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  • 1970-1974  (6)
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  • 1
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Summary Some extensions of the theory of adapting coincidence scaling are presented in the context of neural theory and modelling. Previously the theory of adapting coincidence scaling has been successfully applied to quite a number of specific problems mainly drawn from psychophysical theories of vision: van de Grind et al. (1970a, b); Koenderink et al. (1970a, b). Here emphasis is on neurophysiological problems and after a brief discussion of the “coding” and “component” problems of neural network modelling and a survey of basic coincidence scaling mechanisms a paradigm for neural encoding is treated in some detail. This paradigm (Fig. 6A) is similar to the neuromimes developed and studied by Harmon (1959, 1961) and Küpfmüller and Jenik (1961) for deterministic input signals. On the basis of the introductory discussion of the coding problem it is assumed that the neural code in the peripheral part of the nervous system that we choose as our hunting ground, viz. the retina, is an average event rate code with a Poisson point process as a carrier. Thus the paradigm for neural encoding is studied for such a stochastic input point process. It is then among other things shown that such a simple encoder can generate a wide variety of multimodal interval distributions for certain choices of its parameters. Next we turn to a classic coincidence model of vision and give extremely accurate simulation results to substitute for the lacking analytic solution of the underlying K-fold coincidence problem. A shortcoming of this model is analysed in terms of elementary neural operations and it is shown that the problem of specifying a generalized version of the model ties in with the problem of developing models to explain the quantal signals (bumps) observed on the generator potential during intracellular recordings from the eccentric cell of Limulus. A cybernetic principle for “bump” size adaptation is formulated on the basis of the apparent and possibly significant similarity of this adaptation process with the event rate reduction principle embodied in the so called V R-machine (van de Grind et al., 1970a) which is one of our set of adapting coincidence scalers.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Summary In the context of the quantum theory of vision scalers, coincidence scalers, adapting coincidence scalers and dead time mechanisms have been used as basic constituents of network models: van de Grind et al. (1970a), Koenderink et al. (1970a, b). The possibilities that these devices offer to construct network models of vision are presently further analysed. First of all a mechanistic analysis is given of the event rate reduction characteristics of “dead time boxes”. Next the interaction of these devices with scalers is discussed in relation with a number of “fluctuation models” of vision proposed in the literature. A critical evaluation of these fluctuation models shows an important defect of most of them, viz. that unrealizable detection criteria are postulated. Our reconsideration of this detection problem then leads to the proposal of some specific realizable detectors. An application of the developed theory of mechanisms (‘machines’) to the explanation of the flash detection characteristics of Limulus concludes the paper. Applications of the presented ideas to neural theory and modelling are treated hi a separate paper (van de Grind et al., 1970b) and for applications of the theory to psychophysically oriented visual modelling studies the reader is referred to Koenderink et al. (1970a, b) and van de Grind et al. (1970a).
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Inventiones mathematicae 20 (1973), S. 267-312 
    ISSN: 1432-1297
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 30 (1973), S. 371-380 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Values of the proton collisional excitation and deexcitation cross sections for all transitions between the Fe+12 ground configuration levels are calculated using semi-classical Coulomb excitation theory. Rate constants for these processes are then derived for coronal temperatures and are shown to be comparable in all cases to the corresponding electron rate constants.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 30 (1973), S. 381-384 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theoretical values for the relative intensities of the Fe XIII lines λ110747, λ110798, and λ3388 are presented as functions of electron density using recent values of the cross-section for collisionl excitation by protons. Our results are compared with those of Chevalier and Lambert.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 31 (1973), S. 81-89 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Improved values of the proton impact excitation cross sections at coronal energies for all the Fe+12 ground configuration (3s 23p 2) transitions are presented. These were obtained by direct computer integration of the Schroedinger equation (with the states expressed in intermediate coupling) resulting from the semi-classical Coulomb excitation theory formulation of the process. Comparison is made with previous results. The associated rate constants at coronal temperatures are given and compared with the corresponding electron impact excitation rate constants. Some cross-section values for the Fe+13 3s 23p 2 P 1/2→2 P 3/2 excitation are also presented.
    Type of Medium: Electronic Resource
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