Atomic scale imaging of monocrystalline Si （001） surface by molecular dynamic simulation

Non-contact atomic force microscopy(nc-AFM) atomic-scale imaging process of monocrystalline silicon surface using capped single-wall carbon nanotube tip is simulated by molecular dynamic method. The simulation results show that the nc-AFM imaging force mainly comes from the C-Si and C-C chemical covalent bonding forces, especially the former, the nonbonding Van der Waals force change is small during the range of stable imaging height. When the tip-surface distance is smaller than the stable imaging height, several neighboring carbon atoms at the tip apex are attracted, and some of them jump onto the sample surface. Finally the tip apex configuration is destroyed with the tip indenting further.     

海藻糖对固定化酶的保护作用

研究了海藻糖对固定化纤维素酶在干燥和存放过程中的保护作用 ,发现海藻糖能有效地减少固定化酶干燥过程中酶的热失活 ,而且能提高固定化纤维素酶存放过程中的热稳定性 .但温度越高海藻糖的保护效果越差 .借助红外分析和差示扫描量热方法 ,初步推测了海藻糖对固定化纤维素酶保护的机理为 :一是糖的羟基同酶分子以氢键的形式结合 ,提高了酶的热变性温度 ;二是糖分子包裹在酶分子周围 ,或填充在酶分子的空间结构内 ,特别是酶的活性部位附近 ,并形成玻璃态 ,将酶蛋白的空间结构固定住而避免酶的失活 .     

TOOL FORCE MODEL FOR DIAMOND TURNING

A new tool force model to be presented is based upon process geometry and the characteristics of the force system, in which the forces acting on the tool rake face, the cutting edge rounding and the clearance face have been considered, and the size effect is accountable for the new model. It is desired that the model can be well applicable to conventional diamond turning and the model may be employed as a tool in the design of diamond tools. This approach is quite different from traditional investigations primarily based on empirical studies. As the depth of cut becomes the same order as the rounded cutting edge radius, sliding along the clearance face due to elastic recovery of workpiece material and plowing due to the rounded cutting edge may become important in micro-machining, the forces acting on the cutting edge rounding and the clearance face can not be neglected. For this reason, it is very important to understand the influence of some parameters on tool forces and develop a model of the relatio