Anti-Ischemic Activity of n-Tyrozol under Conditions of Repeated Transient Myocardial Ischemia in Rats.

We studied anti-ischemic activity of n-tyrozol under conditions of repeated transient myocardial ischemia in rats caused by repeated (5×3 min) occlusion of the left coronary artery. n-Tyrozol administered intraperitoneally in a dose of 20 mg/kg daily over 4 days before the ischemia modeling (the last injection 15 min prior to the start of the experiment) produced a clear-cut anti-ischemic effect: it reduced ST elevation and promoted more complete recovery of ECG during reperfusion. During reperfusion periods, n-tyrozol significantly decreased the risk of ventricular fibrillation and shortened the duration of tachyarrhythmia episodes (ventricular tachycardia and fibrillation).

Rate-equation approach to irreversible island growth with cluster diffusion.

A self-consistent rate-equation (RE) approach to irreversible island growth and nucleation is presented which takes into account cluster mobility. As a first application, we consider the irreversible growth of compact islands on a two-dimensional surface in the presence of monomer deposition (with rate F) and monomer diffusion (with rate D(1)) while the mobility of an island of size s is assumed to satisfy D(s)=D(1)s(-µ) where µ>0. Results are obtained for the dependence of the island-density and island-size distribution (ISD) on the parameters D(1)/F, µ, and coverage θ. For all values of µ, we find excellent agreement between our self-consistent RE results and simulation results for the island and monomer densities, up to and even somewhat beyond the coverage corresponding to the peak island density. We also find good agreement between our self-consistent RE and simulation results for the portion of the ISD corresponding to island sizes less than the average island-size S. However, for larger island sizes the effects of correlations become important and as a result the agreement is not as good. Using our self-consistent RE approach we also demonstrate that the discrepancies between simulations and recent mean-field predictions for the exponent τ(µ) describing the power-law size dependence of the ISD for µ<1 can be explained almost entirely by geometric effects. Our results are also compared with those obtained using a simpler mean-field Smoluchowski approach. In general, we find that, except for the case µ=1/2 (for which the island and monomer densities are reasonably well predicted), such an approach leads to results which are in poor agreement with the simulations.

Effects of cluster diffusion on the island density and size distribution in submonolayer island growth.

The effects of cluster diffusion on the submonolayer island density and island-size distribution are studied for the case of irreversible growth of compact islands on a 2D substrate. In our model we assume instantaneous coalescence of circular islands, while the cluster mobility is assumed to exhibit power-law decay as a function of island size with exponent µ. Results are presented for µ=1/2,1, and 3/2 corresponding to cluster diffusion via Brownian motion, correlated evaporation condensation, and edge diffusion respectively, as well as for higher values including µ=2,3, and 6. We also compare our results with those obtained in the limit of no cluster mobility (µ=∞). In agreement with theoretical predictions of power-law behavior of the island-size distribution (ISD) for µ<1, for µ=1/2 we find N(s)(θ)~s(-τ) [where N(s)(θ) is the number of islands of size s at coverage θ] up to a crossover island-size S(c). However, the value of the exponent τ obtained in our simulations is higher than the mean-field (MF) prediction τ=(3-µ)/2. Similarly, the measured value of the exponent ζ corresponding to the dependence of S(c) on the average island-size S (e.g., S(c)~S(ζ)) is also significantly higher than the MF prediction ζ=2/(µ+1). A generalized scaling form for the ISD [N(s)(θ)=θ/S(1+τζ)f(s/S(ζ))] is also proposed for µ<1, and using this form excellent scaling is found for µ=1/2. However, for finite µ≥1 neither the generalized scaling form nor the standard scaling form N(s)(θ)=θ/S(2)f(s/S) lead to scaling of the entire ISD for finite values of the ratio R of the monomer diffusion rate to deposition flux. Instead, the scaled ISD becomes more sharply peaked with increasing R and coverage. This is in contrast to models of epitaxial growth with limited cluster mobility for which good scaling occurs over a wide range of coverages.