Thermal hazards related to the use of potassium and sodium methoxides in the biodiesel industry

The introduction of sodium and potassium methoxides in processes leading to biodiesel production has triggered several questions about their stability under actual biofuel manufacturing conditions. In most biodiesel production facilities, basic homogenous catalysis is obtained through the introduction of caustic potash (KOH) or caustic soda (NaOH) in the reactor. In this process, the hydroxides are converted into their corresponding methoxide forms (CH₃OK/Na), which then become the actual catalysts in the reactor. Supplying the actual catalyst directly, instead of the low cost hydroxides, may offer several advantages, but may also introduce new hazards that deserve further characterisation work. From a review of the available literature, it was found that very little was known about the thermal decomposition properties of these methoxides. Therefore, as a starting point, l’Institut National de l’Environnement Industriel et des Risques (France) and the Canadian Explosives Research Laboratory (Canada) have recently undertaken a joint effort to better characterise their thermal behaviour. This was achieved by means of a variety of calorimetric techniques including differential scanning calorimetry, accelerating rate calorimetry and ‘large scale’ thermogravimetry–differential thermal analysis. It was found that these chemicals can become self-reactive close to room temperature under specific physical conditions.     

Fluorescent Properties of the Amidinophenylporphyrins Interacting with DNA

5,10,15,20‐Tetrakis(4‐amidinolphenyl)porphyrin, its Zn complex and amidinolphenyl bispophyrin interacting with calf thymus DNA were investigated by fluorescence emission spectra and fluorescence life time measurements were also shown. The binding modes of these compounds were recorded and lifetimes of luminescence were measured as a function of the nature to understand the interaction with DNA. The results suggest those amidinoporphyrins are promising new photodynamic therapeutic agents.     

Numerical Algorithms for Network Modeling of Yield Stress and other Non-Newtonian Fluids in Porous Media

Many applications involve the flow of non-Newtonian fluids in porous, subsurface media including polymer flooding in enhanced oil recovery, proppant suspension in hydraulic fracturing, and the recovery of heavy oils. Network modeling of these flows has become the popular pore-scale approach for understanding first-principles flow behavior, but strong nonlinearities have prevented larger-scale modeling and more time-dependent simulations. We investigate numerical approaches to solving these nonlinear problems and show that the method of fixed-point iteration may diverge for shear-thinning fluids unless sufficient relaxation is used. It is also found that the optimal relaxation factor is exactly equal to the shear-thinning index for power-law fluids. When the optimal relaxation factor is employed it slightly outperforms Newton??s method for power-law fluids. Newton-Raphson is a more efficient choice (than the commonly used fixed-point iteration) for solving the systems of equations associated with a yield stress. It is shown that iterative improvement of the guess values can improve convergence and speed of the solution. We also develop a new Newton algorithm (Variable Jacobian Method) for yield-stress flow which is orders of magnitude faster than either fixed-point iteration or the traditional Newton??s method. Recent publications have suggested that minimum-path search algorithms for determining the threshold pressure gradient (e.g., invasion percolation with memory) greatly underestimate the true threshold gradient when compared to numerical solution of the flow equations. We compare the two approaches and reach the conclusion that this is incorrect; the threshold gradient obtained numerically is exactly the same as that found through a search of the minimum path of throat mobilization pressure drops. This fact can be proven mathematically; mass conservation is only preserved if the true threshold gradient is equal to that found by search algorithms.     

Depth‐integrated free‐surface flow with a two‐layer non‐hydrostatic formulation

This paper presents the derivation of a depth‐integrated wave propagation and runup model from a system of governing equations for two‐layer non‐hydrostatic flows. The governing equations are transformed into an equivalent, depth‐integrated system, which separately describes the flux‐dominated and dispersion‐dominated processes. The depth‐integrated system reproduces the linear dispersion relation within a 5 error for water depth parameter up to kd = 11, while allowing direct implementation of a momentum conservation scheme to model wave breaking and a moving‐waterline technique for runup calculation. A staggered finite‐difference scheme discretizes the governing equations in the horizontal dimension and the Keller box scheme reconstructs the non‐hydrostatic terms in the vertical direction. An semi‐implicit scheme integrates the depth‐integrated flow in time with the non‐hydrostatic pressure determined from a Poisson‐type equation. The model is verified with solitary wave propagation in a channel of uniform depth and validated with previous laboratory experiments for wave transformation over a submerged bar, a plane beach, and fringing reefs. Copyright © 2011 John Wiley & Sons, Ltd.     

Multi-layer ambipolar light-emitting organic field-effect transistors

Mutli-layer light-emitting organic field-effect transistors (OLETs) are shown to have high internal quantum efficiencies approaching 5%, a value much higher than the conventional organic light-emitting diodes (OLEDs). This work re-examines some data reported in the literature on OLETs and put forward a model that explains the charge transport and light emission process. Our analyses suggest that the reported improvements on the internal quantum efficiency of OLETs are directly linked to charge recombination and light emission and is independent of the drain-source current as well as the gate-induced charge density in the accumulation layer. Such independence allows the internal quantum efficiency to increase as the drain-source current decreases. The process differs from the charge transport in OLEDs where recombination and light emission are directly tied to the injected space charge densities thereby preventing the internal quantum efficiency of OLEDs to increase even when the device current is lowered.