A Monte Carlo computer model has been developed to study the propagation of light in tissues. Light attenuation is assumed to result from absorption and isotropic scattering. The model has been used to predict the distribution of absorbed dose in homogeneous tissues of different absorption/scattering ratios, for illumination both by external light beams and via implanted optical fibers. The photon flux into optical fibers placed in the tissue as detectors has also been investigated. The results are interpreted in relation to the use of visible light irradiation for photo radiation therapy.

We propose a microscopical theory of superconductivity in CuO2 layer within the effective two-band Hubbard model in the strong correlation limit. By applying a projection technique for the matrix Green function in terms of the Hubbard operators, the Dyson equation is derived. It is proved that in the mean-field approximation d-wave superconducting pairing mediated by the conventional exchange interaction occurs. Allowing for the self-energy corrections due to kinematic interaction, a spin-fluctuation d-wave pairing is also obtained. Tc dependence on the hole concentration and kdependence of the gap function are derived. The results show that the exchange interaction (which stems from the interband hopping) prevails over the kinematic interaction (which stems from the intraband hopping).

We have observed, by 2D positron annihilation, the rigid-shaped Fermi surface related to the chains in the compound series (R)BdnC\\iOi-s for R = Y, Dy, Ho, and Pr. In the case of Y we have sighted the clear signature of the ridge in the fourth Brillouin zone and have observed the effect of substituting Cu with Ni, Zn, and Al. The presence of the ridge is also seen in PrBa2Cu307-<5 which has an insulating character. This shows that chains have a Fermi surface but contribute little to conductivity. This observation is discussed in view of the above alloying experiments, and in view of the recent model of Fehrenbacher and Rice.