超声导波频散曲线反演皮质骨参数的研究

皮质骨参数的变化可以反映骨质的健康状况,因此文章提出了一种频散能量匹配算法来反演皮质骨参数。首先,通过频散特性方程计算出预定义参数下的频散曲线数据库;其次,利用时域有限差分算法建立皮质骨声场模型,将仿真的时域信号通过功率谱估计得到频散能量信息,并与数据库进行匹配,通过分析匹配结果的能量从而得到皮质骨的厚度、纵波速度和横波速度。仿真结果显示：与理论值相比,厚度的平均相对误差为3.8%,纵波速度与横波速度的平均相对误差分别为0.6%、0.9%。对三组离体牛胫骨皮质骨进行反演,离体实验结果显示：与真实值相比,厚度相对误差为4.9%,且实验频散曲线与反演得到的理论频散曲线吻合。因此文中所提出的反演算法可以有效获取皮质骨的厚度,横波速度和纵波速度,从而为评价骨质的健康状况提供可靠的依据。     

不同缓冲材料的堆码包装振动特性分析

目的 研究物流运输中采用不同缓冲材料的堆码包装件的振动特性。方法 以缓冲材料聚乙烯泡沫(EPE)和聚苯乙烯泡沫(EPS)为研究对象,采用三维建模软件SoildWorks和有限元仿真软件Workbench建立有限元模型进行模态与谐响应分析,结合扫频振动试验和随机振动试验对各层堆码件的振动响应特性进行分析。结果 2类包装件共振频率处的第一激励能量都大于第二激励能量,振动幅值随层数增加而升高。EPE包装件第一和第二共振频率的激励能量占比分别为35.7%和3%,EPS包装件第一和第二共振频率的激励能量占比分别为26.8%和16.8%。EPE包装件共振区域主要分布于15～40 Hz,而EPS包装件共振频率区域分布于15～40 Hz和60～80 Hz。三层堆码件的中上层包装件受第一共振频率控制,EPS材料的底层包装件受多个共振频率影响,EPE材料的底层包装件受到第二共振频率控制。结论 经过循环载荷作用后的EPE的吸振缓冲性能优于EPS的。通过试验与有限元仿真数据绘制了相应的防振性能曲线,同时验证了有限元仿真的可靠性。这为堆码产品选择不同缓冲材料组合提供了的理论指导。     

Curvature continuous path generation for autonomous vehicle using B-spline curves

In this paper we introduce a roadmap algorithm for generating collision-free paths in terms of cubic B-spline curves for unmanned vehicles used in mining operations. The algorithm automatically generates collision-free paths that are curvature continuous with an upper bounded curvature and a small slope discontinuity of curvature at knots, when we are given the locations of the obstacles, the boundary geometry of the working area, positions and directions of the vehicle at the start, loading, and the goal points. Our algorithm also allows us to find a switch back point where the vehicle reverses its direction to enter the loading area. Examples are provided to demonstrate the effectiveness of the proposed algorithms.     

改进的Koblitz曲线上数字签名算法

标量乘法的效率决定着椭圆曲线密码体制的性能,而JSF算法是当前最流行的计算椭圆曲线双标量乘的算法;Koblitz曲线上的快速标量乘算法是标量乘法研究的重要课题。Lee[12]算法采用Frobenius映射扩展正整数k并将其扩展后的系数改写成二进制形式有效地提高标量乘算法效率。将JSF应用到扩展后的系数中,以较小存储空间为代价来提高算法效率,并将算法运用到改进的ECDSA算法中,减少乘法运算次数,加速签名及验证过程,节约数字签名时间。     

Radical parametrizations of algebraic curves by adjoint curves

We present algorithms for parametrizing by radicals an irreducible curve, not necessarily plane, when the genus is less than or equal to 4 and the curve is defined over an algebraically closed field of characteristic zero. In addition, we also present an algorithm for parametrizing by radicals any irreducible plane curve of degree d having at least a point of multiplicity d−r, with 1≤r≤4 and, as a consequence, every irreducible plane curve of degree d≤5 and every irreducible singular plane curve of degree 6.     

四元数扩维无迹卡尔曼滤波算法及其在大失准角快速传递对准中的应用

针对快速传递对准中量测失准角为大角度的情况,在非线性欧拉角误差模型基础上,推导了一种基于乘性四元数的等效快速传递对准模型.为解决四元数在无迹卡尔曼滤波（UKF）算法中的应用问题,提出了一种基于四元数的状态扩维无迹卡尔曼滤波（Q--AUKF）算法.该算法将系统噪声增广到状态向量中,解决了乘性四元数噪声无法进行向量意义下四则运算的问题.针对四元数加权均值规范化的限制,采用平均四元数算法保证其正交规范化要求.最后将其应用到快速传递对准中的仿真实验结果表明,在量测误差角为大角度的情况下,该算法具有更高的估计精度与收敛速度.     

Analyzing CAD competence with univariate and multivariate learning curve models

Understanding how learning occurs, and what improves or impedes the learning process is of importance to academicians and practitioners; however, empirical research on validating learning curves is sparse. This paper contributes to this line of research by collecting and analyzing CAD (computer-aided design) procedural and cognitive performance data for novice trainees during 16-weeks of training. The declarative performance is measured by time, and the procedural performance by the number of features used to construct a design part. These data were analyzed using declarative or procedural performance separately as predictors (univariate), or a combination of declarative or procedural predictors (multivariate). Furthermore, a method to separate the declarative and procedural components from learning curve data is suggested.     

Tangential cover for thick digital curves

The recognition of digital shapes is a deeply studied problem. The arithmetical framework, initiated by Reveillès [Géométrie discrète, calcul en nombres entiers et algorithmique, Thèse d’Etat, 1991], provides a powerful theoretical basis, as well as many algorithms to deal with digital objects. The tangential cover, first presented in Feschet and Tougne [Optimal time computation of the tangent of a discrete curve: application to the curvature, in: G. Bertrand, M. Couprie, L. Perroton (Eds.), 8th Discrete Geometry for Computer Imagery, Lecture Notes in Computer Science, vol. 1568, Springer, Berlin, 1999, pp. 31-40] and Feschet [Canonical representations of discrete curves, Pattern Anal. Appl. 8(1-2) (2005) 84-94] is a useful tool for representing geometric digital primitives. It computes the set of all maximal segments of a digital curve and permits either to obtain minimal length polygonalization or asymptotic convergence of tangents estimations. Nevertheless, the arithmetical approach does not tolerate the introduction of irregularities, which are however inherent to the acquisition of digital shapes. The present paper is an extension of Faure and Feschet [Tangential cover for thick digital curves, in: D. Coeurjolly, I. Sivignon, L. Tougne, F. Dupont (Eds.), DGCI 2008, Lecture Notes in Computer Science, vol. 4992, Springer, Berlin, 2008, pp. 358-369], in which we propose a new definition for a class of the so-called “thick digital curves” that applies well to a large class of digital object boundaries. We then propose an extension of the tangential cover to thick digital curves and provide an algorithm with an O(nlogn) time complexity, where n denotes the number of points of specific subparts of the thick digital curve. In order to keep up with this low complexity, some critical points must be taken into account. We describe all required implementation details in this paper.