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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, U.K. and Cambridge, USA : Blackwell Science Ltd
    Plant pathology 45 (1996), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: We propose and illustrate a likelihood-based method for fitting spatio-temporal stochastic models for the spread of a plant disease to experimental observations. The models considered are individual-based, with members of the population occupying discrete sites on a two-dimensional lattice. The disease is assumed to be characterized by presence/absence, and infection of susceptible individuals by infected individuals is represented as a stochastic process. The method described can be applied to estimate parameters in models of this kind when observations consisting of temporal sequences of disease maps are available. The use of measures of spatial aggregation as measured from simulated and real epidemics is proposed as a means of assessing the relative merits of alternative models for the spread of a disease. To illustrate the technique we fit and compare two models, which differ in the relationship between infective pressure and distance, to observations of an epidemic of citrus tristeza virus (CTV). It is demonstrated that a model in which this relationship is a power-law is superior to one which uses a negative exponential and the importance of model choice for the design of control strategies is discussed briefly.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 558-564 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a study of the effect of high (∼1×105 V/cm) perpendicular electric fields on the electronic structure of a GaAs-Ga0.7Al0.3As superlattice represented by five quantum wells separated by 70-A(ring) barriers. An exact solution is obtained by using the transfer-matrix technique to match the Airy functions at the interfaces. The method of phase-shift analysis is employed to evaluate the energy levels, the width of the Stark resonances, the real-space wave functions, and the time of flight associated with the field-induced phenomena. Wells of 50- and 70-A(ring) width are used to elucidate the relationship between level depth and field. The quantum states above the semiclassical confining barrier, which have so far been represented by a continuum, are correctly accounted for. These states are mainly localized in the barrier material. It is shown that the real-space localization and bandwidth of these states are significantly altered by the external field. In particular, we evaluate the time delay for electrons above the barrier due to the field-induced change in the density of states, which is related to the presence of the above higher-lying confined states and which would be observed in current–voltage measurements.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 449-455 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The summation of the perturbation series for the hydrogen Zeeman effect using the renormalized series technique is studid. Improved results are obtained compared to those obtained from the unrenormalized series; the method has the advantage of not requiring any information on the largeorder behavior of the perturbation series coefficients.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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