Descripción: We study the intermittency properties of the energy and helicity cascades in two 15363 direct numerical simulations of helical rotating turbulence. Symmetric and antisymmetric velocity increments are examinedas well as probability density functions of the velocity field and of the helicity density. It is found that the direct cascade of energy to small scales is scale invariant and nonintermittentwhereas the direct cascade of helicity is highly intermittent. Furthermorethe study of structure functions of different orders allows us to identify a recovery of isotropy of strong events at very small scales in the flow. Finallywe observe the juxtaposition in space of strong laminar and persistent helical columns next to time-varying vortex tanglesthe former being associated with the self-similarity of energy and the latter with the intermittency of helicity. © 2010 American Institute of Physics.

Descripción: We have employed the Douglas-Kroll-Hess approximation to derive the perturbative Hamiltonians involved in the calculation of NMR spin-spin couplings in molecules containing heavy elements. We have applied this two-component quasirelativistic approach using finite perturbation theory in combination with a generalized Kohn-Sham code that includes the spin-orbit interaction self-consistently and works with Hartree-Fock and both pure and hybrid density functionals. We present numerical results for one-bond spin-spin couplings in the series of tetrahydrides C H4, Si H4, Ge H4, and Sn H4. Our two-component Hartree-Fock results are in good agreement with four-component Dirac-Hartree-Fock calculations, although a density-functional treatment better reproduces the available experimental data. © 2005 American Institute of Physics.