A bidomain threshold model of propagating calcium waves

We present a bidomain fire-diffuse-fire model that facilitates mathematical analysis of propagating waves of elevated intracellular calcium (Ca) in living cells. Modelling Ca release as a threshold process allows the explicit construction of travelling wave solutions to probe the dependence of Ca wave speed on physiologically important parameters such as the threshold for Ca release from the endoplasmic reticulum (ER) to the cytosol, the rate of Ca resequestration from the cytosol to the ER, and the total [Ca] (cytosolic plus ER). Interestingly, linear stability analysis of the bidomain fire-diffuse-fire model predicts the onset of dynamic wave instabilities leading to the emergence of Ca waves that propagate in a back-and-forth manner. Numerical simulations are used to confirm the presence of these so-called "tango waves" and the dependence of Ca wave speed on the total [Ca]. The original publication is available at www.springerlink.com (Journal of Mathematical Biology

An algorithm for approximate multiparametric convex programming

For multiparametric convex nonlinear programming problems we propose a recursive algorithm for approximating, within a given suboptimality tolerance, the value function and an optimizer as functions of the parameters. The approximate solution is expressed as a piecewise affine function over a simplicial partition of a subset of the feasible parameters, and it is organized over a tree structure for efficiency of evaluation. Adaptations of the algorithm to deal with multiparametric semidefinite programming and multiparametric geometric programming are provided and exemplified. The approach is relevant for real-time implementation of several optimization-based feedback control strategies

Framing Financial Responsibility : An analysis of the limitations of accounting

In organisations, accounting—understood broadly as calculative practices—is claimed to serve as a critical vehicle when introducing forms of individual financial responsibility. Whereas most prior accounting research has been preoccupied with asserting this claim, this paper opens an opportunity to examine the limitations of accounting as a technology of responsibilisation. It does so by moving the empirical focus beyond the borders of people’s work settings and into the private sphere of everyday life, investigating governmental efforts to turn high school students into financially responsible citizens. The analysis, informed by framing theory, reveals that the efficiency of accounting is conditioned by people’s calculative understanding. Hence, in situations where individuals are expected to lack this basic calculative competency, accounting is presumed to be inappropriate as a means of introducing financial responsibility. This has implications for re-considering how the relation between accounting and responsibility is constituted