Generation and application of replication-competent Venus-expressing H5N1,H7N9,and H9N2 influenza A viruses

The generation and application of replication-competent influenza A virus(IAV) expressing a reporter gene represent a valuable tool to elucidate the mechanism of viral pathogenesis and establish new countermeasures to combat the threat of influenza. Here, replication-competent IAVs with a neuraminidase(NA) segment harboring a fluorescent reporter protein, Venus, were generated in the background of H5N1, H7N9, and H9N2 influenza viruses, the three subtypes of viruses with imminent pandemic potential. All three reporter viruses maintained virion morphology, replicated with similar or slightly reduced titers relative to their parental viruses, and stably expressed the fluorescent signal for at least two passages in embryonated chicken eggs. As a proof of concept, we demonstrated that these reporter viruses,used in combination with a high-content imaging system, can serve as a convenient and rapid tool for the screening of antivirals and host factors involved in the virus life cycle. Moreover, the reporter viruses demonstrated similar growth properties and tissue tropism as their parental viruses in mice, among which the H7N9 NA-Venus virus could potentially be used in ex vivo studies to better understand H7N9 pathogenesis or to develop novel therapeutics.

Numerical studies of reverse flows controlled by undulating leading edge

The improved delayed detached-eddy simulation(IDDES) method is used to simulate the reverse flows past an NACA0012 airfoil at medium(10°) and large(30°) angles of attack. The numerical results of the baseline configuration are compared with the available measurements. The effects of the undulating leading edge with four different amplitudes are compared and analyzed at angle of attack of 10°. Based on these analyses, the amplitude of A/C=0.04 yields the best performance. Compared with the uncontrolled case, the performances of the undulating leading edge are greatly improved with reducing of the aerodynamic fluctuations. Furthermore, the mechanisms of performance are explored by comparing the local flow structures near the undulations.

A high-resolution gas-kinetic scheme with minimized dispersion and controllable dissipation reconstruction

In order to simulate multiscale problems such as turbulent flows effectively, the high-order accurate reconstruction based on minimized dispersion and controllable dissipation(MDCD) is implemented in the second-order accurate gas-kinetic scheme(GKS) to improve the accuracy and resolution. MDCD is firstly extended to non-uniform grids through the modification of dissipation and dispersion coefficients for uniform grids based on the local stretch ratio. Remarkable improvements in accuracy and resolution are achieved on general grids. Then a new scheme, MDCD-GKS is constructed, with the help of MDCD reconstruction, not only for conservative variables, but also for their gradients. MDCD-GKS shows good accuracy and efficiency in typical numerical tests.MDCD-GKS is also coupled with the improved delayed detached-eddy simulation(IDDES) hybrid model and applied in the fine simulation of turbulent flow around a cylinder, and the prediction is in good agreement with experiments when using the relatively coarse grid. The high accuracy and resolution of the developed GKS guarantee its high efficiency in practical applications.

An Improved Gas-Kinetic Scheme for Multimaterial Flows

The efficiency of recently developed gas-kinetic scheme for multimaterial flows is increased through the adoption of a new iteration method in the kinetic non-mixing Riemann solver and an interface sharpening reconstruction method at a cell interface.The iteration method is used to determine the velocity of fluid interface,based on the force balance between both sides due to the incidence and bounce back of particles at the interface.An improved Aitken method is proposed with a simple hybrid of the modified Aitken method(Aitken-Chen)and the Steffensen method.Numerical tests validate its efficiency with significantly less calls to the function not only for the average number but also for the maximum.The new reconstruction is based on the tangent of hyperbola for interface capturing(THINC)but applied only to the volume fraction,which is very simple to be implemented under the stratified frame-work and capable of resolving fluid interface in mixture.Furthermore,the directional splitting is adopted rather than the previous quasi-one-dimensional method.Typical numerical tests,including several watergas shock tube flows,and the shock-water cylinder interaction flow show that the improved gas-kinetic scheme can capture fluid interfaces much sharper,while preserving the advantages of the original one.