Slicing Algorithm and Partition Scanning Strategy for 3D Printing Based on GPU Parallel Computing

Aiming at the problems of over stacking, warping deformation and rapid adjustment of layer thickness in electron beam additive manufacturing, the 3D printing slicing algorithm and partition scanning strategy for numerical control systems are studied. The GPU (graphics processing unit) is used to slice the 3D model, and the STL (stereolithography) file is calculated in parallel according to the normal vector and the vertex coordinates. The voxel information of the specified layer is dynamically obtained by adjusting the projection matrix to the slice height. The MS (marching squares) algorithm is used to extract the coordinate sequence of the binary image, and the ordered contour coordinates are output. In order to avoid shaking of the electron gun when the numerical control system is forming the microsegment straight line, and reduce metal overcrowding in the continuous curve C⁰, the NURBS (non-uniform rational b-splines) basis function is used to perform curve interpolation on the contour data. Aiming at the deformation problem of large block components in the forming process, a hexagonal partition and parallel line variable angle scanning technology is adopted, and an effective temperature and deformation control strategy is formed according to the European-distance planning scan order of each partition. The results show that the NURBS segmentation fits closer to the original polysurface cut line, and the error is reduced by 34.2% compared with the STL file slice data. As the number of triangular patches increases, the algorithm exhibits higher efficiency, STL files with 1,483,132 facets can be cut into 4488 layers in 89 s. The slicing algorithm involved in this research can be used as a general data processing algorithm for additive manufacturing technology to reduce the waiting time of the contour extraction process. Combined with the partition strategy, it can provide new ideas for the dynamic adjustment of layer thickness and deformation control in the forming process of large parts.     

基于地理信息系统的中药材生态适宜性定量化研究

目的:中药材品质与其生长环境密切相关.为应用数学模型对中药材产地适宜性进行定量化研究,需要对影响中药材生长的生态因子和气候数据的插值进行研究.方法:首先从生态学和统计分析角度研究对影响中药材生长的生态指标的判断标准,以及如何计算所选择的生态因子最适宜范围值和每个生态因子的权重值.其次,由于气象要素是中药材适宜区分析的基础数据,同时气象要素的空间分布与地形环境密切相关,为此研究基于DEM的多元线性回归插值方法以使得插值结果最大程度接近于真实值.结论:从数量化角度探讨了中药材产地适宜性的因子体系选择和插值问题,并针对其中存在的关键问题进行研究.     

Geostatistical exploration of spatial variation of summertime temperatures in the Detroit metropolitan region

Background

Because of the warming climate urban temperature patterns have been receiving increased attention. Temperature within urban areas can vary depending on land cover, meteorological and other factors. High resolution satellite data can be used to understand this intra-urban variability, although they have been primarily studied to characterize urban heat islands at a larger spatial scale.

Objective

This study examined whether satellite-derived impervious surface and meteorological conditions from multiple sites can improve characterization of spatial variability of temperature within an urban area.

Methods

Temperature was measured at 17 outdoor sites throughout the Detroit metropolitan area during the summer of 2008. Kriging and linear regression were applied to daily temperatures and secondary information, including impervious surface and distance-to-water. Performance of models in predicting measured temperatures was evaluated by cross-validation. Variograms derived from several scenarios were compared to determine whether high-resolution impervious surface information could capture fine-scale spatial structure of temperature in the study area.

Results

Temperatures measured at the sites were significantly different from each other, and all kriging techniques generally performed better than the two linear regression models. Impervious surface values and distance-to-water generally improved predictions slightly. Restricting models to days with lake breezes and with less cloud cover also somewhat improved the predictions. In addition, incorporating high-resolution impervious surface information into cokriging or universal kriging enhanced the ability to characterize fine-scale spatial structure of temperature.

Conclusions

Meteorological and satellite-derived data can better characterize spatial variability in temperature across a metropolitan region. The data sources and methods we used can be applied in epidemiological studies and public health interventions to protect vulnerable populations from extreme heat events.     

A comparison of freehand three-dimensional ultrasound reconstruction techniques

Three-dimensional freehand ultrasound imaging produces a set of irregularly spaced B-scans, which are typically reconstructed on a regular grid for visualization and data analysis. Most standard reconstruction algorithms are designed to minimize computational requirements and do not exploit the underlying shape of the data. We investigate whether an approximation with splines holds any promise as a better reconstruction method. A radial basis function approximation method is implemented and compared with three standard methods. While the radial basis approach is computationally expensive, it produces accurate reconstructions without the kind of visible artefacts common with the standard methods. The other potential advantages of radial basis functions, such as the direct computation of derivatives, make further investigation worthwhile.     

