ON COMPARISONS BETWEEN COMPUTED AND OBSERVED GRAIN BOUNDARY STRUCTURES AND PROPERTIES IN METALS

A detailed assessment is given of the extent to which agreement has been obtained between experimentally observed and calculated structures and/or properties of grain boundaries in metals. All of the calculations employed pair-wise interaction models. Published work as well as new results obtained by the authors are cited. Topics include : boundary "width" ; primary and secondary relaxations (i.e., grain boundary dislocations) ; magnitude of the boundary energy ; lattice translations across the boundary and atomic positions in the boundary core ; and fast diffusion in boundaries. It is concluded in general that the pair-potential modeling has been a valuable tool in grain boundary research and has often produced detailed results which are in at least semi-quantitative agreement with observations. However, in some cases the agreement is poor and, as might be expected, it is clear that the technique is not capable of producing realistic results in all cases. Various problems are pointed out and discussed

Temperature and prey capture : opposite relationships in two predator taxa

1. All other things equal, predator capture rates are expected to depend on encounter rate with prey, prey escape capability (including prey defences), and on predator agility. Ectotherm predators and their prey both respond to increasing temperature by increased activity, i.e. predators increase their search area and prey may enhance their escape capability. This means that, as temperature changes, the ability of a predator to catch prey will decrease, increase, or remain unchanged depending on the relative effect of temperature on predator and prey. Their responses may further be differentially moulded by light conditions depending on whether the predator is diurnally or nocturnally active. It was hypothesised that flying Diptera are vulnerable to carabid beetles only at low temperatures and over the full temperature range for spiders because carabids, in contrast to spiders, are not built to catch swiftly moving prey. 2. The first experiment examined the spontaneous locomotor activity of the predators and of fruit flies at different temperatures (5, 10, 15, 20, 25, and 30 degrees C) and light conditions (light, dark). A second experiment examined the effect of temperature and light on the predation rate of two carabid beetles (Pterostichus versicolor and Calathus fuscipes) and two spiders (Clubiona phragmitis and Pardosa prativaga) using fruit flies (Drosophila melanogaster) as prey. 3. All four predators and the fruit fly increased their locomotory activity at higher temperatures. Activity of the carabid beetles peaked at intermediate temperatures; spiders and fruit flies were most active at the highest temperatures. Predation rate of the spiders increased with temperature whereas the beetles caught flies only at low temperatures (5 and 10 degrees C). 4. Diurnal variation in temperature may bring different prey groups within the set of potential prey at different times of the day or at different seasons. The ability of many carabid beetles to forage at low temperatures may have nutritional benefits and increases the diversity of interactions in terrestrial food webs