The high/low conductance switching in stretching process of 4,4′-bipyridine molecular junction is a distinctive phenomenon in molecular electronics, which is still a mystery and has been unsolved for more than one decade. Based on the techniques and processes of experimental measurement, the <i>ab initio</i>-based adiabatic molecule-junction-stretch simulation (AMJSS) method is developed, by which the stretching processes of 4,4′-bipyridine molecular junctions are calculated. The conductance traces of the molecular systems in the stretching processes are studied and the mystery of high/low conductance switching in the stretching processes of 4,4′-bipyridine molecular junction is decoded by using the one-dimensional transmission combined with the three-dimensional correction approximation (OTCTCA) method. The numerical results show that, in the stretching process of 4,4′-bipyridine molecular junction, the upper terminal nitrogen atom in the pyridine ring is easy to vertically adsorb on the second gold layer of the probe electrode. At the same time, the molecule produces unique lateral-pushing force to push the tip atoms of the probe electrode aside. Thus, the high conductance plateau arises. With the molecular junction further stretched, the upper terminal nitrogen atom of the molecule shifts from the second gold layer to the tip gold atom of the probe electrode with the tip gold atom moving back to the original lattice position. Consequently, the conductance value decreases by about 5–8 times, and the low conductance plateau is presented. According to our calculations, the phenomenon of high/low conductance switching in the stretching process of 4,4′-bipyridine molecular junction also indicates that, single surface gold atom often lies on the surface of substrate electrode. Moreover, the phenomenon of high/low conductance switching can only be found when the molecule is adsorbed on the surface gold atom of the substrate electrode. Thus, using conductance traces measured in the stretching processes of molecular junction and with the help of theoretical calculations, the interface structures of molecular junctions can be recognized efficiently. Our study not only decodes the physical process and intrinsic mechanism of the high/low conductance switching phenomenon of 4,4′-bipyridine molecular junction, but also provides significant technique information for using pyridine-based molecule to construct functional molecular devices, such as molecular switch, molecule memory, molecular sensor, etc.

Sustained release carrier for the bone morphogenetic protein-2 (BMP-2) is currently a hot subject of research on the bone tissue engineering. In this work, two kinds of heparinized silk fibroin scaffolds were prepared. The binding ability to BMP-2, in vitro sustained release property and the alkaline phosphatase (ALP) activity of the scaffolds were investigated. Results showed that the heparinized silk fibroin scaffolds could bind BMP-2 well and sustained release the BMP-2. The scaffolds with BMP-2 could improve the MG-63 cell growth and cell differentiation with high ALP activity. So the heparinized silk fibroin scaffolds could be an ideal sustained release carrier for BMP-2. Keywords silk fibroin scaffold; BMP-2; alkaline phosphatase; sustained release 骨形态发生蛋白(BMPs)是一种多功能生长因子, 属于转化生长因子-β 超家族的成员 [1]. 其中骨形态发生

The microstructures of Cu75.15Al24.85 alloy before and after treatment at 15 GPa pressure and 750℃ for 15 min are analyzed by optical metallograph, X-ray diffraction, scanning electron microscopy and differential scanning calorimeter, and its resistivity is also obtained through resistivity measuring instrument. According to the obtained results, the effects of high pressure treatment on the microstructure and resistivity are investigated. The results show that high pressure treatment can refine the microstructure, and increase the resistivity of the alloy. When the pressure is 3 GPa, the refinement is more remarkable and the resistivity reaches a maximal value.