The adsorption and dissociation of methane on the IrO 2 (110) surface were investigated by density functional theory calculations. The adsorption energy of methane obtained in this study is −0.41 eV on the stoichiometric surface and −0.63 eV on the oxygen-rich surface, which are significantly higher than those calculated recently on other different catalytic systems. Analyses from density of states and electron density difference show a special interaction between the C−H bonding orbital and the d z 2 orbital of surface iridium atom. In addition, the first hydrogen atom abstraction of methane by the IrO 2 (110) surface is a reaction with low barrier and high exothermic energy. The lower reaction barrier than the desorption energy indicates that the IrO 2 (110) surface could provide not only high sticking coefficient but also high turnover frequency in methane dissociation reaction.

We have used density functional theory (DFT) calculations to investigate the oxidation of ammonia (NH3) on a RuO2(110) surface. We characterized the possible reaction pathways for the dehydrogenation of NH x species (x = 1−3) and the formation of the oxidation products N2, NO, and H2O. The presence of oxygen atoms on coordinatively unsaturated sites (Ocus) promoted the oxidation of NH3 on the surface. The oxidation of NH3 is possible on both stoichiometric and oxygen-rich RuO2(110) surfaces; in the absence of Ocus (stoichiometric surface), however, NH3 molecules prefer desorption over oxidation. Moreover, the Ocus atoms are the major oxidants in this process; the formations of H2O and NO from bridge oxygen atoms (Obr) are both unfavorable reactions. According to our energetic analysis, in the NH x dehydrogenation pathways, H atom migration from NH2-cus to Obr has the highest barrier by 0.86 eV; it is much lower than the interaction energy of NH3 on the RuO2(110) surface. In terms of nitrogen-atom-containing products, NO, N2, and N2O are all possible products of the oxidation of NH3. The formation of the gaseous oxidation products H2O and NO is determined by their binding energies, whereas that of N2 is controlled by the diffusion of Ncus atoms on the surface. In addition, the selectivity toward the nitrogen-atom-containing products N2 and NO is dominated by the coverage of Ocus atoms on the surface; a higher coverage of Ocus atoms results in greater production of NO.

Background The mechanism of human immunodeficiency virus (HIV) transmission via heterosexual intercourse is unknown. We sought to determine whether the presence of inflammatory cells in the vagina is associated with the presence of genital tract HIV type 1 (HIV-1) RNA. Methods Analysis of a longitudinal prospective cohort was performed. Women with HIV-1 infection were assessed with use of paired plasma and cervicovaginal lavage specimens. Viral load measurements were performed using nucleic acid sequence—based amplification. White blood cells found in the genital tract (GT WBCs) were quantified using a hemacytometer. Common lower genital tract infections assessed for association with viral shedding (i.e., genital tract viral load [GTVL]) included bacterial vaginosis, candidiasis, and trichomoniasis. Generalized estimating equations were used to estimate the prevalence and odds of detectable GTVL by GT WBC. The association was examined both in the presence and in the absence of lower genital tract infections. Results A total of 97 women and 642 visits were included in the analysis. Median duration of follow-up was 30.4 months. Thirty women (31%) had detectable GTVL at any visit. The median CD4 cell count at baseline was 525 cells/μL. Most women were antiretroviral therapy naive at baseline. After adjustment for plasma viral load, the odds of detectable GTVL increased as GT WBC increased, with an odds ratio of 1.36 (95% confidence interval, 1.1–1.7) per 1000-cell increase in GT WBC among women without lower genital tract infections. After adjustment for plasma viral load and lower genital tract infections by incorporating them in a regression model, GT WBC remained significantly associated with GTVL, with an adjusted odds ratio of 1.22 (95% confidence interval, 1.08–1.37). Conclusions The presence of GT WBC is associated with an increased risk of detectable GTVL.

The use of highly active antiretroviral therapy (HAART) has resulted in dramatic reductions in morbidity and mortality of HIV infected individuals. With increasing life expectancy, a growing population of women will experience menopausal transitions while infected with HIV. Changes associated with menopause may affect HIV disease progression, and HIV-infected women may experience menopause in a different way from that of uninfected women. Age at natural menopause among non-HIV-infected white and Hispanic women is on the average 51 years, and that of African American women is 49 years. Several studies have shown that the mean age of menopause in HIV-infected women is 47-48 years. This is likely due to factors other than HIV infection that predict early menopause, such as drug use, smoking, and low socioeconomic status. It may be difficult to separate out HIV symptoms from menopausal symptoms. The additive effects of menopause, HIV infection, and HAART on changes involving bone, lipid, and glucose metabolism need further investigation. Likewise, there is a need for a better understanding of the prevalence and manifestations of depression among these women.

The oxidation of ammonia (NH 3 ) and the reduction of nitrogen (N 2 ) are two important processes in chemistry. In this study, we used density functional theory calculations to investigate the adsorptions of NH x (x ) 0-3) and N 2 on IrO 2 (110) surfaces, with density of states (DOS) analysis providing information relating to bond character and state interactions. These adsorbates have higher binding energies on the IrO 2 (110) surface than on the RuO 2 (110) surface because the former forms stronger σ bonds with the adsorbed molecules. The surface adsorptions of NH 2 and NH on the IrO 2 (110) surface proceed with similar binding energies and similar hybridizations of the nitrogen atoms. In addition, the orientations of NH 2 and NH adsorbed on the IrO 2 (110) surface are governed by lateral interactions with surface oxygen atoms (O cus or O br ), rather than by hydrogen bonding. We calculated the binding energy for the adsorption of N 2 on the IrO 2 (110) surface to be 1.10 eV. The weakening of the NtN triple bond was evident from our DOS results; strong bonding forces, including σ-and π-type interactions, exist between the N 2 molecule and the surface, suggesting that N 2 molecules are moderately activated by IrO 2 (110) surfaces.

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