二射影对应面束与二次曲面

利用正投影法首次系统说明了固有线为底的二射影对应面束,如果平移或旋转其中之一,可以分别形成各种二次柱面、二次锥面、单叶双曲面和双曲抛物面。二射影对应面束,如果选择合适的截平面,可以得到两对对应合同线束。合同线束是否同向共面是二次曲面存在圆截口的充分必要条件。     

射影线束形成的二阶曲线及其退化形式

论文用图示法首次系统表达了在二射影平面场中,存在3种形式的射影对应线束。这些对应线束形成二阶曲线时有一定的变化规律。其中底都为非固有点的二线束形成双曲线;底为固有点和非固有点的二线束形成抛物线;底都为固有点的二线束,只要旋转其中之一就可以分别形成双曲线、抛物线和椭圆。这些结论为我们实现二阶曲线之间的转换奠定了理论基础。     

空间两射影对应点列形成的单叶双曲面

空间两条交叉直线为底的射影对应点列,对应点连线包络成单叶双曲面。如果移动其中任一点列的位置,单叶双曲面的形状变化有一定的规律。通过对单叶双曲面截交线形状的系统分析,首次提出单叶双曲面上存在抛物线型截交线。针对二射影对应点列作图法的简化,为我们进一步开发应用CAD软件自动生成该曲面提供了理论支持。     

一种用射影线束族生成曲线的方法

以两射影对应线束对应真线交点的轨迹是二阶曲线为基础，研究了射影线束族的形成原理，讨论了射影线束与线束族，射影线束族与线束族对应直线交点所构成的平面曲线及其性质，同时利用计算机绘制了部分曲线。     

小康心得：诊断原理

6类线在不长距离上（55m以内）可以支持万兆是没问题的，前提是链路首先要合格，并且不能和其它链路捆绑成一束太大的电缆束，否则外部串扰会过大，影响正常工作。本次故障在实际检查时，发现电缆束很小，但万兆服务器端口自适应却只有100M。     

Gray微束定位辐射准确性的研究

对Gray微束装置的定位辐射准确度进行了全面的实验研究。微束定位辐射的能力表现在辐射点的准确度高低和离子分布区域的大小二个方面，辐射点的准确度取决于样品架的回访精度和图像处理系统的样品识别准确度；离子的分布取决于瞄准器的结构。通过对3.5MeV的^3He^2 离子辐射后CR39样品上留下束斑的大小和中心位置的分析，得到了有关Gray微束定位辐射能力的数据。在辐射点准确度方面，仅由样品架参与工作时，真实辐射点落在以预定辐射点为中心，以1.5和1.25μm为半径的圆内的概率分别为99.1%和97.9%，如果样品架和图像处理系统共同作用，那么真实辐射点落在相应区域内的概率分别为98.4%和96.4%，在离子的分布上，大于99.5%的离子分布以及在以真实辐射点为中心、以7.5μm为直径的圆内，其中的99.1%又集中在直径5μm的同心圆内。     

中心为非固有点的线束对应

在两线束射影对应中，当两线束中心为非固有点时，两线束的射影关系式如何确定？本文给出了适当的解析方法。实践证明：当两线束中心之一为非固有点时，所得曲线为双曲线，抛物线或退化的二次曲线；当两线束中心均为非固有点时，所得曲线是双曲线或退化的二次曲线。     

新型斜聚束探头的研究

新型斜聚束探头的研究北方交通大学张建合，郑中兴奥氏体不锈钢粗晶材料组织不均，采用斜探头检查时出现林状反射波。为提高分辨力，采用手动接触聚焦探伤技术，使射入的声波在一定深度汇聚成均匀细长且信噪比高的声束，适于检测裂纹类缺陷和声衰减大的材料。该项技术是在...     

