Deformation of Silica Aerogel During Fluid Adsorption

Aerogels are very compliant materials - even small stresses can lead to large deformations. In this paper we present measurements of the linear deformation of high porosity aerogels during adsorption of low surface tension fluids, performed using a Linear Variable Differential Transformer (LVDT). We show that the degree of deformation of the aerogel during capillary condensation scales with the surface tension, and extract the bulk modulus of the gel from the data. Furthermore we suggest limits on safe temperatures for filling and emptying low density aerogels with helium.Comment: 8 pages, 5 figures, submitted to PR

Hydrocarbon degradation, plant colonization and gene expression of alkane degradation genes by endophytic Enterobacter ludwigii strains

The genus Enterobacter comprises a range of beneficial plant-associated bacteria 2 showing plant growth-promotion. Enterobacter ludwigii belongs to the Enterobacter 3 cloacae complex and has been reported to include human pathogens but also plant-4 associated strains with plant beneficial capacities. To assess the role of Enterobacter 5 endophytes in hydrocarbon degradation, plant colonization, abundance and expression of 6 CYP153 genes in different plant compartments, three plant species (Italian ryegrass, 7 birdsfoot trefoil and alfalfa) were grown in sterile soil spiked with 1% diesel and 8 inoculated with three endophytic Enterobacter ludwigii strains. Results showed that all 9 strains were capable of hydrocarbon degradation and efficiently colonized the 10 rhizosphere and plant interior. Two strains, ISI10-3 and BRI10-9, showed highest 11 degradation rates of diesel fuel up to 68% and performed best in combination with Italian 12 ryegrass and alfalfa. All strains expressed the CYP153 gene in all plant compartments, 13 indicating an active role in degradation of diesel in association with plants.Higher Education Commission of Pakistanhttp://www.sciencedirect.com/science/journal/0269749

Differential drought-induced modulation of ozone tolerance in winter wheat species

Recent reports challenge the widely accepted idea that drought may offer protection against ozone (O3) damage in plants. However, little is known about the impact of drought on the magnitude of O3 tolerance in winter wheat species. Two winter wheat species with contrasting sensitivity to O3 (O3 tolerant, primitive wheat, T. turgidum ssp. durum; O3 sensitive, modern wheat, T. aestivum L. cv. Xiaoyan 22) were exposed to O3 (83ppb O3, 7h d−1) and/or drought (42% soil water capacity) from flowering to grain maturity to assess drought-induced modulation of O3 tolerance. Plant responses to stress treatments were assessed by determining in vivo biochemical parameters, gas exchange, chlorophyll a fluorescence, and grain yield. The primitive wheat demonstrated higher O3 tolerance than the modern species, with the latter exhibiting higher drought tolerance than the former. This suggested that there was no cross-tolerance of the two stresses when applied separately in these species/cultivars of winter wheat. The primitive wheat lost O3 tolerance, while the modern species showed improved tolerance to O3 under combined drought and O3 exposure. This indicated the existence of differential behaviour of the two wheat species between a single stress and the combination of the two stresses. The observed O3 tolerance in the two wheat species was related to their magnitude of drought tolerance under a combination of drought and O3 exposure. The results clearly demonstrate that O3 tolerance of a drought-sensitive winter wheat species can be completely lost under combined drought and O3 exposure