Fabrication and Characterization of 150-mm Silicon-on-Polycrystalline Silicon Carbide Substrates

Silicon-on-insulator (SOI) substrates can reduce radiofrequency (RF) substrate losses due to their buried oxide (BOX). On the other hand, the BOX causes problems since it acts as a thermal barrier. Oxide has low thermal conductivity and traps heat generated by devices on the SOI. This paper presents a hybrid substrate which uses a thin layer of polycrystalline silicon and polycrystalline silicon carbide (Si-on-poly-SiC) to replace the thermally unfavorable BOX and the silicon substrate. Substrates of 150 mm were fabricated by wafer bonding and shown to be stress and strain free. Various electronic devices and test structures were processed on the hybrid substrate as well as on a low-resistivity SOI reference wafer. The substrates were characterized electrically and thermally and compared with each other. Results showed that the Si-on-poly-SiC wafer had 2.5 times lower thermal resistance and exhibited equal or better electrical performance compared with the SOI reference wafer.     

Adaptive feedback linearization for position control of a switched reluctance motor: Analysis and simulation

In this paper a non-linear adaptive feedback-linearizing control is designed for a fifth-order model of a three-phase switched reluctance motor (SRM) which includes both electrical and mechanical dynamics. This non-linear adaptive control structure compensates for all the non-linearities between inputs and outputs, allows the use of a linear controller for motion tracking and improves the performance by reducing torque ripple of the SRM. A validated non-linear model of the SRM is used for the system simulation, while the control algorithm contains an adaptive scheme based on the parametrized model. Simulation results are given to demonstrate the effectiveness of the control method.     

Damage evolution and infrared thermography in woven composite laminates under fatigue loading

An analytical model based on cumulative damage has been used for predicting the damage evolution in composite materials. The model is verified with experimental data from a carbon/epoxy composite fatigued under tension–tension load. Fatigue tests of specimens have been monitored with an infra-red thermography system. By analysing the temperature of the external surface during the application of cyclic loading, it is possible to evaluate the damage evolution. The model agrees well with the experimental data, and it can be used to predict the evolution of damage in composites.     

Détermination expérimentale des propriétés hydriques des pâtes de ciment durcies—Mise en évidence des phénomènes d'hystérésis

Résumé Dans cet article, les auteurs comparent les propriétés structurales et hydriques de deux pates de ciment durcies, l'une ordinaire (CO) et l'autre (CH) représentative de bétons à très hautes performances dont l'utilisation est croissante à l'heure actuelle dans le domaine de la construction. L'analyse de la structure poreuse montre le caractère fortement compact de la microstructure de la pate de ciment durcie CH. Ce caractère est également illustré par les isothermes de désorption et d'adsorption de vapeur d'eau. Les courbes obtenues dans deux laboratoires sont comparées. Elles mettent en évidence la faible sensibilité des matériaux à très hautes performances vis-à-vis des variations de l'humidité relative de leur environnement, dans le domaine HR>50%. Ceci laisse prévoir des déformations hygrométriques (retrait de dessiccation) réduites dans ce domaine, par rapport aux matériaux ordinaires. Les résultats des mesures de perméabilité à la vapeur d'eau montrent l'influence du paramètre teneur en eau. La pate CH présente, dans le domaine des fortes humidités relatives, une perméabilité plus faible que celle de la pate CO. La perméabilité à la vapeur d'eau de ces pates de ciment durcies reste toutefois très faible par rapport à celle d'autres matériaux de construction.

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Experimental determination of moisture properties of hardened cement pastes, showing hysteresis effects

In this paper, the structure and moisture properties of two hardened cement pastes are compared. One paste (CO) is an ordinary mix. The other paste (CH) is representative of high-performance concretes which are today more and more widely used in construction. The pore structure analysis shows the very dense microstructure of the hardened cement paste CH. This feature is also pointed out with water vapour desorption and adsorption isotherms. The curves obtained in two laboratories are compared. They highlight that high-performance materials are fairly insensitive to environmental relative humidity variations, in the range RH>50%. Smaller hygral strains (drying shrinkage) can be expected in this range, as compared to ordinary mixes. The results of water vapour permeability measurements show the influence of the water content. The permeability obtained for the hardened cement paste CH is lower than for CO, in the high relative humidity range. The water vapour permeability of these hardened cement pastes is, however, very low as compared to other building materials.

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Note de la rédaction Mme V. Baroghel Bouny travaille au Laboratoire Central des Ponts et Chaussées (LCPC), Membre Titulaire de la RILEM.     

