可见光促进合成三氟甲基取代的四氢呋喃和四氢吡喃（英文）

利用相对廉价易得、操控简便的三氟甲基磺酰氯为三氟甲基自由基前体,在可见光催化下通过非活化烯烃的自由基1,2-烷氧基-三氟甲基化反应实现了一系列三氟甲基化的四氢呋喃和四氢吡喃化合物的高效合成.     

Sc3C2@C80与[12]CPP纳米环之间非共价相互作用的理论研究

金属富勒烯嵌套于纳米环内形成主客体系, 二者产生的主客体作用可诱导内部金属团簇的取向, 影响分子的电子结构等性质. 本文基于密度泛函理论(DFT)计算, 对碳纳米环[12]CPP(CPP=环苯撑, 主体分子)与金属富勒烯Sc₃C₂@C₈₀(客体分子)形成的主客体配合物的结构和性质进行了研究. 计算结果表明, 在最稳定构型中, [12]CPP呈现椭圆形, Sc₃C₂@C₈₀与[12]CPP的质心不再重合. Sc₃C₂@C₈₀在[12]CPP内旋转对构型总体能量影响仅为13.51 kJ/mol. [12]CPP向Sc₃C₂@C₈₀转移了0.03 e, 主客体分子之间存在弱相互作用. 对二者相互作用的分析结果表明, 色散作用在弱相互作用中占主导地位.     

南京市临江路跨城南河桥主桥型比选

本文对南京市临江路跨城南和桥梁上部结构进行了分析比选,旨在为工程建设与城市景观、经济指标之间选取最优方案。     

现代彩色图像分割技术综述

图像分割是进行图像理解与分析的基础,是图像工程技术中的一个重要问题,也是图像处理的经典难题。彩色图像比灰度图像具有更多的视觉信息,因而受到了越来越多的重视。文章将彩色图像的分割技术分为三大类,并分别加以系统概括,分析了各种方法的优缺点。     

河北省故城县土地规模化经营研究——以棉花种植为例

土地规模化经营是发展现代农业,实现规模效益,促进农村经济增长的关键性问题.对于土地制度还不健全的中国来说,应建立中国特色的适度规模经营模式.该文以河北省故城县为研究对象,通过对当地棉花种植农户在耕地面积、地块数和年劳动投入、物质投入(包括化肥投入、机械投入、农药投入、灌溉投入)及年产量等方面的抽样调查数据,计算得出样本均值,利用由非线性柯布-道格拉斯生产函数转化的多元线性回归模型建立数据之间的联系,并借助于Eviews软件对其进行回归分析.根据所得结果分析土地规模、细碎度与投资收益(用棉花产量衡量)的关系,从而对规模化经营作出评价,确立适宜的土地规模化经营模式,并根据当地情况提出相应的对策建议.     

图像阈值分割算法研究

图像阈值分割的方法很多,但目前很难找到适用于各种场合的分割方法。本文针对实际情况对几种分割方法进行了分析比较及实验研究。在此基础上引入了遗传算法,加快了算法的收敛速度。最后将一种改进的遗传算法用于优化图像分割,取得了较好的分割效能。     

Uncoupled achromatic condition of a dog-leg system with the presence of RF cavities

To merge the beam from either of the two injectors to the main linac, a dog-leg system will be employed in the second Medium Energy Beam Transport （MEBT2） line of the China ADS driving accelerator. The achromatic condition has to be guaranteed to avoid beam center excursion against energy jitter. RF cavities were found to be indispensable to control the bunch length growth in the dog-leg system of MEBT2. The full uncoupling between transverse and longitudinal plane is desired to minimize the growth of projected rms emittances. The uncoupled achromatic condition of this dogleg system with the presence of RF bunching cavities will be deduced using the transfer matrices method. It is found that, to fulfill the uncoupling condition, the distance between the bunching cavities is uniquely determined by the maximum energy gain of the RF cavities. The theoretical analysis is verified by the simulation code TraceWin. The space charge effect on the uncoupled achromatic condition and the beam emittance growth will Mso be discussed.     

Uncoupled achromatic condition of a dog-leg system with the presence of RF cavities

To merge the beam from either of the two injectors to the main linac, a dog-leg system will be employed in the second Medium Energy Beam Transport(MEBT2) line of the China ADS driving accelerator. The achromatic condition has to be guaranteed to avoid beam center excursion against energy jitter. RF cavities were found to be indispensable to control the bunch length growth in the dog-leg system of MEBT2. The full uncoupling between transverse and longitudinal plane is desired to minimize the growth of projected rms emittances. The uncoupled achromatic condition of this dogleg system with the presence of RF bunching cavities will be deduced using the transfer matrices method. It is found that, to fulfill the uncoupling condition, the distance between the bunching cavities is uniquely determined by the maximum energy gain of the RF cavities. The theoretical analysis is verified by the simulation code TraceWin. The space charge effect on the uncoupled achromatic condition and the beam emittance growth will also be discussed.     

旅游步道对缙云山群落物种多样性的影响

为了探寻旅游步道的设立对景区群落物种多样性的影响,在重庆缙云山自然保护区内的典型地段设立样地,调查人行步道以及公路旁植物群落的物种多样性,用物种丰富指数、Sinpson指数、Shannon-Wiener指数和Pielou均匀度比较分析了不同层次物种多样性的变化.结果显示人为干扰严重的区域草本层优势度较高,乔木层和灌木层的各项多样性指数均呈现出随着与步道距离的增加而逐渐增加的趋势,而草本层却出现相反的变化趋势.小路对群落物种多样性的影响比公路更剧烈.