Gallium/aluminum interdiffusion between n-GaN and sapphire

The distribution profiles of Ga and Al near the interface of the n-GaN/sapphire system were measured by x-ray energy dispersive spectroscopy (XEDS). The results are obtained by the corrected XED spectra. First, the gallium diffusing into the sapphire substrate obeys the law of remainder probability function. The gallium diffusion coefficient DGa=2.30×10-13 cm2s-1 was calculated by theoretical fitting. Second, the diffusion is associated with the GaN growth process at high temperature. Compared to the diffusion of Ga into the sapphire substrate, much less Al antidiffusion from the substrate to the GaN film, with diffusion coefficient DA1 approximately equal to 4.8×10-15 cm2s-1, was observed in the film. © 1998 American Institute of Physics.published_or_final_versio

Down-regulation of the caffeic acid \u3cem\u3eO\u3c/em\u3e-methyltransferase gene in switchgrass reveals a novel monolignol analog

Background Down-regulation of the caffeic acid 3-O-methyltransferase EC 2.1.1.68 (COMT) gene in the lignin biosynthetic pathway of switchgrass (Panicum virgatum) resulted in cell walls of transgenic plants releasing more constituent sugars after pretreatment by dilute acid and treatment with glycosyl hydrolases from an added enzyme preparation and from Clostridium thermocellum. Fermentation of both wild-type and transgenic switchgrass after milder hot water pretreatment with no water washing showed that only the transgenic switchgrass inhibited C. thermocellum. Gas chromatography–mass spectrometry (GCMS)-based metabolomics were undertaken on cell wall aqueous extracts to determine the nature of the microbial inhibitors. Results GCMS confirmed the increased concentration of a number of phenolic acids and aldehydes that are known inhibitors of microbial fermentation. Metabolomic analyses of the transgenic biomass additionally revealed the presence of a novel monolignol-like metabolite, identified as trans-3, 4-dimethoxy-5-hydroxycinnamyl alcohol (iso-sinapyl alcohol) in both non-pretreated, as well as hot water pretreated samples. iso-Sinapyl alcohol and its glucoside were subsequently generated by organic synthesis and the identity of natural and synthetic materials were confirmed by mass spectrometric and NMR analyses. The additional novel presence of iso-sinapic acid, iso-sinapyl aldehyde, and iso-syringin suggest the increased activity of a para-methyltransferase, concomitant with the reduced COMT activity, a strict meta-methyltransferase. Quantum chemical calculations were used to predict the most likely homodimeric lignans generated from dehydration reactions, but these products were not evident in plant samples. Conclusions Down-regulation of COMT activity in switchgrass resulted in the accumulation of previously undetected metabolites resembling sinapyl alcohol and its related metabolites, but that are derived from para-methylation of 5-hydroxyconiferyl alcohol, and related precursors and products; the accumulation of which suggests altered metabolism of 5-hydroxyconiferyl alcohol in switchgrass. Given that there was no indication that iso-sinapyl alcohol was integrated in cell walls, it is considered a monolignol analog. Diversion of substrates from sinapyl alcohol to free iso-sinapyl alcohol, its glucoside, and associated upstream lignin pathway changes, including increased phenolic aldehydes and acids, are together associated with more facile cell wall deconstruction, and to the observed inhibitory effect on microbial growth. However, iso-sinapyl alcohol and iso-sinapic acid, added separately to media, were not inhibitory to C. thermocellum cultures

Attribution of extreme precipitation in the lower reaches of the Yangtze River during May 2016

May 2016 was the third wettest May on record since 1961 over central eastern China based on station observations, with total monthly rainfall 40% more than the climatological mean for 1961–2013. Accompanying disasters such as waterlogging, landslides and debris flow struck part of the lower reaches of the Yangtze River. Causal influence of anthropogenic forcings on this event is investigated using the newly updated Met Office Hadley Centre system for attribution of extreme weather and climate events. Results indicate that there is a significant increase in May 2016 rainfall in model simulations relative to the climatological period, but this increase is largely attributable to natural variability. El Ni ̃no years have been found to be correlatedwith extreme rainfall in the Yangtze River region in previous studies—the strong El Ni ̃no of 2015–2016 may account for the extreme precipitation event in 2016. However, on smaller spatial scales we find that anthropogenic forcing has likely played a role in increasing the risk of extreme rainfall to the north of the Yangtze and decreasing it to the south

Magnetic nanobraids of iron-doped amorphous silica

Using silicon, iron oxide, and graphite powders as source materials, braid-like nanostructures of iron-doped amorphous silica were fabricated by vapor-phase transport. Each braid was composed of a bunch of entangled nanowires with uniform size. The formation of the nanobraids was mainly due to simultaneous nucleation in a vapor–liquid–solid process. Magnetic measurement showed that the iron-doped silica nanobraids were ferromagnetic at room temperature.Published versio

Magnetic nanobelts of iron-doped zinc oxide

Magnetic nanobelts of iron-doped zinc oxide were fabricated by vapor–phase transport using zinc oxide, iron oxide, and graphite as source materials. The nanobelts grew mainly along [1010] orientation and enclosed by ±(0001) and ±(1210) surfaces. The measurements of x-ray diffraction, energy-dispersive x-ray spectroscopy, and high-resolution transmission electron microscopy demonstrated that iron was doped into the nanobelts. As a result, the nanobelts were magnetic.Published versio