lester larkin

This research evaluated the impact of supplementing user models with additional data about cognitive features of the student. Supplemental data included individual differences variables such as: developmental stage of the learner (Piagetian), spatial ability, ...

When polytetrafluoroethylene (PTFE) was pyrolyzed in air in the temperature range of 500° to 650°C (932° to 1202°F), the predominate product was COF2. Above 650° C the major products were CF4 and CO2. Other fluorocarbons were produced in lesser amounts. PTFE pyrolyzed in the presence of SiO2 also formed SiF4. Between 550° and 600°C production of COF2 was as high as 63%. Experimental exposure of rats showed COF2 to be the most toxic component of the pyrolysis gases.

Microsatellite DNA markers of ten simple sequence repeat (SSR) loci were used to examine somaclonal variation in randomly selected micropropagated plantlets derived from three different Populus tremuloides donor trees (genotypes). The plantlets were obtained from tissue cultures of dormant vegetative buds, and those derived from the same donor tree, grown in the greenhouse, did not exhibit any sign of visible morphological variation. No microsatellite DNA variation was observed among 13 somaclones of one tree and 4 somaclones of another tree at eight of the ten SSR loci. However, despite the small number of micropropagated progeny per tree sampled, microsatellite DNA variation was detected among the plantlets derived from the same donor trees at two SSR loci. The primer pair for the SSR locus PTR5 revealed somaclonal variation in 1 out of the 13 plantlets obtained from one genotype, while the primer pair for the PTR2 SSR locus revealed somaclonal variation in one out of the four plantlets obtained from another genotype. The variation at the PTR2 locus resulted in the appearance of a new allele of increased size, possibly due to an addition of the repeat units, while the variation at the PTR5 locus resulted in the appearance of third allele, presumably due to the presence of a single extra chromosome or duplication of a chromosomal segment. These results demonstrate that the genetic fidelity of micropropagated plants of P. tremuloides cannot always be assured and somaclonal variation can occur even when tissues of well organized vegetative buds are used for tissue cultures; that somaclonal variation cannot always be detected at the gross morphological level; and that microsatellite DNA markers provide useful and sensitive markers for determining the clonal fidelity and somaclonal variation in P. tremuloides.