Matrix models and population viability analysis (PVA) have become useful tools to understand population attributes and dynamics. Demography analysis gives valuable information for the management of threatened species, and can be used to create action plans for their conservation. PVA is particularly useful in those species with small population sizes difficult to sample. By calculating the individual fate of each member of the population, PVA simulates temporal population changes and estimates extinction risk over a time period. Here we use these models to analyse the population of axolotl Ambystoma mexicanum, which has decreased more than six times within only 5 years. Its natural environment (the Xochimilco aquatic system within Mexico City) has deteriorated significantly in the last decades. The matrix analysis showed large oscillations in the axolotl population growth rate (damping behaviour), which could explain the fast density reduction in only few generations. Younger ages (eggs and larvae) showed the highest sensitivity and elasticity values, suggesting that the lack of food sources such as zooplankton or the increased predation by exotic carp and tilapia are capable to reduce axolotl density. PVA shows low extinction probabilities using laboratory data for younger ages. However, a small reduction in egg or larvae survival rate is capable to increase extinction probabilities to 100% in 20 years. Based on these results, we found that the best strategy to restore the axolotl population is to increase the survival rate of eggs and larvae by restoring the habitat, eradicating introduced fish and improving water quality, rather than implementing a reintroduction programme.

A wave-driven seawater pump, composed of a resonant and an exhaust duct joined by a variable-volume air compression chamber, is studied. The time dependent form of Bernoulli's equation, adapted to incorporate losses due to friction, vortex formation at the mouths and radiation damping, describes the pump behaviour. A dimensional analysis of the pump equations shows that a proposed scale-model will perform similar to a full-scale seawater pump. Fluid oscillations in the ducts perform similar to a damped, two-mass spring system, excited by the waves. A resonant condition can be maintained, for different wave frequencies, by varying the volume of air in the compression chamber. The dimensional analysis shows that the basic behaviour of the pump is linear and that its performance can be significantly increased by optimising the design of the duct mouths. Linear estimates of the resonant air chamber volume and flow rate through the pump are derived.

Suspension cultures of calli derived from hypocotyls of Helianthus anuus L. and H. petiolaris ssp. petiolaris Nutt. have produced somatic embryos. Calli were induced on the basal medium MS according to Murashige and Skoog [18] with 2,4-dichlorophenoxyacetic acid (2,4-D). They were transferred to eight liquid media with the same salts, vitamins and aminoacids but with a different growth regulator composition, and further subcultured monthly into fresh medium. Globular-, heart-, torpedo- and horseshoe-shaped embryos were observed in suspension cultures. We counted the embryos at each stage of development after 4 months of culture, and compared the relative effect of genotypes and media. The 2,4-D addition was proved necessary to induce embryogenesis and the embryo maturation. The presence of abscisic acid (ABA) and benzylaminopurine (BAP) allowed furtherance of embryo development.

The selective bacteriostatic effect of triphenylmethane dyes has long been known. It has been found by several authors (Churchman, 1928, and others) that these dyes used in gram staining also inhibit the growth of the grampositive microorganisms. The relations between bacteriostatic power and chemical structure of these dyes were studied by Browning and Gilmour (1913), Kligler (1918), Fairbrother and Renshaw (1922), and other authors. It has been established, for instance, that methylation or ethylation of the amine groups increases efficacy, whereas more complex radicles have a contrary effect. About the mechanism of the selective bacteriostatic effect of the above mentioned dyes, different theories have been elaborated. These were extensively discussed by Churchman (1928), Stearn and Steam (1930), Ingraham (1933), and others (cf. Fischer, Hoffmann, and Prado, 1944). It is generally acknowledged that leucobases of bacteriostatically active dyes are relatively inactive. The special structure of the triphenylmethane dyes permits, however, the formation of numerous other leuco-derivatives besides the proper leucobases. This fact was seldom considered in work on those dyes. The general structure of the best known leuco-derivatives of triphenylmethane dyes is shown below:

Peak performance of most OWC systems occurs at resonance with the driving waves. At resonance, oscillations increase linearly in time until damping inhibits further growth. In parametric resonance, oscillations increase exponentially in time, possibly allowing for increasing the performance of OWC systems. This type of resonance occurs when one of the parameters in an oscillator varies periodically. Some ideas are presented to improve the performance of OWC systems using this phenomenon.