Dual Fermion Dynamical Cluster Approach for Strongly Correlated Systems

We have designed a new multi-scale approach for Strongly Correlated Systems by combining the Dynamical Cluster Approximation (DCA) and the recently introduced dual-fermion formalism. This approach employs an exact mapping from a real lattice to a DCA cluster of linear size Lc embedded in a dual fermion lattice. Short-length-scale physics is addressed by the DCA cluster calculation, while longer-length-scale physics is addressed diagrammatically using dual fermions. The bare and dressed dual Fermionic Green functions scale as O(1/Lc) so perturbation theory on the dual lattice converges very quickly. E.g., the dual Fermion self-energy calculated with simple second order perturbation theory is of order O(1/Lc^3), with third order and three body corrections down by an additional factor of O(1/Lc^2)

Solving the parquet equations for the Hubbard model beyond weak coupling

We find that imposing crossing symmetry in the iteration process considerably extends the range of convergence for solutions of the parquet equations for the Hubbard model. When crossing symmetry is not imposed, the convergence of both simple iteration and more complicated continuous loading (homotopy) methods is limited to high temperatures and weak interactions. We modify the algorithm to impose the crossing symmetry without increasing the computational complexity. We also imposed time reversal and a subset of the point group symmetries, but they did not further improve the convergence. We elaborate the details of the latency hiding scheme which can significantly improve the performance in the computational implementation. With these modifications, stable solutions for the parquet equations can be obtained by iteration more quickly even for values of the interaction that are a significant fraction of the bandwidth and for temperatures that are much smaller than the bandwidth. This may represent a crucial step towards the solution of two-particle field theories for correlated electron models. © 2013 American Physical Society

Proximity of the superconducting dome and the quantum critical point in the two-dimensional Hubbard model

We use the dynamical cluster approximation to understand the proximity of the superconducting dome to the quantum critical point in the two-dimensional Hubbard model. In a BCS formalism, Tc may be enhanced through an increase in the d-wave pairing interaction (Vd) or the bare pairing susceptibility (χ0d). At optimal doping, where Vd is revealed to be featureless, we find a power-law behavior of χ 0d(ω=0), replacing the BCS log, and strongly enhanced T c. We suggest experiments to verify our predictions. © 2011 American Physical Society

Predictors of childhood severe malaria in a densely populated area: Douala, Cameroon

The physiopathology of malaria is complex. More understanding would be useful for a better management of the disease. This study was undertaken to describe clinical presentation and some biochemical parameters in childhood malaria in order to identify some factors of disease severity. Eighty six (86) children (0 to 15 years old) were recruited in Douala, clinical data recorded and blood sample collected. Thirty one (31) healthy children were also targeted to serve as control. Blood glucose, hemoglobin, transaminases and nitric oxide were determined by spectrophotometry. C reactive protein (CRP) was also investigated. The results confirmed that severe malaria significantly affects children under 5 years. Severe malaria was associated with hyperpyrexia and prostration. Coma, convulsions and unconsciousness were more indicative of cerebral malaria. Hemoglobin and blood glucose levels decreased significantly in severe malaria patients compared with uncomplicated malaria patients or controls (P < 0.001). On the contrary, blood transaminases and CRP levels increased significantly in malaria patients compared to controls (P < 0.001). From these results, it is clear that childhood severe malaria is associated with prostration, coma, unconsciousness, convulsions and hyperpyrexia. Low levels of haemoglobin and glycemia, as well as high levels of transaminases and CRP has been identified as predictor of malaria severity.Keywords: Childhood malaria, clinical presentation, physiopatholog

Antihepatotoxic and Antioxidant Activities of Methanol Extract and Isolated Compounds from Ficus chlamydocarpa

Free radicals, in particular radical oxygen species (ROS), play an important role in the aetiology and pathogenesis of various diseases. Current research in many countries focuses on the use of local medicinal plants as a promising source of liver protective agents. This paper describes the hepatoprotective effects of the methanol extract and four isolated compounds from Ficus chlamydocarpa on CCl4-induced liver damage, as well as the possible antioxidant mechanisms involved in this protection. The DPPH test, along with the ß-Carotene-Linoleic Acid Model System and Ferric-Reducing Antioxidant Power assays, as well as the inhibition of microsomal lipid peroxidation were used to measure radical-scavenging and antioxidant activities. Pretreatment of rats with the methanol extract of F. chlamydocarpa before CCl4administration, significantly prevented serum increase of hepatic enzyme markers, glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT), in a dose-dependent manner. The hepatoprotection was also associated with a significant enhancement in hepatic reduced glutathione (GSH) and a marked decrease of liver malondialdehyde (MDA). Among the four compounds 1-4, isolated from the methanol extract, α-amyrin acetate (1) and luteolin (4) showed a significant hepatoprotective activity, as indicated by their ability to prevent liver cell death and lactate dehydrogenase (LDH) leakage during CCl4intoxication

Why do women choose private over public facilities for family planning services? A qualitative study of post-partum women in an informal urban settlement in Kenya

BACKGROUND: Nearly 40 % of women in developing countries seek contraceptives services from the private sector. However, the reasons that contraceptive clients choose private or public providers are not well studied. METHODS: We conducted six focus groups discussions and 51 in-depth interviews with postpartum women (n = 61) to explore decision-making about contraceptive use after delivery, including facility choice. RESULTS: When seeking contraceptive services, women in this study preferred private over public facilities due to convenience and timeliness of services. Women avoided public facilities due to long waits and disrespectful providers. Study participants reported, however, that they felt more confident about the technical medical quality in public facilities than in private, and believed that private providers prioritized profit over safe medical practice. Women reported that public facilities offered comprehensive counseling and chose these facilities when they needed contraceptive decision-support. Provision of comprehensive counseling and screening, including side effects counseling and management, determined perception of quality. CONCLUSION: Women believed private providers offered the advantages of convenience, efficiency and privacy, though they did not consistently offer high-quality care. Quality-improvement of contraceptive care at private facilities could include technical standardization and accreditation. Development of support and training for side effect management may be an important intervention to improve perceived quality of care