cobalt (ii) chloride was used as a precursor to prepare co 3 o 4 nanotubes in reverse micelles. tween 80 was added as surfactant. the products were characterized by x-ray diffraction (xrd), scanning electron microscopy (sem) and transmission electron microscopy. the diameter of co 3 o 4 nanotubes was about 58 nm and the average length of them was around 261 nm. the study provides a simple and e...

A set is called NP-simple if it lies in NP, and its complement is infinite, and does not contain any infinite subsets in NP. Hartmanis, Li and Yesha [HLY86] proved that no set which is hard for NP under many-one (Karp) reductions is NP-simple unless NP ∩ coNP ⊆ SUBEXP. However, we can exhibit a relativized world in which there is an NP-simple set that is complete under Turing (Cook) reductions,...

A module M is called epi-retractable if every submodule of M is a homomorphic image of M. Dually, a module M is called co-epi-retractable if it contains a copy of each of its factor modules. In special case, a ring R is called co-pli (resp. co-pri) if RR (resp. RR) is co-epi-retractable. It is proved that if R is a left principal right duo ring, then every left ideal of R is an epi-retractable ...

the estimation of pollution fields, especially in densely populated areas, is an important application in the field of environmental science due to the significant effects of air pollution on public health. in this paper, we investigate the spatial distribution of three air pollutants in tehran’s atmosphere: carbon monoxide (co), nitrogen dioxide (no2), and atmospheric particulate matters less ...