In the present study,the flow over the stepped spillway was numerically investigated by using Flow3D model.The effect of step angle on different properties of Nappe flow regime such as the water surface profile,locati...In the present study,the flow over the stepped spillway was numerically investigated by using Flow3D model.The effect of step angle on different properties of Nappe flow regime such as the water surface profile,location of free-surface aeration inception,Froude number at the spillway’s toe,and pressure,flow velocity,air concentration and cavitation index were evaluated.The realizable k–εwas applied as the turbulence model,and Volume of Fluid(VOF)model was used to determine the free surface flow profiles of the spillway.The model was verified using experimental data.In order to investigate the different characteristics of Nappe flow regime,17 numerical runs was designed,in which,four step angles,four flow discharge were considered to investigate the flow characteristics over the stepped spillway.The results indicated that the numerical model is well suited with the experimental data over the stepped spillway(RMSE=0.147 and ARE=6.9%).In addition,with increasing the step angles,the aeration inception point is generally moved downstream.By increasing the step angles from zero to 10 degrees,the Froude number does not change significantly,however,at the angle of 15 degrees,the Froude number decreases by about 42 percent.展开更多
In this article,we present a theoretical study on the sub-bandgap refractive indexes and optical properties of Sidopedβ-Ga_(2)O_(3) thin films based on newly developed models.The measured sub-bandgap refractive index...In this article,we present a theoretical study on the sub-bandgap refractive indexes and optical properties of Sidopedβ-Ga_(2)O_(3) thin films based on newly developed models.The measured sub-bandgap refractive indexes ofβ-Ga_(2)O_(3) thin film are explained well with the new model,leading to the determination of an explicit analytical dispersion of refractive indexes for photon energy below an effective optical bandgap energy of 4.952 eV for theβ-Ga_(2)O_(3) thin film.Then,the oscillatory structures in long wavelength regions in experimental transmission spectra of Si-dopedβ-Ga_(2)O_(3) thin films with different Si doping concentrations are quantitively interpreted utilizing the determined sub-bandgap refractive index dispersion.Meanwhile,effective optical bandgap values of Si-dopedβ-Ga_(2)O_(3) thin films are further determined and are found to decrease with increasing the Si doping concentration as expectedly.In addition,the sub-bandgap absorption coefficients of Si-dopedβ-Ga_(2)O_(3) thin film are calculated under the frame of the Franz–Keldysh mechanism due to the electric field effect of ionized Si impurities.The theoretical absorption coefficients agree with the available experimental data.These key parameters obtained in the present study may enrich the present understanding of the sub-bandgap refractive indexes and optical properties of impurity-dopedβ-Ga_(2)O_(3) thin films.展开更多
The growth of wind energy penetration level in distribution system raises the concern about its impact on the operation of the power system, especially voltage stability and power loss. Among the major concerns, this ...The growth of wind energy penetration level in distribution system raises the concern about its impact on the operation of the power system, especially voltage stability and power loss. Among the major concerns, this paper studied the impact of connecting wind Turbine (WT) in radial distribution system with different penetration levels and different power factor (lead and lag) on power system voltage stability and power loss reduction. Load flow calculation was carried out using forward-backward sweep method. The analysis proceeds on 9- and 33-bus radial distribution systems. Results show that voltage stability enhancement and power loss reduction should be considered as WT installation objective.展开更多
