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  • 11
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    Sulfate-reducing bacteria in temporarily oxic sediments with bivalves. (1991)
    In:  EPIC3Marine Ecology Progress Series, 78, pp. 97-102
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 12
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    Burrowing macrozoobenthos as major determinant of bacteria in sediments (1991)
    In:  EPIC3Kieler Meeresforsch ,Sonderh. 8, pp. 86-91
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 13
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    Growth and production of the seaweed, Himantothallus grandifolius, at King George Island (1985)
    In:  EPIC3Antarctic nutrient cycles and food webs (W R Siegfried, P R Condy, R M Laws, eds ) Springer, Berlin, pp. 104-108
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , peerRev
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  • 14
    Electronic Resource
    Electronic Resource
    Selective mesenteric phlebography in patients with carcinoid tumors (1979)
    Springer
    Abdominal imaging 4 (1979), S. 179-189 
    Details
    ISSN: 1432-0509
    Keywords: Abdominal angiography, indications ; Intestine, neoplasm ; Carcinoid tumors, diagnosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Seventeen patients were investigated to localize carcinoid tumor growth in the small intestine and liver. Portography, selective phlebography of the intestinal veins, arteriography, and hormone assay (Serotonin, substance P) after simultaneous catheterization of the celiac artery and portal and caval veins were performed. Most of the patients have been operated on and findings at surgery have been compared with the preoperative localization methods. In 3 cases with small bowel carcinoids and typical fibroplastic changes of the mesentery, phlebography as well as arteriography demonstrated well the degree of mesenteric involvement. None of the methods demonstrated the primary tumors. Arteriography was superior in demonstration of liver metastasis. The hormone assay was a useful complement to angiographic techniques in the diagnosis and localization of tumor growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01887521
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  • 15
    Electronic Resource
    Electronic Resource
    A theory of the pattern induced flight orientation of the fly Musca domestica (1973)
    Springer
    Biological cybernetics 12 (1973), S. 185-203 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The theory presented here describes the visual orientation behavior of fixed flying insects (the fly Musca domestica) in the presence of elementary patterns. The theory, which is based on a number of experimental results, Reichardt (1973), is a phenomenological one whose main purpose is to provide an organizational framework for treating a complex phenomenon without the need of detailed assumptions about the neural mechanisms actually involved. A simple hypothesis concerning the basic structure of the pattern fixation process leads to an equivalent stochastic equation of the Langevin type, which can be linearized for simple single-stripe panoramas. A critical experiment supports these theoretical assumptions. In addition, the effect on pattern fixation behavior of adding contrast noise to the background of the panorama, is quantitatively predicted by the theory. In the more general case of a panorama consisting of many vertical stripes, the Fokker-Planck equation associated with the Langevin equation, no longer linear, is solved. Making use of an experimentally proven “superposition principle”, the stationary pattern fixation behavior of the fly in an arbitrary panorama consisting of a collection of vertical stripes is predicted. In this context, concepts like pseudo-invariance and phase-transition can be applied to the insects orientation behavior. The theory presented here seems to contain rich classification properties, which might provide the foundations for an understanding of more complex pattern discrimination processes. Possible extensions of the theory, as well as some similarities to human eye fixation, are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00270572
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  • 16
    Electronic Resource
    Electronic Resource
    Considerations on models of movement detection (1973)
    Springer
    Biological cybernetics 13 (1973), S. 223-227 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A general characterization of multi-input movement detection models is given in terms of the Volterra series formalism. When nonlinearities of order higher than the second are negligible, an n-input system can be decomposed into a set of 2-input systems, summing linearly. For a (symmetrical) 2-input system which has significant nonlinearities only up to the second order, the correlation model is its most general expression, if the infinite time average of the output is taken. Specific observations from optomotor experiments (e.g. phase invariance and contrast frequency dependence) can be interpreted in a general way in terms of properties of the Volterra representation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00274887
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  • 17
    Electronic Resource
    Electronic Resource
    On the representation of multi-input systems: Computational properties of polynomial algorithms (1980)
    Springer
    Biological cybernetics 37 (1980), S. 167-186 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract This paper introduces a theoretical framework for characterizing and classifying simple parallel algorithms and systems with many inputs, for example an array of photoreceptors. The polynomial representation (Taylor series development) of a large class of operators is introduced and its range of validity discussed. The problems involved in the polynomial approximation of systems are also briefly reviewed. Symmetry properties of the input-output map and their implications for the system structure (i.e. its kernels) are studied. Finally, the computational properties of polynomial mappings are characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00355455
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  • 18
    Electronic Resource
    Electronic Resource
    Properties of individual movement detectors as derived from behavioural experiments on the visual system of the fly (1988)
    Springer
