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  • 1985-1989  (16)
  • 1988  (10)
  • 1985  (6)
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  • 1985-1989  (16)
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  • 1
    Electronic Resource
    Electronic Resource
    Theory of Ostwald ripening for open systems (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 4710-4714 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Diffusion-controlled coarsening (Ostwald ripening) of a precipitate is analyzed for the case of an open system, immersed in a reservoir of constant solute concentration. Equivalence of the evolution of such open systems and closed systems studied previously is established in the limit of infinite systems. The cause of this equivalence is screening of the bulk of the system from the reservoir by diffusive interactions between the precipitated particles. The applicability to large, but finite systems is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448995
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Reduction of dissipation in a thermal engine by means of periodic changes of external constraintsa) (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2453-2456 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider a thermal engine driven by chemical reactions, which take place in a continuous flow, stirred tank reactor fitted with a movable piston. Work can be produced by means of a heat engine coupled to the products and to an external heat bath, and by the piston. Two modes of operation are compared, each with fixed input rate of chemicals: one with periodic variation of an external constraint [mode (b)], in which we vary the external pressure, and one without such variation [mode (a)]. We derive equations for the total power output in each of the two modes. The power output in mode (b) can be larger than that of mode (a) for the same chemical throughput and for the same average value of the external pressure. For a particularly simple case it is shown that the total power output in mode (b) is larger than that in (a) if work is done by the piston. At the same time the entropy production is decreased and the efficiency is increased. The possibility of an increased power output is due to the proper control of the relative phase of the externally varied constraint and its conjugate variable, the external pressure and the volume. This control is achieved by the coupling of nonlinear kinetics to the externally varied constraint. Details of specific mechanisms and the occurrence of resonance phenomena are presented in the following article.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448289
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  • 3
    Electronic Resource
    Electronic Resource
    Stabilization of unstable states, relaxation, and critical slowing down in a bistable system (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6234-6241 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The unstable branch of stationary states in an illuminated thermochemical bistable system is stabilized with an external feedback loop which does not otherwise alter the autonomous system. The technique allows the measurement of the entire set of stationary states available to the system. Trajectories of transition between branches of stationary states (relaxation) are investigated theoretically and experimentally. Critical slowing down in the speed of the trajectories is predicted and measured as the points of marginal stability are approached. Trajectories are observed to spread as they depart from the unstable stationary state and then to coalesce as they approach a stable stationary state. These results are obtained due to experimental spread in initial conditions and not from noise along the relaxation trajectory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449571
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  • 4
    Electronic Resource
    Electronic Resource
    Propagating and stationary structures in chemical reaction–diffusion systemsf a@f ) (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 113-122 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider propagating fronts and stationary patterns in chemical reaction–diffusion systems with nonlinear rate mechanisms maintained far from equilibrium. We study analytically and numerically the dependence on diffusion coefficients of the direction of propagation of the concentration profile which is obtained when two homogeneous steady states are placed in contact under identical constraints. We analyze the possible concentration profiles in a two-variable system with two stable stationary states for various values of diffusion coefficients and reaction time scales, and show that the direction of propagation depends on the diffusion coefficients. Finally, we show that a stationary pattern can develop behind the propagating concentration profile, a process for which there is some experimental evidence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448784
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  • 5
    Electronic Resource
    Electronic Resource
    A quantitative study of chemical waves in the Belousov–Zhabotinsky reaction (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1924-1936 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements are reported of velocities, amplitudes, and profiles in space and time of chemical waves in the Belousov–Zhabotinsky reaction at various temperatures, depths of solution, and initial reactant concentrations. The measurements are made in a thin layer of a quiescent, but excitable solution by means of light absorption by ferroin, the tris(1,10-phenanthroline) ferrous sulfate complex. Propagating wave profiles are recorded on a linear photodiode array (25.6 mm length) with a spatial resolution of 50 μ. The determinations of velocity corroborate previous experimental findings. New results include experimental verification of the constancy of the concentration profile of the wave in space and time; determination of two characteristic time constants in the relaxation of the wave profile; trends in wave amplitude with variation of initial reactant concentrations and age of the reaction mixture; wave velocity as a function of temperature, and solution depth; and measurements of wave annihilation. Observations of additional structure include the onset of mosaic structure, that is the transition from a homogeneous to an inhomogeneous state due to the passage of the wave, and initiation spikes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448376