目的探讨骨骼肌质量指数(Skeletal muscle mass index,SMI)、肌少症指数(Sarcope-nia index,SI)与呼吸危重症患者营养状态及预后的关系。方法选取2021年9月至2023年8月南通市第一人民医院收治的呼吸危重患者132例。采用改良危重症营养...目的探讨骨骼肌质量指数(Skeletal muscle mass index,SMI)、肌少症指数(Sarcope-nia index,SI)与呼吸危重症患者营养状态及预后的关系。方法选取2021年9月至2023年8月南通市第一人民医院收治的呼吸危重患者132例。采用改良危重症营养风险评分表(The modi-fied nutrition risk in critically ill,mNUTRIC)评估患者营养状况,根据评分结果分为低风险患者(n=83)、高风险患者(n=49),比较低风险患者与高风险患者的SMI、SI。以离开ICU为时间终点评估预后,分为死亡组(n=37)和存活组(n=95),比较死亡组与存活组患者的一般资料,采用多因素Logistic回归模型分析影响呼吸危重症患者死亡的因素,受试者工作特征(Receiver operator characteristic,ROC)曲线分析SMI、SI预测呼吸危重症患者死亡的风险价值。结果与低风险患者相比,高风险患者的SMI、SI降低(P<0.05)。以离开重症监护室(Intensive care unit,ICU)为评估时间终点,与存活组相比,死亡组年龄、入院24 h内的急性生理评分、年龄评分及慢性健康评分(Acute physiology and chronic health evaluation scoring system,APACHEⅡ)评分及降钙素原(Procalcitonin,PCT)水平较高,白蛋白(Albumin,ALB)、SI和SMI则较低(P<0.05)。多因素Logistic回归模型显示,高APACHEⅡ评分及低SMI、SI值是影响呼吸危重症死亡的独立危险因素。ROC曲线显示,SMI、SI单独预测呼吸危重症患者死亡的曲线下面积(Area under curve,AUC)为0.784(0.720~0.839)、0.726(0.657~0.788),采用SMI、SI联合预测AUC为0.890(0.835~0.938),联合预测效能较单独预测效能更好(P<0.05)。结论SMI、SI与呼吸危重症患者营养状态关系密切,两者联合预测呼吸危重症患者死亡的临床价值高于单独预测。展开更多
针对源网荷储优化调度时分布式电源的间歇性引起主动配电网节点电压波动以及有功网损增加等问题,提出一种改进风光场景聚类联合虚拟储能的源网荷储低碳优化调度方法。首先,为有效应对风光出力不确定的挑战,提出一种基于密度噪声应用空...针对源网荷储优化调度时分布式电源的间歇性引起主动配电网节点电压波动以及有功网损增加等问题,提出一种改进风光场景聚类联合虚拟储能的源网荷储低碳优化调度方法。首先,为有效应对风光出力不确定的挑战,提出一种基于密度噪声应用空间聚类(density-based spatial clustering of applications with noise,DBSCAN)的迭代自组织数据分析算法(iterative self-organizing data analysis techniques algorithm,ISODATA),并以DB指数、Dunn指数和轮廓系数对风光场景聚类效果的优劣进行评价。其次,引入阶梯式碳交易机制,建立以主动配电网综合运行成本最低为目标的优化调度模型。同时,提出用户参与满意度和电网依赖度两种运行评价指标。最后,在IEEE 33节点系统上进行算例仿真分析,结果验证了DBSCAN-ISODATA算法的合理性。并且所提低碳优化调度方法能够有效降低系统碳排放量与运行成本,实现了主动配电网低碳经济稳定运行。展开更多
文摘In the present study,the flow over the stepped spillway was numerically investigated by using Flow3D model.The effect of step angle on different properties of Nappe flow regime such as the water surface profile,location of free-surface aeration inception,Froude number at the spillway’s toe,and pressure,flow velocity,air concentration and cavitation index were evaluated.The realizable k–εwas applied as the turbulence model,and Volume of Fluid(VOF)model was used to determine the free surface flow profiles of the spillway.The model was verified using experimental data.In order to investigate the different characteristics of Nappe flow regime,17 numerical runs was designed,in which,four step angles,four flow discharge were considered to investigate the flow characteristics over the stepped spillway.The results indicated that the numerical model is well suited with the experimental data over the stepped spillway(RMSE=0.147 and ARE=6.9%).In addition,with increasing the step angles,the aeration inception point is generally moved downstream.By increasing the step angles from zero to 10 degrees,the Froude number does not change significantly,however,at the angle of 15 degrees,the Froude number decreases by about 42 percent.
基金This study was financially supported by the National Natural Science Foundation of China(No.12074324)the Shenzhen Municipal Science and Technology Innovation Council(No.JCJY20180508163404043).
