1,675 research outputs found

    Valence changes associated with the metal-insulator transition in Bi1−x_{1-x}Lax_xNiO3_3

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    Perovskite-type BiNiO3_3 is an insulating antiferromagnet in which a charge disproportionation occurs at the Bi site. La substitution for Bi suppresses the charge disproportionation and makes the system metallic. We have measured the photoemission and x-ray absorption (XAS) spectra of Bi1−x_{1-x}Lax_{x}NiO3_{3} to investigate how the electronic structure changes with La doping. From Ni 2p2p XAS, we observed an increase of the valence of Ni from 2+ toward 3+. Combined with the core-level photoemission study, it was found that the average valence of Bi remains ∼4+\sim 4+ and that the Ni valence behaves as ∼(2+x)+\sim (2+x)+, that is, La substitution results in hole doping at the Ni sites. In the valence-band photoemission spectra, we observed a Fermi cutoff for x>0x>0, consistent with the metallic behavior of the La-doped compounds. The Ni 2p2p XAS, Ni 2p2p core-level photoemission, and valence-band photoemission spectra were analyzed by configuration-interaction cluster-model calculation, and the spectral line shapes were found to be consistent with the gradual Ni2+→^{2+} \to Ni3+^{3+} valence change.Comment: 6 pages, 7 figure

    Phase diagram of the Hubbard chain with two atoms per cell

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    We obtain the quantum phase diagram of the Hubbard chain with alternating on-site energy at half filling. The model is relevant for the ferroelectric perovskites and organic mixed-stack donor-acceptor crystals. For any values of the parameters, the band insulator is separated from the Mott insulator by a dimer phase. The boundaries are determined accurately by crossing of excited levels with particular discrete symmetries. We show that these crossings coincide with jumps of charge and spin Berry phases with a clear geometrical meaning.Comment: 5 pages including 2 figures To be published in Phys. Rev. B (Rapid Communications

    Epigenetic regulatory pathways involving microRNAs may modulate the host immune response following major trauma

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    BACKGROUND Posttraumatic nosocomial pneumonia is a common complication resulting in significant morbidity. Trauma-induced immunocompromise is associated with an enhanced susceptibility to pneumonia. In this study, we explore the hypothesis that posttranscriptional epigenetic regulation of gene expression may be an important factor in determining this immune phenotype. We describe the pattern of production of microRNAss (miRs) and their association with nosocomial pneumonia following severe trauma. METHODS A convenience sample of 30 ventilated polytrauma patients (UKCRN ID: 5637) and 16 healthy controls were recruited. Messenger RNA and protein levels of key cytokines were quantified within 2 hours of the injury and at 24 hours. Three miRs per cytokine were then selected based on miRBase target prediction scores and quantified using polymerase chain reaction. Nosocomial pneumonia was defined using the Centers for Disease Control and Prevention definitions. RESULTS Median Injury Severity Score (ISS) was 29, and 47% of the patients developed nosocomial pneumonia. miR-125a and miR-202 decreased by 34% and 77%, respectively, immediately following injury, whereas their target, IL-10, increased messenger RNA levels 3-fold and protein levels 180 fold. Tumor necrosis factor α (TNF-α) and IL-12 gene expression decreased by 68% and 43%, respectively, following injury, and this was mirrored by a 10-fold increase in miR-181, an miR predicted to target TNF-α transcripts. Lower levels of miR-125a and miR-374b were associated with the later acquisition of hospital-acquired pneumonia. CONCLUSION Alteration in the expression of miRs with highly predicted complementarity to IL-10 and TNF-α may be an important mechanism regulating the posttraumatic immunosuppressive phenotype in intensive care unit patients. LEVEL OF EVIDENCE Retrospective observational study, level III
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