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Koksal Erenturk 《Journal of The Franklin Institute》2010,347(7):1171-1185
This study presents application of a fuzzy controller to a nonlinear two-mass system control. The proposed controller structure is strengthened with a gray estimator. Firstly, a complete state-space mathematical model for a nonlinear two-mass system is developed and numerically simulated. Then, a fuzzy controller is designed to regulate the speed of the system. In order to perform a dynamic and powerful control action, future error values are estimated by gray modeling technique. The gray estimators of the torsional torque and the load machine speed are tested with open-loop and closed-loop control structures to test the robustness of the proposed method for step changes in input parameters. It is observed that the tracking ability of the gray estimators is not influenced for different operation modes. The performances of the control structures, which are supported with gray estimators, are given and no additional feedbacks are required for robust control action. The simulation results are confirmed by experimental results and conclusions are given. 相似文献
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居民重组是城市系统的复杂问题。我们首次在长春市居民中进行了问卷调查,将877例有效问卷进行了统计分析,针对居民重组的影响因素进行了Logistic回归,结果入选了8项主要因素。 相似文献
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《Information processing & management》2001,37(4):639-657
The paper introduces a new method for the visualization of information retrieval. Angle attributes of a document are used to construct the angle–angle-based visual space. The retrieved documents are perceived, several traditional information retrieval evaluation models are visualized and interpreted, and new non-traditional retrieval control means based on the model are explored in the two-dimensional angle display space. The impacts of different metrics on the visualization of information retrieval are discussed. Ambiguity, future research directions and other relevant issues are also addressed. 相似文献
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本文应用连续流循环模型研究传热的不可逆性和工质的内不可逆性对高温吸收式热泵性能的影响，导出高温吸收式热泵的两个重要性能参数——最大供热率及其所对应的供热系数．并对传热面积及有关性能作了优化分析，得到一些有意义的新结果． 相似文献
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The steady two-dimensional stagnation point flow toward a stretching/shrinking sheet with the bottom surface of the sheet heated by convection from a hot fluid is considered. The governing partial differential equations are transformed into ordinary differential equations, before being solved numerically. Results for the skin friction coefficient and the local Nusselt number as well as the temperature profiles are presented for different values of the governing parameters. Effects of the governing parameters on the heat transfer characteristics are thoroughly examined. Different from a stretching sheet, it is found that the solutions for a shrinking sheet are non-unique. 相似文献
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A method is presented for constructing a nonreduced observer for a finite dimensional linear system. The systems considered are nth order, time-invariant or time-varying forced linear systems which are assumed to be bounded and uniformly completely state reconstructible. The observer dynamics are derived from an optimal estimation formulation which is related to the concept of observability. The cost functional used in this formulation includes a parameter which determines the relative weighting of the system output and the estimate of the initial system state. The result is a practical method of estimating the state of a linear system from noiseless measurements of the input and output. The results are also of theoretical significance in that a direct connection between reconstructibility and the existence of observers is established. 相似文献
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The aim of this paper is the development of a general class of input shapers with distributed time delay which leads to retarded spectral properties. The design of the shaper is formulated as a multi-objective optimization problem, where response time and robustness, expressed in terms of residual vibrations, are the main objectives. As a part of the optimization formulation, common requirements for input shapers such as non-decreasing step response and unity steady state gain are considered in the design. Moreover, additional optional requirements, such as smoothness of a step response, jerk and even jounce limits can be added to optimization procedure. The resulting problem can be solved using convex optimization techniques. Several illustrative examples are presented in comparison with classical input shaping techniques. Finally, implementation aspects are discussed. The paper is accompanied by an implementation in MATLAB, including a user-friendly interface for the interactive shaper design. 相似文献
