共查询到20条相似文献，搜索用时 31 毫秒
1.
研究了二氯二(三来膦)钯催化下及聚乙二醇存在下劳卤与二氧化碳的羰基化反应,提供了芳香族羰酸的简便合成法.本法优点是反应条件温和,反应在常压下进行;对多卤化物有良好的化学选择性,芳碘优先发生羰基化而分子中的氯和滇原子不受影响。 相似文献
2.
本文提出了一种离散余弦变换电路VLSI实现的可测试性设计。它采用基于算法结构变换的并行实现,所用乘法的数量大大减少,降低了硬件面积占用和功率消耗。为提高DCT的可靠性,在本设计中加入可测性设计方法,采用一种新的内建自测试(BIST)技术。实验表明该设计对运算器的内部结构和运算速度影响小,并具有较高的故障覆盖率。本文的方法适用于高可靠性要求下的数字信号处理的VLSI实现。 相似文献
3.
提出一种新的显示立体图像的方法,用计算机制作随机条形散斑体视对,利用其衍射和人眼的双目辐合来综合立体图,本方法为动态立体显示、彩色立体显示以及实际不存在物体的显示提供了可行的手段,也为研究人的视觉机理提供了一个有效的工具. 相似文献
4.
T.J. Moir 《Journal of The Franklin Institute》2009,346(3):237-252
A new method is proposed for finding the inverse of the covariance (or correlation) matrix. The technique is based on a previous method known as automatic variance control. The technique naturally gives rise to the inverse due to the properties of negative feedback itself rather than by traditional invertion methods. The method can be applied to the non-stationary problem and can form part of a recursive parameter estimation scheme. 相似文献
5.
Hong Zhu Chuan Chen Li-Zhi Liao Michael K. Ng 《Journal of The Franklin Institute》2018,355(4):1819-1845
The core issue of multiple graphs clustering is to find clusters of vertices from graphs such that these clusters are well-separated in each graph and clusters are consistent across different graphs. The problem can be formulated as a multiple orthogonality constrained optimization model which can be shown to be a relaxation of a multiple graphs cut problem. The resulting optimization problem can be solved by a gradient flow iterative method. The convergence of the proposed iterative scheme can be established. Numerical examples are presented to demonstrate the effectiveness of the proposed method for solving multiple graphs clustering problems in terms of clustering accuracy and computational efficiency. 相似文献
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Assigning appropriate weights for the linear combination data fusion method in information retrieval
In data fusion, the linear combination method is a very flexible method since different weights can be assigned to different systems. However, it remains an open question which weighting schema should be used. In some previous investigations and experiments, a simple weighting schema was used: for a system, its weight is assigned as its average performance over a group of training queries. However, it is not clear if this weighting schema is good or not. In some other investigations, different numerical optimisation methods were used to search for appropriate weights for the component systems. One major problem with those numerical optimisation methods is their low efficiency. It might not be feasible to use them in some situations, for example in some dynamic environments, system weights need to be updated from time to time for reasonably good performance. In this paper, we investigate the weighting issue by extensive experiments. The key point is to try to find the relation between performances of component systems and their corresponding weights which can lead to good fusion performance. We demonstrate that a series of power functions of average performance, which can be implemented as efficiently as the simple weighting schema, is more effective than the simple weighting schema for the linear data fusion method. Some other features of the power function weighting schema and the linear combination method are also investigated. The observations obtained from this study can be used directly in fusion applications of component retrieval results. The observations are also very useful for optimisation methods to choose better starting points and therefore to obtain more effective weights more quickly. 相似文献
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A method to easily manufacture and assemble a polydimethylsiloxane (PDMS) based microfluidic device is described. The method uses low cost materials and re-usable laser cut polymethyl methacrylate (PMMA) parts. In addition, the thickness of PDMS layers can be controlled and both PDMS layer surfaces are flat, which allows for multi-layer PDMS structures to be assembled. The use of mechanical clamping to seal the structure allows for easy cleaning and re-use of the manufactured part as it can be taken apart at any time. In this way, selected layers can be re-used or replaced. The process described can be easily adopted and utilised without the need for any costly clean room facilities or equipment such as oxygen bonders, making it ideal for laboratories, universities, and classrooms exploring microfluidics applications. 相似文献
9.
