Applied Mathematics Letters
Applied Mathematics Letters > 2012 > 25 > 10 > 1327-1334
Applied Mathematics Letters > 2012 > 25 > 11 > 1721-1724
Applied Mathematics Letters > 2012 > 25 > 10 > 1327-1334
Applied Mathematics Letters > 2012 > 25 > 11 > 1721-1724