Electron-phonon interaction and antiferromagnetic correlations

We study effects of the Coulomb repulsion on the electron-phonon interaction (EPI) in a model of cuprates at zero and finite doping. We find that antiferromagnetic correlations strongly enhance EPI effects on the electron Green's function with respect to the paramagnetic correlated system, but the net effect of the Coulomb interaction is a moderate suppression of the EPI. Doping leads to additional suppression, due to reduced antiferromagnetic correlations. In contrast, the Coulomb interaction strongly suppresses EPI effects on phonons, but the suppression weakens with doping.Comment: 4 pages and 5 figure

Local magnetic moments in iron and nickel at ambient and Earth's core conditions

Some Bravais lattices have a particular geometry that can slow down the motion of Bloch electrons by pre-localization due to the band-structure properties. Another known source of electronic localization in solids is the Coulomb repulsion in partially filled d- or f-orbitals, which leads to the formation of local magnetic moments. The combination of these two effects is usually considered of little relevance to strongly correlated materials. Here we show that it represents, instead, the underlying physical mechanism in two of the most important ferromagnets: nickel and iron. In nickel, the van Hove singularity has an unexpected impact on the magnetism. As a result, the electron-electron scattering rate is linear in temperature, in violation of the conventional Landau theory of metals. This is true even at Earth's core pressures, at which iron is instead a good Fermi liquid. The importance of nickel in models of geomagnetism may have therefore to be reconsidered.Comment: Supplementary Information available at https://www.nature.com/articles/ncomms16062#supplementary-informatio

TANNINS FROM RUBUS AND FRAGARIA BERRIES FOR THE CONTROL OF GASTRIC INFLAMMATION: IN VITRO AND IN VIVO STUDIES

Gastritis and ulcers are very common inflammatory-based diseases which can be caused by Helicobacter pylori (H. pylori) infection, chemical factors or immunological disorders[3]. H. pylori is the leading cause of gastritis[1], it colonizes the gastric mucosa of over 80% of human population in developing countries[3] and at least 50% of the world\u2019s human population[36]. Gastric epithelial cells, during H. pylori infection, show increased levels of cytokines/chemokines including IL-1\u3b2, IL-6, TNF\u3b1 and IL-8[66]. Epithelial cells stimulated with TNF\u3b1, IL-1\u3b2 or bacterial infection, release a variety of cytokines (TNF\u3b1, IL-1\u3b2, IL-8) and increase expression of cyclooxygenase-2 (COX-2) and inducible NO synthase (iNOS). The activation of nuclear factor \u3baB (NF-\u3baB) is deeply involved in the control of transcription of inflammatory mediators in the stomach[95]. Ellagitannins (ET) have shown anti-inflammatory and anti-H.pylori properties; however, their anti-inflammatory activity at gastric level was not previously investigated. Rubus berries (raspberries and blackberries) and Fragaria berries (strawberries) are considered a rich source of phenolic compounds, including anthocyanins, tannins, ET and ellagic acid (EA) derivatives conjugated[308]. The aim of the present research was to evaluate the effects of tannins, in particular ET, from Rubus and Fragaria berries, the most common sources of ET in the European diet, on gastric inflammation. Tannin enriched extracts (TEs) were prepared from Rubus fruticosus L. (blackberry), Rubus idaeus L. (raspberry), Fragaria X ananassa Duch. (strawberry) and Fragaria vesca L. (wild strawberry). The anti-inflammatory activity was tested in vitro on gastric cell line AGS stimulated by TNF\u3b1 and IL-1\u3b2. TEs inhibited TNF\u3b1-induced NF-\u3baB driven transcription and reduced NF-kB nuclear translocation. TEs inhibited also IL-8 secretion induced by TNF\u3b1 and IL-1\u3b2 at low concentrations (IC50 range: 0.5\u20138.8 \ub5g/mL). The effect of an in vitro gastric digestion on TEs activity was also evaluated. Sanguiin H-6, lambertianin C, (the major ET present in Rubus berries) and agrimoniin (ET from Fragaria berries), were found to be responsible, at least in part, for the effect of the mixtures. In vivo the protective effect of TEs was evaluated in a rat model of ethanol-induced gastric lesions. Rats were treated orally for ten days with 20 mg/kg/day of TEs, and ethanol was given one hour before the sacrifice. Gastric mucosa was isolated and used for the determination of IL-8 release, NF-\u3baB nuclear translocation, Trolox equivalents, superoxide dismutase and catalase activities. TEs of blackberry and raspberry decreased Ulcer Index by 88% and 75% respectively and protected from the ethanol-induced oxidative stress in rats. CINC-1 (the rat homologue of IL-8) secretion in the gastric mucosa was reduced in the animals receiving blackberry and raspberry TEs. The effect of TEs on CINC-1 was associated to a decrease of NF-\u3baB nuclear translocation in TEs treated animals. The anti-inflammatory activity exerted by TEs occurs at extremely low concentrations, even below the concentration of 1 \u3bcg/mL, values that are considered easy to reach by the ingestion of a portion of berries (approximately 5 mg/mL). These results show that tannins interfere with the metabolic cascade deriving from the activation and translocation of NF-\u3baB that in turn activates the transcription of target genes involved in inflammation, including IL-8. ET do not require any absorption to reach the stomach and their concentrations are not reduced by metabolic processes in this district. In this study was demonstrated for the first time that ET from blackberries and raspberries are able to protect the stomach against the gastric lesions caused by ethanol. The outcome of this research suggests the use of ET as integration in dietary regimens designed for treat or prevent inflammatory gastric diseases

