基于相场描述的拉压不对称强度结构拓扑优化

运用了基于相场描述的拓扑优化方法,来寻找在拉伸和压缩中表现出不对称强度行为的连续体结构的最优布局。依据Drucker-Prager屈服准则和幂率插值方案,优化问题可以描述为在局部应力约束下的最小化结构的体积。用qp放松法来解决应力约束的奇异性,并采用基于P-norm函数的聚合方法对应力约束进行凝聚,该方法实现了约束个数的降低,同时引入了稳定转化法来处理大量的局部应力约束和高度非线性的应力行为,以修正应力,提高优化收敛的稳定性。在优化问题求解时,使用拉格朗日乘子法对目标函数和应力约束进行处理。利用伴随变量法进行灵敏度分析,并通过求解Allen-Cahn方程更新相场函数设计变量。数值算例证明了该优化模型和相应数值技术的有效性,相关算例还揭示了考虑拉压不同强度和考虑同拉压强度约束时得到的结构优化拓扑构型具有显著的差异。     

安培环路定理的拓扑学描述

近年来拓扑学在量子力学中得到了广泛的运用.本文将安培环路定理积分式重新表达为一矢量场在轮胎参数面上的第一类陈数积分.数值模拟展示了该积分值为一整数即第一陈数,其代表矢量场的整体性质:当经历连续变换时,矢量场的局部数值发生改变但整体积分值即陈数仍保持不变;若陈数发生改变,则表明矢量场变换的连续性条件发生破坏,矢量场出现奇点.进一步通过高斯映射将该矢量场从参数轮胎面映射到单位球面上,并给出了第一陈数的直观几何意义.理论和数值结果揭示了安培环路定理的拓扑学本质,表明拓扑概念在经典物理学中也会有广泛应用.     

压印光刻中的两步对正技术

压印光刻中套刻需要粗、精两级对正.实验采用一对斜纹结构光栅作为对正标记.利用物镜组观察光栅标记图像的边界特征进行粗对正,其准确度在精对正信号的捕捉范围内;利用光电接收器件阵列组合接收光栅莫尔信号,在莫尔信号的线区进行精对正.由于线性区的斜率大, 精对正过程中得到相应x,y方向的对正误差信号灵敏度高,利用高灵敏度对正误差信号作为控制系统的驱动信号,对承片台进行驱动定位,实现精对正.最终使X,Y方向上的重复对正准确度分别达到了± 21 nm(± 3σ)和±24 nm(± 3σ).     

基于移动可变形孔洞方法的超弹性结构拓扑优化

现有隐式拓扑优化方法在进行超弹性结构拓扑优化设计时,具有设计变量多、中间设计有限元分析存在严重的收敛性和设计结果无法直接导入CAD/CAE系统等问题。为解决这些问题,提出了一种基于移动可变形孔洞的显式拓扑优化方法来进行承受大变形的超弹性结构设计,材料本构采用常用的Mooney-Rivlin模型。首先,介绍了移动可变形孔洞方法的基本思想和可变形孔洞的显式描述方法;其次,构造了基于移动可变形孔洞方法的超弹性结构拓扑优化的数学列式,给出了相应的灵敏度结果;最后,通过数值算例验证了本方法的有效性。数值结果表明,该方法可以通过较少的设计变量和非常稳健的优化过程,给出边界由B样条曲线描述且可与CAD/CAE软件无缝连接的超弹性结构设计。     

Polypeptide folding on a conformational‐space network: Dependence of network topology on the structural discretization procedure

Mapping the conformational space of a polypeptide onto a network of conformational states involves a number of subjective choices, mostly in relation to the definition of conformation and its discrete nature in a network framework. Here, we evaluate the robustness of the topology of conformational‐space networks derived from Molecular Dynamics (MD) simulations with respect to the use of different discretization (clustering) methods, variation of their parameters, simulation length and analysis time‐step, and removing high‐frequency motions from the coordinate trajectories. In addition, we investigate the extent to which polypeptide dynamics can be reproduced on the resulting networks when assuming Markovian behavior. The analysis is based on eight 500 ns and eight 400 ns MD simulations in explicit water of two 10‐residue peptides. Three clustering algorithms were used, two of them based on the pair‐wise root‐mean‐square difference between structures and one on dihedral‐angle patterns. A short characteristic path length and a power‐law behavior of the probability distribution of the node degree are obtained irrespective of the clustering method or the value of any of the tested parameters. The average cliquishness is consistently one or two orders of magnitude larger than that of a random realization of a network of corresponding size and connectivity. The cliquishness as function of node degree and the kinetic properties of the networks are found to be most dependent on clustering method and/or parameters. Although Markovian simulations on the networks reproduce cluster populations accurately, their kinetic properties most often differ from those observed in the MD simulations. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Comparative study of pretreatment methods for the determination of metals in atmospheric aerosol by electrothermal atomic absorption spectrometry

