基于最大基线倾角智能逼近的凸壳新算法

本文评述了有代表性的折半分治递归凸壳算法,并利用同构化凸壳基本定理提出效率更高的最大倾角智能逼近凸壳新算法。本新算法的同构化特点是：1）找出给定二维点集最外点（指最左、最右、最高、最低点）,即其X轴、Y轴坐标值最大、最小的四个初始极点;2）用该初始极点,把原二维点集分布域划分为四个子分布域;3）分别在这四个子分布域中,各基于自身最新所得极点依次动态构造其基线倾角最大的当前极点,并用这些极点作凸边,来逐步智能逼近和最终生成该给定二维点集的凸壳。     

基于改进量化约束集的块效应消除算法

低比特率时,基于块离散余弦变换（BDCT）的图像压缩方法常常会引起块效应。量化约束集（QCS）作为关于编码模型的重要先验信息在块效应消除方法中被广泛地采用。利用量化误差的统计特性,提出了一种改进的量化约束集（MQCS）。实验结果表明当在现有的基于凸集投影（POCS）的去块算法中以新的约束集代替传统量化约束集,峰值信噪比（PSNR）和主观图像质量有不同程度的提高,性能与窄量化约束集（NQCS）相当。     

平面点集凸壳的一种近似算法

提出了一种计算海量平面点集凸壳的快速近似算法——点集坐标旋转法(PSCR)。该算法采用点集不断旋转并求X(Y)坐标极值的方法得到平面点集的近似凸壳。它充分利用了成熟的数据库技术,能够在比较短的时间内计算出海量平面点集的近似凸壳。它不需要空间索引的支持,并能获得比较理想的近似效果。     

多输入多输出—非正交多址接入系统融合用户调度的下行波束赋形设计

针对多输入多输出—非正交多址接入（MIMO-NOMA）技术中用户间干扰较大的问题,提出了一种融合用户调度的波束赋形（BF）算法。首先,在进行用户调度时,为了同时兼顾簇内用户干扰和簇间用户干扰,根据各用户信道的差异性,利用L1-范数正则化方法对所有用户分组情况进行初步稀疏化处理,进而从各用户信道相关性角度出发,将信道相关性大的两个用户分为一簇;其次,结合部分发射功率控制（FTPC）策略实现簇内用户功率分配;最后,根据和速率最大化准则构建一目标优化函数,进而利用连续凸逼近（SCA）算法对其进行求解,以获得波束赋形矩阵。理论分析和链路仿真表明,与传统的正交多址接入技术相比,在系统容量方面实现了84.3%的提升;与传统的相关性用户分簇方法相比,在公平性方面实现了20.2%的提升。实验结果表明,该方案不仅有效地抑制了簇内用户干扰和簇间用户干扰,同时,又保证了用户间的公平性。     

Mastercam在数控加工中的应用研究

介绍了Mastercam软件的CAD/CAM功能.结合叶轮凸模型芯的数控加工实例,阐述了在Mastercam环境下进行零件造型、刀轨生成、仿真加工、后处理程序、机床加工等数控加工的一整套过程,并在数控加工中就如何保证加工精度和提高加工效率进行了研究和探索,取得了一定的成效.     

A new stereological principle for test lines in three-dimensional space

A new principle is presented to generate isotropic uniform random (IUR) test lines hitting a geometric structure in three-dimensional space (3D). The principle therefore concerns the estimation of surface area, volume, membrane thickness, etc., of arbitrary structures with piecewise smooth boundary. The principle states that a point-sampled test line on an isotropic plane through a fixed point in 3D is effectively an invariant test line in 3D. Particular attention is devoted to the stereology of particles, where an alternative to the surfactor method is obtained to estimate surface area. An interesting case arises when the particle is convex. The methods are illustrated with synthetic examples.     

高速加工中心自动换刀装置的研究

针对我国目前弧面分度凸轮自动换刀装置设计制造水平不足的现状,设计一套结构简单、加工方便的自动换刀完成自动换刀,并详述了换刀的实现过程。新的自动换刀装置精度高、运行平稳、价格合理,能够取代弧面分度凸轮机构。     

不锈钢封头在低温临氢工况下的开裂分析

利用硬度检测和马氏体含量检测、金相组织及现场裂纹观察等手段,对某低温临氢奥氏体不锈铜凸形封头的开裂原因进行了分析并进行了理论研究。认为该封头的开裂属于氢致裂纹（HIC）,缘于冷加工形变、氢在不同温度下的扩散以及低温等因素的交互作用。冷加工变形所造成的马氏体相变、位错密度的升高是造成氢致裂纹的主要原因;残余应力为裂纹的形成与扩展创造了有利条件;氢在马氏体中的溶解度随温度变化而不同,从-50℃至-100℃溶解度降低幅度较大,析出的氢是造成封头开裂的直接因素。亚稳定型奥氏体不锈钢元件在冷加工成形后进行固溶处理是降低其氢脆敏感度的有效手段。     

A new family of metrics for compact, convex (fuzzy) sets based on a generalized concept of mid and spread

One of the most important aspects of the (statistical) analysis of imprecise data is the usage of a suitable distance on the family of all compact, convex fuzzy sets, which is not too hard to calculate and which reflects the intuitive meaning of fuzzy sets. On the basis of expressing the metric of Bertoluzza et al. [C. Bertoluzza, N. Corral, A. Salas, On a new class of distances between fuzzy numbers, Mathware Soft Comput. 2 (1995) 71-84] in terms of the mid points and spreads of the corresponding intervals we construct new families of metrics on the family of all d-dimensional compact convex sets as well as on the family of all d-dimensional compact convex fuzzy sets. It is shown that these metrics not only fulfill many good properties, but also that they are easy to calculate and easy to manage for statistical purposes, and therefore, useful from the practical point of view.     

Convex piecewise-linear fitting

We consider the problem of fitting a convex piecewise-linear function, with some specified form, to given multi-dimensional data. Except for a few special cases, this problem is hard to solve exactly, so we focus on heuristic methods that find locally optimal fits. The method we describe, which is a variation on the K-means algorithm for clustering, seems to work well in practice, at least on data that can be fit well by a convex function. We focus on the simplest function form, a maximum of a fixed number of affine functions, and then show how the methods extend to a more general form.