脱氧核苷酸横向电输运特性的理论计算

采用基于密度泛函(DFT)的非平衡态格林函数方法(non-equilibrium Green functions,NEGF),讨论电极距离对分子电子结构和电流的影响,计算四种脱氧核苷酸的I-V特性曲线和透射谱.结果表明,电极距离小于1.55nm时,电极距离对脱氧核苷酸分子的电子结构影响较大,当电极距离大于1.55nm时,LUMO和HOMO附近各能级的变化趋于平缓,电子能隙变化非常小.电极距离固定时,较低偏压(0.1~0.8V)不会改变四种脱氧核苷酸分子的相对电流大小.偏压较大时(0.8~1.0V),T和C的电流迅速增加并远大于A和G.     

乔治·格林及格林函数法

乔治.格林是一位重要的数学物理学家.简要介绍了乔治.格林的生平和科学研究经历,揭示了帮助他取得重要科学研究成果的主要因素,介绍了格林函数法的建立过程及其重要性.     

DNA碱基与电极的耦合强度对横向电输运的影响

采用基于密度泛函理论的非平衡格林函数方法,研究了以Au(111)面为电极、DNA的单个碱基(包括主链上的糖基和磷酸基)置于其问的两电极体系的电输运特性,在电极距离固定的情况下,通过改变碱基与电极的接触距离,分别计算了零偏压下DNA碱基处于不同耦合强度时的横向电导和传输谱.结果表明碱基的横向电输运性质受耦合强度的影响较大;除了鸟嘌呤G的氢键靠近电极时电导比腺嘌呤A小之外,碱基的电导排序符合G＞A＞C＞T.     

在闭合时间路径温度场论中直接计算推迟和超前格林函数的费曼规则

在闭合时间路径温度场论基础上,导出了直接计算推迟和超前格林函数的一种费曼规则.利用该费曼规则计算了φ³理论中的两点自能和三点顶角函数修正.验证了三点非线响应函数满足的推广的涨落耗散定理     

镍晶格中的晶格格林函数

在含缺陷体系的模拟中,格林函数作为一种重要的多尺度耦合方法,可以将缺陷产生的局域应变场和长程应力场耦合起来.在镍基高温合金蠕变的初期阶段,位错主要分布在基体相中,通过格林函数的多尺度桥接模式,可得到基体相中位错芯的平衡构型,为位错-杂质复合体间相互作用提供计算基础.基于晶格动力学理论和声子谱计算中的力常数矩阵,通过第一布里渊区特殊k点取样以及傅里叶变换,计算完整镍晶格中晶格格林函数,可用于镍基材料的多尺度模拟计算.     

Identification of intrinsic gapped behavior in spin-1/2 ladder with staggered dimerization

The zero- and low-temperature behaviors of spin-1/2 two-leg ladder with staggered dimerization are investigated by the Green’s function theory. At zero temperature, the ground state phase diagram is explored, wherein the leg-dimer and rung-singlet phases are revealed, which reflect two different intrinsic gapped behaviors. The former is attributed to the bond alternation along the legs, while the latter is due to the strong rung coupling. It is found that the quantum phase transition from one to another is of the first order, which can be clearly signaled by the rung entanglement entropy. At finite temperatures, the temperature dependence of thermodynamic quantities such as the magnetic susceptibility, specific heat, thermal Drude weight and rung entanglement entropy are calculated to characterize the corresponding quantum phases. It is shown that the magnetic behaviors clearly manifest a typical antiferromagnetism at low temperature, which is in accordance with the experimental results. It is also found that the intrinsic gapped low-lying excitations are responsible for the observed thermodynamic behaviors.     

沿一条确定的轨迹积分求解N维基态量子波函数的新方法

介绍了一个沿着一条确定的轨迹积分求解N维基态量子波函数的新方法,通过对哈密顿里的位热引入标度因子g^2,将波函和能量按1／g展开,并应用求解经典的Hamilton-Jacobi方程的方法,找到一条确定的轨迹,使薛定谔方程从二阶偏微分方经为一系列沿这条轨迹的一阶常微分方程,基态波函数可以表示为沿这条确定轨迹的一系列积分,而能量则可以用位势极小值处的一系列微分表示,在此基础上,导得一个全新的微扰展开系列和相应的,N维量子波函数的格林函数,作为例子,交此方法应用于库伦吸引位和斯塔克（Stark）效应。     

金属腔内场线耦合干扰敏感性

研究了金属腔内电磁场与单导线耦合对线两端部件产生干扰的敏感性问题。利用并矢格林函数计算腔内场分布, 利用Agrawal模型计算获得导线两端负载的干扰响应, 从腔体尺寸、内部干扰源位置及导线位置三个方面分析了建模的微小变化对导线负载干扰的影响。结果表明, 腔体尺寸的微小变化会带来负载干扰响应的很大变化, 在谐振点处该影响尤其明显;腔内干扰源位置的微小变化可能会带来负载干扰响应的巨大变化;干扰响应对导线距离金属腔壁高度的微小变化不敏感, 但单导线位置的微小变化可能带来负载干扰的较大变化。     

