[Avodah] Power assist doors on Shabbos

[Daniel Israel]

Does anyone know how power assist doors work, and whether they can 
be used on Shabbos?  I'm talking about the kind of door one often 
finds in nursing homes and other public places that can be swung 
open like regular doors, but there is also a button on the side of 
the doorway which can be used to cause the door to open 
automatically.

In my experience, if one pulls on such doors gently and not all the 
way open, the power assist does not kick in.  Does anyone know if 
it is permissible to open such a door (not using the button).  Does 
it matter if the power-assist kicks on or not?

Thanks.

P.S. A more general question: answering these types of shailos 
requires understanding both the halacha and the technology.  In 
E"Y, I know Machom Tzomet specializes in this sort of thing.  Is 
there anywhere in chu"l doing comparable work?

--
Daniel M. Israel
dmi1 at cornell.edu