A combined BIE-FE method for the Stokes equations

A numerical algorithm for the biharmonic equation in domains with piecewise smooth boundaries is presented. It is intended for problems describing the Stokes flow in the situations where one has corners or cusps formed by parts of the domain boundary and, due to the nature of the boundary conditions on these parts of the boundary, these regions have a global effect on the shape of the whole domain and hence have to be resolved with sufficient accuracy. The algorithm combines the boundary integral equation method for the main part of the flow domain and the finite-element method which is used to resolve the corner/cusp regions. Two parts of the solution are matched along a numerical ‘internal interface’ or, as a variant, two interfaces, and they are determined simultaneously by inverting a combined matrix in the course of iterations. The algorithm is illustrated by considering the flow configuration of ‘curtain coating’, a flow where a sheet of liquid impinges onto a moving solid substrate, which is particularly sensitive to what happens in the corner region formed, physically, by the free surface and the solid boundary. The ‘moving contact line problem’ is addressed in the framework of an earlier developed interface formation model which treats the dynamic contact angle as part of the solution, as opposed to it being a prescribed function of the contact line speed, as in the so-called ‘slip models’. Keywords: Dynamic contact angle; finite elements; free surface flows; hybrid numerical technique; Stokes equations.

Fe-sulphate-rich evaporative mineral precipitates from the Rio Tinto, southwest Spain

The soluble metal sulphate salts melanterite, rozenite, rhomboclase, szornolnokite, copiapite, coquimbite, hexahydrite and halotrichite, together with gypsum, have been identified, some for the first time oil the banks of the Rio Tinto, SW Spain. Secondary Fe-sulphate minerals call form directly from evaporating acid, sulphate-rich Solutions as a result of pyrite oxidation. Chemical analyses of mixtures of these salt minerals indicate concentrations of Fe (up to 31 wt.%), Mg (up to 4 wt.%), Cu (up to 2 wt.%) and Zn (up to wt.%). These minerals are shown to act as transient storage Cor metals and can store on average up to 10% (9.5 - 11%) and 22% (20-23%) Zn and Cu respectively, of the total discharge of the Rio Tinto during the summer period. Melanterite and rozenite precipitates at Rio Tinto are only found in association with very acidic drainage waters (pH <1.0) draining directly from pyritic waste piles. Copiapite precipitates abundantly oil the banks of the Rio Tinto by (1) direct evaporation of the river water; or (2) as part of a paragenetic sequence with the inclusion of minor halotrichite, indicating natural dehydration and decomposition. The natural occurrences are comparable with the process of paragenesis from the evaporation of Rio Tinto river water under laboratory experiments resulting in the formation of aluminocopiapite, halotrichite, coquimbite, voltaite and gypsum.

The influence of Fe-rich coatings on the dissolution of anorthite at pH 2.6

Surface coatings are very common on mineral grains in soils but most laboratory dissolution experiments are carried out on pristine, uncoated mineral grains. An experiment designed to unambiguously isolate the effect of surface coatings on mineral dissolution from any influence of solution saturation state is reported. Two aliquots of 53 to 63 mum anorthite feldspar powder were used. One was dissolved in pH 2.6 HCl, the other in pH 2.6 FeCl3 solution, both for similar to6000 h in flow-through reactors. An amorphous Fe-rich, Al-, Ca- and Si-free orange precipitate coated the anorthite dissolved in the FeCl3 solution. BET surface area of the anorthite increased from 0.16 to 1.65 m(2) g(-1) in the HCl experiment and to 3.89 m(2) g(-1) in the FeCl3 experiment. The increase in surface area in the HCl experiment was due to the formation of etch pits on the anorthite grain surface whilst the additional increase in the FeCl3 experiment was due to the micro- and meso-porous nature of the orange precipitate. This precipitate did not inhibit or slow the dissolution of the anorthite. Steady state dissolution rates for the anorthite dissolved in the HCl and FeCl3 were similar to2.5 and 3.2 X 10(-10) mol(feldspar) m(-2) s(-1) respectively. These rates are not significantly different after the cumulative uncertainty of 17% in their value due to uncertainty in the inputs parameters used in their calculation is taken into account. Results from this experiment support previous theoretical and inference-based conclusions that porous coatings should not inhibit mineral dissolution. Copyright (C) 2003 Elsevier Ltd.

