A priori estimates for free boundary problem of incompressible inviscid magnetohydrodynamic flows

In the present paper, we prove the a priori estimates of Sobolev norms for a free boundary problem of the incompressible inviscid MHD equations in all physical spatial dimensions $n=2$ and 3 by adopting a geometrical point of view used in Christodoulou-Lindblad CPAM 2000, and estimating quantities such as the second fundamental form and the velocity of the free surface. We identify the well-posedness condition that the outer normal derivative of the total pressure including the fluid and magnetic pressures is negative on the free boundary, which is similar to the physical condition (Taylor sign condition) for the incompressible Euler equations of fluids.Comment: 34 page

A global maximum principle for optimal control of general mean-field forward-backward stochastic systems with jumps

In this paper we prove a necessary condition of the optimal control problem for a class of general mean-field forward-backward stochastic systems with jumps in the case where the diffusion coefficients depend on control, the control set does not need to be convex, the coefficients of jump terms are independent of control as well as the coefficients of mean-field backward stochastic differential equations depend on the joint law of $(X(t),Y(t))$. Two new adjoint equations are brought in as well as several new generic estimates of their solutions are investigated for analysing the higher terms, especially, those involving the expectation which come from the derivatives of the coefficients with respect to the measure. Utilizing these subtle estimates, the second-order expansion of the cost functional, which is the key point to analyse the necessary condition, is obtained, and whereafter the stochastic maximum principle.Comment: 32 page