Numerical Convergence Analysis of the Frank-Kamenetskii Equation.

This work investigates the convergence dynamics of a numerical scheme employed for the approximation and solution of the Frank-Kamenetskii partial differential equation. A framework for computing the critical Frank-Kamenetskii parameter to arbitrary accuracy is presented and used in the subsequent numerical simulations. The numerical method employed is a Crank-Nicolson type implicit scheme coupled with a fourth order spatial discretisation as well as a Newton-Raphson update step which allows for the nonlinear source term to be treated implicitly. This numerical implementation allows for the analysis of the convergence of the transient solution toward the steady-state solution. The choice of termination criteria, numerically dictating this convergence, is interrogated and it is found that the traditional choice for termination is insufficient in the case of the Frank-Kamenetskii partial differential equation which exhibits slow transience as the solution approaches the steady-state. Four measures of convergence are proposed, compared and discussed herein.

Comment on "Atmospheric chemistry of iodine anions: elementary reactions of I-, IO- and IO2- with ozone studied in the gas-phase at 300 K using an ion trap" Teiwes et al., Phys. Chem. Chem. Phys., 2018, 20, 20608.

This Comment describes an analytical solution for the set of differential equations solved numerically in the original article by Teiwes et al.

Ketone Body Acetoacetate Buffers Methylglyoxal via a Non-enzymatic Conversion during Diabetic and Dietary Ketosis.

The α-oxoaldehyde methylglyoxal is a ubiquitous and highly reactive metabolite known to be involved in aging- and diabetes-related diseases. If not detoxified by the endogenous glyoxalase system, it exerts its detrimental effects primarily by reacting with biopolymers such as DNA and proteins. We now demonstrate that during ketosis, another metabolic route is operative via direct non-enzymatic aldol reaction between methylglyoxal and the ketone body acetoacetate, leading to 3-hydroxyhexane-2,5-dione. This novel metabolite is present at a concentration of 10%-20% of the methylglyoxal level in the blood of insulin-starved patients. By employing a metabolite-alkyne-tagging strategy it is clarified that 3-hydroxyhexane-2,5-dione is further metabolized to non-glycating species in human blood. The discovery represents a new direction within non-enzymatic metabolism and within the use of alkyne-tagging for metabolism studies and it revitalizes acetoacetate as a competent endogenous carbon nucleophile.

Digital simulation of chronoamperometry at an electrode within a hemispherical polymer drop containing an enzyme: comparison of a hemispherical with a flat disk electrode.

Current-time and steady state current behaviour was simulated for the cases of a hemispherical and flat inlaid disk electrodes located under a hemispherical polymer drop containing an enzyme which converts a substrate diffusing into the drop into a product that is electroactive at the electrode. As well, a cylindrical electrode with length much greater than its diameter and coated with a layer of polymer/enzyme was treated. The ratio of steady state currents at the hemispherical to the disk electrode is not, as has sometimes been assumed, always equal to π/2; indeed this is only approached for polymer drops with large spillover ratio, that is, having a radius much larger than that of the electrodes. Steady state currents for all electrode geometries (including the cylinder) go through a maximum for some spillover ratio and then approach a constant value for larger spillover ratios. This constant value is the same as that for the diffusion limited current in a semi-infinite medium. For a cylindrical electrode, the steady state current tends towards zero for large spillover ratios.