1. Mechanical Engineering Department; Polytechnic University of Puerto Rico, Hato Rey; PR 00918 Puerto Rico
2. Department of Materials Science, Rheology Research Center; University of Wisconsin, 1500 Engineering Drive; Madison, WI 53706-1687 USA
3. Department of Engineering Physics, Engineering Mechanics Program; University of Wisconsin, 1500 Engineering Drive; Madison, WI 53706-1687 USA