The implications of HIV infection on the management of valvular heart disease in Southern Africa

There is very limited information on the disease profile and treatment approaches in HIV patients with valvular heart disease (VHD) in developing countries. HIV infection impacts on patients with VHD in three settings: HIV/Aids as a comorbid disease in patients with underlying valve disease, infective endocarditis secondary to immunosuppression, and non-infective valve involvement from myocardial failure or from marantic endocarditis. The clinical presentation of infective endocarditis does not differ between HIV and non-HIV patients, with the exception that intravenous drug abuse is a common cause in specific populations. While peri-operative mortality and morbidity is high in acute infective endocarditis, surgical interventions do not increase the postoperative risk for complications or death and should therefore not be withheld. There is also little evidence to suggest that HIV or antiretroviral drugs increase the rate of cardiac-related pregnancy complications or that pregnancy may alter the course of HIV infection. Since antiretroviral therapy has been associated with considerable improvement in clinical status prior to surgery, as well as in long term outcomes, all patients with valve disease in whom intervention is likely should undergo HIV testing and staging so that highly active antiretroviral treatment (HAART) may be instituted timeously. Conclusion: The high prevalence of HIV in our population makes consideration of this comorbidity an essential facet in the routine evaluation and management of patients with VHD. There is solid evidence that these patients do no worse than non-HIV patients undergoing medical treatment or percutaneous/surgical intervention – open-heart surgery may be offered safely to patients with HIV if proper precautions are taken

Full Relativistic Electronic Structure and Fermi Surface Sheets of the First Honeycomb-Lattice Pnictide Superconductor SrPtAs

We report full-potential density functional theory (DFT)-based {\it ab initio} band structure calculations to investigate electronic structure properties of the first pnictide superconductor with a honeycomb-lattice structure: SrPtAs. As a result, electronic bands, density of states, Fermi velocities and the topology of the Fermi surface for SrPtAs are obtained. These quantities are discussed in comparison to the first available experimental data. Predictions for future measurements are provided

Contrasting Pressure Effects in Sr2VFeAsO3 and Sr2ScFePO3

We report the resistivity measurements under pressure of two Fe-based superconductors with a thick perovskite oxide layer, Sr2VFeAsO3 and Sr2ScFePO3. The superconducting transition temperature Tc of Sr2VFeAsO3 markedly increases with increasing pressure. Its onset value, which was Tc{onset}=36.4 K at ambient pressure, increases to Tc{onset}=46.0 K at ~4 GPa, ensuring the potential of the "21113" system as a high-Tc material. However, the superconductivity of Sr2ScFePO3 is strongly suppressed under pressure. The Tc{onset} of ~16 K decreases to ~5 K at ~4 GPa, and the zero-resistance state is almost lost. We discuss the factor that induces this contrasting pressure effect.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jpn. No.12 (2009

On Electron Transport in ZrB12, ZrB2 and MgB2

We report on measurements of the temperature dependence of resistivity, $\rho(T)$, for single crystal samples of ZrB$_{12}$, ZrB$_{2}$ and polycrystalline samples of MgB$_{2}$. It is shown that cluster compound ZrB$_{12}$ behaves like a simple metal in the normal state, with a typical Bloch -- Gr\"uneisen $\rho(T)$ dependence. However, the resistive Debye temperature, $T_{R}=300 K$, is three times smaller than $T_{D}$ obtained from specific heat data. We observe the $T^{2}$ term in $\rho(T)$ of these borides, which could be interpreted as an indication of strong electron-electron interaction. Although the $\rho (T)$ dependence of ZrB$_{12}$ reveals a sharp superconductive transition at $T_{c}=6.0 K$, no superconductivity was observed for single crystal samples of ZrB$_{2}$ down to $1.3 K$.Comment: 5 pages, 4 figure

Electronic Structure of New AFFeAs Prototype of Iron Arsenide Superconductors

This work is provoked by recent discovery of new class prototype systems AFFeAs (A=Sr,Ca) of novel layered ironpnictide High-Tc superconductors (Tc=36K). Here we report ab initio LDA results for electronic structure of the AFFeAs systems. We provide detailed comparison between electronic properties of both new systems and reference LaOFeAs (La111) compound. In the vicinity of the Fermi level all three systems have essentially the same band dispersions. However for iron fluoride systems F(2p) states were found to be separated in energy from As(4p) ones in contrast to La111, where O(2p) states strongly overlaps with As(4p). Thus it should be more plausible to include only Fe(3d) and As(4p) orbitals into a realistic noninteracting model than for La111. Moreover Sr substitution with smaller ionic radius Ca in AFFeAs materials leads to a lattice contruction and stronger Fe(3d)-As(4p) hybridization resulting in smaller value of the density of states at the Fermi level in the case of Ca compound. So to some extend Ca system reminds RE111 with later Rare Earths. However Fermi surface of new fluorides is found to be nearly perfect two-dimensional. Also we do not expect strong dependence of superconducting properties with respect to different types of A substitutes.Comment: 5 pages, 4 figure

Magnetic Ordering in V-Layers of the Superconducting System of Sr2VFeAsO3

Results of transport, magnetic, thermal, and 75As-NMR measurements are presented for superconducting Sr2VFeAsO3 with an alternating stack of FeAs and perovskite-like block layers. Although apparent anomalies in magnetic and thermal properties have been observed at ~150 K, no anomaly in transport behaviors has been observed at around the same temperature. These results indicate that V ions in the Sr2VO3-block layers have localized magnetic moments and that V-electrons do not contribute to the Fermi surface. The electronic characteristics of Sr2VFeAsO3 are considered to be common to those of other superconducting systems with Fe-pnictogen layers.Comment: 4 pages, 4 figures, To appear in JPSJ 79 (2010) 12371

Contrast of LiFeAs with isostructural, isoelectronic, and non-superconducting MgFeGe

Stoichiometric LiFeAs at ambient pressure is an 18 K superconductor while isoelectronic MgFeGe is not, despite their extremely similar electronic structures. To investigate possible sources of this distinctively different superconducting behavior, we quantify the differences using first principles density functional theory, establishing first that the Fe total 3d occupations are identical in the two compounds. Individual 3d orbital occupations also differ very little ($\sim 0.01$). The differences in Fermi surfaces (FSs) do not seem significant; however a redistribution of bands just above the Fermi level does represent a possibly significant distinction. Because the bands and FSs of LiFeAs are less in agreement with experiment than for other iron-pnictides, we study the effects of additional exchange-correlations effects beyond GGA (the generalized gradient approximation) by applying the modified Becke-Johnson potential (mBJ) exchange potential, which gives much improved bandgaps in insulators compared to GGA and might be useful for semimetals such as the Fe-based superconductors. Overall, we conclude that the mBJ corrections do not improve the description of LiFeAs as compared to experiment

Electronic structure and possible pseudogap behavior in iron based superconductors

Starting from the simplified analytic model of electronic spectrum of iron - pnictogen (chalcogen) high - temperature superconductors close to the Fermi level, we discuss the influence of antiferromagneting (AFM)scattering both for stoichiometric case and the region of possible short - range order AFM fluctuations in doped compounds. Qualitative picture of the evolution of electronic spectrum and Fermi surfaces (FS) for different dopings is presented, with the aim of comparison with existing and future ARPES experiments. Both electron and hole dopings are considered and possible pseudogap behavior connected with partial FS "destruction" is demonstrated, explaining some recent experiments.Comment: 5 pages, 4 figures, published versio