Iron Sulfide-Coated Sand for Remediation of Arsenic(III)-Contaminated Anoxic Groundwater.

This study investigated the feasibility of using reduced iron sulfide (FeS) as a permeable reactive barrier (PRB) material for remediating As(III) contaminated groundwater under anoxic conditions. FeS is more advantageous than more commonly used materials such as zero valent iron (ZVI) or Fe(III)-based materials in treating As(III)-contaminated groundwater, under anoxic conditions, as other Fe(III)-based adsorbents display a lower removal capacity and may release immobilized arsenic back into solution by reductive dissolution. To use nano-sized FeS as a PRB material, a method was developed to coat a natural sand giving a coating 1.2 to 4.0 mg FeS/g. The removal capacity of the FeS-coated sand was 30%, 70% and 300% at pH 5, 7 and 9, respectively, of the maximum capacity of nanoscale FeS. Although some reduction of uptake capacity was observed at pH 5 and 7, these capacities are greater to iron or aluminum based adsorbents under anoxic conditions. Spectroscopic methods such as x-ray absorption spectroscopy and x-ray photoelectron spectroscopy showed that the As(III) uptake mechanisms of FeS-coated sand as the precipitation of orpiment (As2S3) at pH 5 and the adsorption of arsenite at pH 9. The prominent differences in As(III) removal mechanisms as a function of pH also affects the column capacity of FeS-coated sand. At pHs where precipitation dominates, the column capacity is closely related to the amount of sulfide and column capacity was greater than that of batch system due to the continuous supply of sulfide from the dissolution of FeS. In contrast, at pH 9 where adsorption dominates, the As(III) removal capacity of the column system is comparable as long as the sorption non-linearity is considered and the retention time is adequately long. Overall, this dissertation supports FeS as a promising material for use in a PRB to remove As(III) under anoxic conditions.Ph.D.Environmental EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64782/1/hankr_1.pd

A candidate LiBH4 for hydrogen storage: Crystal structures and reaction mechanisms of intermediate phases

First-principles calculation and x-ray diffraction simulation methods have been used to explore crystal structures and reaction mechanisms of the intermediate phases involved in dehydriding of LiBH4. LiBH4 was found to dehydride via two sequential steps: first dehydriding through LiBH, followed by the dehydriding of LiBH through LiB. The first step, which releases 13.1 wt. % hydrogen, was calculated to have an activation barrier of 2.33 eV per formula unit and was endothermic by 1.28 eV per formula unit, while the second step was endothermic by 0.23 eV per formula unit. On the other hand, if LiBH4 and LiBH each donated one electron, possibly to the catalyst doped on their surfaces, it was found that the barrier for the first step was reduced to 1.50 eV. This implies that the development of the catalyst to induce charge migration from the bulk to the surface is essential to make LiBH4 usable as a hydrogen storage material in a moderate temperature range, which is also important to stabilize the low-temperature structure of Pnma (no. 62) LiBH on dehydrogenation. Consequently, the high 13.1 wt. % hydrogen available from the dehydriding of LiBH4 and LiBH and their phase stability on Pnma when specific catalysts were used suggest that LiBH4 has good potential to be developed as the hydrogen storage medium capable of releasing the Department of Energy target of 6.5 wt. % for a hydrogen fuel cell car in a moderate temperature range

Structural dynamics and divergence of the polygalacturonase gene family in land plants

A distinct feature of eukaryotic genomes is the presence of gene families. The polygalacturonase (PG) (EC3.2.1.15) gene family is one of the largest gene families in plants. PG is a pectin-digesting enzyme with a glycoside hydrolase 28 domain. It is involved in numerous plant developmental processes. The evolutionary processes accounting for the functional divergence and the specialized functions of PGs in land plants are unclear. Here, phylogenetic and gene structure analysis of PG genes in algae and land plants revealed that land plant PG genes resulted from differential intron gain and loss, with the latter event predominating. PG genes in land plants contained 15 homologous intron blocks and 13 novel intron blocks. Intron position and phase were not conserved between PGs of algae and land plants but conserved among PG genes of land plants from moss to vascular plants, indicating that the current introns in the PGs in land plants appeared after the split between unicellular algae and multicelluar land plants. These findings demonstrate that the functional divergence and differentiation of PGs in land plants is attributable to intronic loss. Moreover, they underscore the importance of intron gain and loss in genomic adaptation to selective pressure

Orthogonality properties of transverse eigenmodes of phase conjugate optical resonators

The orthogonality properties of the transverse eigenmodes of optical resonators which have phase conjugate mirrors at both ends are derived. As in conventional resonators and also resonators with only one phase conjugate mirror, it is shown that the transverse eigenmodes are essentially biorthogonal, a relation which is satisfied between the set of modes propagating in one direction around the resonator and the adjoint set of modes propagating in the reverse direction

Clinical Characteristics and Risk Factors for Nosocomial Candidemia in Medical Intensive Care Units: Experience in a Single Hospital in Korea for 6.6 Years

The aim of this study was to determine candidemia incidence among patients in a medical intensive-care unit (MICU) and the associated mortality rate and to identify risk factors associated with candidemia. We retrospectively performed a 1:3 matched case-control study of MICU patients with candidemia. Controls were matched for sex, age, and Acute Physiology and Chronic Health Evaluation (APACHE) II score. Candidemia incidence was 9.1 per 1,000 admissions. The most common pathogen was Candida albicans. Crude mortality was 96% among candidemia patients and 52% among controls (P<0.001). Mortality differed significantly between the groups according to Kaplan-Meier survival analysis (P=0.024). Multivariate analysis identified the following independent risk factors for candidemia: central venous catheterization (odds ratio [OR] = 3.2, 95% confidence interval [CI]=1.2-9.0), previous steroid therapy (OR=4.7, 95% CI=1.8-12.1), blood transfusion during the same admission period (OR=6.3, 95% CI=2.4-16.7), and hepatic failure upon MICU admission (OR=6.9, 95% CI=1.7-28.4). In conclusion, we identify an additional independent risk factor for candidemia, the presence of hepatic failure on MICU admission. Therefore, increased awareness of risk factors, including hepatic failure, is necessary for the management of candidemia