A new model for thermodynamic analysis on wetting behavior of superhydrophobic surfaces

Superhydrophobic surfaces have shown inspiring applications in microfluidics, and self-cleaning coatings owing to water-repellent and low-friction properties. However, thermodynamic mechanism responsible for contact angle hysteresis (CAH) and free energy barrier (FEB) have not been understood completely yet. In this work, we propose an intuitional 3-dimension (3D) droplet model along with a reasonable thermodynamic approach to gain a thorough insight into the physical nature of CAH. Based on this model, the relationships between radius of three-phase contact line, change in surface free energy (CFE), average or local FEB and contact angle (CA) are established. Moreover, a thorough theoretical consideration is given to explain the experimental phenomena related to the superhydrophobic behavior. The present study can therefore provide some guidances for the practical fabrications of the superhydrophobic surfaces.     

高超声速三维内收缩式进气道/乘波前体一体化设计研究评述

论述了国内外在高超声速三维内收缩式进气道研究方面的最新研究动态,重点阐述了三维变截面内乘波式进气道的研究进展.介绍了常规矩形进口进气道与乘波体外形一体化相关研究,并对三维内收缩式进气道与前体的一体化问题提出了关注. 最后,对高超声速进气道与前体一体化设计的研究趋势进行了展望,提出三维内收缩式进气道与乘波前体的``双乘波'一体化设计可能为高超声速研究带来新的变革.      

ACTIVE CONTROL OF A FLEXIBLE CANTILEVER PLATE WITH MULTIPLE TIME DELAYS

Active control of a flexible cantilever plate with multiple time delays is investigated using the discrete optimal control method. A controller with multiple time delays is presented. In this controller, time delay effect is incorporated in the mathematical model of the dynamic system throughout the control design and no approximations and assumptions are made in the controller derivation, so the system stability is easily guaranteed. Furthermore, this controller is available for both small time delays and large time delays. The feasibility and efficiency of the proposed controller are verified through numerical simulations in the end of this paper.     

Active control and experiment study of a flexible hub-beam system

The first-order approximation coupling （FOAC） model was proposed recently for dynamics and control of flexible hub-beam systems. This model may deal with system dynamics for both low and high rotation speed, while the classical zeroth-order approximation coupling （ZOAC） model is only available for low rotation speed. This paper assumes the FOAC model to present experimental study of active positioning control of a flexible hub-beam system. Linearization and nonlinear control strategies are both considered. An experiment system based on a DSP TMS320F2812 board is introduced. The difference between linearization and nonlinear control strategies are studied both numerically and experimentally. Simulation and experimental results indicate that, linearized controller can make the system reach an expected position with suppressed vibration of flexible beam, but the time taken to position is longer than expected, whereas nonlinear controller works well with precise positioning, suppression of vibration and time control.     

控制存在延时的建筑结构地震作用下的最优控制方法

直接从时滞微分方程进行控制律设计,对控制存在延时的建筑结构在地震作用下的最优控制方法进行了研究。在控制时滞量为采样周期的整数倍和非整数倍的两种情况下,通过采用零阶保持器,将包含时滞的连续系统转化为形式上不包含时滞的标准离散线性系统,然后进行控制律的设计。所得出的控制律表达式中,除了含有当前的状态反馈外,还包含有前若干步控制项的线形组合。最后对某三自由度结构模型进行了仿真计算,结果表明,延时对控制效果有较大的影响,延时并非愈短愈好。     

可动氧与载体对钴基催化剂的乙烷氧化脱氢性能的影响

 报道了未担载的氧化钴与担载在SiO2和Al2O3上的氧化钴的乙烷氧化脱氢行为,发现未担载的氧化钴在150℃的低温下就有活性．XRD研究表明,Co3O4为活性晶相组分,其含量与催化剂的焙烧温度密切相关,经500℃和1000℃焙烧的未担载的氧化钴中Co3O4晶相分别占100％和66％．对于担载型氧化钴催化剂,载体与氧化钴间的相互作用以及不同的氧化钴担载量导致催化性能发生明显改变．氧化钴与载体间的作用越强,催化活性越低．Co3O4也是担载型氧化钴催化剂的活性晶相．催化剂的O2－TPD－MS和H2－TPR研究结果表明,反应的活性氧物种为在低温下易脱除和易还原并具有较高流动性的可动氧．     

A new rigid benzene‐bridged macrotricyclic ligand

A macrotricyclic ligand composed of two benzene rings connected by four 2,2′‐oxydiphenoxide bridges ( 2 ) has been prepared by treating 1,2,4,5‐tetrakis[2‐(2‐hydroxyphenoxy)phenoxymethyl]benzene with 1,2,4,5‐tetrakis(bromomethyl)benzene in acetonitrile in the presence of potassium carbonate. Ligand 2 is of interest because of its similarity to macrocycle 1 which interacts strongly with cesium ions. The proposed more direct route of treating an excess of 2,2′‐oxydiphenol with 1,2,4,5‐tetrakis(bromomethyl)benzene to prepare 2 did not give the desired macrocycle but gave bis(tribenzo‐11‐crown‐3) ( 8 ). An X‐ray crystal structure study of 2 showed that the benzene rings which are linked by the four 2,2′‐oxydiphenoxide bridges are connected in a nonsymmetric pattern. The structure of 8 was also determined using X‐ray diffraction methods, and is reported.     

Synthesis of α‐fluoro‐β‐trifluoromethyl alka‐2,4‐dienes

The palladium/copper(I) iodide cocatalyzed coupling reaction of (Z)‐α‐fluoro‐β‐trifluoromethylstannanes ( 1 ) with vinyl iodides ( 2 ) has been explored giving substituted α‐fluoro‐β‐trifluoromethyl dienes ( 3 ) in 33–95% yields. In studies we have conducted so far, a larger number of the configurations of the products remained unchanged (cases 3a, 3e–h ), though in several cases (cases 3b–d ) two configurations of the products were obtained. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:208–211, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20284     

介孔分子筛MCM-41的水热稳定性

介孔分子筛MCM-41在催化、吸附分离以及化学组装制备先进材料等方面具有潜在的巨大应用价值,但MCM-41的低水热稳定性使其在催化研究领域中的应用受到了极大的限制。因此,提高介孔分子筛的水热稳定性具有十分重要的科研和实际应用意义。笔者对介孔分子筛MCM-41低水热稳定性的原因作了简要分析,并系统地介绍了近几年来在提高介孔分子筛水热稳定性方面的研究工作。