Charge-density waves in the Hubbard chain: evidence for 4k_F instability

Charge density waves in the Hubbard chain are studied by means of finite-temperature Quantum Monte Carlo simulations and Lanczos diagonalizations for the ground state. We present results both for the charge susceptibilities and for the charge structure factor at densities \rho=1/6 and 1/3; for \rho=1/2 (quarter filled) we only present results for the charge structure factor. The data are consistent with a 4k_F instability dominating over the 2k_F one, at least for sufficiently large values of the Coulomb repulsion, U. This can only be reconciled with the Luttinger liquid analyses if the amplitude of the 2k_F contribution vanishes above some U^*(\rho).Comment: RevTeX, 4 two-column pages with 7 colour figures embedded in tex

L'indice de compétition interindividuelle de Schütz

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Modelagem do volume do povoamento para Mimosa scabrella Benth. na regição metropolitana de Curitiba Stand volume modelling of Mimosa scabrella benth. from Curitiba metropolitan region

O objetivo desta pesquisa foi modelar o volume total com casca do povoamento da bracatinga (Mimosa scabrella Benth.). Coletaram-se dados em bracatingais com regeneração induzida pelo fogo, em 14 municípios da Região Metropolitana de Curitiba (RMC), Estado do Paraná - Brasil. Utilizou-se uma base de dados constituída por 229 unidades amostrais de 100 a 400 m². Em cada parcela, mensurou-se o diâmetro à altura do peito, bem como a altura total de todas as árvores, em bracatingais de 3 a 18 anos de idade. Para a estimativa do volume total com casca, testaram-se vários modelos de regressão selecionados da literatura, o que gerou uma matriz com 58 variáveis independentes, visando construir modelos por meio do método Stepwise. As equações de melhor ajuste foram validadas utilizando-se o teste Qui-quadrado, a análise gráfica de resíduos e o erro-padrão da estimativa. Várias equações tiveram bom desempenho, apresentaram valores de coeficiente de determinação ajustados superiores a 0,995, erro-padrão da estimativa inferior a 3% e adequada distribuição de resíduos. As duas equações de melhor desempenho foram validadas, apresentando erro-padrão da estimativa de 2,37% e 2,13%, valor não-significativo para o teste do Qui-quadrado e equilibrada distribuição dos resíduos.<br>The objective of this research was to model the stand volume outside bark of Mimosa scabrella Benth. stands, from the Curitiba Metropolitan Region (CMR), Parana State - Brazil. To reach this aim, a database of 229 permanent and temporary sample plots measuring from 100 to 400 m² each, from 14 municipalities in the CMR, was used. In each sample plot, the diameter at breast height and the total height of all 3- to 18-year-old bracatinga trees were measured. To estimate the total volume, regression models selected from the literature were tested. A set of 58 independent variables was generated also to construct models by the Stepwise method. The equations of best fitting were validated by the Chi square tests ( 2), residual graphic analysis, and the absolute and relative standard error of estimate. Several equations showed good performance, adjusted coefficient of determination higher than 0.995, relative standard error of estimate lower than 3% and adequate residual distribution. The best two equations presented Syx: 2.37% and Syx: 2.13%, non-significant values for the &#967;2 test and unbiased distribution of the residuals

Kaposi sarcoma risk in HIV-infected children and adolescents on combination antiretroviral therapy from sub-Saharan Africa, Europe, and Asia

BACKGROUND  The burden of Kaposi sarcoma (KS) in human immunodeficiency virus (HIV)-infected children and adolescents on combination antiretroviral therapy (cART) has not been compared globally. METHODS  We analyzed cohort data from the International Epidemiologic Databases to Evaluate AIDS and the Collaboration of Observational HIV Epidemiological Research in Europe. We included HIV-infected children aged <16 years at cART initiation from 1996 onward. We used Cox models to calculate hazard ratios (HRs), adjusted for region and origin, sex, cART start year, age, and HIV/AIDS stage at cART initiation. RESULTS  We included 24 991 children from eastern Africa, southern Africa, Europe and Asia; 26 developed KS after starting cART. Incidence rates per 100 000 person-years (PYs) were 86 in eastern Africa (95% confidence interval [CI], 55-133), 11 in southern Africa (95% CI, 4-35), and 81 (95% CI, 26-252) in children of sub-Saharan African (SSA) origin in Europe. The KS incidence rates were 0/100 000 PYs in children of non-SSA origin in Europe (95% CI, 0-50) and in Asia (95% CI, 0-27). KS risk was lower in girls than in boys (adjusted HR [aHR], 0.3; 95% CI, .1-.9) and increased with age (10-15 vs 0-4 years; aHR, 3.4; 95% CI, 1.2-10.1) and advanced HIV/AIDS stage (CDC stage C vs A/B; aHR, 2.4; 95% CI, .8-7.3) at cART initiation. CONCLUSIONS  HIV-infected children from SSA but not those from other regions, have a high risk of developing KS after cART initiation. Early cART initiation in these children might reduce KS risk