A non-perturbative treatment of the generalized Su-Schreiffer-Heeger Hamiltonian on a dimer

Starting from the Hamiltonian for a dimer which includes all the electronic and electron-phonon terms consistent with a non-degenerate orbital, by a sequence of displacement and squeezing transformation we obtain an effective polaronic Hamiltonian. The renormalized electronic interactions differ from the results of semiclassical or perturbative treatments. The properties of the variationally determined ground state of two particles in the orbital are discussed for variable dimer length in the adiabatic limit.Comment: 6 pages, 3 figures, to be published in Int. Journal of Modern Physics

A model Hamiltonian for MgB2 which takes into account its unusual phononic features

Taking as a starting point the results of LDA calculations, which show that in MgB2 the phonons have a strong quartic anharmonicity and that the bond-stretching electron-phonon interaction (EPI) has both a linear and a large quadratic component, we propose a model Hamiltonian which succesfully matches a number of experimental evidences. We relate the single critical temperature for both superconducting gaps to a phonon-induced inter-band coupling whose amplitude increases with temperature. We also obtain phonon frequencies and linewidths depending on the band filling, as well as band energies and hybridization amplitudes depending on the phonon number.Comment: 19 pages, no figures, accepted on The European Physical Journal

Effective inter-band coupling in MgB2 due to anharmonic phonons

We investigate the origin of the inter-band coupling in MgB2 by focusing on its unusual phononic features, namely, the strong anharmonicity of the phonons and the presence of both linear and quadratic electron-phonon interactions of the Su-Schrieffer-Heeger (SSH) type. The bare electronic Hamiltonian has two bands with intra- and inter-band hopping, which lead to two decoupled hybridized bands. The phonon Hamiltonian including the anharmonic terms is diagonalized approximately by a squeezing transformation, which causes the softening of the phonon frequency. The linear SSH coupling amplitude is reduced, consistently with the estimates from first-principle calculations. Additionally, the quadratic coupling generates an effective phonon-induced interaction between the hybridized bands, which is non-vanishing even in the limit of vanishing inter-bare-band hopping amplitude.Comment: 11 page

Distance-depending electron-phonon interactions from one- and two-body electronic terms in a dimer

For a dimer with a non-degenerate orbital built from atomic wave functions of Gaussian shape we evaluate all the electron-phonon couplings derived from the one-body and two-body electronic interactions, considering both the adiabatic and extreme non-adiabatic limit. Not only the values of the coupling parameters in the two limits, but also the expressions of the corresponding terms in the Hamiltonian differ. Depending on the distance between the dimer ions, some of the two-body couplings are comparable, or even larger than the one-body ones.Comment: 8 pages, 3 figures, to be published in Int. Journal of Modern Physics

Comparative study of Pierre Bonnard's "Nude crouching in the tub" and D. H. Lawrence's "Gloire de Dijon Roses"

The present article analyses the poem Gloire de Dijon by D. H. Lawrence and Pierre Bonnard's painting Nude Crouching in the Tub. Both structural and contextual elements are taken into consideration to compare and contrast the writer.s and the painter.s modes of representation.El presente artículo analiza el poema Gloire de Dijon del poeta inglés D. H. Lawrence y la obra del pintor francés Pierre Bonnard Nude Crouching in the Tub. Se comparan los modos de representación del poeta y el pintor teniendo en cuenta elementos contextuales y estructurales de las obras mencionadas

Principles and practices of referral between schools and social agencies, with illustrations from a selected locality.

Thesis (Ed.M.)--Boston Universit

Reply to ‘Swim encounters with Killer Whales (Orcinus orca) off Northern Norway: interactive behaviours directed towards Human Divers and Snorkellers obtained from opportunistic underwater video recordings'

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Ecotourism on 29/08/2017, available online: http://www.tandfonline.com/10.1080/14724049.2017.1368272.This is a reply to the research note ‘Swim Encounters with Killer Whales (Orcinus orca) off Northern Norway: Interactive Behaviours directed towards Human Divers and Snorkellers obtained from Opportunistic Underwater Video Recordings’ by C. Pagel, M. Scheer and M. Lück published on the Journal of Ecotourism in the December 2016 issue. This research note gives us the opportunity to reflect on the following aspects: (1) the concepts of sustainability and ecotourism, (2) the researchers’ position in terms of animal ethics, (3) the relevance of the empirical context where the fieldwork occurs and the related research ethics aspect, (4) the difficulty of evaluating risk of injury. We comment on each of these aspects and discuss them in the attempt to clarify research challenges, propose some reflection points and possible alternative approaches for improving research quality in wildlife tourism

Model Calculation of Electron-Phonon Couplings in a Dimer with a Non-Degenerate Orbital

We evaluate all the electron-phonon couplings derived from the one-body electronic interactions, in both the adiabatic and extreme non-adiabatic limit, for a dimer with a non-degenerate orbital built from atomic wave functions of Gaussian shape. We find largely different values of the coupling parameters in the two cases, as well as different expressions of the corresponding terms in the Hamiltonian.Comment: 5 postscript figure