Algebraically special, expanding and twisting gravitational fields with vanishing NUT parameter

The system of Einstein-Maxwell equations for fields mentioned in the title is simplified. Known pure radiation solutions are systematized and new solutions are given by separating the variables.Comment: revte

Ambiguous Dependence Of Minimal Plant Generation Time On Nuclear DNA Content

AMBIGUOUS DEPENDENCE OF MINIMAL PLANT GENERATION TIME ON NUCLEAR DNA CONTENT Victor B. Ivanov The minimum generation time (MGT) of plant development was suggested to depend on nuclear DNA content, which varies in plants over wide limits1. In ephemeral species with the shortest MGT, the average C values were significantly lower than in annual species, whereas the average C values in annual species were lower than those in perennial plants. However, nobody has paid attention to the ratio of annual to perennial species number as a function of C values. Here I show that with increasing C the ratio of annual to perennial species increases to C values equal to 7-8 pg (monocots) and 6-7 pg (eudicots) and then decreases and that the fraction of annuals is abundant not at the lowest, but at some higher C levels. Hence, C value increase exerts an ambiguous effect on MGT. The C value is not the only factor, which determines the duration of the plant development. Nevertheless, the nuclear DNA content exerts a pronounced effect on MGT together with other diverse factors affecting the rate of plant development, especially at higher C values