on dual modality densitometry using Artificial Neural Network (ANN), which offers the advantage of measuring the void fraction independent of the liquid phase changes. An experimental setup was implemented to generate the required input data for training the network.ANNs were trained on the registered counts of the transmission and scattering detectors in different liquid phase densities and void fractions. Void fractions were predicted by ANNs with mean relative error of less than 0.45% in density variations range of 0.735 up to 0.98 gcm⁻³. Applying this method would improve the performance of two-phase flow meters and eliminates the necessity of periodical recalibration.     

Local mismatch and noise investigation for pre and post multilayer pHEMTs

The key objective of this study is to investigate the local mismatch of pre and post multilayer structure on the active devices. Five pre and post multilayer structure pHEMTs on the same wafer within the same cell between adjacent devices are considered. As the study of local mismatch ensures good yields and a way to gain insights about the technology various comparisons are made including the effects of multilayer structuring. The threshold voltage, built-in potential and the net doping concentration of the 2-DEG of the devices are extracted through capacitance-voltage data. The underlying electrical parameter of the transistors as well as the RF figure of merit has been analyzed. The microwave noise related parameters namely minimum noise figure, associate gain, noise resistance, magnitude of the optimum reflection are also discussed and investigated. Centre-to-edge mismatch results in minor variation in performance between devices. These studies would help within the advancement of solid, proficient and low cost generation of future compact structure in 3-D multilayer MMICs.     

A mixed framework for transform domain Wyner–Ziv video coding

This paper presents a mixed framework based on an efficient intra key frame coding and an improved side information (SI) generation scheme in transform domain Wyner–Ziv (WZ) video coding. The performance of the WZ video coding strongly depends on the quality of the SI. The SI can be generated from the decoded key frames resulted from intra key frame video coding. The better the decoded key frames are the better would be the SI generation. In this paper, a Burrows–Wheeler transform (BWT) based intra-frame video coding is proposed to generate improved decoded key frames. Furthermore, an improved SI generation scheme with multilayer perceptron (MLP) is proposed. Comparative analysis with other standard techniques of WZ video coding reveals that the proposed scheme has better standing as compared to its counterparts in terms of both coding efficiency and improved perceptual quality.     

Extension of Reflectance and Transmission Coefficient Matrix to C-method for study of periodic multilayer system

The C-method is one of the most efficient and versatile method designed for diffraction gratings. The boundary conditions of the grating can be greatly simplified when the coordinate systems coincide with the surfaces of the grating. Reflectance and Transmission Coefficient Matrix (RTCM) with clearly physical concept is a powerful propagation algorithm proposed for steady and fast calculation of multilayer gratings. In this paper, the C-method is extended to treat the multilayer diffraction grating with the identical or nonidentical surface shapes. Numerical examples including diffraction efficiencies of both dielectric and metallic grating are presented. In addition, the excellent convergence for various adjacent-heights and diffracted orders of our propagation algorithm for TE and TM polarizations is also included.