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651.
Transport of uranium within surface and subsurface environments is predicated largely on its redox state. Uranyl reduction may transpire through either biotic (enzymatic) or abiotic pathways; in either case, reduction of U(VI) to U(IV) results in the formation of sparingly soluble UO2 precipitates. Biological reduction of U(VI), while demonstrated as prolific under both laboratory and field conditions, is influenced by competing electron acceptors (such as nitrate, manganese oxides, or iron oxides) and uranyl speciation. Formation of Ca-UO2-CO3 ternary complexes, often the predominate uranyl species in carbonate-bearing soils and sediments, decreases the rate of dissimilatory U(VI) reduction. The combined influence of uranyl speciation within a mineralogical matrix comparable to natural environments and under hydrodynamic conditions, however, remains unresolved. We therefore examined uranyl reduction by Shewanella putrefaciens within packed mineral columns of ferrihydrite-coated quartz sand under conditions conducive or nonconducive to Ca-UO2-CO3 species formation. The results are dramatic. In the absence of Ca, where uranyl carbonato complexes dominate, U(VI) reduction transpires and consumes all of the U(VI) within the influent solution (0.166 mM) over the first 2.5 cm of the flow field for the entirety of the 54 d experiment. Over 2 g of U is deposited during this reaction period, and despite ferrihydrite being a competitive electron acceptor, uranium reduction appears unabated for the duration of our experiments. By contrast, in columns with 4 mM Ca in the influent solution (0.166 mM uranyl), reduction (enzymatic or surface-bound Fe(III) mediated) appears absent and breakthrough occurs within 18 d (at a flow rate of 3 pore volumes per day). Uranyl speciation, and in particular the formation of ternary Ca-UO2-CO3 complexes, has a profound impact on U(VI) reduction and thus transport within anaerobic systems. 相似文献
652.
Bernd Müller-Bierl Olivia Louis Yves Fierens Nico Buls Robert Luypaert Johan de Mey 《Magma (New York, N.Y.)》2014,27(4):349-361
Objective
Bone density is distributed in a complex network of interconnecting trabecular plates and rods that are interspersed with bone marrow. A computational model to assess the dependence of the relaxation rate on the geometry of bone can consider the distribution of bone material in the form of two components: cylinders and open walls (walls with gaps). We investigate whether the experimentally known dependence of the transverse relaxation rate on the trabecular bone structure can be usefully interpreted in terms of these two components.Materials and methods
We established a computer model based on an elementary computational cell. The model includes a variable number of open walls and infinitely long cylinders as well as multiple geometric parameters. The transverse relaxation rate is computed as a function of these parameters. Within the model, increasing the trabecular spacing with a fixed trabecular radius is equivalent to thinning the trabeculae while maintaining constant spacing.Results
Increasing the number of cylinder and wall gap elements beyond their nearest neighbors does not change the transverse relaxation rate. Although the absolute contribution to the relaxation due to open walls is on average more important than that due to cylinders, the latter drops off rapidly. The change on transverse relaxation rate is larger for changing cylinder geometry than for changing wall geometry, as it can be seen from the effect on the relaxation rate when trabecular spacing is varied, compared to varying the size of wall gaps.Conclusion
Our results provide strong evidence that trabecular thinning, which is associated with increasing age, decreases the relaxation rates. The effect of thinning plates and rods on the transverse relaxation can be understood in terms of simple cylinders and open walls. A reduction in the relaxation rate can be seen as an indication of thinning cylinders, corresponding to reduced bone stability and ultimately, osteoporosis. 相似文献653.
