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分布式光伏并网后功率因数变化分析及光伏对电网的影响
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作者 朱德志 徐沛 王红林 《镇江高专学报》 2024年第4期84-89,共6页
低压并网工商业分布式光伏发电项目投资成本逐步降低,越来越多的企业开始投资光伏电站。分布式光伏并网后注入有功电流会导致原来电力系统的计量电能表的功率因数发生变化,许多企业在光伏发电高峰期间出现功率因数不合格情况。分析研究... 低压并网工商业分布式光伏发电项目投资成本逐步降低,越来越多的企业开始投资光伏电站。分布式光伏并网后注入有功电流会导致原来电力系统的计量电能表的功率因数发生变化,许多企业在光伏发电高峰期间出现功率因数不合格情况。分析研究光伏低压并网对计量电能表功率因数变化及对电网的影响。 展开更多
关键词 分布式光伏发电 功率因数变化 光伏并网点选择
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基于功率因数变化量的干式空心电抗器匝间短路故障在线监测方法 被引量:24
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作者 赵春明 敖明 +1 位作者 王永红 孟子贺 《电力电容器与无功补偿》 北大核心 2020年第3期87-93,共7页
干式空心电抗器匝间短路故障频发,现有的监测方法存在准确度低,可靠性差及成本高等问题。为此,提出了一种基于功率因数变化量的匝间短路故障在线监测方法。建立了匝间短路故障电抗器的电路模型,在不同位置数值计算了故障电抗器电气参数... 干式空心电抗器匝间短路故障频发,现有的监测方法存在准确度低,可靠性差及成本高等问题。为此,提出了一种基于功率因数变化量的匝间短路故障在线监测方法。建立了匝间短路故障电抗器的电路模型,在不同位置数值计算了故障电抗器电气参数的变化量。在此基础上,确定了以功率因数为被监测量,并采用谐波分析法求取功率因数,最后搭建了试验平台进行试验研究。研究结果表明,匝间短路故障后,总电流变化很小,功率因数明显变大,各种电气参数的变化量均与短路位置有关。试验结果与理论分析结果相一致,验证了监测方法的正确性和有效性。 展开更多
关键词 干式空心电抗器 功率因数变化 匝间短路 在线监测
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“因数和积的变化规律”教学反思
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作者 邱正发 《小学教学研究》 2003年第9期28-29,共2页
连续经历了两次“因数和积的变化规律”的教学,两次所给学生空间的不同,学生的思维方式和学习方式也有根本的改变,颇有感受。
关键词 因数和积的变化规律” 教学反思 小学 数学教学 学习方式 教学方法 评析
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因数位置颠倒管见
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作者 刘广聚 《山东教育》 1998年第Z3期69-69,共1页
关键词 乘法交换律 小学数学 倒管 被乘数 变化因数 学习衔接 兖矿集团 不合道理 长方形 数学科学
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梭织物剪切刚度与交织结构的关系 被引量:5
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作者 徐广标 汪玲 王府梅 《东华大学学报(自然科学版)》 CAS CSCD 北大核心 2006年第1期41-45,共5页
通过分析剪切变形过程中纱线间的力学作用,研究织物结构与剪切刚度的关系。建立了织物剪切刚度与具体结构参数之间的理论方程。在58种精纺毛型织物试样的实验基础上,对已有的精纺毛型织物剪切刚度理论方程中经纬纱摩擦因数变化率与织物... 通过分析剪切变形过程中纱线间的力学作用,研究织物结构与剪切刚度的关系。建立了织物剪切刚度与具体结构参数之间的理论方程。在58种精纺毛型织物试样的实验基础上,对已有的精纺毛型织物剪切刚度理论方程中经纬纱摩擦因数变化率与织物结构参数之间的关系进行研究,结合理论方程讨论了影响织物剪切刚度的因素。 展开更多
关键词 梭织物 剪切刚度 理论方程 摩擦因数变化 结构参数
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一种改进的模糊控制电容投切方法的研究 被引量:6
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作者 李清慧 周玉国 +1 位作者 宋悦 刘子飞 《电测与仪表》 北大核心 2013年第12期79-82,99,共5页
为提高无功补偿中电容投切的控制效果,提出一种改进的模糊控制投切方法。该方法采用三输入单输出的形式,以电压、功率因数及功率因数变化率作为输入设计模糊控制系统,既解决了电容投切造成的电压波动问题,又对系统状态进行了有效预判。... 为提高无功补偿中电容投切的控制效果,提出一种改进的模糊控制投切方法。该方法采用三输入单输出的形式,以电压、功率因数及功率因数变化率作为输入设计模糊控制系统,既解决了电容投切造成的电压波动问题,又对系统状态进行了有效预判。利用MATLAB软件对其进行计算、仿真,其结果符合无功补偿原则和实际设计要求。这种改进的电容投切方案,消除了不必要的往复投切,避免了投切振荡,提高了系统跟随性,获得了理想的控制效果。 展开更多
关键词 模糊控制 三入单出 功率因数变化 无功补偿 电容投切
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湿式离合器接合过程摩擦振颤机理研究 被引量:9
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作者 杨立昆 李和言 马彪 《振动与冲击》 EI CSCD 北大核心 2016年第9期117-122,共6页
通过建立4自由度动力学模型,研究了湿式离合器在接合过程中的摩擦振颤问题。基于稳态的非线性LuGre摩擦模型,通过特征值方法进行稳定性分析,并基于MATLAB/Simulink对该动力学模型进行数值仿真。结果表明,摩擦因数随相对滑动速度的负梯... 通过建立4自由度动力学模型,研究了湿式离合器在接合过程中的摩擦振颤问题。基于稳态的非线性LuGre摩擦模型,通过特征值方法进行稳定性分析,并基于MATLAB/Simulink对该动力学模型进行数值仿真。结果表明,摩擦因数随相对滑动速度的负梯度变化及接触界面的压力波动是摩擦振颤发生的主要原因,在不稳定状态下,静、动摩擦因数之差越大,压力波动频率越接近不稳定模态固有频率,振颤越强烈;同时阻力矩激励也会对摩擦振颤产生与压力波动相同的效果。 展开更多
关键词 离合器振颤 摩擦因数负梯度变化 接触压力波动 阻力矩激励
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空心电力电抗器绝缘故障在线监测 被引量:4
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作者 张琪 《电力电容器与无功补偿》 北大核心 2019年第5期116-121,127,共7页
在对干式空心电抗器匝间绝缘在线监测技术进行研究的基础上,提出了检测损耗因数作为干式空心电抗器匝间绝缘故障在线监测的方法,探究了正常情况及匝间短路时空心电力电抗器电气参数和损耗因数的计算方法。以10 kV级串、并联空心电力电... 在对干式空心电抗器匝间绝缘在线监测技术进行研究的基础上,提出了检测损耗因数作为干式空心电抗器匝间绝缘故障在线监测的方法,探究了正常情况及匝间短路时空心电力电抗器电气参数和损耗因数的计算方法。以10 kV级串、并联空心电力电抗器为研究对象,对两台电力电抗器的不同位置匝间短路故障下各种电气参数及变化率进行了计算。结果表明,在不同温度下,通过监测损耗因数的变化,能准确地识别电力电抗器的绝缘故障。 展开更多
关键词 空心电力电抗器 匝间短路 损耗因数变化 在线监测
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精密车削过程的切削力建模研究 被引量:4
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作者 丁志超 闫舒洋 孙玉文 《机械工程师》 2020年第11期13-16,19,共5页