利用脉冲非线性状态反馈控制混沌 总被引：3，自引：0，他引：3
研究了脉冲非线性反馈控制方法控制Lorenz系统的混沌问题，首先从理论上论证了控制方法的正确性．然后设计出了三种控制器并给出了控制器应满足的条件，理论分析和数值模拟结果表明混沌Lorenz系统中的不稳定不动点能被稳定控制，而且Hopf分岔也能产生，给出了相应的数值模拟结果，例如不动点、极限环(IP)轨道，采用脉冲控制方法的优点是控制代价小，工程上易于实现，最后指出，对于其他具有平衡点对称的混沌系统如蔡氏电路系统的混沌控制，此控制策略同样有效。 相似文献
10.
NCEP/NCAR再分析数据在风能资源评估中的应用研究 总被引：1，自引：1，他引：0
规划风电场短期测风数据的测试相关预测（Measure-Correlate-Predict MCP）是反映风电场风能长期平均水平的主要技术手段,对于预测规划风电场代表年年发电量具有重要意义。然而工程实践中,气象站长期参考数据常受到各类客观因素的影响,数据质量不能满足MCP要求,进而造成对规划风电场风能资源的错误评估。NCEP/NCAR数据是由美国环境预报中心(NCEP)和国家大气研究中心(NCAR)联合推出的再分析数据集,该数据作为一种可替代的长期参考数据得到了广泛的应用。本文对NCEP/NCAR数据在风能资源评估中的应用进行研究,提出了适用于该数据的MCP分析方法——风指数法。通过算例分析后发现,以NCEP/NCAR再分析数据为长期参考数据,风指数法为计算方法的短期测风数据MCP分析原则具有较高的可靠性和工程实用价值。 相似文献
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Performance analysis of a spreading sequence estimator for spread spectrum transmissions 总被引：4，自引：0，他引：4
C. Bouder 《Journal of The Franklin Institute》2004,341(7):595-614
Direct sequence spread spectrum transmissions (DS-SS) are now widely used for secure communications, as well as for multiple access. They have many interesting properties, including low probability of interception. Indeed, DS-SS transmitters use a periodical pseudo-random sequence to modulate the baseband signal before transmission. A receiver which does not know the sequence cannot demodulate the signal.In this paper, we propose a new method which can estimate the spreading sequence in a noncooperative context. The method is based on eigenanalysis techniques. The received signal is divided into windows, from which a covariance matrix is computed. We show that the sequence can be reconstructed from the two first eigenvectors of this matrix, and that useful information, such as desynchronisation time, can be extracted from the eigenvalues.The main achievement of the present paper is a performance analysis of the proposed spreading sequence estimation procedure. An analytical approach is first considered owing to matrix perturbation theory and Wishart matrix properties. Then, complementary Monte Carlo simulations are performed to show the effectiveness of the proposed method. 相似文献
12.
朱文杰 《中国科学院研究生院学报》1995,(1)
哈密尔顿系统具有很多本质的性质，如保面积、保能量和动量等，而最重要的是自治哈密尔顿系统相流的辛性质，这为保相面积和相体积提供了保证，因此我们希望差分格式在被用来求哈密尔顿系统的数值解时能保持这种辛性质。在文献［１─３］中，冯康等人发展了哈密尔顿系统辛差分格式的一整套理论。本文主要考虑辛ＲＫＮ方法及显式辛格式的阶条件，并给出一些高阶辛ＲＫＮ格式，还提出一种利用低阶格式构造高阶格式的方法。此方法对辛格式和非辛格式均适用。限于篇幅，本文略去大部分定理的证明并尽可能简化说明。 相似文献
13.
Early attempts to formulate information systems (IS) strategies concentrated on the analytical task of deriving IS strategies from business plans. The limitations of the static plans that often resulted from these formal studies were, however, soon discovered. The critics suggested informal and incremental planning to ensure flexibility, creativity and strategic thinking to comprise emergent strategies as well as planned strategies.In previous IS planning research, there appears to be a contradiction between the published planning methods and the generally held views about effective implementation of IS planning process. The explicit methods described in IS literature predominantly assume a comprehensive IS planning process. Despite the fact that many researchers consider incremental approaches to be more effective, methods that can be used to facilitate incremental IS planning are few, not detailed enough and not comprehensive.The four cycles method introduced in this paper attempts to combine the strengths of both the comprehensive and incremental planning to be able to recognise emerging trends and to make an e-business strategy. The method provides a basic schedule for organising planning activities. IS planning is seen as a continuous process that is periodically adjusted to the expectations of the participating managers. Practising managers can use the method to facilitate implementation of an incremental and continuous IS planning process. For e-business strategy research, the paper provides a theoretically based method that can be tested in future action research projects.The first results of conducted action research show that the method should not be used as a checklist but as a choice list. Each period had a constant focus on external developments and the fit with internal possibilities. The method provided a flexible and dynamic basis for actions. The emergent nature of the changes and the difficulty of formalising creativity and innovation placed restrictions on the planning process. We learned that a thematic approach where each cycle is given a creative subject helped to “open up” the users in the organisation. Future research should focus on the inter-organisational nature of e-business strategy. If it is difficult to get top management participation, it will be even more difficult with more organisations involved. 相似文献
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分析了《非煤矿床地下开采》课程教学存在问题,给出了课堂比较教学法实施方案;确定了预期能够显著提高教学效果的模型教学建设内容;针对教学、实验、实践三位一体的教学课程体系,认为应以实验、实践教学为主,理论教学为辅;探讨了过程控制的方法。 相似文献
15.
