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We study the deposition of tetrahedral amorphous carbon (ta-C) films from molecular dynamics simulations based on a machine-learned interatomic potential trained from density-functional theory data. For the first time, the high sp^{3} fractions in excess of 85% observed experimentally are reproduced by means of computational simulation, and the deposition energy dependence of the film's characteristics is also accurately described. High confidence in the potential and direct access to the atomic interactions allow us to infer the microscopic growth mechanism in this material. While the widespread view is that ta-C grows by "subplantation," we show that the so-called "peening" model is actually the dominant mechanism responsible for the high sp^{3} content. We show that pressure waves lead to bond rearrangement away from the impact site of the incident ion, and high sp^{3} fractions arise from a delicate balance of transitions between three- and fourfold coordinated carbon atoms. These results open the door for a microscopic understanding of carbon nanostructure formation with an unprecedented level of predictive power.

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– The objective was to compare the erosive effect of some commonly used acidic drinks and milk products on a bovine tooth enamel model system. Conditions were selected to be sufficiently severe to cause erosion. Loss of material after erosion experiments was measured by recording the depth of the surface profile after repeated and prolonged exposure. Changes in the enamel surface were observed by scanning electron microscopy. The reparative mechanisms were studied by immersing test teeth in saliva, with or without (2 ppm) fluoride, after severe demineralization in the test products. According to the t‐test for paired means, cola beverages and orange beverages differed from beer, coffee with or without sugar, strawberry yoghurt, buttermilk, and carbonated mineral water at the level P0.01. Each of the last‐mentioned test products differed from sports drinks, diet cola beverages and orange juice less significantly. In addition, bathing of teeth in saliva between exposures to the test products did not influence the erosive depth. The results, based on in vitro conditions that ensured erosion, are useful for comparative purposes but cannot be directly extended to the oral cavity under normal use conditions.