Non-dynamical stochastic resonance: Theory and experiments with white and various coloured noises

Summary We describe the simplest system which shows stochastic resonance. A linear(ized) theory for white and (almost) arbitrarily coloured noise is presented. The presented new system has new, unique properties which originate from itsnon-dynamical character; for example, the strength and phase shift of periodic response of the system is independent of the frequency. Experiments have been carried out with the following noise processes: (physical) white noise, (physical) Lorentzian noise and (physical) 1/f noise. With a small extension of the system, its linear-response regime can be significantly increased. As the system is similar to some simple models of neurones, the new results might have not only physical but also biological importance. Paper presented at the International Workshop “Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena”, Elba, 5–10 June 1994.     

Spin flip in inelastic scattering: A possible explanation of the observed backward-angle peak

Utilizing an analogy between the spin-orbit field and a magnetic field, it is shown that a plane-wave Born-approximation calculation in two dimensions gives a good qualitative account of the observed features of the probability of spin flip in inelastic scattering. Comparisons of the two-dimensional model and the collective model DWBA are given for the reaction ⁵⁸Ni(p, p′)⁵⁸Ni(2⁺) at 20 MeV and 100 MeV.     

Differentiation of electrophilic and ambiphilic carbenes

Comparative selectivities toward alkenes of CH₃CCl, CCl₂, and CH₃OCCl establish the former two carbenes as electrophiles; the latter is an ambiphile.     

Thermal rearrangement of divinylcyclopropane systems. A new formal total synthesis of (±)-quadrone

The key step of a new approach to the total synthesis of the structurally and physiologically interesting sesquiterpenoid (±)-quadrone (1) involves thermal (Cope) rearrangement of the highly functionalized divinylcyclopropane derivative 8. The product 9 of this process is converted into 19, thus completing a formal total synthesis of (±)-1.     

Homolytic reactions of polyfluoroaromatic compounds. X. Biphenylyl radicals in the thermolysis of aroyl peroxides in polyfluoroaromatic solvents

The thermolyses of a number of aroyl peroxides in hexafluorobenzene, and of benzoyl peroxide in octafluorotoluene, gave the corresponding biaryls which were isolated by steam distillation. Mass spectrometry of the residues showed evidence of biphenylyl radicals arising from the arylation of the peroxides themselves or, possibly, of the derived aroic acids. Terphenyls, and the corresponding σ-intermediate radicals, could be found, and the relative molecular masses of the latter components showed that subsequent arylation of the main binuclear products was not the main source of terphenyls.