Mercury transport through a capped sediment

Laboratory simulation cells were employed to evaluate the effectiveness of a sand cap for containing highly mercury-contaminated lake sediments and the resultant impacts on the mercury fate beneath the cap. Sand cap can delay and reduce the migration of mercury into the overlying water; however, due to the small partition coefficient of mercury between sand and water, a capping material with higher partition coefficient is better for the long-term containment of mercury. In the following study, efforts were made to identify and investigate an active capping material which works effectively at containing and inhibiting the methylation of mercury. Based on information from literature and our primary experimental results, iron sulfide (FeS) was selected for the following study. By amendment of laboratory synthesized iron sulfide (Syn-FeS) into sediment slurries spiked with Hg(II) under anoxic conditions, the inhibition effects of FeS on the methylation of mercury were investigated. A commercial iron sulfide (CIS), which was a mixture of several iron-sulfide species, was also investigated in the experiment. Experimental results showed that both Syn-FeS and CIS were good inhibitors of Hg(II) methylation. It was found that MeHg production was not correlated to total dissolved mercury in pore water. Via batch sorption experiment, the interaction between aqueous Hg(II) and Syn-FeS was studied under anaerobic conditions. The study included effects of the pH of both initial Hg(II) solution and equilibrium suspension on sorption, mechanism of interactions between Hg(II) and FeS, and the stability of immobilized mercury regarding oxidation. Experimental results showed that FeS works effectively at immobilizing aqueous Hg(II) via mostly precipitation reaction and also some adsorption on the solid surface. Finally, in the simulation cells, Syn-FeS and CIS were amended into uncapped sediment or sand cap to investigate their effectiveness at containing mercury and inhibiting the transformation of mercury to MeHg. Results show that, with the addition of iron sulfides, the release of mercury into overlying water was reduced and the methylation of mercury was inhibited

Thermodynamic Analysis of Wind Energy Systems

This chapter studies the efficiency performance of wind energy systems evaluated by energy and exergy analyses. The theories of energy and exergy analyses along with efficiency calculation for horizontal-axis wind turbines (WTs) are provided by a lucid explanation. A 1.5 MW WT is selected for the thermodynamic analysis using reanalyzed meteorological data retrieved from the National Aeronautics and Space Administration’s (NASA) Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2), data set. Matlab scripts are developed to calculate the energy and exergy efficiencies using the MERRA-2 data set. The energy efficiency presents higher magnitude than the exergy efficiency based on the theoretical derivation and the calculated time series of efficiencies. Comparison of impacts of four meteorological variables (wind speed, pressure, temperature, and humidity ratio) on WT efficiencies shows that although wind speed dominates the turbine’s efficiency performance, other meteorological variables also play important roles. In addition, uncertainties of the meteorological variables are represented by the best-fit distributions, which are critically important for evaluating the reliability of wind power performance considering realistic meteorological uncertainty

Dendritic growth velocities in undercooled melts under static magnetic fields

Dendritic growth in undercooled melts has been an interesting topic for metallurgists, physicists and mathematicians. In recent years, attention has been focused on the effects of melt flow on dendritic growth. Significant thermoelectric currents form in undercooled growth due to the presence of relatively large thermal gradients. Numerical simulations showed that the application of a static magnetic field exerts a complex influence on melt flow due to Lorentz force, damping and thermoelectrically driven convection, affecting growth kinetics in undercooled metallic melts. To verify the simulated results, bulk melts of high purity nickel were undercooled using the glass fluxing technique under static magnetic fields of up to 6 T. A high-speed camera was used for in situ monitoring of the recalescence process of the undercooled samples. The dendritic growth velocities at different melt undercoolings were calculated by simulating the recorded images of the recalescence process. The measured data confirms the predicted effect of heat and mass transport through thermoelectric magnetohydrodynamics flow on dendritic growth

Robust methods for accurate diagnosis using pan-microbiological oligonucleotide microarrays

Abstract Background To address the limitations of traditional virus and pathogen detection methodologies in clinical diagnosis, scientists have developed high-throughput oligonucleotide microarrays to rapidly identify infectious agents. However, objectively identifying pathogens from the complex hybridization patterns of these massively multiplexed arrays remains challenging. Methods In this study, we conceived an automated method based on the hypergeometric distribution for identifying pathogens in multiplexed arrays and compared it to five other methods. We evaluated these metrics: 1) accurate prediction, whether the top ranked prediction(s) match the real virus(es); 2) four accuracy scores. Results Though accurate prediction and high specificity and sensitivity can be achieved with several methods, the method based on hypergeometric distribution provides a significant advantage in term of positive predicting value with two to sixty folds the positive predicting values of other methods. Conclusion The proposed multi-specie array analysis based on the hypergeometric distribution addresses shortcomings of previous methods by enhancing signals of positively hybridized probes.http://deepblue.lib.umich.edu/bitstream/2027.42/112825/1/12859_2009_Article_3270.pd