We visit two new exhibitions in London by two very different US artists. First, we’ll hear from the curator of the UK’s first Noah Davis exhibition. The  glorious, sweeping show at the Barbican serves as a worthy tribute to the late, great painter. Then: we’ll hear from high-spirited octogenarian Joseph Kosuth, whose show at Sprüth Magers features works from his six decades spent as a pioneer of conceptual and installation art.