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不平衡电网下模块化多电平换流器的直流环流均衡策略

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电工技术学报 2024年第2期39卷 541-553页

作者：潘子迅杨晓峰赵锐崔晨阳郑琼林北京交通大学电气工程学院北京100044

不平衡电网下模块化多电平换流器(MMC)存在三相直流环流不均衡问题,易导致相间电流应力和热应力差异,降低其在不平衡工况下安全运行能力。该文从桥臂功率角度分析不平衡电网下三相MMC直流环流不均衡现象和基于零序电压注入的直流环流均... 详细信息

不平衡电网下模块化多电平换流器(MMC)存在三相直流环流不均衡问题,易导致相间电流应力和热应力差异,降低其在不平衡工况下安全运行能力。该文从桥臂功率角度分析不平衡电网下三相MMC直流环流不均衡现象和基于零序电压注入的直流环流均衡机理。提出一种零序电压注入的直流环流均衡方法,通过网侧电流与直流环流偏差量计算得到零序电压相位,经过比例谐振控制器生成零序电压注入量,进而实现直流环流的快速、有效均衡。在所提出的控制策略的基础上,研究该方法对MMC桥臂电流峰值、有效值及子模块电容电压纹波的影响规律。仿真与实验结果验证了该文理论分析与控制策略的有效性。

关键词：不平衡电网模块化多电平换流器直流环流零序电压注入桥臂电流子模块电容电压

Theoretical and Experimental Study of a Numerical Aperture for Multimode PCS Fiber Optics Using an Imaging Technique

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Chinese Physics Letters 2012年第11期29卷 119-122页

作者： Saman q.Mawlud Nahlah q.Muhamad Department of Physics Education CollageScientific DepartmentSalahaddin UniversityErbilKurdistan RegionIraq

We study theoretically and experimentally the properties of numerical aperture(NA)of multimode graded-index plastic core silica(PCS)fibers by using an image technique.A He-Ne laser at wavelength 632.8 nm and output power 1 mW is used as the transmitter light *** output beam images and intensity profiles of an optical fiber are investigated by using an imaging *** laser beam profiles captured by a sensitive digital Nikon camera are processed and analyzed by using a Gaussian intensity distribution in a 2D graph.A MathCAD 14 program is used for converting the image of the laser output beam into *** theoretical and experimental values of the numerical aperture for the used optical fiber in this study are found to be 0.5 and 0.4924,*** theoretical value of V-number is also calculated to be approximately 2482.

关键词： technique fiber PCS

Acasta片麻杂岩多期次热事件:来自锆石、榍石和磷灰石的原位微区年代学证据

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中国科学：地球科学 2024年第3期54卷 693-707页

作者：梅清风杨进辉孙金凤李秋立吴石头凌潇潇彭澎王浩中国科学院地质与地球物理研究所岩石圈演化国家重点实验室北京100029 中国科学院大学地球与行星科学学院北京100049 中国科学院大学计算地球动力学重点实验室北京100049

本文使用激光剥蚀电感耦合等离子体质谱(LA-ICPMS)和二次离子质谱(SIMS)对Acasta片麻杂岩样品碎片(大小约1cm2)中的锆石、磷灰石和榍石进行了原位微区定年,以制约Acasta片麻杂岩的热演化历史.这些样品碎片中的锆石显示多期年龄,反映了... 详细信息

本文使用激光剥蚀电感耦合等离子体质谱(LA-ICPMS)和二次离子质谱(SIMS)对Acasta片麻杂岩样品碎片(大小约1cm2)中的锆石、磷灰石和榍石进行了原位微区定年,以制约Acasta片麻杂岩的热演化历史.这些样品碎片中的锆石显示多期年龄,反映了继承锆石的存在或者锆石结晶后的再生长过程.结合前人研究,本文锆石数据揭示, Acasta片麻杂岩经历的多期岩浆事件发生时间分别为:>3.96、约3.72和约3.57Ga.样品AY199中榍石的PbPb等时线年龄为(2911±22)Ma(95%置信水平, MSWD=1.5),与Acasta片麻杂岩记录的太古宙最后一次岩浆事件年龄一致.样品AC478和AY066中榍石U-Pb年龄分别为(1932±270)Ma(95%置信水平, MSWD=2.3)和(1813±45)Ma(95%置信水平, MSWD=2.3).样品P090803-C中磷灰石的Pb-Pb等时线年龄为(1833±26)Ma(95%置信水平,MSWD=1.4).样品AC478、AY199和AY066中磷灰石U-Pb年龄分别为(1850±20)Ma(95%置信水平, MSWD=1.3)、(1827±100)Ma(95%置信水平, MSWD=6.3)和(1807±58)Ma(95%置信水平, MSWD=3.9).样品AC478和AY066中的榍石U-Pb年龄以及本文所有样品中的磷灰石Pb-Pb或U-Pb年龄相同,均为约1.9~1.8Ga,指示Wopmay造山作用导致的矿物U-Pb体系重置,证明了Wopmay造山作用的峰期温度超过了磷灰石的U-Pb体系封闭温度,并接近或者超过榍石的U-Pb体系封闭温度.

关键词：锆石榍石磷灰石 Acasta片麻杂岩 Wopmay造山带

A TWO-LEVEL GENETIC ALGORITHM FOR SCHEDULING IN ASSEMBLY ISLANDS WITH FIXED-POSITION LAYOUTS

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Journal of Systems Science and Systems Engineering 2010年第2期19卷 150-161页

作者： George q.HUANG Department of Industrial and Manufacturing Systems Engineering The University of Hong Kong

This paper focuses on the scheduling problem in assembly islands environment with fixed-position layouts. In such configuration, the product normally remains in one location for its entire manufacturing period while machines, materials and workers are moved to an assembly site called an assembly island. This production layout has some unique features such as moving assembly workers, tools and materials; limited space at assembly site; considerable distance between islands. The authors first give the definition and mathematical model for the scheduling problem and then propose a two-level genetic algorithm to obtain a near optimal solution to minimize the makespan. Experimental results show that this algorithm is effective. The performance analysis of the proposed algorithm indicates that it is more efficient in the airline or shipbuilding industry than in the machine or tool final assembly companies.

