The aim of this paper is to understand the common characteristics of the generalized flyby trajectory around natural elongated bodies. Such flyby trajectories provide a short-term mechanism to clear away vicinal objec...The aim of this paper is to understand the common characteristics of the generalized flyby trajectory around natural elongated bodies. Such flyby trajectories provide a short-term mechanism to clear away vicinal objects or temporally capture ejecta into circling orbits. The gravitational potential of elongated bodies is described by a unified approximate model, i.e., the rotating mass dipole which is two point masses connected with a constant massless rod The energy power is used to illustrate the flyby effect in terms of the instantaneous orbital energy. The essential of the single flyby trajectory is studied analytically, and the relationship between the flyby trajectory and its Jacobi integral is also illustrated. Sample trajectories are given to show the variational trend of the energy increment with respect to differen orbital periapsides. The distribution of natural ejecting orbits is presented by varying the parameters of the approximate model.展开更多
Smoothed particle hydrodynamics（SPH） is a mesh-free adaptive Lagrangian particle method with attractive features for dealing with the free surface flow.This paper applies the SPH method to simulate the large-amplitu...Smoothed particle hydrodynamics（SPH） is a mesh-free adaptive Lagrangian particle method with attractive features for dealing with the free surface flow.This paper applies the SPH method to simulate the large-amplitude lateral sloshing both with and without a floating body,and the vertical parametrically-excited sloshing in a two-dimensional tank.The numerical results show that the SPH approach has an obvious advantage over conventional mesh-based methods in handling nonlinear sloshing problems such as violent fluid-solid interaction,and flow separation and wave-breaking on the free fluid surface.The SPH method provides a new alternative and an effective way to solve these special strong nonlinear sloshing problems.展开更多
Stimulatory regulators for DNA methyltransferase activity,such as Dnmt3L and some Dnmt3b isoforms,affect DNA methylation patterns,thereby maintaining gene body methylation and maternal methylation imprinting,as well a...Stimulatory regulators for DNA methyltransferase activity,such as Dnmt3L and some Dnmt3b isoforms,affect DNA methylation patterns,thereby maintaining gene body methylation and maternal methylation imprinting,as well as the methylation landscape of pluripotent cells.Here we show that metastasis-related methyltransferase 1(Merm1),a protein deleted in individuals with Williams-Beuren syndrome,acts as a repressive regulator of Dnmt3a.Merm1 interacts with Dnmt3a and represses its methyltransferase activity with the requirement of the binding motif for S-adenosyl-L-methionine.Functional analysis of gene regulation revealed that Merm1 is capable of maintaining hypomethylated rRNA gene bodies and co-localizes with RNA polymerase I in the nucleolus.Dnmt3a recruits Merml,and in return,Merml ensures the binding of Dnmt3a to hypomethylated gene bodies.Such interplay between Dnmt3a and Merml facilitates transcriptional elongation by RNA polymerase I.Our findings reveal a repressive factor for Dnmt3a and uncover a molecular mechanism underlying transcriptional elongation of rRNA genes.展开更多
基金supported by the National Basic Research Program of China(973 Program),(Grant 2012CB720000)China Postdoctoral Science Foundation(Grant 2014M560076)Support from Shanghai Satellite Engineering Research Institute(Grant 13dz2260100)is also acknowledged
文摘The aim of this paper is to understand the common characteristics of the generalized flyby trajectory around natural elongated bodies. Such flyby trajectories provide a short-term mechanism to clear away vicinal objects or temporally capture ejecta into circling orbits. The gravitational potential of elongated bodies is described by a unified approximate model, i.e., the rotating mass dipole which is two point masses connected with a constant massless rod The energy power is used to illustrate the flyby effect in terms of the instantaneous orbital energy. The essential of the single flyby trajectory is studied analytically, and the relationship between the flyby trajectory and its Jacobi integral is also illustrated. Sample trajectories are given to show the variational trend of the energy increment with respect to differen orbital periapsides. The distribution of natural ejecting orbits is presented by varying the parameters of the approximate model.
基金National Science Foundation of China under Grant No. 51279133Open Research Fund Program of State Key Laboratory of Hydro-science and Engineering under Grant No. SKLHSE-2011-C-02
文摘Smoothed particle hydrodynamics（SPH） is a mesh-free adaptive Lagrangian particle method with attractive features for dealing with the free surface flow.This paper applies the SPH method to simulate the large-amplitude lateral sloshing both with and without a floating body,and the vertical parametrically-excited sloshing in a two-dimensional tank.The numerical results show that the SPH approach has an obvious advantage over conventional mesh-based methods in handling nonlinear sloshing problems such as violent fluid-solid interaction,and flow separation and wave-breaking on the free fluid surface.The SPH method provides a new alternative and an effective way to solve these special strong nonlinear sloshing problems.
文摘Stimulatory regulators for DNA methyltransferase activity,such as Dnmt3L and some Dnmt3b isoforms,affect DNA methylation patterns,thereby maintaining gene body methylation and maternal methylation imprinting,as well as the methylation landscape of pluripotent cells.Here we show that metastasis-related methyltransferase 1(Merm1),a protein deleted in individuals with Williams-Beuren syndrome,acts as a repressive regulator of Dnmt3a.Merm1 interacts with Dnmt3a and represses its methyltransferase activity with the requirement of the binding motif for S-adenosyl-L-methionine.Functional analysis of gene regulation revealed that Merm1 is capable of maintaining hypomethylated rRNA gene bodies and co-localizes with RNA polymerase I in the nucleolus.Dnmt3a recruits Merml,and in return,Merml ensures the binding of Dnmt3a to hypomethylated gene bodies.Such interplay between Dnmt3a and Merml facilitates transcriptional elongation by RNA polymerase I.Our findings reveal a repressive factor for Dnmt3a and uncover a molecular mechanism underlying transcriptional elongation of rRNA genes.
