Extremal digraphs avoiding distinct walks of length 3 with the same endpoints

In this paper, we determine the maximum size of digraphs on n vertices which avoid two distinct walks of length 3 with the same initial vertex and the same terminal vertex. The digraphs attaining this maximum size are also characterized. Combining this with previous results, we obtain a full solution to a problem proposed by X. Zhan in 2007.     

一类变号(k,n-k)共轭边值问题正解的存在性

通过构造一个特殊的锥,利用范数形式的锥拉伸锥压缩不动点定理,在允许非线性项变号无下界且没有任何单调性假设的条件下,得出了一类高阶(k,n-k)共轭两点边值问题方程组正解的存在性结论.     

Busemann–Petty Problems for General L_p-Intersection Bodies

For 0 p 1, Haberl and Ludwig defined the notions of symmetric L p-intersection body and nonsymmetric L p-intersection body. In this paper, we introduce the general L p-intersection bodies.Furthermore, the Busemann–Petty problems for the general L p-intersection bodies are shown.     

Computation of hydrodynamic mass and damping coefficients for a cavitating marine propeller flow using a panel method

The present paper deals with the numerical calculation of hydrodynamic mass and damping coefficients under consideration of unsteady sheet cavitation on marine propeller flows. In the first part of the paper, the mathematical and numerical background behind the numerical method is introduced. The numerical calculations carried out in this work are based on a low-order panel method. Panel methods belong to the class of collocation techniques and are applied to obtain a numerical solution of a potential flow based system of boundary integral equations. They are suitable for the present application because of their short computation time which makes them applicable in the design process of marine propellers.Additionally, two different approaches for the determination of hydrodynamic masses and damping are introduced in this work. The hydrodynamic masses and damping are important in studies of the ship motion in seaway and in the analysis of vibrations of a vessel and its appendages. The developed approaches are applied on a propeller flow in heave motion. Hereby, the calculations are performed for a non-rotating and rotating propeller under non-cavitating and cavitating conditions. The results obtained from the simulations are discussed in detail and an outlook is given.     

Modified fully discretized projection method for the incompressible Navier–Stokes equations

The stability and convergence of a second-order fully discretized projection method for the incompressible Navier–Stokes equations is studied. In order to update the pressure field faster, modified fully discretized projection methods are proposed. It results in a nearly second-order method. This method sacrifices a little of accuracy, but it requires much less computations at each time step. It is very appropriate for actual computations. The comparison with other methods for the driven-cavity problem is presented.     

pH控制硫酸锰骨架的演化及其晶体结构

在DMF/H2O/CH3OH的混合体系中,反应温度为170℃,Mn SO4·4H2O盐溶液在p H=5和7的条件下,加热72小时,最终得到了结构不同的硫酸锰骨架[Mn2(SO4)3]·(H3O)2(1)和[Mn3(SO4)2(OH)2(H2O)2](2)。化合物结构通过单晶X-射线和红外光谱所表征,相应的晶胞参数:化合物1,立方晶系,空间群:P213,a=10.2009(12),V=1061.49(37)3,Goo F=1.158,Flack parameter 0.02(2),R1=0.0186(I2sigma);化合物2,四方晶系,空间群:Pbcm,a=7.3214(15),b=9.984(2),c=13.291(3),V=971.5(4)3,Goo F=1.063,R1=0.0227(I2sigma);单晶X射线分析显示化合物1是一个三维单手性硫酸锰骨架,化合物2是一个非手性羟基硫酸锰骨架。实验结果说明,p H值对硫酸锰骨架的改变起重要作用。     

Surplus division and investment incentives in supply chains: A biform-game analysis

In this paper, we use a biform-game approach for analyzing the impact of surplus division in supply chains on investment incentives. In the first stage of the game, firms decide non-cooperatively on investments. In the second stage, the surplus is shared according to the Shapley value. We find that all firms have inefficiently low investment incentives which, however, depend on their position in the supply chain. Cross-subsidies for investment costs can mitigate, but not eliminate the underinvestment problem. Vertical integration between at least some firms.yields efficient investments, but may nevertheless reduce the aggregated payoff of the firms. We show how the size of our effects depends on the structure of the supply chain and the efficiency of the investment technology. Various extensions demonstrate that our results are qualitatively robust.     

Solvability of the boundary value problem for stationary magnetohydrodynamic equations under mixed boundary conditions for the magnetic field

The global solvability of the boundary value problem for stationary magnetohydrodynamic equations under the Dirichlet boundary condition for the velocity and mixed boundary conditions for the magnetic field is proved.     

几个由积分形成的数列的极限

围绕着若干个由积分定义的数列展开讨论，求出了这些数列的极限，并指出它们是一些已知的数列极限的推广。