Non-equilibrium molecular dynamics simulation study of the frequency dependent conductivity of a primitive model electrolyte in a nanopore

The frequency dependence of electrical conductivity in a 0.1 molar univalent restricted primitive model electrolyte confined in cylindrical pores is studied by non-equilibrium molecular dynamics simulations. At high frequencies, conductivity is independent of pore size and approaches the zero value limit. The phase lag is independent of pore size and approaches the value π/2 at high frequency. At low frequencies, the conductivity is relatively constant and approaches the zero frequency (dc) conductivity value. For pores with radius smaller than 3 times the ion diameter, severe confinement effects lead to different low frequency behaviour. In these very small pores, axial collisions increase at low frequency and lead to much lower conductivity and a negative phase shift. The current response in severely confined electrolytes can be analogous to an LRC circuit with resonance at a characteristic frequency.     

复杂形状的金属橡胶隔振器当量弹性模量研究

给出了计算金属橡胶鼓形隔振器的当量弹性模量的方法.计算了拉伸和剪切作用下复杂形状隔振器的弹性特征量,利用当量弹性模量和有限元方法来研究隔振器的变形,通过算例和实验结果进行验证.结果表明,当量弹性模量比较准确地描述了复杂形状金属橡胶隔振器的性能,为其进一步研究奠定了基础.图6,表1,参8.     

Dynamic analysis of erbium-doped optically pumped waveguide lasers using a time-domain travelling wave model

A simple and straightforward dynamic model of Er3+-doped optically pumped waveguide lasers using a time-domain algorithm is developed. The theoretical model is based on (a) time-dependent rate equations of a quasi-two-level system for the population densities and (b) time-dependent travelling wave equations for the pump and signal power which are solved simultaneously in the time domain. In addition, the longitudinal distribution of spontaneous emission noise is also taken into consideration. Using the fast Fourier transform, the spectrum profile of the time-domain signal power is calculated. In this paper, the transient responses of population densities, pump and signal power are investigated for Er3+-doped Ti:LiNbO3 waveguide lasers. To demonstrate the sophistication of this time-domain model, the influence of the cross-coupled effect of the travelling waves due to the optical feedback of an etched grating is also studied. Dynamic response of the waveguide laser with and without a grating are compared. This revised version was published online in June 2006 with corrections to the Cover Date.     

Theoretical investigations of the vapour-liquid equilibrium and dielectric properties of dipolar Yukawa fluids in an external field

In a low field approximation, using the dipolar Yukawa fluid model (in mean spherical approximation as a reference system) a consistent field-dependent free energy expression is proposed for the calculation of the vapour-liquid equilibrium of polar fluids in an applied electric field. A perturbation theory high field approximation expression of the free energy is also proposed to study the field-dependent properties of fluids. In the high field approximation, equations for the field-dependent polarization and for the nonlinear dielectric constant (or Piekara constant) are also predicted. It has been discussed that our approximations are appropriate to describe the vapour-liquid-like phase equilibria and the magnetization curves of magnetic fluids.     

Forces between charged surfaces in a solvent primitive model electrolyte

Grand canonical Monte Carlo (GCMC) simulations have been performed to investigate the components of the force between parallel charged surfaces in an electrolyte. The solvent primitive model (SPM) was used to investigate the effect of neutral hard sphere solvent particles on the force between the surfaces. The effects of particle size, wall charge density, charge valency of the electrolyte, and the exclusion of neutral hard sphere are discussed. When solvent particles are considered, the total force between the charged surfaces is always repulsive, even for divalent counterions. This is different from the earlier conclusion reached with a restricted primitive model electrolyte. The repulsive force decreases in going from monovalent counterions to divalent counterions.     

Diffusivity and conductivity of a primitive model electrolyte in a nanopore

Equilibrium and non-equilibrium molecular dynamics simulations are applied to obtain the diffusion coefficient and electric conductivity of ions in dilute electrolytes confined in neutral cylindrical pores. The electrolyte is described with the restricted primitive model and the wall of the pore is modelled as a soft wall. The equilibrium molecular dynamics simulations show that the axial diffusion coefficient of ions decreases with increasing confinement. For a fixed pore radius the diffusion coefficient decreases with increasing number density of the ions. The current response of the system to an applied electric field is maintained at constant temperature by Gaussian isokinetic equations of motion, and at constant concentration by periodic boundary conditions with recycling of ions in the axial direction. The electric conductivity is calculated from the current density and the electric field applied for different pore sizes. In contrast to the trend in diffusivity, conductivity increases slightly in smaller pores. For a very small pore, however, conductivity is lower than the bulk, because oppositely charged ions moving in opposite directions under the electric field cannot avoid collisions with each other in a narrow channel.