72 research outputs found
The symmetry of charge order in cuprates
Charge-ordered ground states permeate the phenomenology of 3d-based
transition metal oxides, and more generally represent a distinctive hallmark of
strongly-correlated states of matter. The recent discovery of charge order in
various cuprate families fueled new interest into the role played by this
incipient broken symmetry within the complex phase diagram of high-Tc
superconductors. Here we use resonant X-ray scattering to resolve the main
characteristics of the charge-modulated state in two cuprate families: Bi2201
and YBCO. We detect no signatures of spatial modulations along the nodal
direction in Bi2201, thus clarifying the inter-unit-cell momentum-structure of
charge order. We also resolve the intra-unit-cell symmetry of the charge
ordered state, which is revealed to be best represented by a bond-order with
modulated charges on the O-2p orbitals and a prominent d-wave character. These
results provide insights on the microscopic description of charge order in
cuprates, and on its origin and interplay with superconductivity.Comment: A high-resolution version with supplementary material can be found
at:
http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/CDW_symmetry.pd
Doping dependent charge order correlations in electron-doped cuprates
Understanding the interplay between charge order (CO) and other phenomena
(e.g. pseudogap, antiferromagnetism, and superconductivity) is one of the
central questions in the cuprate high-temperature superconductors. The
discovery that similar forms of CO exist in both hole- and electron-doped
cuprates opened a path to determine what subset of the CO phenomenology is
universal to all the cuprates. Here, we use resonant x-ray scattering to
measure the charge order correlations in electron-doped cuprates (La2-xCexCuO4
and Nd2-xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and
superconductivity. Detailed measurements of Nd2-xCexCuO4 show that CO is
present in the x = 0.059 to 0.166 range, and that its doping dependent
wavevector is consistent with the separation between straight segments of the
Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166,
but decreases at lower doping levels, indicating that it is not tied to the
appearance of antiferromagnetic correlations or the pseudogap. Near optimal
doping, where the CO wavevector is also consistent with a previously observed
phonon anomaly, measurements of the CO below and above the superconducting
transition temperature, or in a magnetic field, show that the CO is insensitive
to superconductivity. Overall these findings indicate that, while verified in
the electron-doped cuprates, material-dependent details determine whether the
CO correlations acquire sufficient strength to compete for the ground state of
the cuprates.Comment: Supplementary information available upon reques
Doping-dependent charge order correlations in electron-doped cuprates
Understanding the interplay between charge order (CO) and other phenomena (for example, pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. We use resonant x-ray scattering to measure the CO correlations in electron-doped cuprates (La2−xCexCuO4 and Nd2−xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2−xCexCuO4 show that CO is present in the x = 0.059 to 0.166 range and that its doping-dependent wave vector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166 but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wave vector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall, these findings indicate that, although verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates
ARPES: A probe of electronic correlations
Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct
methods of studying the electronic structure of solids. By measuring the
kinetic energy and angular distribution of the electrons photoemitted from a
sample illuminated with sufficiently high-energy radiation, one can gain
information on both the energy and momentum of the electrons propagating inside
a material. This is of vital importance in elucidating the connection between
electronic, magnetic, and chemical structure of solids, in particular for those
complex systems which cannot be appropriately described within the
independent-particle picture. Among the various classes of complex systems, of
great interest are the transition metal oxides, which have been at the center
stage in condensed matter physics for the last four decades. Following a
general introduction to the topic, we will lay the theoretical basis needed to
understand the pivotal role of ARPES in the study of such systems. After a
brief overview on the state-of-the-art capabilities of the technique, we will
review some of the most interesting and relevant case studies of the novel
physics revealed by ARPES in 3d-, 4d- and 5d-based oxides.Comment: Chapter to appear in "Strongly Correlated Systems: Experimental
Techniques", edited by A. Avella and F. Mancini, Springer Series in
Solid-State Sciences (2013). A high-resolution version can be found at:
http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Reviews/ARPES_Springer.pdf.