文摘In this article,we present a theoretical study on the sub-bandgap refractive indexes and optical properties of Sidopedβ-Ga_(2)O_(3) thin films based on newly developed models.The measured sub-bandgap refractive indexes ofβ-Ga_(2)O_(3) thin film are explained well with the new model,leading to the determination of an explicit analytical dispersion of refractive indexes for photon energy below an effective optical bandgap energy of 4.952 eV for theβ-Ga_(2)O_(3) thin film.Then,the oscillatory structures in long wavelength regions in experimental transmission spectra of Si-dopedβ-Ga_(2)O_(3) thin films with different Si doping concentrations are quantitively interpreted utilizing the determined sub-bandgap refractive index dispersion.Meanwhile,effective optical bandgap values of Si-dopedβ-Ga_(2)O_(3) thin films are further determined and are found to decrease with increasing the Si doping concentration as expectedly.In addition,the sub-bandgap absorption coefficients of Si-dopedβ-Ga_(2)O_(3) thin film are calculated under the frame of the Franz–Keldysh mechanism due to the electric field effect of ionized Si impurities.The theoretical absorption coefficients agree with the available experimental data.These key parameters obtained in the present study may enrich the present understanding of the sub-bandgap refractive indexes and optical properties of impurity-dopedβ-Ga_(2)O_(3) thin films.
文摘The growth of wind energy penetration level in distribution system raises the concern about its impact on the operation of the power system, especially voltage stability and power loss. Among the major concerns, this paper studied the impact of connecting wind Turbine (WT) in radial distribution system with different penetration levels and different power factor (lead and lag) on power system voltage stability and power loss reduction. Load flow calculation was carried out using forward-backward sweep method. The analysis proceeds on 9- and 33-bus radial distribution systems. Results show that voltage stability enhancement and power loss reduction should be considered as WT installation objective.
文摘目的探讨骨骼肌质量指数(Skeletal muscle mass index,SMI)、肌少症指数(Sarcope-nia index,SI)与呼吸危重症患者营养状态及预后的关系。方法选取2021年9月至2023年8月南通市第一人民医院收治的呼吸危重患者132例。采用改良危重症营养风险评分表(The modi-fied nutrition risk in critically ill,mNUTRIC)评估患者营养状况,根据评分结果分为低风险患者(n=83)、高风险患者(n=49),比较低风险患者与高风险患者的SMI、SI。以离开ICU为时间终点评估预后,分为死亡组(n=37)和存活组(n=95),比较死亡组与存活组患者的一般资料,采用多因素Logistic回归模型分析影响呼吸危重症患者死亡的因素,受试者工作特征(Receiver operator characteristic,ROC)曲线分析SMI、SI预测呼吸危重症患者死亡的风险价值。结果与低风险患者相比,高风险患者的SMI、SI降低(P<0.05)。以离开重症监护室(Intensive care unit,ICU)为评估时间终点,与存活组相比,死亡组年龄、入院24 h内的急性生理评分、年龄评分及慢性健康评分(Acute physiology and chronic health evaluation scoring system,APACHEⅡ)评分及降钙素原(Procalcitonin,PCT)水平较高,白蛋白(Albumin,ALB)、SI和SMI则较低(P<0.05)。多因素Logistic回归模型显示,高APACHEⅡ评分及低SMI、SI值是影响呼吸危重症死亡的独立危险因素。ROC曲线显示,SMI、SI单独预测呼吸危重症患者死亡的曲线下面积(Area under curve,AUC)为0.784(0.720~0.839)、0.726(0.657~0.788),采用SMI、SI联合预测AUC为0.890(0.835~0.938),联合预测效能较单独预测效能更好(P<0.05)。结论SMI、SI与呼吸危重症患者营养状态关系密切,两者联合预测呼吸危重症患者死亡的临床价值高于单独预测。
文摘针对源网荷储优化调度时分布式电源的间歇性引起主动配电网节点电压波动以及有功网损增加等问题,提出一种改进风光场景聚类联合虚拟储能的源网荷储低碳优化调度方法。首先,为有效应对风光出力不确定的挑战,提出一种基于密度噪声应用空间聚类(density-based spatial clustering of applications with noise,DBSCAN)的迭代自组织数据分析算法(iterative self-organizing data analysis techniques algorithm,ISODATA),并以DB指数、Dunn指数和轮廓系数对风光场景聚类效果的优劣进行评价。其次,引入阶梯式碳交易机制,建立以主动配电网综合运行成本最低为目标的优化调度模型。同时,提出用户参与满意度和电网依赖度两种运行评价指标。最后,在IEEE 33节点系统上进行算例仿真分析,结果验证了DBSCAN-ISODATA算法的合理性。并且所提低碳优化调度方法能够有效降低系统碳排放量与运行成本,实现了主动配电网低碳经济稳定运行。
