脉冲激光沉积动力学研究进展

脉冲激光沉积技术是现代常用的先进薄膜材料制备技术之一.文章在简要介绍脉冲激光沉积技术及其进展的基础上,较全面地介绍了脉冲激光沉积动力学的基本物理图像和动力学构架,深入地探讨了激光烧蚀靶材过程、等离子体膨胀过程和薄膜沉积过程的动力学规律,阐述了我国学者在脉冲激光沉积动力学研究方面的贡献,例如包括脉冲激光沉积三个工艺过程自洽的统一模型,等离子体膨胀的冲击波模型,基于局域能量动量守恒定律的新等离子体演化动力学模型,包括热源项、蒸发项、等离子体屏蔽效应和动态物性参数的烧蚀热传导模型,考虑电子碰撞效应和能带结构变化的修正双温模型,能统一描写从纳秒级到飞秒级脉冲激光烧蚀规律的统一双温模型等.     

Regioselective acylation of nucleosides and their analogs catalyzed by Pseudomonas cepacia lipase: enzyme substrate recognition

The substrate recognition of Pseudomonas cepacia lipase in the acylation of nucleosides was investigated by means of rational substrate engineering for the first time. P. cepacia lipase displayed excellent 3′-regioselectivities (96 to >99%) in the lauroylation of 2′-deoxynucleosides 1a-1e, while low to good 3′-regioselectivities (59-89%) in the lauroylation of ribonucleosides 1f-1j. It might be due to the unfavorable hydrogen bond interaction between 2′-hydroxyl group of 1f-1j and phenolic hydroxyl group of tyrosine residue present in the alternate hydrophobic pocket of the enzyme, which stabilizes the conformation of 5′-acylation transition state and thus increases the amount of the minor regioisomer. In addition, various ester derivatives of floxuridine were synthesized successfully by the lipase with high conversions (99%) and good to excellent 3′-regioselectivities under mild conditions. The recognition of various acyl donors by the enzyme was examined. The enzymatic recognition of acyl groups was rationalized in terms of the structure of the active site of the lipase, especially the size, shape, and physicochemical properties.     

电子辐照掺锂硅中深能级

用深能级瞬态谱法,从与锂有关的缺陷的产生和锂对电照缺陷的退火的影响两个侧面,研究了不同合氧量硅中锂和电照缺陷的相互作用。指出了氧能抑制锂和电照缺陷的相互作用,只有当锂浓度不是远小于氧浓度时,锂才能有作用。E(0.17),E(0.21),E(0.38),E(0.50),H(0.42)和H(0.47)等与锂有关的缺陷分别在不同的条件下被观测到。对比了硅中氢和锂在与电照缺陷相互作用方面的相似与不同之处。     

Highly Efficient Regioselective Synthesis of 5′-<Emphasis Type="Italic">O</Emphasis>-lauroyl-5-azacytidine Catalyzed by <Emphasis Type="Italic">Candida antarctica</Emphasis> Lipase B

Enzymatic regioselective acylation of 5-azacytidine with vinyl laurate was successfully conducted with an immobilized lipase from Candida antarctica type B (i.e., Novozym 435) for the first time. The acylation of 5-azacytidine took place at its primary hydroxyl group and the desired product 5′-O -lauroyl-5-azacytidine could be prepared with high reaction rate, high conversion, and excellent regioselectivity. The influences of several key variables on the enzymatic acylation were also systematically examined. Pyridine was found to be the best reaction medium. The optimum initial water activity, the molar ratio of vinyl laurate to 5-azacytidine and reaction temperature were 0.07, 30:1, and 50 °C, respectively. Under the optimized conditions described above, the initial reaction rate, the substrate conversion, and the regioselectivity were as high as 0.58 mM/min, 95.5%, and >99%, respectively, after a reaction time of around 5 h.     

镓填充二氧化硅纳米管的电子束诱导的反常膨胀

研究了镓填充二氧化硅纳米管的电子束诱导的膨胀现象, 确认微球系统中镓液体在电子束辐照下存在反常膨胀现象. 首先分析了相关的实验过程和现象, 指出此膨胀过程可以视为准静态过程; 然后根据傅里叶热传导定律, 在准静态热力学的框架下定量讨论了该系统在电子束辐 照下微球中镓液体相对体积随温度变化规律, 进一步确定系统的相对膨胀率和系统的膨胀系数, 发现反常膨胀系数是正常热膨胀系数的5-9倍. 最后指出这种反常膨胀是由系统的电离效应和残存效应共同引起的, 两者造成系统的粒子数密度急剧增加, 从而导致系统的内部压强急剧增加, 产生体积反常膨胀.     

