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Abstract: In the present work we investigated the joint kinetics of the overall water and calcium uptake in Yellow Dent corn during the alkaline treatment process with three different temperature profiles. The behavior of the difference of moisture gain and calcium gain in the whole grain and the behavior of calcium gain in the pericarp and in the internal part of the grain suggest that the water and calcium uptake in alkaline solution is a complex process governed by a series of kinetic stages of diffusion and reaction with loss of material. Results show that even though the diffusion pathways for the water and calcium uptake during alkaline treatment are the same, the rates of diffusion and reaction with loss of material of water and calcium in different component parts of the grain are different and greatly influence by temperature. Comparing the three kinetic stages observed during soaking at room temperature (24°C) the effect of soaking at an initial boiling temperature value of 98°C was found to accelerate the three kinetic stages by 1080min and to observe an additional fourth kinetic stage during the last minutes of the soaking period. The results also show that the alkaline cooking at 98°C of the corn kernel during 15min greatly accelerates the calcium reaction with pericarp material that results in the loss of most of the pericarp structure during the first 30min of the steeping stage. Comparing the four kinetic stages observed during soaking at an initial boiling temperature value the effect of the cooking period was found to accelerate the four kinetic stages by 1155min and to observe an additional fifth kinetic stage during the last minutes of the steeping stage. [Copyright &y& Elsevier]

We evaluated the combined effects of food (0.5 × 106, 1.0 × 106 and 2.0 × 106 cells ml−1 of Chlorella vulgaris) and temperature (15, 20 and 25 °C) on life history variables of B. havanaensis. Regardless of Chlorella density there was a steep fall in the survivorship of B. havanaensis at 25 °C. Both food level and temperature affected the fecundity of B. havanaensis. At any given food level, rotifers cultured at 15 °C showed extended but low offspring production. At 25 °C, offspring production was elevated, the duration of egg laying reduced and the fecundity was higher during the latter part of the reproductive period. The effect of food level was generally additive, at any given temperature, and higher densities of Chlorella resulted in higher offspring production. Average lifespan, life expectancy at birth and generation time were 2–3 times longer at 15 °C than at 25 °C. At 20 °C, these remained at intermediate levels. The shortest generation time (about 4 days) was observed at 25 °C. Gross and net reproductive rates and the rate of population increase ( r) increased with increasing temperature and generally, at any given temperature, higher algal food levels contributed to higher values in these variables. The r varied from 0.11 to 0.66. The survival patterns and lower rates of reproduction at 15 °C suggest that the winter temperatures (10–15 °C) prevailing in many waterbodies in Mexico City allow this species to sustain throughout the year under natural conditions. [ABSTRACT FROM AUTHOR]

Brachionus havanaensis is a common rotifer in the North American continent. Its frequent occurrence in relatively high densities and availability throughout the year in several Mexican freshwater bodies prompted us to understand the population dynamics of this species in relation to food level (Chlorella vulgaris at 0.5x106, 1.0x106 and 2.0x106 cells ml-1) and temperature (15°, 20°, and 25°C). We found that regardless of the temperature, an increase in food level resulted in an increase in the population growth of the rotifers. However, at any food level, rotifers cultured at 15°C did not increase beyond 8 ind. ml-1; on the other hand at comparable food concentrations at both 20 and 25°C, the population densities were higher than 600 ind. ml-1. The rate of population increase per day (d-1) of B. havanaensis varied from 0.02 to 0.29 d-1 depending on the food density and temperature. Our results also showed that regardless of the food level, at 15°C B. havanaensis had no statistically significant relation between the number of eggs per female and the population abundance. On the other hand, significant inverse relationships were observed between the egg ratio and population density of B. havanaensis grown at 20° and 25°C, regardless of the food level. When the daily growth rates were plotted against the population densities of the previous day, we found a significantly inverse relation for rotifers grown at 20° and 25°C, but not at 15°C, for all tested food levels. There were statistically significant effects of food level, temperature, and the interaction of both parameters on both the peak population density and the rate of population increase, although temperature had a far greater influence than did food. [ABSTRACT FROM AUTHOR]