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Three different types of mixed-oxides ceramic ball heads have been investigated for their wear behaviour against acetabular cups of the same materials in a hip joint simulator. Mixed-oxides ceramics have been indicated in literature as a promising compromise between strength and wear but no reports are available on the influence of a percentage of zirconia in a ceramic femoral head when sliding against itself. Mixed-oxides ceramic acetabular cups and femoral heads were tested on a simulator apparatus with a sinusoidal load in presence of bovine calf serum. The experimental results did not show any significant difference between the experimental and commercial ceramic material couplings. These results were found to be in accord with those developed in Part 1.

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This article explains the fundamental elements of the relationship between Spain and NATO in view of its 40th anniversary of membership of the Atlantic Alliance. This work, both in its historical reconstruction and its analysis of the challenges that characterise Spain's position in the organisation, aims to examine three key elements of this relationship: the ambiguous position of Spanish elites and society with respect to NATO membership and the relationship with the US; the legalistic and multilateral nature, with an explicit preference for the EU, of national defence policy; and the complexity of the 'Southern Flank', that is, the system of multiple and different threats to Spain's security from North Africa, where NATO struggles to provide a satisfactory response. The article concludes by underlining the unusual relevance, for a middle power like Spain, of domestic factors in determining both the country's international posture and the main aspects of its military doctrine.