精密车削加工过程中的切削力对刀具磨损和工件的加工质量有着重要的影响,是选取切削加工参数的重要参考因素。文中基于金属切削机理和材料本构关系建立了一种新的精密车削力解析预测模型。首先,分别建立了考虑刃口圆弧半径与变化的滑动... 精密车削加工过程中的切削力对刀具磨损和工件的加工质量有着重要的影响,是选取切削加工参数的重要参考因素。文中基于金属切削机理和材料本构关系建立了一种新的精密车削力解析预测模型。首先,分别建立了考虑刃口圆弧半径与变化的滑动摩擦因数影响的剪切力系数模型和犁耕力系数模型;然后提出一种考虑材料强化效应影响的剪切流动应力求解方法;最后通过车削实验验证所建模型的有效性。 展开更多
关键词 车削力模型 刃口圆弧半径 变化的滑动摩擦因数 材料强化效应
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Association between TLR7 copy number variations and hepatitis B virus infection outcome in Chinese 被引量:2
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作者 Fang Li Xu Li +2 位作者 Gui-Zhou Zou Yu-Feng Gao Jun Ye 《World Journal of Gastroenterology》 SCIE CAS 2017年第9期1602-1607,共6页
AIM To explore whether copy number variations (CNVs) of toll-like receptor 7 (TLR7) are associated with susceptibility to chronic hepatitis B virus (HBV) infection. METHODS This study included 623 patients (495 males ... AIM To explore whether copy number variations (CNVs) of toll-like receptor 7 (TLR7) are associated with susceptibility to chronic hepatitis B virus (HBV) infection. METHODS This study included 623 patients (495 males and 128 females) with chronic hepatitis B virus infection (CHB) and 300 patients (135 females and 165 males) with acute hepatitis B virus infection (AHB) as controls. All CHB patients were further categorized according to disease progression after HBV infection (CHB, liver cirrhosis, or hepatocellular carcinoma). Copy numbers of the TLR7 gene were measured using the AccuCopy method chi(2) tests were used to evaluate the association between TLR7 CNVs and infection type. P values, odds ratios, and 95% confidence intervals (CIs) were used to estimate the effects of risk. RESULTS Among male patients, there were significant differences between the AHB group and CHB group in the distribution of TLR7 CNVs. Low copy numberof TLR7 was significantly associated with chronic HBV infection (OR = 0.329, 95% CI: 0.229-0.473, P > 0.001). Difference in TLR7 copy number was also found between AHB and CHB female patients, with low copy number again associated with an increased risk of chronic HBV infection (OR = 0.292, 95% CI: 0.173- 0.492, P < 0.001). However, there were no significant differences in TLR7 copy number among the three types of chronic HBV infection (CHB, liver cirrhosis, or hepatocellular carcinoma). In addition, there was no association between TLR7 copy number and titer of the HBV e antigen. CONCLUSION Low TLR7 copy number is a risk factor for chronic HBV infection but is not associated with later stages of disease progression. 展开更多
关键词 Toll-like receptor 7 Hepatitis B virus Copy number variations Gene susceptibility
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Deformation inhomogeneity due to sample-anvil friction in cylindrical compression test 被引量:3
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作者 Xian-jue YE Xiao-juan GONG +2 位作者 Biao-biao YANG Yun-ping LI Yan NIE 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2019年第2期279-286,共8页
Finite element(FEM)analysis was used to systematically evaluate the inhomogeneity of deformation in cylindrical samples with various sample-anvil friction coefficients,m.It was found that the level of friction strongl... Finite element(FEM)analysis was used to systematically evaluate the inhomogeneity of deformation in cylindrical samples with various sample-anvil friction coefficients,m.It was found that the level of friction strongly influences the deformation homogeneity,which increases significantly with the friction coefficient although the overall geometry of the samples almost remains the same when m >0.4.The position,at which the effective strain along the maximum radial direction in a compressed sample is equal to the equivalent strain of the sample,does not vary greatly with respect to both equivalent strain of the sample and m.Hardness measurements of compressed cylindrical 5056B Al alloy samples revealed a change of effective strain distribution similar to that revealed by FEM analysis.There exists a quantitative relationship between the hardness and the effective strain if no recrystallization or recovery occurs during the compression process. 展开更多
