Although theory established the necessary conditions for diversification in temporally heterogeneous environments, empirical evidence remains controversial. One possible explanation is the difficulty of designing experiments including the relevant range of temporal grains and the appropriate environmental trade-offs. Here, we experimentally explore the impact of the grain on the diversification...

This investigation was done in order to study the response of grain yield and yield components of bread wheat cultivars to drought stress in western Iran in 2008-2009. The main plots were levels of drought stress (full irrigation, stress at early stem elongation, flowering and grain filling stages) and subplots were five cultivars (Chamran, Dez and Verinak). The results indicated that the effec...

Grain boundary motion may be accompanied with vacancy generation [1–4]. A typical case where a moving grain boundary produces vacancies is in primary recrystallisation, when the growth of a recrystallised grain at the cost of a grain with a large dislocation density involves release of excess free volume. Vacancies are also generated during grain growth, when the total volume of the grain bound...

The occurence of polygonal structures is widespread in nature 1]. Extensive investigations on the statistics of two-dimensional networks have been performed for biological tissues 2, 3], clusters of metal grains 4, 5], systems of soap bubbles 6, 7, 8], emulsion lattices 9], gas bubbles in Lang-muir monolayers 10], magnetic froth 11] or convective patterns in hydrody-namics 12, 13, 14]. The stro...

^Smithsonian Tropical Research Institute, Box 2072, Balboa, Republic of Panama ^Archaeobiology Program, Department of Anthropology, National Museum of Natural History, Smithsonian Institution, Washington DC 20560, USA ^Department of Anthropology, Peabody Museum, Harvard University, 11 Divinity Avenue, Cambridge, Massachusetts 02130, USA ^Institute of Archaeology, University of Haifa, Mount Carm...