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建筑中结构化的空间构造——整体性的结构与空间要素形式的结构 被引量:2
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作者 周露 田华 何晓姗 《建筑与文化》 2019年第11期216-217,共2页
建筑结构对空间的意义的思考,可追溯至古代哥特建筑。近代以来,多米诺结构体系、荷兰结构主义、结构法等都在努力从结构自身的逻辑出发,探索其对空间诠释的多样性。结构化的空间构造即从整体性的结构与空间要素形式的结构两个角度出发,... 建筑结构对空间的意义的思考,可追溯至古代哥特建筑。近代以来,多米诺结构体系、荷兰结构主义、结构法等都在努力从结构自身的逻辑出发,探索其对空间诠释的多样性。结构化的空间构造即从整体性的结构与空间要素形式的结构两个角度出发,对建筑结构与空间的相互关系进行探讨。 展开更多
关键词 结构化的空间构造 整体性的结构 空间要素形式的结构 多米诺结构体系 荷兰结构主义
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一种基于MDS-卷积码的LDPC码构造方法 被引量:3
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作者 乔华 董明科 项海格 《电子学报》 EI CAS CSCD 北大核心 2008年第1期117-121,共5页
近年来,结构化低密度奇偶校验(LDPC)码的构造方法受到了广泛地关注.本文提出了一种利用最大距离分割(MDS)编码构造结构化LDPC码的思路.该思路将基于两个信息符号的RS码构造LDPC码的方法扩展至适用于所有的MDS码.本文以具有MDS特性的卷... 近年来,结构化低密度奇偶校验(LDPC)码的构造方法受到了广泛地关注.本文提出了一种利用最大距离分割(MDS)编码构造结构化LDPC码的思路.该思路将基于两个信息符号的RS码构造LDPC码的方法扩展至适用于所有的MDS码.本文以具有MDS特性的卷积码为例详细描述该构造方法的细节,并构造了码长从255比特到4095比特的高码率LDPC码.由于卷积码的MDS定义不同于线性分组码,因此本文给出了一种对卷积码截短的方法及其必要的证明.仿真结果表明,本文构造MDS-Conv-LDPC码的性能优于随机构造的LDPC码. 展开更多
关键词 低密度奇偶校验码 最大距离分割码 卷积码 结构化构造方法
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光通信系统中LDPC码构造方法的研究进展
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作者 袁建国 汪哲 +3 位作者 孙雪敏 郭乔 胡潇月 吴英冬 《激光杂志》 北大核心 2017年第11期1-7,共7页
随着光通信系统的迅速发展,低密度奇偶校验(Low-Density Parity-Check,LDPC)码因其纠错能力强、构造方法灵活、译码复杂度低等优点而成为光通信系统中的研究与应用热点。由于LDPC码纠错性能主要取决于其校验矩阵的构造,因而文章针对适... 随着光通信系统的迅速发展,低密度奇偶校验(Low-Density Parity-Check,LDPC)码因其纠错能力强、构造方法灵活、译码复杂度低等优点而成为光通信系统中的研究与应用热点。由于LDPC码纠错性能主要取决于其校验矩阵的构造,因而文章针对适用于光通信系统中LDPC码的校验矩阵构造方法展开了综述性研究。文章从LDPC码的概念、校验矩阵及其Tanner图表达方式、影响LDPC码性能的因素以及LDPC码的随机构造方法和结构化构造方法等方面,综述了光通信系统中LDPC码构造方法的研究进展。分析总结了目前适用于光通信系统中LDPC码构造方法研究中亟待解决的关键问题,为今后深入开展相关研究提供理论指导。 展开更多
关键词 低密度奇偶校验码 校验矩阵 随机构造 结构化构造 光通信系统
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卫星激光通信中LDPC码构造方法的研究进展
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作者 袁建国 刘议靖 蒯家松 《激光杂志》 CAS 北大核心 2022年第1期1-7,共7页
激光因其单色性好、功率密度大等特性被提出应用于卫星通信系统中以应对未来通信业务需求,但激光通信在传输过程中受大气等因素影响会造成其传输可靠性降低。而低密度奇偶校验(Low-Density Parity-Check, LDPC)码因其灵活的构造方法、... 激光因其单色性好、功率密度大等特性被提出应用于卫星通信系统中以应对未来通信业务需求,但激光通信在传输过程中受大气等因素影响会造成其传输可靠性降低。而低密度奇偶校验(Low-Density Parity-Check, LDPC)码因其灵活的构造方法、较低的编译码复杂度、纠错能力强等优点已被证明适用于卫星激光通信。本文从LDPC码的分类及其校验矩阵构造方法等方面对适用于卫星激光通信系统中的LDPC码进行探讨与分析,详细论述了Gallager、Mackay与PEG(Progressive Edge Growth)三种随机构造方法和组合构造、有限几何构造与循环置换矩阵三种结构化构造方法以及基于原模图扩展的循环置换矩阵混合构造方法。在此基础上,分析、归纳与总结了适用于卫星激光通信的LDPC码构造方法的研究进展与现状,为卫星激光通信中LDPC码的深入研究提供理论指导。 展开更多
关键词 卫星激光通信 低密度奇偶校验码 随机构造 结构化构造 原模图
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Ultrastructural Studies on the Development of Oil Cells in Litsea pungens 被引量:2
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作者 初庆刚 胡正海 《Acta Botanica Sinica》 CSCD 2001年第4期339-347,共9页
The developmental process of oil cells in the shoot of Litsea pungens Hemsl. has been studied with transmission electron microscopy. According to the development of the three layers of cell wall, the developmental pro... The developmental process of oil cells in the shoot of Litsea pungens Hemsl. has been studied with transmission electron microscopy. According to the development of the three layers of cell wall, the developmental process could be divided into 4 stages. In stage 1, the cell wall consisted only of a primary (the outmost) cellulose layer, which might further be divided into two substages, the oil cell initial, and the vacuolizing oil cell. During this stage, there were some small electron translucent vesicles and dark osmiophilic droplets of variant sizes in the different-shaped plastids. It was