The facts concerning the occurrence of superconductivity in R 2- z Ce z CuO 4 and in R 2- z Th z CuO 4 are studied using a combination of simple tools: a hard-sphere model, the self-consistent bond-valence-sum method and Madelung potential calculations. Doping by isolated substitutional Ce should produce Ce 3+ , and not Ce 4+ , causing us to conclude that the dopants are not isolated, but pairs, which make the material p type and not n type. The (...) L = 0 magnetic rare-earth ions Gd and Cm are unsplit pair breakers, unlike the other magnetic rare-earth ions which lead to superconductivity. As the rare-earth ions become smaller, the c -axis length shortens; then the O ions rotate after they come into contact with one another. Eu 1.85 Th 0.15 CuO 4 does not superconduct because quadrivalent Th is too large to fit at the dopant site, but Eu 1.85 Ce 0.15 CuO 4 does superconduct because Ce fits. (shrink)

The up‐ and down‐regulation of the salivary gland secretion protein (Sgs) genes during the third larval instar of Drosophila melanogaster are controlled by fluctuations of the titre of the steroid hormone 20‐hydroxyecdysone (20E). Induction of these genes by a low hormone titre is a secondary response to 20E mediated by products of 20E‐induced ‘early’ genes. Surprisingly, in the case of the Sgs‐4 gene this response also requires a direct contribution of the 20E‐receptor complex. A model is presented which proposes that (...) the Sgs genes, and other 20E‐regulated genes with similar temporal expression profiles, are regulated by complex hormone response units. The hormonal signal is effectively transmitted by these response units only after binding of additional factors, e.g. secretion enhancer binding proteins, which act together in a synergistic manner with the 20E receptor and early gene products to establish a stage‐ and tissuespecific expression pattern. (shrink)