A fundamental mechanism for carbon-film lubricity identified by means of ab initio molecular dynamics

Different hypotheses have been proposed to explain the mechanism for the extremely low friction coefficient of carbon coatings and its undesired dependence on air humidity. A decisive atomistic insight is still lacking because of the difficulties in monitoring what actually happens at the buried sliding interface. Here we perform large-scale ab initio molecular dynamics simulations of both undoped and silicon-doped carbon films sliding in the presence of water. We observe the tribologically-induced surface hydroxylation and subsequent formation of a thin film of water molecules bound to the OH-terminated surface by hydrogen bonds. The comparative analysis of silicon-incorporating and clean surfaces, suggests that this two-step process can be the key phenomenon to provide high slipperiness to the carbon coatings. The water layer is, in fact, expected to shelter the carbon surface from direct solid-on-solid contact and make any counter surface slide extremely easily on it. The present insight into the wettability of carbon-based films can be useful for designing new coatings for biomedical and energy-saving applications with environmental adaptability.Comment: 22 pages, 4 figures, 1 tabl

Insigths into the tribochemistry of silicon-doped carbon based films by ab initio analysis of water/surface interactions

Diamond and diamond-like carbon (DLC) are used as coating materials for numerous applications, ranging from biomedicine to tribology. Recently, it has been shown that the hydrophilicity of the carbon films can be enhanced by silicon doping, which highly improves their biocompatibility and frictional performances. Despite the relevance of these properties for applications, a microscopic understanding on the effects of silicon is still lacking. Here we apply ab initio calculations to study the interaction of water molecules with Si-incorporated C(001) surfaces. We find that the presence of Si dopants considerably increases the energy gain for water chemisorption and decreases the energy barrier for water dissociation by more than 50%. We provide a physical rational for the phenomenon by analysing the electronic charge displacements occuring upon adsorption. We also show that once hydroxylated, the surface is able to bind further water molecules much strongly than the clean surface via hydrogen-bond networks. This two-step process is consistent with and can explain the enhanced hydrophilic character observed in carbon-based films doped by silicon

Imagined Surfaces: the ‘Undetermined Capacity’ in Henry James

This is the final version of the article. It first appeared from Durham University at http://community.dur.ac.uk/postgraduate.english/ojs/index.php/pgenglish/article/view/177.This article explores the various kinds of surfaces that recur in Henry James’s writings in the forms of imagery, characterization, narrative content, and linguistic style. It focuses especially on the surfaces that suggest and make possible spaces of ‘undetermined capacity’. Reading a range of texts, including The Europeans, ‘The Real Thing’, ‘The Jolly Corner’, his notebook entries, and those in which he probes the connections between the creative process and the ‘act of life’, this essay shows how James unsettles the metaphysical assumption that depth/substance holds more meaning than surface/appearance. Although James is known for his investigation into the inner life of the mind, the surface is a key image in his conception of artistic creation. It is an inextricable part of how James makes the ineffable or the unfathomable – blanks, voids, possibilities – gain imagined substance. This essay argues that the obscure but charged spaces of ‘undetermined capacity’ that his texts generate, through the representation of surfaces, enable the creativity of the writer as well as the imagination of the reader. These ideas are applied to the potentiality of a literary text

Seesaw mechanism and the neutrino mass matrix

The seesaw mechanism of neutrino mass generation is analysed under the following assumptions: (1) minimal seesaw with no Higgs triplets, (2) hierarchical Dirac masses of neutrinos, (3) large lepton mixing primarily or solely due to the mixing in the right-handed neutrino sector, and (4) unrelated Dirac and Majorana sectors of neutrino masses. It is shown that large mixing governing the dominant channel of the atmospheric neutrino oscillations can be naturally obtained and that this constrained seesaw mechanism favours the normal mass hierarchy for the light neutrinos leading to a small $U_{e3}$ entry of the lepton mixing matrix and a mass scale of the lightest right handed neutrino $M\simeq 10^{10} - 10^{11}$ GeV. Any of the three main neutrino oscillation solutions to the solar neutrino problem can be accommodated. The inverted mass hierarchy and quasi-degeneracy of neutrinos are disfavoured in our scheme.Comment: LaTeX, 3 pages, no figures. Talk given at 6th International Workshop on Topics in Astroparticle and Underground Physics (TAUP 99), September 6-10, 1999, Paris, Franc