Redirect Notice
 The previous page is sending you to https://www.sciencedirect.com/science/article/pii/S0007153669800227/pdf?md5=3f3019bb935f6b4cc28a03a8bc4e43b3&pid=1-s2.0-S0007153669800227-main.pdf&_valck=1.

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