In-situ phase mapping and transformation study in fusion welds

Spatially resolved X-ray diffraction (SRXRD) technique has been applied using synchrotron radiation to map the phases present in fusion welds in situ with a sub-millimetre resolution. For titanium, exhibiting an allotropic transformation from a hcp α-phase to a bcc β-phase at ∼922°C, the following results have been obtained for the heat-affected zone (HAZ). (i) Co-existence of both α- and β-Ti phases in the HAZ as derived from the phase concentration profiles. (ii) The width of the HAZ was found to be 3.33±0.33 mm as defined by the existence of the high-temperature bcc phase in this zone. (iii) Peak profile and ex-situ post-weld ESCA analyses revealed additional hcp patterns attributable to two TiOx phases formed in an overlayer during the welding process by oxygen diffusion from the ambient at high temperature. The thickness of this TiOx overlayer varied from 50–85 nm, increasing towards the weld pool. The SRXRD technique provides real-time chemical dynamics and in situ phase mapping data for modelling of kinetics of phase transformation and microstructural evolution in allotropic and other more complex systems, under steep thermal gradients and non-isothermal materials processing conditions. This revised version was published online in November 2006 with corrections to the Cover Date.     

Nature of Intergranular Phase in Nonohmic ZnO Ceramics Containing 0.5 Mol% Bi2O3

The intergranular phase obtained by sintering a binary mixture of ZnO + 0.5 mol% Bi₂O₃ was isolated by using a dilute solution of HCIO₄, which etches ZnO preferentially. The combined results of selected-area electron diffraction and microscopy, microprobe analysis, and X-ray diffraction strongly indicate that the intergranular material is a polycrystalline phase of tetragonal β-Bi₂O₃ ( P 42₁ c ), rather than the amorphous ZnO-Bi₂O₃ phase reported earlier. It appears that the nonohmic behavior in this prototype metal-oxide varistor must be an interfacial property associated with the semiconducting ZnO grains separated by thin layers of high-resistivity Bi₂O₃.     

交-交变频传动的SVC系统的研制与效果评价

根据静止型无功补偿装置（SVC）的设计与装置投动后的调试、测试结果,阐述了SVC系统研制的基本思路与设计原理,进行了滤波、补偿效果的比较与评价,并总结了SVC的技术特点。     

THE INFLUENCE OF NUTRITIONAL FACTORS ON SYNTHESIS OF SALMONELLA TOXIN

The nutritional requirements for the synthesis of a cholera toxin-like toxin from Salmonella enteritidis serotype braenderup were examined. Toxin levels of both culture filtrates and sonicates were determined by the modified Chinese hamster ovary (CHO) floating cell assay. With few exceptions, most amino acids which contained charged polar R groups were stimulatory for Salmonella toxin synthesis. Glycerol enhanced toxin production to the largest extent; however, glucose was a poor carbon source suggesting that Salmonella toxin elaboration may be subject to catabolite repression. Biotin and Mn⁺⁺ were shown to increase the synthesis as well as release of this toxin. An ideal defined medium, supplemented with all the nutritional factors shown to stimulate toxin synthesis, was formulated. The amount of Salmonella toxin produced in this supplemented medium was about 82% of the total toxin elaborated when cultured in Casamino acids plus yeast extract.     

Staphylococcus aureus Growth and Enterotoxin Production in Mushrooms

An enterotoxin A (SEA) producing strain of Staphylococcus aureus was inoculated onto mushrooms and incubated under simulated pre-and post-canning conditions. S. aureus grew and produced SEA in mushrooms incubated at 25°C in 10% to 20% NaCl. Growth and SEA production occurred when mushrooms were stored in plastic bags at 37°C, but not at 25°C. Mushrooms heat-processed at 121.1°C supported S. aureus growth and SEA production. No SEA was recovered from mushrooms inoculated with 1 or 10 ng SEA/g and heated at 121.1°C for 4.5 min. At higher inoculated SEA levels (100 and 1,000 ng/g), SEA was detectable after 10 min of heating. Staphylococcal enterotoxin could be present in canned mushrooms as a result of pre-, but more likely post-processing contamination.     

从先进核电厂仿真器到数字核电厂之现状与发展方向

进入21世纪后各种尖端科技进展很快,例如高性能计算能力、超高速网络、云平台等。本文探讨如何应用这些尖端科技,进行从先进核电厂工程仿真器往上提升成为数字核电厂之初期规划与发展方向。     

A Distribution Factor Method with Cubic Interpolationg Correction for Analysis of Building Frames

A more accurate approximating method for the analysis of building frames than the original distribution factor method described in Reference [7] is presented. The relative magnitudes of the joint displacements (w, α, β) on a particular floor are rather insensitive to the lateral load and are dependent largely on the local stiffness of the beams and columns of the floor of interest. These relative magnitudes are called distribution factors. The distribution factors corresponding to unit u, v, and θ displacements, respectively, can be determined floor by floor. The absolute magnitudes are then obtained by linear combination of the distribution factors. The coefficients of the linear combination are called the mixing factors. There are nine mixing factors per floor, three for each displacement (w, α, β) corresponding to unit u, v, and θ, respectively. The mixing factors are found after the lateral loads are imposed. This paper makes corrections on the displacements for very tall buildings where uneven elongations of columns along the height are important. A new distribution pattern in terms of cubic polynomials with an additional ten unknowns per floor is added to the original sets of distribution factors. The total number of unknowns per floor for a three-dimensional building is 22 (9 mixing factors + 10 coefficients of the cubic polynomial + 3 horizontal displacements u, v, θ) irrespective of the complexity. Less than 5% errors in the computed nodal displacements are achieved. The method is particularly suitable for microcomputers.