电力变压器匝间故障将导致绝缘击穿,甚至造成整个电网事故的发生,为此,应用在线频率响应分析法检测变压器绕组变形。通过安装于变压器套管表面的非侵入式电容传感器（NICS）将测试信号通过高压套管注入变压器绕组从而实现了绕组变形的...电力变压器匝间故障将导致绝缘击穿,甚至造成整个电网事故的发生,为此,应用在线频率响应分析法检测变压器绕组变形。通过安装于变压器套管表面的非侵入式电容传感器（NICS）将测试信号通过高压套管注入变压器绕组从而实现了绕组变形的在线监测。开发了基于脉冲信号注入法的变压器绕组变形在线监测系统。着重阐述了测试信号的选择,在线信号的注入,保护电路的设计。分析了信号源和采样频率对频响特性测试结果的影响。对一台型号为35 k VA/10 k V/400 V的配电变压器进行测试,并与安捷伦频谱网络分析仪4395A的测试结果进行对比发现,在0~5 MHz频率范围内,两条频响曲线的相关系数为0.955 3。结果表明,该系统能在在线状态下准确、快速地获取变压器绕组数10 MHz内的频响特性。监测系统具有较高的灵敏度和重复性,能有效检测变压器绕组变形。展开更多
The aromatic character of divalent three, five and seven-membered rings C2H2M, C4H4M and C6H6M(M=C, Si, Ge, Sn and Pb) is investigated through magnetic and geometric criteria by Density Functional Theory (DFT )method ...The aromatic character of divalent three, five and seven-membered rings C2H2M, C4H4M and C6H6M(M=C, Si, Ge, Sn and Pb) is investigated through magnetic and geometric criteria by Density Functional Theory (DFT )method using 6-311++G(3df,2p) basis set of the GAUSSIAN 98 program. The result of Nucleus-independent Chemical Shifts (NICS) (0.5) calculations show an aromatic character for singlet state of C2H2M(M=C, Si, Ge, Sn and Sn) and nonaromatic character for triplet states of C2H2M(except M=Ge and Pb). NICS (0.5) calculations show nonaromatic character for the singlet state of C4H4C and antiaromatic character for C4H4M(M=Si, Ge, Sn and Pb). In contrast, NICS (0.5) calculations indicate antiaromatic character for the triplet state of C4H4C and nonaromatic character to C4H4M(M=Si, Ge, Sn and Pb). NICS (0.5) calculations show a slightly homoaromatic character for the singlet state of C6H6M and anti-aromatic character for triplet state of C6H6M.展开更多
基于对语音、视频处理实时性和稳定性的高要求,以可编程数字信号处理器(Digital Signal Processor,DSP)为主体进行研究,通过分析DSP处理器的系统总体,介绍系统中不同环节的作用,设计出可以有效提高数据传输实时性和稳定性的数字信号处...基于对语音、视频处理实时性和稳定性的高要求,以可编程数字信号处理器(Digital Signal Processor,DSP)为主体进行研究,通过分析DSP处理器的系统总体,介绍系统中不同环节的作用,设计出可以有效提高数据传输实时性和稳定性的数字信号处理系统,以提高语音和视频处理效率,助力企业实现可持续发展。展开更多
目的采用meta分析探讨能谱增强CT中标准化碘密度(normalized iodine concentrations,NIC)诊断结直肠癌淋巴结转移的价值。方法检索建库至2022年10月期间PubMed、Embase、Cochrane、Web of Science、CBM、CNKI、万方、维普数据库,筛选NI...目的采用meta分析探讨能谱增强CT中标准化碘密度(normalized iodine concentrations,NIC)诊断结直肠癌淋巴结转移的价值。方法检索建库至2022年10月期间PubMed、Embase、Cochrane、Web of Science、CBM、CNKI、万方、维普数据库,筛选NIC诊断结直肠癌淋巴结转移相关的文献。采用诊断准确性研究的质量评价工具-2对文献进行偏倚风险评价,运用Meta-DiSc1.4进行数据统计,计算Spearman相关系数并绘制综合受试者工作特征曲线(sROC)以分析有无阈值效应引起的异质性。I2<50%采用固定效应合并效应量;I2≥50%采用随机效应合并效应量。采用Stata 14.0进行敏感性分析,以Deeks漏斗图检测发表偏倚。结果纳入7篇文献,共计717枚淋巴结,转移淋巴结314枚、非转移淋巴结403枚。按照能谱增强CT中的动脉期(arterial phase,AP)和静脉期(venous phase,VP)将其分为两个亚组。Meta DiSc1.4显示,两亚组均不存在阈值效应引起的异质性(均P>0.05)。进而根据I2结果,选择对应的效应模型合并效应量。结果(AP、VP)分别为:灵敏度=0.76(0.71~0.80)、0.67(0.61~0.73);特异度=0.71(0.66~0.75)、0.87(0.82~0.91);阳性似然比=2.83(1.85~4.31)、5.39(3.79~7.67);阴性似然比=0.33(0.23~0.46)、0.34(0.22~0.54);诊断比值比(diagnostic odds ratio,DOR)=10.00(4.38~22.82)、17.27(10.39~28.69);曲线下面积(area under the curve,AUC)=0.8354、0.8945。亚组-AP及亚组-VP敏感性分析显示研究稳定,并且不存在发表偏倚(P>0.05)。结论NIC有助于区分结直肠癌患者转移性和非转移性淋巴结。在灵敏度方面,AP的NIC更优;在特异度、阳性似然比、阴性似然比、DOR、AUC方面,VP的NIC具有更高的诊断价值。展开更多