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Calculation of the rate of entropy production for a model chemical reaction (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1064-1066 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate of entropy production due to chemical reaction is calculated for a variety of parameter values in the reversible Oregonator model. The average values over cycles of oscillation are compared to those in the coexisting stationary states. The present work corrects an earlier calculation [A. K. Dutt, J. Chem. Phys. 86, 3959 (1987)]. Contrary to previous impressions and claims, there is no consistent relationship between the magnitudes of the entropy production in coexisting stationary and oscillatory states, in this case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455258
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  • 7
    Electronic Resource
    Electronic Resource
    Experiments on bifurcation of periodic states into tori for a periodically forced chemical oscillator (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5536-5546 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study experimentally continuous transitions from quasiperiodic to periodic states for a time-periodically forced chemical oscillator. The chemical reaction is the hydration of 2,3-epoxy-1-propanol, and is carried out in a continuous stirred tank reactor (CSTR). Periodic oscillatory states are observed to arise in the autonomous system through supercritical Hopf bifurcations as either the total flow rate or the cooling coil temperature is changed. Under conditions of oscillation for the autonomous system, small-amplitude periodic variation of the total flow rate generates an attracting two-torus from the stable limit cycle. From the experiments we determine the structure of the toroidal flow, stroboscopic phase portraits, and circle maps as a function of the forcing amplitude and period. A continuous transition from the quasiperiodic to a periodic state, in which the two-torus contracts to a closed curve (Neimark–Sacker torus bifurcation), is observed as the forcing amplitude is increased at a constant forcing period, or as the forcing period is changed at a constant moderate forcing amplitude. Qualitative theoretical predictions compare well with the experimental observations. This paper presents the first experimental observation of a Neimark–Sacker torus bifurcation in a forced chemical oscillator system, and relates the bifurcation diagram of the unforced system to that of the forced system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454565
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  • 8
    Electronic Resource
    Electronic Resource
    Erratum: Calculation of the rate of entropy production for a model chemical reaction [J. Chem. Phys. 89, 1064 (1988)] (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 7039-7039 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455755
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  • 9
    Electronic Resource
    Electronic Resource
    Efficiency of a combustion reaction in power production (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2730-2734 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We analyze a thermal engine in which the source of heat is the combustion reaction CH4+2O2→CO2+2H2O. The efficiency of the thermal engine is defined as the ratio of the power output of the engine to the power input. We compare the efficiency in two modes of operation, one in which the input and output of chemical species are constants and one in which their corresponding fluxes have an imposed oscillatory component of a given amplitude and frequency. The ratio of efficiency in the oscillatory mode to the stationary flux mode can be as high as 1.3 for an amplitude of variation of the input and output fluxes plus or minus 40% of the stationary value. At low amplitudes of variation (10%), a single peak is present in a plot of the ratio of efficiency vs frequency of the fluxes. For higher amplitudes there are two peaks in that plot. One peak is associated with a response of the system that has the same period as the fluxes and the other occurs in a frequency range for which the periodic response is twice that of the perturbation. We calculate plots of the oscillatory output flux and the power output divided by that flux, which is an analog of a thermodynamic force, as a function of time, to show the importance of both resonance effects and the phase relation between the flux and the thermodynamic force in determining the ratio of efficiency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454003
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  • 10
    Electronic Resource
    Electronic Resource
    Explicit solutions of normal form of driven oscillatory systems in entrainment bands (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5715-5720 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: As in a prior article (Ref. 1), we consider an oscillatory dissipative system driven by external sinusoidal perturbations of given amplitude Q and frequency ω. The kinetic equations are transformed to normal form and solved for small Q near a Hopf bifurcation to oscillations in the autonomous system. Whereas before we chose irrational ratios of the frequency of the autonomous system ωn to ω, with quasiperiodic response of the system to the perturbation, we now choose rational coprime ratios, with periodic response (entrainment). The dissipative system has either two variables or is adequately described by two variables near the bifurcation. We obtain explicit solutions and develop these in detail for ωn/ω=1; 1:2; 2:1; 1:3; 3:1. We choose a specific dissipative model (Brusselator) and test the theory by comparison with full numerical solutions. The analytic solutions of the theory give an excellent approximation for the autonomous system near the bifurcation. The theoretically predicted and calculated entrainment bands agree very well for small Q in the vicinity of the bifurcation (small μ); deviations increase with increasing Q and μ. The theory is applicable to one or two external periodic perturbations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455581
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