Collaboration networks are studied as an example of growing bipartite networks. These have been previously observed to exhibit structure such as positive correlations between nearest-neighbour degrees. However, a detailed understanding of the origin of such and the growth dynamics is lacking. Both of these issues are analysed empirically and simulated using various models. A new growth model is presented, incorporating empirically necessary ingredients such as bipartiteness and sublinear preferential attachment. This, and a recently proposed model of team assembly, both agree roughly with some empirical observations and fail in several others.
In a methane/argon discharge used for deposition of hydrogenated amorphous carbon (a-C:H), energetic ion bombardment yields radicals on solid surfaces by two mechanisms: (i)fragmentation of hydrocarbon ions at their impact on the surface and (ii)sputtering of the already deposited a-C:H film. To discriminate between these two mechanisms, the emission intensity of CH(A-X) in the vicinity of a negatively biased electrode was measured as a function of the ion impact energy. The threshold energy for yielding the excited CH radical was found to be ∼2 eV for fragmentation and ∼80 eV for sputtering. The fragmentation yield is much larger on a metal surface than on a-C:H layer. The sputtering yield dominates over the fragmentation yield for the high impact energy(>150 eV).
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