The turbulence characteristics of plasmas with internal transport barriers in the HL-2A tokamak are analyzed by means of linear gyrokinetic simulations. It is found that turbulence is dominated by the ion temperature ...The turbulence characteristics of plasmas with internal transport barriers in the HL-2A tokamak are analyzed by means of linear gyrokinetic simulations. It is found that turbulence is dominated by the ion temperature gradient(ITG)mode together with large-scale modes characterized by high-frequency electromagnetic fluctuation, which are destabilized by the steep ion temperature gradient in the weak magnetic shear regime. Comparison with solutions of analytical dispersion relations shows that their linear features match well with the beta-induced Alfvén eigenmode branch of the shear Alfvénic spectrum. It is further clarified that the large population of fast ions in these plasmas plays a stabilization role through the dilution mechanism in high-n ITG mode regimes.展开更多
运用密度泛函理论对13种化合物进行几何结构全优化和频率计算,并计算了其芳香性指标NICS(Nucleus-Independent Chemical Shifts)值,研究了取代基对芳香性的影响以及芳香性与分子稳定性的关系。结果表明吸电子基团可以增加苯环的芳香性,...运用密度泛函理论对13种化合物进行几何结构全优化和频率计算,并计算了其芳香性指标NICS(Nucleus-Independent Chemical Shifts)值,研究了取代基对芳香性的影响以及芳香性与分子稳定性的关系。结果表明吸电子基团可以增加苯环的芳香性,供电子基团可以减低苯环的芳香性,随着体系稳定性的增加,苯环的芳香性降低。展开更多
文摘电力变压器匝间故障将导致绝缘击穿,甚至造成整个电网事故的发生,为此,应用在线频率响应分析法检测变压器绕组变形。通过安装于变压器套管表面的非侵入式电容传感器（NICS）将测试信号通过高压套管注入变压器绕组从而实现了绕组变形的在线监测。开发了基于脉冲信号注入法的变压器绕组变形在线监测系统。着重阐述了测试信号的选择,在线信号的注入,保护电路的设计。分析了信号源和采样频率对频响特性测试结果的影响。对一台型号为35 k VA/10 k V/400 V的配电变压器进行测试,并与安捷伦频谱网络分析仪4395A的测试结果进行对比发现,在0~5 MHz频率范围内,两条频响曲线的相关系数为0.955 3。结果表明,该系统能在在线状态下准确、快速地获取变压器绕组数10 MHz内的频响特性。监测系统具有较高的灵敏度和重复性,能有效检测变压器绕组变形。
基金Payame Noor University, Zanjan Branch foundations(伊朗)资助项目
文摘The aromatic character of divalent three, five and seven-membered rings C2H2M, C4H4M and C6H6M(M=C, Si, Ge, Sn and Pb) is investigated through magnetic and geometric criteria by Density Functional Theory (DFT )method using 6-311++G(3df,2p) basis set of the GAUSSIAN 98 program. The result of Nucleus-independent Chemical Shifts (NICS) (0.5) calculations show an aromatic character for singlet state of C2H2M(M=C, Si, Ge, Sn and Sn) and nonaromatic character for triplet states of C2H2M(except M=Ge and Pb). NICS (0.5) calculations show nonaromatic character for the singlet state of C4H4C and antiaromatic character for C4H4M(M=Si, Ge, Sn and Pb). In contrast, NICS (0.5) calculations indicate antiaromatic character for the triplet state of C4H4C and nonaromatic character to C4H4M(M=Si, Ge, Sn and Pb). NICS (0.5) calculations show a slightly homoaromatic character for the singlet state of C6H6M and anti-aromatic character for triplet state of C6H6M.
