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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4889-4900 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive picture of three-dimensional (3D) isotropic magnetohydrodynamic (MHD) turbulence is presented based on the first 5123-mode numerical simulations performed. Both temporal and spatial scaling properties are studied. For finite magnetic helicity H the energy decay is governed by the constancy of H and the decrease of the ratio of kinetic and magnetic energy Γ=EK/EM. A simple model consistent with a series of simulation runs predicts the asymptotic decay laws E∼t−1/2, EK∼t−1. For nonhelical MHD turbulence, H(similar, equals)0, the energy decays faster, E∼t−1. The energy spectrum follows a k−5/3 law, clearly steeper than k−3/2 previously found in 2D MHD turbulence. The scaling exponents of the structure functions are consistent with a modified She–Leveque model ζpMHD=p/9+1−(1/3)p/3, which corresponds to a basic Kolmogorov scaling and sheet-like dissipative structures. The difference between the 3D and the 2D behavior can be related to the eddy dynamics in 3D and 2D hydrodynamic turbulence. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 824-834 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of different dynamic gradient-diffusion type subgrid models is evaluated in large-eddy simulations (LES) of magnetohydrodynamic (MHD) turbulence with a maximum of 643 collocation points. The reference data stems from high-resolution direct numerical simulations of decaying and forced MHD turbulence with up to 5123 spectral modes. Comparisons between LES' and the grid filtered reference systems are carried out regarding the temporal evolution of the global quantities kinetic and magnetic energy, cross helicity, magnetic helicity, and the spectra of energy and energy flux. The influence of the subgrid models on the statistical properties of the simulated flows is also examined. Apart from unconditionally dissipative models, direct divergence modeling and the effects of additional explicit filtering in combination with a tensor-diffusivity term are considered. A new genuine MHD subgrid model, based on the cross-helicity invariant, is presented and observed to perform outstandingly well. © 2002 American Institute of Physics.
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  • 3
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 50 (2005), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Research has often focused on pelagic food chains and processes of lakes; less is known about the contribution of benthic energy flows to whole-lake ecosystem energetics. This stems from the fact that the shoreline and littoral habitats, which provide a key linkage between sediment and water column, have only recently become a significant focus for study.2. This study aimed to quantify the feeding and phosphorus allocation of a juvenile fish community in a littoral zone of a shallow lake in response to the biomass succession of the invertebrate prey community. Habitats comprising reed and adjacent open water were sampled over two consecutive years during day and night.3. Although there were substantial year-to-year differences in the biomass of invertebrates, the fish community composition, diet consumption rates and phosphorus allocations were very similar in both study years. Biomasses and predation impacts by juvenile fish on prey groups were substantially higher within the reeds than in the adjacent open water habitat. This may be explained by the refuge-seeking behaviour of the fish.4. In general, invertebrates were negligibly influenced by fish feeding, with the exception for a strong top-down control of large cladocerans. In response to the resulting low Daphnia biomass, fish were forced to switch to a higher degree of benthivory. Consequently, juvenile fish in littoral reed stands may shift benthic-derived energy and phosphorus via the excretion of soluble reactive phosphorus into the open water.
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  • 6
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1721-1728 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new x-ray scattering environment is presented which can be employed at high temperatures up to 2000 K and high pressures up to 150 bar. This device is especially designed for angle-dispersive scattering experiments. It consists of a thick closed-end aluminum cylinder equipped with a steel flange. Incident and scattered radiation passes through continuous Be windows which cover an angle range up to 55°. The high potential of this scattering setup is demonstrated by representative example experiments at high temperatures and high pressures, which could be carried out in combination with a single-crystal sapphire cell. Inelastic-, elastic-, and anomalous scattering experiments using synchrotron radiation and energy dispersive static measurements employing a conventional tube device are reported. © 2001 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 49 (2004), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Research has often focused on the pelagic areas of lakes; the littoral zone has received less attention. The few studies concerning fish distribution in littoral habitats have concentrated on stands of submersed macrophytes, whereas other littoral habitat types have seldom been investigated.2. This study aimed to predict the occurrence of juvenile fish in several littoral habitats of a shallow lake as a function of food availability, complexity of habitat structure, water depth and substrate. Habitats comprising reed, woody structures, and two open water areas differing in depth were sampled for fish and invertebrate biomasses on two shores, over 6 months and during both daylight and at night.3. The juvenile fish community consisted almost exclusively of 0+ and 1+ roach and perch. There was a strong diel component in habitat use, with a predominant occurrence of fish in complex habitats (mainly woody structures) during the day, and a partial migration towards the open habitats at night, more strongly expressed in roach than in perch.4. The diet of all fish groups was relatively constant over the seasonal cycle, and was independent of habitat. There was a higher degree of planktivory in roach than in perch, but both species fed on benthic macroinvertebrates to a substantial extent.5. According to a logistic regression model, the biomass of potential food organisms in the different habitats had little predictive effect on the spatial distribution of the fish, whereas the structural complexity of the habitats combined with the diel cycle explained about 28% of the occurrence patterns in 0+ and 1+ perch and 1+ roach.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Chemie 129 (1998), S. 633-642 
    ISSN: 1434-4475
    Keywords: Keywords. Molecular calculations; ab initio Calculations; Conformational analysis; Levcromakalim; Potassium channel opener.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung.  Die Konformationen des Kaliumkanalöffners Levcromakalim werden mit Hilfe quantenchemischer Molekülrechnungen untersucht, um die energetisch günstigsten Strukturen zu bestimmen. Der Einfluß der intramolekularen Wasserstoffbrücke auf die Konformationen und die Dynamik des Moleküls wird analysiert. Die Geometrien verschiedener rigider Analoga werden mit den konformativen Möglichkeiten des Levcromakalims verglichen, um Ähnlichkeiten der Molekülgestalt festzustellen.
    Notes: Summary.  The conformations of the potassium channel opener levcromakalim are analyzed with the aid of quantum chemical calculations in order to determine the energetically most favourable structures. The influence of intramolecular hydrogen bonding on the conformations and on the rotational potential of the molecule is investigated. The structures of different conformationally restricted analogs are compared with the energetically accessible conformational space of levcromakalim with emphasis on similarities in molecular shape.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    International journal of earth sciences 82 (1993), S. 1-2 
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
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