A comparative study of pretreatment methods for the determination of 10 elements (As, Cd, Pb, V, Ni, Mn, Cr, Cu, Fe, Al) in atmospheric aerosols by electrothermal atomic absorption spectrometry (ETAAS) was conducted. For the digestion of the particulates collected in filters, six methods were compared using a mixture of HNO₃ and HF with or without the addition of various oxidative agents (HClO₄ or H₂O₂) or acids (HCl). The comparative study was performed using loaded cellulose filter samples, which were digested in Parr bombs and heated in a conventional oven at 170 °C for 5 h. The extraction efficiency and blanks were compared and it was proved that the digestion method using only HNO₃–HF extracted most of the metals and gave the lowest blanks. The HNO₃–HF mixture was selected for the development of an improved microwave digestion method specific for aerosol-loaded filters. The operating parameters were optimized, so that quantitative recovery of the reference materials NIST 1649a urban dust and NIST 1648 urban particulate matter was achieved. The blank of cellulose and teflon filters were also determined and compared. Teflon filters present the lowest blanks for all the elements. The obtained limits of detection for each type of filters were adequate for environmental monitoring purposes. ETAAS instrumental operation was also optimized for the compensation and the elimination of interferences. The temperature optimization was performed for each metal in every type of filter and optimized parameters are proposed for 10 elements.     

EIGHT-POINT STRAIGHT-LINE-NET-DIAGRAMS OF BINARY SIX-PHASE (n+4) MULTISYSTEMS (Ⅱ)——DERIVATION FROM THEORY OF PHYSICALLY REAL NETS

Based on the theory of physically real nets, the 8- point straight-line nets of bi-nary 6- phase (n + 4) multisystems (31 in toto) have been derived directly from the l-point straight-line nets. This result is in complete agreement with that derived fromthe theory of closed nets, indicating the incorrectness of the previous conclusion thatthere is only one 8-point straight-line net which corresponds to only one 8- pointstraight-line-net-diagram for binary 6- phase multisystems.     

微波合成SrTiO3的工艺、结构与性能研究

应用微波会成这一材料合成新方法制备SrTiO3，研究了不同工艺条件下微波合成产物的结构，确定出制备纯净SrTiIO。的合成条件．对微波合成的工艺及其影响因素进行详细的探索，从合成产物的显微结构、粒度分布、比表面积、烧结性能等方面比较了微波合成与常规固相合成的差别，结果表明微波合成与各种常规方法相比有合成时间短、合成工艺简单、合成产物性能好等特点，是一种有发展潜力的材料合成技术．     

基于一种柔性二羧酸和不同双咪唑配体构筑的两例钴-穿插网格

利用一种柔性二羧酸,辅以不同的双咪唑配体在水热条件下构筑了两例具有穿插特征的钴配位聚合物,{[Co(bimb)(L)]·H₂O}_n(1)和{[Co(bbix)(L)]₂}_n(2)(H₂L=4,4'-(2,2'-oxybis(ethane-2,1-diyl)bis(oxy))dibenzoic acid, bimb=1,1'-(1,4-butanediyl)bis(imidazole), bbix=1,4-bis(benzimidazole-1-ylmethyl)-benzene)。单晶X-射线衍射研究发现配合物1为2D→3D 4-连sql拓扑构型的三重穿插网格;配合物2为3D 4-连6⁶ dia拓扑构型的六重穿插网格。该结构分析结果表明作为辅助配体的双咪唑配体的构型对配合物的穿插特征有重要影响。另外,我们还研究了配合物1和2的热稳定性及磁性。     

Polymer networks by molecular dynamics simulation: Formation, thermal, structural and mechanical properties

A molecular dynamics simulation method is presented and used in the study of the formation of polymer networks. We study the formation of networks representing the methylene repeating units as united atoms. The network formation is accomplished by cross-linking polymer chains with dedicated functional end groups. The simulations reveal that during the cross-linking process, initially branched molecules are formed before the gel point; approaching the gel point, larger branched entities are formed through integration of smaller branched molecules, and at the gel point a network spanning the simulation box is obtained; beyond the gel point the network continues to grow through the addition of the remaining molecules of the sol phase onto the gel (the network); the final completion of the reaction occurs by intra-network connection of dangling ends onto unsaturated cross-linkers. The conformational properties of the strands in the undeformed network are found to be very similar with the conformational properties of the chains before cross-linking. The uniaxial deformation of the formed networks is investigated and the modulus determined from the stress-strain curves shows reciprocal scaling with the precursor chain length for networks formed from sufficiently large precursor chains (N ≥ 20).