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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 43 (1978), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The circadian petal movement rhythm of Kalanchoë flowers has been studied. The amplitude of the rhythm can be drastically reduced by an appropriate stimulus of a light pulse. It has also been shown that it is possible to stop the rhythm permanently by administering a single light pulse to the flowers. This is interpreted to indicate that the light pulse has sent the circadian rhythm into a stable state of singularity.The conditions which attenuate the rhythm have been investigated both theoretically (on the basis of a previously published model for circadian rhythms) and experimentally. 120 min red light of 230 μW · cm−2, starting briefly before the second petal closure about 30 h after transfer to constant safe light conditions is optimal in inducing rhythm-damping. Damping requires the same duration when the light is given at the corresponding phase during the third or fourth cycle of the rhythm. However, in the first cycle 240 min red light of 230 μW · cm−2 is required to get optimal damping of the rhythm.Conditions to achieve damping for other irradiances are investigated. Individual recordings are presented which show the behaviour of the rhythm when perturbed by light stimuli close to its singularity.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 28 (1973), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The circadian petal rhythm of Kalanchoë blossfeldiana Poellniz was studied theoretically and experimentally. Results of experiments in which (i) two light pulses and (ii) repeated light pulses were given to the flowers are compared with predictions based on a previously published feedback model. In this model both the amplitude and the phase of the rhythm are affected by light pulses. Results from the present phase shift studies are shown to be in good agreement with the model.The results are also discussed in relation to a constant amplitude model like that suggested by Pittendrigh for the eclosion rhythm of Drosophila.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 9 (1971), S. 431-445 
    ISSN: 1741-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Description / Table of Contents: Sommaire La pression du sang artériel et la proportion de pulsations du volume ont été mésurées expérimentalement comme fonctions de temps, pour un segment du bras humain. En utilisant ces courbes et un type de programme d'identification, commun dans les vérifications techniques, on a calculé un modèle mathématique pour l'arbre artériel inclu dans le segment. Ce modèle mathématique mena à la construction d'un circuit électrique analogue, pour simuler la dépendance du temps de la proportion de pulsations du volume sur la pression artérielle. Dans les deux cas les résultats montrent un accord étroit entre les courbes simulées et les courbes physiologiques déterminées expérimentalement. L'inertie du sang et des vaisseaux paraît être négligeable, tandis que les adaptations non-linéaires doivent être inclues quand on utilise des vastes rangées de pression.
    Abstract: Zusammenfassung Der Arterienblutdruck und die Geschwindigkeit des Volumenpulsierens wurden experimentell für ein Segment des menschlichen Arms als Funktionen der Zeit gemessen. Unter verwendung dieser Kurven und einer Art von Identifizierungsprogramm, das in der Regeltechnik üblich ist, wurde ein mathematisches Modell für den, in das Segment eingeschlossenen Arterienbaum berechnet. Dieses mathematische Modell führte zu dem Entwurf einer analogen elektrischen Schaltung zur Nachahmung der zeitlichen Abhängigkeit der Geschwindigkeit des Raumpulsierens von dem Arteriendruck. In beiden Fällen geben die Resultate eine naheliegende Übereinstimmung zwischen den nachgeahmten Kurven und den experimentell ermittelten, physiologischen Kurven. Es wird gezeigt, dass die Trägheit von Blut und Gefässen unbedeutend ist, während nicht-lineare Nachgiebigkeit berücksichtigt werden muss, wenn es sich um grosse Druckbereiche handelt.
    Notes: Abstract The arterial blood pressure and the rate of volume pulsations were measured experimentally as functions of time for a segment of the human arm. Using these curves and a type of identification program, common in control engineering, a mathematical model was calculated for the arterial tree included in the segment. This mathematical model led to the construction of an electrical analogue circuit for simulating the time-dependence of the rate of volume pulsations on the arterial pressure. In both cases the results show a close agreement between the simulated curves and the physiological curves determined experimentally. The inertia of blood and vessels is shown to be negligible, while non-linear compliances must be included when dealing with wide pressure ranges.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 9 (1971), S. 721-724 
    ISSN: 1741-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Conclusion In many control problems, e.g. in biology, time delays of the order of seconds or more play an important role. The present device is intended for simulations of such problems. Its accuracy (0·1 per cent) is of the same magnitude as that for most analogue computer components. It has been used in preliminary experiments (Fig. 5) to study biological rhythms. However, many differential equations with time delay, including those with more complicated weighting functions than that in Fig. 5, can be successfully studied using this method.
    Type of Medium: Electronic Resource
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