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  • 1990-1994  (1)
  • 1985-1989  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Mathematical model and simulation of retina and tectum opticum of lower vertebrates (1987)
    Springer
    Acta biotheoretica 36 (1987), S. 179-212 
    Details
    ISSN: 1572-8358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The processing of information within the retino-tectal visual system of amphibians is decomposed into five major operational stages, three of them taking place in the retina and two in the optic tectum. The stages in the retina involve (i) a spatially local high-pass filtering in connection to the perception of moving objects, (ii) separation of the receptor activity into ON- and OFF-channels regarding the distinction of objects on both light and dark backgrounds, (iii) spatial integration via near excitation and far-reaching inhibition. Variation of the spatial range of excitation and inhibition allows to account for typical activities observed in a variety of classes of retina ganglion cells. Mathematical description of the operations in the tectum opticum include (i) spatial summation of retinal output (mainly of class-2 and class-3 retina ganglion cells), and (ii) direct or indirect lateral inhibition between tectal cells. In the computer simulation, first the output of the mathematical retina model is computed which, then, is used as the input to the tectum model. The full spatio-temporal dynamics is taken into account. The simulations show that different combinations of strength of lateral inhibition on the one side and the response properties of the retina ganglion cells on the other side determine the response properties of tectal cell types involved in object recognition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00052064
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Principles of self-generation and self-maintenance (1985)
    Springer
    Acta biotheoretica 34 (1985), S. 125-137 
    Details
    ISSN: 1572-8358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Living systems are characterized as self-generating and self-maintaining systems. This type of characterization allows integration of a wide variety of detailed knowledge in biology. The paper clarifies general notions such as processes, systems, and interactions. Basic properties of self-generating systems, i.e. systems which produce their own parts and hence themselves, are discussed and exemplified. This makes possible a clear distinction between living beings and ordinary machines. Stronger conditions are summarized under the concept of self-maintenance as an almost unique character of living systems. Finally, we discuss the far-reaching consequences that the principles of self-generation and self-maintenance have for the organization, structure, function, and evolution of single- and multi-cellular organisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046778
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Oscillatory modes in a nonlinear second-order differential equation with delay (1990)
    Springer
    Journal of dynamics and differential equations 2 (1990), S. 423-449 
    Details
    ISSN: 1572-9222
    Keywords: Nonlinear differential equations of second order with deviating argument ; oscillations ; periodic solutions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Solution properties of the nonlinear second-order delay-differential equation x(t)=−ax(t)+f[x(t−Τ)] are studied wheref is a piecewise constant function which mimics negative feedback. We show that the solutions can be obtained by a simple geometrical construction which, in principle, can be implemented using a ruler and a compass. Analytical results guarantee the existence and stability properties of limit cycle solutions. Computer-aided constructions reveal a remarkable richness of different types of dynamical behaviors including a variety of unconventional bifurcation schemes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01054042
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    Paper (German National Licenses)
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