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局部变换法和Watson算法是属于逐点添加、局部优化的离散点集Delaunay三角剖分的常用方法,不同的加点次序对这两种算法的局部优化影响较大。研究发现按位置相邻次序加点的方法易产生外接圆较大的扁平三角形,引起较多三角形的局部优化,而按随机次序加点,网格生成过程中网格单元相对匀称,局部优化的三角形较少。以激光点扫描采集的数据为例,统计分析了局部优化三角形的数量及分布特征,点数大于50000时,相邻次序加点方法局部优化三角形的总量是随机次序加点方法的1.6倍以上。建立离散数据的矩形空间索引,按索引轮流加点,点序对局部优化的影响降低,相邻次序加点方法局部优化的三角形总量是随机次序加点方法的1.1~1.3倍,其中随机次序加点与没有空间索引的随机次序相比,局部优化的三角形数量仅增加了约1%。 相似文献
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通过对2005年与2000年入河污染物总量的分析表明,点源在入河污染物总量中的占比逐年下降,面源的占比迅速增加,尤其是TP(总磷)入河量已经超过点源;面源污染呈"总量持平,结构调整"态势;面源污染物总量构成中,农村居民生活位居第一,其次是水产养殖、水田径流等。在面源污染成因分析基础上,相应提出了太湖流域平原水网区面源污染控制的对策建议。 相似文献
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Subhash Chandra Panja Pradip Kumar Ray 《Quality and Reliability Engineering International》2007,23(7):833-848
The operations of one of the vital subsystems of Indian Railways (IR) signaling called a ‘point‐and‐point machine’, which guides a train in changing its direction of movement from one track to another, are affected by a number of problems in relation to its intensity of use, repair and maintenance, and environmental stress. In this paper, the reliability modeling of a point‐and‐point machine is elaborately described taking into account the effect of the problems on its operational efficiency. It is observed that even when derating the system specifications (i.e. lowering the speed of the train), the reliability of the point‐and‐point machine system has been poor (0.44 after 1100 days of continuous operation) with existing preventive and corrective measures. Two graphical methods, namely, Nelson–Aalen and total‐time‐on‐test plots, are used to analyze the trend of the failure time data for a set of representative point‐and‐point machines in the Kharagpur Division of IR. The parametric model as recommended for estimating the reliability of the point‐and‐point machine is capable of correctly predicting its failure rate probability. The analysis of data obtained from a homogeneous Poisson process of the point‐and‐point machine system also leads to a better assessment of the reliability pattern with which the problems as mentioned above may be adequately and properly addressed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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介绍了目前露点温度传感器领域的研究现状,阐述了光学式、谐振式、电学式、热学式、重量式、化学式露点温度传感器的原理及构造,指出光学式露点温度传感器测量精度极高,其中冷镜式露点仪可作为湿度计量标准;谐振式露点温度传感器具有体积小、成本低、响应时间短、灵敏度高、可靠性好的特点;电学式露点温度传感器灵敏度高、功耗小,便于实现小型化、集成化;重量法是准确度最高的湿度绝对测量方法;化学法常用来测量低湿环境下的有机混合气体。探讨了露点温度传感器在环境监测、工业制造、医疗诊断等领域的应用情况,指出未来露点温度传感器将会向高精度、高稳定性、高响应的方向发展,且应用范围将进一步拓展,以满足极端环境下的测量需求。 相似文献
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目的 针对阶梯垛型点云边界检测中,现有边界提取算法效率不高的问题,提出一种适用于阶梯垛型点云的快速边界提取算法。方法 首先使用Kd–Tree对点云数据进行拓扑关系构建,其次搜索采样点及其近邻点,构建单位平面向量,并进行向量叠加,根据叠加后的向量模长来判断是否为候选边界点,然后使用近邻点最大夹角法来进行边界点精提取,最后使用Kinect相机获取阶梯垛型点云数据,进行算法对比验证。结果 实验结果表明,文中算法在保证垛型边界提取精度的同时,比经典边界提取算法的运行时间缩短了75.14%,比优化前的边界提取算法运行时间缩短了11.06%。结论 提出的边界提取算法能够快速准确地提取阶梯垛型点云边界,可为自动码垛系统的设计提供参考。 相似文献
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应用Voronoi图的点群范围自动识别 总被引:2,自引:0,他引:2
运用动态阈值对点群Delaunay三角网进行"蚕食"处理,获得不同视觉邻近距离下的点群分布范围多边形,在多边形边界外侧构建一系列虚拟边界点,在构建中使用两个重要参数:扩展距离、扩展方向.由虚拟边界点与初始点群共同组成新点群,通过对新点群Voronoi图的构建,确定边界点Voronoi区域的准确范围.最后,以点群状分布的教育资源优化配置为例,说明了该方法的具体应用. 相似文献
