50 research outputs found
Phonon anomalies and lattice dynamics in superconducting oxychlorides CaCuOCl
We present a comprehensive study of the phonon dispersion in an underdoped,
superconducting CaCuOCl crystal. We interpret the results using
lattice dynamical calculations based on a shell model, and we compare the
results, to other hole-doped cuprates, in particular to the ones isomorphic to
LaSrCuO (LSCO). We found that an anomalous dip in the Cu-O bond
stretching dispersion develops in oxychlorides with a simultaneous marked
broadening of the mode. The broadening is maximum at that corresponds to the charge-modulations propagation vector. Our analysis
also suggests that screening effects in calculations may cause an apparent
cosine-shaped bending of the Cu-O bond-stretching dispersion along both the
( 0 0) and ( 0) directions, that is not observed on the data close to
optimal doping. This observation suggests that the discrepancy between
experimental data and \textit{ab-initio} calculations on this mode originates
from an overestimation of the doping effects on the mode
Sharp optical phonon softening close to optimal doping in LaBaCuO
We report a direct observation of a sharp Kohn-like anomaly in the doubly
degenerate copper-oxygen bond-stretching phonon mode occurring at
in LaBaCuO with
, thanks to the high resolution of
inelastic x-ray scattering. This anomaly is clearly seen when the inelastic
signal is analysed using a single mode but is also consistent with a two mode
hypothesis possibly due to a splitting of the degenerate modes due to symmetry
breaking stripes. Our observation shows that the effect persists at the stripe
propagation vector in a superconducting system close to optimal doping
Observation of low energy dispersive modes in un- derdoped (La, Nd) 2−x Sr x CuO 4
We find excitations lower in energy than known phonon modes in underdoped LaSrCuO (x=0.08), with both inelastic X-Ray scattering (IXS) and inelastic neutron scattering (INS). A non dispersive excitation at 9 meV is identified and is also seen by INS in (La,Nd)SrCuO, with 40 Nd substitution. INS also identifies a still lower energy dispersive mode at low q in the Nd free sample. These modes are clearly distinct from the longitudinal acoustic phonon and correspond in energy to the Zone Centre modes measured by optical spectroscopy and associated with stripe dynamics
Phonon dispersion in 1-layer cuprate HgBa2CuO4+d
We investigate the low energy acoustical and optical modes in
using inelastic x-ray scattering (IXS). The
experimental phonon dispersion and the dynamical structure factor are compared
with an atomic shell model, and the set of the atomic potentials obtained are
discussed. Our results are also compared with those obtained by Raman
spectroscopy and with density-of-state data measured by inelastic neutron
scattering
Efficacy of a new technique - INtubate-RECruit-SURfactant-Extubate - "IN-REC-SUR-E" - in preterm neonates with respiratory distress syndrome: Study protocol for a randomized controlled trial
Background: Although beneficial in clinical practice, the INtubate-SURfactant-Extubate (IN-SUR-E) method is not successful in all preterm neonates with respiratory distress syndrome, with a reported failure rate ranging from 19 to 69 %. One of the possible mechanisms responsible for the unsuccessful IN-SUR-E method, requiring subsequent re-intubation and mechanical ventilation, is the inability of the preterm lung to achieve and maintain an "optimal" functional residual capacity. The importance of lung recruitment before surfactant administration has been demonstrated in animal studies showing that recruitment leads to a more homogeneous surfactant distribution within the lungs. Therefore, the aim of this study is to compare the application of a recruitment maneuver using the high-frequency oscillatory ventilation (HFOV) modality just before the surfactant administration followed by rapid extubation (INtubate-RECruit-SURfactant-Extubate: IN-REC-SUR-E) with IN-SUR-E alone in spontaneously breathing preterm infants requiring nasal continuous positive airway pressure (nCPAP) as initial respiratory support and reaching pre-defined CPAP failure criteria. Methods/design: In this study, 206 spontaneously breathing infants born at 24+0-27+6 weeks' gestation and failing nCPAP during the first 24 h of life, will be randomized to receive an HFOV recruitment maneuver (IN-REC-SUR-E) or no recruitment maneuver (IN-SUR-E) just prior to surfactant administration followed by prompt extubation. The primary outcome is the need for mechanical ventilation within the first 3 days of life. Infants in both groups will be considered to have reached the primary outcome when they are not extubated within 30 min after surfactant administration or when they meet the nCPAP failure criteria after extubation. Discussion: From all available data no definitive evidence exists about a positive effect of recruitment before surfactant instillation, but a rationale exists for testing the following hypothesis: a lung recruitment maneuver performed with a step-by-step Continuous Distending Pressure increase during High-Frequency Oscillatory Ventilation (and not with a sustained inflation) could have a positive effects in terms of improved surfactant distribution and consequent its major efficacy in preterm newborns with respiratory distress syndrome. This represents our challenge. Trial registration: ClinicalTrials.gov identifier: NCT02482766. Registered on 1 June 2015
ETUDE DE L'EVOLUTION DES BANDES D'EXCITATION POLARONIQUE EN FONCTION DU DOPAGE ET DE LA TEMPERATURE DANS LA FAMILLE DE SUPRACONDUCTEUR A HAUTE TEMPERATURE CRITIQUE (ND 2 XCE XCUO 4 Y)
ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
Detection of biogenic amorphous calcium carbonate (ACC) formed by bacteria using FTIR spectroscopy
International audienceWhile the formation of intracellular amorphous calcium carbonate (ACC) by living organisms is widespread, its detection in prokaryotes remains difficult owing to its susceptibility to transform or dissolve upon sample preparation. Because of these challenges, a large number of ACC-forming prokaryotes may have been undetected and their abundance in the natural environment is possibly underestimated. This study identifies diagnostic spectral markers of ACC-forming prokaryotes that facilitate their detection in the environment. Accordingly, ACC formed by cyanobacteria was characterized using Fourier transform infrared (FTIR) spectroscopy in near-IR, mid-IR, and far-IR spectral regions. Two characteristic FTIR vibrations of ACC, at ∼ 860 cm−1 and ∼ 306 cm−1, were identified as reliable spectral probes to rapidly detect prokaryotic ACC. Using these spectral probes, several Microcystis strains whose ACC-forming capability was unknown, were tested. Four out of eight Microcystis strains were identified as possessing ACC-forming capability and these findings were confirmed by scanning electron microscopy (SEM) observations. Overall, our findings provide a systematic characterization of prokaryotic ACC that facilitate rapid detection of ACC forming prokaryotes in the environment, a prerequisite to shed light on the role of ACC-forming prokaryotes in the geochemical cycle of Ca in the environment
Ca 2 CuO 2 Cl 2 , a redetermination from single-crystal X-ray diffraction data
International audienc