Guarinoex Jordan, from the Universidad de Puerto Rico, Rio Piedras, discusses a mathematical model created to show the role of peer pressure on cigarette smoking among teen-agers. Jordan, who participated in the Mathematical & Theoretical Biology Institute (MTBI) at Cornell this summer and returned for the MTBI winter program early this month, was one of six students making research presentations on Jan. 17 in the Polson Room of Warren Hall. Students in the program, directed by Carlos Castillo-Chavez, associate professor and director of Cornell's Biometrics Unit, will return to campus in June to continue their research. Charles Harrington/University Photography