We are investigating a formal representation of time units and calendars, as restricted temporal entities for reasoning about activities. We examine characteristics of time units, and provide a categorization of the hierarchical relations among them. Hence we define an abstract hierarchical unit structure (a calendar structure) that expresses specific relations and properties among the units th...

13 Address correspondence to: 14 Gerardo Gamba, M.D., Ph.D. 15 Vasco de Quiroga No. 15, Tlalpan 14000 Mexico City, Mexico 16 e-mail: [email protected] or [email protected] 17 18

Mbssbauer and near-infrared spectral measurements have been made on several tourmaline minerals representing both the elbaite-schorl and dravite-schorl series. The specimens were characterized by cell dimension measurements, and by partial chemical analyses by electron microprobe. M'ssbauer data for the iron-bearing specimens further substantiated the presence of ferrous and ferric cations in b...

The pH-rate profiles for the cyclization of primary 2,3-dimethyl and 2,2,3-trimethyl-hydantoinamides (2-UAm and 3-UAm respectively) differ strikingly from those for the cyclizations of the corresponding N-methylated amides 2-MUAm and 3-MUAm; which are dominated by the water reaction, spanning some 6 pH units. For the cyclization of UAm the plateau extends over no more than two pH units. The dif...