Internal currents in response to a load change during fuel cell start-up

The transient response of proton exchange membrane fuel cells during start-up is an important issue for backup power systems. These require a very short start-up time which limits the use of batteries during a blackout. In this study the fuel cell was initially inerted with nitrogen at the cathode and thus the start-up procedures occurred in two stages: gas supply in open-circuit and load connection. The influence of the current time-profile, the cell voltage at the connection and the gas flow rates on the voltage variation were investigated using a segmented fuel cell permitting the measurements of the internal local currents. We found that the voltage during the filling of the cathode is not sufficient to determine which fraction of the cathode was filled with oxygen. In the case of a step change in current, the start-up time decreases as the voltage at the moment the cell is connected increases. In response to a ramp, the asymptotic power value is reached quickly.     

Generalized Thin-Plate Spline Warps

The Thin-Plate Spline warp has been shown to be a very effective parameterized model of the optic flow field between images of various types of deformable surfaces, such as a paper sheet being bent. Recent work has also used such warps for images of a smooth and rigid surface. Standard Thin-Plate Spline warps are however not rigid, in the sense that they do not comply with the epipolar geometry. They are also intrinsically affine, in the sense of the affine camera model, since they are not able to simply model the effect of perspective projection.     

Organo‐ and Iron(0) Catalysis for an Enantioselective Michael Addition–Hemiketalization–Fragmentation Sequence to Protected ω‐Hydroxy‐nitroketones

By combining an organocatalyzed Michael addition of 1,3‐diketones to hydroxy‐nitroolefins with a subsequent, innovative iron(0)‐catalyzed fragmentation, key enantioenriched ketones possessing additional nitro and protected alcohol functions could efficiently be prepared under excellent enantiocontrol (typically 95% ee). The reaction was made possible by the discovery that photochemical activation of iron pentacarbonyl [Fe(CO)₅], a cheap widely available complex, efficiently catalyzed a Claisen‐type fragmentation under mild conditions, avoiding decomposition of the intermediates and products.

     

Microstructure and textural evolution during cold rolling and annealing of commercially pure titanium sheet

The effects of cold rolling and annealing on the microstructure and textural evolution of a commercially pure titanium (CP-Ti) sheet were investigated. Electron backscatter diffractometry demonstrates that the deformation during rolling is accommodated by twinning and slip. Additionally, twinning is the dominant deformation mechanism when the cold rolling reduction is less than 40%. During rolling, $\left\{11\overline{2}2\right\}〈11\overline{2}\overline{3}〉$ contraction twinning (CT) and $\left\{10\overline{1}2\right\}〈10\overline{1}1〉$ extension twinning (ET) are activated. And, the intensity of the (0002) pole along the ND gradually increases with increasing deformation. During annealing, the fraction of low angle grain boundaries (LAGBs) and the intensity of the (0002) pole along the ND gradually decrease slightly with increasing annealing time, while twinning lamellae disappear rapidly. When the annealing time reaches 60 min, 20% cold-rolled sheet recrystallizes almost completely.     

In situ observation of plaster microstructure evolution during thermal loading

Gypsum microstructural evolution at elevated temperatures has been characterized in situ by environmental scanning electron microscopy and high‐temperature X‐ray tomography. As temperature increases, the observed changes in gypsum crystal morphology are related to the consequences of water loss that leads to crystal reorganization in order to minimize the specific surface. The influence of environmental scanning electron microscopy experimental conditions on the mechanisms observed is also discussed. High‐temperature X‐ray tomography gives quantitative information on porosity evolution with thermal loading. The results obtained are successfully correlated with macroscopic shrinkage measurements performed during dilatometry tests. Copyright © 2016 John Wiley & Sons, Ltd.     

Next-Generation Imaging:New Insights from Multicolor Microscopy in Liver Biology and Disease

1.Introduction Our current understanding of the complex biology of solid organs,such as the liver,has been tremendously advanced by a wide variety of methodolog...     

Fast <Emphasis Type="Italic">In Situ</Emphasis> X-Ray Microtomography Observations of Solidification and Semisolid Deformation of Al-Cu Alloys

The aim of this paper is to report recent results concerning the microstructure evolution observed by continuous in situ x-ray microtomography in Al-Cu alloys during various treatments. These treatments include solidification and tensile deformation in the semisolid state both in solidification and in isothermal conditions. During solidification, x-ray microtomography allows measurement of various microstructure parameters and characterization of the physical mechanisms occurring at the scale of the dendrites. During deformation, liquid flow towards the deformed zone can be observed and quantified together with pore and crack formation in liquid films. These observations are discussed with reference to the formation of defects during solidification.