56 research outputs found

    Ateneo Theater since 1986

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    Influence of the Water Content on the Diffusion Coefficients of Li⁺ and Water across Naphthalenic Based Copolyimide Cation-Exchange Membranes

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    The transport of lithium ions in cation-exchange membranes based on sulfonated copolyimide membranes is reported. Diffusion coefficients of lithium are estimated as a function of the water content in membranes by using pulsed field gradient (PFG) NMR and electrical conductivity techniques. It is found that the lithium transport slightly decreases with the diminution of water for membranes with water content lying in the range 14 < λ < 26.5, where λ is the number of molecules of water per fixed sulfonate group. For λ < 14, the value of the diffusion coefficient of lithium experiences a sharp decay with the reduction of water in the membranes. The dependence of the diffusion of lithium on the humidity of the membranes calculated from conductivity data using Nernst–Planck type equations follows a trend similar to that observed by NMR. The possible explanation of the fact that the Haven ratio is higher than the unit is discussed. The diffusion of water estimated by 1H PFG-NMR in membranes neutralized with lithium decreases as λ decreases, but the drop is sharper in the region where the decrease of the diffusion of protons of water also undergoes considerable reduction. The diffusion of lithium ions computed by full molecular dynamics is similar to that estimated by NMR. However, for membranes with medium and low concentration of water, steady state conditions are not reached in the computations and the diffusion coefficients obtained by MD simulation techniques are overestimated. The curves depicting the variation of the diffusion coefficient of water estimated by NMR and full dynamics follow parallel trends, though the values of the diffusion coefficient in the latter case are somewhat higher. The WAXS diffractograms of fully hydrated membranes exhibit the ionomer peak at q = 2.8 nm⁻1, the peak being shifted to higher q as the water content of the membranes decreases. The diffractograms present additional peaks at higher q, common to wet and dry membranes, but the peaks are better resolved in the wet membranes. The ionomer peak is not detected in the diffractograms of dry membranes.The authors acknowledge financial support provided by the DGICYT (Dirección General de Investigación Cientifíca y Tecnológica) through Grant MAT2011-29174-C02-02

    Incomplete periacetabular acetabuloplasty

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    Exposure to lead when manufacturing cookware from scrap metal: A public health threat in the artisanal sector in DR Congo

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    AIM The objective of this study was to investigate the exposure to lead (Pb) among artisan workers manufacturing cookware from scrap metal and their community. METHODS We conducted a cross-sectional survey in six cookware manufacturing workshops and, for comparison, eight carpentry workshops (negative controls) and 14 lead batteries repairing workshops (positive controls). All workshops are located in areas without mining activities of Lubumbashi city. We collected surface dust samples of the workspaces, and blood and urine samples of the workers and residents from the sites where the workshops are installed. Element determination was performed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). RESULTS In the artisanal cookware manufacturers (ACM) group, bood and urinary lead concentration geometric mean {121.5 μg/L [interquartile range(IQR 79.1-206.5)] and [3.3 μg/g (1.5-7.1)]} were estimated to be about twice as high as the negative control group {[60.2 μg/L (37.2-94.0)] and [0.9 μg/g, (0.3-3.8)]} and half the value of the positive control goup {[241.8 μg/L (82.8-591.7)] and [7.2 μg/g (1.1-26.3)]}. Among residents from the site of the workshop, children had higher urinary Pb concentrations [6.2 μg/g (2.3-19.3)] than the workers. CONCLUSION This investigation demonstrates a substantial occupational Pb exposure among ACM and warns on the hazards for residents, especially children, due to the installation of these activities in residential&nbsp;sites.</p
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