Forrez I Carballa M Fink G Wick A Hennebel T Vanhaecke L Ternes T Boon N Verstraete W 《Water research》2011,45(4):1763-1773
Pharmaceutical and personal care products, biocides and iodinated contrast media (ICM) are persistent compounds, which appear in ng to μg L−1 in secondary effluents of sewage treatment plants (STPs). In this work, biogenic metals manganese oxides (BioMnOx) and bio-palladium (Bio-Pd) were applied in lab-scale membrane bioreactors (MBR) as oxidative and reductive technologies, respectively, to remove micropollutants from STP-effluent. From the 29 substances detected in the STP-effluent, 14 were eliminated in the BioMnOx-MBR: ibuprofen (>95%), naproxen (>95%), diuron (>94%), codeine (>93%), N-acetyl-sulfamethoxazole (92%), chlorophene (>89%), diclofenac (86%), mecoprop (81%), triclosan (>78%), clarithromycin, (75%), iohexol (72%), iopromide (68%), iomeprol (63%) and sulfamethoxazole (52%). The putative removal mechanisms were the chemical oxidation by BioMnOx and/or the biological removal by Pseudomonas putida and associated bacteria in the enriched biofilm. Yet, the removal rates (highest value: 2.6 μg diclofenac L−1 d−1) need to improve by a factor 10 in order to be competitive with ozonation. ICM, persistent towards oxidative techniques, were successfully dehalogenated with a novel reductive technique using Bio-Pd as a nanosized catalyst in an MBR. Iomeprol, iopromide and iohexol were removed for >97% and the more recalcitrant diatrizoate for 90%. The conditions favorable for microbial H2-production enabling the charging of the Pd catalyst, were shown to be important for the removal of ICM. Overall, the results indicate that Mn oxide and Pd coupled to microbial catalysis offer novel potential for advanced water treatment. 相似文献
654.
Sebastian Valouch Christian Hönes Siegfried W. Kettlitz Nico Christ Hung Do Michael F.G. Klein Heinz Kalt Alexander Colsmann Uli Lemmer 《Organic Electronics》2012,13(11):2727-2732
We demonstrate a small molecule solution processed hole interfacial layer approach to improve the dark current characteristics of polymer photodiodes. The two hole blocking materials under investigation 3-phenyl-4(1′-naphthyl)-5-phenyl-1,2,4-triazole (TAZ) and 2-[3,5-bis(1-phenylbenzimidazol-2-yl)phenyl]-1-phenylbenzimidazole (TPBi) are spincoated from ethanol as an orthogonal solvent on top of a P3HT:PCBM active layer. We reduce the dark current at a bias voltage of −1 V by a factor of 17.2 by introducing a TAZ interfacial layer while keeping the responsivity unchanged. 相似文献
655.
Bram Cantaert Yi‐Yeoun Kim Henning Ludwig Fabio Nudelman Nico A. J. M. Sommerdijk Fiona C. Meldrum 《Advanced functional materials》2012,22(5):907-915
Soluble macromolecules are essential to Nature's control over biomineral formation. Following early studies where macromolecules rich in aspartic and glutamic acid were extracted from nacre, research has focused on the use of negatively charged additives to control calcium carbonate precipitation. It is demonstrated that the positively charged additive poly(allylamine hydrochloride) (PAH) can also cause dramatic changes in calcite morphologies, yielding thin films and fibers of CaCO3 analogous to those produced with poly(aspartic acid) via a so‐called PILP (polymer‐induced liquid precursor) phase. The mechanism by which PAH induces these effects is investigated using a range of techniques including cryo transmission electron microscopy (TEM), Raman microscopy, and thermogravimetric analysis, and the data show that hydrated Ca2+/PAH/CO32? droplets initially form in solution, before coalescing and ultimately crystallizing to give calcite, together with small quantities of vaterite. It is suggested that it is the initial formation of hydrated Ca2+/PAH/CO32? droplets that is key to this process, rather than a specific polymer/mineral interaction. These results are discussed in terms of their relevance to biomineralization processes and highlight the opportunity for using counter‐ion‐induced phase separation of polyelectrolytes as a method for generating minerals with non‐crystallographic morphologies. 相似文献
656.
Jens Kreisel Mads C. Weber Nico Dix Florencio Sánchez Pamela. A. Thomas Josep Fontcuberta 《Advanced functional materials》2012,22(23):5044-5049
The integration of functional oxides on silicon requires the use of complex heterostructures involving oxides of which the structure and properties strongly depend on the strain state and strain‐mediated interface coupling. The experimental observation of strain‐related effects of the individual components remains challenging. Here, a Raman scattering investigation of complex multilayer BaTiO3/LaNiO3/CeO2/YSZ thin‐film structures on silicon is reported. It is shown that the Raman signature of the multilayers differs significantly for three different laser wavelengths (633, 442, and 325 nm). The results demonstrate that Raman scattering at various wavelengths allows both the identification of the individual layers of functional oxide multilayers and monitoring of their strain state. It is shown that all of the layers are strained with respect to the bulk reference samples, and that strain induces a new crystal structure in the embedded LaNiO3. Based on this, it is demonstrated that Raman scattering at various wavelengths offers a well‐adapted, non‐destructive probe for the investigation of strain and structure changes, even in complex thin‐film heterostructures. 相似文献
657.
