Institution: | (1) 145 CLRC, Penn State Altoona, Altoona, PA 16601, USA. e-mail: dkb5@psu.edu, US;(2) Via Loreto Vecchia 9/10/A, 17100 Savona, Italy. e-mail: mariagnese@savonaonline.it Research partially supported by Funds 40% of MURST of Italy., IT;(3) Department of Mathematics, Pennsylvania State University, 333 McAllister Building, University Park, State College, PA 16802, USA. e-mail: simpson@math.psu.edu Research partially supported by NSF grant DMS-9393478., US |