Xinwei Wang Chao Han Yuanjin Yu Zhaohua Yang 《Journal of The Franklin Institute》2018,355(7):3274-3287
A modified adaptive backstepping tracking method is proposed to improve the tracking performance of the magnetic bearing system with nonlinear magnetic toque. For a magnetically suspended momentum wheel, two dimensional gyroscopic torque can be produced when the rotor shaft is actively deflected by the active magnetic bearing. High precision rapid tracking control of shaft deflection is desiderated to provide high precision and wide bandwidth outputting torque. The nonlinearity of magnetic bearing is analyzed initially, and the stiffness coefficients of magnetic bearing can be treated as bounded continuous functions with respect to deflection angles. A fuzzy function based adaptive law is proposed to estimate the stiffness coefficients. Combining with a modified backstepping method, the proposed control strategy can deal with the nonlinearity efficiently when the shaft deflects rapidly, and its stability is proved by Lyapunov stability theory. To validate the effectiveness of this method, numerous simulations are performed and the results indicate that this method improves the tracking precision when tracking high frequency reference deflection angles. 相似文献
16.
内容分析方法及在人力资源管理研究中的运用 总被引：2，自引：0，他引：2
基于以往文献系统分析了内容分析方法的内涵、适合的人力资源管理研究问题,运用过程中的关键环节和优势及局限,初步明确了内容分析方法的特征及在人力资源管理研究中的意义。 相似文献
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网络产业接入定价与互联互通管制--对我国电信业互联互通问题的分析 总被引：7，自引：0，他引：7
随着我国电信、电力等网络产业改革的进展,互联互通问题也逐渐凸现出来。本文介绍了国外对垂直性的网络产业中互联互通管制的实践和相关的接入定价方法,并分析了目前困扰我国电信业的互联互通问题。通过分析本文认为:接入价格是实现有效互联互通的经济基础,接入价格应被设计为仅仅实现有效互联互通目标,而不能兼顾其他政策目标;过低的接入价格水平是目前电信业互联互通不畅的主要原因;我国目前应该选择以长期增量成本为基础的接入定价;在接入成本的计算方法上,应以长期增量成本法为主,短期内可以采用完全分配成本法作为一种过渡手段。 相似文献
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决策是一个比较复杂的过程,其过程包括评估和排序等相关步骤。本文立足模糊相似优先比决策方法,探讨模糊相似优先比决策方法与模糊相对比较决策方法的异同,同时人为地构造出一种特殊的模糊优先比矩阵,通过分析该矩阵在模糊相似优先比决策中的特点,得出有关结论,使模糊相似优先比决策方法更加完善,该结论也可作为对模糊相似优先比决策方法的思考与补充。 相似文献
20.
Dengue fever is one of the major health problems in India. Interaction with specific receptor(s) at the cell surface is one
of the first events in the pathogenesis of Dengue virus. However, relatively little is known about these receptors. Cellular
receptors in human monocytes and mouse neural cells are main target for the viral infection. The envelope protein of the virus
(E-protein) plays important role in attachment of virus to target cells and their interaction with cellular receptors. The
modulation of receptor gene(s) and/or protein(s) can be used as a method for interfering with virus entry and can thus become
a new method for disease prevention. The receptors can be purified by affinity chromatography using E-protein as ligand. It
has been reported that addition of highly sulfated heparan sulfate prevents E-protein binding to target cells suggesting that
heparan sulfate is utilized by dengue envelope protein to bind to target cells. 相似文献