Power transformer insulation systems are subjected to many stresses during normal operation due to lightning and switching.If the spectrum of incoming surge voltage matches the winding one,the corresponding resonance ...Power transformer insulation systems are subjected to many stresses during normal operation due to lightning and switching.If the spectrum of incoming surge voltage matches the winding one,the corresponding resonance will be excited.Therefore external transients occurring in power systems might trigger internal overvoltages with large maximum value in transformer windings.Overvoltages having such characteristic have been the root cause of many power transformer failures.The paper presents an approach to the identification of sensitive zones in the transformer windings based on the measurements of overvoltages inside windings and frequency dependences of admittance of the power transformer.The frequency characteristic of the transformer winding may determine those regions in the frequency spectrum.The presented approach might be used both for design optimization and diagnostics of distribution and power transformers.展开更多
This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening ...This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening and damage process.Simultaneously,it established a constitutive model capable of describing the entire process of rock pre-peak compaction and post-peak strain softening deformation,considering the nonlinear effects of the initial compaction stage of rocks,combined with damage mechanics theory and effective medium theory.In addition,this research verified the rationality of the constructed damage constitutive model using results from uniaxial and conventional triaxial compression tests on Miluo granite,yellow sandstone,mudstone,and glutenite.The results indicate that based on the improved Logistic function,the theoretical damage model accurately describes the entire evolution of damage characteristics during rock compression deformation,from maintenance through gradual onset,accelerated development to deceleration and termination,in a simple and unified expression.At the same time,the constructed constitutive model can accurately simulate the stress-strain process of different rock types under uniaxial and conventional triaxial compression,and the theoretical model curve closely aligns with experimental data.Compared to existing constitutive models,the proposed model has significant advantages.The damage model parameters a,r and β have clear physical meanings and interact competitively,where the three parameters collectively determine the shape of the theoretical stress−strain curve.展开更多
In order to simplify the boundary conditions of pavement temperature field,the "Environment-Surface" system which considered the natural environment and pavement surface was established.Based on this system,...In order to simplify the boundary conditions of pavement temperature field,the "Environment-Surface" system which considered the natural environment and pavement surface was established.Based on this system,the partial differential equations of the one-dimensional heat conduction in the pavement were established on the basis of the heat transfer theory.Furthermore,the function forms of the initial and boundary conditions of the equations were created through the field experiments.The general solution of the pavement one-dimensional heat conduction partial differential equations was acquired by using Green's function,and the explicit expression of pavement temperature field under specific constraint conditions was derived.For the purpose of analysis,the pavement temperatures in different seasons were calculated using the explicit expression of pavement temperature field,and the calculation accuracy was analyzed through the comparison between measured and calculated values.Then,the relationship between fitting accuracy and calculation accuracy of pavement temperatures was analyzed.The analysis results show that: the usage of "Environment-Surface" system simplifies the calculation of pavement temperature field; the relative error between calculated and measured values is generally less than 7% and is seldom influenced by seasons; there is a positive correlation between the calculation accuracy and the fitting accuracy of pavement surface temperature; high fitting accuracy would result in less error of pavement temperature prediction.展开更多
目的 探讨三维酰胺质子转移加权(three-dimensions amide proton transfer weighted,3D-APTw)成像在评估肝细胞癌(hepatocellular carcinoma,HCC)病理分级中的价值。材料与方法 前瞻性招募2020年10月至2023年4月经手术病理证实为HCC并进...目的 探讨三维酰胺质子转移加权(three-dimensions amide proton transfer weighted,3D-APTw)成像在评估肝细胞癌(hepatocellular carcinoma,HCC)病理分级中的价值。材料与方法 前瞻性招募2020年10月至2023年4月经手术病理证实为HCC并进行Edmondson-Steiner四级(Ⅰ~Ⅳ)分级的患者共43例。将Ⅰ级和Ⅱ级HCC定为低级别HCC,Ⅲ级和Ⅳ级病变定为高级别HCC。采用飞利浦3.0 T MRI设备在术前对患者进行扫描,分别采集T1WI、T2WI、弥散加权成像、酰胺质子转移加权(amide proton transfer weighted,APTw)及多期增强图像。由两位经验丰富的放射科医生独立测量HCC及正常肝实质的APTw值。采用Mann-Whitney U非参数检验分析组间差异。采用受试者工作特征(receiver operating characteristic,ROC)曲线分析APTw值的诊断效能,计算曲线下面积(area under the curve,AUC)、阈值及其敏感度和特异度。采用Spearman相关分析,评估APTw与HCC的组织学分级之间的相关性。结果 低级别HCC的APTw值(2.15%±0.13%)低于高级别HCC(2.63%±0.13%),差异具有统计学意义(P=0.03)。APTw值鉴别高级别及低级别HCC的AUC为0.69(95%CI:0.53~0.82),最佳阈值为1.85%时,敏感度和特异度分别为90.00%和42.31%。Spearman相关性分析结果显示APTw值与HCC病理分级呈正相关,相关系数r=0.43(P=0.003)。结论 APTw值可用于鉴别高级别及低级别HCC,3D-APTw成像在术前预测HCC病理分级中有一定的价值。展开更多
文摘Power transformer insulation systems are subjected to many stresses during normal operation due to lightning and switching.If the spectrum of incoming surge voltage matches the winding one,the corresponding resonance will be excited.Therefore external transients occurring in power systems might trigger internal overvoltages with large maximum value in transformer windings.Overvoltages having such characteristic have been the root cause of many power transformer failures.The paper presents an approach to the identification of sensitive zones in the transformer windings based on the measurements of overvoltages inside windings and frequency dependences of admittance of the power transformer.The frequency characteristic of the transformer winding may determine those regions in the frequency spectrum.The presented approach might be used both for design optimization and diagnostics of distribution and power transformers.
