Water activity in polyol systems

Water activities of binary and ternary mixtures containing polyols were measured using an electronic hygrometer with temperature ranging from (10 to 35) degrees C. The concentrations of the mixtures varied according to the solubility limit for each polyol (D-sorbitol, D-mannitol, xylitol, meso-erythritol, and glycerol). Results were compared with the group contribution-based models ASOG and UNIFAC. The predictions using parameters from the literature were poor, probably as a consequence of the strongly polar hydroxyl groups bounded to consecutive carbon atoms in the polyol molecule. Better agreement was obtained by readjusting some of the interaction parameters. The data bank used in this procedure included water activity data as well as polyol solubility data taken from the literature. The best results were achieved using the UNIFAC-Larsen model with an average relative deviation of 0.9% for water activity and solubility data.45465466

A hawkmoth crossroads? Species richness, seasonality and biogeographical affinities of Sphingidae in a Brazilian Cerrado

The aim of the study was (1) to describe the biodiversity of the sphingid assemblage in a Cerrado area in the Triangulo Mineiro region, south-east of Brazil; (2) to evaluate the seasonal variations in species composition; (3) to compare the faunistic relationships between the Cerrado biome and adjacent ecosystems; and (4) to analyse the biogeographical pattern of species distribution in the Neotropical region in a historical context. Panga Ecological Station (PES), 30 km south of the city of Uberlandia, and other areas of the Triangulo Mineiro region, Minas Gerais state, south-eastern Brazil. Moth richness and abundance were monitored monthly at the PES from August 2003 to July 2004, with additional collections at this locality in 2001/2002, 2005 and 2006. Complementary moth richness and abundance data were also collected in other areas of the Triangulo Mineiro region. All collections were made using light traps, and the hawkmoths were mounted and identified. Cluster analysis, rarefaction curves and estimators of total species richness were used to compare the Cerrado hawkmoth assemblage with assemblages derived from other surveys in the Neotropics. In total, 61 hawkmoth species were recorded for the study region and their occurrence was markedly seasonal. The hawkmoth assemblage in the study area presented the closest similarity with rain forest areas and with a tropical dry forest area in Central America. The area shared species with both rain forest and seasonally dry tropical forest (SDTF) ecosystems, including supposedly endemic species previously recorded only in the latter areas. Rarefaction curves and estimators of the total number of species showed species richness to be comparable with other highly diverse forest areas in the Neotropics, such as the Brazilian Amazon and Costa Rica. This short-term study is the first systematic survey of hawkmoths in the Cerrado. It has recorded around 22% of the South American fauna and highlighted the high species richness of the region, which compares favourably with that in other rain forest ecosystems. The survey indicates high regional diversity, and has shown that the Cerrado harbours a hawkmoth fauna comprising both rain forest elements, probably distributed along humid gallery forest corridors, and SDTF elements, supporting the idea of a historical Pleistocene arc connecting the Caatinga domain and other seasonal dry forest areas across the Cerrado region.364662674Hovanitz Memorial Award Program [520872/96-7]Hovanitz Memorial Award Program [520872/96-7

The chromium spin density wave: magnetic X-ray scattering studies with polarisation analysis

We report on X-ray magnetic diffraction studies of the spin density wave antiferromagnetism formed in the conduction electron band of chromium. Non-resonant X-ray magnetic scattering was used to directly determine that chromium has zero orbital magnetisation. Furthermore, the azimuthal dependence of this scattering provides unique evidence that chromium forms a linearly polarised wave. In the vicinity of the K absorption edge, resonant X-ray magnetic scattering was observed. A consistent model of the magnetic scattering has been derived from the resonant and non-resonant magnetic amplitudes. The enhancement of the magnetic intensity arises primarily from dipole transitions from the core Is level to 4p states. Quadrupole transitions to the magnetic 3d states are essentially non-existent due to their sensitivity to land the absence of) orbital moment. This effect is predicted from atomic considerations of the 3d(5) (L = 0) transition metal ions.201192