关键词 compression friction coefficient barreling cylinder deformation inhomogeneity
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Bose-Einstein Condensation in Linear Sigma Model at Hartree Approximation
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作者 SHU Song LI Jia-Rong 《Communications in Theoretical Physics》 SCIE CAS CSCD 2008年第5期1261-1264,共4页
The BEG of charged pions is investigated in the framework of O(4) linear sigma model. By using Cornwall- Jackiw-Tomboufis formalism, we have derived the gap equations for the effective masses of the mesons at finite... The BEG of charged pions is investigated in the framework of O(4) linear sigma model. By using Cornwall- Jackiw-Tomboufis formalism, we have derived the gap equations for the effective masses of the mesons at finite temperature and finite isospin density. The critical temperature and phase diagram of BEG are discussed in the non-chiral limit at Hartree approximation. 展开更多
关键词 finite temperature field theory Bose Einstein condensation phase transitions
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教学“积随因数变化的规律”有感
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作者 张桂芹 《中小学数学(小学版)》 2004年第7期41-42,共2页
对于一个因数不变,积随另一个因数变化的规律,学生掌握起来并不困难,但如果两个因数都变,积的变化规律就复杂了。单凭老师课堂上的泛泛而讲,让学生真正掌握好这部分知识是很难的。难怪讲授这部分知识时,总有老师发牢骚:“讲了几... 对于一个因数不变,积随另一个因数变化的规律,学生掌握起来并不困难,但如果两个因数都变,积的变化规律就复杂了。单凭老师课堂上的泛泛而讲,让学生真正掌握好这部分知识是很难的。难怪讲授这部分知识时,总有老师发牢骚:“讲了几节课,学生还不会”。为此。教学这部分知识前,我对这部分内容及教学方法进行了深入的研究和探索。结果发现用“记录法”讲授这部分知识,非常有效,原先几节课还讲不清的内容,只用一节课就让学生掌握得非常好。具体方法是: 展开更多
关键词 “积随因数变化的规律” 小学 数学教学 教学方法 课堂练习
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Detection of Shigella gyrA mutations and correlations between gyrA mutations and quinolones resistance 被引量:1
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作者 CHONG ZHEN WANG XUE PING LI XUE QIN QIAN LI SHaG QIAN 《Journal of Microbiology and Immunology》 2005年第2期101-104,共4页
118 clinical strains of Shigella were serotyped, in which 116 strains were tested to be S. flexneri. The susceptibilities of the S .flexneri strains to quinolones were measured by the disk-diffusion method. It was fou... 118 clinical strains of Shigella were serotyped, in which 116 strains were tested to be S. flexneri. The susceptibilities of the S .flexneri strains to quinolones were measured by the disk-diffusion method. It was found that most S .flexneri strains were susceptible to norfloxacin and ciprofloxacin, but resistant to nalidixic acid. To study the correlation between gyrA mutations and quinolones resistance, a fragment within the gyrA gene was amplified by PCR. The SSCP (Single-Strand Conformation Polymorphism) analysis was applied to detect mutations in PCR products of different strains. The mutations were then confirmed by DNA sequencing. Altogether, two types of mutation were revealed, in which one type was single mutation ( C42-T), and the other was double mutations ( C42-T and A54- G). By statistical analysis, C42-T (encoding Ser83-keu substitution) was shown to have correlation with nalidixic-acid resistance in the clinical strains of Shigella, while A54-G (encoding Asp87-Gly substitution) was shown to have correlations with both norfloxacin resistance and ciprofloxacin resistance. 展开更多
关键词 Shigella Quinolones resistance PCR-SSCP gyrA mutations
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Experimental study on explosive mechanism of spontaneous combustion gangue dump 被引量:1
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作者 PAN Rong-kun YU Ming-gao LU Lai-xiang 《Journal of Coal Science & Engineering(China)》 2009年第4期394-398,共5页
