101,607 research outputs found

    Meromorphy and topology of localized solutions in the Thomas–MHD model

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    The one-dimensional MHD system first introduced by J.H. Thomas [Phys. Fluids 11, 1245 (1968)] as a model of the dynamo effect is thoroughly studied in the limit of large magnetic Prandtl number. The focus is on two types of localized solutions involving shocks (antishocks) and hollow (bump) waves. Numerical simulations suggest phenomenological rules concerning their generation, stability and basin of attraction. Their topology, amplitude and thickness are compared favourably with those of the meromorphic travelling waves, which are obtained exactly, and respectively those of asymptotic descriptions involving rational or degenerate elliptic functions. The meromorphy bars the existence of certain configurations, while others are explained by assuming imaginary residues. These explanations are tested using the numerical amplitude and phase of the Fourier transforms as probes of the analyticity properties. Theoretically, the proof of the partial integrability backs up the role ascribed to meromorphy. Practically, predictions are derived for MHD plasmas

    Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations

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    A self-regulating magnetic flux pumping mechanism in tokamaks that maintains the core safety factor at q≈1q\approx 1, thus preventing sawteeth, is analyzed in nonlinear 3D magnetohydrodynamic simulations using the M3D-C1^1 code. In these simulations, the most important mechanism responsible for the flux pumping is that a saturated (m=1,n=1)(m=1,n=1) quasi-interchange instability generates an effective negative loop voltage in the plasma center via a dynamo effect. It is shown that sawtoothing is prevented in the simulations if β\beta is sufficiently high to provide the necessary drive for the (m=1,n=1)(m=1,n=1) instability that generates the dynamo loop voltage. The necessary amount of dynamo loop voltage is determined by the tendency of the current density profile to centrally peak which, in our simulations, is controlled by the peakedness of the applied heat source profile.Comment: submitted to Physics of Plasmas (23 pages, 15 Figures

    Measuring information growth in fractal phase space

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    We look at chaotic systems evolving in fractal phase space. The entropy change in time due to the fractal geometry is assimilated to the information growth through the scale refinement. Due to the incompleteness, at any scale, of the information calculation in fractal support, the incomplete normalization ∑ipiq=1\sum_ip_i^q=1 is applied throughout the paper. It is shown that the information growth is nonadditive and is proportional to the trace-form ∑ipi−∑ipiq\sum_ip_i-\sum_ip_i^q so that it can be connected to several nonadditive entropies. This information growth can be extremized to give, for non-equilibrium systems, power law distributions of evolving stationary state which may be called ``maximum entropic evolution''.Comment: 10 pages, 1 eps figure, TeX. Chaos, Solitons & Fractals (2004), in pres

    Latent curing of epoxy-thiol thermosets

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    Epoxy-thiol curing is a click reaction which allows quantitative yield of the end products. The base-catalyzed reaction is rapid at low temperatures so it is most often desirable to harness reactivity by using latent catalysts. In this work, we used triazabicyclodecene tetraphenylborate (TBD·HBPh4) as a photobase generator (PB). We activated the PB either thermally or by UV light and monitored reaction kinetics by DSC and FTIR methods. Depending on the catalytic system used, the rate of the thiol-epoxy reaction was ordered as follows: Neat base > UV activated PB > thermally activated PB > uncatalyzed system. A series of isothermal and non-isothermal DSC experiments were run on non-irradiated and irradiated samples in order to study the effect of PB content and UV irradiation duration on PB activation efficiency and latency/storage stability. The data from DSC were analyzed using model-free linear isoconversional methods to estimate kinetic parameters such as activation energies. In addition, the kinetics data for both activation methods were shown to be accurately represented by multi-term Kamal models. The storage stability of the systems were studied at room temperature and was shown to fit well to the predictions of the kinetic model.Postprint (author's final draft
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