1. Assistant Professor, Iowa State Univ., Ames, IA 50011, US (Corresponding author), e-mail: jashlock@iastate.edu
2. Professor Emeritus, Purdue Univ., West Lafayette, IN 47906, US, e-mail: drnevich@purdue.edu
3. Professor, Univ. of Colorado at Boulder, Boulder, CO 80309, US, e-mail: pak@colorado.edu