In order to explore the reason for the frequency explosion of spontaneous combustion coal gangue dump and get to know their explosion mechanism, established the experiment platform about spontaneous combustion coal ga... In order to explore the reason for the frequency explosion of spontaneous combustion coal gangue dump and get to know their explosion mechanism, established the experiment platform about spontaneous combustion coal gangue dump interoperable water. The gangue dump was heated using the external heat source, and rainy weather through water mist was simulated. Simulated experiment about explosion of spontaneous combustion coal gangue dump was carried out on the different conditions of the rainfall or not. The unusual gases produced in the course of gangue combustion and the changes in temperature were observed, and their impacts on the explosion of gangue dump were analyzed. The experimental results show that overall warming phenomenon of the gangue dump after watering occurred, the amount of H2 is three times than that before watering, and the amount of CO is far greater than that on the conditions of no-watering, at the same time combining with local observation and tests. It is found that the content of the oxygen reduce with the temperature increasing; however, gangue dump internal hydrogen content increase unusually on the rainfall conditions at 90 ℃, but the local measuring points reach the explosion limit. The existence of the CO and H2 is the main reason for inducing the explosion of spontaneous combustion coal gangue dump. 展开更多
关键词 coal gangue spontaneous combustion gangue dump explosive mechanism
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Vegetation Dynamics and Its Relationship with Climatic Factors in the Changbai Mountain Natural Reserve 被引量:5
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作者 H0U Guanglei ZHANG Hongyan WANG Yeqiao 《Journal of Mountain Science》 SCIE CSCD 2011年第6期865-875,共11页
This study examined the temporal variation of the Normalized Difference Vegetation Index (NDVI) and its relationship with climatic factors in the Changbai Mountain Natural Reserve (CMNR) during 2000 - 2009. The re... This study examined the temporal variation of the Normalized Difference Vegetation Index (NDVI) and its relationship with climatic factors in the Changbai Mountain Natural Reserve (CMNR) during 2000 - 2009. The results showed as follows. The average NDVI values increased at a rate of 0.0024 year-1. The increase rate differed with vegetation types, such as 0.0034 year-1 for forest and 0.0017 year-1 for tundra. Trend analyses revealed a consistent NDVI increase at the start and end of the growing season but little variation or decrease observed in July during the study period. The NDVI in CMNR showed a stronger correlation with temperature than with precipitation, especially in spring and autumn. A stronger correlation was observed between NDVI and temperature in the tundra zone (2,000-2,600m) than in the coniferous forest (1,100-1,700m) and Korean pine-broadleaved mixed forest (7oo-1,1oom) zones. The results indicate that vegetation at higher elevations is more sensitive to temperature change. NDVI variation had a strong correlation with temperature change (r=0.7311, p〈0.01) but less significant correlation with precipitation change. The result indicates that temperature can serve as a main indicator of vegetation sensitivity in the CMNR. 展开更多
关键词 Changbai Mountain Natural Reserve Remote sensing SPOT/VGT NDVI Climatic factors
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英语口语标准化的不可行
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作者 吴林兵 《时代文学》 北大核心 2009年第6期115-117,共3页
标准化英语口语是不可能的。口语中多样的语言要素使标准化难以实行;从社会语言学角度讲,口音接受度的不断提高使标准易变且难以另人信服;英语作为国际语言的新发展,为口语的多样化提供了空间。
关键词 标准口语 语言因数变化 口音的接受
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