Van Straalen NM Roelofs D Van Gestel CA De Boer TE 《Environmental science & technology》2010,44(23):9239-40; author reply 9241
658.
Conjugated polymers find applications in a range of devices such as light-emitting diodes, field-effect transistors and solar cells. The elementary electronic response of these semiconductors to electric fields is understood in terms of nanoscale perturbations of charge density. We demonstrate a general breaking of spatial charge symmetry by considering the linear Stark effect in the emission of single chromophores on individual chains. Spectral shifts of several nanometres occur due to effective dipoles exceeding 10 D. Although the electric field does not ionize the exciton, some molecules exhibit field-induced intensity modulations. This quenching illustrates the equivalence of charge symmetry breaking and polaron-pair or charge-transfer-state formation, and provides a microscopic picture of permanent charging, which leads to doping and exciton dissociation in actual devices. In addition to using this tuneable emission in single-photon electro-optic modulators, hysteresis in the Stark shift suggests a route to designing nanoscale memory elements such as molecular switches. 相似文献
659.
Microbial fuel cells for sulfide removal 总被引:3,自引:0,他引:3
Rabaey K Van de Sompel K Maignien L Boon N Aelterman P Clauwaert P De Schamphelaire L Pham HT Vermeulen J Verhaege M Lens P Verstraete W 《Environmental science & technology》2006,40(17):5218-5224
Thus far, microbial fuel cells (MFCs) have been used to convert carbon-based substrates to electricity. However, sulfur compounds are ubiquitously present in organic waste and wastewater. In this study, a MFC with a hexacyanoferrate cathodic electrolyte was used to convert dissolved sulfide to elemental sulfur. Two types of MFCs were used, a square type closed to the air and a tubular type in which the cathode compartment was open to the air. The square-type MFCs demonstrated a potential-dependent conversion of sulfide to sulfur. In the tubular system, up to 514 mg sulfide L(-1) net anodic compartment (NAC) day(-1) (241 mg L(-1) day(-1) total anodic compartment, TAC) was removed. The sulfide oxidation in the anodic compartment resulted in electricity generation with power outputs up to 101 mW L(-1) NAC (47 W m(-3) TAC). Microbial fuel cells were coupled to an anaerobic upflow anaerobic sludge blanket reactor, providing total removals of up to 98% and 46% of the sulfide and acetate, respectively. The MFCs were capable of simultaneously removing sulfate via sulfide. This demonstrates that digester effluents can be polished by a MFC for both residual carbon and sulfur compounds. The recovery of electrons from sulfides implies a recovery of energy otherwise lost in the methane digester. 相似文献
660.
This research compares the As and Cr chemistry of dislodgeable residues from chromated copper arsenate (CCA)-treated wood collected by two different techniques (directly from the board surface either by rubbing with a soft bristle brush or by rinsing from human hands after contact with CCA-treated wood) and demonstrates that these materials are equivalent in terms of both the chemical form and bonding of As and Cr and in terms of the As leaching behavior. This finding links the extensive chemical characterization and bioavailability testing that has been done previously on the brush-removed residue to a material that is derived from human skin contact with CCA-treated wood. Additionally, this research characterizes the arsenic present in biological fluids (sweat and simulated gastric fluid) following contact with these residues. The data demonstrate that in biological fluids the arsenic is present primarily as free arsenate ions. Arsenic-containing soils were also extracted into human sweat to evaluate the potential for arsenic dissolution from soils at the skin surface. For soils from field sites, only a small fraction of the total arsenic is soluble in sweat. Based on comparisons to reference materials that have been used for in vivo dermal absorption studies, these findings suggest that the actual relative bioavailability via dermal absorption of As from CCA residues and soil may be well below the current default value of 3% used by U.S. EPA. 相似文献