55 research outputs found
Synthesis of (+)-Officinalic Acid
A new concept for the biosynthesis of officinalic acid (1), a C30-metabolitefrom the fungus Laricifomes officinalis, had led to an efficient synthesis of the racemic form of this compound. The key step involves a Diels-Alder dimerization of the readily available enone acid (±)-3, which furnishes (±)-officinalic acid in 420/0 yield. A byproduct formed in the same reaction in 10% yield has been named isoofficinalic acid and shown by spectroscopic techniques to possess structure 11
Observation of out-of-phase bilayer plasmons in YBa_2Cu_3O_7-delta
The temperature dependence of the c-axis optical conductivity \sigma(\omega)
of optimally and overdoped YBa_2Cu_3O_x (x=6.93 and 7) is reported in the far-
(FIR) and mid-infrared (MIR) range. Below T_c we observe a transfer of spectral
weight from the FIR not only to the condensate at \omega = 0, but also to a new
peak in the MIR. This peak is naturally explained as a transverse out-of-phase
bilayer plasmon by a model for \sigma(\omega) which takes the layered crystal
structure into account. With decreasing doping the plasmon shifts to lower
frequencies and can be identified with the surprising and so far not understood
FIR feature reported in underdoped bilayer cuprates.Comment: 7 pages, 3 eps figures, Revtex, epsfi
Femtosecond Quasiparticle and Phonon Dynamics in Superconducting YBa2Cu3O7 Studied by Wideband Terahertz Spectroscopy
We measure the anisotropic mid-infrared response of electrons and phonons in
bulk YBa2Cu3O7 after femtosecond photoexcitation. A line shape analysis of
specific lattice modes reveals their transient occupation and coupling to the
superconducting condensate. The apex oxygen vibration is strongly excited
within 150 fs demonstrating that the lattice absorbs a major portion of the
pump energy before the quasiparticles are thermalized. Our results attest to
substantial electron-phonon scattering and introduce a powerful concept probing
electron-lattice interactions in a variety of complex materials.Comment: 4 pages, 4 figures + supplementary materia
Quantitative comparison of single- and two-particle properties in the cuprates
We explore the strong variations of the electronic properties of
copper-oxygen compounds across the doping phase diagram in a quantitative way.
To this end we calculate the electronic Raman response on the basis of results
from angle-resolved photoemission spectroscopy (ARPES). In the limits of our
approximations we find agreement on the overdoped side and pronounced
discrepancies at lower doping. In contrast to the successful approach for the
transport properties at low energies, the Raman and the ARPES data cannot be
reconciled by adding angle-dependent momentum scattering. We discuss possible
routes towards an explanation of the suppression of spectral weight close to
the points which sets in abruptly close to 21% doping.Comment: 7 pages, 4 figure
The Mysterious Pseudogap in High Temperature Superconductivity, an Infrared View
We review the contribution of infrared spectroscopy to the study of the
pseudogap in high temperature superconductors. The pseudogap appears as a
depression of the frequency dependent conductivity in the c-axis direction and
seems to be related to a real gap in the density of states. It can also be seen
in the Knight shift, photoemission and tunneling experiments. In underdoped
samples it appears near room temperature and does not close with temperature.
Another related phenomenon that has been studied by infrared is the depression
in the ab-plane scattering rate. Two separate effects can be discerned. At high
temperatures there is broad depression of scattering below 1000 cm-1 which may
be related to the gap in the density of states. At a lower temperature a
sharper structure is seen, which appears to be associated with scattering from
a mode at 300 cm-1, and which governs the carrier life time at low
temperatures. This mode shows up in a number of other experiments, as a kink in
ARPES dispersion, and a resonance at 41 meV in magnetic neutron scattering.
