酶在有序介孔材料上的固定化

本文回顾了近年来有序介孔材料用于酶的固定化的研究进展;对比了不同固定化方法对介孔材料固定化酶活性的影响以及各种固定化方法的优缺点;分析了影响酶在有序介孔材料上的固定化因素,并分别对这些影响因素进行了讨论;对酶在有序介孔材料上固定化的发展和潜在的应用进行了讨论,指出介孔材料固定化酶的潜在应用.     

有限长碳纳米管中的分子输运

采用非平衡分子动力学方法研究了有限长度、开口单壁碳纳米管中氦分子的输运过程.结果表明氦分子在小管径碳纳米管中主要以超扩散方式运动.当碳纳米管直径大于某一阈值时发生从超扩散向弹道输运方式的转变,而随着管径的继续增大,分子输运重新以超扩散的方式进行.这种转变与纳米管端口效应有密切的联系.当碳纳米管内部分子通过弹道方式高速运动时,这种运动在端口处由于端部势垒的影响而被抑制,造成端部阻塞现象,其本质是受端部势垒和碳纳米管管径共同影响的结果.     

Intruder Motion in Two-Dimensional Shaken Granular Beds

The dynamical behavior of an intruder immersed in a two-dimensional shaken granular bed is experimentally investigated. With two types of background particles, f-Г phase diagrams depicting the intruder＇s motion are measured and compared. It is found that even with the same size and density ratio of the intruder to the background particles, the intruder exhibits a distinct behavior at given vibrational conditions： rising behavior in one granular bed; sinking behavior in another granular bed. We slightly tune the size and density ratio to confirm the reliability of the experimental results. In addition, we examine the influences of interstitial air, convection and the initial position on the intruder＇s motion, speculating that the opposite motion could be traced to the material properties of the background particles.     

Heterogeneous Nucleation Induced by Capillary Wave During Acoustic Levitation

The rapid solidification of acoustically levitated drops of Pb-61.9 wt. %Sn eutectic alloy is accomplished. A surface morphology of spreading ripples is observed on a sample undercooled by 15 K. The ripples originate from the centre of sample surface, which is also the heterogeneous nucleation site for eutectic growth. The Faraday instability excited by forced surface vibration has brought about these ripples. They are retained in the solidified sample if the sound pressure level exceeds the threshold pressure required for the appearance of capillary waves. Theoretical calculations indicate that both the pressure and displacement maxima exist in the central part of a levitated drop. The pressure near the sample centre can promote heterogeneous nucleation, which is in agreement qualitatively with the experimental results.     

乙烯基Ia3d介孔硅分子筛的环氧化及其固定化青霉素酰化酶(英文)

采用直接共聚法合成表面含有乙烯基的具有立方相Ia3d结构的介孔硅分子筛(V-ClMS),然后对乙烯基团进行环氧化制备得到表面环氧基功能化的介孔硅分子筛(E-CIMS),采用X射线衍射、N2吸附-脱附、透射电镜、热重分析和13C固体核磁共振对制备的介孔硅分子筛进行了表征.结果表明,表面含有乙烯基的V-ClMS介孔硅分子筛能被一步成功合成,并易于发生环氧化而获得表面环氧基功能化的E-CIMS介孔硅分子筛.将E-CIMS介孔硅分子筛作为载体用于固定化青霉素G酰化酶(PGA),研究了表面环氧基团对固定化PGA初活性和操作稳定性的影响.结果表明,随着表面环氧基团数量的增加,介孔硅分子筛孔径减小,表面疏水性增加,导致载酶量和初活性减小.但介孔硅分子筛表面适量的环氧基团能增强E-CIMS介孔硅分子筛与PGA之间的相互作用,从而提高固定化PGA的操作稳定性.     

