针对水电机组状态监测数据量逐步增大,数据质量差的问题,提出了一种基于改进K维树(K-Dimensional Tree,KD-Tree)与基于密度的空间聚类算法(Density-Based Spatial Clustering of Applications with Noise,DBSCAN)的水电机组状态监测数...针对水电机组状态监测数据量逐步增大,数据质量差的问题,提出了一种基于改进K维树(K-Dimensional Tree,KD-Tree)与基于密度的空间聚类算法(Density-Based Spatial Clustering of Applications with Noise,DBSCAN)的水电机组状态监测数据清洗方法,首先对输入数据建立KD-Tree,再使用DBSCAN在最近邻样本上扫描完成聚类,聚类结束以后会分离出噪声点,将噪声点去除即可完成对水电机组状态监测数据清洗。选取某水电站状态监测系统上导摆度数据1 088条,再以相同时间间隔插入随机数据100条,通过算例与常规DBScan、K-means、OCSVM算法对比聚类性能与时间性能,所提出的方法识别正确率最高,为97.78%,消耗时间最少,为0.007 732 s,数据清洗效果最优,并可以大幅减少计算时间。展开更多
There is considerable concern about the potential impact of climate change on agriculture, such as the accumulation of chilling hours needed to break the dormancy of many perennial plants, like fruit trees. Therefore,...There is considerable concern about the potential impact of climate change on agriculture, such as the accumulation of chilling hours needed to break the dormancy of many perennial plants, like fruit trees. Therefore, this study aimed to determine if there had been a significant change in air temperatures and chill hours, chill units, and chill portion accumulation in South Carolina over the last two decades. Two decades of daily maximum (T<sub>max</sub>) and minimum (T<sub>min</sub>) air temperature records were obtained from weather stations in thirty-one counties in South Carolina. Hourly temperature data, reconstructed from the daily data, were used to calculate the daily and annual chill hours, chill units, and chill portions accumulation using four different chill models for each location and year. The chill models included the T(t) °C model, the 0°C °C model, the Utah model, and the Dynamic model. For each county, regression analyses were conducted to evaluate the historical trends. Despite year-to-year variability, the tendency was a statistically significant (α = 0.05) increase in air temperature, averaging 0.089°C per year for 20 out of 31 counties in South Carolina. The other 11 counties had no significant change in temperature. The average temperature increase in the 31 counties was 0.072°C per year. The temperature increase resulted in a decrease in annual chill accumulation during the fall to spring, averaging 17.7 chill hours, 8.6 chill hours, 17.0 chill units, and 0.40 chill portions per year calculated with the T(t) °C, 0°C °C, Utah, and Dynamic models, respectively. However, whether this decrease in chill values was statistically significant or not depended on the chill model used. This study did not investigate the cause of the observed historical trends in temperature and chill accumulation. Still, if the trends continue, they could significantly impact the future of the temperate fruit tree industry in the state.展开更多
Within this paper, the process of statistical safety analysis has been presented, which involves the following steps： formulation of basic principles of statistical safety analysis, initial events analysis, accident ...Within this paper, the process of statistical safety analysis has been presented, which involves the following steps： formulation of basic principles of statistical safety analysis, initial events analysis, accident sceneries progress analysis, risk calculation, and risk calculation results analysis. On this basis, it has been concluded that the bucket wheel excavator SRs 1200×24/4×0（400 kW）＋VR safety criteria is the mechanism for the hoist of rotor＇s arrow failure modes, because in that case whole bucket wheel excavator failure would necessarily happen （excavator falling down on counterweight）. Therefore, excavator units statistical safety analysis is accomplished preventively to obtain its effective maintenance management.展开更多
文摘目的 基于决策树法构建重症监护室多重耐药菌(multidrug-resistant organism,MDRO)感染风险预测模型,为临床开展MDRO防治提供参考。方法 采用回顾性分析方法,收集2022年1月至2024年1月在重症监护室住院的210例医院感染患者临床资料,根据是否发生MDRO感染分为MDRO组61例和非MDRO组149例。使用多因素Logistic回归分析和决策树法构建MDRO感染预测模型,比较2种模型的预测效能。结果 Logistic回归分析显示,年龄(OR=1.036,95%CI:1.002~1.072)、住院时间(OR=1.289,95%CI:1.072~1.550)、低蛋白血症(OR=2.604,95%CI:1.186~2.719)、抗菌药使用>3种(OR=3.250,95%CI:1.566~3.791)是MDRO感染的危险因素(均P<0.05);决策树模型显示,住院时间是重症监护室MDRO感染最重要的预测因子。Logistic回归模型预测MDRO感染的曲线下面积(area under the curve,AUC)为0.719(95%CI:0.653~0.778),决策树模型预测MDRO感染的AUC为0.813(95%CI:0.753~0.863),决策树模型预测效能优于Logistic回归模型(Z=2.666,P=0.008)。结论 构建的重症监护室MDRO感染决策树模型预测效能较高,可作为筛选潜在MDRO感染的有效工具之一。
文摘There is considerable concern about the potential impact of climate change on agriculture, such as the accumulation of chilling hours needed to break the dormancy of many perennial plants, like fruit trees. Therefore, this study aimed to determine if there had been a significant change in air temperatures and chill hours, chill units, and chill portion accumulation in South Carolina over the last two decades. Two decades of daily maximum (T<sub>max</sub>) and minimum (T<sub>min</sub>) air temperature records were obtained from weather stations in thirty-one counties in South Carolina. Hourly temperature data, reconstructed from the daily data, were used to calculate the daily and annual chill hours, chill units, and chill portions accumulation using four different chill models for each location and year. The chill models included the T(t) °C model, the 0°C °C model, the Utah model, and the Dynamic model. For each county, regression analyses were conducted to evaluate the historical trends. Despite year-to-year variability, the tendency was a statistically significant (α = 0.05) increase in air temperature, averaging 0.089°C per year for 20 out of 31 counties in South Carolina. The other 11 counties had no significant change in temperature. The average temperature increase in the 31 counties was 0.072°C per year. The temperature increase resulted in a decrease in annual chill accumulation during the fall to spring, averaging 17.7 chill hours, 8.6 chill hours, 17.0 chill units, and 0.40 chill portions per year calculated with the T(t) °C, 0°C °C, Utah, and Dynamic models, respectively. However, whether this decrease in chill values was statistically significant or not depended on the chill model used. This study did not investigate the cause of the observed historical trends in temperature and chill accumulation. Still, if the trends continue, they could significantly impact the future of the temperate fruit tree industry in the state.
文摘Within this paper, the process of statistical safety analysis has been presented, which involves the following steps： formulation of basic principles of statistical safety analysis, initial events analysis, accident sceneries progress analysis, risk calculation, and risk calculation results analysis. On this basis, it has been concluded that the bucket wheel excavator SRs 1200×24/4×0（400 kW）＋VR safety criteria is the mechanism for the hoist of rotor＇s arrow failure modes, because in that case whole bucket wheel excavator failure would necessarily happen （excavator falling down on counterweight）. Therefore, excavator units statistical safety analysis is accomplished preventively to obtain its effective maintenance management.
