2,664 research outputs found
Forward-backward SDEs with distributional coefficients
Forward-backward stochastic differential equations (FBSDEs) have attracted
significant attention since they were introduced almost 30 years ago, due to
their wide range of applications, from solving non-linear PDEs to pricing
American-type options. Here, we consider two new classes of multidimensional
FBSDEs with distributional coefficients (elements of a Sobolev space with
negative order). We introduce a suitable notion of a solution, show existence
and uniqueness of a strong solution of the first FBSDE, and weak existence for
the second. We establish a link with PDE theory via a nonlinear Feynman-Kac
representation formula. The associated semi-linear second order parabolic PDE
is the same for both FBSDEs, also involves distributional coefficients and has
not previously been investigated; our analysis uses mild solutions, Sobolev
spaces and semigroup theory.Comment: 40 pages, no figures - new improved version with shorter proof of Thm
18, extended results in Thm 25 and Thm 27. Other minor clarifications adde
Fast synchrotron X-ray tomographic quantification of dendrite evolution during the solidification of Mg-Sn alloys
The evolution of dendritic microstructures during the solidification of a Mg-15 wt%Sn alloy was investigated in situ via fast synchrotron X-ray microtomography. To enable these in situ observations a novel encapsulation method was developed and integrated into a fast, pink beam, imaging beamline at Diamond Light Source. The dendritic growth was quantified with time using: solid volume fraction, tip velocity, interface specific surface area, and surface curvature. The influence of cooling rate upon these quantities and primary phase nucleation was investigated. The primary dendrites grew with an 18-branch, 6-fold symmetry structure, accompanied by coarsening. The coarsening process was assessed by the specific surface area and was compared with the existing models. These results provide the first quantification of dendritic growth during the solidification of Mg alloys, confirming existing analytic models and providing experimental data to inform and validate more complex numeric models
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