采用Fokker-Planck方程研究了甘油分子在周期性外力作用下通过甘油通道(glycerol protein ficilita-tor,GlpF)定向输运的问题.根据平均力势(potential of mean force,PMF)的分布把GlpF分成14个区域,分别讨论了不同区域对甘油分子定向输运的影响.研究发现,GlpF的中间区域对甘油分子的输运起到关键作用.
An analysis of tortuosity for streamlines in porous media is presented by coupling the circle and square models. It is assulued that some particles in porous media do not overlap and that fluid in porous media is incompressible. The relationship between tortuosity and porosity is attained with different configurations by using a statistical method. In addition, the tortuosity fractal dimension is expressed as a function of porosity. Those correlations do not include any empirical constant. The percolation threshold and tortuosity fractal dimension threshold of porous media are also presented as： φc = 0.32, DT,： = 1.07. The predicted correlations of the tortuosity and the porosity agree well with the existing experimental and simulated results.
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.
The dynamics of fluid flow through nanochannels is different from those in macroscopic systems. By using the molecular dynamics simulations, we investigate the influence of surface polarity of nanotube on the transport properties of the water fluid. The nanotube used here resembles the carbon nanotube, but carries charges of q on some atoms; overall, the nanotube is charge-neutral. Our simulation results show that water flux decreases sharply with the increasing of q for q 〈 1.6 e; however, the water flux for shells far away from nanotube wM1 increases slightly when q 〉 1.6 e. The mechanism behind the interesting phenomenon is discussed. Our findings may have implications for development of nano-fluidic devices and for understanding the movement of confined fluid inside the hydrophilic nanochannel.
