Thermal rectification in carbon nanotube intramolecular junctions: Molecular dynamics calculations

We study heat conduction in (n, 0)/(2n, 0) intramolecular junctions by using molecular dynamics method. It is found that the heat conduction is asymmetric, namely, heat transports preferably in one direction. This phenomenon is also called thermal rectification. The rectification is weakly dependent on the detailed structure of connection part, but is strongly dependent on the temperature gradient. We also study the effect of the tube radius and intramolecular junction length on the rectification. Our study shows that the tensile stress can increase rectification. The physical mechanism of the rectification is explained

Electrical conductivity measured in atomic carbon chains

The first electrical conductivity measurements of monoatomic carbon chains are reported in this study. The chains were obtained by unraveling carbon atoms from graphene ribbons while an electrical current flowed through the ribbon and, successively, through the chain. The formation of the chains was accompanied by a characteristic drop in the electrical conductivity. The conductivity of carbon chains was much lower than previously predicted for ideal chains. First-principles calculations using both density functional and many-body perturbation theory show that strain in the chains determines the conductivity in a decisive way. Indeed, carbon chains are always under varying non-zero strain that transforms its atomic structure from cumulene to polyyne configuration, thus inducing a tunable band gap. The modified electronic structure and the characteristics of the contact to the graphitic periphery explain the low conductivity of the locally constrained carbon chain.Comment: 21 pages, 9 figure

Chemo-mechanical interactions in clay: a correlation between clay mineralogy and Atterberg limits

Among some few others tests, the evaluation of the Atterberg limits is a very basic soil mechanical test allowing a first insight into the chemical reactivity of clays. Basically, the liquid limit and the plasticity index are highly and mainly influenced by the ability of clay minerals to interact with liquids. In this contribution, a correlation between the Atterberg limits and clay mineralogy is proposed. This correlation increases the understanding between clay mineralogists and engineers in soil mechanics; additionally a wealth of information in clay mineralogy literature is now available to predict the mechanical behaviour of clays via index tests. (C) 2003 Elsevier B.V. All rights reserved

New group structures for Carbon onions and Carbon nanotubes via affine extensions of non-crystallographic Coxeter groups

We present results underlining the conjecture that affine extensions for non-crystallographic Coxeter groups are suitable mathematical objects for the description of the symmetries of Carbon onions and Carbon nanotubes. It is the hope that these considerations will shed new light on open questions concerning structure, stability and formation of these fullerenes.Comment: 13 pages, submitted to Phys. Lett.

Strain Modulated Superlattices in Graphene

Strain engineering of graphene takes advantage of one of the most dramatic responses of Dirac electrons enabling their manipulation via strain-induced pseudo-magnetic fields. Numerous theoretically proposed devices, such as resonant cavities and valley filters, as well as novel phenomena, such as snake states, could potentially be enabled via this effect. These proposals, however, require strong, spatially oscillating magnetic fields while to date only the generation and effects of pseudo-gauge fields which vary at a length scale much larger than the magnetic length have been reported. Here we create a periodic pseudo-gauge field profile using periodic strain that varies at the length scale comparable to the magnetic length and study its effects on Dirac electrons. A periodic strain profile is achieved by pulling on graphene with extreme (>10%) strain and forming nanoscale ripples, akin to a plastic wrap pulled taut at its edges. Combining scanning tunneling microscopy and atomistic calculations, we find that spatially oscillating strain results in a new quantization different from the familiar Landau quantization observed in previous studies. We also find that graphene ripples are characterized by large variations in carbon-carbon bond length, directly impacting the electronic coupling between atoms, which within a single ripple can be as different as in two different materials. The result is a single graphene sheet that effectively acts as an electronic superlattice. Our results thus also establish a novel approach to synthesize an effective 2D lateral heterostructure - by periodic modulation of lattice strain.Comment: 18 pages, 5 figures and supplementary informatio

Novel insights in the interpretation of the faecal egg count reduction test to monitor anthelmintic efficacy

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Identification of Electron Donor States in N-doped Carbon Nanotubes

Nitrogen doped carbon nanotubes have been synthesized using pyrolysis and characterized by Scanning Tunneling Spectroscopy and transmission electron microscopy. The doped nanotubes are all metallic and exhibit strong electron donor states near the Fermi level. Using tight-binding and ab initio calculations, we observe that pyridine-like N structures are responsible for the metallic behavior and the prominent features near the Fermi level. These electron rich structures are the first example of n-type nanotubes, which could pave the way to real molecular hetero-junction devices.Comment: 5 pages, 4 figures, revtex, submitted to PR