A Kinetic Transition from Low to High Fragility in Cu-Zr Liquids

Researchers have reported that Cu-Zr liquids are kinetically strong at the best glass-forming compositions. Here we systematically study the temperature dependence of viscosity and diffusion of Cu-Zr liquids using molecular dynamics simulations, and the results illustrate that the better glass formers are actually more fragile close to the glass transition. There is a kinetic transition from low to high fragility when the optimal glass-forming liquids are quenched into glass states. This transition is associated with the more rapid decrease of the excess entropy of the liquids above and close to the glass transition temperature, Tg, compared to other compositions. Accompanied by the transition to high fragility, peaks in the thermal expansivity and specific heat are observed at the optimal compositions. Furthermore, the Stokes Einstein relation is examined over a wide composition range for Cu-Zr alloys, and the results indicate that glass-forming ability closely correlates with dynamical heterogeneity.     

A Transition from Eutectic Growth to Dendritic Growth Induced by High Undercooling Conditions

Cu-8 wt.% A1 eutectic alloy was undercooled by up to 187K (0.14TE) using a drop tube technique. The crystal growth and phase selection mechanisms were investigated during containerless rapid solidification. It is found that the microstructural morphology is characterized by lamellar eutectic growth at small undercoolings. However, if the liquid alloy is undercooled by more than 25K, eutectic growth will be suppressed completely and the dendritic growth of (Cu) solid solution dominates its solidification process. When the undercooling exceeds 153 K, a microstructural transition from coarse dendrite to equiaxed dendrite takes place.     

High undercooling of bulk water during acoustic levitation

The experiments on undercooling of acoustically levitated water drops with the radius of 5-8 mm are carried out, and the maximum undercooling of 24 K is obtained in such a containerless state. Various factors influencing the undercoolability of water under acoustic levitation are synthetically analyzed. The experimental results indicate that impurities tend to decrease the undercooling level, whereas the dominant factor is the effect of ultrasound. The stirring and cavitation effects of ultrasound tend to stimulate the nucleation of water and prevent further bulk undercooling in experiments. The stirring effect provides some extra energy fluctuation to overcome the thermodynamic barrier for nucleation. The local high pressure caused by cavitation effect increases the local undercooling in water and stimulates nucleation before the achievement of a large bulk undercooling. According to the cooling curves, the dendrite growth velocity of ice is estimated, which is in good agreement with the theoretical prediction at the lower undercooling. The theoretical calculation predicts a dendrite growth velocity of 0.23 m/s corresponding to the maximum undercooling of 24 K, at which the rapid solidification of ice occurs.     

声悬浮条件下大体积水的深过冷

采用声悬浮方法进行了Φ 5~8 mm大体积水的深过冷实验, 获得了高达24 K的过冷度. 分析了在声悬浮过程中影响水过冷能力的诸多因素, 发现杂质虽然对过冷度有一定的影响, 但并不是最主要的因素. 超声波对水滴的搅拌作用和空化效应制约着深过冷的获得. 同时, 研究了冰枝晶的生长速度、顶端半径与过冷度的关系, 并理论预测了24 K过冷度下冰的生长速度约为0.23 m/s, 实现了大体积水的快速凝固.     

非晶态合金表面的水润湿动力学

采用分子动力学模拟方法研究了改进的Simple pointcharge模型SPC/E水滴在Cu_(50)Zr_(50)非晶薄膜上的润湿行为和铺展过程.通过与CuZr(110)和(100)晶面对比研究发现,水滴在Cu_(50)Zr_(50)非晶薄膜表面上表现出较高的铺展速度.水滴在非晶合金表面的铺展过程中形成了明显的吸附层;而在晶态表面,水滴铺展前沿呈脚状形态.分析结果表明非晶表面的水分子在吸附层内呈现完全无序的单层排列方式,而在晶态表面,特别是(100)晶面,吸附层水分子呈双层有序排列.这种吸附层结构的差异导致了吸附层内水分子方向的差异:非晶表面吸附层内水分子方向倾向平行于表面,而晶态基底上吸附层内的水分子倾向于指向液滴内部.由此造成了非晶表面吸附层中的水分子与液滴内部以相对较弱的氢键相互作用,这使得上层水分子能够较容易扩散至吸附层前沿,促进液滴铺展.