Modification of poly(vinyl cinnamate) photo-alignment layers using polymerizable mesogens

Polymerizable mesogens were blended with poly(vinyl cinnamate) (PVCi) in order to improve the alignment properties of liquid crystals (LC) on the layer surface. Two types of cyanobiphenyl monomers, which have short (n=0) and long (n=11) spacers, were prepared, respectively. Polarized UV exposure at the elevated temperature increased the inclusion of the monomers into the network of the photo-products. Compositional studies showed that the short-spacer monomer improved homogeneous LC alignment and thermal stability, whereas the long-spacer monomer contributed to generate homeotropic LC alignment.     

双语句子对齐算法分析

双语语料对齐是自然语言处理的一个重要研究课题。对双语平行语料库的研究工作主要有构建、对齐和标注等方面,其中研究不同级别的对齐技术是一个重要的中心课题,对齐不仅是进一步利用平行语料库获取一些语言知识的必要前提．也是机器翻译系统利用双语知识的重要前期处理。重点介绍典型的句子对齐方法,并总结出每种方法的优缺点,具体分析了汉维双语句子对齐的方法。     

倒角类冲压零件轮廓缺陷视觉检测

倒角类冲压零件轮廓缺陷视觉检测对于提高生产效率、保障产品质量非常重要。针对倒角类冲压零件形状奇异、轮廓不规则,图像本身实物边缘与背景像素是逐渐过渡的,存在模糊性,缺陷特征弱小等难题,提出了模糊集合的轮廓提取算法和缺陷匹配的识别方法,检测并标记缺陷位置。首先,采用模糊集合强化边缘信息,在不需确定阈值的情况下,准确有效地提取冲压零件的轮廓。其次,利用轮廓的点、线特征,通过HOUGH变换对冲压零件进行定位。然后,以冲压件模板图像位姿特征为期望值,实时校正待检测的冲压件图像,实现精确对准。最后,采用差分相似匹配算法识别出缺陷。实验结果表明,提出的检测方法能够快速、准确地识别占整个零件0.4%以上的小缺陷,并标记位置,满足工业要求。     

Structural and magnetic properties of backward extruded Nd–Fe–B ring magnets made by different punch chamfer radius

Radially oriented Nd–Fe–B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer radius changing from 2, 5 to 8 mm, the cracks in the inner wall decrease obviously while the crystallographic alignment drops. Furthermore, the mechanism of caxis growth was suggested to be a combination of shear deformation in the corner and solution-precipitation under the stress parallel to radial direction. The alignment drops on the top of ring because the grains grow freely and some textured grains grow through nucleation and recrystallization. In the present work, the optimal punch chamfer radius is found to be 2 mm, and in this case, the remanence,coercivity, and maximum energy product of the ring magnet achieve 1.4 T, 670 kJám, and 342 kJám,respectively.     

高速高精度印刷电路板表面贴装自动光学检测系统的研究

为满足高精密度、微型化印刷电路板表面贴装要求,实现全自动、可靠性高、速度快的贴装生产,研究了一种新的自动光学检测系统。该装置主要由光路系统、线阵摄像机、量化存储单元、模板库、专用高速图像处理单元、监视单元等模块组成,实现设备标定、缺陷识别、对中校正和位姿补偿等功能。实验证明：该检测系统可以满足高精密度印刷电路板的高速高精度贴装生产的实时检测要求,达到了较好的检测效果。     

Block copolymers in electric fields

The structural versatility of block copolymers on the nanometer scale make them highly promising candidates for many applications in soft matter nanotechnology, including optics, electronics, and acoustics. In order to harvest the full potential of nanostructured block copolymer materials and achieve widespread use outside of academia, adaptable strategies are required to control and manipulate their spatial orientation, periodicity, connectivity, and long-range order. Over the past two decades the use of an external electric field has been well established as a viable tool to control a wide variety of structural parameters of nanostructured block copolymers on both mesoscopic and nanoscopic length scales. Covering a wide range of experimental and theoretical work, this review aims to illustrate major scientific advances of the past years, focusing in particular on the underlying physics that governs the fundamental interactions between an external electric field and block copolymer mesophases and its impact on phase behaviour and orientational order in bulk, solution, and thin films.     

Three-dimensional threading approach to protein structure recognition

We describe a gapped structural threading method starting from aligning the query protein sequence to the dominant eigenvector of the structure contact-matrix. A mathematically straightforward iteration scheme provides a self-consistent optimum global sequence-structure alignment. The computational efficiency of this method makes it possible to search whole protein structure databases for structural homology without relying on sequence similarity. The sensitivity and specificity of this method are discussed, along with a case of blind test prediction. This method will provide a versatile tool for protein structure prediction and protein domain recognition complementary to existing tools that rely on sequence homology.     

Synthesis of a Hydrothermally Stable,Periodic Mesoporous Material Containing Magnetite Nanoparticles,and the Preparation of Oriented Films

Magnetite nanoparticles modified covalently with triethoxysilane having a quaternary dicetyl ammonium ion are used together with tetraethylorthosilicate as building blocks to prepare a mesoporous material. Cetyltrimethylammonium bromide is used as a structure‐directing agent under conditions typically used for mesoporous MCM‐41 silicas. The resulting mesoporous material (MAG‐MCM‐41), containing up to 15 wt % of magnetite is characterized by transmission electron microscopy (TEM), isothermal gas adsorption, and X‐ray diffraction. In contrast to siliceous MCM‐41, mesoporous MAG‐MCM‐41 exhibits a remarkable hydrothermal stability. The magnetic properties of MAG‐MCM‐41 are characterized by DC and AC magnetic susceptibility, and by isothermal hysteresis cycles, confirming the long‐range magnetic ordering above 400 K. As evidenced by atomic force microscopy and TEM, the ability to respond to magnetic fields is used to orient films of MAG‐MCM‐41 with the channels perpendicular to a support.     

Constrained Ordinal Optimization—A Feasibility Model Based Approach

Ordinal Optimization (OO) is a useful simulation-based approach for stochastic optimization problems such as the problems in Discrete Event Dynamic Systems (DEDS). However, OO cannot be applied directly for the problem since many infeasible decisions cannot be excluded from ordinal comparison without extensive computation involving the expectation operation. In this paper, a new approach for solving constrained ordinal optimization (COO) problems is presented. The key idea of our method for constrained OO problems is to estimate the feasibility of decisions and to choose selected subset based on the estimated feasibility. Any crude method such as the one based on rough set theory developed in our previous work can be applied to determine the decision feasibility efficiently. The algorithm for subset selection and the procedure of Blind Picking with Feasibility Model (BPFM) for COO are derived in the paper. The infeasible decisions are excluded by an imperfect feasibility model in the procedure of subset selection. The performance of the new method is evaluated and compared with the regular OO method. Numerical testing with two examples including the planning problem of a practical remanufacturing system shows that to meet the same required alignment probability, BPFM is more efficient than pure Blind Picking in regular OO. The research presented in this paper is supported in part by the National Outstanding Young Investigator Grant (6970025), National Science Foundation (60243001, 60274011, 60574067) and 863 High Tech Development Plan (2001AA413910) of China. The research effort of Ho is supported in part by U.S. Army Research Office (contract DAAD19-01-1-0610), U.S. Air Force Office of Scientific Research (contract F49620-01-1-0288).