Inorganic synthesis of Fe-Ca-Mg carbonates at low temperature

A set of free-drift experiments was undertaken to synthesize carbonates of mixed cation content (Fe, Ca, Mg) from solution at 25 and 70 degrees C to better understand the relationship between the mineralogy and composition of these phases and the solutions from which they precipitate. Metastable solid solutions formed at 25 degrees C which are not predicted from the extrapolation of higher temperature equilibrium assemblages; instead, solids formed that were intermediary in chemical composition to known magnesite-siderite and dolomite solid solutions. A calcite-siderite solid solution precipitated at 25 degrees C, with the percentage of CaCO3 in the solid being proportional to the aqueous Ca/Fe ratio of the solution, while Mg was excluded from the crystal structure except at relatively high aqueous Mg/Ca and Mg/Fe ratios and a low Ca content. Alternatively, at 70 degrees C Mg was the predominant cation of the solid solutions. These results are compatible with the hypothesis that the relative dehydration energies of Fe, Ca and Mg play an important role in the formation of mixed cation carbonates in nature. (C) 2009 Elsevier Ltd. All rights reserved.

Differences in phosphorus retention and release in soils amended with animal manures and sewage sludge

Excessive levels of P in agricultural soils pose a threat to local water quality. This study evaluated (i) time-dependent changes in soil P sorption (expressed as a phosphorus sorption index, PSI) and P availability (as resin P) during incubation (100 d) with poultry litter, cattle slurry, sewage sludge, or KH2PO4, added on a P-equivalent basis (100 mg P kg(-1)), and (ii) the subsequent kinetics of P release, measured by repeated extractions with a mixed cation-anion exchange resin. Soil exchangeable Ca and ammonium oxalate-extractable Fe and Al were also determined at 100 d of incubation. The small decrease in P sorption in the litter and sludge treatments (25%), compared with that in the slurry and KH2PO4 treatments (52%) between 20 and 100 d of incubation was attributed partly to the formation of new adsorption sites for P. Subsequent P release was described by a power equation: Resin P = a(extraction number)(b), where the constants a and b represent resin P obtained with a single extraction and the rate of P release per resin extraction, respectively. On average, the rate of P release decreased in the order: KH2PO4 and slurry > litter > sludge, and was inversely related to exchangeable Ca content of the incubated soils (R-2 = 0.57). The slower rates of P release in the litter and sludge treatments (P < 0.001) are attributed to the large values for exchangeable Ca (1050-2640 and 1070-2710 mg kg(-1), respectively) in these amended soils. Future research concerned with short-term declines in environmentally harmful levels of P in recently amended soils should consider the differential effects of the amendments on soil P dynamics.

Enhanced phosphopeptide isolation by Fe(III)-IMAC using 1,1,1,3,3,3-hexafluoroisopropanol

IMAC can be used to selectively enrich phosphopeptides from complex peptide mixtures, but co-retention of acidic peptides together with the failure to retain some phosphopeptides restricts the general utility of the method. In this study Fe(III)-IMAC was qualitatively and quantitatively assessed using a panel of phosphopeptides, both synthetic and derived from proteolysis of known phosphoproteins, to identify the causes of success and failure in the application of this technique. Here we demonstrate that, as expected, peptides with a more acidic amino acid content are generally more efficiently purified and detected by MALDI-MS after Fe(III)-IMAC than those with a more basic content. Modulating the loading buffer used for Fe(III)-IMAC significantly affects phosphopeptide binding and suggests that conformational factors that lead to steric hindrance and reduced accessibility to the phosphate are important. The use of 1,1,1,3,3,3-hexafluoroisopropanol is shown here to significantly improve Fe(III)-IMAC enrichment and subsequent detection of phosphopeptides by MALDI-MS.

Enhanced phosphopeptide isolation by Fe(III)-IMAC using 1,1,1,3,3,3-hexafluoroisopropanol

IMAC can be used to selectively enrich phosphopeptides from complex peptide mixtures, but co-retention of acidic peptides together with the failure to retain some phosphopeptides restricts the general utility of the method. In this study Fe(III)-IMAC was qualitatively and quantitatively assessed using a panel of phosphopeptides, both synthetic and derived from proteolysis of known phosphoproteins, to identify the causes of success and failure in the application of this technique. Here we demonstrate that, as expected, peptides with a more acidic amino acid content are generally more efficiently purified and detected by MALDI-MS after Fe(III)-IMAC than those with a more basic content. Modulating the loading buffer used for Fe(III)-IMAC significantly affects phosphopeptide binding and suggests that conformational factors that lead to steric hindrance and reduced accessibility to the phosphate are important. The use of 1,1,1,3,3,3-hexa-fluoroisopropanol is shown here to significantly improve Fe(III)-IMAC enrichment and subsequent detection of phosphopeptides by MALDI-MS.