Precision and consistency of contour interpolation

We investigated conditions under which observers can interpolate occluded contours by a single, stable, smooth contour. Observers viewed partly-occluded contours defined by linear segments and estimated the position and tangent orientation of the contour at multiple locations within the occluded region. We measured the precision and consistency of observers' settings as indices of successful interpolation. We found that although increasing the relative offset between inducers led to a decrease in both precision and consistency, increasing turning angle affected primarily precision. We discuss conditions under which interpolation settings are consistent with a single, stable smooth contour.     

三维人体虚拟内窥的实验研究

目的对三维人体虚拟内窥系统进行初步的实验研究。方法建立了虚拟摄像机几何模型和定位方法,根据人体的三维影像数据,以不同分辨率对虚拟人体进行不同角度的观察。并对虚拟内窥镜的观察结果用光线跟踪方法检测表面和用三线性插值方法绘制表面图。结果实现虚拟内窥结果的可视化,研制出基于微机的虚拟内窥系统和对三维人体影像数据虚拟内窥的结果。结论虚拟内窥是实现医学虚拟诊断、虚拟治疗和虚拟教学的很有前途的手段之一     

基于光电容积脉搏波的呼吸频率监测

目的呼吸频率是人体生理信息监测中一个重要的生理指标,做好呼吸频率的监测对于一些疾病的及时诊疗有重大意义。光电容积脉搏波中包含许多生理信息,而本研究即从光电容积脉搏波中提取呼吸频率。方法首先识别出光电容积脉搏波,提取出脉搏波的包络、间隔、幅度、面积信号4个特征参数,并利用三次样条插值和频谱分析从中提取各自对应的频率,采用加权平均得到最终的呼吸频率,并将本文提取的呼吸频率同给定的标准呼吸频率进行对比。结果在时域和频域具有较好的相关性,并且不同数据多次测量的统计结果显示测量误差较小。结论本方法能有效地从光电容积脉搏中提取呼吸频率,且计算简单,为实现呼吸频率的实时、连续、无创监测提供了一定的理论依据。     

图像域自适应线性自回归MRI图像客观质量提升算法研究

目的磁共振成像(magnetic resonance imaging,MRI)是临床医学影像检查的重要手段,然而受限于检查时间,高客观质量的MRI图像难以获得,有效提高MRI图像分辨率成为研究热点。本文为高效地提高MRI图像分辨率,减少患者检查时间,提出图像域的基于线性自回归模型自适应客观质量提升算法。方法首先,创建基于距离权重的自回归模型获得插值系数;其次,利用自适应算法解决自回归算法中插值矩阵病态的问题;最后,通过对标准数据库中具有不同噪声水平的图像进行测试。结果本算法重建图像的峰值信噪比(peak signal to noise ratio,PSNR)平均值比经典算法提高1.8~4 d B,结构相似度(structural similarity index measurement,SSIM)指标平均提高0.02~0.06。结论图像域自适应线性自回归MRI图像客观质量提升算法在有效提高MRI图像分辨率的同时,保持了较高的客观质量。     

2010—2013 年陕西省出生缺陷空间分布及空间聚集性

目的：探讨2010至2013年陕西省出生缺陷的空间分布特征及空间聚集性。方法：对陕西省各调查县出生缺 陷发生数据进行空间分布描述，利用普通克里格法对陕西省出生缺陷发生状况进行建模预测，运用空间自相关方法 对陕西省县(市、区)级层面数据进行空间统计分析。结果：陕西省胎、婴儿出生缺陷发生率为219.196/万；空间插值 预测图显示陕西省出生缺陷的分布具有明显的地理分布特征；全局空间自相关分析结果显示陕西省出生缺陷发生存 在空间聚集现象，局部空间自相关分析显示彬县、淳化县、扶风县、泾阳县、礼泉县、乾县、武功县、兴平市、永 寿县为出生缺陷发生的“正热点”地区，佳县、米脂县、清涧县、绥德县、吴堡县、榆阳区、子洲区为出生缺陷发 生的“负热点”地区。结论：2010至2013年陕西省出生缺陷发生存在明显的空间聚集性，通过空间插值预测与空间 自相关可以直观地反映出出生缺陷发生的全省状况，为进一步进行干预提供参考。