Halogen-induced charge transfer polymerization of pyrrole in aqueous media

Simultaneous polymerization and doping of pyrrole have been carried out in the presence of a halogenic electron acceptor, bromine (Br₂) or iodine (I₂), in aqueous dispersion or in a two-phase solvent system. The morphology of the polypyrrole (PPY) so produced is granular and porous. The electrical conductivity of the PPY-I₂ charge transfer (CT) complex is of the order of 10¹ ohm⁻¹ cm⁻¹ while that of the PPY-Br₂ complex is about one order of magnitude less. Both complexes are stable in the atmosphere. The physicochemical properties of the PPY-I₂ and PPY-Br₂ CT complexes prepared under various experimental conditions are examined in detail.     

Rapid determination of chlorophylls in vegetable oils by laser-based fluorometry

The presence of chlorophylls in vegetable oils is considered undesirable due to their adverse effects on oxidative deterioration, bleachability and hydrogenation. The usual methods for determination of chlorophylls in vegetable oils are absorption spectrophotometry, fluorometry and liquid chromatography using fluorescence detectors. This paper outlines a fluorometric method using a laser as the excitation source. The chlorophylls in crude palm oil, rapeseed oil, soya bean oil and olive oil were determined directly by laser-based fluorometry using (a) a helium-neon laser (632-8 nm, 5 mW) as the excitation source and an optical-multichannel analyser (OMA) with an intensified diode array as the detector, and (b) a helium-neon laser and a photomultiplier tube as the detector. The method is especially suitable for the detection of chlorophylls in crude palm oil since no pre-extraction step is required. The levels of chlorophylls measured in vegetable oils using the laser technique was also compared against values obtained by conventional spectrophotometric methods. The simplicity and rapid quantification of laser based fluorometry suggest that this technique can be readily applied to the detection or a wide variety of fluorescing species in vegetable oils.     

Explicit robust schemes for implementation of a class of principal value-based constitutive models: Symbolic and numeric implementation

The issue of developing effective and robust schemes to implement a class of the Ogden-type hyperelastic constitutive models is addressed. To this end, special purpose functions (running under MACSYMA) are developed for the symbolic derivation, evaluation, and automatic FORTRAN code generation of explicit expressions for the corresponding stress function and material tangent stiffness tensors. These explicit forms are valid over the entire deformation range, since the singularities resulting from repeated principal-stretch values have been theorectically removed. The required computational algorithms are outlined, and the resulting FORTRAN computer code is presented.     

A neural network control system with parallel adaptive enhancementsapplicable to nonlinear servomechanisms

In this paper, we present a technique for using an additional parallel neural network to provide adaptive enhancements to a basic fixed neural network-based nonlinear control system. This proposed parallel adaptive neural network control system is applicable to nonlinear dynamical systems of the type commonly encountered in many practical position control servomechanisms. Properties of the controller are discussed, and it is shown that if Gaussian radial basis function networks are used for the additional parallel neural network, uniformly stable adaptation is assured and the approximation error converges to zero asymptotically. In the paper, the effectiveness of the proposed parallel adaptive neural network control system is demonstrated in real-time implementation experiments for position control in a servomechanism with asymmetrical loading and changes in the load     

Enhancement of oxide break-up by implantation of fluorine inpoly-Si emitter contacted p+-n shallow junctionformation

In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p⁺-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF₂-implanted device is much larger than that of the boron-implanted device     

Study on the propagation of inlet flow distortion in axial compressor using an integral method

 An integral method is investigated and developed in the current work. The effects of the parameters of inlet distortions on the trend of downstream flow feature in compressor are simulated. Other than the drag-to-lift ratio of the blade and the inlet incidence angle, it is found that the distorted inlet velocity is another essential parameter to control the distortion in propagation. Based on this study, a novel critical distortion line and corresponding critical distortion factor are proposed to express the effect of the two essential inlet parameters on the propagation of distortion, namely, the inlet incidence angle and the distorted inlet velocity. From the viewpoint of compressor efficiency, the propagation of inlet flow distortion is further described by a compressor critical performance and its critical characteristic. The results present a useful physical insight to an axial flow compressor behavior and asymptotic behavior of the propagation of inlet distortion, and confirm the active role of compressor in determining the velocity distribution when compressor responds to an inlet flow distortion. Received: 20 December 2001 / Accepted: 21 August 2002 The authors would like to thank HQ RSAF for permission to publish this work, their financial support and encouragement. The first author wants to acknowledge Prof. Frank Marble of California Institute of Technology, for bringing the problem to the author's attention and for his helpful discussion.     

高职高专电工学课程教学改革

针对高职高专培养应用型人才的要求，分析了目前电工学课程教学的现状，提出了电工学课程改革方案。     

Pd-Ge contact to n-GaAs with the TiW diffusion barrier

Pd-Ge based ohmic contact to n-GaAs with a TiW diffusion barrier was investigated. Electrical analysis as well as Auger electron spectroscopy and the scanning electron microscopy were used to study the contact after it was subjected to different furnace and rapid thermal annealing and different aging steps. All analyses show that TiW can act as a good barrier metal for the Au/Ge/Pd/n-GaAs contact system. A value of 1.45 × 10⁻⁶ Ω-cm² for the specific contact resistance was obtained for the Au/TiW/Ge/Pd/n-GaAs contact after it was rapid thermally annealed at 425°C for 90 s. It can withstand a thermal aging at 350°C for 40 h with its ρ_c increasing to 2.94 × 10⁻⁶Ω-cm² and for an aging at 410°C for 40 h with its ρ_c increasing to 1.38 × 10⁻⁵ Ω-cm².