Neutron scattering measurements of phonons in nickel at elevated temperatures

Measurements of elastic and inelastic neutron scatterings from elemental nickel were made at 10, 300, 575, 875, and 1275 K. The phonon densities of states (DOSs) were calculated from the inelastic scattering and were fit with Born–von Kármán models of the lattice dynamics. With ancillary data on thermal expansion and elastic moduli, we found a small, negative anharmonic contribution to the phonon entropy at high temperature. We used this to place bounds on the magnetic entropy of nickel. A significant broadening of the phonon DOS at elevated temperatures, another indication of anharmonicity, was also measured and quantified

Quantum Pieri rules for isotropic Grassmannians

We study the three point genus zero Gromov-Witten invariants on the Grassmannians which parametrize non-maximal isotropic subspaces in a vector space equipped with a nondegenerate symmetric or skew-symmetric form. We establish Pieri rules for the classical cohomology and the small quantum cohomology ring of these varieties, which give a combinatorial formula for the product of any Schubert class with certain special Schubert classes. We also give presentations of these rings, with integer coefficients, in terms of special Schubert class generators and relations.Comment: 59 pages, LaTeX, 6 figure

Phonon Density of States of LaFeAsO1-xFx

We have studied the phonon density of states (PDOS) in LaFeAsO1-xFx with inelastic neutron scattering methods. The PDOS of the parent compound(x=0) is very similar to the PDOS of samples optimally doped with fluorine to achieve the maximum Tc (x~0.1). Good agreement is found between the experimental PDOS and first-principle calculations with the exception of a small difference in Fe mode frequencies. The PDOS reported here is not consistent with conventional electron-phonon mediated superconductivity