Evidence for a Bulk Complex Order-Parameter in Y0.9Ca0.1Ba2Cu3O7-delta Thin Films

We have measured the penetration depth of overdoped Y0.9Ca0.1Ba2Cu3O7-delta (Ca-YBCO) thin films using two different methods. The change of the penetration depth as a function of temperature has been measured using the parallel plate resonator (PPR), while its absolute value was obtained from a quasi-optical transmission measurements. Both sets of measurements are compatible with an order parameter of the form: Delta*dx2-y2+i*delta*dxy, with Delta=14.5 +- 1.5 meV and delta=1.8 meV, indicating a finite gap at low temperature. Below 15 K the drop of the scattering rate of uncondensed carriers becomes steeper in contrast to a flattening observed for optimally doped YBCO films. This decrease supports our results on the penetration depth temperature dependence. The findings are in agreement with tunneling measurements on similar Ca-YBCO thin films.Comment: 11 pages, 4 figure

Phonon softening and dispersion in the 1D Holstein model of spinless fermions

We investigate the effect of electron-phonon interaction on the phononic properties in the one-dimensional half-filled Holstein model of spinless fermions. By means of determinantal Quantum Monte Carlo simulation we show that the behavior of the phonon dynamics gives a clear signal of the transition to a charge-ordered phase, and the phase diagram obtained in this way is in excellent agreement with previous DMRG results. By analyzing the phonon propagator we extract the renormalized phonon frequency, and study how it first softens as the transition is approached and then subsequently hardens in the charge-ordered phase. We then show how anharmonic features develop in the phonon propagator, and how the interaction induces a sizable dispersion of the dressed phonon in the non-adiabatic regime.Comment: 7 pages, 6 figure

Static vs. dynamical mean field theory of Mott antiferromagnets

Studying the antiferromagnetic phase of the Hubbard model by dynamical mean field theory, we observe striking differences with static (Hartree-Fock) mean field: The Slater band is strongly renormalized and spectral weight is transferred to spin-polaron side bands. Already for intermediate values of the interaction $U$ the overall bandwidth is larger than in Hartree-Fock, and the gap is considerably smaller. Such differences survive any renormalization of $U$. Our photoemission experiments for Cr-doped V$_2$O$_3$ show spectra qualitatively well described by dynamical mean field theory.Comment: 6 pages, 5 figures - one figure added and further details about quasiparticle dispersio

Adaptive hard and tough mechanical response in single-crystal B1 VNx ceramics via control of anion vacancies

High hardness and toughness are generally considered mutually exclusive properties for single-crystal ceramics. Combining experiments and ab initio molecular dynamics (AIMD) atomistic simulations at room temperature, we demonstrate that both the hardness and toughness of single-crystal NaCl-structure VNx/MgO(001) thin films are simultaneously enhanced through the incorporation of anion vacancies. Nanoindentation results show that VN0.8, here considered as representative understoichiometric VNx system, is ~20% harder, as well as more resistant to fracture than stoichiometric VN samples. AIMD modeling of VN and VN0.8 supercells subjected to [001] and [110] elongation reveal that the tensile strengths of the two materials are similar. Nevertheless, while the stoichiometric VN phase systematically cleaves in a brittle manner at tensile yield points, the understoichiometric compound activates transformation-toughening mechanisms that dissipate accumulated stresses. AIMD simulations also show that VN0.8 exhibits an initially greater resistance to both {110} and {111} shear deformation than VN. However, for progressively increasing shear strains, the VN0.8 mechanical behavior gradually evolves from harder to more ductile than VN. The transition is mediated by anion vacancies, which facilitate {110} and {111} lattice slip by reducing activation shear stresses by as much as 35%. Electronic-structure analyses show that the two-regime hard/tough mechanical response of VN0.8 primarily stems from its intrinsic ability to transfer d electrons between 2nd-neighbor and 4th-neighbor (i.e., across vacancy sites) V-V metallic states. Our work offers a route for electronic-structure design of hard materials in which a plastic mechanical response is triggered with loading

Effect of hypoxia on gene expression in cell populations involved in wound healing

Wound healing is a complex process regulated by multiple signals and consisting of several phases known as haemostasis, inflammation, proliferation, and remodelling. Keratinocytes, endothelial cells, macrophages, and fibroblasts are the major cell populations involved in wound healing process. Hypoxia plays a critical role in this process since cells sense and respond to hypoxic conditions by changing gene expression. This study assessed the in vitro expression of 77 genes involved in angiogenesis, metabolism, cell growth, proliferation and apoptosis in human keratinocytes (HaCaT), microvascular endothelial cells (HMEC-1), differentiated macrophages (THP-1), and dermal fibroblasts (HDF). Results indicated that the gene expression profiles induced by hypoxia were cell-type specific. In HMEC-1 and differentiated THP-1, most of the genes modulated by hypoxia encode proteins involved in angiogenesis or belonging to cytokines and growth factors. In HaCaT and HDF, hypoxia mainly affected the expression of genes encoding proteins involved in cell metabolism. This work can help to enlarge the current knowledge about the mechanisms through which a hypoxic environment influences wound healing processes at the molecular level