Coordination environment of [UO2Br4](2-) in ionic liquids and crystal structure of [Bmim](2)[UO2Br4]

The complex formed by the reaction of the uranyl ion, UO22+, with bromide ions in the ionic liquids 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmiml[Tf2N]) and methyl-tributylammonium bis(trifluoromethylsulfonyl)imide ([MeBu3N][Tf2N]) has been investigated by UV-Vis and U L-III-edge EXAFS spectroscopy and compared to the crystal structure of [Bmim](2)[UO2Br4]. The solid state reveals a classical tetragonal bipyramid geometry for [UO2Br4](2-) with hydrogen bonds between the Bmim(+) and the coordinated bromides. The UV-Vis spectroscopy reveals the quantitative formation of [UO2Br4](2-) when a stoichiometric amount of bromide ions is added to UO2(CF3SO3)(2) in both Tf2N-based ionic liquids. The absorption spectrum also suggests a D-4h symmetry for [UO2Br4](2-) in ionic liquids, as previously observed for the [UO2Cl4](2-) congener. EXAFS analysis supports this conclusion and demonstrates that the [UO2Br4](2-) coordination polyhedron is maintained in the ionic liquids without any coordinating solvent or water molecules. The mean U-O and U-Br distances in the solutions, determined by EXAFS, are, respectively, 1.766(2) and 2.821(2)angstrom in [Bmim][Tf2N], and, respectively, 1.768(2) and 2.827(2) angstrom, in [MeBu3N][Tf2N]. Similar results are obtained in both ionic liquids indicating no significant influence of the ionic liquid cation either on the complexation reaction or on the structure of the uranyl species. (C) 2009 Elsevier Ltd. All rights reserved.

An experimental investigation into the influence of user state and environment on fading characteristics in wireless body area networks at 2.45 GHz

Using seven strategically placed, time-synchronized bodyworn receivers covering the head, upper front and back torso, and the limbs, we have investigated the effect of user state: stationary or mobile and local environment: anechoic chamber, open office area and hallway upon first and second order statistics for on-body fading channels. Three candidate models were considered: Nakagami, Rice and lognormal. Using maximum likelihood estimation and the Akaike information criterion it was established that the Nakagami-m distribution best described small-scale fading for the majority of on-body channels over all the measurement scenarios. When the user was stationary, Nakagami-m parameters were found to be much greater than 1, irrespective of local surroundings. For mobile channels, Nakagami-m parameters significantly decreased, with channels in the open office area and hallway experiencing the worst fading conditions.

Nature as historical protagonist: environment and society in pre-industrial England

This article compares chronologies reconstructed from historical records of prices, wages, grain harvests, and population with corresponding chronologies of growing conditions and climatic variations derived from dendrochronology and Greenland ice-cores. It demonstrates that in pre-industrial, and especially late medieval, England, short-term environmental shocks and more enduring shifts in environmental conditions (sometimes acting in concert with biological agencies) exercised a powerful influence upon the balance struck between population and available resources via their effects upon the reproduction, health and life expectancy of humans, crops, and livestock. Prevailing socio-economic conditions and institutions, in turn, shaped society's susceptibility to these environmental shocks and shifts.