Visible region extraction from a sequence of rational Bézier surfaces

A method for computing the visible regions of free-form surfaces is proposed in this paper. Our work is focused on accurately calculating the visible regions of the sequenced rational Bézier surfaces forming a solid model and having coincident edges but no inner-intersection among them. The proposed method calculates the silhouettes of the surfaces without tessellating them into triangle meshes commonly used in previous methods so that arbitrary precision can be obtained. The computed silhouettes of visible surfaces are projected onto a plane orthogonal to the parallel light. Then their spatial relationship is applied to calculate the boundaries of mutual-occlusion regions. As the connectivity of the surfaces on the solid model is taken into account, a surface clustering technique is also employed and the mutual-occlusion calculation is accelerated. Experimental results showed that our method is efficient and robust, and can also handle complex shapes with arbitrary precision. Project supported by the National Basic Research Program (973) of China (No. 2002CB312106) and the National Natural Science Foundation of China (Nos. 60533070, and 60403047). The third author was supported by the project sponsored by a Foundation for the Author of National Excellent Doctoral Dissertation of China (No. 200342) and a Program for New Century Excellent Talents in University (No. NCET-04-0088), China     

谈绕桩绳索的摩擦力

通过对绕桩绳索摩擦力的分析，进一步说明在摩擦系数一定的情况下，正压力是决定最大静摩擦力(或滑动摩擦力)的唯一因素。     

A NEW ALGORITHM FOR FAST HIDDEN SURFACE REMOVAL OF COMPLEX OBJECTS

ＡＮＥＷＡＬＧＯＲＩＴＨＭＦＯＲＦＡＳＴＨＩＤＤＥＮＳＵＲＦＡＣＥＲＥＭＯＶＡＬＯＦＣＯＭＰＬＥＸＯＢＪＥＣＴＳＦｕＹｕｑｉｎｇ（富煜清）；ＨｕａｎｇＪｉｎｆａ（黄金法）；ＬｉｎＦｅｎｇ（林峰）（ＤｅｐａｒｔｎｉｅｎｔｏｆＲａｄｉｏＥｎｓｉｎｅｅｒｉ...     

折线型坡面时土压力的近似计算

针对折线形坡面，通过经典库仑土压力理论，对挡土墙的土压力作出近似的计算。     

布儒斯特角显微镜和单分子膜表面形貌研究技术

用布儒斯特角显微镜研究了花生酸分子成膜过程中单分子膜表面形貌的动态变化，发现在气／液界面上花生酸分子首先形成岛状分布，随着表面压的增加形成完整的单分子膜，而当表面压达到崩溃压后薄膜出现裂纹，分子膜重叠，形成多层膜。分析了花生酸单分子膜的形成机理。     

自组装膜的表面反应及自组膜的构筑

界面反应已成为界面自组装构筑的一个重要反应方面.从自组装膜的形成及自组装膜的气相、液相、膜上分子交联反应以及膜表面大分子寡聚体的设计组装等几个方面的表面反应对近年来自组装膜构筑方面的进展予以分析和综述.引用文献23篇.     

西北干旱区地表水与地下水资源转换的几个问题探讨

从山区至平原，地表水与地下水之间在不同地质地貌单元相互转换，是我国西北干旱区山前平原水资源的主要特点，直接影响到水资源开发利用模式的变化。随着和水利用率不断提高，减少了地下水补给来源，引起地下水位下降，泉水量削减，甚至枯竭，迫使泉灌区边城井灌。这在水资源西藏高原、森林资源、持续发展     

《人民日报》英文版(People’s Daily)对中美贸易摩擦报道研究--基于语料库的批评性话语分析

2018年3月22日,美国总统特朗普正式签署美国政府对华贸易备忘录,这标志着“中美贸易战摩擦”的序幕正式拉开。本文以《人民日报》英文版(People’s Daily)为研究对象,用抽样选取的方式将该报纸上从2018年3月22日(星期四)到2019年3月28日(星期四)有关中美贸易摩擦的相关报道全部摘录下来,根据每篇报道的话语特点将其分成三个阶段,以内容分析和基于语料库的批判性话语分析为研究方法,分析得出中美贸易摩擦不同阶段的话语特点,进而得出相应的研究结论,同时提出一些富有实操价值的改进建议,为我国主流报纸更好地向世界传播中国思想、讲好中国故事献计献策。     

Application of response surface methodology in medium optimization for pyruvic acid production of <Emphasis Type="Italic">Torulopsis glabrata</Emphasis> TP19 in batch fermentation

Response surface methodology （RSM） was used to optimize the fermentation medium for enhancing pyruvic acid production by Torulopsis glabrata TP19. In the first step of optimization, with Plackett-Burman design, ammonium sulfate, glucose and nicotinic acid were found to be the important factors affecting pyruvic acid production significantly. In the second step, a 23 full factorial central composite design and RSM were applied to determine the optimal concentration of each significant variable. A second-order polynomial was determined by the multiple regression analysis of the experimental data. The optimum values for the critical components were obtained as follows： ammonium sulfate 0.7498 （10.75 g/L）, glucose 0.9383 （109.38 g/L） and nicotinic acid 0.3633 （7.86 mg/L） with a predicted value of maximum pyruvic acid production of 42.2 g/L. Under the optimal conditions, the practical pyruvic acid production was 42.4 g/L. The determination coefficient （R^2） was 0.9483, which ensures adequate credibility of the model. By scaling up fermentation from flask to jar fermentor, we obtained promising results.     

Tribology Performance and Adhesive Strength Evaluation of TiAlSiN Coating

Scratch test and friction test were performed to evaluate the internal and external interface behaviors of TiAlSiN coating, respectively. The critical compressive and shearing stress of coating failure during scratch test were calculated and the values are 30.84 MPa and 4.98 MPa respectively. The average friction coefficients of TiAlSiN coating against 2Cr12Ni4Mo3VNbN steel are 0.70 (sliding speed 50 m/min), 0.63 (sliding speed 100 m/min), and 0.81 (sliding speed 150 m/min). The elements diffusion was analyzed by EDS. Al and Si element of coating material diffuse to the steel disc, except Ti element. The oxidation decreases with the increase of sliding speed, but the adhesion increases with the increase of sliding speed. More Al element diffuses to the steel disc at the high sliding speed, but the diffusion of Si element keeps almost constant at different sliding speeds.