Effect of poling field on the aging rate of a strontium modified lead zirconate titanate

The effect of poling field on the d₃₃ aging rate at 25 and 200°C of a strontium modified lead zirconate titanate is presented.     

Use of functionalised silica in catalysis and organic synthesis

Uses of silica in the immobilisation of enzymes and functionalized reagents for resolution of racemic mixtures and synthesis of peptides, oligonucleotide and other compounds are discussed. Silica is superior over organic polymers in its high chemical stability, and being virtually nonswellable. This inhibits the influence of the solvent on physical and chemical behaviour of attached moeties and permits automisation of batch processes.     

Behavior of Bond-Critical Regions Wrapped with Fiber-Reinforced Polymer Sheets in Normal and High-Strength Concrete

This paper reports on the third phase of a multiphase study undertaken at the American University of Beirut (AUB) to examine the effect of fiber-reinforced polymer (FRP) sheets in confining tension lap splice regions in reinforced concrete beams. Results of the first two phases showed that glass and carbon fiber-reinforced polymer (GFRP and CFRP) sheets were effective in increasing the bond strength and improving the ductility of the mode of failure of tension lap splices in high-strength concrete (HSC) beams with nominal concrete strength of 70 MPa. The experimental results of the two phases were used to propose a new FRP confinement parameter, Ktr,f, that accounts for the bond strength contribution of FRP sheets wrapping tension lap splice regions in HSC beams. In this third phase of the AUB study, the trend of the results of phases 1 and 2 and the validity of the analytical model proposed were verified if normal-strength concrete (NSC) is used instead of HSC. Seven beams with nominal concrete strength of 27.58 MPa (4 ksi) were tested in positive bending. Each beam was designed with a tension lap splice in a constant moment region in the midspan of the beam. The main test variables were the configuration (1 strip, 2 strips, or a continuous strip) and the number of layers (1 layer or 2 layers) of the CFRP sheets wrapping the splice region. The test results demonstrated that CFRP sheets were effective in enhancing the bond strength and ductility of failure mode of tension lap splices in NSC in a very similar way to HSC. In addition, the FRP confinement index proposed earlier for HSC was proven to be valid in the case of NSC.     

Effect of edge shading on the performance of silicon solar cell

Non-uniform solar radiation incident on solar cells is of significant concern in cell performance. It may result in non-uniform cell local heating and borders de-activation. Edge shading is a problem occurring in photovoltaic concentrator systems, due to tracking low accuracy and misalignment. An increase in both open circuit voltage and fill factor resulted from shading the edges of the cell by opaque frames of different widths. On the contrary, short circuit current density showed a drop by introducing such frames, illustrating that cell shading is responsible for the formation of series and parallel sub-cells operating at different operating conditions.     

Spectrophotometric assay of 2,4-dienoyl coenzyme a reductase with 5-phenyl-2,4-pentadienoyl-coenzyme a as substrate

The spectrophotometric assay of 2,4-dienoyl coenzyme A (CoA) reductase (EC 1.1.1.34) was modified to improve the linearity and sensitivity of this method. 5-Phenyl-2,4-pentadienoyl-CoA, which has an absorbance maximum at 340 nm with an extinction coefficient of 44,300 M⁻¹ cm⁻¹, was synthesized and used as substrate. This compound is reduced by nicotinamide adenine dinucleotide phosphate (NADPH)-dependent 2,4-dienoyl-CoA reductase to 5-phenyl-3-pentenoyl-CoA. When a tissue homogenate serves as an enzyme source, the product is further metabolized by Δ³Δ²-enoyl-CoA isomerase (EC 5.3.3.8) to 5-phenyl-2-pentenoyl-CoA, which is hydrated to 5-phenyl-3-hydroxypentanoyl-CoA by enoyl-CoA hydratase (EC 4.2.1.17). The modified assay method, which measures the decrease in absorbance at 340 nm due to the reduction of 5-phenyl-2,4-pentadienoyl-CoA and the oxidation of NADPH, is linear for a longer period of time and is twice as sensitive as the conventional assay with 2,4-decadienoyl-CoA as substrate.     

Protective coatings for carbon bonded carbon fibre composites

Carbon bonded carbon fibre composites (CBCF) were modified by direct reaction with molten silicon in order to obtain a silicon carbide layer on the composite surface. Subsequently, the Si-infiltrated CBCF material was coated with a silica-based glass containing yttria and alumina by means of a slurry-dipping technique. On heat treatment the glass yielded a glass-ceramic layer thus giving a multi-layered oxidation and erosion protection system. The microstructural characterisation of the coating was conducted by standard microscopy techniques and by X-ray diffraction. The controlled crystallization of the glass-produced cristobalite, yttrium silicate (Y₂Si₂O₇, keiviite, β-form) and mullite as main crystalline phases. These are excellent ceramic materials for oxidation and erosion protection of SiC-coated carbon-based composites since their coefficients of thermal expansion (CTE) closely match that of SiC. The possibility of healing (closure) of micro cracks by a thermal treatment at 1375 °C, thus exploiting the viscous flow of the residual glass in the glass-ceramic, was explored in order to extend the service life of the protection system.     

Meaningful electronic signatures based on an automatic indexing method

Legal information certification and secured storage combined with documents electronic signature are of great interest when digital documents security and conservation are in concern. Therefore, these new and evolving technologies offer powerful abilities, such as identification, authentication and certification. The latter contribute to increase the global security of legal digital archives conservation and access. However, currently used cryptographic and hash coding concepts cannot intrinsically enclose cognitive information about both the signer and the signed content. Indeed, an evolution of these technologies may be necessary to achieve full text researches within hundreds or thousands of electronically signed documents. This article aims at describing a possible model along with associated processes to create and make use of these new electronic signatures called “meaningful electronic signatures” as opposed to traditional electronic signatures based on bit per bit computation.     

Hot-electron transport in In0.53Ga0.47As

A set of physical constants for In_0.53Ga_0.47As as required for transport calculations is obtained by reviewing the literature. Velocities for fields up to 100 kV/cm, calculated by the Monte Carlo method using these constants, are presented for the temperatures of 95 and 300 K. The calculated values are found to be in good agreement with the available experimental results.     

CMOS RF switched capacitor bandpass filter tuned by ring VCO

A new RF switched capacitor bandpass filter and its command circuit made up of a ring voltage controlled oscillator with ‘XOR’ gates are proposed. Implemented in a standard CMOS technology, this circuit is intended to be used in a subset of professional mobile phone applications [380–520 MHz]. Experiments carried out on a prototype show a tunable center frequency range of 260 MHz [240–500 MHz], with a quality factor that can be as high as 300.