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排序方式: 共有229条查询结果,搜索用时 93 毫秒
1.
H. Rust Ch. Tnnler W. Heintz D. Haschke M. Nuala R. Jakab 《Nuclear Engineering and Design》1995,157(3)
As required by the Swiss Federal Nuclear Safety Inspectorate (HSK) all Switzerland's five nuclear power plants have to install a containment filtered venting system. The integrity of the containment (the last barrier for radioactive releases to the environment) can be threatened by overpressure due to inadequate heat removal. Design requirements have been provided for a specific class of severe accident scenarios. In general the capacity of the system is considered sufficient if it is able to vent the steam production corresponding to a decay heat level of 1% of the thermal reactor power. The mitigation capacity for the reduction of released radioactive material is specified by a retention factor of 1000 for aerosols to prevent or limit a long term ground contamination and a factor of 100 for elementary iodine for prevention or limiting of thyroid doses and to avoid short term evacuation. Besides existing requirements for design, maintenance and operation, additional claims such as passivity and operability at any pressure conditions inside the containment have to be met. Passivity implies that the system can be initiated after a severe accident without any operator action. The system also has to allow early manual venting. Various filtered venting systems are presently available. The nuclear power plants of Beznau, Gosgen, Leibstadt and Muhleberg have already selected such systems and already implemented them or are going to install them step by step. Beznau selected the Sulzer-EWI system which is using a water pool with nozzles-baffle plates and mixing elements to achieve the required filtration of the aerosols. In both Beznau units, the systems are installed and in standby mode. Gosgen, a pressurized water reactor as well as Beznau, is going to implement a filter system developed by Siemens-KWU, known as sliding pressure venting process, combining a venturi scrubber in a water pool and a mesh filter. The boiling water reactor of Leibstadt also selected the same system as Beznau while Müheberg choose the ABB system but not in the common design. The venturi pipes are thereby integrated in the water pool of the outer torus. The system in all five nuclear power plants is fully operable and in standby mode since December 1993. 相似文献
2.
Asbestos fibers cause dose-dependent, persistent increases in mRNA levels of c-jun and c-fos proto-oncogenes in rat pleural mesothelial (RPM) cells, the progenitor cells of asbestos-induced mesothelioma (N. Heintz, Y. M. W. Janssen, and B. T. Mossman. Proc. Natl. Acad. Sci. USA, 90: 3299-3303, 1993). Here we report that addition of N-acetyl-L-cysteine decreases asbestos-mediated induction of c-fos and c-jun mRNA levels in a dose-dependent fashion. Exposure of RPM cells to asbestos causes depletion of total cellular glutathione, a response that can be abolished by pretreatment with N-acetyl-L-cysteine. Pretreatment of cells with buthionine sulfoximine, an agent which diminishes glutathione pools, increases the magnitude of induction of c-fos and c-jun mRNA by asbestos. To determine whether asbestos-induced effects on proto-oncogene expression could be attributed to extracellular generation of active oxygen species (AOS), RPM cells were exposed to H2O2 or xanthine and xanthine oxidase, a generating system of AOS. These oxidant stresses did not decrease cellular glutathione levels nor alter mRNA levels of c-fos or c-jun. However, increased mRNA levels of manganese-containing superoxide dismutase and heme oxygenase were observed, indicating that RPM cells respond to AOS by increased expression of genes encoding antioxidant enzymes. These data indicate that the signaling pathways leading to c-fos/c-jun proto-oncogene induction by asbestos are not triggered directly by formation of extracellular AOS. However, intracellular thiol levels appear to influence the expression of c-fos and c-jun, suggesting a redox-sensitive component in the signaling cascade which modulates gene expression of c-fos and c-jun by asbestos. 相似文献
3.
