Redirect Notice
 The previous page is sending you to https://www.sciencedirect.com/science/article/pii/S0007153681800101/pdf?md5=d4491063e042267f9bd81feddc0ea2ba&pid=1-s2.0-S0007153681800101-main.pdf.

 If you do not want to visit that page, you can return to the previous page.