Stable calculation of Gaussian-based RBF-FD stencils

Traditional finite difference (FD) methods are designed to be exact for low degree polynomials. They can be highly effective on Cartesian-type grids, but may fail for unstructured node layouts. Radial basis function-generated finite difference (RBF-FD) methods overcome this problem and, as a result, provide a much improved geometric flexibility. The calculation of RBF-FD weights involves a shape parameter $\epsilon$. Small values of $\epsilon$ (corresponding to near-flat RBFs) often lead to particularly accurate RBF-FD formulas. However, the most straightforward way to calculate the weights (RBF-Direct) becomes then numerically highly ill-conditioned. In contrast, the present algorithm remains numerically stable all the way into the $\epsilon \to 0$ limit. Like the RBF-QR algorithm, it uses the idea of finding a numerically well-conditioned basis function set in the same function space as is spanned by the ill-conditioned near-flat original Gaussian RBFs. By exploiting some properties of the incomplete gamma function, it transpires that the change of basis can be achieved without dealing with any infinite expansions. Its strengths and weaknesses compared with the Contour-Padé, RBF-RA, and RBF-QR algorithms are discussed.     

Impact of bending on flexible metal oxide TFTs and oscillator circuits

Thin‐film circuits on plastic capable of high‐frequency signal generation have important applications in large‐area, flexible hybrid systems, enabling efficient wireless transmission of power and information. We explore oscillator circuits using zinc‐oxide thin‐film transistors (ZnO TFTs) deposited by the conformal, layer‐by‐layer growth technique of plasma‐enhanced atomic layer deposition. TFTs on three substrates—glass, 50‐µm‐thick freestanding polyimide, and 3.5‐µm‐thick spin‐cast polyimide—are evaluated to identify the best candidate for high‐frequency flexible oscillators. We find that TFTs on ultrathin plastic can endure bending to smaller radii than TFTs on commercial 50‐µm‐thick freestanding polyimide, and their superior dimensional stability furthermore allows for smaller gate resistances and device capacitances. Oscillators on ultrathin plastic with minimized parasitics achieve oscillation frequencies as high as 17 MHz, well above the cutoff frequency f_T. Lastly, we observe a bending radius dependence of oscillation frequency for flexible TFT oscillators and examine how mitigating device parasitics benefits the oscillator frequency versus power consumption tradeoff.     

How reasonable are oil production scenarios from public agencies?

According to the long-term scenarios of the International Energy Agency (IEA) and the US Energy Information Administration (EIA), conventional oil production is expected to grow until at least 2030. EIA has published results from a resource-constrained production model which ostensibly supports such a scenario. The model is here described and analyzed in detail. However, it is shown that the model, although sound in principle, has been misapplied due to a confusion of resource categories. A correction of this methodological error reveals that EIA's scenario requires rather extreme and implausible assumptions regarding future global decline rates. This result puts into question the basis for the conclusion that global “peak oil” would not occur before 2030.     

Degradation of low‐density polyethylene during extrusion. VI. Effects of oxygen content in air gap

In our previous papers polyethylene degradation during extrusion coating has been studied and the type of degradation products that are formed and from which step they originate have been discussed. A trained sensory panel has rated the off‐flavor intensities in water samples that have been in contact with various extruded films. Encouraged by the results from these investigations and the documented synergism between aldehydes and ketones and aldehydes and carboxylic acids in off‐flavor intensity, the present study was aimed at confirming the belief that the off‐flavor depends on the presence of oxidative degradation products that have migrated from the film into the water. By decreasing the oxygen concentration in the atmosphere surrounding the extruded melt presence of the highly oxidized species (i.e., carbonyl compounds and carboxylic acids) would decrease and thus the off‐flavor in the water should decline. From this study it could be concluded that the extrusion temperature and the oxygen content in the atmosphere nearest the molten film before quenching are the most important parameters for oxidative degradation and residence time in the air gap influence the amount of oxidative degradation products formed. Furthermore we concluded that the off‐flavor intensity is strongly correlated to the surface oxidation index of the film. Carboxylic acids are present in the water extracts of extruded films and are related to the off‐flavor intensities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1767–1775, 2005     

An efficient method for smart well production optimisation

A method for dynamic optimisation of water flooding with smart wells is presented. The method finds the optimal injection and production rates for every well segment of the smart wells. We formulate the problem as a constrained optimisation problem and state this problem as an augmented Lagrangian saddle point problem. Comparisons are made with a more traditional optimal control method based on solving the adjoint systems of equations. In the examples tested the method obtains same maximum profit while using less computational effort.     

Periodic Control for Improved Low-Temperature Catalytic Activity

The influence of transient changes in the gas composition on the low-temperature activity of a commercial three-way catalyst and a Pt/Al₂O₃ model catalyst has been studied. By introducing well-controlled periodic O₂ pulses to simple gas mixtures of CO or C₃H₆ (in N₂), a substantial improvement of the low temperature oxidation activity was observed for both catalysts. The reason for low activity at low temperatures is normally attributed to self-poisoning by CO or hydrocarbons. The improved catalytic performance observed here is suggested to origin from the transients causing a surface reactant composition that is favourable for the reaction rate.     

Photochemical modification of polymers—photocrosslinking,surface photografting,and lamination

The molecular mechanism, the kinetics and the process development of photocrosslinking of diene elastomers, of high density and low density polyethylenes, and of new linear and dendritic unsaturated polyesters using UV-irradiation are described. New methods for modification of various polymers by surface photografting are presented, the effects on adhesion and adsorption, and the mechanism of the reactions related to the shortlived high energy states of aromatic ketones as initiators are presented and discussed. The development of surface photografting as a new method for UV-initiated lamination of various polymer films and sheets is described, the molecular mechanism and the kinetics of the reactions are discussed, and the mechanical and barrier properties of the laminates are presented.     

Photo-Assisted Processes for Improved Catalytic Activity and Selectivity of Environmentally Harmful Emissions

Photoenhanced activity of several supported noble metal/metal oxide combinations has been explored. Significant activity is observed for supported Pt and Pd samples. Specifically, the so called light-off temperatures for CO oxidation are found to decrease upon illumination. Evidence for a photocatalytic non-thermal mechanism rather than a photo-assisted thermal process is found through the wavelength dependence for CO oxidation on a Pt/alumina catalyst. The difficulty of separating real photocatalytic from other photo-assisted effects in the case of porous samples is discussed.