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During operation of PWR plants, thermal transients occur and induce fatigue stresses at critical locations in the nuclear steam supply system. Assessment of cumulative usage factor at these locations is one the major concerns regarding plant life extension.A system based on real time fatigue monitoring his been developed by EDF. The principle of the system, that records plant operating parameters and calculate thermohydraulic conditions, local stresses and usage factor resulting from each individual transient, is firstly presented.Demonstration experiments, concerning two higly stressed locations of reactor coolant system (charging line nozzle and surge line), carried out in two 900 MW units are then described.Finally, analysis of these experiment results is commented. The system allows automatic transients book keeping and usage factor assessment. EDF intends to equip all its PWR units with such fatigue monitoring systems.  相似文献   
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Artificial Neural Networks (ANNs) have been successfully employed for predicting and forecasting groundwater levels up to some time steps ahead. In this paper, we present an application of feed forward neural networks (FFNs) for long period simulations of hourly groundwater levels in a coastal unconfined aquifer sited in the Lagoon of Venice, Italy. After initialising the model with groundwater elevations observed at a given time, the developed FNN should able to reproduce water level variations using only the external input variables, which have been identified as rainfall and evapotranspiration. To achieve this purpose, the models are first calibrated on a training dataset to perform 1-h ahead predictions of future groundwater levels using past observed groundwater levels and external inputs. Simulations are then produced on another data set by iteratively feeding back the predicted groundwater levels, along with real external data. The results show that the developed FNN can accurately reproduce groundwater depths of the shallow aquifer for several months. The study suggests that such network can be used as a viable alternative to physical-based models to simulate the responses of the aquifer under plausible future scenarios or to reconstruct long periods of missing observations provided past data for the influencing variables is available.  相似文献   
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The thermal behavior of magnesium potassium phosphate cement (MKPC) during the early reaction period has been monitored by isothermal conduction calorimetry at 298 K. It is found that the typical heat evolution curve of the MKPC hydration has one endothermic valley and two distinct exothermic peaks. It is believed that the endothermic valley corresponds to the dissolution of potassium dihydrogen phosphate and the exothermic peaks are related to the dissolution of magnesia and the formation of magnesium potassium phosphate hexahydrate, respectively. The influences of the water to powder ratio, the magnesium to phosphate molar ratio and the setting retarder content on the reaction can be reflected in a change of shape and intensity of the peaks on the heat flow curve. The variation trend is consistent with the change of the setting time of MKPC pastes.  相似文献   
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We show experimental evidence of surface phonon scattering in the high-/spl kappa/ dielectric being the primary cause of channel electron mobility degradation. Next, we show that midgap TiN metal-gate electrode is effective in screening phonon scattering in the high-/spl kappa/ dielectric from coupling to the channel under inversion conditions, resulting in improved channel electron mobility. We then show that other metal-gate electrodes, such as the ones with n+ and p+ work functions, are also effective in improving channel mobilities to close to those of the conventional SiO/sub 2//poly-Si stack. Finally, we demonstrate this mobility degradation recovery translates directly into high drive performance on high-/spl kappa//metal-gate CMOS transistors with desirable threshold voltages.  相似文献   
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A modeling procedure which provides an accurate large-signal response for variation in bias, input power level, and fundamental frequency for FET/HEMT transistors is designed. A procedure for measuring the large-signal input response on an easily implemented system is presented. The technique is illustrated by designing a nonlinear PHEMT model, which includes an accurate large-signal input response and works with variations in the aforementioned input conditions. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14, 122–133, 2004.  相似文献   
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