Propagation of fronts in activator-inhibitor systems with a cutoff

We consider a two-component system of reaction-diffusion equations with a small cutoff in the reaction term. A semi-analytical solution of fronts and how the front velocities vary with the parameters are given for the case when the system has a piecewise linear nonlinearity. We find the existence of a nonequilibrium Ising-Bloch bifurcation for the front speed when the cutoff is present. Numerical results of solutions to these equations are also presented and they allow us to consider the collision between fronts, and the existence of different types of traveling waves emerging from random initial conditions.     

Hydrogen as a cause of doping in zinc oxide

Zinc oxide, a wide-band-gap semiconductor with many technological applications, typically exhibits n-type conductivity. The cause of this conductivity has been widely debated. A first-principles investigation, based on density functional theory, produces strong evidence that hydrogen acts as a source of conductivity: it can incorporate in high concentrations and behaves as a shallow donor. This behavior is unexpected and very different from hydrogen's role in other semiconductors, in which it acts only as a compensating center and always counteracts the prevailing conductivity. These insights have important consequences for control and utilization of hydrogen in oxides in general.     

Alkylation of benzene with 4-methylcyclohexanol in the presence of sulfuric acid

Alkylation of benzene with 4-methylcyclohexanol in the presence of methylcyclohexane and 96, 88, and 80% H₂SO₄ has been studied. It was established that depending on the solubility of the starting components in sulfuric acid, alkylation occurs in the inorganic phase or on the interface between the organic and inorganic phases. The yield and composition of the catalysate are determined to a significant degree by the extent of the alkylation process and intramolecular hydride transfers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 121–125, January, 1990.