基金Project(52074299)supported by the National Natural Science Foundation of ChinaProjects(2023JCCXSB02,BBJ2024083)supported by the Fundamental Research Funds for the Central Universities,China。
文摘This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening and damage process.Simultaneously,it established a constitutive model capable of describing the entire process of rock pre-peak compaction and post-peak strain softening deformation,considering the nonlinear effects of the initial compaction stage of rocks,combined with damage mechanics theory and effective medium theory.In addition,this research verified the rationality of the constructed damage constitutive model using results from uniaxial and conventional triaxial compression tests on Miluo granite,yellow sandstone,mudstone,and glutenite.The results indicate that based on the improved Logistic function,the theoretical damage model accurately describes the entire evolution of damage characteristics during rock compression deformation,from maintenance through gradual onset,accelerated development to deceleration and termination,in a simple and unified expression.At the same time,the constructed constitutive model can accurately simulate the stress-strain process of different rock types under uniaxial and conventional triaxial compression,and the theoretical model curve closely aligns with experimental data.Compared to existing constitutive models,the proposed model has significant advantages.The damage model parameters a,r and β have clear physical meanings and interact competitively,where the three parameters collectively determine the shape of the theoretical stress−strain curve.
基金Projects(2012zzts019,2012QNZT048)supported by the Fundamental Research Funds for the Central Universities of Central South University,ChinaProject(201306370121)supported by the State Scholarship Fund of China+3 种基金Project(JT20090898002)supported by Traffic Technology Fund of Hainan Province,ChinaProject(2012M521563)supported by the China Postdoctoral Science FoundationProject(51248006)supported by The National Natural Science Foundation of ChinaProject(511114)supported by the Natural Science Foundation of Hainan Province,China
文摘In order to simplify the boundary conditions of pavement temperature field,the "Environment-Surface" system which considered the natural environment and pavement surface was established.Based on this system,the partial differential equations of the one-dimensional heat conduction in the pavement were established on the basis of the heat transfer theory.Furthermore,the function forms of the initial and boundary conditions of the equations were created through the field experiments.The general solution of the pavement one-dimensional heat conduction partial differential equations was acquired by using Green's function,and the explicit expression of pavement temperature field under specific constraint conditions was derived.For the purpose of analysis,the pavement temperatures in different seasons were calculated using the explicit expression of pavement temperature field,and the calculation accuracy was analyzed through the comparison between measured and calculated values.Then,the relationship between fitting accuracy and calculation accuracy of pavement temperatures was analyzed.The analysis results show that: the usage of "Environment-Surface" system simplifies the calculation of pavement temperature field; the relative error between calculated and measured values is generally less than 7% and is seldom influenced by seasons; there is a positive correlation between the calculation accuracy and the fitting accuracy of pavement surface temperature; high fitting accuracy would result in less error of pavement temperature prediction.
文摘目的 探讨三维酰胺质子转移加权(three-dimensions amide proton transfer weighted,3D-APTw)成像在评估肝细胞癌(hepatocellular carcinoma,HCC)病理分级中的价值。材料与方法 前瞻性招募2020年10月至2023年4月经手术病理证实为HCC并进行Edmondson-Steiner四级(Ⅰ~Ⅳ)分级的患者共43例。将Ⅰ级和Ⅱ级HCC定为低级别HCC,Ⅲ级和Ⅳ级病变定为高级别HCC。采用飞利浦3.0 T MRI设备在术前对患者进行扫描,分别采集T1WI、T2WI、弥散加权成像、酰胺质子转移加权(amide proton transfer weighted,APTw)及多期增强图像。由两位经验丰富的放射科医生独立测量HCC及正常肝实质的APTw值。采用Mann-Whitney U非参数检验分析组间差异。采用受试者工作特征(receiver operating characteristic,ROC)曲线分析APTw值的诊断效能,计算曲线下面积(area under the curve,AUC)、阈值及其敏感度和特异度。采用Spearman相关分析,评估APTw与HCC的组织学分级之间的相关性。结果 低级别HCC的APTw值(2.15%±0.13%)低于高级别HCC(2.63%±0.13%),差异具有统计学意义(P=0.03)。APTw值鉴别高级别及低级别HCC的AUC为0.69(95%CI:0.53~0.82),最佳阈值为1.85%时,敏感度和特异度分别为90.00%和42.31%。Spearman相关性分析结果显示APTw值与HCC病理分级呈正相关,相关系数r=0.43(P=0.003)。结论 APTw值可用于鉴别高级别及低级别HCC,3D-APTw成像在术前预测HCC病理分级中有一定的价值。
