this study aimed to evaluate the potential of image ratioing techniques to detect and map the extent and particle composition of sand dunes in the erg of gavkhouni in isfahan province. the 6/4 ratio index and also a new index called sadi which was calculated using landsat band 3, 6 and 7 were applied to a georeferenced landsat tm image. to evaluate the performance of ratio techniques, the extra...

the percent of normal precipitation index (pnpi) is a widely used drought index to provide good estimations about the intensity, magnitude and spatial extent of droughts. the objective of this study was analyzing spatial pattern of drought by pnpi index. in this paper, according to the data of 40 stations in iran, during 1967-2009, the pattern of drought hazard is evaluated. influenced zone of ...

The city of Tehran undergoes an increasing growth in population as well as industrial activities, both of which increase the concentration of air pollutants. The current research tries to turn a limited and focused system of air contamination measurement and control to an unlimited and extensive one that examines the concentration of each of the contaminants in any area of Tehran. Accordingly, ...

background: given the increasing importance of suspended particles and reporting weather conditions in the amount of ultraviolet radiation in many countries, in this study, the data of the maximum amounts of pollution by suspended particles with the size of 10, 2.5 and1 microns (pm10, pm2.5, pm1) which were reported in 1-hour time-series and global ultraviolet index (uvi) were used to predict t...

Let X be a smooth curve defined over Q̄, let a, b ∈ P(Q̄) and let fλ(x) ∈ Q̄(x) be an algebraic family of rational maps indexed by all λ ∈ X(C). We study whether there exist infinitely many λ ∈ X(C) such that both a and b are preperiodic for fλ. In particular, we show that if P,Q ∈ Q̄[x] such that deg(P ) 2 + deg(Q), and if a, b ∈ Q̄ such that a is periodic for P (x)/Q(x), but b is not preperiodic f...

Let C r ((0; 1]) denote the metric space of C r self-maps of 0; 1] and C s;r ((0; 1]) denote the metric space of C s families of maps in C r ((0; 1]) with the parameter space 0; 1]. Let Hs;r be the unimodal families with non-constant topological entropy in C s;r ((0; 1]). We show that for s 0, r 2, there is an open and dense subset Gs;r of Hs;r such that each family in Gs;r has a map with a hom...