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31.
互联网组播技术可以从根本上改善网络带宽的利用率,使发送者和路由器的处理消耗以及发送延迟降到最低的程度。IGMP是一种应用比较广泛的组播用户组管理协议,但是本身没有认证功能。PAP(密码认证协议)提供了一种简单的可以使端对端使用2次握手建立身份验证的协议。论文提出一种IGMP改进方案,把PAP认证协议添加在IGMP v3协议的扩展字段中,用于组播路由的最后一跳认证。 相似文献
32.
为了研究CCD与CMOS像素传感器对γ射线电离辐射的响应差异,对比研究了4类像素传感器的结构特点和辐射响应特性。通过辐射实验,对各传感器在不同辐射水平条件下的光子响应事件分布、平均灰度值以及典型光子响应事件进行研究。研究结果表明:光子响应程度均与辐射剂量率相关;CCD像素传感器的沟道传输方式使每列像元间的辐射响应更容易相互干扰;平均灰度值随剂量率的增大存在明显的梯度,各积分周期内输出信号灰度值围绕均值上下波动,CCD像素传感器输出信号灰度浮动范围较小;CMOS像素传感器各像元对光子的响应更加明显,CCD像素传感器各像元的响应信号易与相邻像元发生串扰;各类像素传感器典型辐射响应事件区域中发生光子响应的像元数量随剂量率的增大而增多,响应事件并非单个光子的行为,而是反映了多个光子在区域内同时沉积能量的过程。本研究为开发像素传感器的γ射线辐射探测技术和应用提供了重要的理论分析和实验数据支撑。 相似文献
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34.
Recep Ucan Umit Tunca Gurkan Hizal 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):2019-2025
The controlled polymerization of methyl methacrylate (MMA) in bulk was initiated with p‐chlorobenzenediazonium tetrafluoroborate ( 1 ) and Cu(II) or Cu(I)/Cu(II)/N,N,N′,N″,N″‐pentamethyldietylene triamine (PMDETA) complex system at various temperatures (20, 60, and 90 °C). The proposed polymerization mechanism is based on the Meerwein‐type arylation reaction followed by a reverse atom transfer radical polymerization. In this mechanism, aryl radicals formed by the reaction with 1 and Cu(I) and/or PMDETA initiated the polymerization of MMA. The polymerization is controlled up to a molecular weight of 46,000 at 90 °C. Chain extension was carried out to confirm the controlled manner of the polymerization system. In all polymerization systems, the polydispersity index and initiator efficiency ranged from 1.10–1.57 to 0.10–0.21, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2019–2025, 2003 相似文献
35.
Zan Ting-quan 《应用数学和力学(英文版)》1988,9(10):985-992
This series of papers is prepared to develop systematically the complicated dynamical behaviors of nonlinear ecosystem and its internal mechanism. In this paper, we state briefly the increasing importance of ecology, describe and comment on the situations and reasons why ecology theory is behind practice. Then, we point out a procedure which modern ecology research should obey, and discuss the four basic characteristics of ecosystem in detail: level, opening, nonlinear and far from equilibrium. At last, we discuss systematically equilibrium and nonequilibrium, stable and unstable, environmental stochasticity and dynamical stochasticity, and conclude that there exists a bridge between deterministic behaviors and stochastic behaviors, which will result in a new model for ecological prediction.Supported by Youth Fund of Chinese Academy of Science and Youth Fund of Lanzhou University. 相似文献
36.
Yu-Chiang Chao Yi-Sa Huang Hsin-Ping Wang Ssu-Ming Fu Chien-Hao Huang Yen-Chun Liang Wen-Cheng Yang Yu-Sheng Huang Gao-Fong Chang Hsiao-Wen Zan Hsin-Fei Meng Chen-Hsiung Hung Chien-Chung Fu 《Organic Electronics》2011,12(11):1899-1902
A hydrogel sensing film for a real-time and indicator-free detection of Zn2+ is developed by embedding a fluorescent indicator 11,16-bis(phenyl)-6,6,21,21-tetramethyl-m-benzi-6,21-porphodimethene in a hydrogel host poly(2-hydroxyethyl methacrylate). The sensing film shows high stability and selectivity to Zn2+. The sensitivity of the sensing film is increased by fabricating a micron-sized pillar array on the surface of the sensing film to increase the surface area. For Zn2+ concentrations of 10−4 and 10−3 M, the response time is 30 and 3 s, respectively. 相似文献
37.
传统DEA模型在数据两分(偏好与规避)的基础上考察决策单元的有效性,在某些场合不再适用,文章根据决策者的偏好将数据分为三类:规避、偏好、中性类,在此基础上构造评价相对有效性的DEA模型.相较而言,基于数据三分法的DEA模型更具一般性,利用该模型,文章考察了中国近年投入产出绩效问题. 相似文献
38.
Wide‐Area Strain Sensors based upon Graphene‐Polymer Composite Coatings Probed by Raman Spectroscopy 下载免费PDF全文
Arun Prakash Aranga Raju Amanda Lewis Brian Derby Robert J. Young Ian A. Kinloch Recep Zan Kostya S. Novoselov 《Advanced functional materials》2014,24(19):2865-2874
Functional graphene optical sensors are now viable due to the recent developments in hand‐held Raman spectroscopy and the chemical vapor deposition (CVD) of graphene films. Herein, the strain in graphene/poly (methyl methacrylate) sensor coatings is followed using Raman band shifts. The performance of an “ideal” mechanically‐exfoliated single crystal graphene flake is compared to a scalable CVD graphene film. The dry‐transferred mechanically exfoliated sample has no residual stresses, whereas the CVD sample is in compression following the solvent evaporation during its transfer. The behavior of the sensors under cyclic deformation shows an initial breakdown of the graphene‐polymer interface with the interface then stabilizing after several cycles. The Raman 2D band shift rates per unit strain of the exfoliated graphene are ≈35% higher than CVD graphene making the former more strain sensitive. However, for practical wide‐area applications, CVD graphene coatings are still viable candidates as a Raman system can be used to read the strain in any 5 μm diameter spot in the coating to an absolute accuracy of ≈0.01% strain and resolution of ≈27 microstrains (μs), which compares favorably to commercial photoelastic systems. 相似文献
39.
该文主要研究一种面向到达时间差(TDOA)被动定位的定位节点选择方法。首先,通过经典的闭式解析算法将TDOA非线性方程转化为伪线性方程,并使用位置误差的协方差矩阵来度量定位精度。其次,在可用节点数量给定的条件下,在数学上将定位节点选择问题转化为最小化位置误差协方差矩阵的迹这一非凸优化问题。然后,将非凸优化问题凸松弛并化为半正定规划问题,从而快速有效地求解出最优的定位节点组合。仿真结果表明,所提节点优选方法的性能非常接近穷尽搜索方法,而且克服了穷尽搜索方法运算复杂度高、时效性差的不足,从而验证了所提方法的有效性。
相似文献40.