The structure and dynamics of water inside armchair carbon nanotube

In this paper we present some simulation results about the behaviour of water molecules inside a single wall carbon nanotube (SWNT). We find that the confinement of water in an SWNT can induce a wave-like pattern distribution along the channel axis, similar phenomena are also observed in biological water channels. Carbon nanotubes(CNTs) can serve as simple nonpolar water channels. Molecular transport through narrow CNTs is highly collective because of tight hydrogen bonds in the protective environment of the pore. The hydrogen bond net is important for proton and other signal transports. The average dipoles of water molecules inside CNTs (7,7), (8,8) and (9,9) are discussed in detail. Simulation results indicate that the states of dipole are affected by the diameter of SWNT. The number of hydrogen bonds, the water--water interaction and water--CNT interaction are also studied in this paper.     

He-Ne激光辐照铁棍山药贮藏保鲜的研究

用工作波长632.8 nm、功率为2.5 mW的He-Ne激光器辐照铁棍山药,30 min后,其芦头芽萌发受抑,山药茎含水量、可溶性总糖和可溶性蛋白含量分别从70.203 9%下降到66.615 4 4%、从72.213 25 mg·g-1下降到25.878 88 mg·g-1、从508.539 4 μg·g-1下降到258.423 1 μg·g-1,丙二醛(MDA)和超氧阴离子含量分别从0.62 mmol·g-1变为8.033 122 mmol·g-1、从32.997 13 μg·g-1变为35.536 42 μg·g-1,贮藏前期的超氧化物歧化酶(SOD)活性从494.864 U·g-1变为1 105.85 U·g-1,贮藏后期的SOD活性从1 105.85 U·g-1变为959.167 U·g-1.     

环形聚乙炔分子桥的电导研究

我们选择了由40个CH基团组成的环形聚乙炔链作为分子桥,基于Landauer-Buttiker理论,利用求解散射波函数的方法,研究了这种环状聚乙炔分子桥与金属多端连接的电导随能量的变化关系.结果表明,在给定入射端的条件下,电导在正负能量上是对称的,当各个端口满足旋转对称性时,相对于入射端对称的两个出射端的电导相同.当分子桥耦合较弱时,电导对能量的变化相当敏感.     

Asymmetry of the water flux induced by the deformation of a nanotube

The behavior of nano-confined water is expected to be fundamentally different from the behavior of bulk water.At the nanoscale,it is still unclear whether water flows more easily along the convergent direction or the divergent one,and whether a hourglass shape is more convenient than a funnel shape for water molecules to pass through a nanotube.Here,we present an approach to explore these questions by changing the deformation position of a carbon nanotube.The results of our molecular dynamics simulation indicate that the water flux through the nanotube changes significantly when the deformation position moves away from the middle region of the tube.Different from the macroscopic level,we find water flux asymmetry(water flows more easily along the convergent direction than along the divergent one),which plays a key role in a nano water pump driven by a ratchet-like mechanism.We explore the mechanism and calculate the water flux by means of the Fokker-Planck equation and find that our theoretical results are well consistent with the simulation results.Furthermore,the simulation results demonstrate that the effect of deformation location on the water flux will be reduced when the diameter of the nanochannel increases.These findings are helpful for devising water transporters or filters based on carbon nanotubes and understanding the molecular mechanism of biological channels.     

Effect of an electric field on dewetting transition of nitrogen-water system

We investigate the influence of an external electric field on the dewetting behavior of nitrogen-water systems between two hydrophobic plates using molecular dynamics simulations. It is found that the critical distance of dewetting increases obviously with the electric field strength, indicating that the effective range of hydrophobic attraction is extended. The mechanism behind this interesting phenomenon is related to the rearrangement of hydrogen bond networks between water molecules induced by the external electric field. Changes in the hydrogen bond networks and in the dipole orientation of the water molecules result in the redistribution of the neutral nitrogen molecules, especially in the region close to the hydrophobic plates. Our findings may be helpful for understanding the effects of the electric field on the long-range hydrophobic interactions.     

相位不变性的若干讨论

考察了经典波动理论中的相位不变性,并且提出它作为物理学基本原理的直观依据———物理量的序列不变性.序列不变性是相对论原理的一个反映.从相位不变性出发,在给定时空变换关系下(伽利略变换和洛伦兹变换),得到波矢、频率和描述波包(类似于经典粒子)运动的群速度的坐标变换公式.另外,讨论了薛定谔方程、克莱因-戈尔登方程的相位坐标变换问题.对于薛定谔方程,我们认为量子力学中的复概率幅解放了经典波动情形下(波函数的实部具有独立物理意义)必须满足的相位不变性的约束,从而扩展了物理学的疆域,使它成为非相对论量子力学的基础;对于克莱因-戈尔登方程,它的解满足相位不变性,虽然对复波函数一般很难定义物理量序列的概念,但是对于克莱因-戈尔登方程,我们认为它也隐藏了某种序列不变性,并且结合倪光炯教授的双组分(正反粒子成分)观念给出了定义这种序列的一种可能性.     

金属/C2H2/金属结构中的电子输运

在紧束缚近似下,利用转移矩阵法对“金属/C2H2/金属”结构的分子导线的电子输运性质进行了研究。通过转移矩阵法求出转移矩阵和散射矩阵,从而解析地得到体系的透射系数和态密度的变化,并详细分析了透射系数对C2H2与金属的耦合强度及两个(CH)间的耦合强度的依赖关系。我们的结果显示这种结构的分子导线有着较好的开关特性。