An O(N) Algorithm for Stokes and Laplace Interactions of Particles

A method for computing Laplace and Stokes interactions among N spherical particles arbitrarily placed in a unit cell of a periodic array is described. The method is based on an algorithm by Greengard and Rokhlin [J. Comput. Phys. 73, 325 (1987)] for rapidly summing the Laplace interactions among particles by organizing the particles into a number of different groups of varying sizes. The far-field induced by each group of particles is expressed by a multipole expansion technique into an equivalent field with its singularities at the center of the group. The resulting computational effort increases only linearly with N. The method is applied to a number of problems in suspension mechanics with the goal of assessing the efficiency and the potential usefulness of the method in studying dynamics of large systems. It is shown that reasonably accurate results for the interaction forces are obtained in most cases even with relatively low-order multipole expansions

Inclusion of Lubrication Forces in Dynamic Simulations

A new method is described for incorporating close-field, lubrication forces between pairs of particles into the multiparticle Stokes flow calculations. The method is applied to the suspensions of both spherical as well as cyliridrical particles, and results computed by the method are shown to be in excellent agreement with the exact known results available in the literature

A Method for Computing Stokes Flow Interactions Among Spherical Objects and its Application to Suspensions of Drops and Porous Particles

A method for computing Stokes flow interactions in suspensions of spherical objects is described in detail and applied to the suspensions of porous particles, drops, and bubbles to determine their hydrodynamic transport coefficients

Research on vacuum plume and its effects

AbstractIn vacuum environment, the exhaust flow of attitude control thrusters would expand freely and produce the plume, which possibly causes undesirable contamination, aerodynamic force and heating effects to the spacecraft. Plume work station (PWS) is developed by Beihang University (BUAA) for numerically simulating the vacuum plume and its effects. An approach which combines the direct simulation Monte Carlo (DSMC) method and difference solution of Navier–Stokes (N–S) equations is applied. The internal flows in nozzles are simulated by solving the NS equations. The flow parameters at nozzle exit are used as the inlet boundary condition for the DSMC calculation. Experimental studies are carried out in a supersonic low density wind tunnel which could simulate the 60–80km altitude environment to investigate the plume and its effects. To demonstrate the capability of PWS, numerical simulations are performed for the vacuum plume of several typical attitude control thrusters. The research results are of great help for the engineering design

A Runge-Kutta discontinuous Galerkin solver for 2D Boltzmann model equations: Verification and analysis of computational performance

The high-order Runge-Kutta discontinuous Galerkin (DG) method is extended to the 2D kinetic model equations describing rarefied gas flows. A DG-type discretization of the equilibrium velocity distributions is formulated for the Bhatnagar-Gross-Krook and ellipsoidal statistical models which enforce a weak conservation of mass, momentum and energy in the collision relaxation term. The RKDG solutions have up to 3rd-order spatial accuracy and up to 4th-order time accuracy. Verification is carried out for a steady 1D Couette flow and a 2D thermal conduction problem by comparison with DSMC and analytical solutions. The computational performance of the RKDG method is compared with a widely used second-order finite volume method

The Expression Levels of XLF and Mutant P53 Are Inversely Correlated in Head and Neck Cancer Cells.

XRCC4-like factor (XLF), also known as Cernunnos, is a protein encoded by the human NHEJ1 gene and an important repair factor for DNA double-strand breaks. In this study, we have found that XLF is over-expressed in HPV(+) versus HPV(-) head and neck squamous cell carcinoma (HNSCC) and significantly down-regulated in the HNSCC cell lines expressing high level of mutant p53 protein versus those cell lines harboring wild-type TP53 gene with low p53 protein expression. We have also demonstrated that Werner syndrome protein (WRN), a member of the NHEJ repair pathway, binds to both mutant p53 protein and NHEJ1 gene promoter, and siRNA knockdown of WRN leads to the inhibition of XLF expression in the HNSCC cells. Collectively, these findings suggest that WRN and p53 are involved in the regulation of XLF expression and the activity of WRN might be affected by mutant p53 protein in the HNSCC cells with aberrant TP53 gene mutations, due to the interaction of mutant p53 with WRN. As a result, the expression of XLF in these cancer cells is significantly suppressed. Our study also suggests that XLF is over-expressed in HPV(+) HNSCC with low expression of wild type p53, and might serve as a potential biomarker for HPV(+) HNSCC. Further studies are warranted to investigate the mechanisms underlying the interactive role of WRN and XLF in NHEJ repair pathway

Numerical Simulation of 2D Supersonic Magnetohydrodynamic Channel and Study on Hall Effect

AbstractIn this research effort, numerical simulation of two-dimensional magnetohydrodynamic (MHD) channel is performed and Hall effect is studied. The computational model consists of the Navier-Stokes (N-S) equations coupled with electrical-magnetic source terms, Maxwell equations and the generalized Ohm's law. Boundary conditions for the electrical potential equation considering Hall effect are derived. To start with, the MHD channel with single-pair electrodes is studied and flow of the electric current is in accordance with physical principle. Then the MHD channel with five-pair electrodes is numerically simulated. The results show that the electrical current concentrates on the downstream of the anode and the upstream of the cathode due to Hall effect, and the flow field becomes asymmetrical. At the current value of the magnetic interaction parameter, the electrical-magnetic force affects the flow remarkably, decreasing the outlet Mach number and increasing the outlet pressure; what's more, the flow structure in the channel becomes extremely complex. Performances of MHD channels with continual electrodes and segmented electrodes are compared. The results show that performance of the MHD channel with segmented electrodes is better than that with continual electrodes with the increase of Hall parameter