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本文报道了我国黑龙江产桔梗科沙参属的10种1变种的染色体数目和核型，对其中
7种作了减数分裂行为的观察。 其中6种1变种为首次报道，并发现2n=68的4x种。该
属染色体基数多为17(x＝17)，但Adenophora trachelioides和A．remotiflora的基数为18
(x=18)，为该属独特基数。核型的共同特征是：小型，以中部(m)、近中部(sm)着丝点
染色体为主，至少具一对近端着丝点染色体和一对随体染色体。该属染色体的演化处于二种
水平： 数目变化(包括多倍化和非整倍体变化)和结构变异。 多倍化是该属物种形成的主要
途径之一。结合其它性状讨论了这些种的分类，并确立1个四倍体新种(A. amurica)和1个新组合(A．pereskiifolia ssp．alternifolia)。 相似文献
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《普罗米修斯》2012,30(1):34-60
Selectivity and concentration in research funding has become unavoidable in Australia today. Some of the reasons for this are reviewed relative to international economic, scientific/technical and conceptual developments. The resulting need to develop an evaluative culture in and for Australia is discussed. The reasons for undertaking evaluations are outlined, and a working definition of ‘research evaluation’ that may be suitable within the Australian context is developed. The parameters that may deserve consideration in designing an evaluation are detailed, and a series of conceptual and practical guidelines are forwarded. Several barriers to implementing evaluations that may apply to Australia are addressed. Finally, the implications of the concept ‘accountability’ for both the recipients of government support and government itself are briefly raised. 相似文献
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Turbulence is a universal form of fluid motion. It is the key issue in fluid mechanics. Very recently, it has become a bottleneck in some key engineering research of national importance, such as aeronautics, astronautics and navigation. Developed turbulence and the onset of turbulence, i.e. transition, are two interrelated parts of turbulence. The hypersonic boundary-layer transition is a strategic focus in the fluid mechanics community. This article reviews recent developments in the study of the hypersonic boundary-layer transition, research facilities and experimental techniques. The hypersonic quiet wind tunnel is introduced as a necessary device to obtain real flight data in near space. Near-wall measurement techniques, such as temperature-sensitive paint, near-wall particle image velocimetry and Rayleigh-scattering visualization, are shown. The most important issues in the recent development of the transition in the hypersonic boundary layer are addressed. The instability and nonlinear interaction of different instability modes are discussed. The recent contributions from China, especially at Peking University, are also introduced. 相似文献
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Tourism firms operate in a competitive sector where innovating is often a condition for survival. This article presents a theoretical framework for understanding tourist firms’ innovative behaviour and innovation systems in tourism. The innovativeness of tourism firms and its determinants are investigated by analysing quantitative as well as qualitative data comparing Spain and Denmark. A taxonomy of tourism firms is suggested and the firms’ characteristics which influence their innovativeness are presented. Additionally, the role of innovation networks is discussed, as is the role of innovation systems. The article suggests that large size, professionalism, but also entrepreneurship among small tourism firms are important determinants of innovation. Varied innovation networks are another determinant as are supportive innovation systems. These determinants favour Spanish firms, which are more innovative than Danish ones. In the final section, policy recommendations are presented. 相似文献
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In this paper, a Russell non-radial measure of eco-efficiency is proposed. Data Envelopment Analysis (DEA) is used for the computations. The inputs considered are the damage indicators provided by the Ecoindicator 99 methodology for Life Cycle Impact Assessment (LCIA). The single output is consumer price, used as a surrogate of economic value. After projecting onto the efficient frontier using input orientation and obtaining efficient target values for the damage indicators, additional DEA models are solved in order to compute corresponding scale elasticities bounds. The proposed approach is illustrated on a small sample of household electric and electronic products. The results confirm that mobile phones, desktop computers and vacuum cleaners are eco-efficient and, of these, only mobile phones are scale efficient. Bounds on the scale elasticity of all products are reported. Most products show decreasing eco-efficiency returns to scale. 相似文献
