共查询到20条相似文献,搜索用时 109 毫秒
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圆孔衍射光强分布的数值计算 总被引:24,自引:5,他引:19
利用数值积分的方法,计算了由点光源经圆孔衍射形成的光强分布,分别得到夫琅禾费及菲涅耳衍射图样,宽定量分析了满足夫琅禾费衍射的条件。 相似文献
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基于快速傅里叶变换的衍射现象的数值仿真 总被引:2,自引:1,他引:1
根据夫琅禾费衍射与傅里叶变换的关系,通过构建数值遮光屏,并利用快速傅里叶变换,可以获得夫琅禾费衍射图样的二维仿真及其相对光强的三维分布图.利用Matlab实现了对单缝、圆孔及多缝的衍射现象的仿真.结果显示,该方法思路清晰,结果准确可靠,可作为教学中分析夫琅禾费衍射现象的另一种有效方法. 相似文献
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微波分光仪波源特性分析 总被引:1,自引:1,他引:0
通过实验测定与理论分析认为,微波分光仪波源不是理想的平面波源,而是发散的准球面波源;用其进行衍射研究不应看做是典型的夫琅禾费衍射,而应将其作为夫琅禾费衍射与菲涅尔衍射的过渡区衍射来处理。 相似文献
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Wiersig J 《Physical review letters》2006,97(25):253901
We study the formation of long-lived states near avoided resonance crossings in open systems. For three different optical microcavities (rectangle, ellipse, and semistadium) we provide numerical evidence that these states are localized along periodic rays, resembling scarred states in closed systems. Our results shed light on the morphology of long-lived states in open mesoscopic systems. 相似文献
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本文提出用图形逼近和取尺寸上、下限值的几何平均值的方法,计算椭圆外导体-矩形内导体同轴线特性阻抗。矩形截面内导体的内切共焦椭圆和外接共焦椭圆,通过保角变换,变成同心圆。矩形变成近于矩形的闭合曲线,二同心圆分别为它的最小值和最大值,取二者的几何平均值,与同轴椭圆截面外导体同时变成的同心圆,构成一个标准同轴线,得到了特性阻抗公式。并由此推导出椭圆外导体-微带内导体、圆形外导体-方形内导体、圆形外导体-矩形内导体及圆形外导体-微带内导体等各种同轴线的特性阻抗的初等函数表示式。给出了上述几种同轴线的特性阻抗准确数值。
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In this study free vibration of simply supported and clamped super elliptical plates is investigated. This class of plates includes a wide range of external boundaries varying from an ellipse to a rectangle. Although studies on the upper and lower bounds of these plate geometries, namely circle and rectangle, are quite extensive, contributions on the mid-shapes, especially for simply supported boundary edges are very limited. The Kirchhoff plate model with isotropic and homogeneous material is studied. The super elliptical powers are chosen from 1 to 10. The Ritz method is employed for the solution of the energy equations of the plates. The effects of Poisson's ratio, which should not be neglected for simply supported plates with curved boundaries, and the aspect ratio of the plate are both examined in detail. The effect of thickness variation is also considered in this study. In order to avoid long computational run times, physically pertinent trial functions are utilized. The frequency parameters obtained are presented and compared with published results for plate shapes that match the current cases. 相似文献
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本文介绍作者近些年来对椭圆、矩形、扇形、任意三角形、正多边形、环形等各种非圆断面通道层流摩擦阻力与换热理论的研究成果,给出大量新的速度与温度场表达式,以及摩擦阻力与换热的新的计算公式。本文对传统的层流阻力与换热理论进行了一次系统的补充与完善,同时考虑到工程需要,对所有繁杂的理论公式都进行了化简,给出形式简单而且精度相当高的近似公式。 相似文献
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The results of two-dimensional micromagnetic modeling of magnetization patterns in Permalloy ellipses under the influence of rotating constant-amplitude magnetic fields are discussed. Ellipses of two different lateral sizes have been studied, 0.5 μm×1.5 μm and 1 μm×3 μm. The amplitude of the rotating magnetic field was varied between simulations with the condition that it must be large enough to saturate or nearly saturate the ellipse with the field applied along the long axis of the ellipse. For the smaller ellipse size it is found that the magnetization pattern forms an S state and the direction of the net magnetization lags behind the direction of the applied field. At a critical angle of the rotating magnetic field the direction of the magnetization switches by a large angle to a new S state. Both the critical angle and the angle interval of the switch depend on field amplitude. For this new state, it is instead the applied field direction that lags behind the magnetization direction. The transient magnetization patterns correspond to multi-domain patterns including two vortices, but this state never exists for the equilibrated magnetization patterns. The behavior of the larger ellipse in rotating field is different. With the field applied along the long-axis of the ellipse, the magnetization of the ellipse is nearly saturated with a vortex close to each apex of the ellipse. As the field is rotated, this magnetization pattern remains and the net-magnetization direction lags behind the direction of the field until for a certain angle of the applied field an equilibrium multi-domain state is created. Comparisons are made with corresponding experimental results obtained by performing in-field magnetic force microscopy on Permalloy ellipses. 相似文献
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书籍扫描图像畸变模型的可视化描述及应用 总被引:3,自引:3,他引:0
利用设备无关显示技术在计算机屏幕上显示一条仿真曲线、一个矩形和一个箭头,可视化地描述在扫描时书籍页边的变形情况、页面上的均匀条带及成像系统对称中心的位置。通过调整仿真曲线,使之较好地反映页边实际变形,并使矩形的大小和位置及箭头的位置合适,可对存在严重畸变的书籍扫描图像进行较好的校正,而无需用户精确地测量这些随具体情况而变化的参数。校正后,用OCR(Optical Character Recognition)软件进行文字识别时,总的平均纠错率为94.5%,页平均纠错率最高达99.6%。用TWAIN(Technology Without An Interesting Name)标准直接从扫描仪读取图像数据,并用椭圆拟合方法方便地测量扫描仪的成像畸变系数。 相似文献
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用黑斑的椭圆性质在二值化图像中探测眼睛 总被引:3,自引:0,他引:3
在人脸探测过程中 ,双眼的探测非常重要 ,这是因为人的眼睛是人脸上最容易探测到的特征部位。通过双眼探测还可以对人脸进行定位 ,使人脸的尺寸归一化。探讨了一种基于二值化图像中黑斑几何形状分析的双眼探测方法。因为人眼的形状比较接近椭圆 ,故在研究黑斑的几何性质时 ,重点研究黑斑的椭圆性质。所谓黑斑的椭圆性质是指按照黑斑的面积和二阶矩计算出的椭圆参数。椭圆的主要参数有椭圆的面积、质心、长短轴的长度和方向角 (椭圆长轴与水平方向的夹角 )。为了描述黑斑与椭圆的近似程度 ,定义了椭圆硬度的概念。根据眼睛黑斑椭圆参数的测试数据建立了探测眼睛的数学模型 ,并给出了根据此模型得到的双眼探测的实验结果 相似文献
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It is shown that a fluid heated from below can reconstruct an incomplete initial pattern in the sense of an associative memory. This property of the fluid is based on the formal similarity between the order parameter equations of the fluid close to its instability point and those used in pattern recognition by means of synergetic computers. Under certain external conditions the system may additionally show multistable behaviour and discriminate between two offered initial patterns with different symmetries, such as a square and a rectangle. 相似文献