Compression induced shear damage in brittle solids by scattered microcracking

Failure observation and numerical analysis were conducted to understand how shear damage develops in brittle solids under biaxial compression. A biaxial compression often induces shear damaged in brittle solids, which is preceded by a formation of huge number of array cracks. Cracks in the array appeared gradually as applied compression increased. They were almost similar in shape; gently curved but were possible to approximate a troop of straight cracks almost parallel to each other without loss of essential characteristics. Under a uniaxial compression, a brittle material tends to fail exhibiting a crack growth almost parallel to the loading axis. In this situation, the crack propagates rather in a stable fashion since the stress intensity factor at crack tip generally decreases with crack extension. Under a biaxial compression, however, such a stable crack growth is strongly inhibited. Consequently, an array of microcracks often appears as a presage of the macroscopic shear failure. A mechanism of the appearance of damaged zone with increase of applied compression was discussed using a scattered cracking model. It was found that each crack composing the damaged zone has a possibility to open due to crack-to-crack interaction and a localized tensile stress appeared both in the interior and in the exterior of the damaged zone. The localized tension appeared in the interior of the damaged zone may increase a crack density, while that appeared in the exterior of the damaged zone would bring an enlargement of the damaged zone

Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment

Biodiversity is rapidly declining1, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes4 across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades

A hydrogen-driven biocatalytic approach to recycling synthetic analogues of NAD(P)H

We demonstrate a recycling system for synthetic nicotinamide cofactor analogues using a soluble hydrogenase with turnover number of >1000 for reduction of the cofactor analogues by H2. Coupling this system to an ene reductase, we show quantitative conversion of N-ethylmaleimide to N-ethylsuccinimide. The biocatalyst system retained >50% activity after 7 h