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  • 1985-1989  (8)
  • 1986  (8)
Material
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  • 1985-1989  (8)
Year
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 868-878 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Periodic perturbations are applied to the input rates of acetaldehyde and oxygen, one at a time, in the combustion of acetaldehyde in a CSTR. We measure periodic responses in five entrainment bands as we vary the frequency and amplitude of the external periodic perturbation. Outside of entrainment bands we find quasiperiodic responses. Next-phase maps of the experimental results are constructed in real time and used in the observation and interpretation of entrainment and quasiperiodic behavior. Within the fundamental entrainment band, we measure critical slowing down and enhancement of the response amplitude. As the bath temperature is increased, so that the oscillatory system approaches a Hopf bifurcation, we observe an increase in the amplitude enhancement. The predictions of a five-variable thermokinetic model agree with the experimental results.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6489-6503 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time delay processes in chemical kinetics occur naturally and can be imposed by means of a delayed feedback. We study the temporal evolution of homogeneous chemical reaction mechanisms (the autonomous system) describable by ordinary differential equations subjected to an imposed time delay, a delayed feedback. A natural delay process can be decomposed into analogous components. At short delays the delayed feedback is shown to stabilize different types of unstable stationary states of the autonomous systems, as well as induce bistability in a monostable system. At longer delays transitions into chaos are predicted. First we study the chaotic response of autonomous bistable systems which support only stationary states. A recipe for finding chaos is given. Chaos occurs for a small parameter range in which the delayed feedback repeatedly reinjects trajectories into the neighborhood of one of the marginally stable points of the autonomous system. Secondly, we consider the imposition of a delayed feedback to a system in which periodic oscillations occur and show this leads to both chaos and hyperchaos when memory effects in the delay cause the system to be reinjected into the neighborhood of a saddle-focus point. The examples studied in detail are thermo-illuminated chemical reactions, but we also consider the applicability of our results to reactions in continuously stirred tank reactors and biochemical processes. The results of this study show that natural time delays can regulate a wide range of dynamical behavior in biochemical processes.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 879-886 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Periodic perturbations are applied to the input rates of acetaldehyde and oxygen simultaneously in the combustion of acetaldehyde in a CSTR. With the two perturbations at the same frequency, we measure bistability in entrainment and hysteresis as a function of the phase shift between the two perturbations. The application of a perturbation in the flowrate of one reactant to the system already entrained to a perturbation of the flowrate of the second reactant can cause the system: to become quasiperiodic in both perturbations; to become entrained to both perturbations; to remain entrained, but not phase locked, to the first perturbation; or to become quasiperiodic in the first perturbation but entrained to the second perturbation. We measure the effects of frequency modulated and amplitude modulated acetaldehyde flowrate perturbations; the results compare well with predictions made by a five-variable thermokinetic model.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3857-3864 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Diffusion-controlled reactions between solute particles and immobile spherical sinks are studied, using the Monte Carlo method to perform averages over sink configurations. The average steady-state solute concentration profile c¯(r) in a locally perturbed solution is determined for sink volume fractions φ≤0.3, by numerically solving the diffusion equation in the monopolar+dipolar approximation of diffusive couplings between the sinks. At low volume fractions the analytical result c¯(r)∝r−1 exp(−r/λ), with the screening length λ∝φ−1/2, is recovered, whereas for φ(approximately-greater-than)0.1 significant deviations from this functional form are found. The Monte Carlo method is shown to be most accurate and efficient in the region 10−3(approximately-less-than)φ(approximately-less-than)10−1 in which (a) a system of only 25 sinks suffices, and (b) the monopolar approximation alone is sufficiently accurate. In this regime the reaction rate coefficient calculated numerically is found to be in good agreement with previous analytical theories.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 1492-1499 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Propagating chemical pulses are observed in the illuminated dimerization reaction of S2O6F2 when this bistable system is suitably perturbed. The dependence of the speed of propagation on incident laser power and the temporal evolution of the absorption profile along the laser beam are measured. The results compare well with calculations based on a previously developed model. The propagating chemical pulse is compared to chemical waves in an excitable medium.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 90 (1986), S. 923-926 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 67 (1986), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The gene lk in peas (Pisum sativum L.) confers the erectoides phenotype. This phenotype possesses much reduced internode and petiole lengths and is practically insensitive to applied GA1, compared with Lk plants. Application of the ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG), resulted in increased internode elongation and increased GA-sensitivity in lk plants, but not in the Lk line, L53. The ethylene-releasing compound, ethephon, had the reverse effect when applied to the Lk line, L58, reducing internode length and GA-sensitivity. Ethylene production was higher in lk segregates than in Lk segregates under the conditions used, and the shoot anatomy of lk segregates was consistent with these higher ethylene levels.These results suggest that the phenotypic effects of gene lk may be due, at least in part, to increased ethylene production in erectoides plants. However, AVG application to lk plants did not produce true phenocopies of comparable lk plants and ethephon application to Lk plants did not produce the erectoides phenotype. Further work is therefore required to determine whether the effect of the gene lk on ethylene production is the primary action of this gene or merely a secondary consequence.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 324 (1986), S. 250-253 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Mach originally7 used rotating discs and drums to study the bright and dark bands that appear where ramps of luminance meet plateaux as, for example, at the borders of the penumbra of a shadow. He later devised optical methods to cast shadows8. For the studies reported here we used gratings formed ...
    Type of Medium: Electronic Resource
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