P granules are germ granules contained in Caenorhabditis elegans germ cells.The first germ cell is specified by the one-cell embryo in which P granules localize to the posterior.Previous studies suggested that the mechanism of the localization phenomena is induced by liquid-liquid phase transition(LLPT),in which the polarity proteins control the saturation point of P granules.In the present study,we propose that the P granules phase transition can be triggered by the cytoplasmic streaming.A two-phase flow model is employed to simulate the localization of P granules,i.e.,the cytoplasm is considered as a liquid phase,and the droplet-like P granules are another liquid phase.With the presence of the cytoplasmic streaming,P granules,initially distributing uniformly in the entire one-cell embryo,eventually condense/dissolve in the cytoplasm phase,regulated by difference between the saturation pressure and the hydrodynamic pressure.The numerical results reveal that the cytoplasmic streaming has significant effects on the localization of P granules,as well as the embryo division.
The DNA sequencing technology has achieved a leapfrog development in recent years. As a new generation of the DNA sequencing technology, nanopore sequenc- ing has shown a broad application prospect and attracted vast research interests since it was proposed. In the present study, the dynamics of the electric-driven translocation of a homopolymer through a nanopore is investigated by the dissipative particle dynam- ics （DPD）, in which the homopolymer is modeled as a worm-like chain （WLC）. The DPD simulations show that the polymer chain undergoes conformation changes during the translocation process. The different structures of the polymer in the translocation process, i.e., single-file, double folded, and partially folded, and the induced current block- ades are analyzed. It is found that the current blockades have different magnitudes due to the polymer molecules traversing the pore with different folding conformations. The nanoscale vortices caused by the concentration polarization layers （CPLs） in the vicinity of the sheet are also studied. The results indicate that the translocation of the polymer has the effect of eliminating the vortices in the polyelectrolyte solution. These findings are expected to provide the theoretical guide for improving the nanopore sequencing tech- nique.
The transport of water and ions through carbon nanotubes （CNTs） is crucial in nanotechnology and biotechnology. Previous investigation indicated that the ions can hardly pass through （6,6） CNTs due to their hydrated shells. In the present study, utilizing molecular dynamics simulation, it is shown that the energy barrier mainly originating from the hydrated water molecules could be overcome by applying an electric field large enough in the CNT axis direction. Potential of mean force is calculated to show the reduction of energy barrier when the electric field is present for （Na＋, K＋, C1 ） ions. Consequently, ionic flux through （6,6） CNTs can be found once the electric field becomes larger than a threshold value. The variation of the coordination numbers of ions at different locations from the bulk to the center of the CNT is also explored to elaborate this dynamic process. The thresholds of the electric field are different for Na＋, K＋, and CI- due to their characteristics. This consequence might be potentially applied in ion selectivity in the future.
