Strongly linked current flow in polycrystalline forms of the superconductor MgB2. by Larbalestier, D, Cooley, L, Rikel, M, Polyanskii, A, Jiang, J, Patnaik, S, Cai, X, Feldmann, D, Gurevich, A, Squitieri, A, Naus, M, Eom, C, Hellstrom, E, Cava, R, Regan, K, Rogado, N, Hayward, M, He, T, Slusky, J, Khalifah, P, Inumaru, K, Haas, M