1. create a constant mesh variable: every grid(coarse or refined) point has the same scalar or vector from the query result (not mesh variable
2. Cannot use Python Expression Editor as the "particles" as argument (Mesh variables) only has two data entries.
3.  key tech: Use %f
DefineScalarExpression("x0sc", "%f" %x0)
DefineScalarExpression("y0sc", "%f" %y0)
DefineScalarExpression("z0sc", "%f" %z0)