[en] Solar scientist are well aware of the low energy density of solar radiation. A fully tracking collector at the sunniest spot on this planet will receive a little excess of 3000 kWh per year per m² of solar radiation (beam plus diffused). In most places the figure is far lower. Conversion efficiencies, from solar radiation to electricity, vary from a fraction of 1% for a photo-synthesis-hybrid-thermal converter, to to a maximum well below 40% for the highest temperature thermal systems. It is this low output per unit area that presents the major problem in achieving economic viability, discontinuity in the energy supply being, by comparison, a minor inconvenience. The economics of various solar conversion systems is presented, using an unsophisticated approach in order to see more vividly the issues involved. Economic viability depends not only on cost and output but on the cost of alternatively energy supplies at site in question

[en] The authors have shown that toxicity of paraquat for Escherichia coli is increased over 1-fold in strains defective in the biosynthesis of spermidine compared to isogenic strains containing spermidine. The increased sensitivity of these spermidine-deficient mutants to paraquat is eliminated by growth in medium containing spermidine or by endogenous supplementation of spermidine by the use of a speE⁺D⁺ plasmid. No paraquat toxicity is seen in the absence of oxygen, even in amine-deficient strains, indicating that superoxide is the agent responsible for the increased toxicity. However, the specific mechanisms responsible for the increased paraquat toxicity in the spermidine-deficient mutants remain to be determined. The marked sensitivity to paraquat of E. coli deficient in spermidine is of particular interest, since such mutants have no other phenotypic properties that can be easily assayed. This increased sensitivity has been used as the basis of a convenient method for scoring for mutants in polyamine biosynthesis and for the detection of plasmids containing the biosynthetic genes