3 results for Scholarly text, ScholarlyCommons@AUT

  • Curvature dependence of propagating velocity for a simplified calcium model

    Zhang, W (2014-02-20)

    Scholarly text
    Auckland University of Technology

    It is known that curvature relation plays a key role in the propagation of two-dimensional waves in an excitable model. Such a relation is believed to obey the eikonal equation for typical excitable models (e.g., the FitzHugh-Nagumo (FHN) model), which states that the relation between the normal velocity and the local curvature is approximately linear. In this paper, we show that for a simplified model of intracellular calcium dynamics, although its temporal dynamics can be investigated by analogy with the FHN model, the curvature relation does not obey the eikonal equation. Further, the inconsistency with the eikonal equation for the calcium model is because of the dispersion relation between wave speed s and volume-ratio parameter γ in the closed-cell version of the model, not because of the separation of the fast and the slow variables as in the FHN model. Hence this simplified calcium model may be an unexpected excitable system, whose wave propagation properties cannot be always understood by analogy with the FHN model.

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  • The immediate threat to our oceans

    Vopel, K (2011-07-13)

    Scholarly text
    Auckland University of Technology

    "We are about to fundamentally change the chemistry of our ocean. The greatest risk to our marine environment is the accelerating enrichment of seawater with anthropogenic CO2. This CO2 pollution results from our ignorance of the fundamental processes that link the marine environment with the atmosphere and the land. The overall human CO2 emissions over the industrial era amount to close to 560 billion tons. A little less than half of this CO2 remains in the atmosphere acting as greenhouse gas leading to climate change. The remainder is, at present, removed in roughly equal parts into the ocean and by land vegetation. We are emitting roughly 10 billion tons of carbon annually, a rate that exceeds the natural emissions by a factor of nearly 100. About 87% of this release originates from fossil fuel combustion and cement production and another 12% from deforestation. The ocean is a complex system well designed for maintaining a balance between inputs and outputs of carbon but the current rapid rise in atmospheric CO2 exceeds its capacity to maintain this balance.

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  • A debt behaviour model

    Zhang, W (2014-02-20)

    Scholarly text
    Auckland University of Technology

    A stochastic model with hidden discrete Markov processes is constructed to understand the behavior of debtors.

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