Influence of flux creep on dynamic behavior of magnetic levitation systems with a high-T/sub c/ superconductor

Significant flux creep may be generated in some high-T/sub c/ superconductors with weak pinning, which could yield an influence on the dynamic behavior of a high-T/sub c/ superconductor-magnet levitation system. To investigate this influence, this article presents a numerical analysis of dynamic features of the levitation generated by an interaction between a high-T/sub c/ superconductor (HTSC) and a permanent magnet (PM) after the flux creep in the superconductor is taken into account in a macro-model of superconductivity. The influence is comprehensively displayed by comparing the predictions of dynamic responses of such systems in which the flux creep in the superconductor is and is not taken into account. The obtained results show that whether or not the flux creep results in a noticeable influence to the levitation of superconductor-magnet systems is mainly dependent upon properties of superconductivity and applied excitation, e.g., critical current density of superconductors, and amplitude and frequency of external excitations. When the critical current density is less than 4.5/spl times/10/sup 8/ A/m/sup 2/, and the system is subjected to a periodic excitation, the influence of flux creep should be taken into account in the theoretical analysis.     

枸杞子掺伪检测方法的研究进展

枸杞子以其药用价值和营养品质深受消费者的青睐,广泛应用于食品和保健品行业。但是市场上枸杞子恶意掺杂、掺假现象日益严重,此行为严重影响枸杞子品质、危害消费者健康、损害消费者权益、扰乱市场正常秩序,如何正确鉴别枸杞子真伪成为广大消费者普遍关注的问题。本文对枸杞子的主要掺伪现象进行了综述,并介绍了性状鉴别、显微鉴别、化学成分分析鉴别、分子生物学技术鉴别和基于红外光谱、近红外光谱和拉曼光谱法、机器视觉和电子舌等技术的快速检测方法在枸杞子品种和产地掺伪检测中的应用情况,对不同检测方法的优缺点进行对比分析。通过对枸杞子掺伪主要检测方法的比较,为市场监督枸杞子的品质提供理论基础和研究依据。     

Recommendations for toxicological investigations of drug-facilitated sexual assaults

The recent increase in reports of drug-facilitated sexual assaults has caused alarm in the general public and prompted forensic toxicologists from across North America to address the toxicological issues surrounding this matter. The authors have developed recommendations and guidelines to inform law enforcement, medical, and scientific personnel of the requirements for performing successful toxicological examinations in cases of drug-facilitated rape.     

The role of calcium in blended fly ash geopolymers

In this research effort, the role of calcium in geopolymers was investigated through a series of syntheses where a high-calcium fly ash was blended with a low-calcium fly ash. Increased calcium content led to accelerated set-up times, increased compressive strength, and increased product formation. Powder X-ray diffraction results showed the majority of that product to be geopolymer framework with only minor contributions from calcium silicate phases. Thermal analysis confirmed the absence of a calcium silicate hydrate phase. Analysis of fly ash dissolution showed that calcium aided in aluminosilicate dissolution and therefore the geopolymerization reaction. While aiding in this reaction, calcium became incorporated into the pore structure of the geopolymer as a counter-balancing cation, according to ion exchange experiments. Thus, geopolymer synthesis with increased calcium content through the use of a high-calcium fly ash under these experimental conditions produced a quick-setting, strong, calcium incorporated geopolymer material.     

Tensile behaviour of patch-repaired CFRP laminates

The present study examines the tensile behaviour of composite structures repaired by bonding external patches. Various patches of different stacking sequences placed on both sides of the parent plate were considered. Damage development and the failure process of the repaired plates were analyzed and a parent plate fracture model has been proposed. Optimised patch repairs were calculated by finite element modelling. It was found that high stress concentration along the longitudinal edges of circular patches and/or at the transverse edges of the hole leads to early damage initiation in the parent plate. However, the position of damage initiation and the process of damage progression depend particularly on the properties of repair patches. In order to optimise patch repairs, finite element modelling was used and it was founded possible to attain over 90% of the strength of an unnotched specimen. The optimised patch design can be characterised by an optimal strength ratio R^*, which should be minimized when selecting repair parameters.     

Pressure dependence of morphology and phase composition of SiC films deposited by microwave plasma chemical vapor deposition on cemented carbide substrates

SiC films were deposited on cemented carbide substrates by employing microwave plasma chemical vapor deposition method using tetramethylsilane (Si(CH₃)₄) diluted in H₂ as the precursor. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and scratching technique were used to characterize morphology, composition, phases present and adhesion of the films. Experimental results show that the deposition pressure has great influence on morphologies and phase composition of the films. In sequence, SiC films with a cauliflower-like microstructure, granular films with terrace-featured SiC particles coexisting with Co₂Si compound and clusters of nanometer SiC nanoplatelets appear as a function of the deposition pressure. In terms of plasma density and substrate temperature, this sequential appearance of microstructures of SiC films was explained. Adhesion tests showed that among the three types of films studied, the films with the terrace-featured SiC particles have relatively higher adhesion. Such knowledge will be of importance when the SiC films are used as interlayer between diamond films and cemented carbide substrates.     

May the force be with you [electrostatics applications]

Although commonly viewed as a serious hazard, static electricity can transform the effectiveness of many industrial processes. Here, the author reports on some of the latest developments in harnessing electrostatic forces     

Oxidative degradation of diethyl phthalate by photochemically-enhanced Fenton reaction

A kinetic investigation into the photo-degradation of aqueous diethyl phthalate by Fenton reagent was conducted in this study. The obtained results showed the enhancement of diethyl phthalate (DEP) decomposition by UV irradiation with the Fenton reaction. It was found that H2O2 concentration, Fe2+ concentration, and aqueous pH value were the three main factors that could significantly influence the degradation rates of DEP. The highest degradation percentage (75.8%) of DEP was observed within 120 min at pH 3 in the UV/H2O2/Fe2+ system, with original H2O2 and Fe2+ concentrations of 5.00 x 10(-4) and 1.67 x 10(-4)mol L(-1), respectively. The present study provides an effective approach to the treatment of wastewater containing DEP.