A novel 2D Mn(II) dicarboxylate with nanometer channels: hydrothermal synthesis,crystal structures and luminescence properties

A novel two-dimensional supramolecular complex, Mn(HA)₂(H₂O)₂ (1) (H₂A: 9-ethylcarbazole-3,6-dicarboxylic acid) has been prepared by hydrothermal synthetic method and characterized by X-ray single crystal diffraction, IR spectra, elemental analysis and TG analysis. The result confirms that complex (1) crystallizes in the space group C2/c with a = 31.30(2) Å, b = 5.088(4) Å, c = 20.517(14) Å, β = 119.863(9)°, Z = 4, V = 2834(3)ų. The 2D supramolecular open framework (1), which contains 9.773 × 7.447 Å nanometer channels, is constructed through hydrogen bonds and aromatic π ? π interactions. Furthermore, the solid-state fluorescent analyses show that complex 1 exhibits a broad emission with the maximal emission at 416 nm.     

Sandpile Dynamics Driven by Degree on Scale-Free Networks

We introduce a sandpile model driven by degree on scale-free networks, where the perturbation is triggered at nodes with the same degree. We numerically investigate the avalanche behaviour of sandpile driven by different degrees on scale-free networks. It is observed that the avalanche area has the same behaviour with avalanche size. When the sandpile is driven at nodes with the minimal degree, the avalanches of our model behave similarly to those of the original Bak-Tang-Wiesenfeld （BTW） model on scale-free networks. As the degree of driven nodes increases from the minimal value to the maximal value, the avalanche distribution gradually changes from a clean power law, then a mixture of Poissonian and power laws, finally to a Poisson-like distribution. The average avalanche area is found to increase with the degree of driven nodes so that perturbation triggered on higher-degree nodes will result in broader spreading of avalanche propagation.     

Continuous Weight Attack on Complex Network

We introduce a continuous weight attack strategy and numerically investigate the effect of continuous weight attack strategy on the Barabasi-Albert （BA） scale-free network and the Erdos-Rdnyi （ER） random network. We use a weight coefficient ω to define the attack intensity. The weight coefficient ω increases continuously from 1 to infinity, where 1 represents no attack and infinity represents complete destructive attack. Our results show that the continuous weight attack on two selected nodes with small ω （ω≈ 3） could achieve the same damage of complete elimination of a single selected node on both BA and ER networks. It is found that the continuous weight attack on a single selected edge with small ω （ω≈ 2） can reach the same effect of complete elimination of a single edge on BA network, but on ER network the damage of the continuous weight attack on a single edge is c/ose to but always smaller than that of complete elimination of edge even if ω is very large.     

Spatiotemporal Characteristic of Epidemic Spreading in Mobile Individuals

We numerical simulate the propagation behaviour and people distribution trait of epidemic spreading in mobile individuals by using cellular automaton method. The simulation results show that there exists a critical value of infected rate fluctuating amplitude, above which the epidemic can spread in whole population. Moreover, with the value of infected rate fluctuating amplitude increasing, the spatial distribution of infected population exhibits the spontaneous formation of irregular spiral waves and convergence phenomena, at the same time, the density of different populations will oscillate automatically with time. What is more, the traits of dynamic grow clearly and stably when the time and the value of infected rate fluctuating amplitude increasing. It is also found that the maximal proportion of infected individuals is independent of the value of fluctuating amplitude rate, but increases linearly with the population density.     

Increasing Superplasticity and Strong Dynamic Behaviour of Zr--Cu--Ni--Al Bulk Metallic Glass

The plasticity and the dynamic fragility of bulk metallic glass of a Zr62 CuxsNiloAllo alloy are studied by three- point beam bending methods. We find that the alloy behaves super plastic not only at room temperature, but also at high temperatures. More importantly, it is found that the superplasticity increases with increasing temperature. In addition, the dynamic fragility parameter m for the supercooled liquid of this alloy is measured to be 34.87 and the supercooled liquid of Zr62 CuxsNixoAlxo alloy behaves as a strong liquid.