Showing in separate galleries, the longtime friends both address architecture and modernism. The Lebanonese-born Raad presents highly schematic drawings and wall constructions that evoke the new museums and other cultural infrastructure now springing up in the Middle East. Diao, born in China but resident in the U.S. since 1955, offers dozens of paintings, drawings and photographs riffing on Russian architect Konstantin Melnikov’s 1927 Moscow studio, known for its cylindrical space and hexagonal windows.