Pt(110)表面自吸附原子能量和力的改进分析型嵌入原子法分析

采用改进分析型嵌入原子法计算了Pt(110)表面自吸附原子的能量和法向力.当Pt吸附原子位于Pt(110)表面第一层原子的二重对称洞位上0.11nm时最稳定.Pt吸附原子的最佳迁移路径是由一个二重对称洞位沿密排方向迁移到最近邻的另一个二重对称洞位.在吸附原子远离表面的过程中，将依次经过排斥、过渡和吸引等三个区域.在排斥区和过渡区，由于吸附原子与表面原子间强的相互作用势，吸附原子的能量和法向力的形貌图均为(110)面原子排列的复形，与对势理论和嵌入原子法得到的结果一致.在吸引区，由于多体相互作用及晶体中原子 关键词： 金属表面 自吸附 能量 力     

利用杨辉三角形对称性推导高阶运动微分方程

利用Mathematica数学软件计算函数r=r(q(t),t)各变量之间偏导和高阶导数的关系，发现具有杨辉三角形对称性.结合杨辉三角形的对称性规律和牛顿第二定律推导出了高阶运动微分方程，并讨论了理想约束系统下的高阶运动微分方程. 关键词： 杨辉三角形 牛顿第二定律 高阶运动微分方程 高阶力变率 高阶速度能量 理想约束     

Simulation on the Effect of Brownian Motion on Nanoparticle Trajectories in a Pulsed Microplasma Cluster Source

We describe a simulation of the nanoparticle trajectories in a pulsed cluster beam source. Clusters, formed by condensation of atomic vapor in a helium bath, and considered here as rigid spheres having a diameter of 1.5nm, were tracked during their travel inside the source cavity, an aerodynamic lens, and a cylindrical nozzle. Steady state supersonic laminar flow of helium is considered in an axi-symmetric geometry aiming to simulate, within some limitations, the conditions under which cluster formation takes place in a pulsed microplasma cluster source. In spite of the unsteady nature of the pulsed source, the time scale characterizing particle motion in the flow field is significantly smaller than the characteristic time constant for the evolution of gas pressure in the source. For this reason, a steady simulation can shed some light on the understanding of processes governing nanoparticle motion in a pulsed vaporization source. The extent to which the Brownian diffusion can affect the particle extraction from the source is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the source internal walls. However, it does not hinder the aerodynamic focalization produced by the lens even in nano-size cluster regime. This result is qualitatively confirmed by experiment.     

An Improved Anharmonic Force Field of Difluoromethanimine, F2C NH

The anharmonic force field of difluoromethanimine, F₂C NH, has been reinvestigated theoretically using a coupled-cluster singles and doubles approach, augmented for structural optimization and harmonic force field by a contribution of connected triple excitations, CCSD(T). The cubic and quartic force constants have been obtained by numerical derivatives computed from analytical quadratic force constants calculated by second-order Møller-Plesset perturbation theory, MP2. The quadratic force constants and the equilibrium structure of F₂C NH have then been scaled by a global least-squares fitting procedure to the spectroscopic data and parameters experimentally determined for this molecule. This force field, obtained in the internal coordinates space and therefore valid for all isotopomers of difluoromethanimine, yields a complete set of spectroscopic molecular constants providing a critical assessment of the experimental rotational and centrifugal distortion constants, fundamentals, overtones, and combination bands determined so far for F₂C NH. In addition, the final force field can be used to make predictions of all important vibrational and rotational parameters which should be accurate and useful for new spectroscopic investigations.     

Effect of the three-body force on triton asymptotic normalization constants by the hyperspherical harmonics expansion method

We investigate the change in the calculated value of asymptotic normalization constant (ANC) by the hyperspherical harmonics expansion method with the inclusion of three nucleon force (3BF) in addition to two nucleon force. We see that ANC does not change very much with the inclusion of 3BF indicating that the 3BF does not alter the asymptotic behaviours of HHE wavefunction significantly.     

Calculated elastic constants of dilute alloys based on bcc metals

The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for a number of dilute alloys based on Mo, Nb, W, Ta and V.     

The effect of a coriolis force on Taylor-Couette flow

Taylor-Couette flow subject to a Coriolis force is studied experimentally and numerically. In the experiment, the Couette apparatus is mounted on a turntable with the axis of the cylinders orthogonal to the rotation vector of the turntable. The Coriolis force stabilizes the fluid against the onset of Taylor vortices and alters the velocity fields, both above and below the transition from the initial flow. At small dimensionless turntable frequencies, the transition yields time-independent Taylor vortices which are tilted with respect to the cylinder axis. At larger there is a direct transition to turbulence. We determine the first-order correction to the classical Couette initial flow, to account for the effects of the Coriolis force, by expanding in powers of. We present numerical results for the axial velocity (the only nonvanishing correction term to order) in the infinite-cylinder approximation.     

Drag force on a moving heavy quark with deformed string configuration

To study drag force on a moving heavy quark through a plasma, we use a deformed AdS space-time, in which deformation parameter c describes non-conformality in AdS/QCD. In this case, the quark is mapped to a probe string in the AdS space. Considering the probable contribution of the deformation parameter in the probe string, we apply a general form of c-dependent string ansatz in the drag force computation. Then, we find the acceptable value of this parameter as it satisfies QCD calculations. Using this result, we also discuss the diffusion constant which is in agreement with the phenomenological result for the non-relativistic limit. Also, we show that while in absence of a deformation parameter, the probe string is a strictly increasing function of radial coordinate, the c-dependent probe string has a maximum value versus z.     

Small amplitude dust-acoustic soliton energy in dusty plasmas with suprathermal polarization force

The effect of suprathermal polarization force on both linear and weakly nonlinear dust-acoustic solitary structures in a three-component dusty plasma is investigated. For this purpose, a new expression of the polarization force acting on dust particles that include the electronic suprathermal effect is derived. The results are applied to two different experimental dusty plasmas. We have found that the polarization force acting on the dust grains decreases as the electron suprathermality becomes more significant. In addition, we have shown that, for a given value of the spectral index κ , the polarization force magnitude fluctuates from one plasma to another. The changes arising in the propagation of small-amplitude dust-acoustic (DA) solitons due to the presence of this suprathermal polarization force are also analysed. Interestingly, an increase in the magnitude of the polarization force leads to an increase in the amplitude and width of DA soliton and provides more energy to the motion of this soliton.     

Force-field dependence of the conformational properties of α,ω-dimethoxypolyethylene glycol

A molecular dynamics (MD) study of α,ω-dimethoxypolyethylene glycol has been carried out under various conditions with respect to solvent composition, ionic strength, chain length, force field and temperature. A previous MD study on a 15-mer of polyethyleneglycol (PEG) suggested a helical equilibrium structure that was stabilised by hydrogen bonding and bridging water molecules. Experiments show that PEG is highly soluble in water, and indicate that clustering is not favoured. In the present study using different force fields, the GROMOS force fields 45A3 and 53A6, a variation on the latter 53A6_OE, and a force field by Smith et al. produced different results. For the GROMOS force fields 45A3 and 53A6 no helical structure was found, but formation of more or less compact random coils in aqueous solution due to hydrophobic interactions was observed. For the other two force fields used, α,ω-dimethoxypolyethylene glycol stayed flexible and more or less elongated in aqueous solution, more in agreement with experimental observations and the previous MD study.