one and two dimensional contaminant transport by pure diffusion through single layer of fine grained soil was investigated using one and two dimensional laboratory models. these models simulates a simple hydrogeologic situation underneath a solid waste landfill comprising a fine grained soil overlying a bed rock. sodium chloride solution was sued as a contaminant source above a compacted clayey...

Toppling failure is one of the most common modes of failure of rock slopes in layered rock strata. Flexural toppling is one of the well-known modes of the failure. This type of failure occurs due to bending stress. In this article, a brief yet comprehensive review of toppling failure is presented. Firstly, the conditions and general mechanism of the failure are described. Then, experimental, th...

Review of theoretical models for cost-effectiveness and of procedures currently being used by different levels of decision makers to evaluate the projects or alternatives is the main objective of this article. To come to some conclusion that which theoretical model would be more effective to be applied for allocating the limited resources among different projects. the performance evaluation pro...

One of the central issues in the study of discourse anaphora is concerned with the problem of anaphoric distribution in discourse, namely how to account for the choice of a particular referential/anaphoric form at a particular point in discourse. Needless to say, anaphoric distribution in discourse is a very complex phenomenon, involving, among other things, structural, cognitive and pragmatic ...

Although a complete nanotechnology does not yet exist, we can already foresee some new directions in theoretical computer science that will be required to help us design maximally efficient computers using nano-scale components. In particular, we can devise novel theoretical models of computation that are intended to faithfully reflect the computational capabilities of physics at the nano-scale...

A catastrophe is a type of instability in a simple dynamic system whose unfolding (=evolution) is structurally stable. Examples of commonly experienced catastrophes are sudden changes in a real system, e.g. switches between two states in a buckling plate or the breakdown of stability as in a bridge which collapses. These physical models show the direction for more abstract models as in the case...