We calculate ground-state energies and density distributions of Hubbard superlattices characterized by periodic modulations of the on-site interaction and the on-site potential. Both density-matrix renormalization group and density-functional methods are employed and compared. We find that small variations in the on-site potential v i can simulate, cancel, or even overcompensate effects due to much larger variations in the on-site interaction U i . Our findings highlight the importance of nanoscale spatial inhomogeneity in strongly correlated systems, and call for a reexamination of model calculations assuming spatial homogeneity. A large part of the complexity of strongly correlated systems arises from the multiple phases that coexist or compete in their phase diagrams. Metallic and insulating phases are separated by metal-insulator transitions, and subject to the formation of various types of long-range order, such as antiferromagnetism, superconductivity, and charge-or spindensity waves. The relative stability of such phases is determined by differences in appropriate thermodynamic potentials, or, at zero temperature, in their ground-state energies. Identification of the appropriate order parameters and calculation of the ground-state energies of the various phases is a complicated problem, and the nature of the phase diagram of many strongly correlated systems is still subject to considerable controversy. It is widely believed, however, that a minimal model containing the essence of strong correlations, and displaying many of the above-mentioned phases, is the homogeneous Hubbard model, which in one dimension and standard notation readsMuch theoretical effort is thus going into the analysis of the homogeneous Hubbard model and the clarification of the nature of its ground state. In a parallel development, nanoscale spatial inhomogeneity has been observed experimentally to be a ubiquitious feature of strongly correlated systems, 1-8 but although its importance is widely recognized, the consequences of such inhomogeneity are still insufficiently understood. The present paper investigates the effects of, and the competition between, two different manifestations of nanoscale inhomogeneity in strongly correlated systems, namely local variations in the on-site potential and in the on-site interaction. We base our analysis on the inhomogeneous Hubbard model

SUMMARYIn an attempt to understand better the immunoregulatory disorders in paracoccidioidomycosis (PCM), the possible correlation between interleukin pattern, lymphoproliferation, C-reactive protein (CRP) and specific antibody levels was investigated in the polarized clinical forms of this disease. We studied 16 PCM patients, eight with the disseminated disease (four under treatment and four non-treated) and eight with the chronic disease. The patients with disseminated disease exhibited high antibody titres specific to Paracoccididoides brasiliensis antigen compared with patients with the chronic form of disease. Tumour necrosis factor (TNF), IL-1, IL-6 and CRP in the serum of non-treated disseminated PCM patients were increased, which correlated positively with the low mitogenic response of peripheral blood mononuclear cells (PBMC) to phytohaemagglutinin (PHA) (P<0-01) and with the high antibody titres (P<00001) of these patients. Moreover, we found in the disseminated PCM patients positive correlations between IL-1 and IL-6 (P=00007); IL-1 and TNF (P=0-0045); IL-1 and IL-6 with the high antibody titres (P = 0-0834 and P = 0-0631, respectively); IL-1, IL-6 and TNF with CRP levels. By contrast, no correlations were found with those interleukins in the treated disseminated and chronic patients or in controls. It was interesting to find an inverse correlation between IL-4 and antibody production in non-treated disseminated PCM (r = -0 4770); moreover, a significant correlation (P = 0-0820) was found in chronic PCM patients with respect to the low level of either IL-4 and antibody titres against fungus antigen. Chronic PCM patients also had IL-2 levels inversely correlated with antibody production (r = -0-6313; P = 0-0628). Inverse correlations were also observed between IL-2 and IL-6 levels in non-treated disseminated patients (P = 0 0501) and between IL-2 and IL-4 in chronic patients (P=0-013 1). The inflammatory cytokines might have a pivotal role in the genesis and in control of some aspects of the disease, such as granulomatous reaction, hypergammaglobulinaemia and depression of T cell-mediated immunity in PCM.

SUMMARYIn this study, we report an increase of the number of antibody-secreting cells and the augmentation of antibody production against unrelated antigens in mice infected with the fungus P. brasiliensis, as well as in mice inoculated with cell wall preparation isolated from P. brasiliensis (CW). The immunomodulatory effect of the live fungus and the CW preparation was dose-dependent, and their actions were mainly restricted to the i.v. or i.p. inoculation simultaneously with the sheep erythrocyte challenge by the i.v. route or restricted to i.p. inoculation of CW when bovine serum albumin (BSA) antigen was used. The dependence of antibody production on different routes of CW inoculation was correlated with the number of antigen-specific B cells in the spleen as determined by direct and reverse plaque-forming cell assays. The immunization schedules using CW preparation caused a preferential production of IgM and IgG3 antibodies. The results also showed that the hyperactive humoral immune response of mice induced by i.p. inoculation of CW was devoid of polyclonal B cell activation compared with the effects observed for the lipopolysaccharide (LPS)-treated groups. Paracoccidioides brasiliensis CW components may have potent immunological properties related to the non-specific B cell activation found in paracoccidioidomycosis.