Anodic Polarization of Copper Single Crystal Planes in Sulphuric Acid

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Vivianite-parasymplesite solid solution: A sink for arsenic in ferruginous environments?

Vivianite, a hydrated ferrous phosphate [FeII3(PO4)2 · 8 H2O] that forms in oxygen-poor, but Fe2+-rich conditions is important in nutrient cycling in anoxic environments. In natural vivianites, isomorphic substitution of divalent cations for structural Fe(II) are typical. However, anion substitution is rare; in particular, arsenate (AsVO43−) substitution has never been documented in natural vivianites. Only partial substitution has been reported in synthetic analogues, and parasymplesite [FeII3(AsO4)2 · 8 H2O], the arsenic end member of the vivianite mineral group, is found in hydrothermal deposits. In this study, we detail structural changes in synthesised As-vivianites (FeII3[(PO4)1−x(AsO4)x]2 · 8 H2O) with systematically increased degrees of As(V) substitution (0.22 ≤ x ≤ 0.95). As(V) was successfully incorporated into the vivianite crystal structure, creating a homogenous, solid solution between AsVO43− and PO43−. Like both end members, the intermediate As-vivianites crystallised in the monoclinic system (C2/m space group), and retained the platelet crystal habit of As-free vivianite, even at the highest As(V) substitution. This uniform incorporation of As(V), and its replacement of PO43−, provides a potentially stable sink for arsenic in anoxic soils and sediments, and may have implications in ferruginous early Earth oceans

NT-proBNP for Risk Prediction in Heart Failure:Identification of Optimal Cutoffs Across Body Mass Index Categories

OBJECTIVES The goal of this study was to assess the predictive power of N-terminal pro–B-type natriuretic peptide (NT-proBNP) and the decision cutoffs in heart failure (HF) across body mass index (BMI) categories. BACKGROUND  Concentrations of NT-proBNP predict outcome in HF. Although the influence of BMI to reduce levels of NT-proBNP is known, the impact of obesity on prognostic value remains uncertain. METHODS Individual data from the BIOS (Biomarkers In Heart Failure Outpatient Study) consortium were analyzed. Patients with stable HF were classified as underweight (BMI = 40 kg/m(2)) obese. The prognostic rote of NT-proBNP was tested for the endpoints of all-cause and cardiac death. RESULTS The study population included 12,763 patients (mean age 66 +/- 12 years; 25% women; mean left ventricular ejection fraction 33% 113%). Most patients were overweight (n = 5,176), followed by normal weight (n = 4,299), mildly obese (n = 2,157), moderately obese (n = 612), severely obese (n = 314), and underweight (n = 205). NT-proBNP inversely correlated with BMI (beta = -0.174 for 1 kg/m(2); P < 0.001). Adding NT-proBNP to clinical models improved risk prediction across BMI categories, with the exception of severely obese patients. The best cutoffs of NT-proBNP for 5-year all-cause death prediction were lower as BMI increased (3,785 ng/L, 2,193 ng/L, 1,554 ng/L, 1,045 ng/L, 755 ng/L, and 879 ng/L, for underweight, normal weight, overweight, and mildly, moderately, and severely obese patients, respectively) and were higher in women than in men. CONCLUSIONS NT-proBNP maintains its independent prognostic value up to 40 kg/m(2) BMI, and tower optimal risk-prediction cutoffs are observed in overweight and obese patients

Glacier algae accelerate melt rates on the western Greenland Ice Sheet

Melting of the Greenland Ice Sheet (GrIS) is the largest single contributor to eustatic sea level and is amplified by the growth of pigmented algae on the ice surface that increase solar radiation absorption. This biological albedo reducing effect and its impact upon sea level rise has not previously been quantified. Here, we combine field spectroscopy with a novel radiative transfer model, supervised classification of UAV and satellite remote sensing data and runoff modelling to calculate biologically-driven ice surface ablation and compare it to the albedo reducing effects of local mineral dust. We demonstrate that algal growth led to an additional 5.5–8.0 Gt of runoff from the western sector of the GrIS in summer 2016, representing 6–9 % of the total. Our analysis confirms the importance of the biological albedo feedback and that its omission from predictive models leads to the systematic underestimation of Greenland’s future sea level contribution, especially because both the bare ice zones available for algal colonization and the length of the active growth season are set to expand in the future

Oxidation of caffeine by sodium N-bromo-<i>p</i>-toluene sulphonamide in Helmedium

225-227Kinetics of oxidation of caffeine by sodium N-bromo-p-toluenesulphonamide (BAT) in HCI medium has been studied at 288 K. The rate shows a first order dependence on [BAT]. fractional orders in [H+] and [CI-] and is independent of [caffeine].Addition of the reaction product, p-toluenesulphonamide and varying ionic strength Qf the medium have no effect on the rate. The rate constant decreases with decrease in the dielectric constant of the medium. The solvent isotope effect has been studied in D2O medium. Activation parameters have been evaluated from the Arrhenius plots. The proposed reaction mechanism and the derived rate laws are consistent with the observed kinetics

Kinetic and mechanistic studies on the oxidation of D-cycloserine by sodium N-bromobenzenesulphonamide in hydrochloric acid medium

77-81<span style="font-size:12.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-in;mso-fareast-language:en-in;mso-bidi-language:ar-sa"="" lang="EN-IN">Oxidation of D-cycloserine (CS) by sodium Nbromobenzenesulphonamide or bromamine-B (BAB) in HCI medium (0.1 to 0.6 mol dm·3) and constant ionic strength (0.8 mol dm-3) has been investigated at 40°C. The rate is first order in [BAB]o and is fractional order each in [CS]o and <span style="mso-bidi-font-style: italic">[H+]. The reaction is catalysed by chloride ion. Addition of reaction product, benzene sulphonamide and variation of ionic strength of the medium have no effect on rate. The reaction fails to induce the polymerisation of acrylonitrile. The rate constant increases with decrease in the dielectric constant of the medium. The rate increases in D2O medium and the in verse solvent isotope effect k (D2O) / k(H2O) = 1.70. Proton inventory studies made in H2O-D2O mixtures have been employed to calculate the isotopic fractionation factors. Composite activation parameters for the reaction have been determined from Arrhenius plot. Michaelis-Menten type of kinetics is observed and activation parameters for the rate-limiting step have been computed. The proposed mechanism assumes the simultaneous catalysis by H+ and CI ions and is consistent with the observed kinetic results.</span