Science Arts & Métiers (SAM)is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. It has been observed that the penetration depth during laser welding (LW) under vacuum or reduced ambient pressure could be significantly greater than that during welding under atmospheric pressure. Previous explanations of this phenomenon usually limit to specific wavelength laser welding and have difficulties in explaining why the variation will disappear, as the welding speed increases. Here, we propose that this variation is caused by the temperature difference of keyhole wall under variable ambient pressure based on a correct physical description of related processes.A new surface pressure model, dependent on ambient pressure, is proposed for describing the evaporation process during laser material interaction under variable ambient pressure. For laser welding of a 304 stainless steel with 2.0 kW laser power and 3 m/min welding speed, it is shown that the average keyhole wall temperature is around 2900 K under atmospheric pressure, and only around 2300 K under vacuum, which results in significant penetration depth variations. Interestingly, it is also shown that as the welding speed increases, the average temperature of the front keyhole wall gradually rises due to the reduction of the mean incident angle of laser, and the magnitude of this increase is larger in welding under vacuum than under atmospheric pressure. It allows us to explain why the penetration depth improvement decreases to zero with the increase of welding speed.

The debate about poverty and conservation draws mainly on local case studies, particularly of the impacts of protected areas. Although it is clear that local and contingent variables have important effects on the social and economic impacts of protected area establishment, it is not known whether there is a general relationship between national wealth and the area, number and type of protected area designated. Here we conduct such an analysis. Our results suggest that wealthy countries have a larger number of protected areas of smaller size than poorer countries. However, we find few significant relationships between indicators of poverty and the extent of protected areas at a national scale. Our analysis therefore confirms that relationships between poverty and conservation action are dynamic and locally specific. This conclusion has implications for opposing positions within the debate on poverty and conservation. Critics of conservation who build upon local case studies to argue that protected areas make a significant contribution to poverty risk exaggerating the scale of the problem. However, conservation advocates also need to temper their enthusiasm. Outcomes in which both poverty alleviation and conservation goals are achieved may be possible in specific circumstances but clear choices will often need to be made between conservation and livelihood goals.

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Solvothermal treatment of a mixture of Co(OAc)(2), NaN(3), NaN(CN)(2), HF, MeCN, and H(2)O generated an AlB(2)-like metal-organic framework, namely, [{(Co(3)F)(3)(trta)(2)(H(2)O)(9)}{Co(Hbta)(3)}(2)].11H(2)O (1) (H(3)trta = N,N,N-tris-tetrazol-5-yl-amine; H(3)bta = N,N-bis-tetrazol-5-yl-amine), in which supertrianglar supramolecular building blocks (SBBs) {(Co(3)F)(3)(trta)(2)} act as 12-connected nodes of hexagonal prisms. The unprecedented ligand N,N,N-tris-tetrazol-5-yl-amine is in situ generated via metal-assisted reactions of NaN(CN)(2), MeCN, and NaN(3), and a possible mechanism involves both 1,3-dipolar cycloaddition and nucleophilic addition. The F-centered Co(3) triangles are bridged by trta groups to result in supertriangular {(Co(3)F)(3)(trta)(2)} SBBs that are further arranged in a frustrated triangular lattice. The long-range ordering temperature is reduced to 4.8 K due to strong spin frustration.