空间相干与入射光子能量对临床类同轴X射线相衬成像影响

在临床实际应用中,X射线源是一个具有有限尺寸的多色光源.基于Fresnel-Kirchhoff衍射理论,考虑空间相干的影响,新的类同轴X射线相衬成像公式被导出.分别代表吸收效应与相位效应的吸收衬度传递函数和相位衬度传递函数从新公式得到.吸收衬度传递函数和相位衬度传递函数的曲线由Matlab给出,不同源半径的最佳成像位置也被计算.理论分析结果如下:1）当光源半径足够大时空间相干效应须被考虑,减小源半径可以增强相位效应|2）源半径与最佳成像位置间有确定关系,并在本文中给出|3）源尺寸效应对相位效应影响不是无限的|4）减小入射X射线光子能量将会显著增强相位效应,但不会对最佳成像位置有影响,因此,上述结论可以被拓展到多色光情况.为了验证理论结果,本文给出了对一个表面破损的光学玻璃微聚焦相衬成像的实验结果.其中一些实验结果与理论分析符合很好,但也有一些实验未达到预期,相关的解释文中也已给出.     

空间相干与入射光子能量对临床类同轴X射线相衬成像影响

在临床实际应用中,X射线源是一个具有有限尺寸的多色光源.基于Fresnel-Kirchhoff衍射理论,考虑空间相干的影响,新的类同轴X射线相衬成像公式被导出.分别代表吸收效应与相位效应的吸收衬度传递函数和相位衬度传递函数从新公式得到.吸收衬度传递函数和相位衬度传递函数的曲线由Matlab给出,不同源半径的最佳成像位置也被计算.理论分析结果如下:1）当光源半径足够大时空间相干效应须被考虑,减小源半径可以增强相位效应|2）源半径与最佳成像位置间有确定关系,并在本文中给出|3）源尺寸效应对相位效应影响不是无限的|4）减小入射X射线光子能量将会显著增强相位效应,但不会对最佳成像位置有影响,因此,上述结论可以被拓展到多色光情况.为了验证理论结果,本文给出了对一个表面破损的光学玻璃微聚焦相衬成像的实验结果.其中一些实验结果与理论分析符合很好,但也有一些实验未达到预期,相关的解释文中也已给出.     

Electronic transport in the multi-terminal graphene nanodevices

We examined the ac transport attribute of the multi-terminal structures in the absence and presence of magnetic field. We found that the ac response depends on the structural configurations and that the admittance varies with the features of the attached nanoribbons. In the vicinity of Dirac point the dc conductance manifests a dip or peak and the imaginary part (emittance) vanishes or not, depending on whether the attached ribbon is semiconductive or metallic. In the presence of magnetic field, the emittance becomes asymmetric reflecting the dynamic behaviors of electron and hole.     

Induced phase transition of BECs in optical lattices by impurity

In this work, the influence of imparity on BECs in optical lattices is investigated, and the possibility of MI-SF transition induced by impurity is verified. After the numerical calculation, the schematic phase diagram is discussed with an emphasis on the role of impurity. When n10 = n20, the phase boundaries coincide with each other; when n10 < n20 and U12 < 0, the phase boundaries do not intersect at all; when n10 < n20 and U12 > 0, the phase boundaries may or may not intersect, depending on the values of...     

Towards a theory of dissociative recombination

Current experiments in storage rings at Aarhus and Stockholm reveal that ions such as CH ₃ ⁺ , OH ₃ ⁺ , OH ₂ ⁺ and CH ₅ ⁺ recombine and fragment into three parts more often than into just two. Analysis of the possible resonances between free electron and bound electron states for the ions require a detailed examination of the correlation effects as well as the coupling to nuclear degrees of freedom. The problem is well suited for the propagator approach. An analysis of the structure of the self-energy kernel shows the presence of possible resonances with degenerate electronic states which are unstable according to the Jahn-Teller theorem and provides channels for multiple fragmentation.     

微量子腔结边电荷极化结构中的线性和二阶非线性动态电导性质的研究

采用有效哈密顿量和有相互作用的分立势模型,利用格林函数和耦合参量得出了量子点(腔)在有结边电荷积累极化时的线性和二阶非线性交流电导虚部(emittance)的明确表达式.发现在经典情况下,电导虚部和电化学电容都等于经典的几何电容.在非经典情况下,如果发生全反射,电导虚部和电化学电容相等,但两者皆不等于经典的几何电容.在有隧穿的情况下,电导虚部和电化学电容以及经典电容三者都不相等.该结果对于量子器件中的电容测量具有指导作用.关键词：格林函数交流电导电化学电容     

卡西米尔效应的格林函数计算方法

介绍了卡西米尔效应的严格格林函数表达式.作为应用,计算了4种边界条件下两平行板之间的卡西米尔能量.     

A green function approach to shear viscosity coefficient

Modified transport equations are derived from Kadanoff and Baym kinetic equations, suitable for the study of thermal transport coefficients. These equations include the Hartree average energy term which has been ignored in the previous studies of thermal transport coefficients. They are linearised and the successive perturbation method is employed to solve them. The solutions are applied to shear viscosity coefficient of gases and the results are compared with the recent experimental measurements for several complex and simple gases. The potential assumed is a hard core one with a perturbation tail. The agreements are particularly good for gases with low molecular weight and in the high temperature range. For complex molecules even in the low temperature range, the agreement is better than the previous calculations. The formula derived yields the explicit temperature dependence of the viscosity coefficient.