Structure and electronic properties of silicon carbide nanotube(SiCNT) with and without adsorption of NO₂ are calculated with CASTEP package based on density functional theory.A stable adsorption between nanotube and gas molecule is formed and conductivity of the SiCNT is improved obviously.It is shown that SiCNT is a potential candidate for gas sensors.It is expected to provide a useful guidance in developing SiCNT-based sensors for NO₂ molecules.

We present a randomsuccessive nucleation growth model,a two-and a three-dimensional aggregation generation-by-generation model to investigate percolation properties of fractal aggregations with various neighbor conditions and lattice size.Itshows that the percolationthreshold of fractal aggregationisindependent of the lattice size.It dependents onspatial dimension andneighbor conditions,andis aninherent property of the fractal system.The fractal aggregate grows infinitely withthe same fractaldimension whenthe growth probabilityis equal tothe percolationthreshold.The fractal dimension is just a linear function of thespatial dimension.