The ratio-type estimators have been introduced for estimating the mean and total population, but in recent years based on the ratio methods several estimators for population variance have been proposed. In this paper two families of estimators have been suggested and their approximation mean square error (MSE) have been developed. In addition, the efficiency of these variance estimators are com...

erosion and sediment movement phenomena are one of the most complex issues in management of rivers drainage areas that in water projects are very important. that its measurement wants high time and cost. issue of surface runoff in river basin is a complex issue that human knowledge and understanding about its physical laws a viewpoint of some mathematical formulas is limited. in this study to i...

wireless sensor networks attracting a great deal of research interest. accurate localization of sensor nodes is a strong requirement in a wide area of applications. in recent years, several techniques have been proposed for localization in wireless sensor networks. in this paper we present a localization scheme with using only one mobile anchor station and received signal strength indicator tec...