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有源配电网故障场景下的电压暂降仿真与评估方法研究 被引量:19
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作者 贾东梨 刘科研 +3 位作者 盛万兴 孟晓丽 胡丽娟 何开元 《中国电机工程学报》 EI CSCD 北大核心 2016年第5期1279-1288,共10页
针对含有分布式电源的配电网进行电压暂降仿真与评估问题,提出基于点估计法的电压暂降仿真与评估方法。首先建立故障信息模型,包括对故障线路率、故障点、故障类型、故障持续时间、故障阻抗等,以及分布式电源输出功率的随机模型,然后基... 针对含有分布式电源的配电网进行电压暂降仿真与评估问题,提出基于点估计法的电压暂降仿真与评估方法。首先建立故障信息模型,包括对故障线路率、故障点、故障类型、故障持续时间、故障阻抗等,以及分布式电源输出功率的随机模型,然后基于点估计法将随机概率密度问题转换为多个确定性问题。通过计算随机变量的期望、标准差、三阶中心矩,利用Cornish-Fisher级数来表示每个节点电压暂降的概率密度函数,以及计算电压暂降指标SARFI,发现网络的薄弱环节。通过对含两个不同类型分布式电源的IEEE13-bus和IEEE 33-bus系统的测试,并与Monte Carlo法进行对比,证明了算法的有效性。通过对不同类型风机模型的应用,证实了该文提出算法的可行性和高效性。 展开更多
关键词 电压暂降 故障分析 有源配电网 随机评估方法 分布式电源
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A Screening Program for Overweight Status Among Schoolgirls in Saudi Arabia: A Proposed Co-design Project to Tackle the Problem
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作者 Elham A. Aljaaly 《Journalism and Mass Communication》 2017年第5期225-243,共19页
The paper realizes the importance of communicating with schools to conduct nutritional screening, assessment and intervention programs for obesity and related risk factors to tackle the problem at earlier stage. The s... The paper realizes the importance of communicating with schools to conduct nutritional screening, assessment and intervention programs for obesity and related risk factors to tackle the problem at earlier stage. The screening program was conducted by dietetics' students "under supervision" as part of their practice and community services to apply some assessment method for mritional status. Two intermediate schools for girls in Jeddah city were involved in the screening stage, followed by a full nutritional assessment and implementation of a designed intervention program at one of the schools. At screening stage, interview questionnaires for diet histories and anthropometric measurements used to screen overweight status and related food patterns. National and international references data used for assessment and comparison. Following screening approach, a designed comprehensive nutritional assessment and intervention program was piloted at one of the screened schools for overweight status. For screening stage: the overall prevalence of overweight girls is 61% (n = 81 out of 133) of the population, 73% (n = 91) of girls were centrally obese. Almost 3/4 of all students reported no participations in any type of physical activities/exercises. Dietary behaviors included non-consumption of breakfast (83%) and low intake of fruit and vegetables (38%). For intervention stage, the present report concentrates on data concerning post intervention changes in Body Mass Index (BMI) and Waist Circumference (WC). By the 30 days of intervention there were significant changes in values for BMI according to Saudi growth chart (p value = 0.009) with no changes among the control group. No statistically significant difference in the mean WC of the group. Study's results suggest that approaching young girls through schools to screen, assess and intervene overweight status and risk factors is vital. Although the non-random selection of only two schools for screening the prevalence of overweight status among school girls prevent the geralizability of the study findings to wider population, previous studies used random selection of schools and large sample sizes showed a high prevalence of overweight status among Saudi students Therefore, designing and piloting of an intervention program for implementation at a national level is useful to tackle theproblem. 展开更多
关键词 screening program nutritional assessment overweight status intervention programs diet histories ANTHROPOMETRY dietetic students
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