Acoustic, piezoelectric, and dielectric nonlinearities of AlN in coupled resonator filters for high RF power levels

Coupled resonator filters (CRFs) are the new generation of BAW filters recently designed for the front-end modules of mobile transmission systems. Looking for designers' requirements, CRF devices have been characterized and modeled. The model based on equivalent circuits relies on material constants such as stiffness and electro-coupling coefficients, and works only for linear-mode propagation. Because of their positions between antennas and power amplifiers, they often work under high RF power, inducing nonlinear response in the AlN piezoelectric layer. In this work, we analyze for the first time the nonlinear behavior of AlN material particularly for coupled BAW resonators. To characterize the nonlinear effects in CRFs, we measure the 1-dB gain compression point (P1dB) and the intercept point (IP(3)). Then, we develop a nonlinear model of CRFs using harmonic balance (HB) simulation in commercially available software. The HB environment allows fitting simulations to measurements in terms of P(1dB) and IP(3). We find that a high RF power induces nonlinear changes in the material constants' real parts: elastic stiffness c(33) (4.9%), piezoelectric e(33) (17.4%), and permittivity ?(33) (5.2%). These nonlinear variations of material constants describe the nonlinear behavior of CRF devices using the same deposit process for AlN material.     

Solid respirometry to characterize nitrification kinetics: a better insight for modelling nitrogen conversion in vertical flow constructed wetlands

We developed an original method to measure nitrification rates at different depths of a vertical flow constructed wetland (VFCW) with variable contents of organic matter (sludge, colonized gravel). The method was adapted for organic matter sampled in constructed wetland (sludge, colonized gravel) operated under partially saturated conditions and is based on respirometric principles. Measurements were performed on a reactor, containing a mixture of organic matter (sludge, colonized gravel) mixed with a bulking agent (wood), on which an ammonium-containing liquid was applied. The oxygen demand was determined from analysing oxygen concentration of the gas passing through the reactor with an on-line analyzer equipped with a paramagnetic detector. Within this paper we present the overall methodology, the factors influencing the measurement (sample volume, nature and concentration of the applied liquid, number of successive applications), and the robustness of the method. The combination of this new method with a mass balance approach also allowed determining the concentration and maximum growth rate of the autotrophic biomass in different layers of a VFCW. These latter parameters are essential inputs for the VFCW plant modelling.     

泰国曼谷SOBRR斜拉桥的施工设计

详细介绍了泰国曼谷南外环线上主垮500 m的SOBRR叠合梁斜拉桥的主要施工方法,如节段的安装,悬臂施工主梁的水平锚固、边墩和边主梁联结、边跨平衡重及主跨的合龙等.     

Accurate large-signal GaAs MESFET and HEMT modeling for power MMIC amplifier design

This article describes, from an industrial user's point of view, how large-signal GaAs MESFET and HEMT modeling can be done accurately and efficiently for power MMIC amplifier design. The method is based on commercially available CAD tools enhanced by in-house software (e.g., small-signal parameter extraction, generation of load-pull contours). The Materka model is shown to predict accurately the large-signal characteristics of GaAs MESFETs, but not of pseudomorphic HEMTs. For these devices, a modified Angelov model is found to be adequate. A method for determining the numerous large-signal model parameters is presented. Model verification is achieved by comparing simulated and on-wafer measured data like static I(V)-characteristics, multiple bias S-parameters, gain compression characteristics, and load-pull contours. Results of device scaling and calculations of optimum load impedances are discussed. The close fit to the measured data proves that an excellent basis for large-signal power MMIC design has been established.     

Attraction personnelle et attraction sociale : Lorsque la saillance catégorielle annule la relation similitude-attraction.

Research on interpersonal attraction has repeatedly demonstrated that people are more attracted to similar others. In the present article, our goal is to show that this similar-attraction relationship is moderated by people's current level of self-categorization. Students were required to constitute work groups by selecting five classmates who shared to varying degrees similar attitudes. Under standard conditions (no group salience) participants' choice supported the similar-attraction relationship. However, when implicitly reminded of their gender identity, participants did not show anymore attraction to others who shared more similar attitudes. The results are discussed in terms of the self-categorization theory and suggestions are made to distinguish between two forms of attraction: interpersonal attraction and social attraction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of δ phase precipitation on the stress corrosion cracking resistance of alloy 718 in PWR primary water

The negative influence of δ phase on the intergranular stress corrosion cracking (IGSCC) resistance of alloy 718 is commonly taken for granted. In addition, δ phase formed at low temperature (about 1023 K) do not present the same characteristics than the one formed at higher temperatures (from 1173 to 1273 K). The aim of the present study is then to understand how δ phase precipitation could enhance crack initiation in alloy 718, whatever the form of δ phase is. For that purpose, several heat treatments leading to δ phase precipitation were realized on two alloy 718 heats, one sensitive to IGSCC and the second not. Specific slow strain rate tensile tests carried out on thin tensile specimens in simulated PWR primary medium at 633 K conclusively prove that δ phase has no effect on the intrinsic sensitivity to intergranular crack initiation of tested heats.     

Surface nano-aggregation and photocatalytic activity of TiO2 on H-type activated carbons

The main objective of this work is to detect any associative or synergistic effects between TiO₂ and activated carbon in 4-chlorophenol photodegradation. Different activated carbons (AC) were prepared from Tabebuia pentaphyla wood by means of physical activation with CO₂ or by extensive carbonization under N₂ flow at temperatures from 450 °C up to 1000 °C during 1 h. Results indicate a clear correlation between photocatalytic activities of titania with texture and surface chemistry of AC. Kinetic results of 4-chlorophenol photodegradation indicate that for most of mixed TiO₂ and AC solids a synergistic effect between both solids is observed. Surface nano-aggregation of TiO₂ on AC was observed by scanning electronic microscopy and dispersion of TiO₂ nanoparticles was improved as a function of more basic surface pH of AC. In conclusion, an increase of electronic density in carbon support clearly introduces an enhancement in titania's photoactivity for 4CP photodegradation. This beneficial effect indicates that it is possible to obtain clean water in a much shorter period of time by employing some selected AC in conjunction with TiO₂.     

Réalisation de filtres multidiélectriques sur un substrat biréfringent,déformable et de faible épaisseur (mylar)

La répartition spectrale d'un filtre interférentiel à bande étroite est fixée par le type d'empilement et le choix des diélectriques.Nous étudions une technique qui permet de changer le pouvoir de transmission d'un filtre terminé, en faisant varier l'épaisseur optique du substrat. Ce substrat, qui fait partie intégrante du filtre, est élastique et biréfringent. Cette variation peut être obtenue soit par déformation élastique du substrat qui entraîne une modification de l'épaisseur mécanique, soit par utilisation d'un polariseur qui permet de changer la valeur de l'indice utilisé.     

Services de transfert de données sur machines parallèles

We study in this paper the feasibility of using general purpose distributed memory parallel computers to implement some functions of high speed networks. We concentrate on the switching problem of the xtp high performance protocol (dealing with the network and transport layers of the osi stack), and on smds (switched multimegabit data service). We use methods and tools developed within the Pampa project (parallelizing methods, formal specification tools) to parallelize and prototype these kinds of switching systems on parallel architectures, and to make performance evaluations.