180 research outputs found
Dilation-induced phases of gases absorbed within a bundle of carbon nanotubes
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
The kinetic compensation effect (KCE), observed in many fields of science, is
the systematic variation in the apparent magnitudes of the Arrhenius parameters
, the energy of activation, and , 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 become the same at a
common compensation temperature . 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 , 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 and . 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
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
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