Two-photon photoconductivity in SiC photodiodes and its application to autocorrelation measurements of femtosecond optical pulses

Received: 18 June 1997     

Comparing representations and reasoning in children and adolescents with two-year college students

Problem solving and justification of a diversified group of two-year college students was compared with approaches of younger elementary and secondary school students working on the same tasks. The students in this study were engaged in thoughtful mathematics. Both groups found patterns, justified that their patterns were reasonable and, utilized similar strategies for their solutions and methods of justification. They were also able to make connections and build isomorphisms among the various problems.     

Cardiac arrhythmias and circle maps-A classical problem

The periodic forcing of nonlinear oscillations can often be cast as a problem involving self-maps of the circle. Consideration of the effects of changes in the frequency and amplitude of the periodic forcing leads to a problem involving the bifurcations of circle maps in a two-dimensional parameter space. The global bifurcations in this two-dimensional parameter space is described for periodic forcing of several simple theoretical models of nonlinear oscillations. As was originally recognized by Arnold, one motivation for the formulation of these models is their connection with theoretical models of cardiac arrhythmias originating from the competition and interaction between two pacemakers for the control of the heart.     

exo-endo-Isomers of phosphine-substituted tricarbonyl-(η-Cyclohepta−1,3−Diene)Iron complexes)

Nucleophilic addition to the tricarbonyl(15-η-cycloheptadienylium)iron cation by phosphines forms either the 5-exo or 5-endo isomer depending on reaction conditions and solvent used; in dichloromethane, direct attack at the ring gives the 5-exo phosphine substituted product whereas in acetonitrile, a red intermediate is observed and the 5-endo isomer is formed probably via a metal-assisted pathway.