The formal expression of pro positional attitudes, especially when nested (iterated), is an important problem for A I . An interesting first-order extensional logical system for such expression has been proposed by Creary. In this system concepts (and concepts of concepts, etc.) are made explicit. The system includes "concept functions", which are special functions which act on and deliver conc...

Soil salinity is one of the problems threatening agricultural lands. Parts of this phenomenon are related to geologic formations and saltpans, while some major factors are resulted from irrelevant agricultural activities, issue of irrigation, and improper cultivation systems which lead to increase in soil salinity. To avoid such consequences that would end up with ecosystem degradation, suitabl...

the relationship between topography, soil factors, and distribution of ecological vegetation groups in the nodoushan arid rangelands of yazd province (iran) was investigated. the present species were recorded in each vegetation group using a randomized-systematic sampling method. plant cover and density were estimated quantitatively using the transect and quadrate methods, and the two-way indic...

subalpine ecosystems are highly fragile as compared to biological andenvironmental factors. landslide is one of the ruinous upshots of this ecosystem. one of theimpressionable areas in the cause of natural factor is masoleh watershed in western alborzmt, (iran). in order to landslide hazard zonation, landslide index and frequency ratio methodbased on twelve causative factors such as slope, slop...