During the past two decades, significant efforts have been made to study contaminant transport in the presence of colloids. Several researchers reported that colloidal particles could enhance the migration of contaminants in groundwater by reducing retardation factor. When the colloidal particles are present in the aquifer, the subsurface system can be considered as a three-phase system with two solid phases and an aqueous phase. The interaction between contaminants, colloids, and solid matrix should be considered in assessing the fate and transport of the contaminant in the groundwater flow system. In this study, a one-dimensional numerical model is developed by employing a fully implicit finite difference method. This model is based on mass balance equations and mass partition mechanisms between the carriers and solid matrix, as well as between the carriers and contaminants in a saturated homogeneous porous medium. This phenomenon is presented by two approaches: equilibrium approach and fully kinetic first-order approach. The formulation of the model can be simplified by employing equilibrium partitioning of particles. However, contaminant transport can be predicted more accurately in realistic situations by kinetic modeling. To test the sensitivity of the model, the effect of the various chemical and physical coefficients on the migration of contaminant was investigated. The results of numerical modeling matched favorably with experimental data reported in the literature.
This paper focuses on the uplink transmission in a cellular system in which the channels in two neighboring cells are modeled as two mutually interfering multiple access channels (2-IMAC). The base stations (BSs) are equipped with multiple antennas while each user has only one antenna and K users are active in each cell. By increasing the number of users, it is shown in [1] that for single-antenna BSs, using interference alignment, each cell can approach the interference-free degrees of freedom (DOF) provided that the bandwidth is sufficiently large. But as the number of users grows, the correlation between adjacent subcarriers increases and this degrades the performance of interference alignment. The proposed scheme incorporates the concept of cyclic delay diversity (CDD) to reduce the correlation among subcarriers with the help of multiple antennas at the BSs. Simulation results show the performance improvement of the proposed scheme.
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