28 research outputs found

    Dilation-induced phases of gases absorbed within a bundle of carbon nanotubes

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    A study is presented of the effects of gas (especially H2) absorption within the interstitial channels of a bundle of carbon nanotubes. The ground state of the system is determined by minimizing the total energy, which includes the molecules' interaction with the tubes, the inter-tube interaction, and the molecules' mutual interaction (which is screened by the tubes). The consequences of swelling include a significant increase in the gas uptake and a 3 per cent increase in the tubes' breathing mode frecuency.Comment: 4 page

    Breakdown of Kinetic Compensation Effect in Physical Desorption

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    The kinetic compensation effect (KCE), observed in many fields of science, is the systematic variation in the apparent magnitudes of the Arrhenius parameters EaE_a, the energy of activation, and őĹ\nu, the preexponential factor, as a response to perturbations. If, in a series of closely related activated processes, these parameters exhibit a strong linear correlation, it is expected that an isokinetic relation will occur, then the rates kk become the same at a common compensation temperature TcT_c. The reality of these two phenomena continues to be debated as they have not been explicitly demonstrated and their physical origins remain poorly understood. Using kinetic Monte Carlo simulations on a model interface, we explore how site and adsorbate interactions influence the Arrhenius parameters during a typical desorption process. We find that their transient variations result in a net partial compensation, due to the variations in the prefactor not being large enough to completely offset those in EaE_a, both in plots that exhibit a high degree of linearity and in curved non-Arrhenius plots. In addition, the observed isokinetic relation arises due to a transition to a non-interacting regime, and not due to compensation between EaE_a and ln‚Ā°őĹ\ln{\nu}. We expect our results to provide a deeper insight into the microscopic events that originate compensation effects and isokinetic relations in our system, and in other fields where these effects have been reported.Comment: 11 pages, 17 figures, 3 table

    Intriguing examples of inhomogeneous broadening

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    Three problems are considered in which inhomogeneous broadening can yield unusual consequences. One problem involves the energy levels of atoms moving within nanopores of nearly cylindrical cross section. A second involves atomic or molecular motion in a quasi-one dimensional interstitial channel within a bundle of carbon nanotubes. The third problem involves motion within a groove between two nanotubes at the surface of such a bundle. In each case, the density of states at low energy is qualitatively different from that occurring in the perfectly homogeneous case.Comment: 15 pages, 5 figure