High-temperature superconductivity in the two-dimensional t-J model: Gutzwiller wavefunction solution

A systematic diagrammatic expansion for Gutzwiller wavefunctions (DE-GWFs) proposed very recently is used for the description of the superconducting (SC) ground state in the two-dimensional square-lattice t–J model with the hopping electron amplitudes t (and $t^{\prime}$) between nearest (and next-nearest) neighbors. For the example of the SC state analysis we provide a detailed comparison of the methodʼs results with those of other approaches. Namely, (i) the truncated DE-GWF method reproduces the variational Monte Carlo (VMC) results and (ii) in the lowest (zeroth) order of the expansion the method can reproduce the analytical results of the standard Gutzwiller approximation (GA), as well as of the recently proposed 'grand-canonical Gutzwiller approximation' (called either GCGA or SGA). We obtain important features of the SC state. First, the SC gap at the Fermi surface resembles a ${{d}_{{{x}^{2}}-{{y}^{2}}}}$ wave only for optimally and overdoped systems, being diminished in the antinodal regions for the underdoped case in a qualitative agreement with experiment. Corrections to the gap structure are shown to arise from the longer range of the real-space pairing. Second, the nodal Fermi velocity is almost constant as a function of doping and agrees semi-quantitatively with experimental results. Third, we compare the doping dependence of the gap magnitude with experimental data. Fourth, we analyze the k-space properties of the model: Fermi surface topology and effective dispersion. The DE-GWF method opens up new perspectives for studying strongly correlated systems, as it (i) works in the thermodynamic limit, (ii) is comparable in accuracy to VMC, and (iii) has numerical complexity comparable to that of the GA (i.e., it provides the results much faster than the VMC approach).Foundation for Polish Science (FNP)/TEAM programNational Science Centre (NCN)/MAESTR

Low-grade proteinuria is highly prevalent in HIV-positive patients on antiretroviral treatment

Objectives: HIV-positive patients are at an increased risk for chronic kidney disease. However, these data mainly derive from cohorts with a high percentage of African-American patients, representing a specific ethnical risk group for chronic kidney disease. The aim of this study was to estimate the prevalence and risk factors specifically for early signs of kidney dysfunction in a large, predominantly white cohort of HIV patients. Design: Cross-sectional study. Methods: Prevalence of low-grade proteinuria was measured by quantitative analysis of urinary protein-to-creatinine ratio (cutoff >70mg/g) and further differentiated by assessing a1-microglobulin (tubular proteinuria) and albumin-to-creatinine ratio (glomerular proteinuria) of HIV patients attending the University Hospital in Cologne, Germany. Together with standard and HIV-related laboratory findings and medical history, risk factors for each form of proteinuria were identified using multivariate forward selection. Results: Of 945 enrolled patients, 55% were identified with low-grade proteinuria, 41% with tubular proteinuria, and 20% with glomerular proteinuria. Older age was a risk factor for all forms of proteinuria in multivariate analysis. Low-grade proteinuria was also associated with concomitant diabetes and exposure to nucleoside reverse transcriptase inhibitor [ anytime during HIV infection, not tenofovir (TDF)-specific], whereas tubular proteinuria was linked to current and any exposure to nucleoside reverse transcriptase inhibitor (TDF-specific). Further risk factors for glomerular proteinuria were hypertension and diabetes in this cohort. Conclusion: Low-grade, glomerular and tubular proteinuria are highly prevalent in this large white HIV cohort. Older age represents a nonmodifiable risk factor for all forms of proteinuria. Glomerular proteinuria is associated with modifiable cardiovascular, but not HIV-related risk factors, whereas tubular proteinuria is linked to TDF exposure. (C) 2014 Wolters Kluwer Health | Lippincott Williams & Wilkin

Chemical and Biological Gradients along the Damma Glacier Soil Chronosequence, Switzerland

Soils are the product of a complex suite of chemical, biological, and physical processes. In spite of the importance of soils for society and for sustaining life on earth, our knowledge of soil formation rates and of the influence of biological activity on mineral weathering and geochemical cycles is still limited. In this paper we provide a description of the Damma Glacier Critical Zone Observatory and present a first synthesis of our multi disciplinary studies of the 150-yr soil chronosequence. The aim of our research was to improve our understanding of ecosystem development on a barren substrate and the early evolution of soils and to evaluate the influence of biological activity on weathering rates. Soil pH, cation exchange capacity, biomass, bacterial and fungal populations, and soil organic matt er show clear gradients related to soil age, in spite of the extreme heterogeneity of the ecosystem. The bulk mineralogy and inorganic geochemistry of the soils, in contrast, are independent of soil age and only in older soils (&gt;100 yr) is incipient weathering observed, mainly as a decreasing content in albite and biotite by coincidental formation of secondary chlorites in the clay fraction. Further, we document the rapid evolution of microbial and plant communities along the chronosequence.</p