A Model for High Temperature Superconductors using the Extended Hubbard Model

We derive a method to study the phase diagram for high temperature superconductors (HTCS). Our starting point is the Hubbard Hamiltonian with a weak attractive interaction to obtain the formation of bound pairs. We consider this attractive potential at different positions for different compounds accordingly to the experimental results of the coherence length. We then construct a wave function of the BCS type by a variational method using the Fourier transform of this extended Hubbard potential and then derive an energy gap equation. This approach allows us to obtain the critical temperature as function of the doping concentration which gives very good agreement with the experimental phase diagrams of YBaCuO and La(Sr,Ba)CuO compounds.Comment: 9 pages, RevTex preprint style, 2 figs. packed with uufile

Reducing nonideal to ideal coupling in random matrix description of chaotic scattering: Application to the time-delay problem

We write explicitly a transformation of the scattering phases reducing the problem of quantum chaotic scattering for systems with M statistically equivalent channels at nonideal coupling to that for ideal coupling. Unfolding the phases by their local density leads to universality of their local fluctuations for large M. A relation between the partial time delays and diagonal matrix elements of the Wigner-Smith matrix is revealed for ideal coupling. This helped us in deriving the joint probability distribution of partial time delays and the distribution of the Wigner time delay.Comment: 4 pages, revtex, no figures; published versio

Upper critical field Hc2H_{c2} calculations for the high critical temperature superconductors considering inhomogeneities

We perform calculations to obtain the $H_{c2}$ curve of high temperature superconductors (HTSC). We consider explicitly the fact that the HTSC possess intrinsic inhomogeneities by taking into account a non uniform charge density $\rho(r)$. The transition to a coherent superconducting phase at a critical temperature $T_c$ corresponds to a percolation threshold among different superconducting regions, each one characterized by a given $T_c(\rho(r))$. Within this model we calculate the upper critical field $H_{c2}$ by means of an average linearized Ginzburg-Landau (GL) equation to take into account the distribution of local superconducting temperatures $T_c(\rho(r))$. This approach explains some of the anomalies associated with $H_{c2}$ and why several properties like the Meissner and Nernst effects are detected at temperatures much higher than $T_c$.Comment: Latex text, add reference

Fibrosis assessment using FibroMeter combined to first generation tests in hepatitis C

AIM: To evaluate the performance of FibroMeter combined to the first generation tests aspartate aminotransferase-to-platelet ratio index (APRI) or Forns index to assess significant fibrosis in chronic hepatitis C (CHC). METHODS: First generation tests APRI or Forns were initially applied in a derivation population from Rio de Janeiro in Brazil considering cut-offs previously reported in the literature to evaluate significant fibrosis. FibroMeter was sequentially applied to unclassified cases from APRI or Forns. Accuracy of non-invasive combination of tests, APRI plus FibroMeter and Forns plus FibroMeter was evaluated in the Brazilian derivation population. APRI plus FibroMeter combination was validated in a population of CHC patients from Angers in France. All patients were submitted to liver biopsy staged according to METAVIR score by experienced hepatopathologists. Significant fibrosis was considered as METAVIR F ≥ 2. The fibrosis stage classification was used as the reference for accuracy evaluation of non-invasive combination of tests. Blood samples for the calculation of serum tests were collected on the same day of biopsy procedure or within a maximum 3 mo interval and stored at -70 °C. RESULTS: Seven hundred and sixty CHC patients were included (222 in the derivation population and 538 in the validation group). In the derivation population, the FibroMeter AUROC was similar to APRI AUROC (0.855 0.815, = 0.06) but higher than Forns AUROC (0.769, < 0.001). The best FibroMeter cut-off to discriminate significant fibrosis was 0.61 (80% diagnostic accuracy; 75% in the validation population, = 0.134). The sequential combination of APRI or Forns with FibroMeter in derivation population presented similar performance compared to FibroMeter used alone (79% 78% 80%, respectively, = 0.791). Unclassified cases of significant fibrosis after applying APRI and Forns corresponded to 49% and 54%, respectively, of the total sample. However, the combination of APRI or Forns with FibroMeter allowed 73% and 77%, respectively, of these unclassified cases to be correctly evaluated. Moreover, this combination resulted in a reduction of FibroMeter requirement in approximately 50% of the entire sample. The stepwise combination of APRI and FibroMeter applied to the validation population correctly identified 74% of patients with severe fibrosis (F ≥ 3). CONCLUSION: The stepwise combination of APRI or Forns with FibroMeter may represent an accurate lower cost alternative when evaluating significant fibrosis, with no need for liver biopsy

