共查询到20条相似文献，搜索用时 109 毫秒
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对宇宙中最普遍的运动——椭圆运动及双曲线单支运动进行定量分析,并研究其运动规律。通过分析椭圆运动与力的关系,推导总结其相互的逻辑关系。 相似文献
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提出了基于八分弧的对一般圆锥曲线扫描转换算法。该算法中利用八分弧将圆锥曲线分成八个区域进行扫描转换，在每个八分弧中确定算法跟踪的方向，使用梯度的分量来确定运动的方向从而画八分弧，并以椭圆为例给出了相应的算法过程。 相似文献
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本文区分并探讨了“技术”和“用户”驱动的创新战略对技术创新绩效影响的作用机制， 创新性地引入“价值网络资源异质性”和“价值网络资源耦合性”作为情境变量，并以298家高技术企业为研究对象，运用层次回归法对理论模型进行了实证检验。研究表明，技术驱动和用户驱动的创新战略均对高技术企业的技术创新绩效具有显著的正向影响；价值网络资源异质性对技术驱动的创新战略与技术创新绩效具有正向调节作用，而对用户驱动的创新战略与技术创新绩效的负向调节作用不显著；价值网络资源耦合性对技术驱动的创新战略与技术创新绩效具有正向调节作用，在用户驱动的创新战略与技术创新绩效之间也具有正向调节作用。 相似文献
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本文设计了以可编程控制器PLC和触摸屏为核心的切割机控制系统。该控制系统针对不同属性的金属可采取不同的切割模式和切割速度。整个切割过程由PLC控制,通过触摸屏设置各项切割参数,采用变频调速技术对驱动砂轮转动的电机进行无级调速,采用细分式驱动技术控制步进电机运动,实现了砂轮转速的任意设定和工件切割速度的自适应调节,提高了切割机的控制精度,增强了系统切割不同材料的适应性和稳定性。 相似文献
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本文考虑一个二阶非线性微分方程，它是作为卫星绕着椭圆轨道作周期运动的模型而提出的。我们用初等方法证明了奇周期解的存在性，并且扩大了过去文献中给出的参数范围。 相似文献
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在人体运动跟踪建模中,需要对样本集的多样性特征进行贫化处理,以提高全关节驱动模式运动状态跟踪的准确性。传统方法采用量子进化和粒子滤波算法进行人体运动跟踪贫化算法实现,算法在全关节多样化样本特征运动模式下,跟踪效果不好。提出一种采用动态分层二值进化处理的改进的量子进化粒子滤波全关节驱动模式跟踪方法,解决多样本特征的贫化问题。进行人体全关节驱动模式动力学分析及人体运动跟踪模型构建,通过动态分层处理技术,获得二值前景图像,求得人体关节的全方位信息特征,通过动态分层二值进化方法,准确地找到各关节位置,构建亮度模型函数,实现贫化处理。实验表明,改进算法能实现对体操运动员运动幅度大的肘、腕、踝部位均得到了准确的跟踪结果,贫化效果较好,运动状态估计精度较高。 相似文献
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徐帅 《内蒙古科技与经济》2004,(11):69-70
本文详细介绍了CZX928多功能机床手动进给系统进行数控改造的设计原理。用一般微机作控制管理编程系统，通过PCL839伺服接口，实现对API步进电机的开环伺服驱动，再通过一级齿轮减速驱动丝杠实现对两轴工作台运动的控制，提高了该机床加工复杂曲面的能力。 相似文献
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密码技术是信息安全的关键技术，密码算法又是密码技术的核心。谈文简单介绍了公开密码密钥体制，并给出了ECC的优点。但椭圆曲线密码体制中有限域上的运算速度极大地影响它的实现速度。本文通过论述椭圆曲线密码体制中有限域理论，分析了素域、二进制有限域中加法、采法的实现算法，并给出了利于硬件实现的算法。 相似文献
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A novel technique for optimal placement of piezoelectric actuators on smart structures 总被引：3，自引：0，他引：3
The problem of positioning of actuators and sensors on smart materials has been a point of interest in recent years. This is due to the fact that in many practical applications there are limitations in space, weight, etc. of the smart structures, which make the problem of positioning more complex. In addition, it is required that the actuators/sensors have the best possible performance. The development of smart structures technology in recent years has provided numerous opportunities for vibration control applications. The use of piezoelectric ceramics or polymers has shown great promise in the development of this technology. The employment of piezoelectric material as actuators in vibration control is beneficial because these actuators only excite the elastic modes of the structures without exciting the rigid-body modes. This is important since very often only elastic motions of the structures are needed to be controlled. The purpose of this paper is to introduce a novel approach developed for optimizing the location of piezoelectric actuators for vibration suppression of flexible structures. A flexible fin with bonded piezoelectric actuators is considered in this study. The frequency response function (FRF) of the system is then recorded and maximization of the FRF peaks is considered as the objective function of the optimization algorithm to find the optimal placement of the piezoelectric actuators on the smart fin. Three multi-layer perceptron neural networks are employed to perform surface fitting to the discrete data generated by the finite element method (FEM). Invasive weed optimization (IWO), a novel numerical stochastic optimization algorithm, is then employed to maximize the weighted summation of FRF peaks. Results indicate an accurate surface fitting for the FRF peak data and an optimal placement of the piezoelectric actuators for vibration suppression is achieved. 相似文献
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This paper addresses the issue of the active vibration control of the transverse modes in a flexible elastic systems. The control is implemented by discrete sets of piezoelectric actuators that apply the optimal forces. The performance index is a time-dependent quadratic functional of state variables and their time derivatives, and control forces which are determined by minimizing the objective functional subject to a penalty term on the control functions. A combination of Galerkin and variational approaches are employed to determine the control forces in the time domain explicitly in terms of coupled amplitudes and velocities. The effectiveness of the proposed method is demonstrated by applying it to a physical problem controlled by piezoelectric patch actuators. 相似文献
