14,250 research outputs found

    On the speed of convergence to the asymptotic cone for non-singular nilpotent groups

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    We study the speed of convergence to the asymptotic cone for Cayley graphs of nilpotent groups. Burago showed that {(Zd,1nρ,id)}n∈N\{(\mathbb{Z}^d, \frac{1}{n} \rho,id)\}_{n\in\mathbb{N}} converges to (Rd,d∞,id)(\mathbb{R}^d,d_{\infty},id) and its speed is O(1n)O(\frac{1}{n}) in the sense of Gromov-Hausdorff distance. Later Breuillard and Le Donne gave estimates for non-abelian cases, and constructed an example whose speed of convergence is slower than O(1n)O(\frac{1}{\sqrt{n}}). For 22-step nilpotent groups, we show that if the Mal'cev completion is non-singular, then the speed of convergence is O(1n)O(\frac{1}{n}) for any choice of generating set. In terms of subFinsler geometry, this condition is also equivalent to the absence of abnormal geodesics on the asymptotic cone.Comment: 18pages,11 figure

    Electron impact excitations of S2 molecules

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    Low-energy electron impact excitations of S_2 molecules are studied using the fixed-bond R-matrix method based on state-averaged complete active space SCF orbitals. Integral cross sections are calculated for elastic electron collision as well as impact excitation of the 7 lowest excited electronic states. Also, differential cross sections are obtained for elastic collision and excitation of the a^1 Delta_g, b^1 Sigma_g^+ and B^3 Sigma_u^- states. The integrated cross section of optically allowed excitation of the B^3 Sigma_u^- state agrees reasonably well with the available theoretical result.Comment: 12 pages, 3 figures. Chemical Physics Letters, in pres
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