Scarabaeoidea (Insecta : Coleoptera) in the Brazilian Cerrado : current state of knowledge

Besouros pertencentes à superfamília Scarabaeoidea ocupam habitats variados, possuem hábitos alimentares diversifi cados, desempenham importante papel ecológico e diversas espécies apresentam importância agrícola. No entanto, estudos com esse grupo na região do Cerrado são escassos. Nesta revisão realizou-se um levantamento dos artigos publicados nos últimos 30 anos a respeito dos Scarabaeoidea no Cerrado. Foram recuperados 64 artigos, realizados em nove unidades da federação, que focavam quatro temas principais espécies praga, aspectos bioecológicos, biodiversidade e importância ecológica, e técnicas e metodologias de coleta de Scarabaeoidea. Os resultados desta revisão indicam que poucos estudos foram realizados com os Scarabaeoidea no Cerrado brasileiro nas últimas décadas frente à importância e diversidade desse grupo de insetos.Beetles belonging to the superfamily Scarabaeoidea occupy different habitats, present feeding habits diversifi ed, play an important ecological role and several species have agricultural importance. However, studies with this group in the Brazilian Cerrado are scarce. In this review we carried out a survey of scientifi c articles published in the past 30 years concerning Scarabaeoidea in the Cerrado. Were found 64 studies in nine Brazilian states. The studies focused on four main topics: pest species, bioecology, biodiversity and ecological importance, techniques and methodologies for collecting Scarabaeoidea. The results of this review indicate that few studies have been conducted with Scarabaeoidea in the Cerrado in recent decades compared to the importance and diversity of this group of insects

Inheritance of resistance to bacterial spot in tomato

A herança da resistência do tomateiro (Lycopersicon esculentum) à mancha-bacteriana (Xanthomonas campestris pv. vesicatoria, raça T2) foi estudada, em condições de campo, cruzando-se os genótipos resistentes 'Ohio 8245' e 'Hawaii 7998' com os genótipos suscetíveis 'CNPH 401-08' e 'CNPH 416.81.01.02', em um esquema dialélico desconsiderando-se os recíprocos. Foram obtidas cinco famílias, cada uma constituída por seis gerações: Genitor1, Genitor2, F1, F2 e os retrocruzamentos (RC1 e RC2). A família 'Ohio 8245 ' Hawaii 7998' apresentou menor média para severidade da doença, seguida por 'Hawaii 7998 ' CNPH 416.81.01.02' e 'Ohio 8245 ' CNPH 416.81.01.02', as quais, apresentaram maiores estimativas de herdabilidade e de predição de ganho por seleção. Em todas combinações, a herança da resistência genética à mancha-bacteriana foi do tipo quantitativa, com estimativa do número de genes variando de quatro a oito genes, conforme a família analisada. Foi observada segregação transgressiva nas famílias 'Ohio 8245 ' CNPH 401-08', 'Hawaii 7998 ' CNPH 401-08' e 'Hawaii 7998 ' CNPH 416.81.01.02'. Os efeitos gênicos foram do tipo aditivo para todas as famílias e os dados ajustados ao modelo aditivo-dominante, com o componente aditivo apresentando maior magnitude.The inheritance of resistance to bacterial spot (Xanthomonas campestris pv. vesicatoria, race T2) in tomato (Lycopersicon esculentum) was investigated in a field trial. The genotypes 'Ohio 8245' and 'Hawaii 7998' (resistant), 'CNPH 401-08' and 'CNPH 416.81.01.02' (susceptible) were crossed in a diallel scheme without reciprocals. Each cross was labeled as one family, represented by six different generations: Parent1, Parent2, F1, F2 and Backcrosses to parents (BC1 and BC2). The family 'Ohio 8245 ' Hawaii 7998' presented the lowest disease severity, followed by the family 'Hawaii 7998 ' CNPH 416.81.01.02' and by the family 'Ohio 8245 ' CNPH 416.81.01.02'. These last two families showed both higher broad and narrow sense inheritability estimates and the highest prediction of selection gain. The resistance was found to be quantitative, with four to eight genes involved, depending on the family. Transgressive segregation was observed in the 'Ohio 8245 ' CNPH 401-08', the 'Hawaii 7998 ' CNPH 401-08' and the 'Hawaii 7998 ' CNPH 416.81.01.02' families. The relevance of the additive effects was observed and for all the families the data fitted to additive-dominant model, with the additive component showing greater magnitude