Angle-resolved photoemission in doped charge-transfer Mott insulators

A theory of angle-resolved photoemission (ARPES) in doped cuprates and other charge-transfer Mott insulators is developed taking into account the realistic (LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon interaction, and a random field potential. In most of these materials the first band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the coherent part of the ARPES spectra with the oxygen hole spectral function calculated in the non-crossing (ladder) approximation and with the exact spectral function of a one-dimensional hole in a random potential. Some unusual features of ARPES including the polarisation dependence and spectral shape in YBa2Cu3O7 and YBa2Cu4O8 are described without any Fermi-surface, large or small. The theory is compatible with the doping dependence of kinetic and thermodynamic properties of cuprates as well as with the d-wave symmetry of the superconducting order parameter.Comment: 8 pages (RevTeX), 10 figures, submitted to Phys. Rev.

Towards automatic designing of 2D biaxial woven and braided fabric reinforced composites

10.1177/0021998302036013461Journal of Composite Materials36131541-1579JCOM

Multiscale approach for three-phase CNT/polymer/fiber laminated nanocomposite structures

The free vibration analysis of laminated nanocomposite plates and shells using first-order shear deformation theory and the Generalized Differential Quadrature (GDQ) method is presented. Each layer of the laminate is modelled as a three-phase composite. An example of such composite material is given by a polymeric matrix reinforced with Carbon Nanotubes (CNTs). CNTs enhance the mechanical properties of the polymer matrix and the nanocomposite is treated as an isotropic material; a micromechanics model is used to compute the engineering constants of the isotropic hybrid material. This approach based on the Eshelby-Mori-Tanaka scheme takes into account the agglomeration of the nanoparticles in the matrix. The second step consists in combining this enriched matrix with unidirectional and oriented reinforcing fibers to obtain a fibrous composite with improved mechanical features. The overall mechanical properties of each orthotropic ply are evaluated through different micromechanics approaches. Each technique is illustrated in details and the transversely isotropic properties of the three-phase layers are completely defined. The effects of both CNTs agglomeration and the mass fraction of these particles are investigated comparing with the results obtained by various homogenization techniques