文摘基于对语音、视频处理实时性和稳定性的高要求,以可编程数字信号处理器(Digital Signal Processor,DSP)为主体进行研究,通过分析DSP处理器的系统总体,介绍系统中不同环节的作用,设计出可以有效提高数据传输实时性和稳定性的数字信号处理系统,以提高语音和视频处理效率,助力企业实现可持续发展。
文摘目的采用meta分析探讨能谱增强CT中标准化碘密度(normalized iodine concentrations,NIC)诊断结直肠癌淋巴结转移的价值。方法检索建库至2022年10月期间PubMed、Embase、Cochrane、Web of Science、CBM、CNKI、万方、维普数据库,筛选NIC诊断结直肠癌淋巴结转移相关的文献。采用诊断准确性研究的质量评价工具-2对文献进行偏倚风险评价,运用Meta-DiSc1.4进行数据统计,计算Spearman相关系数并绘制综合受试者工作特征曲线(sROC)以分析有无阈值效应引起的异质性。I2<50%采用固定效应合并效应量;I2≥50%采用随机效应合并效应量。采用Stata 14.0进行敏感性分析,以Deeks漏斗图检测发表偏倚。结果纳入7篇文献,共计717枚淋巴结,转移淋巴结314枚、非转移淋巴结403枚。按照能谱增强CT中的动脉期(arterial phase,AP)和静脉期(venous phase,VP)将其分为两个亚组。Meta DiSc1.4显示,两亚组均不存在阈值效应引起的异质性(均P>0.05)。进而根据I2结果,选择对应的效应模型合并效应量。结果(AP、VP)分别为:灵敏度=0.76(0.71~0.80)、0.67(0.61~0.73);特异度=0.71(0.66~0.75)、0.87(0.82~0.91);阳性似然比=2.83(1.85~4.31)、5.39(3.79~7.67);阴性似然比=0.33(0.23~0.46)、0.34(0.22~0.54);诊断比值比(diagnostic odds ratio,DOR)=10.00(4.38~22.82)、17.27(10.39~28.69);曲线下面积(area under the curve,AUC)=0.8354、0.8945。亚组-AP及亚组-VP敏感性分析显示研究稳定,并且不存在发表偏倚(P>0.05)。结论NIC有助于区分结直肠癌患者转移性和非转移性淋巴结。在灵敏度方面,AP的NIC更优;在特异度、阳性似然比、阴性似然比、DOR、AUC方面,VP的NIC具有更高的诊断价值。
基金supported by the National Key Research and Development Program of China (Grant No. 2017YFE0301201)partially by the National Natural Science Foundation of China (Grant Nos. U1967206 and 11775069)。
文摘The turbulence characteristics of plasmas with internal transport barriers in the HL-2A tokamak are analyzed by means of linear gyrokinetic simulations. It is found that turbulence is dominated by the ion temperature gradient(ITG)mode together with large-scale modes characterized by high-frequency electromagnetic fluctuation, which are destabilized by the steep ion temperature gradient in the weak magnetic shear regime. Comparison with solutions of analytical dispersion relations shows that their linear features match well with the beta-induced Alfvén eigenmode branch of the shear Alfvénic spectrum. It is further clarified that the large population of fast ions in these plasmas plays a stabilization role through the dilution mechanism in high-n ITG mode regimes.
文摘运用密度泛函理论对13种化合物进行几何结构全优化和频率计算,并计算了其芳香性指标NICS(Nucleus-Independent Chemical Shifts)值,研究了取代基对芳香性的影响以及芳香性与分子稳定性的关系。结果表明吸电子基团可以增加苯环的芳香性,供电子基团可以减低苯环的芳香性,随着体系稳定性的增加,苯环的芳香性降低。