The nature and standard potential of the stannite ion in sodium hydroxide solutions

The nature of the stannite ion, produced by the anodic dissolution of tin, in sodium hydroxide solutions was determined by emf measurements. The results are best explained if the ion has the formula Sn(OH)^?₃. A new value for the standard potential of the reaction

$Sn{(OH)}_3^{?}(aq)+2e=Sn(s)+3{OH}^{?}(aq);E_{296}^0=0.880V$

is proposed.     

A comparative study between three sensorless control strategies for PMSG in wind energy conversion system

This paper presents a comparative study of sliding mode, artificial neural network and model reference adaptive speed observers for a speed sensorless permanent magnet synchronous generator (PMSG) in wind energy conversion system (WECS). Wind velocity and position sensorless operating methods for wind generation system using observer are proposed only by measuring phase voltages and currents. Maximum wind energy extraction is achieved by running the wind turbine generator in variable-speed mode. In addition the three speed observers are compared to verify the robustness against parameter variations.     

Moisture Effects on the Material Properties of a Jute/Epoxy Laminate: Impulse Excitation Technique Contribution

Natural fibers have enormous potential and offer many advantages. However, the lack of confidence in their structural performance has limited their wider adoption. Among concerns, include susceptibility to higher water absorption. The aim of this paper is to characterize the impact of the water absorption of jute/epoxy composite material using a new approach. This material has a potential to be used in automobile industries (door panels, dashboards, etc.) and in the civil engineering (skins of the sandwich panels in the building). The method of characterization used is original and based on the impulse excitation approach. The mechanical properties identified are correlated to those obtained by classical methods of characterization such as: three points bending and shear tests. Results show clearly that the rate of water absorption decreases physical (resonant frequency) and mechanical properties (Young’s modulus) of jute/epoxy laminate. At the mass saturation, we recorded a decrease in the proper frequency around 10%, and the Young’s modulus in this case loses 28% to 38% of its initial value. In addition, water bath temperature had an important impact on the coefficient of diffusion as well as on the degradation of mechanical properties.     

Interpreting the hydrogen adsorption on organic groups functionalized MOF-5s by statistical physics model

The hydrogen adsorption isotherms at equilibrium on four adsorbents (MOF-5 and three modified MOF-5s named, CH₃-MOF-5, Br-MOF-5 and Cl-MOF-5) were studied using a monolayer model with four adsorption sites energies. The analytical expression of this model was developed using the grand canonical ensemble in statistical physics by taking some working hypotheses involving some physicochemical parameters which can describe the adsorption process. These parameters are: four numbers of hydrogen adsorbed molecules per site (n₁, n₂, n₃ and n₄), four receptor site densities (N_M1, N_M2, N_M3 and N_M4), four saturation adsorbed quantities (Q₁, Q₂, Q₃ and Q₄) and four adsorption energies (??₁, ??₂, ??₃ and ??₄). The evolutions of these parameters in relation with temperature were discussed to understand and interpret the adsorption process at different temperatures. Fitting results revealed that the adsorption of hydrogen on MOF-5 is an exothermic physisorption process. The adsorption surface is inhomogeneous with many site energies. The fitting of the adsorption site is achieved by an aggregate of hydrogen molecules. The adopted model expression is used to derive the thermodynamic potential functions which govern the sorption mechanism such as entropy S_a, free enthalpy of Gibbs G and internal energy E_int.     

Compositional characteristics and aromatic profile of date palm seeds from seven varieties grown in Tunisia

This paper reports a discrimination study based on the physico‐chemical characteristics, fatty acids and profile of volatile compounds of the seeds from seven date palm varieties (Phoenix dactylifera L.) grown in Tunisia. Date seeds contained 10.49–14.76% moisture; 6.28–11.2% fat (on a dry weight basis); 2.67–12.85% protein; 0.91–6.06% reducing sugar; 0.61–2.98% sucrose and 0.97–1.17% ash. Gas liquid chromatography revealed that the oil fraction of the date palm seeds contained eighteen fatty acids, with oleic acid (30.77–42.50%) and lauric acid (18.51–27.48%) as the main unsaturated and saturated ones. Volatile profile showed differences among varieties. In total, forty‐five compounds were identified, mainly alcohols, aldehydes and unsaturated hydrocarbons ones. This study provides evidence that the seeds of date may be a potential source of valuable nutrients with interesting functionality.