Nitrate radicals are being recognized as key intermediates in a growing list of important chemical processes in the atmosphere. Here, the role of nitrate radicals (NO3) in tropospheric chemistry is discussed, with special emphasis on results from field measurements, most of which have been made by differential optical absorption spectroscopy (DOAS), with matrix-isolation electron spin resonance being an alternative technique. Nitrate radicals were observed in the atmosphere at peak mixing ratios of 350 ppt. Long-term observation of NO3 shows that 24-h averages in rural air masses are closer to a few ppt. Nevertheless, the NO3 radical plays an important role in the non-photochemical conversion of NOx to HNO3. Also, NO3 is a strong oxidizing agent and initiates the night-time removal of atmospheric trace species such as olefins, aromatic hydrocarbons, and organic sulfur compounds. Finally, night-time peroxy radical production and release of reactive halogen species from sea salt aerosol might be initiated by NO3 reactions. 相似文献
4.
Thomas Guillemet Jean‐Marc Heintz Bruno Mortaigne Yongfeng Lu Jean‐François Silvain 《Advanced Engineering Materials》2018,20(1)
5.
In order to determine the impact of rainwater construction material on the development of a biofilm, three materials were tested: concrete, clay, and PVC. The biofilm attachment was initially more effective on clay coupons, but, after a period of three days, concrete coupons produced a greater quantity of biofilm than clay and PVC, in that order. The heterotrophic plate count in the rainwater indicated that this quantity tended to first increase following a rainfall, and then decrease. The new materials seemed to attach themselves to the existing biofilm on the wall and/or sediment in the form of small particles. The presence of fecal coliforms in the biofilm coupons was noted after major rainfall events, and this was correlated with the increase in fecal coliforms in the water. This study concluded that the most favorable support for biofilm development is concrete, clay, and PVC, in that order. 相似文献
6.
El‐Hajjaji Soundous Grard Amaury De Laubier Juliette Di Tanna Sybille Lain Aurlie Patz Viviane Sindic Marianne 《International Journal of Dairy Technology》2019,72(3):466-471
This study aims to describe the procedures and practices used in local production of raw milk butter. The demand for local products is increasing; hence, there is a need to describe the practices used in the artisanal production of raw milk butter. Therefore, a survey of 147 raw milk butter producers was carried out. The results from the survey indicate that there is not one single way to produce butter at artisanal level. In terms of maturation, six temperature sequences were distinguished. Attention is required at every step of production starting from breeding. 相似文献
7.
基建仓库项目位于莱瓦顿的Harlingervaart运河岸边,作为周边建筑的仓库,它具有独特的趣味性良好的形体感,因此被认为是立于运河沿岸广场上的一座雕塑。建筑的入口处挑出悬臂,并且顺势突出建筑南侧的体量 相似文献
8.
This paper proposes an analytical model for line (1D) and point contacts (2D), based upon the Ertel’s hypothesis to predict the evolution of film thickness in steady-state and transient conditions in elastohydrodynamic lubrication. This theoretical approach, applied to a velocity ramp at constant deceleration, is perfectly supported by experimental results in terms of film thickness distribution during the deceleration process and in terms of central film thickness at the vanishing of the entrainment velocity. This work emphasizes the role of the transport effects of the lubricant at the instantaneous entrainment velocity on the time and length scales at which the film thickness disturbances induced by the deceleration process occur until the complete halting of the surfaces. 相似文献
9.
10.
Patrick Brézillon Juliette Brézillon 《Information Systems and E-Business Management》2008,6(3):279-293
Enterprises often embed decision-making processes in procedures in order to address issues in all cases. However, procedures
often lead to sub-optimal solutions for any specific decision. As a consequence, each actor develops the practice of addressing
decision making in a specific context. Actors contextualize decision making when enterprises are obliged to decontextualize
decision making to limit the number of procedures and cover whole classes of decision-making processes by generalization.
Practice modeling is not easy because there are as many practices as contexts of occurrence. This chapter proposes a way to
deal effectively with practices. Based on a conceptual framework for dealing with context, we present a context-based representation
formalism for modeling decision making and its realization by actors. This formalism is called contextual graphs and is discussed
using the example of modeling car drivers’ behaviors.
This article is part of the “Handbook on Decision Support Systems” edited by Frada Burstein and Clyde W. Holsapple (2008)
Springer. 相似文献