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  • 1
    Electronic Resource
    Electronic Resource
    Spectral functions for the 2D Hubbard model (1995)
    Springer
    Journal of low temperature physics 99 (1995), S. 305-310 
    Details
    ISSN: 1573-7357
    Keywords: 74.20.−z ; 74.65.+n ; 71.28.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Spectral functions and quasiparticle bands are calculated with the modified alloy analogy approximation and are found to be in excellent agreement with the Monte Carlo data of Bulut et al. The Fermi surfaces also agree and have anomalously large volumes for large U near half-filling. In the modified alloy analogy this is a symptom of the breakdown of Fermi liquid theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00752298
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  • 2
    Electronic Resource
    Electronic Resource
    The normal and superconducting states of the 2D Hubbard model (1995)
    Springer
    Journal of low temperature physics 99 (1995), S. 403-408 
    Details
    ISSN: 1573-7357
    Keywords: 74.20.−z ; 74.65.+n ; 71.28.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A Green's function decoupling method is shown to yield quasiparticle bands for the 2D Hubbard model in excellent agreement with the Monte Carlo results of Bulut et al. The same approach gives d-wave superconductivity with Tc in the range 10–100K for a band-width of 4eV, on-site interaction U = 2eV and the Fermi level close to a van Hove singularity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00752316
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  • 3
    Electronic Resource
    Electronic Resource
    Factors affecting aluminium sorption by calcium pectate (1993)
    Springer
    Plant and soil 149 (1993), S. 87-94 
    Details
    ISSN: 1573-5036
    Keywords: aluminium ; calcium ; calcium pectate ; polygalacturonic acid ; solution pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Extracellular processes, particularly the adsorption of aluminium (Al) by pectate in the cell wall, have been proposed as important in the expression of Al toxicity to plant roots. In vitro studies were conducted on the effects of Al concentration (generally ≤ 32 μM), calcium (Ca) concentration (0.05 to 10 mM) and pH (3.2 to 5.4) on Al sorption by Ca pectate. There was a rapid reaction between Al and Ca pectate, there being no difference in Al remaining in solution after reaction times of 1 to 16 min, and only a slight decrease after 24 h. Increased Al concentration in solution increased linearly the sorption of Al by Ca pectate, with 70 to 84% of the Al originally in solution sorbed with ≤32 μM Al. In contrast, Al sorption decreased with increased Ca concentration in solution, and as pH decreased from 5.4 to 3.2. Only ≤30% of the sorbed Al was desorbed after 1 h by 1 mM CaCl2, 10 mM CaCl2 or 1 mM HCl. The amount of Al desorbed increased with a desorption period of 5 h, particularly with 1 mM HCl. These studies suggest that Al sorbed by Ca pectate in root cell walls is in equilibrium with Al in solution, and that Al toxicity is associated with the strong binding between Al and Ca pectate external to the cytoplasm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010765
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  • 4
    Electronic Resource
    Electronic Resource
    Chromatographic techniques for the separation of Al and associated organic ligands present in soil solution (1995)
    Springer
    Plant and soil 171 (1995), S. 29-34 
    Details
    ISSN: 1573-5036
    Keywords: aluminium ; chromatography ; dissolved organic carbon ; organic acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Organic acids including humic, fulvic, aliphatic and aromatic acids comprise part of the dissolved organic carbon (DOC) present in soil solution. They act as ligands for trace metals and are effective detoxifiers of monomeric aluminium (Al). Solid phase extraction (SPE) techniques permit fractionation of the DOC into organic classes but yield no information on the pre-existing Al/organic acid complexes. Aliphatic and aromatic acids may be separated and determined by High Performance Liquid Chromatography (HPLC); however, the conditions used dissociate the organic acid Al complexes. Humic and fulvic acids are of a variable and ill-defined nature and only limited information exists regarding their binding of Al. This paper reports on fractionation studies of soil solutions, using both SPE and molecular weight cut-off filters, to characterise the DOC components and on the subsequent development of a size exclusion chromatography (SEC) system for the separation of organically complexed Al into different species using a low ionic strength mobile phase at pH 4.2. Model complexes of Al and Cu citrate were used to evaluate chromatographic performance of a Fractogel TSK HW-40(S) column (1×30 cm). For soil solution samples, the column eluate, after passing through a UV detector, was directly coupled to an Inductively Coupled Plasma Atomic Emission Spectrometer (ICPAES) for on-line multi-element detection to characterise DOC and trace metal distribution. Fractionation studies revealed that polysaccharides constituted the major proportion of the DOC which passed the 10000 dalton molecular weight cut-off filter. Analysis of soil solutions from an organically amended soil by the SEC-ICPAES system showed that Al, Fe and Mn eluted as multiple peaks prior to the bed volume, indicating their presence as complexes with organic ligands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009560
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  • 5
    Electronic Resource
    Electronic Resource
    Quantitative 27Al NMR spectroscopic studies of Al (III) complexes with organic acid ligands and their comparison with GEOCHEM predicted values (1995)
    Springer
    Plant and soil 171 (1995), S. 35-39 
    Details
    ISSN: 1573-5036
    Keywords: aluminium ; equilibrium calculations ; GEOCHEM ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The toxic inorganic monomeric forms of aluminium (Al) that limit plant growth have been shown to be effectively detoxified by complexation with organic acid ligands released by breakdown of added organic materials. The binding capacity of these acids is dependent on the degree of dissociation of their carboxyl groups and their ability to form bonds with Al. 27Al NMR spectroscopy provides a non-invasive technique to study the bonding of Al with potential ligands without disturbing the equilibrium of the system. In single ligand systems containing oxalic acid, three 27Al resonance peaks were observed at 6.4, 11.4 and 16.0 ppm downfield from the Al3+ reference peak at 0 ppm. These were assigned to Alox, Alox2 and Alox3 complexes respectively and were observable at pH values down to 3.5. In the presence of the citrate ligand, two 27Al resonance peaks at 6.1 and 11.3 ppm, assigned respectively to the Alcit and Alcit2 complexes, were observed at pH 3.4. At pH 4.3 and an Al:citrate molar ratio of 1:2, the 6.1 ppm peak was not visible, and the second peak further downfield was split into two unresolved peaks at 10.8 and 12.4 ppm indicating the presence of two forms of the Alcit2 complex. Distribution of Al between the various species, based on integration of the resonance peaks and equilibrium calculations carried out using GEOCHEM, is discussed in light of the stability constants present in the database of GEOCHEM version (v.) 1.23 and GEOCHEM-PC v. 2.0. Large discrepancies between the computed values and the NMR measured values indicate the need to incorporate more recent literature values in the database for realistic equilibrium calculations in systems containing organic acid ligands. The potential of using quantitative 27Al NMR measurements to calculate stability constants is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009561
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