Redirect Notice
 The previous page is sending you to https://www.sciencedirect.com/science/article/pii/S0007153687800116/pdf?md5=cf25936654a7f2804c9ad50f6a33150b&pid=1-s2.0-S0007153687800116-main.pdf&_valck=1.

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