3,707 research outputs found

    Interactions between cadmium and lead with acidic soils: Experimental evidence of similar adsorption patterns for a wide range of metal concentrations and the implications of metal migration

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    The importance of high- and low-affinity surface sites for cadmium and lead adsorption in typical European and Asian soils was investigated. Adsorption experiments on surface and deep horizons of acidic brown (Vosges, France) and red loess soils (Hunan, China) were performed at 25 ◦C as a function of the pH (3.5–8) and a large range of metal concentrations in solution (10−9–10−4 mol l−1). We studied the adsorption kinetics using a Cd2+-selective electrode and desorption experiments as a function of the solid/solution ratio and pH. At a constant solution pH, all samples exhibited similar maximal adsorption capacities (4.0 ± 0.5 µmol/g Cd and 20 ± 2 µmol/g Pb). A constant slope of adsorbed–dissolved concentration dependence was valid over 5 orders of magnitude of metal concentrations. Universal Langmuir and Freundlich equations and the SCM formalism described the adsorption isotherms and the pH-dependent adsorption edge over very broad ranges of metal concentrations, indicating no high- or low-affinity sites for metal binding at the soil surface under these experimental conditions. At pH 5, Cd and Pb did not compete, in accordance with the SCM. The metal adsorption ability exceeded the value for soil protection by two orders of magnitude, but only critical load guarantees soil protection since metal toxicity depends on metal availability

    Permeation of Low-Z Atoms through Carbon Sheets: Density Functional Theory Study on Energy Barriers and Deformation Effects

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    Energetic and geometric aspects of the permeation of low-Z atoms through graphene sheets are investigated. Energy barriers and deformations are calculated via density functional theory for the permeation of H, He, Li and Be atoms at several surface sites and at a hollow site for atoms B, C, O and Ne atoms. Graphene is modeled by large planar polycyclic aromatic hydrocarbons and the convergence of both energy barriers and deformation curves with increasing size of these hydrocarbons is investigated. Effective energy curves are summarized for the atoms under consideration in three different interaction regimes realized different geometrical constraints. In addition to the bare graphene model, the interaction between low-Z atoms and 100% hydrogenated coronene as a model for graphane is also investigated. The adiabatic barriers range from about 5 eV (1 eV = 1.602 x 10-19 J) for H to about 20 eV for Ne. Facilitation of the permeation by temporary chemical bonding is observed for O and C and for B and Be when interacting with hydrogenated coronene. The results are in good agreement with existing experimental and theoretical work and reflect the essential physics of the dynamics of H bombardment of graphite (0001) surfaces. Implications for modeling chemical sputtering of graphite in a mixed-material scenario as it will be the case in the next step fusion experiment ITER and potential building are discussed.Comment: 21 pages, 14 figures, 3 table

    Kinetic-energy release in Coulomb explosion of metastable C3H52+

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    C3H52+, formed by electron impact ionization of propane, undergoes metastable decay into C2H2++CH3+. We have monitored this reaction in a magnetic mass spectrometer of reversed geometry that is equipped with two electric sectors (BEE geometry). Three different techniques were applied to identify the fragment ions and determine the kinetic-energy release (KER) of spontaneous Coulomb explosion of C3H52+ in the second and third field free regions of the mass spectrometer. The KER distribution is very narrow, with a width of about 3% [root-mean square standard deviation]. An average KER of 4.58+/-0.15 eV is derived from the distribution. High level ab initio quantum-chemical calculations of the structure and energetics of C3H52+ are reported. The activation barrier of the reverse reaction, CH3++C2H2+ (vinylidene), is computed. The value closely agrees with the experimental average KER, thus indicating that essentially all energy available in the reaction is partitioned into kinetic energy. (C) 2003 American Institute of Physics

    Sainfoin – New Data on Anthelmintic Effects and Production in Sheep and Goats

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    Gastrointestinal nematodes (GIN) are one of the most important problems affecting health and therefore performance and welfare in small ruminant husbandry. The control of these parasites in the past strongly relied on the repeated use of anthelmintic drugs. This has led to nematode populations which are resistant to most of the currently available anthelmintics. Furthermore customer’s demands for organic and residue free animal products are increasing. The aforementioned problems have given a strong impetus for the development of new non-chemical strategies to control GIN. Previous research has pointed out the anthelmintic potential of sainfoin (Onobrychis viciifolia) and other tanniferous (CT) feed sources in goats and lambs infected with GIN. A recent Swiss experiment focussed on the use of sainfoin and field bean (Vicia faba, cv. Scirocco) as single CT sources as well as in combination for additional synergic effects, to reduce periparturient GIN egg rise of ewes in late gestation and early lactation. Another experiment with Alpine goats concentrated on the influence of sainfoin on milk performance and cheese quality. The results of these experiments will be presented and discussed in connection with previous knowledge on (i) anthelmintic effects of sainfoin and (ii) the influence of sainfoin administration on performance

    Intrinsic charge transport on the surface of organic semiconductors

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    The novel technique based on air-gap transistor stamps enabled realization of the intrinsic (not dominated by static disorder) transport of the electric-field-induced charge carriers on the surface of rubrene crystals over a wide temperature range. The signatures of the intrinsic transport are the anisotropy of the carrier mobility, mu, and the growth of mu with cooling. The anisotropy of mu vanishes in the activation regime at lower temperatures, where the charge transport becomes dominated by shallow traps. The deep traps, deliberately introduced into the crystal by X-ray radiation, increase the field-effect threshold without affecting the mobility. These traps filled above the field-effect threshold do not scatter the mobile polaronic carriers.Comment: 10 pages, 4 figure

    Protease inhibitors prevent plasminogen-mediated, but not pemphigus vulgaris-induced, acantholysis in human epidermis

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    Pemphigus is an autoimmune blistering disease of the skin and mucous membranes. It is caused by autoantibodies directed against desmosomes, which are the principal adhesion structures between epidermal keratinocytes. Binding of autoantibodies leads to the destruction of desmosomes resulting in the loss of cell-cell adhesion (acantholysis) and epidermal blisters. The plasminogen activator system has been implicated as a proteolytic effector in pemphigus. We have tested inhibitors of the plasminogen activator system with regard to their potential to prevent pemphigus-induced cutaneous pathology. In a human split skin culture system, IgG preparations of sera from pemphigus vulgaris patients caused histopathologic changes (acantholysis) similar to those observed in the original pemphigus disease. All inhibitors that were tested (active site inhibitors directed against uPA, tPA, and/or plasmin; antibodies neutralizing the enzymatic activity of uPA or tPA; substances interfering with the binding of uPA to its specific cell surface receptor uPAR) failed to prevent pemphigus vulgaris IgG-mediated acantholysis. Plasminogen-mediated acantholysis, however, was effectively antagonized by the synthetic active site serine protease inhibitor WX-UK1 or by p-aminomethylbenzoic acid. Our data argue against applying anti-plasminogen activator/anti-plasmin strategies in the management of pemphigus
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