Charge Accumulation in Nanoheterogeneous Iridium Oxide Films

Iridium oxide films with different values of crystallinity degree K are synthesized. Properties of the films and their morphological features are examined. The charging of the films in a 1 M H₂SO₄solution is studied voltammetrically. The most amorphous films (K = 0.08–0.26) acquire the largest overall charge q(in a fixed potential range) relative to films with higher crystallinity degrees; however, the qvs. K dependence is not additive, and the charge remains virtually invariant beginning with K 0.26. The contribution of slow charging processes, which is quite perceptible in the amorphous films, is absent in samples with higher crystallinity degrees, which have faster charge kinetics. The fast charging processes, which are not limited by diffusion, occur in boundary regions of IrO₂crystallites (and/or the oxide part of a crystalline hydrated iridium oxide) and the amorphous phase. The transport of charge-compensating ions in the boundary regions occurs without considerable complications, as in the loose network of amorphous phase IrO₂· xH₂O. The assumption about the formation of a metallic highly-conducting IrO₂cluster at K 0.26 is substantiated. The cluster rules out large resistances in the course of charge transport, which is a possible reason for the slow charging of amorphous films with K < 0.26.     

Wreath Products and Universal Equivalence

We consider the question of preservation of universal equivalence for the cartesian and direct wreath products of lattice-ordered groups and groups. We prove that the basic rank is infinite of the quasivariety of torsion-free nilpotent groups of nilpotence length c (c2)     

Dynamics of spatially nonuniform patterning in the model of blood coagulation

We propose a reaction-diffusion model that describes in detail the cascade of molecular events during blood coagulation. In a reduced form, this model contains three equations in three variables, two of which are self-accelerated. One of these variables, an activator, behaves in a threshold manner. An inhibitor is also produced autocatalytically, but there is no inhibitor threshold, because it is generated only in the presence of the activator. All model variables are set to have equal diffusion coefficients. The model has a stable stationary trivial state, which is spatially uniform and an excitation threshold. A pulse of excitation runs from the point where the excitation threshold has been exceeded. The regime of its propagation depends on the model parameters. In a one-dimensional problem, the pulse either stops running at a certain distance from the excitation point, or it reaches the boundaries as an autowave. However, there is a parameter range where the pulse does not disappear after stopping and exists stationarily. The resulting steady-state profiles of the model variables are symmetrical relative to the center of the structure formed. (c) 2001 American Institute of Physics.