Second language scholars, in public research and in public discussions, have suggested that Krashen's construct of i + 1 is similar to Vygotsky's zone of proximal development and that it might therefore be feasible to integrate the two constructs in a way that would be productive for second language acquisition (SLA) research. After surveying publications relevant to the issue, we argue that this enterprise is futile, not only because the concepts are unrelatable, but also because they are rooted in incommensurable theoretical discourses. We also propose a way in which SLA research and theory might deal with incommensurability.
A Zft-L d, packed gas-absorption. column was constructed for the purpose of obtaining longitudinal mixing data on both the liquid and gas phases under nonabsorbing operating conditions. The equipment is described in detail and the operating procedure is given.. The calculation of the liquid-phase Peclet number of an.early run is reported.
Stochastic models of turbulent atmospheric dispersion treat either the particle displacement or particle velocity as a continuous time Markov process. An analysis of these processes using stochastic differential equation theory shows that previous particle displacement models have not correctly simulated cases in which the diffusivity is a function of vertical position. A properly formulated Markov displacement model which includes a time-dependent settling velocity, deposition and a method to simulate boundary conditions in which the flux is proportional to the concentration is presented. An estimator to calculate the mean concentration from the particle positions is also introduced. In addition, we demonstrate that for constant coefficients both the velocity and displacement models describe the same random process, but on two different time scales. The stochastic model was verified by comparison with analytical solutions of the atmospheric dispersion problem. The Monte Carlo results are in close agreement with these solutions.
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