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  • 1
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Zusammenfassung Es wird durch übertragung des von M. v.Laue [10] aufgestellten elektrodynamischen Potentials eines Supraleiters in die allgemeinere, nichtlineare Theorie eine Möglichkeit gewonnen, den Eindeutigkeitsbeweis für das stationäre Feld durchzuführen. Weiterhin liefert dieser Potentialausdruck die bereits aus [11] bekannte Kraftdichte und das Drehmoment in der erweiterten Theorie. Im Anhang wird eine allgemeine Formel für den Unterschied zwischen substantieller und ortsfester änderung einer Funktion bei infinitesimaler Verrückung der Materie gegeben.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Planta 188 (1992), S. 28-38 
    ISSN: 1432-2048
    Keywords: Beat oscillator ; Chaos ; Crassulacean acid metabolism ; Endogenous rhythm ; Kalanchoë (CO2 fixation, rhythm) ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Endogenous free-running regular circadian oscillations of net CO2 exchange in the crassulacean-acidmetabolism (CAM) plantKalanchoë daigremontiana Hamet et Perrier de la Bâthie under constant external conditions in continuous light have been shown to change to irregular non-predictable (chaotic) time behaviour as irradiance or temperature are raised above a critical level. A model of CAM has been constructed with pools of major metabolites of varying concentrations, flows of metabolites leading to exchange between pools, metabolite transformations determined by chemical reactions, and feedback regulations. The model is described by a system of coupled non-linear differential equations. It shows stable rhythmicity in normal dark-light cycles and in continuous light and, like theK. daigremontiana leaves in the experiments, a change to chaos as irradiance is increased. The maintenance of endogenous oscillations in the model is brought about by a hysteresis switch or beat oscillator between two stable oscillation modes. In CAM these stable modes are vacuolar malate accumulation and remobilization. The model shows that the physical nature of the beat oscillator in the leaves can be explained by the balance between active and passive transport at the tonoplast.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Planta 188 (1992), S. 28-38 
    ISSN: 1432-2048
    Keywords: Beat oscillator ; Chaos ; Crassulacean acid metabolism ; Endogenous rhythm ; Kalanchoë (CO2 fixation, rhythm) ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Endogenous free-running regular circadian oscillations of net CO2 exchange in the crassulacean-acidmetabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier de la Bâthie under constant external conditions in continuous light have been shown to change to irregular non-predictable (chaotic) time behaviour as irradiance or temperature are raised above a critical level. A model of CAM has been constructed with pools of major metabolites of varying concentrations, flows of metabolites leading to exchange between pools, metabolite transformations determined by chemical reactions, and feedback regulations. The model is described by a system of coupled non-linear differential equations. It shows stable rhythmicity in normal dark-light cycles and in continuous light and, like the K. daigremontiana leaves in the experiments, a change to chaos as irradiance is increased. The maintenance of endogenous oscillations in the model is brought about by a hysteresis switch or beat oscillator between two stable oscillation modes. In CAM these stable modes are vacuolar malate accumulation and remobilization. The model shows that the physical nature of the beat oscillator in the leaves can be explained by the balance between active and passive transport at the tonoplast.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2048
    Keywords: Key words: Crassulacean acid metabolism ; Circadian rhythm ; Kalanchoë ; Photosynthesis oscillation ; Synchronizer (“zeitgeber”) ; Temperature gradient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier de la Bâthie shows an endogenous circadian rhythm of net CO2 exchange (J CO2 ) under constant conditions in continuous light. Previous studies have shown, however, that above a certain threshold temperature J CO2 changes from rhythmic to arrhythmic behaviour and that this is reversible when the temperature is lowered again. It is now demonstrated here, that this re-initiation of rhythmic J CO2 from arrhythmicity needs a sufficiently strong temperature signal as defined by its abruptness. Rhythmicity reappears only if the temperature is reduced rather rapidly. If the temperature is reduced slowly then arrhythmicity is retained even at a low temperature level which normally would allow rhythmicity. Under these circumstances, however, a distinct temperature increase followed by an abrupt temperature decrease immediately elicits regular oscillations of J CO2 at this lower temperature. We suggest that the strong temperature signals function as a definite synchronizer (“zeitgeber”) which synchronizes different cells and/or different leaf areas which remain desynchronized after application of only slow temperature changes. This is further supported by Fourier transform analyses, revealing a harmonic structure of the superficially arrhythmic time series of J CO2 after application of slow temperature reductions. This conclusion adds a spatial dimension to the otherwise purely time-dependent rhythmicity and arrhythmicity of J CO2 in CAM.
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  • 5
    ISSN: 1432-2048
    Keywords: Circadian rhythm ; Crassulacean acid metabolism ; Kalanchoe ; Model simulations ; Phase setting ; Tonoplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Leaves of Kalanchoë daigremontiana Hamet et Perr. at a photon flux density (PFD) above 220 μmol·m−2s−1 (400–700 nm) or at leaf temperatures above 27.0 °C showed a rapid loss of rhythmicity, and a more or less pronounced damping-out of the endogenous circadian rhythm of CO2 exchange under continuous illumination. This rhythm was reinitiated after reduction of the PFD by 90–120 μmol·m−2·s−1 or reduction of leaf temperature by 3.5–11.0 °C under otherwise unchanged external conditions. The reduction in the magnitude of the external control parameter of the Crassulacean acid metabolism (CAM) rhythm (i.e. PFD or leaf temperature) set the phase of the new rhythm. The maxima of CO2 uptake occurred about 5, 28, 51, 75 h after the reduction. Simulations with a CAM model under comparable conditions showed a similar behaviour. The influence of temperature on the endogenous CAM rhythm observed in K. daigremontiana in vivo could be simulated by incorporating into the model temperature-dependent switch modes for passive efflux of malate from the vacuole to the cytoplasm. Thus, the model indicates that tonoplast function plays an important role in regulation of the endogenous CAM rhythm in K. daigremontiana.
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  • 6
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die RG der Hydrolyse von 37 Carbonsäurehalogeniden in 89.1-vol.-proz. Aceton wurde mit Hilfe eines selbstregistrierenden Leitfähigkeitsgerätes gemessen. Der Einfluß des Lösungsmittels und zugesetzter Amine auf die RG wurde untersucht. Wahrscheinlich spielen je nach Reaktionsbedingungen und Konstitution der Reaktionsteilnehmer SN1- und Additions-Eliminierungs-Mechanismen eine Rolle.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Hydrolyse von Carbonsäure-imidchloriden zu Carbonsäureamiden ver läuft nach einem zweistufigen Mechanismus über Nitrilium-chlorid-Ionenpaare, wobei die Hydrolyse-RG sowohl vom Ionisations-Gleichgewicht als auch dem nucleophilen Angriff des Wassers auf das Ionenpaar bestimmt wird. Substitution nach einem einfachen SN1-Mechanismus läßt sich in einigen Fällen bei Umsetzungen mit Ammoniak nachweisen (kNH3 = k1). Die Bedeutung der Nucleophilität des eintretenden Substituenten bei SN1-Reaktionen wird diskutiert.
    Additional Material: 2 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 39 (1952), S. 254-255 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 1952-01-01
    Print ISSN: 0028-1042
    Electronic ISSN: 1432-1904
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Published by Springer
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