关键词： Assembly islands scheduling genetic algorithm

GLOBAL SUPERCONVERGENCE ESTIMATES OF FINITE ELEMENT METHOD FOR SCHRODINGER EqUATION

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Journal of Computational Mathematics 1998年第6期16卷 521-526页

作者： Lin, q Liu, Xq Acad Sinica Inst Syst Sci Beijing 100080 Peoples R China Xiangtan Teachers Coll Dept Math Hunan 411201 Peoples R China

In this paper, we shall study the initial boundary value problem of Schrodinger equation. The second order gradient superconvergence estimates for the problem are obtained solving by linear finite elements.

关键词： finite element superconvergence estimates interpolation Schrodinger equation

HIGH ACCURACY ANALYSIS OF THE WILSON ELEMENT

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Journal of Computational Mathematics 1999年第2期17卷 113-124页

作者： Luo, P Lin, q Chinese Acad Sci Inst Math Beijing 100080 Peoples R China Chinese Acad Sci Inst Syst Sci Beijing 100080 Peoples R China

In this paper, the Wilson nonconforming finite element is considered for solving a class of second-order elliptic boundary value problems. Based on an asymptotic error expansion for the Wilson finite element, the glob... 详细信息

关键词： finite elements defect correction global superconvergence Wilson element

Rules essential for water molecular undercoordination

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Chinese Physics B 2020年第8期29卷 33-47页

作者： Chang q Sun School of EEE Nanyang Technological UniversitySingapore 639798

A sequential of concepts developed in the last decade has enabled a resolution to multiple anomalies of water ice and its low-dimensionality,*** concepts include the coupled hydrogen bond(O:H–O)oscillator pair,segmental specific heat,three-body coupling potentials,quasisolidity,and *** anomalies include ice buoyancy,ice slipperiness,water skin toughness,supercooling and superheating at the nanoscale,*** shows consistently that molecular undercoordination shortens the H–O bond and stiffens its phonon while undercoordination does the O:H nonbond contrastingly associated with strong lone pair“:”polarization,which endows the low-dimensional water ice with *** supersolid phase is hydrophobic,less dense,viscoelastic,thermally more diffusive,and stable,having longer electron and phonon *** equal number of lone pairs and protons reserves the configuration and orientation of the coupled O:H–O bonds and restricts molecular rotation and proton hopping,which entitles water the simplest,ordered,tetrahedrally-coordinated,fluctuating molecular crystal covered with a supersolid *** O:H–O segmental cooperativity and specific-heat disparity form the soul dictate the extraordinary adaptivity,reactivity,recoverability,and sensitivity of water ice when subjecting to physical *** is recommended that the premise of“hydrogen bonding and electronic dynamics”would deepen the insight into the core physics and chemistry of water ice.

关键词： hydrogen bonding molecular crystals structural transitions in nanoscale materials liquid-liquid transitions

Synthesis of Polynorbornene-Poly(ethylene-co-propylene)Diblock Copolymer

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Chinese Chemical Letters 1998年第5期9卷 447-450页

作者： Wu, q Wen, q Lu, ZJ Zhongshan Univ Inst Polymer Sci Canton 510275 Peoples R China

Transformation of living ring-opening metathesis polymerization into coordination polymerization by converting the titanacyclobutane group attached to a polynorbornene chain into titanocene alkoxide has been used for the synthesis of polynorbornene-poly(ethylene-co-propylene) block copolymer. Preliminary characterizations of the copolymerization products by solvent extraction and C-13 NMR spectrum are reported.

关键词： ring-opening metathesis polymerization coordination polymerization diblock copolymer norbornene ethylene propylene

Overexpression of Arabidopsis Sorting Nexin AtSNX2b Inhibits Endocytic Trafficking to the Vacuole

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Molecular Plant 2008年第6期1卷 961-976页

作者： Nguyen q. Phan Department of Genetics Development and Cell Biology Iowa State University Ames IA 50011 USA Interdepartmental Genetics Program Iowa State University Ames IA 50011 USA Plant Sciences Institute Iowa State University Ames IA 50011 USA

Sorting nexins are conserved proteins that function in vesicular trafficking and contain a characteristic phox homology （PX） domain. Here, we characterize the ubiquitously expressed Arabidopsis thaliana sorting nexin AtSNX2b. Sub-cellular fractionation studies indicate that AtSNX2b is peripherally associated with membranes. The AtSNX2b PX domain binds to phosphatidylinositol 3-phosphate in vitro and this association is required for the localization of GFPAtSNX2b to punctate structures in vivo, identified as the trans-Golgi network, prevacuolar compartment and endosomes. Overexpression of GFP-tagged AtSNX2b produces enlarged GFP-labeled compartments that can also be labeled by the endocytic tracer FM4-64. Endocytic trafficking of FM4-64 to the vacuole is arrested in these GFP-AtSNX2b compartments, and similar FM4-64-accumulating compartments are seen upon overexpression of untagged AtSNX2b. This suggests that exit of membrane components from these enlarged or aggregated endosomes is inhibited. Vacuolar proteins containing an N-terminal propeptide, but not those with a C-terminal propeptide, are also present in these enlarged compartments. We hypothesize that AtSNX2b is involved in vesicular trafficking from endosomes to the vacuole.

关键词： phox homology Overexpression Vacuole