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We report results of new pair creation experiments using ~100 Joule pulses of the Texas Petawatt Laser to irradiate solid gold and platinum targets, with intensities up to ~1.9 × 1021 W.cm−2 and pulse durations as short as ~130 fs. Positron to electron (e+/e−) ratios >15% were observed for many thick disk and rod targets, with the highest e+/e− ratio reaching ~50% for a Pt rod. The inferred pair yield was ~ few ×1010 with emerging pair density reaching ~1015/cm3 so that the pair skin depth becomes < pair jet transverse size. These results represent major milestones towards the goal of creating a significant quantity of dense pair-dominated plasmas with e+/e− approaching 100% and pair skin depth ≪ pair plasma size, which will have wide-ranging applications to astrophysics and fundamental physics.

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In on-farm studies of sustainable agriculture, farmers often have been classified as sustainable according to their organizational affiliation; self identification; or use or non-use of a particular production practice or input, usually synthetic chemicals. Because this is a great oversimplification, researchers recently have been incorporating several dimensions of sustainability into a composite measure. Typically this is a relative measure of sustainability, with scores assigned by comparing individual farmers 'practices to those used by all farmers. In contrast, in the farmer sustainability index (FSI) presented here, practices are scored according to their inherent sustainability. We report on the development of an FSI in a case study involving 33 production practices used by 85 cabbage farmers in Malaysia. We describe its underlying principles, the procedure and rationale for scoring each sustainability item, and the result of combining the constituent items into a composite index.

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