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Large-scale voltage collapse incidences, which result in power outages over large regions and extensive economic losses, are presently common occurrences worldwide. Therefore, the voltage stability analysis of power systems has become a topic of increasing interest. This paper firstly presents a comprehensive evaluation method for conducting static and transient voltage stability analysis in electric power systems. To overcome the limitations associated with single-index systems in the evaluation of voltage stability, the analysis approach employs a multi-index system with four primary criteria based on separate analysis methods with ten sub-criteria based on individual indices. In addition, this paper proposes a comprehensive method for establishing index weights, which combines the subjective analytic hierarchy process weighting method and the objective entropy weighting method. An innovative index-weight optimization method based on the Lagrange conditioned extreme value is presented and sensitivity analysis is applied to test the robust of the proposed method. Finally, Fuzzy-TOPSIS is employed to rank the voltage buses of a power system as the final results, considering system functionality and proportionality. The results obtained for an actual power grid in Hami City, China demonstrate that the proposed method represents an effective approach for determining the weakest bus in power systems.

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Porous bowl-like LiFePO 4 /C composites are prepared by using the ammonium salt and sodium salt processes with a facile precipitation method coupled with spray-drying technology. Both of the as-prepared LiFePO 4 /C composites present high crystallinity, bowl-like morphology, and uniform carbon-layercoated particles. Compared with the traditional ammonium salt process, the sodium salt process, without ammonia nitrogen pollutants, is not only environmentally friendly, but also allows us to introduce appropriate Na + doping within the resultant LiFePO 4 . Moreover, the LiFePO 4 /C composite prepared by using the sodium salt process exhibits better electrochemical performance: a high rate capability (136, 129, and 119 mAh g À1 at 10, 20, and 40 C rate, respectively) and a long cycle stability (60.3 % of initial capacity after 3000 cycles at 10 C, only corresponding to 0.013 % capacity decay per cycle) compared with the other (only exhibits a capacity of 123, 107, and 62 mAh g À1 at rate of 10, 20, and 40 C and retains a 37.5 % of initial capacity after 3000 cycles at 10 C). This good electrochemical performance originates from its special morphology, high crystallinity, stable structure, and Na + doping. Results and DiscussionThe ICP results for the two samples are shown in Table 1. It can be found that the molar ration of Li : Fe : P (0.99 : 0.99 : 1.00) in the LFP/CÀA is in good agreement with the ideal value. However, the molar ratio of Li:Na:Fe:P in the LFP/CÀS sample is [a] B.

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Three non-destructive test (NDT) methods were used to detect the two dimensional C/SiC specimens after low velocity impact (LVI) of various energies. The damage areas characterized by these methods were very different. Both ultrasonic and thermographic images reveal the LVI damages, while X ray is non-sensitive to the interior damage. However, small delaminations were not found by thermography and accurate judgment depends on the experience and the resolution of the infrared camera. And the result acquired from the higher frequency transducer was very confused because of the inherent defects. It is suggested that using both ultrasonic C-scan and thermography to evaluate the LVI damage of C/SiC. It is also suggested using the transducer of low frequency to perform the ultrasonic C-scan.

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