Settling velocity of cubes in Newtonian and power law liquids

New extensive data on the free settling velocity of thirty cubes of various densities and sizes falling in scores of Newtonian and Power law liquids are reported herein to supplement the existing data, for there is very little prior data on cubes in power law liquids. The new data embrace the range of conditions as follows: sphericity of 0.805; power law index, 0.61 to 1 and consistency index, 0.0078-15.31 Pa sⁿ; Reynolds number, 0.0013 to 860. The new results are shown to be consistent with an existing drag correlation which has been tested extensively using the literature data for spherical and non-spherical particles falling in Newtonian and power law liquids with acceptable levels of accuracy.     

利用VTK进行三维肠道重建算法的改进

肠道CT的三维重建是提高肠道疾病诊疗准确性的迫切需要。利用可视化工具包VTK并结合VC++,实现了肠道三维重建。经典三维重建Marching Cubes（简称MC）算法会产生二义性,针对常用的渐近线法消除二义性计算量大的问题,提出了一种改进的MC算法：采用线性插值法求出二义性面与等值面的交点,然后分别连接二义性面对边上的交点形成两条相交直线,最后通过判断直线交点的状态值,来唯一地确定等值线的连接方式,从而快速重建出三维肠道。实验结果表明,利用改进的MC算法比起传统MC算法,在三维重建的质量和效率上都得到了很大的提高。     

基于最近邻Marching Cubes的医学图像三维重建

在医学图像三维可视化中,移动立方体算法（Marching Cubes,MC）是面绘制的经典算法。针对MC算法计算插值点导致执行速度慢、效率不高的缺点,提出一种基于最近邻逼近的MC算法,该方法在n次等分点量化序列中寻找等值面最近邻点代替线性或非线性插值,既避免了插值的大量计算又保证了误差精度,还可改善三角面片结构。利用可视化工具开发包VTK对人体脸部和脚部CT数据集进行三维重建,实验表明改进算法明显缩短了绘制时间,提高了重建效率。     

基于GPU的医学图像快速面绘制

提出了一种医学图像快速面绘制的方法,该方法将新一代图形处理器GeForce 8800的特性和MC（Marching Cubes）算法相结合。利用几何着色器的数据批处理能力在每个立方体中提取等值面并生成三角形带;在片段着色器上采用Phong光照模型对生成三角形渲染显示。建模和显示过程均在GPU上完成,对CPU的依赖低。实验表明,在保证绘制效果的前提下,该方法可在通用PC平台上实现大小为512×512×400的CT数据的实时建模,有很好的实用价值。     

Combining a morphological interpolation approach with a surface reconstruction method for the 3-D representation of tomographic data

In this paper, a new interpolation scheme, based on Mathematical Morphology and a modified Marching Cubes (MC) Algorithm to reconstruct 3-D anatomical structures is presented. The proposed interpolation technique is implemented using morphological operations and incorporates a distance function to improve the computational effectiveness of the technique. The morphological interpolation technique is compared to an existing shape based interpolation method and its advantages include superiority capability on handling various cases such as the branching and holes problem (appearance and disappearance of information) and more accurate volume estimation. Furthermore, the morphological technique is companied with a 3-D reconstruction algorithm capable of representing any anatomical structure from real 3-D medical data. Introducing a novel general rule, the algorithm triangulates all standard cube configurations introduced from the standard MC algorithm, without producing topologically incoherent surfaces or holes. Finally, the technique is implemented in JAVA and its output is in VRML 1.0 format; therefore it can be executed over the internet and implemented for telemedicine applications.     

颅颌面三维重建与网格简化的研究

三维网格简化是十分有意义的研究问题.研究中首先搭建了一个颅颌面CT切片图像三维重构系统.其次,在网格模型顶点删除算法的基础上,提出一种新的三角化所用判据.实验结果表明,应用这一判据,在避免了原算法通过迭代步骤完成三角化的不必要的大量计算的同时,简化模型与原算法结果属同一数量级别,在视觉上无显著差异.     

基于VTK的医学图像快速重建系统

使用数据可视化工具包VTK和重建算法MC开发了一套医学影像三维重建系统。系统针对阻碍实时性的三维重建时空问题，采用顶点合并和哈希映射方法对三角形网格进行优化，有效减少了重建后图像的存储量并提高了显示速度。本系统为构建完整的医学可视化平台奠定了基础。     

Cation exchange synthesis of hollow-structured cadmium sulfide for efficient visible-light-driven photocatalytic hydrogen evolution

Efficient solar absorption and photoinduced charge separation are extremely important for solar-energy conversion on semiconductor photocatalysts. To advance the photocatalytic performance, we developed a general templated-assisted reverse cation exchange strategy to successfully synthesize hollow-structured CdS semiconductors with the textile structural surface. The crystal phase, particle morphology, optical/electrical properties, and photocatalytic performance of the as-syntheszied sample are investiagted by XRD, SEM, TEM, XPS, DSR, PL, ESR photoelectrochemical measurements, and Photocatalytic H₂ evolution test. The final CdS sample exhibits an enhanced photocatalytic hydrogen evolution rate of up to 965 μmol·g⁻¹ h⁻¹, 2.8 times higher than the reported CdS nanorods. Based on the experimental and characterization results, the improved photocatalytic activity of the cadmium sulfide semiconductor can be ascribed to the special hollow cubic structure with a thin shell, which can enhance the light-harvesting ability and provide abundant photocatalytic active sites for facilitating the separation of photogenerated electron/hole pairs. This synthetic strategy may pave a new path for the rational design of efficient sulfur-based semiconductor photocatalysts for solar driven H₂ production.     

压缩体素模型在五坐标数控加工仿真中的应用

针对五坐标数控加工仿真中刀具扫描体和零件毛坯之间布尔运算量大,传统基于空间分解的体素建模方法需要大量计算机内存空间,仿真时间很长,仿真精度低等问题,结合Dexel模型提出了一种压缩体素模型,极大地简化了仿真过程中的布尔运算,同时有效地压缩了仿真模型的数据量,仿真的精度也有所提高。并且根据压缩模型的特点,设计了基于M ach ing Cubes的优化表面三角网格提取算法,加快了仿真结果的图形显示。整个加工过程的仿真速度比传统体素模型提高了8~9倍,在实际应用中取得了良好的效果。