Distances between oriented curves in geometric modeling

We consider the choice of a functional to measure the distance between two parametric curves. We identify properties of such a distance functional that are important for geometric design. Several popular definitions of distance are examined, and new functionals are presented which satisfy the desired properties. This revised version was published online in August 2006 with corrections to the Cover Date.     

一类非线性单调型方程的区域分裂法

本文考虑了一类非线性单调问题的加性Schwgrz交替法和异步平行算法,并得到了在能量模意义下的收敛性结果,最后还讨论了格式的有限元离散。     

A COMPLETE METRIC OF POSITIVE CURVATURE ON R~n AND EXISTENCE OF CLOSED GEODESICS

ＡＣＯＭＰＬＥＴＥＭＥＴＲＩＣＯＦＰＯＳＩＴＩＶＥＣＵＲＶＡＴＵＲＥＯＮＲ~ｎＡＮＤＥＸＩＳＴＥＮＣＥＯＦＣＬＯＳＥＤＧＥＯＤＥＳＩＣＳ￥ＺＨＵＤＡＸＩＮ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｈｅｍａｔｉｃｓ，ＴｉａｎｊｉｎＵｎｉｖｅｒｓｉｔｙｌＴｉａｎｊ?..     

Effect of nitrogen surface doping on the work function and field emission of hydrogenated amorphous carbon films

The effect of nitrogen surface doping on the electron field emission characteristics of hydrogenated amorphous carbon films was studied. It was found that the emission threshold electric field decreased after nitrogen surface doping which indicated the reduction of the emission barrier at the film surface. It was demonstrated that this improvement arose from the decrease of the effective work function due to the formation of a dipole layer induced by chemical termination and chemical structural change on the film surface. PACS 52.75.Xx; 73.30 +y; 73.61.Jc     

γ-LiAlO2晶体生长、改性和热学性质研究

采用快速提拉法生长出了透明、完整的γ-LiAlO2晶体,但是晶体的高熔点和易挥发性限制了γ-LiAlO2晶体质量.采用气相传输平衡法(vapor transport equilibration technique,VTE)工艺对晶体改性,半高宽(FWHM)值从116.9arcsec降至44.2arcsec,继续升高VTE处理温度至1300℃,FWHM值反而升高至55.2arcsec.快速提拉法生长出来晶体,[100]方向和[001]方向的热膨胀系数分别为17.2398×10-6/K,10.7664×10-6/K.经过三步VTE处理后[100]和[001]方向热膨胀系数降至16.6539×10-6/K和10.1784×10-6/K.     

Developing a hybrid emulsion polymerization system to synthesize Fe3O4/polystyrene latexes with narrow size distribution and high magnetite content

A hybrid emulsion polymerization was formulated for synthesizing Fe₃O₄/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe₃O_4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe₃O₄/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007     

涡旋柔性弹簧及组件性能实验研究

本文利用TSL系列弹簧刚度实验仪对用于斯特林制冷机中的单片柔性弹簧及柔性弹簧组件进行了实验研究。测试了四种不同尺寸弹簧刚度的动态特性,研究了单片弹簧的轴向刚度、径向刚度以及力矩特性,然后对柔性弹簧组件进行了实验研究,指出了不同组合方法下的刚度及弯矩特性,得到的数据可以作为斯特林制冷机设计的参考。     

Synthesis of poly-substituted nitrobenzene derivatives from Baylis-Hillman adducts via [3+3] annulation protocol

Poly-substituted nitrobenzenes were synthesized from Baylis-Hillman adducts via the [3+3] annulation strategy as the key step. 1,3-Dinitroalkanes served as the 1,3-dinucleophilic component and the Baylis-Hillman acetates as a 1,3-dielectrophilic part.