observed that some dark and gray osmiophilic materials coalesced to vacuoles in the cytoplasm. In stage 2, a lamellated suberin layer accumulated inside the primary cellulose layer. In stage 3, a thicker and looser inner cellulose wall layer was formed gradually inside the suberin layer. Some dark osmiophilic droplets have been observed in this loose inner cellulose wall layer. The plasmodesmata were blocked up and became a special structure. Then, the big vacuole, which is the oil sac, was full of osmiophilic oil. In stage 4, the oil cell became matured and the cytoplasm disintegrated. The oil sac enveloped from plasmalemma was attached to the cupule, which was formed by the protuberance of the inner cellulose wall layer into the lumen. After the maturity of oil cell, the ground cytoplasm began to disintegrate and became electron opaque or exhibited in a disordered state, and the osmiophilic oil appeared light gray. 展开更多
关键词 Litsea pungens oil cells development ULTRASTRUCTURE suberin layer cupule
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Changing Spatial and Structural Patterns of Non-agricultural Activities in Outward-moving Beijing Urban Fringe 被引量:3
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作者 CAO Guangzhong LIU Tao +1 位作者 LIU Hui MIAO Yangbing 《Chinese Geographical Science》 SCIE CSCD 2012年第6期718-729,共12页
As responses to metropolitan suburbanization and rural urbanization,the formation and evolution of urban fringes should be understood against the background of overall economic development and spatial reconstruction o... As responses to metropolitan suburbanization and rural urbanization,the formation and evolution of urban fringes should be understood against the background of overall economic development and spatial reconstruction of entire metropolises.At the same time,however,endogenous interactions between industrial structure and spatial patterns of non-agricultural activities are also worthy of scholarly attention.Since the 1980s,studies on urban fringes in China have been restricted by the lack of micro-level data.This paper investigates the spatial expansion and structural evolution of the urban fringe by taking the case of Beijing and uses systematic firm-level data in 1996 and 2001 from the National Census of Basic Units.The diversity of distribution patterns across industrial sectors brings about two interrelated results.On the one hand,structural adjustment of non-agricultural industries promotes the expansion and spatial evolution of the urban fringe.On the other hand,the stability and dynamics of industrial structure coexist in the moving urban fringe.This study also reveals that the outward-moving urban fringe is the optimal location for manufacturing,especially heavy manufacturing,as well as traditional producer and consumer services.However,industries with spatial stickiness such as tourism and sports have not moved with the fringe.Most advanced services remain concentrated in the city center.The authors argue that it is essential for understanding and managing urban fringes to take into account spatial evolution and industrial structural adjustment together with their interaction with each other. 展开更多
关键词 urban fringe industrial structure spatial evolution SUBURBANIZATION BEIJING China
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Mineralization enrichment regularity of gold deposit in Shangzhuang, northwestern Jiaodong
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作者 QI Caisong ZHANG Yuan 《Global Geology》 2013年第2期68-74,共7页
