Spatial dynamics of a vegetation model with uptake-diffusion feedback in an arid environment.

Vegetation patterns with a variety of structures is amazing phenomena in arid or semi-arid areas, which can identify the evolution law of vegetation and are typical signals of ecosystem functions. Many achievements have been made in this respect, yet the mechanisms of uptake-diffusion feedback on the pattern structures of vegetation is not fully understood. To well reveal the influences of parameters perturbation on the pattern formation of vegetation, we give a comprehensive analysis on a vegetation-water model in the forms of reaction-diffusion equation which is posed by Zelnik et al. (Proc Natl Acad Sci 112:12,327-12,331, 2015). We obtain the exact parameters range for stationary patterns and show the dynamical behaviors near the bifurcation point based on nonlinear analysis. It is found that the model has the properties of spot, labyrinth and gap patterns. Moreover, water diffusion rate prohibits the growth of vegetation while shading parameter promotes the increase of vegetation biomass. Our results show that gradual transitions from uniform state to gap pattern can occur for suitable value of parameters which may induce the emergence of desertification.

Structural characteristics of nanocrystalline copper after carbon ion implantation.

A gradient structure was produced in a pure copper plate by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer was reduced to nanoscale and the grain size increased gradually along the depth of the treated sample. In situ transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) observation was performed on the nanocrystalline copper after implantation of carbon. Carbon atoms first precipitated along the edges of the copper substrate or at the surface, then formed amorphous carbon layers. Subsequently, onion-like fullerenes were formed under electron-beam irradiation. The effects of ion implantation, electron beam irradiation, nanostructure of the substrate and interaction of C and Cu atoms on the formation of the onion-like fullerenes are discussed.