The mechanism of the OH-initiated oxidation of isoprene in the presence of NO and O 2 has been investigated using a discharge-flow system at and 2 torr total pressure. 298 K OH radical concentration profiles were measured using laser-induced fluorescence as a function of reaction time. The rate constant for the reaction of was measured to OH ϩ isoprene be cm 3 In the presence of NO and O 2 , regeneration of OH(1.10 Ϯ 0.05) ϫ 10 mol s . radicals by the reaction of isoprene-based peroxy radicals with NO was measured and compared to simulations of the kinetics of this system. The results of these experiments are consistent with an overall rate constant of cm 3 (with an uncertainty factor Ϫ12 Ϫ1 Ϫ19 ϫ 10 mol s of 2) for the reaction of isoprene-based hydroxyalkyl peroxy radicals with NO.

We report results of a series of detailed experiments designed to unveil the dynamics of a particle of radius $a$ moving in high-frequency, low-Reynolds-number oscillatory flow. The fundamental parameters in the problem are the Strouhal ($\hbox{\it Sl}$) and the particle Reynolds numbers ($\hbox{\it Re}_p$), as well as the fluid-to-particle density ratio $\alpha$. The experiments were designed to cover a range of $\hbox{\it Sl} \hbox{\it Re}_p$ from 0.015 to 5 while keeping $\hbox{\it Re}_p < 0.5$ and $\hbox{\it Sl} > 1$. The primary objective of the experiments is to investigate stationary history effects associated with the Basset drag, which are maximized when the viscous time scale $a^2/\nu$ is of the same order of the flow time scale $9/\Omega$, where $9$ is a geometrical factor for the sphere, $\nu$ is the kinematic viscosity and $\Omega$ is the angular frequency of the background flow. The theoretically determined behaviour of stationary history effects is confirmed unequivocally by the experiments, which also validate the fractional derivative behaviour (of order $1/2$) of the history drag for the range of parameters under study.

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