    Biological cybernetics 58 (1988), S. 287-294 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The performance of the fly's movement detection system is analysed using the visually induced yaw torque generated during tethered flight as a behavioural indicator. In earlier studies usually large parts of the visual field were exposed to the movement stimuli; the fly's response, therefore, represented the spatially pooled output signals of a large number of local movement detectors. Here we examined the responses of individual movement detectors. The stimulus pattern was presented to the fly via small vertical slits, thus, nearly avoiding spatial integration of local movement information along the horizontal axis of the eye. The stimulus consisted of a vertically oriented sine-wave grating which was moved with a constant velocity either clockwise or counterclockwise. In agreement with the theory of movement detectors of the correlation type, the time-course of the detector signal is modulated with the spatial phase of the stimulus pattern. It can even assume negative values for some time during the response cycle and thus signal the wrong direction of motion. By spatially integrating the response over sufficiently large arrays of movement detectors these response modulations disappear. Finally, one obtains a signal of the movement detection system which is constant while the pattern moves in one direction and only changes its sign when the pattern reverses its direction of motion. Spatial integration thus represents a simple means to obtain a meaningful representations of motion information.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00363937
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  • 19
    Electronic Resource
    Electronic Resource
    Elementary pattern discrimination (behavioural experiments with the fly Musca domestica) (1986)
    Springer
    Biological cybernetics 53 (1986), S. 285-306 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract This paper investigates the problem of spontaneous pattern discrimination by the visual system of the fly. The indicator for discrimination and attractivity of a pattern is the yaw torque of a test fly. It is shown that the pattern discrimination process may be treated as a special (“degenerate”) case of figureground discrimination which has been described in detail in earlier publications. Decisive for the discrimination process is the fact that pattern discrimination by the fly is mediated by motion detectors which respond not only a pattern velocity but also to structural properties of pattern contrast. This is demonstrated by the transition from the existing twodimensional array of motion detectors to a continuous detector field which enabled us to calculate instantaneous detector responses to instationary pattern motion. The new approach, together with the special theory for figure-ground discrimination, is then applied to predict spontaneous discriminations of onedimensional periodic patterns. It is shown that predictions and experimental results are in good agreement. The second set of discrimination experiments deals with two dimensional dot patterns for which a quantitative theory is not yet available. However, it is shown that the attractivity of a dot pattern crucially depends on both the orientation and the direction of motion relative to the fly's eyes. If the contrast of a moving dot elicits an event in a motion detector which through the detector's time constant leads to an interference with an event received by a preceeding dot, the attractivity of the dot pattern is diminished. In the discussion relations are drawn between the concepts of pattern discrimination in honey bees and the theoretical aspects of discrimination put forward in this paper. It is briefly discussed why a two-dimensional motion detector theory might become the key for an understanding of pattern categories like “figural intensity” and “figural quality”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336562
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  • 20
    Electronic Resource
    Electronic Resource
    Visual fixation and tracking by flies: Mathematical properties of simple control systems (1981)
    Springer
    Biological cybernetics 40 (1981), S. 101-112 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The study of the orientation behavior of flies requires the consideration of a few simple control systems for fixation and tracking. In this paper two such control systems are analyzed, in terms of the corresponding difference and differential equations. The first control system corrects with a delay ɛ the angular trajectory proportionally to the error angle ψ; the second control system also corrects proportionally to the error angle ψ but only when the absolute value of ψ is increasing. The differential equations are (0) $$\mathop \psi \limits^ \circ (t) = - \alpha '\psi (t - \varepsilon ) + A'$$ and (*) $$\mathop \psi \limits^o (t) = - \alpha '\psi (t - \varepsilon ) \cdot u[\psi (t - \varepsilon )\mathop \psi \limits^o (t - \varepsilon )] + A'$$ u[ ] being the step function (u[x]=1 if x〉0, otherwise u[x]=0). Under suitable restrictions on the parameters it is proved (a) that the difference equations (0') $$x_{n + 1} = x_n - \alpha x_n + A$$ and (*') $$x_{n + 2} = x_{n + 1} - \alpha x_{n + 1} \cdot u[x_{n + 1} \cdot (x_{n + 1} - x_n )] + A,$$ which can be associated to Eqs. (0) and (*), are “asymptotically equivalent” (for large n) if the time scale is “smoothed” over two time units and (b) that the second equation, with 0〈α〈2, always converge to a set of oscillating solutions of period 2 for arbitrary initial conditions. Numerical simulations show that the delay-differential equations behave in a similar way. We have also demonstrated with computer simulations that both control systems can satisfactorily predict the 3-D trajectory of a fly chasing another fly. The main biological implications of the analysis are: (1) The two control systems are practically equivalent descriptions of the fly's control of flight on a “coarse” time scale (2 times the fly's delay), consistently with an earlier more general derivation of Eq. (0) (Poggio and Reichardt, 1973). (2) On a fine time scale the second control system is characterized by an asymptotic oscillation with period twice the fly's delay. It is conjectured that a wide range of control systems of the same general type must have a similar oscillatory behavior. Finally, we predict the existence of asymptotic oscillations in the angular trajectory and the torque of tracking flies (if a control system of the second type is involved to a significant extent). Such oscillations should have a basic period of twice the effective reaction delay, and should be best detectable outside the binocular region. Closed loop experiments and the analysis of free flight trajectories may provide critical tests of this prediction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00344289
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