Nonlinear stability analyses of vegetative pattern formation in an arid environment.

The development of spontaneous stationary vegetative patterns in an arid isotropic homogeneous environment is investigated by means of various weakly nonlinear stability analyses applied to the appropriate governing equation for this phenomenon. In particular, that process can be represented by a fourth-order partial differential time-evolution logistic equation for the total plant biomass per unit area divided by the carrying capacity of its territory and defined on an unbounded flat spatial domain. Those patterns that consist of parallel stripes, labyrinth-like mazes, rhombic arrays of rectangular patches, and hexagonal distributions of spots or gaps are generated by the balance between the effects of short-range facilitation and long-range competition. Then those theoretical predictions are compared with both relevant observational evidence and existing numerical simulations as well as placed in the context of the results from some recent nonlinear pattern formation studies.

[Bactericidal effect of hydrated lime in aqueous solution]. / Efecto bactericida de la cal hidratada en solución acuosa.

This study determined the bactericidal effect of the supernatants of saturated solutions of common lime and of micronized calcium hydroxide (Ca(OH)2) (1500 mg/L), which was used as a control, compared with disinfectants made of solutions of 0.33% colloidal silver (0.0016 mg/L), toluene sulfachloramine (41 mg/L) with sodium bicarbonate (9 mg/L), and sodium hypochlorite (5 mg/L). The test involved four strains of Vibrio cholerae 01, V. parahaemolyticus, Escherichia coli, Salmonella typhimurium, Shigella flexneri, Sh. sonnei, and Sa. enterititidis. These bacteria were inoculated into the bactericidal substances listed above and, after different incubation times, the number of surviving bacteria was determined in vitro by using a counting plate. The results were expressed in colony-forming units (CFU). An in situ estimate was made of the amount of V. cholerae on 35 strawberries and 35 radishes (having a weight of about 10 g per unit) after they were washed under a flow of potable water, submerged in the supernatant of the saturated lime solution (1.5 g/L), or both. The greatest bactericidal effect was obtained against V. cholerae 01 and was observed in 3 minutes. Other enterobacteria were resistant to the effect for up to 30 minutes.