Flow-through electrodes. IV. Axial diffusion effects

The simple theory of flow-through electrodes was generalized by analysis of axial diffusion phenomena. The effect of axial diffusion coupled with forced convection on the electrochemical behaviour of flow-through electrodes was analyzed assuming laminar flow through a structurless medium (the analysis is thus applicable also to e.g. capillary bundle models with sufficiently small pores' radii). Diffusional effects involving both reactants and products were considered and the electrochemical kinetic equations allowed for both forward and backward reaction orders with respect to substrates and products. Axial ohmic effects were included.The effect of convection in the pre-electrode chamber was taken into account in establishing the boundary conditions at the electrode entrance. A system of differential equations and boundary conditions describing the model was formulated. The integration was carried out by means of Hamming's method with automatic step size adjustment. The effects of various parameters (flow-rate, exchange current density, conductivity of the electrolyte, etc.) were examined in terms of deviations from the simple model. The regions of large, negligible and small (within 10%) deviations were defined and interpreted.     

Characteristics of the oxidation process in the methyl oleate-propionic acid system by means of dielectric constant measurements

In our paper the influence of association in the methyl oleate-propionic acid system on the course of autoxidation of this system was discussed. The course of autoxidation of the a/m system was characterized with the help of peroxide number and dielectric constant measurements.     

A structure of the Bang-Bang representation for 3×3 embeddable matrices

Summary Necessary and sufficient conditions are given for a 3×3 stochastic matrix to be embeddable by 6 elementary stochastic matrices (Poisson matrices). For a 3×3 embeddable matrix, a structure of the minimal Bang-Bang representation, i.e. the one that contains the smallest number of elementary matrices, is obtained. Based on the minimal Bang-Bang representation an algorithm for determining the embeddability of a 3×3 stochastic matrix is given.I would like to thank Søren Johansen for helpful comments and stimulating discussions on the subject of this paper     

Stereocontrolled Synthesis of Chiral Heteroaromatic Propellers with Small Optical Bandgaps

Chiral heteroaromatic propellers based on radially π‐extended hexapyrrolohexaazacoronenes were obtained in a concise synthesis from suitably functionalized donor–acceptor monopyrroles. To overcome steric hindrance, a new cyclodehydrogenation method was developed, and it uses bromine electrophiles as oxidative coupling agents instead of the commonly employed high‐potential oxidants. The new reaction offers high yields of propeller‐shaped targets, even for electron‐deficient precursors, and shows electrophile‐dependent stereoselectivity, with N‐bromosuccinimide and dibromine yielding, respectively D₆‐ and C₂‐symmetric products. The propeller azacoronenes are chiral and can be separated into configurationally stable enantiomers. In addition to providing steric bulk, peripheral functionalization considerably affects the electronic properties of the propellers, which exhibit reduced optical and electrochemical band gaps, and a more clearly defined electroreduction behavior.     

Optical torque controlled by elliptical polarization

We show theoretically and demonstrate experimentally that highly absorbing particles can be trapped and manipulated in a single highly focused Gaussian beam. Our studies of the effects of polarized light on such particles show that they can be set into rotation by elliptically polarized light and that both the sense and the speed of their rotation can be smoothly controlled.