锥束CT系统的3D Shepp-Logan体模仿真及其投影数据重建

为了验证锥束CT成像算法的性能,提出了使用Fortran语言编写的3D Shepp-Logan体模作为算法性能验证的参考模型,并详细介绍了3DShepp-Logan体模的参数设置及编程方法。然后,直接加入到正投影程序中得到投影数据。最后,利用得到的投影数据进行了三维医学图像重建的仿真实验。经过实验验证,表明了使用Fortran语言编写的3DSheppLogan体模来验证算法性能是准确可行的。     

广义的监督局部保留投影算法

针对监督的局部保留投影算法(Supervised Locality Preserving Projection,SLPP)在小样本情况下矩阵的奇异性问题,该文提出了一种广义的监督局部保留投影算法(Generalized Supervised Locality Preserving Projection,GSLPP)。GSLPP在大样本情况下等价于SLPP,在小样本情况下却可以等价转换到一个低维空间中来求解,从而有效解决了小样本问题。最后,实验结果验证了该方法的有效性。     

亚半微米光刻投影物镜温度补偿控制及算法研究

主要介绍一种光刻机投影物镜温度补偿控制的原理及控制算法。根据系统结构、对象特性和过程指标要求,采用了一种智能型线性－模糊控制器,获得了优良的动态和稳态性能。     

基于随机投影和稀疏表示的跟踪算法

针对目标跟踪过程中存在的诸多技术问题,该文提出一种鲁棒的目标跟踪方法。首先,该文采用基于稀疏表示的全局模板描述目标的表观状态,通过构造正负模板以区分目标和背景;然后采用随机投影法对表示模板和候选目标进行降维,以降低算法的时间复杂度;采用粒子滤波法作为目标的运动模型,通过多项式重采样方法进行粒子重采样,以保持粒子的多样性;设计了正负模板更新策略,将正模板分为固定集和更新集,对这两部分在相似度计算和正模板更新时采取不同的处理方法,并且在其中加入目标遮挡的判决机制,从而可以有效避免遮挡的影响;实验结果表明,该算法能够准确跟踪受遮挡、运动模糊等多种复杂场景的目标,与现有跟踪方法相比,所提算法具有更好的准确性和稳定性。     

Resistance projection welding for TO-Can style package

The effects of the process parameters on the joint quality of TO-Can using resistance projection welding were investigated.A capacitor discharge stored energy welding machine was used for joining caps and headers both coated with nickel SPCC steel.The electrode materials used in this study were brass and W-Cu alloy.Experimen-tal results indicated that the peak current of the W-Cu electrode was higher than that of the brass electrode,irrespective of the operating pressure variation.Increased operating pressu...     

Enabling a commercial computational fluid dynamics code to perform certain nonlinear analysis tasks

In this work we enable the commercial computational fluid dynamics code Fluent, to successfully trace a complete solution branch, even past turning points. Here the so-called Recursive Projection Method (RPM) is implemented as a computational shell “wrapped” around Fluent, in conjunction with a pseudo-arc-length method for convergence on the unstable branch. The case study is a mixed convection flow in a stagnation point chemical vapor deposition (CVD) reactor. Multiple steady states coexist over a range of inlet Reynolds numbers, due to the competition of the two dominant physical mechanisms: forced and free convection. Continuation on the solution branch reveals a curve consisting of a stable branch, dominated by free convection, followed, past the first turning point, by an unstable branch. Past a second turning point, follows another stable branch dominated by forced convection. Taking the problem a step further, it is augmented with a chemical model describing the deposition of silicon (Si) from silane (SiH₄), silylene (SiH₂) and hydrogen (H₂). The solution branch does not alter since the gas mixture is dilute and the carrier gas, in this case nitrogen (N₂), and the precursor, in this case SiH₄, are of similar molar masses; the concentration differences cannot lead to solutal convection. Results for the mass fraction distribution inside the reactor and the film growth rates are reported in all parts of the solution branch.     

加快关系数据库中投影运算的方法

投影运算在关系数据库的各种运算中是比较费时的一种.本文给出了一种加快关系数据库中投影运算的方法.本算法的硬件模拟易由 VLSI 技术实现,也易采用并行处理技术.     

用拓扑变换法设计不规则光滑曲面

设计不规则光滑曲面的方法很多,但拓扑变换法以其作图简单、准确、计算方便而独具特色。此方法始于苏联B. H. KOBTYH的论文,由龙译斌教授在《几何变换》一书中引用。但原作图由于投射中心的位置无具体的选定方法,故所生成的设计曲面不是唯一的。本文在原有基础上,增加了数学推导,由实测边界数据计算出投射中心的准确位置,并对设计误差进行了测算,从而使该方法更加完善。     

二次曲线透射结构的分析

所有二次曲线皆为射影形,它们之间存在建立透射结构的可能性。本文从二次曲线问透射性质,分析了建立透射结构的条件,以及各种典型位置的透射结构形式,从而提出了对应曲线的作图。     

Data Driven Order Selection for Projection Estimator of the Spectral Density of Time Series with Long Range Dependence

Fractional exponential (FEXP) models have been introduced by Robinson (1991) and Beran (1993) to model the spectral density of a covariance stationary long-range dependent process. In this class of models, the spectral density f ( x ) of the process is decomposed as f ( x ) = |1 − exp( ix )|^{−2 d} f _*( x ), where f _*( x ) accounts for the short-memory component. In this contribution, FEXP models are used to construct semi-parametric estimates of the fractional differencing coefficient and of the spectral density, by considering an infinite Fourier series expansion of log f _*( x ). A data-driven order selection procedure, adapted from the Mallows' C _p procedure, is proposed to determine the order of truncation. The optimality of the data-driven procedure is established, under mild assumptions on the short-memory component f _*( x ). A limited Monte-Carlo experiment is presented to support our claims.