Direct light field rendering without 2D image generation

Rapid developments in 3D display technologies have enabled consumers to enjoy 3D environments in an increasingly immersive manner through various display systems such as stereoscopic, multiview, and light field displays. However, there is a corresponding increase in the complexity of the conventional multiview rendering process in the attempt to achieve a sufficient level of reality, which may hinder the further commercial viability of 3D display products based on such a conventional approach. This paper proposes a novel method, the so‐called direct light field rendering, which can compose the display 3D panel image without reconstructing all the multiview images beforehand. Interpreting the 3D display as sampling in the light field domain, we attempt to directly compute only the necessary samples, not the entire light fields or multiview images. Our proposed algorithm involves the solving of linear systems of two variables, thereby requiring remarkably low computational complexities. Experimental results show that the computation time and memory usage remain as little as 12% and 1% of those required by the conventional one.     

基于模糊阈值的自适应图像分割方法

针对现有的图像分割中自适应分割方法的研究难点,以及传统的模糊阈值分割法中存在窗宽不能自动获取的问题,在确定隶属函数的前提下,以图像的直方图为依据,利用分段计算和反变换的方法,提出了一种自适应模糊阈值的图像分割方法,并将该方法应用于机场目标的分割;该方法实现其窗口宽度的自适应选取,并且有效改善了模糊阈值法对直方图呈不明显双峰的图像分割困难的缺点,拓展了模糊阈值图像分割方法的适用范围,改善了模糊阈值分割方法的分割效果;实验结果表明,该方法对直方图呈单峰和多峰分布的的图像有较好的分割效果和效率。     

Fast procedure for Non-uniform optimum design of stiffened shells under buckling constraint

For tailoring the non-uniform axial compression, each sub-panel of stiffened shells should be designed separately to achieve a high load-carrying efficiency. Motivated by the challenge caused by numerous variables and high computational cost, a fast procedure for the minimum weight design of non-uniform stiffened shells under buckling constraint is proposed, which decomposes a hyper multi-dimensional problem into a hierarchical optimization with two levels. To facilitate the post-buckling optimization, an efficient equivalent analysis model of stiffened shells is developed based on the Numerical Implementation of Asymptotic Homogenization Method. In particular, the effects of non-uniform load, internal pressure and geometric imperfections are taken into account during the optimization. Finally, a typical fuel tank of launch vehicle is utilized to demonstrate the effectiveness of the proposed procedure, and detailed comparison with other optimization methodologies is made.

     

Chatter stability prediction in milling using time-varying uncertainties

The chatter stability in milling severely affects productivity and quality of machining. Tool wear causes both the cutting coefficient and the process damping coefficient, but also other parameters to change with cutting time. This variation greatly reduces the accuracy of chatter prediction using conventional methods. To solve this problem, we consider the cutting coefficients of the milling system to be both random and time-varying variables and we use the gamma process to predict cutting coefficients for different cutting times. In this paper, a time-varying reliability analysis is introduced to predict chatter stability and chatter reliability in milling. The relationship between stability and reliability is investigated for given depths and spindle speeds in the milling process. We also study the time-varying chatter stability and time-varying chatter reliability methods theoretically and with experiments. The results of this study show that the proposed method can be used to predict chatter with high accuracy for different cutting times.     

Polishing mechanism for ABS parts fabricated by additive manufacturing

Fused deposition modeling (FDM) is a process of fabricating three-dimensional physical models by layered manufacturing. However, the surface quality of acrylonitrile butadiene styrene (ABS) built with FDM technologies is not acceptable and is not satisfactory for most general engineering purposes. In this study, a polishing system was demonstrated to enhance surface finish of ABS parts fabricated by FDM. Polishing mechanism for ABS parts was investigated. The features of this system include high polishing efficiency, no waste chemicals, ease of operation, with excellent dimensional accuracy, and low equipment costs. Improving surface roughness of ABS parts by the use of acetone vapor not only has required dimensional accuracy but also has high process stability. A great reduction in average surface roughness for ABS parts about 98% was obtained. The polishing mechanisms for ABS parts fabricated by additive manufacturing were investigated in this study.     

采样规模与数据采集周期对城市居民用水模式不确定性的影响

用水模式曲线能够反映用户的用水规律,是了解用户用水情况的重要依据.而由于准确性及精细度受到采样规模与监测周期的影响,用水模式存在较大的不确定性.如何设置采样方案,从而得到稳定的用水模式是一个需要研究的重要问题.针对这一问题,探究了居民用水模式曲线随采样规模与数据采集周期的变化规律,提出了用水模式平均不确定性区间宽度(AUIW)的概念,用来表征其不确定性,进而以AUIW小于0.2和AUIW变化率绝对值小于0.01％作为模式曲线稳定的判断标准,确定了不同数据采集周期下获得稳定的模式曲线所需的采样规模.     

基于结团絮凝方式的北方地区河道底泥生态清淤技术试验探讨

在不影响生态环境的前提下,如何对河道底泥进行生态处理,一直是当前国内外研究的重要课题.文章采用结团絮凝方式,对河道底泥生态清淤方式进行试验研究.试验表明:结团絮凝药剂投放量控制在2.9％～5.1％之间,底泥生态清淤效果显著.底泥的污泥比阻和其含水率呈现负相关变化,结团絮凝方式适合于中小河流河道底泥的生态清淤应用.     

基于数据挖掘和本体的入侵警报关联模型

为了突破入侵检测领域的原有瓶颈,提出了一种新的基于数据挖掘和本体的入侵警报关联模型。该模型通过对底层警报的聚类和分类,发现并且筛选攻击,然后根据已建立的基于本体的攻击知识模型,对这些攻击进行关联,以达到识别、跟踪和预测多步攻击的目的。通过对KDD Cup1999和DARPA 2000数据集的模拟实验,验证了模型的有效性。     

A DC-Type Hybrid Step Motor for Large Power Applications

The design, construction, and operation of experimental models of a dc-type hybrid step motor are discussed. This form of hybrid motor consists of a variable-reluctance step motor, the rotor of which is appropriately wound as a multipole dc motor. A computer-aided design procedure is discussed that is used to obtain the optimum parameters of the dc portion of the hybrid motor. The results obtained with two experimental models of this type of hybrid motor are presented. Both prototypes show a marked improvement in the running torque characteristics due to the dc windings. Torque-speed curves indicate load torques of 400 oz-in available at speeds up to several thousand revolutions per minute with one of the proto-types. This type of hybrid motor may be controlled in one of three different ways: a pure step motor, a pure dc motor, or a dc-aided step motor. The relative advantages, disadvantages, and application of each control mode are discussed. Several control strategies-open and closed loop-are presented for speed control as well as point-to-point type control of position. The practical feedback feasibility of this concept for high-power applications in the integral horsepower range is discussed.