This report was preparedas an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employe_,s,makes any warranty, express or implied, or assumes any legal liability or responsibility for the aec_racy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Referonce herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-April 1994 mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Reprint Of historical document PHTD-C93-03.01H, dated October 1993. Data, formatting, and other conventions reflect standards at the original date of printing. Technical peer reviews and editorial reviews may not have been performed.