Scrutinizing Gypsum Board Thermal Performance at Dehydration Temperatures

ABSTRACT: This article investigates the thermal performance of gypsum boards in the dehydration temperature region, where pronounced chemical reactivity is anticipated. Gypsum board samples were gradually heated up to 3008C, using a low heating rate. Temperature measurements at pre-selected board locations indicated three distinct stages of gypsum dehydration; free moisture evaporation, transformation of calcium sulfate dihydrate to calcium sulfate hemi-hydrate and of calcium sulfate hemi-hydrate to calcium sulfate anhydrate. Physical properties of the gypsum board sample, that is density, specific heat, and thermal conductivity, were measured as a function of the dehydration temperature range. Results suggested that the thermal conductivity of the calcium anhydrate sulfate is higher than that of the hemi-hydrate, despite the fact that gypsum porosity increases during the dehydration process. Based on the experimental results, correlations for the thermal conductivity and the dehydration energy as a function of the mass loss during the dehydration process and the initial water content of the gypsum board, respectively, were obtained. KEY WORDS: gypsum, dehydration energy, calcination, thermal properties, conductivity. *Author to whom correspondence should be addressed

Home range and habitat selection of Long-eared Owls (Asio otus) in Mediterranean agricultural landscapes (Crete, Greece)

The Long-eared Owl (Asio otus) in Crete (Greece) is a common agricultural species affected by the recent changes in agro-forestry systems. Concrete studies of habitat selection are needed in order to improve our knowledge of its foraging behaviour in managed rural landscapes. In the present study, we analysed the home range size and habitat selection of 11 Long-eared Owls inside olive groves in the plain of central Crete using radio tracking data and remote sensing images. Six nominal scale and 11 landscape scale predictors were used for habitat selection analysis, using a maximum entropy approach. Home range size ranged between 337 and 969 ha while a 52% of home range overlap was observed suggesting that Long-eared Owls do not defend hunting territories. At the nominal scale, distance to potential roosts (trees) was the most important contributor to model performance, followed by vegetation heterogeneity. Furthermore, local heterogeneity of greenness was a better predictor than simply greenness at the presence location. At the landscape scale the amount of habitat openness significantly improved model performance. Incorporating landscape heterogeneity improved habitat selection prediction compared to using only discrete land cover classification. Results of our study pinpoint that although Long-eared Owls exhibit a wide range of habitat tolerance, they prefer mixed habitat conditions avoiding particularly open areas or dense olive plantations. The research has implications in the face of new reforms of European Common Agricultural policy which emphasised the importance of landscape structure in preserving biodiversity in agricultural areas of Europe

Interplay of index contrast with periodicity in polymer photonic crystals

We report how the strength of resonant Bragg reflection from polymeric photonic crystals (polymer opals) varies linearly with the refractive-index contrast, n, in contrast to the quadratic buildup of Fresnel reflections scaling as (Δn)2. This occurs due to the interplay of disorder and periodicity, in agreement with a simple 1-dimensional periodic model. Goniometry experiments show that opal films exhibit cones of resonantly scattered light, which extend to ±20° angular deviation from the specular direction. The intensity of the scattering cones varies super-linearly with n. Such medium contrast photonic crystals are of significant interest for understanding structural colors exhibited in nature, by structures with inherent disorder. © 2011 American Institute of Physics