Managing Dynamic User Communities in a Grid of Autonomous Resources Autor Alfieri, R, Cecchini, R, Ciaschini, V, dell'Agnello, L, Gianoli, A, Spataro, F, Bonnassieux, F, Broadfoot, P, Lowe, G, Cornwall, L, Jensen, J, Kelsey, D, Frohner, Á, Groep, D, de Cerff, W, Steenbakkers, M, Venekamp, G, Kouril, D, McNab, A, Mulmo, O, Silander, M, Hahkala, J, Lörentey, K