The diagrammatic cumulant expansion for the periodic Anderson model with infinite Coulomb repulsion (U = ∞) is considered here for an hypercubic lattice of infinite dimension (d = ∞). The nearest neighbour hopping of the uncorrelated electrons is described exactly by a conduction band, while two different models of hybridization are treated as a perturbation. The same type of simplifications obtained by Metzner for the cumulant expansion of the Hubbard model in the limit of d = ∞, are also shown to be valid for the periodic Anderson model. The derivation of these properties had to be modified because of the exact treatment of the conduction band. § Associate Member of ICTP,

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The structure formation in steel as a result of double quenching (the second time from the intercritical temperature range A c1 -A c2 ) and high tempering is established. By EBSD, the crystallo graphic features of the ferritic-martensitic structure formed in single and double quenching and stabilized on tempering are studied. The prospects for improving the mechanical properties of low alloy, low carbon Cr⎯Mo-V steel by quenching from the intercritical temperature range are considered Keywords: low alloy low carbon Cr-Mo-V steel, ferritic-martensitic structure, special boundaries, mechanical properties