An official website of the United States government
Here's how you know
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with,
the contents by NLM or the National Institutes of Health.
Learn more:
PMC Disclaimer
|
PMC Copyright Notice
The research reported in this paper was supported, in part, by a grant from the National Science Foundation and, in part, by contract Nonr 225(73) between the Office of Naval Research and Stanford University. Reproduction in whole or in part is permitted for any purpose of the United States Government.