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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 694-698 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report a molecular dynamics simulation of the absorption of water in polymers. We embed a relatively large repeat unit containing several characteristic chemical groups in a molecular dynamics model of water which includes the internal dynamics of the water molecule. Potentials describing the interaction of the water with the repeat unit were taken from the work of Jorgensen and co-workers. We calculated the density of water around oxygen in ester, ether and alcohol groups in the repeat unit. We find in this model that the water is only bound by the alcohol group in agreement with recent experimental results. We have computed the infrared absorption spectrum of the bound and unbound water in this model. We find shifts which should be observable in the position of the stretch and librational frequencies due to binding of the water. We discuss implications for the dual diffusion model of water in polymers.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Agroforestry systems 28 (1994), S. 143-157 
    ISSN: 1572-9680
    Schlagwort(e): agroforestry ; indigenous knowledge ; Orinoco floodplains ; soil nitrogen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Beschreibung / Inhaltsverzeichnis: Resumen Estudios agrícolas en areas tropicales sujetas a inundación estacional han sido limitados. Los suelos aluviales o vegas del Orinoco son más fértiles que suelos cercanos no sujetos a inundación y por lo tanto han sido considerados como areas potenciales para desarrollos agrícolas. Prácticas tradicionales de agroforestería constituyen una alternativa en el control de importantes factores limitantes en la agricultura de vegas. El conocimiento técnico autóctono asociado con prácticas agroforestales tradicionales de vegas fue evaluado y algunos indicadores de la dinámica de nitrógeno y biomas adel sistema fueron monitoreados. La contribución de nitrógeno por sedimentos y hojarasca fue de 1668 and 47 kg ha−1 respectivamente. La selección del tipo de sedimento a depositarse en la parcela agrícola, por medio de barreras de vegetación, y el manejo adecuado de resíduos orgánicos constituyen estrategias tradicionales que aumentan la eficiencia de uso de nutrientes en sistemas agrícolas de vegas.
    Notizen: Abstract Agricultural studies in seasonally flooded areas in the tropics have been limited. Orinoco alluvial soils are more fertile than adjacent non-flooded soils, and have been considered as potential areas for further agricultural development. Traditional agroforestry practices offer some possibilities to overcome the most limiting factors of floodplain cultivation. Indigenous knowledge of these traditional agroforestry practices was assessed and some indicators of the system's nitrogen and biomass dynamics were monitored. Nitrogen inputs by sediment and plant residues were 1668 and 47 kg ha−1, respectively. Traditional selection of sediment by tree-and-grass barriers and litter management strategies increase nutrient-use efficiency in floodplain agroecosystems.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 52 (1988), S. 1461-1478 
    ISSN: 1572-9613
    Schlagwort(e): Nonequilibrium stationary states ; stochastic lattice gas ; high-temperature approximations ; pair correlations ; power law decay
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We report computer simulations and high-temperature approximations of the pair correlation in a stationary nonequilibrium system, a lattice gas subject to a strong uniform driving fieldE. The dynamics of the system is given by hoppings of particles to adjacent empty sites with rates biased for jumps in the direction ofE. We study the anisotropic short-distance behavior as well as the long-distance decay properties of the two-point correlations along the principal axes. The simulations as well as the (approximate) expansion inβ strongly suggest that the correlations in this system have a power law decay,r −D for dimensionsD=2 and 3, even at high temperatures.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 49 (1987), S. 121-137 
    ISSN: 1572-9613
    Schlagwort(e): Stochastic lattice-gas model ; stationary nonequilibrium states ; fast ionic conductors ; metastability ; nonequilibrium first-order phase transitions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Two-dimensional lattice-gas models with attractive interactions and particle-conserving hopping dynamics under the influence of a very large external electric field along a principal axis are studied in the case of off-critical densities. We describe the corresponding nonequilibrium first-order phase transitions, evaluate coexistence and spinodal lines, and make some comparisons with experimental observations on fast ionic conductors.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 49 (1987), S. 89-119 
    ISSN: 1572-9613
    Schlagwort(e): Stochastic lattice-gas model ; stationary nonequilibrium states ; fast ionic conductors ; nonequilibrium critical behavior
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Two-dimensional lattice-gas models with attractive interactions and particleconserving happing dynamics under the influence of a very large external electric field along a principal axis are studied in the case of a critical density. A finite-size scaling analysis allows the evaluation of critical indexes for the infinite system asβ=0.230±0.003,v=0.55±0.2, and α 0. We also describe some qualitative features of the system evolution and the existence of certain anisotropic order even well above the critical temperature in the case of finite lattices.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 55 (1989), S. 745-767 
    ISSN: 1572-9613
    Schlagwort(e): Quantum particle ; classical bath ; two-level approximation ; real-time correlation functions ; frequency shift ; path integral Monte Carlo ; analytic continuation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We investigate the behavior of a two-level quantum system in contact with a classical heat bath, e.g., a solute particle with internal degrees of freedom immersed in a solvent of massive particles. Using a combination of analytical and numerical methods, we obtain precise information about localization, time-displaced correlation functions, and the frequency-dependent susceptibility of such solute particles. We find that these quantities can have a strong dependence on the density of the solvent fluid, with the maximum changes from the behavior of the corresponding isolated quantum system occurring in many cases at very low densities. We compare the exact results with those obtained by path integral Monte Carlo. There is good agreement with the imaginary time correlations, but analytic continuation to real time proves elusive: even with the best numerical data on the former, we can only get very gross features of the latter.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 43 (1986), S. 441-461 
    ISSN: 1572-9613
    Schlagwort(e): Stochastic lattice-gas model ; stationary nonequilibrium states ; superionic conductors ; hopping dynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Two-dimensional lattice-gas models with attractive interactions and particle-conserving hopping dynamics under the influence of a very large external electric field ⇀E along a principal axis are studied in the case of different ratiosγ between the jump rates in the field direction and perpendicular to it using different transition probabilities. We investigate the dependence of the non-equilibrium steady-state properties on the transition mechanism. We find self-similarity with respect to (T, γ) and a coexistence curve critical exponent which, for smallγ, seems independent ofγ. There is some evidence that this exponent might be halfway between the equilibrium mean field and Onsager's values. A crossover toward mean-field behavior for largeγ seems also identified.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 56 (1989), S. 43-58 
    ISSN: 1572-9613
    Schlagwort(e): Nonequilibrium steady state system ; interfaces ; phase ; transitions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present the first study of a driven nonequilibrium lattice system in the two-phase region, withshifted periodic boundary conditions, forcing steps into the interface. When the shift corresponds to small angles with respect to the driving field, we find nonanalytic behavior in the (internal) energy of the system, supporting numerical evidence that interface roughness is suppressed by the field. For larger shifts, the competition between the driving field and the boundary induces the breakup of a single strip with tilted interfaces into many narrower strips with aligned interfaces. The size and temperature dependences of the critical angles of such breakup transitions are studied.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 51 (1988), S. 321-321 
    ISSN: 1572-9613
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 51 (1988), S. 323-323 
    ISSN: 1572-9613
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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