A new cyano-bridged one-dimensional (GdFeIII)-Fe-III coordination polymer with o-phenanthroline as the blocking ligand: synthesis, structure, and magnetic properties

Synthesis, structural characterization, and magnetic properties of a new cyano-bridged one-dimensional iron (III)-gadolinium (III) compound, trans-[Gd(o-phen)(2)(H2O)(2)(mu-CN)(2)Fe(CN)(4)], - 2no-phen (o-phen = 1,10-phenanthroline), have been described. The compound crystallizes in the triclinic P (1) over bar space group with the following unit cell parameters: a = 10.538(14) angstrom, b = 12.004(14) angstrom, c = 20.61(2) angstrom, alpha = 92.41(1)degrees, beta = 92.76(1)degrees, gamma = 11 2.72(1)degrees, and Z = 2. In this complex, each gadolinium (III) is coordinated to two nitrile nitrogens of the CN groups coming from two different ferricyanides, the mutually trans cyanides of each of which links another different Gd-III to create -NC-Fe(CN)(4)-CN-Gd-NC- type 1-D chain structure. The one-dimensional chains are self-assembled in two-dimensions via weak C-H center dot center dot center dot N hydrogen bonds. Both the variable-temperature (2-300 K, 0.01 T and 0.8 T) and variable-field (0-50 000 Gauss, 2 K) magnetic measurements reveal the existence of very weak interaction in this molecule. The temperature dependence of the susceptibilities has been analyzed using a model for a chain of alternating classic (7/2) and quantum (1/2) spins. (c) 2005 Elsevier B.V. All rights reserved.

The synthesis and characterisation of two new iron thioantimonates: [Fe(en)(3)](2)Sb2S5 center dot 0.55H(2)O and [Fe(en)(3)](2)Sb4S8

Two new iron thioantimonates, [Fe(en)(3)](2)Sb2S5 (.) 0.55H(2)O (1) and [Fe(en)(3)](2)Sb4S8 (2). were synthesised under solvothermal conditions from the reactions of Sb2S3, FeCl2 and S in the presence of ethylenediamine at 413 and 438 K, respectively. The products were characterised by single-crystal X-ray diffraction, elemental analysis and SQUID magnetometry. Compound 1 is unusual in containing isolated Sb2S54- anions formed from two corner-sharing SbS33- trigonal pyramids. These units are arranged in rippled layers, 4 A apart, parallel to the bc-plane. Octahedrally coordinated [Fe(en)(3)](2+) cations lie in depressions within these anionic layers. In compound (2), repeated corner linking of SbS33- trigonal pyramids generates SbS2- chains, which may be considered as a polymerised form of the Sb2S54- anions in 1. The SbS2- chains are separated by [Fe(en)(3)](2+) cations. In both compounds, there is an extensive network of hydrogen bonds between the nitrogen atoms of the ethylenediamine ligands and the sulfur atoms of the anions and, in the case of 1, the uncoordinated water molecule. (c) 2005 Elsevier Ltd. All rights reserved.

2D parallel interpenetration of [M-2(bpp)(4)X-4] [M, Fe(II)/Co(II); bpp, 4,4 '-trimethylenedipyridine; X, SCN-SeCN- and N-3(-)] complexes: pseudohalide-dependent conformation of bpp

Three coordination complexes of Co(II)/Fe(II) with 4,4'-trimethylenedipyridine (bpp) and pseudohalides (SCN-, SeCN- and N-3(-)) have been synthesized. The complexes have been characterized by X-ray single crystal structure determination. They are isomorphous having 2D layers in which two independent wavy nets display parallel interwoven structures. Pseudohalide binds metal centers through N terminal and occupies the trans axial positions of the octahedral metal coordination environment. Pseudohalide remains pendant on both sides of the polymeric layer and help the stacking through hydrogen bonding. The conformation of bpp in the interpenetrated nets is observed to be dependent on the choice of pseudohalide. (C) 2008 Elsevier Inc. All rights reserved.