سال:1380 | دوره: | شماره: |تعداد مقالات:6

Many freshwater gastropodes are involved in the life cycle of parasitic flukes. Some of these are important in public heath and veterinary medicine. A comprehensive snail search was undertaken throughout provinces in Iran. In the first step, freshwater bodies of Khuzestan, were searched for potential intermediate host snails. Fifteen taxa, namely 8 prosobranch snails and 7 pulmonate snails were collected during the 1990s. Neritina mesopotamica Martens 1879 was found to be new species for Khuzestan.

A conductance study of the interaction between Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ and Hg2+ ions with thiophen derived schiffs base in acetonitrile solution has been carried out at different temperatures. Formation constants of the resulting 1:1 complexes were determined from the molar conductance - mole ratio data and found to vary in the sequence Pb2+> Hg2+> Cd2+> Cu2+> Ni2+> Co2+> Zn2+. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constant. In all cases, the complexes were found to be enthalpy stabilized but entropy destabilized.

Variations in ratios of chorate (C) dinoflagellate cysts to proximo-chorate (P), proximate (P) and cavate (C) forms recovered from the Rhodano-Swabian sedimentary basin in northern Switzerland have been correlated with sequence boundaries and sedimentary cycles established for this basin. The variations in these ratios and abrupt increases and decreases in the number of recorded species from the same strata corroborate closely the sequence boundaries established by Gygi et al., (1998) using other parameters such as lithology and macrofossil content of the sediments. Highstands of sea level are marked by an abrupt increase in species diversity and in C: PPC ratio. In contrast, lowstands are indicated by rapid decline in the abundance of species and a decrease in C: PPC ratios.

This study was carried out to the southern part of the Derenjal mountains, some ten kilometers north of Shirgesht village in East-Central Iran. Stratigraphy of Derenjal, Shirgesht and Niur localities indicate some Lower Palaeozoic rock units in these areas. Among the above-mentioned rock units, the uppermost part of Derenjal Formation, Shirgesht Formation and Niur Formation were studied from palynological point of view. For this purpose the upper part of the Derenjal, Shirgesht and Niur formations were systematically measured and sampled. Based on appearance and disappearance of the identified palynomorph taxa, six acritarch biozones were established. Biozone-I appears in the uppermost part of the Derenjal Formation and lowermost Shirgesht Formation, and suggests the uppermost Cambrian to lowermost Tremadocian age.Biozones II through V occur in the Shirgesht Formation, representing the Tremadocian to Llanvirnian age. Biozone VI appears in the Niur Formation and suggests an early Silurian age for this Formation. Therefore, there is a major "hiatus" within the Lower Palaeozoic sequence in the studied area. This appears between the Shirgesht and Niur formations and includes the upper Ordovician strata. This hiatus possibly corresponds to the Caledonian Orogeny. In this study a palynological zonation has been established and compared with those of the other parts of the world. The comparison reveals that East-Central Iran has been a part of the Mediterranean acritarch province during the Early/Middle Ordovician age

In this paper, we apply the notion of -open sets in topological spaces to present and study contra- -continuity as a new generalization of contra-continuity (Dontchev, 1996).

In this note we study the transformation semigroup (X,S), where S is a finite union of its subsemigroups