Electron-phonon interaction in the three-band model

We study the half-breathing phonon in the three-band model of a high temperature superconductor, allowing for vibrations of atoms and resulting changes of hopping parameters. Two different approaches are compared. From the three-band model a t-J model with phonons can be derived, and phonon properties can be calculated. To make contact to density functional calculations, we also study the three-band model in the Hartree-Fock (HF) approximation. The paramagnetic HF solution, appropriate for the doped cuprates, has similarities to the local-density approximation (LDA). However, in contrast to the LDA, the existence of an antiferromagnetic insulating solution for the undoped system makes it possible to study the softening of the half-breathing phonon under doping. We find that although the HF approximation and the t-J model give similar softenings, these softenings happen in quite different ways. We also find that the HF approximation gives an incorrect doping and q dependence for the softening and too small a width for the (half-)breathing phonon.Comment: 7 pages, RevTeX, 4 eps figure

Assessing the convergent validity between the automated emotion recognition software Noldus FaceReader 7 and Facial Action Coding System Scoring

This study validates automated emotion and action unit (AU) coding applying FaceReader 7 to a dataset of standardized facial expressions of six basic emotions (Standardized and Motivated Facial Expressions of Emotion). Percentages of correctly and falsely classified expressions are reported. The validity of coding AUs is provided by correlations between the automated analysis and manual Facial Action Coding System (FACS) scoring for 20 AUs. On average 80% of the emotional facial expressions are correctly classified. The overall validity of coding AUs is moderate with the highest validity indicators for AUs 1, 5, 9, 17 and 27. These results are compared to the performance of FaceReader 6 in previous research, with our results yielding comparable validity coefficients. Practical implications and limitations of the automated method are discussed

Photoemission kinks and phonons in cuprates

One of the possible mechanisms of high Tc superconductivity is Cooper pairing with the help of bosons, which change the slope of the electronic dispersion as observed by photoemission. Giustino et al. calculated that in the high temperature superconductor La1.85Sr0.15CuO4 crystal lattice vibrations (phonons) should have a negligible effect on photoemission spectra and concluded that phonons do not play an important role. We show that the calculations employed by Giustino et al. fail to reproduce huge influence of electron-phonon coupling on important phonons observed in experiments. Thus one would expect these calculations to similarly fail in explaining the role of electron-phonon coupling for the electronic dispersion.Comment: To appear in Nature as a Brief Communiction Arisin

Connectedness of habitat fragments boosts conservation benefits for butterflies, but only in landscapes with little cropland

Context Global change pressures (GCPs) imperilspecies and associated ecosystem functions, but studies investigating interactions of landscape-scale pressures remain scarce. Loss of species-rich habitat and agricultural expansion are major threats for biodiversity, but if or how these factors interactively determine community-level shifts and conservation outcomes remains unclear. Objectives We tested whether matrix simplification (dominance of cropland) and reduced connectivity (i.e. landscape-scale habitat loss) either additively, synergistically or antagonistically cause community shifts in butterflies, a group of high conservation relevance. Methods We surveyed butterflies on 30 small calcareous grassland fragments (<1 ha) in Central Germany, representing independent gradients in grassland connectivity (an index combining grassland area and proximity), and matrix quality (landscape proportion of cropland). Using proportional odds logistic regression, we assessed whether connectivity and matrix quality interactively altered the distribution of Red List statuses, and assessed effects of local scale management (mowing, grazing, short-term abandonment). Results We found synergistic, conservation relevant effects: Connectivity boosted the proportion of redlisted species from 20 to 52% in crop land poor landscapes, but not in crop land rich landscapes, particularly driven by endangered and critically endangered species. Grazed sites had the lowest species richness, abundance, and proportions of conservation relevant butterflies. Implications Mitigation measures targeting one landscape-scale pressure only may be inefficient, particularly for red-listed species. Increasing habitat connectivity bolsters butterfly communities and potential pollination services, but only if accompanied by measures to soften the matrix. Hence, halting biodiversity losses needs better understanding and implementation of complex conservation measures at the landscape scale