Liquid phase sintering and oxidation resistance of WC–Ni–Co–Cr cemented carbides

Fully dense WC–Ni–Co–Cr alloys have been consolidated via sinter HIP processing. Dilatometric tests show that shrinkage undergoes several accelerations and decelerations during heating, a phenomenon likely associated to the heterogeneous distribution of Cr in the binder phase. WC grain growth follows trends similar to those described for WC–Co hardmetals, increasing with the C activity and the amount of liquid phase of the cermets. Finally, the oxidation resistance of WC–Ni–Co–Cr cemented carbides is observed to improve as the metal content increases and the C content decreases. In both cases, the oxide layers present a higher proportion of (Co, Ni)WO₄ tungstates. The oxide scales formed on compositions with low metal content contain a higher amount of WO₃ oxide.     

Cascading failures in power grids

Power grids are complex dynamical systems, and because of this complexity it is unlikely that we will completely eliminate blackouts. However, there are things that can be done to reduce the average size and cost of these blackouts. In this article we described two strategies that hold substantial promise for reducing the size and cost of blackouts. Both "reciprocal altruism" and "survivability" respect the necessarily decentralized nature of power grids. Both strategies can be implemented within the context of the existing physical infrastructure of the power grids,which is important because dramatic changes to the physical infrastructure are prohibitively expensive. However, additional engineering and innovation will be needed to bring strategies such as these to implementation and to create power grids with smaller, less costly blackouts.     

Rheology of whey protein isolate-xanthan mixed solutions and gels. Effect of pH and xanthan concentration

Flow properties at pH 5.5-7.5 of whey protein isolate (WPI)-xanthan solutions containing 0-0.5 w/w% xanthan were studied by viscosimetry, although rigidity and fracture properties of the corresponding heat-set gels (90°C, 30 min) were determined by uniaxial compression. All the studied solutions displayed generalized shearthinning flow behaviour. Synergistic WPI-xanthan interactions has been revealed by observing that rheological parameters [σ_msf, K, n, η (γ)] characterizing blends were larger than those calculated from the two separated solutions. Such a behaviour was attributed to segregative phase separation of whey proteins and xanthan. Effects of xanthan on WPI-xanthan gel properties both depended on pH and xanthan concentration. Simultaneous increased xanthan concentration and decreased pH inhibited gelation of WPI-xanthan blends. Regarding gel strength, synergistic WPI-xanthan interactions were observed at pH >7.0 and low xanthan concentration (0.05 or 0.1 w/w%). Antagonism between the two macromolecules occurred at low xanthan concentration and pH ≤6.5, and high xanthan concentration (0.2 or 0.5 w/w%) at all pH tested. Low xanthan concentration rendered mixed gels more brittle than protein gels, and high xanthan concentration decreased pH effects on gel stress-strain relationships. The balance between strong thermal aggregation of concentrated whey proteins - in presence of incompatible xanthan -, high viscosity of blends and repulsive surface forces of protein molecules was thought to be at the origin of WPI-xanthan gel mechanical properties.     

Morphology of electromigration-induced damage and failure in Al alloy thin film conductors

Distinct morphologies of electromigration-induced voids and failures are shown for Al, Al-2%Cu, and Al-2%Cu-l% Si narrow (1–6 μm) unpassivated thin film conductors. SEM and TEM images typically show large non-fatal voids and narrow slit-like open circuit failures for all film conditions and accelerated test conditions. Evidence for transgran-ular slit failures is shown for 1.33 μm wide conductors. A simple model for void growth is presented which accounts for the void morphologies seen. The observed morphologies and the results of void growth modelling suggest that slit voids nucleate after other voids and rapidly produce failure. These conclusions are discussed in terms of ‘classical’ models for electromigration failure processes and resistance and noise power monitoring techniques.     

Direct extraction of nonlinear FET I-V functions from time domainlarge signal measurements

A simplified method for extracting two port nonlinear field effect transistor current sources from time domain microwave voltage and current waveform measurements is presented. This method is based on the use of an appropriate reflective load-pull termination to ensure that the output voltage is 180° out of phase with the input voltage     

Passive Shim Design and a Shimming Approach for Biplanar Permanent Magnetic Resonance Imaging Magnets

This paper presents a new passive shim design method and a novel shimming procedure to correct the magnetic field inhomogeneities generated by C-shape permanent biplanar magnetic resonance imaging magnets. The method expresses the shim distribution as a sum of orthogonal functions multiplied by unknown amplitudes. The oscillating modes of the shim magnetization-thickness function are normalized within a finite disk. By minimizing the shim set weight and constraining the magnetization-thickness function, the method produces a continuous map of the required shim contribution. The map defines the shim shape and a discrete process then determines the regions where no shim contributions are needed. With this methodology, passive shims capable of generating magnetic field harmonics with minimal impurities and ferro-shim pieces can be generated. The paper reports a study of magnetic coupling among the iron pieces and its influence over the magnetic field harmonics of linear and nonlinear iron, and demonstrates that the exclusion of the magnetic coupling in the shimming process produces an unacceptable error in the final shimmed field homogeneity. The proper selection and arrangement of individual shim sizes produces a better conditioned field source matrix and hence improves the design. A number of examples show that the new method can effectively cancel target impurity harmonics while controlling high-order harmonics.     

New polymer electrolytes based on ether sulfate anions for lithium polymer batteries: Part I. Multifunctional ionomers: Conductivity and electrochemical stability

New lithium conducting ionomers based on commercial polyethers were synthesized by chemical modification in order to incorporate not only the anionic function on the polymer backbone but also polar aprotic and (or) protic groups improving both the salt dissociation and the anion-solvating ability of the multifunctional copolymers. The choice of environmentally friendly rather than perfluorinated anionic functions did not appear to compromise for the ionic conductivity. Lastly, the preliminary results on the use of an electrochemically stable and relatively cheap additive sparteine appear promising and could be generalized to a variety of polymer electrolytes for lithium batteries.     

Atherogenic effect of oxidized products of cholesterol

Cholesterol under certain in vitro and possibly in vivo conditions may be oxidized to oxysterols, which are suspected of being initiators of atherosclerotic plaques. Oxysterols inhibit HMG-CoA reductase activity resulting in a decreased cholesterol concentration in the cell membrane, which leads to endothelial membrane injury and probable premature cell death. Exogenous oxidation of cholesterol in human tissues under certain unusual conditions is highly probable. Dietary oxysterols are absorbed in the gastrointestinal tract and are selectively transported by the athrogenic lipoproteins LDL and VLDL. The oxysterols cholestanetriol and 25-OH cholesterol have been shown to be atherogenic. Oxysterols are commonly found in dried egg products, powdered milk, cheeses and in a variety of high temperature dried animal products.     

Extrusion: An environmentally friendly process for PEMFC membrane elaboration

The paper deals with the use of extrusion to process PEMFC filled and unfilled membranes. Several routes including the sulfonation of filled and unfilled extruded membranes and the extrusion of filled and unfilled ionomers are reported. Thanks to the use of selected water-soluble aid process plasticizers, acid and alkaline forms of sulfonated polyethersulfone were, for the first time, successfully extruded. The extrusion process did not lead to any degradation of the ionomer performances. Decreasing the membrane cost while using environmentally friendly elaboration conditions, it should be helpful to an industrial production. In addition, avoiding filler sedimentation it should allow homogeneous composite membranes to be obtained.