Since the infrared technique can be used on a wide range of samples it has
provided evidence that the scattering mode is present in all high temperature
cuprates and that its frequency in optimally doped materials scales with the
superconducting transition temperature. The lanthanum and neodymium based
cuprates do not follow this scaling and appear to have depressed transition
temperatures.Comment: 12 pages, 7 figures, APS Frank Isakson Prize pape
Phase Separation Models for Cuprate Stripe Arrays
An electronic phase separation model provides a natural explanation for a
large variety of experimental results in the cuprates, including evidence for
both stripes and larger domains, and a termination of the phase separation in
the slightly overdoped regime, when the average hole density equals that on the
charged stripes. Several models are presented for charged stripes, showing how
density waves, superconductivity, and strong correlations compete with quantum
size effects (QSEs) in narrow stripes. The energy bands associated with the
charged stripes develop in the middle of the Mott gap, and the splitting of
these bands can be understood by considering the QSE on a single ladder.Comment: significant revisions: includes island phase, 16 eps figures, revte
Review on Superconducting Materials
Short review of the topical comprehension of the superconductor materials
classes Cuprate High-Temperature Superconductors, other oxide superconductors,
Iron-based Superconductors, Heavy-Fermion Superconductors, Nitride
Superconductors, Organic and other Carbon-based Superconductors and Boride and
Borocarbide Superconductors, featuring their present theoretical understanding
and their aspects with respect to technical applications.Comment: A previous version of this article has been published in \" Applied
Superconductivity: Handbook on Devices and Applications \", Wiley-VCH ISBN:
978-3-527-41209-9. The new extended and updated version will be published in
\" Encyclopedia of Applied Physics \", Wiley-VC
Identification of Mycobacterium tuberculosis-Specific Th1, Th17 and Th22 Cells Using the Expression of CD40L in Tuberculous Pleurisy
Important advances have been made in the immunodiagnosis of tuberculosis (TB) based on the detection of Mycobacterium tuberculosis (MTB)-specific T cells. However, the sensitivity and specificity of the immunological approach are relatively low because there are no specific markers for antigen-specific Th cells, and some of the Th cells that do not produce cytokines can be overlooked using this approach. In this study, we found that MTB-specific peptides of ESAT-6/CFP-10 can stimulate the expression of CD40L specifically in CD4+ T cells but not other cells from pleural fluid cells (PFCs) in patients with tuberculous pleurisy (TBP). CD4+CD40L+ but not CD4+CD40Lâ T cells express IFN-Îł, IL-2, TNF-α, IL-17 or IL-22 after stimulation with MTB-specific peptides. In addition, CD4+CD40L+ T cells were found to be mostly polyfunctional T cells that simultaneously produce IFN-Îł, IL-2 and TNF-α and display an effector or effector memory phenotype (CD45RAâCD45RO+CCR7âCD62LâICOSâ). To determine the specificity of CD4+CD40L+ T cells, we incubated PFCs with ESTA-6/CFP-10 peptides and sorted live CD4+CD40L+ and CD4+CD40Lâ T cells by flow cytometry. We further demonstrated that sorted CD4+CD40L+, but not CD4+CD40Lâ fractions, principally produced IFN-Îł, IL-2, TNF-α, IL-17 and IL-22 following restimulation with ESTA-6/CFP-10 peptides. Taken together, our data indicate that the expression of CD40L on MTB-specific CD4+ T cells could be a good marker for the evaluation and isolation of MTB-specific Th cells and might also be useful in the diagnosis of TB
Peri-operative red blood cell transfusion in neonates and infants: NEonate and Children audiT of Anaesthesia pRactice IN Europe: A prospective European multicentre observational study
BACKGROUND: Little is known about current clinical practice concerning peri-operative red blood cell transfusion in neonates and small infants. Guidelines suggest transfusions based on haemoglobin thresholds ranging from 8.5 to 12âgâdl-1, distinguishing between children from birth to day 7 (week 1), from day 8 to day 14 (week 2) or from day 15 (â„week 3) onwards. OBJECTIVE: To observe peri-operative red blood cell transfusion practice according to guidelines in relation to patient outcome. DESIGN: A multicentre observational study. SETTING: The NEonate-Children sTudy of Anaesthesia pRactice IN Europe (NECTARINE) trial recruited patients up to 60 weeks' postmenstrual age undergoing anaesthesia for surgical or diagnostic procedures from 165 centres in 31 European countries between March 2016 and January 2017. PATIENTS: The data included 5609 patients undergoing 6542 procedures. Inclusion criteria was a peri-operative red blood cell transfusion. MAIN OUTCOME MEASURES: The primary endpoint was the haemoglobin level triggering a transfusion for neonates in week 1, week 2 and week 3. Secondary endpoints were transfusion volumes, 'delta haemoglobin' (preprocedure - transfusion-triggering) and 30-day and 90-day morbidity and mortality. RESULTS: Peri-operative red blood cell transfusions were recorded during 447 procedures (6.9%). The median haemoglobin levels triggering a transfusion were 9.6 [IQR 8.7 to 10.9] gâdl-1 for neonates in week 1, 9.6 [7.7 to 10.4] gâdl-1 in week 2 and 8.0 [7.3 to 9.0] gâdl-1 in week 3. The median transfusion volume was 17.1 [11.1 to 26.4] mlâkg-1 with a median delta haemoglobin of 1.8 [0.0 to 3.6] gâdl-1. Thirty-day morbidity was 47.8% with an overall mortality of 11.3%. CONCLUSIONS: Results indicate lower transfusion-triggering haemoglobin thresholds in clinical practice than suggested by current guidelines. The high morbidity and mortality of this NECTARINE sub-cohort calls for investigative action and evidence-based guidelines addressing peri-operative red blood cell transfusions strategies. TRIAL REGISTRATION: ClinicalTrials.gov, identifier: NCT02350348
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