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本文运用湖南省1998-2007年新成立的54573家注册资本在1000万以下的工业中小企业数据具体分析了我国中小企业的生存状况及影响因素。主要的研究方法为生命表方法和加速失效时间模型等生存分析方法。研究主要发现:我国湖南省地区中小企业死亡危险随时间呈"U"型关系,企业在成立9.5年左右时死亡危险开始增大;企业原始规模、企业所在行业的行业规模以及工业增加值率、销售利润率与产值利税率三个效率指标都与企业生存存在显著的正向相关关系;但行业成长、流动资金周转率和全员劳动生产率与企业生存不存在显著的相关关系;垄断企业的生存状况更好,技术密集型中小企业的生存状况较差,区域集聚地区中小企业具有更大的死亡危险;利率对中小企业生存存在显著的负向影响,而基于城市层面的GDP增长率对中小企业生存存在显著的正向影响;相对于私营企业,湖南省地区内资企业和外资企业的生存表现更差。 相似文献
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《Journal of The Franklin Institute》2022,359(7):3238-3290
The space debris removal system (SDRS) of tethered space tug is modelled as a cable dragged flexible spacecraft. The main goal of this paper is to develop a dynamic modeling approach for mode characteristics analysis and forced vibration analysis of the planar motion of a cable dragged flexible spacecraft. Solar arrays of the spacecraft are modelled as multi-beams connected by joints with additional rotating spring where the nonlinear stiffness, damping and friction are considered. Using the Global mode method (GMM), a novel analytical and low-dimensional nonlinear dynamic model is developed for vibration analysis of SDRS to enhance the design capacity for better fulfillment of space tasks. The linear and nonlinear partial differential equations that governing transverse vibration of solar arrays, transverse and longitudinal vibrations of cable are derived, along with the matching and boundary conditions. The natural frequencies and analytical global mode shapes of SDRS are determined, and orthogonality relations of the global mode shapes are established. Dynamical equations of the system are truncated to a set of ordinary differential equations with multiple-DOF. The validity of the method is verified by comparing the natural frequencies obtained from the characteristic equation with those obtained from FEM. Interesting mode localization and mode shift phenomena are observed in mode analysis. Dynamic responses of the system excitated by fluctuation of attitude control torque and short-time attitude control torque are worked out, respectively. Nonlinear behaviors are observed such as hardening, jump and super-harmonic resonances. Residual vibration of the overall system with considering the varous values of nonlinear stiffness, damping coefficient and friction coefficient has shown that the nonlinearity of joints has a great influence on the vibration of the overall system. 相似文献
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Researching Internet Communities: Proposed Ethical Guidelines for the Reporting of Results 总被引：4，自引：0，他引：4
Storm A. King 《The Information Society》1996,12(2):119-128
Communication researchers and social scientists are quickly discovering the value of data that exists in the postings of members of Internet e-mail, Usenet, and real-time groups. The ability to communicate with one's peers, no matter how esoteric the interests, is causing an explosion in the number of new virtual communities. The interpersonal dynamics of these groups are increasingly coming under the scrutiny of academic research. The publicly available archived records of Internet virtual communities are being analyzed for a wide variety of research interests. The ability to do naturalistic observations of group dynamics, as they are exhibited in these exchanges of text, has captured the attention of many researchers. The institutional review boards of major universities are granting researchers exempt or expedited (exempt from full review) status for this work, due to the public nature of the notes being analyzed. These studies often involve the lack of informed consent, where the group members under study are unaware they are being monitored. There is a potential for psychological harm to the members of these groups, depending on the way results are reported. This article explores the ethical considerations that must be taken into account to protect cyberspace participants. The guidelines proposed are based on the American Psychological Association ethical guidelines for use of human subjects in research. An explanation is offered as to how such guidelines can best be applied to the study of Internet communities. The constructs of Group Accessibility (the public/private nature of the actual cyberspace occupied by a group) and Perceived Privacy (the level of privacy that group members assume they have) are defined and proposed as two dimensions by which individual Internet communities may be evaluated in order to assure the ethical reporting of research findings. 相似文献
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低碳并购是生态文明建设中出现的新型并购模式。通过建立DEA模型,首次分析我国不同区域及行业低碳并购的生态效率改善状况。实证研究发现:总体上不同行业的低碳并购生态效率都有所改善,但各个行业整体上都不高,行业间差异较大;效率较高的行业主要分布在资本密集型行业,劳动密集型行业次之,而资源密集型行业最低;清洁生产型行业的效率明显高于污染密集型行业。根本原因在于资本运作、经济结构、行业竞争力、能源结构及低碳技术存在显著的行业差异。我国三大区域的低碳并购生态效率呈波动上升态势,但整体改善幅度都偏低,区域间差异明显:长三角最高,珠三角次之,环渤海最差。主要原因在于资源禀赋、政府干预、市场化水平、能源结构、环境政策及生态文明制度存在区域差异。 相似文献