摄影测量中相机倾斜引起的射影失真研究

根据成像原理,建立了理想光学系统成像的数学模型。通过分析该模型中物与像的对应关系,得出了射影失真产生的根源是光学系统放大率的不恒定,并与相机的外参数:倾角及视场的大小有着非线性的变化关系。提出了正射影失真与负射影失真的概念,对其进行了详尽的理论分析,并给出了数学模型及分布规律。依据上述结论,分析了二维射影对应与仿射对应在摄影测量应用中的实质区别,并利用物像平面间的射影对应关系,使试验中的测量精度达到了测试的要求。     

平面三次和四次代数曲线的射影构成

本文在叠置场上研究平面三次和四次代数曲线的射影构成。提出在射影坐标系里二次线束单参数方程的表示法,并证明它的充分性和必要性。进而证明三个定理:①一次线束和其射影对应的二次线束,所对应直线交点的轨迹为三次平面曲线;②射影三线场对应直线交点构成平面三次曲线;③两成射影对应的二次线束,其对应直线交点的轨迹是四次平面曲线。且写出了上述定理的对偶定理,并在微机APPLE-Ⅱ上作出部分图形。     

用双剪强度理论解混凝土板冲切的轴对称问题

本文采用双剪强度理论，对混凝土板轴对称冲切破坏强度进行了计算。采用刚塑性模型，给出轴对称破坏机构，得到极限应力圆的包络线为二条直线，再利用虚功方程求得破坏荷载的上限。公式形式简单，与已有结果相比符合很好。     

索结构风雨振的动力学行为研究

研究带有运动上水线的两个自由度的索结构风雨振模型,假定索结构振动频率与上水线振动频率相同,利用符号代数语言Mathematica对系统进行数值分析。讨论了密度比、索结构阻尼、偏航角等因素对系统运动的影响,对工程中出现的类似问题提出相应的解决方案。同时得到了索结构和水线的运动相图,结果表明:它们的运动均收敛于稳定的极限环。借助计算规范形程序得到了系统的简化的平均方程,进一步验证了系统存在的定常解。     

一种求含孔洞多边形交、并、差集的新方法

提出了一种基于最小回路确定含孔洞多边形P和Q的交、并、差集的新方法.首先,初始化P和Q外环为逆时针方向,内环为顺时针方向,并通过连接内环极右顶点与其在外环上一可见点v,构造一条双向“桥边”,将内外多环转换为单环.其次,求出P和Q被转换为单环的边序列的交点,并对交点处的关联边进行排序.然后,沿着各个交点处正向边,依照最小转角原则搜索最小回路,并根据其中所含P和Q边所呈现的顺、逆时针方向进行分类.最后,P和Q的交、并、差集即对应不同类别的最小回路.算法简洁且几何意义明显,具有较好的适应性.     

隧道掘进爆破新技术的探讨

近年来，我国交通事业飞速发展，交通隧道的建设越来越多，研究和发展新的隧道爆破技术已引起工程界的关注。本文通过现场试验，研究、探索一种新的隧道爆破技术—隧道无槽掘进爆破技术，加快隧道掘进中的钻爆工序，对实现隧道的快速掘进具有重要意义。     

Finite-circle method for component approximation and packing design optimization

In this article, the finite-circle method is introduced for 2D packing optimization. Each component is approximated with a group of circles and the non-overlapping constraints between components are converted into simple constraints between circles. Three new algorithms—the bisection algorithm, the three-step algorithm, and the improved three-step algorithm with gap—are developed to automatically generate fewer circles approximating the components. The approximation accuracy, the circle number, and the computing time are analyzed in detail. Considering the fact that packing optimization is an NP-hard problem, both genetic and gradient-based algorithms are integrated in the finite-circle method to solve the problem. A mixed approach is proposed when the number of components is relatively large. Various tests are carried out to validate the proposed algorithms and design approach. Satisfactory results are obtained.     

