how can I use a signal defined in one Architecture to another Architecture

Hello everybody,

I want to use the signal defined in one architecture in VHDL to
another architecture. I have two architecture in the same .vhd file
and I am using Component mapping. I required the result of calculation
of a signal to be used in second architecture. Can any one tell how to
defined signal so that it is globally visible to other architectures.

Regards

Khan