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Experimental tests for zirconia/nickel composites determined lower toughness than expected. In this regard, the combination of ab initio density functional theory calculations and high-resolution transmission electron microscopy observations allowed to describe the nature of the zirconia/nickel interface and to justify the absence of any toughening mechanism by grain bridging of the metal particles. In the particular case of nanocomposites, enhanced values of hardness were found. Hardness increases have been justified by a novel model which takes into account the Hall — Petch effect and mean particle size according to the percolation theory. It has been found that this model is not exclusive to zirconia/nickel but can be extended to several other superhard composites.

The periodic effects on the electronic properties of Ni/Co magnetic multilayers grown in the (111) direction are investigated by studying superlattices and finite bilayers formed with the same unit block. Band structures and Fermi surfaces are calculated using a Green-function-matching method within a self-consistent empirical tight-binding model. Our results show strong sp-d hybridization of the electronic levels, the existence of nested multisheet Fermi surfaces, and the occurrence of d-derived spatially extended states in both superlattices and finite bilayers. Nevertheless, the superlattice periodicity increases the band degeneracy in the in-plane direction and changes the energy position of the superlattice electron levels with respect to those of the bilayer. The discrepancies result in different Fermi wave vectors for both systems, which may yield different transport and dynamical coupling characteristics for superlattices and bilayers.

A new heterotrinuclear complex of formula [Cu(2)Zn(Hdmg)(2)(dmg)(2)(H(2)O)].0.5H(2)dmg.H(2)O (C(18)H(34)Cu(2)N(9)O(11)Zn, 1) (H(2)dmg = dimethylglyoxime) has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group Po, with a = 11.414(1) A, b = 11.992(3) A, c =12.567(10) A, alpha = 91.27(6) degrees, beta = 111.46(2) degrees, gamma = 112.24(2) degrees, and Z = 2. The structure consists of a chain of neutral [Cu(2)Zn(Hdmg)(2)(dmg)(2)(H(2)O)] trinuclear units and noncoordinated H(2)dmg and water molecules. The configuration around the zinc atom is distorted trigonal bipyramidal with four oximate oxygens from two [Cu(Hdmg)(dmg)](-) fragments (each one acting as a bidentate ligand through its deprotonated oximate oxygens in cis positions) occupying one axial and the three equatorial positions and an additional oximate oxygen from a symmetry-related [Cu(Hdmg)(dmg)](-) fragment filling the remaining axial position. The environment around Cu(1) and Cu(2) is distorted square pyramidal with four oximate nitrogen atoms building the equatorial plane. An oxygen atom [O(9)] from a water molecule and an oximate oxygen from a symmetry-related [Cu(Hdmg)(dmg)](-) fragment occupy the apical position of the square pyramids around Cu(1) and Cu(2), respectively. The trinuclear units are repeated through inversion centers standing at the middle of the Zn(1).Zn(1)(i) and Cu(2).Cu(2)(ii) vectors leading to a chain which runs parallel to the diagonal of the ac-plane. The Cu(1).Cu(2), Zn(1).Zn(1)(i), and Cu(2).Cu(2)(ii) separations are 5.506(2), 3.390(2), and 3.930(2) A, respectively. 1 exhibits a characteristic ferromagnetic behavior with a continuous increase of the chi(M)T product as the temperature is lowered from 300 to 2.0 K. The field dependence of the magnetization at 2.0 K is consistent with a low-lying quintet state. The only efficient exchange pathways responsible for the overall ferromagnetic coupling in 1 are the diamagnetic zinc(II) ion and the out-of-plane double-oximato bridge, the magnitude of the magnetic coupling between the copper(II) ions through these bridging units being 3.9 and 5.1 cm(-)(1), respectively.

The magnetic moments and the anisotropy energy of surface compounds formed by MnxPt(12x) (x P@0,1# )o n aP t~111! substrate are calculated by means of the fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method. The binary compositions are modeled within the coherent potential approximation. Different Mn concentrations at each layer have been considered in order to understand the influence on the magnetic properties of both the chemical environment of the Mn atoms and the segregation of Pt from the bulk. Special emphasis is devoted to the study of the layered sequences Pt/MnxPt(12x) .

We apply the surface Green function matching (SGFM) method to the study of the electronic states of surfaces and interfaces. We use empirical tight binding Hamiltonians to describe the ideal (100) GaAs-Ge interfaces and the corresponding free surfaces. Electronic band structures and local densities of states are calculated and discussed, with emphasis on the practical aspects of SGFM as a computational technique.

We prove that if the cut locus C ( p ) C(p) of a point p p in a compact connected Riemannian manifold M M is contained in a connected hypersurface N N , then M M is homeomorphic to S m {S^m} if C ( p ) ≠ N C(p) \ne N and M M is homotopically equivalent to R P m {\mathbf {R}}{P^m} if C ( p ) = N C(p) = N .