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  • 1
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 1986-01-31
    Description: Contrary to the orthodox view that optical image quality should "match" the photoreceptor grain, anatomical data from the eyes of various animals suggest that the image quality is significantly superior to the potential resolution of the cone mosaic in most retinal regions. A new theory is presented to explain the existence of this relation and to better appreciate eye design. It predicts that photoreceptors are potentially visible through the natural optics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Snyder, A W -- Bossomaier, T R -- Hughes, A -- New York, N.Y. -- Science. 1986 Jan 31;231(4737):499-501.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/3941914" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Cats ; Humans ; Models, Neurological ; Photoreceptor Cells/*anatomy & histology ; Rats ; Snakes ; Species Specificity ; *Vision, Ocular ; *Visual Perception
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 67 (1992), S. 217-222 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The evolution of visual pigment spectral sensitivities is probably influenced by the reflectance spectra of surfaces in the animal's environment. These reflectances, we conjecture, fall into three main classes: i. Most inorganic and many organic surfaces, including tree bark, dead leaves and animal melanin pigmentation, whose reflectance increases gradually as a function of wavelength, ii. Living leaves, which contain chlorophyll, have a sharp reflectance peak at about 555 nm. iii. Flowers, fruit and other signaling colours that have co-evolved with animal vision typically do not reflect strongly at the same wavelength as leaves, and present a colour contrast against a leafy background. These three spectral functions we call ‘grey-red’, ‘leaf-green’ and ‘leaf-contrast’ respectively. This simple categorisation allows us to interpret the spectral tuning of human cone pigments in a way that might not seem possible given the wide variety of colours present in nature. In particular L-(red) cones will capture the highest possible proportion of photons reflected by leaves, and M-(green) cones will capture about 10% fewer photons both from leaves and from ‘grey-red’ surfaces. These observations have some clear implications for our understanding of the evolution of trichomacy and the trade-off between chromatic and luminance vision in Old-World Primates.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 44 (1977), S. 265-278 
    ISSN: 1432-2234
    Keywords: Cage molecules, electronic structure of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A non-empirical molecular orbital method, particularly suitable for calculations on cage-like molecules, is described. The method uses as basis functions the set of free-electron functions which are the solutions of Schrödinger's equation for an electron confined between two concentric, spherical potential energy barriers. Application of the theory to the SCF calculation of the energies of the delocalized electrons in benzene and tetrasulphur tetranitride shows that the model is capable of interpreting the properties of such systems. However, it does highlight a difficulty in the calculation of excited state energies with one-centre models which appears to be largely unrecognized. Extension of the method to a consideration of all the valence electrons, using P4 as an example, reveals problems the origin of which is an inadequate treatment of the core electrons. It is suggested that these problems may best be dealt with by use of a suitable pseudo potential.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 1992-07-01
    Print ISSN: 0340-1200
    Electronic ISSN: 1432-0770
    Topics: Biology , Computer Science , Physics
    Published by Springer
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