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This study describes the high-precision positioning control of a system with asymmetric hysteresis. A switching system concept is adopted to describe the Preisach-type hysteresis, and a systematic modeling procedure is established to obtain the parameters of the system. A piezoelectric actuator system driven by a voltage amplifier is used to verify the modeling accuracy. A control structure, comprising a feedforward controller and a PD-type feedback controller, is used to realize the high-precision positioning control of the piezoelectric actuator driven stage. To enhance tracking control, a high-frequency modified term is incorporated into the hysteresis model. The experimental results confirm that the addition of this modified term reduces the tracking error and prevents the controlling energy from being saturated. 相似文献
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简要评述了陶瓷基板,微波介质陶瓷,铁电压电陶瓷,半导体陶瓷,铁电薄膜和智能材料等功能陶瓷的研究进展和发展趋势,对我院功能陶瓷的发展提出了一些建议。 相似文献
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[目的/意义]通过构建压电式网络安全事件应急响应体系,为我国企业的应急响应管理提供理论基础和实践参考。[方法/过程]对美国司法部发布的《网络安全事件受害者响应与报告的最佳实践》进行文本分析,从事前、事中和事后三个阶段解读了美国的应急响应实践经验,并结合压电式理论中变化事件、态势感知与关键性对齐的视角,构建了适用中国企业的应急响应体系。[结果/结论]基于美国联邦调查员、检察官以及美国企业在处理网络安全事件的经验总结,提出了一套清单式的响应方案,其中蕴含的全过程管理与关键性对齐的响应策略为我国企业提供了借鉴与参考。 相似文献
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We propose a new approach to obtain ultra-high piezoelectric coefficients that can be infinitely large theoretically, where ferroelectrics with strain-sensitive Curie temperature are necessary. We show the first-principles plus Monte Carlo simulation evidence that many hydrogen-bonded ferroelectrics (e.g. organic PhMDA) can be ideal candidates, which are also flexible and lead-free. Owing to the specific features of hydrogen bonding, their proton hopping barrier will drastically increase with prolonged proton transfer distance, while their hydrogen-bonded network can be easily compressed or stretched due to softness of hydrogen bonds. Their barriers as well as the Curie temperature can be approximately doubled upon a tensile strain as low as 2%. Their Curie temperature can be tuned exactly to room temperature by fixing a strain in one direction, and in another direction, an unprecedented ultra-high piezoelectric coefficient of 2058 pC/N can be obtained. This value is even underestimated and can be greatly enhanced when applying a smaller strain. Aside from sensors, they can also be utilized for converting either mechanical or thermal energies into electrical energies due to high pyroelectric coefficients. 相似文献
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在进行超声换能器电阻抗匹配研究时,发现产生的回波在频域上出现了"双峰"现象,本文主要分析了这种现象产生的原因及其不良影响,并通过调整匹配电路和参数去除了频域的"双峰",使其达到匹配的要求。 相似文献
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Qing Liu Yichi Zhang Jing Gao Zhen Zhou Dong Yang Kai-Yang Lee Andrew Studer Manuel Hinterstein Ke Wang Xiaowen Zhang Longtu Li Jing-Feng Li 《国家科学评论(英文版)》2020,7(2):355
Due to growing concern for the environment and human health, searching for high-performance lead-free piezoceramics has been a hot topic of scientific and industrial research. Despite the significant progress achieved toward enhancing piezoelectricity, further efforts should be devoted to the synergistic improvement of piezoelectricity and its thermal stability. This study provides new insight into these topics. A new KNN-based lead-free ceramic material is presented, which features a large piezoelectric coefficient (d33) exceeding 500 pC/N and a high Curie temperature (Tc) of ∼200°C. The superior piezoelectric response strongly relies on the increased composition-induced structural flexibility due to lattice softening and decreased unit cell distortion. In contrast to piezoelectricity anomalies induced via polymorphic transition, this piezoelectricity enhancement is effective within a broad temperature range rather than a specific small range. In particular, a hierarchical domain architecture composed of nano-sized domains along the submicron domains was detected in this material system, which further contributes to the high piezoelectricity. 相似文献