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Photoreceptor adaptation ensures appropriate visual responses during changing light conditions and contributes to colour constancy. We used behavioural tests to compare UV-sensitivity of budgerigars after adaptation to UV-rich and UV-poor backgrounds. In the latter case, we found lower UV-sensitivity than expected, which could be the result of photon-shot noise corrupting cone signal robustness or nonlinear background adaptation. We suggest that nonlinear adaptation may be necessary for allowing cones to discriminate UV-rich signals, such as bird plumage colours, against UV-poor natural backgrounds. 相似文献
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B. R. Nebel 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1935,7(6):155-156
Ohne ZusammenfassungSchluß. 相似文献
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Markus E Nebel 《Journal of computational biology》2002,9(3):541-573
The secondary structure of an RNA molecule is of great importance and possesses influence, e.g., on the interaction of tRNA molecules with proteins or on the stabilization of mRNA molecules. The classification of secondary structures by means of their order proved useful with respect to numerous applications. In 1978, Waterman, who gave the first precise formal framework for the topic, suggested to determine the number a(n,p) of secondary structures of size n and given order p. Since then, no satisfactory result has been found. Based on an observation due to Viennot et al., we will derive generating functions for the secondary structures of order p from generating functions for binary tree structures with Horton-Strahler number p. These generating functions enable us to compute a precise asymptotic equivalent for a(n,p). Furthermore, we will determine the related number of structures when the number of unpaired bases shows up as an additional parameter. Our approach proves to be general enough to compute the average order of a secondary structure together with all the r-th moments and to enumerate substructures such as hairpins or bulges in dependence on the order of the secondary structures considered. 相似文献
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This rapid spectrophotometric method for determining the OsO4 concentration in fixative and stock solutions is based on the reduction of OsO4 by acidified KI to the blue species of OsI6 =, which is then determined at 649 mµ. The salt K2OsI6 has been isolated from the reaction mixture and characterized. Method: A I ml aliquot of the solution, containing up to 3% OsO4, is diluted to 100 ml with distilled water. To 1 ml of the diluted solution is added, in order: distilled water, 2 ml; 1 M HCI, 1 ml; and 1 M KI, 1 ml. Optical density at 649 mµ is read from 10-120 min thereafter. OsO4 concentration is calculated from the measured molecular extinction coefficient of OsI6 =, 4400 liter/mole cm. 相似文献
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