We study how conserved quantities such as angular momentum and center of mass evolve with respect to the retarded time at null infinity, which is described in terms of a Bondi-Sachs coordinate system. These evolution formulae complement the classical Bondi mass loss formula for gravitational radiation. They are further expressed in terms of the potentials of the shear and news tensors. The consequences that follow from these formulae are (1) Supertranslation invariance of the fluxes of the CWY conserved quantities. (2) A conservation law of angular momentum \`a la Christodoulou. (3) A duality paradigm for null infinity. In particular, the supertranslation invariance distinguishes the CWY angular momentum and center of mass from the classical definitions.
In this paper, we discuss the Weyl problem in warped product spaces. We apply the method of continuity and prove the openness
of the Weyl problem. A counterexample is constructed to show that the isometric embedding of the sphere with canonical metric
is not unique up to an isometry if the ambient warped product space is not a space form. Then, we study the rigidity of the
standard sphere if we fix its geometric center in the ambient space. Finally, we discuss a Shi-Tam type of inequality for the
Schwarzschild manifold as an application of our findings.
A variational formula for the Lutwak affine surface areas j of convex bodies in Rn is
established when 1 ≤ j ≤ n − 1. By using introduced new ellipsoids associated with
projection functions of convex bodies, we prove a sharp isoperimetric inequality for j ,
which opens up a new passage to attack the longstanding Lutwak conjecture in convex