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  • 1
    Electronic Resource
    Electronic Resource
    Nitrogen transformation in arable soils of North-West Germany during the cereal growing season (1996)
    Springer
    Biology and fertility of soils 22 (1996), S. 179-183 
    Details
    ISSN: 1432-0789
    Keywords: Key words Microbial N ; Immobilization ; Remobilization ; NH4+ fixation ; Exchangeable NH4+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In 1991, field experiments on loess (with winter wheat) and sandy soils (with summer barley) were conducted to study N dynamics in the microbial biomass and non-exchangeable NH4 +. The measurements showed a mass change in microbial N, with a maximum increase of 100 kg N ha–1 30 cm–1 from March to July in the loess soil, and a change for only 1 month (May) in the sandy soil. Plots treated with conventional levels of N fertilizer (213 kg N ha–1 on a loess soil to winter wheat and 130 kg ha–1 on the sandy soil to summer barley), reduced levels of N (83% and 62% of the conventional N application), or no N showed no consistent fertilizer N effect on microbial biomass N. From March to July, non-exchangeable NH4 + in loess soils under winter wheat decreased by 110 kg N ha–1 30 cm–1 in conventionally fertilized plots and by 200 kg N ha–1 30 cm–1 in a plot with no N fertilizer. After harvest, the pool of non-exchangeable NH4 + increased due to increasing mineral N concentrations in the soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384452
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Nitrogen transformation in arable soils of North-West Germany during the cereal growing season (1996)
    Springer
    Biology and fertility of soils 22 (1996), S. 179-183 
    Details
    ISSN: 1432-0789
    Keywords: Microbial N ; Immobilization ; Remobilization ; NH inf4 sup+ fixation ; Exchangeable NH inf4 sup+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In 1991, field experiments on loess (with winter wheat) and sandy soils (with summer barley) were conducted to study N dynamics in the microbial biomass and non-exchangeable NH inf4 sup+ . The measurements showed a mass change in microbial N, with a maximum increase of 100 kg N ha-1 30 cm-1 from March to July in the loess soil, and a change for only 1 month (May) in the sandy soil. Plots treated with conventional levels of N fertilizer (213 kg N ha-1 on a loess soil to winter wheat and 130 kg ha-1 on the sandy soil to summer barley), reduced levels of N (83% and 62% of the conventional N application), or no N showed no consistent fertilizer N effect on microbial biomass N. From March to July, non-exchangeable NH inf4 sup+ in loess soils under winter wheat decreased by 110 kg N ha-1 30 cm-1 in conventionally fertilized plots and by 200 kg N ha-1 30 cm-1 in a plot with no N fertilizer. After harvest, the pool of non-exchangeable NH inf4 sup+ increased due to increasing mineral N concentrations in the soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384452
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Analysis of the ground-state wave function of theJ 1-J 2 quantum Heisenberg antiferromagnet (1993)
    Springer
    The European physical journal 93 (1993), S. 21-31 
    Details
    ISSN: 1434-6036
    Keywords: 75.10.Jm ; 75.40.Cx ; 75.50.Ee
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigate the ground-state wave function $$|\psi \rangle = \sum\limits_n {\alpha _n } |n\rangle $$ of the spin-1/2J 1-J 2 model on finite square lattices ofN=16(4×4) andN=24(4×6) sites. We find that the Marshall-Peierls phase rule for coefficientsα n , which was derived for unfrustrated bipartite lattices (J 2=0), holds exactly for comparably large frustration up toJ 2/J 1=0.28 (N=16) and up toJ 2/J 1=0.20 (N=24). But even for strong frustration up toJ 2/J 1≈0.45 the Marshall-Peierls rule describes the phase relationships in the ground state excellently. In the region of dominatingJ 2 a phase rule can be formulated as a product of the rules for two independent antiferromagnets. We find that the violation of the Marshall-Peierls sign rule does not dramatically affect the order parameters up toJ 2/J 1≈0.6. To calculate the magnitude of the coefficientsα n by a variational procedure we search for a represantative relationship between theα n and (a few) parametersP 1,n ...P k, n classifying the Ising basis states |n〉. By comparison with the exact ground state we analyze classification schemes based on pair correlations (Jastrow type wave functions) as well as schemes taking into account cluster parameters. While for small frustrationJ 2/J 1〈0.2 a short-range Jastrow description (nearest-neighbour and next nearestneighbour pairing) seems to be sufficient for the adequate description of the ground state one definitly needs longrange pairing and/or cluster parameters to construct a reasonable trial wave function for strong frustration. As an example for a special Jastrow type wave function we discuss an ansatz coming from the spin-wave theory. Finally, we consider the influence of the anisotropic exchangeJ zz ≠J xx ,J yy on the quality of the short-range Jastrow wave function and find and excellent agreement with the exact ground state already for Ising exchange anisotropiesJ xx =J yy ≈0.5J zz .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01308803
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum fluctuations in structurally disordered antiferrromagnets (1995)
    Springer
    Journal of low temperature physics 99 (1995), S. 359-361 
    Details
    ISSN: 1573-7357
    Keywords: 75.10.Jm ; 75.50.Ee ; 71.55.Jv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present exact diagonalisation data for the ground state of finite two-dimensional spin 1/2 Heisenberg antiferromagnets with structural disorder. The combination of antiferromagnetic coupling and structural disorder creates frustation and a local singlet formation which may strongly influence the magnetic ordering. In detail we study the magnetic radial distribution function, the magnetic order parameter M2 as well as a parameter measuring the spin misfit and present these quantities in dependence on the strength of the structural disorder. We estimate the critical disorder where the antiferromagnetic long-range order breaks down.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00752309
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    Paper (German National Licenses)
    Fulltext
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