arXiv admin note: text overlap with arXiv:cond-mat/0307085,
arXiv:cond-mat/020850
Apoptosis Is Essential for Neutrophil Functional Shutdown and Determines Tissue Damage in Experimental Pneumococcal Meningitis
During acute bacterial infections such as meningitis, neutrophils enter the tissue where they combat the infection before they undergo apoptosis and are taken up by macrophages. Neutrophils show pro-inflammatory activity and may contribute to tissue damage. In pneumococcal meningitis, neuronal damage despite adequate chemotherapy is a frequent clinical finding. This damage may be due to excessive neutrophil activity. We here show that transgenic expression of Bcl-2 in haematopoietic cells blocks the resolution of inflammation following antibiotic therapy in a mouse model of pneumococcal meningitis. The persistence of neutrophil brain infiltrates was accompanied by high levels of IL-1β and G-CSF as well as reduced levels of anti-inflammatory TGF-β. Significantly, Bcl-2-transgenic mice developed more severe disease that was dependent on neutrophils, characterized by pronounced vasogenic edema, vasculitis, brain haemorrhages and higher clinical scores. In vitro analysis of neutrophils demonstrated that apoptosis inhibition completely preserves neutrophil effector function and prevents internalization by macrophages. The inhibitor of cyclin-dependent kinases, roscovitine induced apoptosis in neutrophils in vitro and in vivo. In wild type mice treated with antibiotics, roscovitine significantly improved the resolution of the inflammation after pneumococcal infection and accelerated recovery. These results indicate that apoptosis is essential to turn off activated neutrophils and show that inflammatory activity and disease severity in a pyogenic infection can be modulated by targeting the apoptotic pathway in neutrophils
Measuring Spirituality as a Universal Human Experience: A Review of Spirituality Questionnaires
Spirituality is an important theme in health research, since a spiritual orientation can help people to cope with the consequences of a serious disease. Knowledge on the role of spirituality is, however, limited, as most research is based on measures of religiosity rather than spirituality. A questionnaire that transcends specific beliefs is a prerequisite for quantifying the importance of spirituality among people who adhere to a religion or none at all. In this review, we discuss ten questionnaires that address spirituality as a universal human experience. Questionnaires are evaluated with regard to psychometric properties, item formulation and confusion with well-being and distress. Although none of the questionnaires fulfilled all the criteria, the multidimensional Spiritual Well-Being Questionnaire is promising
Anesthetics Impact the Resolution of Inflammation
Local and volatile anesthetics are widely used for surgery. It is not known whether anesthetics impinge on the orchestrated events in spontaneous resolution of acute inflammation. Here we investigated whether a commonly used local anesthetic (lidocaine) and a widely used inhaled anesthetic (isoflurane) impact the active process of resolution of inflammation.Using murine peritonitis induced by zymosan and a systems approach, we report that lidocaine delayed and blocked key events in resolution of inflammation. Lidocaine inhibited both PMN apoptosis and macrophage uptake of apoptotic PMN, events that contributed to impaired PMN removal from exudates and thereby delayed the onset of resolution of acute inflammation and return to homeostasis. Lidocaine did not alter the levels of specific lipid mediators, including pro-inflammatory leukotriene B(4), prostaglandin E(2) and anti-inflammatory lipoxin A(4), in the cell-free peritoneal lavages. Addition of a lipoxin A(4) stable analog, partially rescued lidocaine-delayed resolution of inflammation. To identify protein components underlying lidocaine's actions in resolution, systematic proteomics was carried out using nanospray-liquid chromatography-tandem mass spectrometry. Lidocaine selectively up-regulated pro-inflammatory proteins including S100A8/9 and CRAMP/LL-37, and down-regulated anti-inflammatory and some pro-resolution peptides and proteins including IL-4, IL-13, TGF-â and Galectin-1. In contrast, the volatile anesthetic isoflurane promoted resolution in this system, diminishing the amplitude of PMN infiltration and shortening the resolution interval (Ri) approximately 50%. In addition, isoflurane down-regulated a panel of pro-inflammatory chemokines and cytokines, as well as proteins known to be active in cell migration and chemotaxis (i.e., CRAMP and cofilin-1). The distinct impact of lidocaine and isoflurane on selective molecules may underlie their opposite actions in resolution of inflammation, namely lidocaine delayed the onset of resolution (T(max)), while isoflurane shortened resolution interval (Ri).Taken together, both local and volatile anesthetics impact endogenous resolution program(s), altering specific resolution indices and selective cellular/molecular components in inflammation-resolution. Isoflurane enhances whereas lidocaine impairs timely resolution of acute inflammation
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