Shangzhuang gold deposit located in the Wangershan fault zone of northwestern Jiaodong is of meso- hypogenic altered rock type. The ore bodies occur at the hanging wall and footwall of Wangershan fault in vein or irre... Shangzhuang gold deposit located in the Wangershan fault zone of northwestern Jiaodong is of meso- hypogenic altered rock type. The ore bodies occur at the hanging wall and footwall of Wangershan fault in vein or irregular shapes with the NE strike, NW trend, 30° -60°~ in dip and the lateral trending of SW. The ores are composed of pyrite, quartz, sericite, bismuthinite, native gold, bismuth sulfosah minerals, chalcopyrite, etc. , shown as brecciated structure and vein structure with metasomatic dissolution textures. The wall rock altera- tion is mainly described as phyllic alteration and silicification. The mineralization of this deposit is controlled by structure and altered rocks. The ore-controlling fault structures of this deposit is Wangershan fault, of which the intersection of major fault and secondary fault is the main ore-bearing position of this gold deposit, and the lar- ger arc curved position is a favorable part for ore body occurrence. On the plane, the ore body is shown as equi- distant pinch-out reproduction. 展开更多
关键词 deposit characteristics ore-controlling regularity Shangzhuang gold deposit
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Spectra response from macromolecular structure evolution of tectonically deformed coal of different deformation mechanisms 被引量:19
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作者 LI XiaoShi JU YiWen +1 位作者 HOU QuanLin LIN Hong 《Science China Earth Sciences》 SCIE EI CAS 2012年第8期1269-1279,共11页
Coals with different deformation mechanisms(brittle deformation,brittle-ductile deformation,and ductile deformation) repre-sent different ways in macromolecular structure evolution based on the metamorphism.The evolut... Coals with different deformation mechanisms(brittle deformation,brittle-ductile deformation,and ductile deformation) repre-sent different ways in macromolecular structure evolution based on the metamorphism.The evolution of coal structure could affect the occurrence condition of coalbed methane(CBM) because the nanopore structure affected by macromolecular struc-ture is the most important reservoir for CBM.This paper analyzes the evolutions and mechanisms of structure and functional group of tectonically deformed coals(TDCs) collected from Huainan-Huaibei coalfield using X-ray diffraction(XRD),Raman spectroscopy,and Fourier Transform Infrared(FTIR) spectroscopy methods.The results show that the macromolecular struc-ture evolutions of TDC are different from the primary structure coal as a result of the different metamorphic grade and defor-mation mechanisms.The different deformation mechanisms variously affect the process of functional group and polyconden-sation of macromolecular structure.Furthermore,the tectonic deformation leads to secondary structural defects and reduces the structure stability of TDC.The coupled evolution on stacking and extension caused by the changes of secondary structural de-fects results from different deformation mechanisms.We consider that the changes of chemical structure and secondary struc-tural defects are the primary reasons for the various structure evolutions of TDC compared with primary structure coal. 展开更多
关键词 tectonicaHy deformed coal METAMORPHISM deformation mechanism macromolecular structure secondary structuraldefect
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