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Our work describes a technique for testing the centricity of optical systems by using the point spread function. It is shown that a specific position of an axial object point can be found for every optical element, where the spherical aberration is either zero or minimal. If we image such a point with an optical element, then its point spread function will be almost identical to the point spread function of the diffraction-limited optical system. This consequence can be used for testing the centricity of precisely fabricated optical elements, because we can simply detect asymmetry of the point spread function, which is caused by the decentricity of the tested optical element. One can also use this method for testing optical elements in connection with a cementing process. Moreover, a simple formula is also derived for calculation of the coefficient of third-order coma, which is caused by the decentricity of the optical surface due to a tilt of the surface with respect to the optical axis, and a simple method for detecting the asymmetry of the point spread function is proposed. 相似文献
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唐代女性服饰开放性风格对现代服饰设计的启示 总被引:1,自引:1,他引:0
唐代经济、政治和文化的高度繁荣,造就了大唐王朝女性服饰的开放性风格,具体表现在服装款式上"衣带渐宽",面料色彩上华丽多彩,着装习惯上"女着男装".唐代女性服饰风格的这种开放性特征,以设计元素上的兼容并蓄、设计手法上的推陈出新以及设计思想上的多元融合,为现代服饰设计提供了借鉴. 相似文献
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点云孔洞修补作为点云数据处理中的关键技术,直接影响点云的质量和完整性。利用遗传算法(genetic algorithm,GA)优化的BP(back propagation,反向传播)神经网络(简称GA-BP神经网络)是一种修补效果较好的散乱点云孔洞修补方法。但基于GA-BP神经网络的散乱点云孔洞传统修补方法的多个步骤需借助逆向软件通过人机交互的方式完成,导致修补过程繁琐且耗时较长。为此,提出了一种基于GA-BP神经网络的散乱点云孔洞自动修补方法。通过计算机编程将孔洞识别、孔洞区域插值和孔洞修补相结合,实现从残缺点云模型直接到完整点云模型的自动修补,无须进行复杂的人机交互和数据转换。实验结果表明,所提出的方法可有效避免因数据转换而造成的数据失真,减少了人机交互工作量,方便而高效地修补了散乱点云的孔洞,且得到的修补点云密度均匀,这对提高点云孔洞修补效率和质量具有重要意义。 相似文献
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Ya. Z. Kazavchinskii 《Journal of Engineering Physics and Thermophysics》1965,9(3):238-241
A presentation is made of new ideas in the theory of thermodynamic similarity which indicate that, instead of the critical point as a reference point for similarity, we may take any other point on the Boyle curve that is far enough from the ideal gas state. 相似文献
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We construct an analytical solution of the problem of the stressed state of a quarter plane loaded by a concentrated force at a certain distance from its corner point. In constructing the required solution, we use a reflection model similar to reflection of elastic stress waves from a free surface. The stressed state at an arbitrary point of the quadrant is constructed as a superposition of two loads one of which is applied at the same point as the concentrated force and the second (imaginary) one is applied at a point symmetric to the indicated point about the free surface. 相似文献
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快速、准确地检测硝酸铵溶液析晶点对乳化炸药生产质量控制十分重要。为研究硝酸铵溶液析晶点的快速、准确的测量方法,从理论上分析了利用温度变化测量硝酸铵溶液析晶点的原理,设计了相应的测量实验装置,对硝酸铵溶液降温过程的温度变化进行了测量。结果表明:硝酸铵溶液降温过程中,在温度降低到析晶点前,溶液一直保持降温状态,当到达析晶点并析出硝酸铵晶体时,溶液温度在短时间内会有一个小幅度上升,升温幅度在0.3 ℃左右。硝酸铵溶液在有水浴的条件下比在空气中降温的测量结果更为准确。根据此原理设计的自动测量装置可以快速测量硝酸铵溶液的析晶点,能够满足炸药生产企业对硝酸铵溶液析晶点快速、准确测量的要求。 相似文献
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基于分子动力学方法,利用嵌入原子势(EAM)函数,在微观尺度下研究了影响单晶铜熔点的多种因素。首先利用势函数计算单晶铜的晶格常数和弹性常数,以此验证本研究所采用势函数的准确性,然后利用能量体积法、径向分布函数法和键对分析技术对模拟得到的结果进行分析,测得单晶铜熔点约为1 380K。分析了模型大小、升温速率、晶体缺陷对铜熔点的影响,研究发现模型大小、升温速率对熔点的影响不大,随着升温速率的增大,达到熔点所需的时间越短。晶体缺陷的存在使金属材料晶格点阵稳定性下降,熔化需要的热量减少,熔点相应降低,与实际熔点情况一致。 相似文献
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David W. Osborne 《Drug development and industrial pharmacy》1987,13(3):393-403
The use of cloud point temperature elevation to predict transdermal delivery enhancers was evaluated by conducting cloud point experiments on penetration enhancers of known ability. The ability of a compound to elevate the cloud point temperature could not be related to penetration enhancement neither in ranking nor magnitude. After comparison of the molecular interactions that cause cloud point elevation and transdermal delivery enhancement, no correlation between these two mechanisms could be established. 相似文献