三级配混凝土静、动载下力学细观破坏机制研究

假定三级配混凝土是由砂浆基质、不同粒径的骨料及其粘结带组成的非均质复合材料,采用非线性有限元方法在细观尺度上数值模拟三级配混凝土弯拉梁在静、动载下的开裂过程。按实际配比计算各种骨料的代表粒径的数目,采用蒙特卡罗方法随机生成骨料分布,骨料形状假定为圆形,最小粒径为12.5mm。骨料、砂浆及其粘结带均采用了非线性本构模型,具体模拟了材料的开裂、拉伸软化、塑性屈服和压碎等非线性。研究中还给出了梁关键部位的应力应变全过程曲线,研究成果还与未考虑材料的非均质性的结果进行了比较。结果表明,混凝土类的多项非均质复合材料的静、动力学性能与其内部的细观结构组成有密切关系,混凝土中最薄弱的部位为粘结界面,混凝土的破坏明显表现出拉应变软化现象和局部化现象。数值模拟结果与有关试验成果较为接近。     

Detection of circlelike overlapping objects in thermal spray images

In this paper, we present a new algorithm for the detection of distorted and overlapping circlelike objects in noisy grayscale images. Its main step is an edge detection using rotated difference kernel estimators. To the resulting estimated edge points, circles are fitted in an iterative manner using a circular clustering algorithm. A new measure of similarity can assess the performance of algorithms for the detection of circlelike objects, even if the number of detected circles does not coincide with the number of true circles. We apply the algorithm to scanning electron microscope images of a high-velocity oxygen fuel (HVOF) spray process, which is a popular coating technique. There, a metal powder is fed into a jet, gets accelerated and heated up by means of a mixture of oxygen and fuel, and finally deposits as coating upon a substrate. If the process is stopped before a continuous layer is formed, the molten metal powder solidifies in form of small, almost circular so-called splats, which vary with regard to their shape, size, and structure and can overlap each other. As these properties are challenging for existing image processing algorithms, engineers analyze splat images manually up to now. We further compare our new algorithm with a baseline approach that uses the Laplacian of Gaussian blob detection. It turns out that our algorithm performs better on a set of test images of round, spattered, and overlapping circles.     

A Mohr-circle graphical method for stress intensity factors in cracked plates under different loadings

The concept of the stress intensity factor circles (SIF circles) was introduced in this paper, as well as the correlation of these circles with Mohr's circles. The main advantage of this graphical representation is the facility in establishing a one-to-one correlation between the values of the angle of a slant crack in a cracked plate submitted to a biaxial normal loading at infinity and different loading modes at infinity. Moreover, the definition of a general transformation of any biaxial state to another equivalent one, such that the stress intensity factors remain invariant in both states, was also established and discussed. The special cases where the reduction of any biaxial state to that of equal tension-tension at infinity, or uniaxial tension, or equal tension-compression, are also investigated. The method yields the possibility of replacing biaxial tests in cracked plates, which are difficult to be executed with the appropriate accuracy and convenience, with uniaxial ones, which are much easier and accurate than the biaxial ones. Examples indicate the validity and the simplicity of the method.     

Interference in the Manufacture of Nuclepore Filters

In connection with the manufacture of Nuclepore filters at Vallecitos, considerations that are probabilistic in nature become important. One such consideration deals with the probabilities of interference of circles of uniform radius placed at random on a surface. Such probabilities have been found by several investigators in different contexts. A second consideration is three dimensional in that one must find the probability that cyclinders formed by passing the circles through a plate of given thickness at random angles will intersect completely through the plate. An approximate solution is found to this problem as a function of the ratio of plate thickness to circle radius. Small scale simulations are included to check the adequacy of the approximations.     

Packing degree optimization of arbitrary circle arrangements by genetic algorithm

Selection of optimal aggregate proportions is the main part of the concrete mix design optimization. Assuming circular aggregates, a new Sequential Packing Algorithm (SPA) is proposed to densify arrangement of arbitrary circles. To achieve the densest packing of circles, the porosity packed circle assemblies is optimized by a Genetic Algorithm (GA) search module. Proper adjustment of the algorithm’s parameters and selection of the initial population are effective tools for speeding up the computational progress. The model exactly solves known problems. Finally, Ideal-grading curve is presented after the implementation of GA on the data set.