Apex Oxygen Research Articles

Regional pulmonary oxygen saturations immediately after birth

BackgroundPartial oxygen saturation (SpO2) increases within minutes during transition from the intrauterine to extrauterine life. This study aims to determine the postnatal course of pulmonary regional oxygen saturation (rSO2) measured by Near-Infrared Spectroscopy (NIRS). MethodsWe conducted an observational study at the delivery room in infants above 35 weeks of gestation who did not need resuscitation and did not develop respiratory distress. Preductal pulse oximetry (Covidien NellcorTM) and right pulmonary apex oxygen saturation (raSO2) and basal oxygen saturation (rbSO2) (Covidien INVOSTM) were measured, starting from the postnatal third minute of life, until the 15th minute. The correlations between SpO2 and pulmonary rSO2 were analyzed. ResultsOf the 110 infants included in the study, 87 were term and 23 were late preterms. The gestational age and birth weight were 38.5 ± 1.36 weeks and 3285 ± 508 g, respectively. Median (5th–95th percentile) raSO2 and rbSO2 were 79% (58–95%) and 78% (46–95%) at the third minute, respectively. The rSO2 values measured from both sides increased and reached a steady-state around postnatal 9 min, similar to SpO2 values. The pulmonary NIRS values were significantly higher for babies born by C-Section compared to babies born by vaginal delivery (p < 0.05). ConclusionWe found that rSO2 measurements increased within minutes in the postnatal period in late preterm and term babies without respiratory distress and reached a plateau at the postnatal 9th minute. The normal values obtained from this preliminary study may be used to predict the prognosis of cases with respiratory distress.

Potential vulnerability of oak forests to climate change-induced flooding: effects of mild oxygen deficiency on Quercus robur and Quercus petraea seedling physiology.

Flooding is characterized by saturation of soil pores with water, leading to hypoxic conditions which affect plant root development and metabolism. We investigated the oxygen deficiency tolerance observed in Quercus robur and Quercus petraea and seek to understand whether it can be explained by enhanced efficiency in oxygen use in the roots, as estimated through radial oxygen loss visualization in relation to growth measurements and root apex respiration. The study showed that root growth, under oxygen deficiency conditions, was significantly reduced only in Q. robur seedlings. Root respiration was maintained in Q. robur, whereas it was decreased in Q. petraea. Both species set up a barrier against radial oxygen loss, though measurement of apex oxygen leakage showed greater oxygen efficiency in Q. robur seedlings. This strategy might allow Q. robur to maintain its respiration and thus to survive longer under oxygen deficiency conditions by facilitating the seedling establishment in transient flooded soils.

Pressure induced self-doping and dependence of critical temperature in stoichiometry YBa2Cu3O6.95 predicted by first-principle and BVS calculations

This paper deals with the pressure effect on self-doping and critical temperature in optimum oxygen stoichiometry YBa2Cu3O6.95 of high temperature superconductor (HTS) based on a numerical study combined the first-principle with bond valence sum (BVS) calculations. The microscopic electronic properties and equilibrium ionic position configurations in the superconductor under external pressure are firstly calculated using the first-principle method. The results show that the apex oxygen in the cuprate superconductor shifts towards CuO2 plane due to pressure effect, and the minimum buckling angle of CuO2 plane is correlated with the maximum critical temperature. A BVS formalism is then utilized for evaluating the valences of all ions in the superconductor on the basis of the electronic and ionic properties and the hole concentration in both CuO2 plane and Cu-O chain are deduced. It demonstrates that the pressure-induced charge redistribution leads to a self-doping process of the hole-transfer into CuO2 plane from both Cu-O chain and Y site in the cuprate superconductor, which is the dominant mechanism of pressure effect on the superconductive properties. In order to quantitatively predict critical temperature profile of YBa2Cu3O6.95 under pressure, a modified formula describing pressure-induced charge transfer taking into account pressure dependence of the optimum hole concentration is developed. The predicted results exhibit good agreements with the experimental data in the literature, and the model parameters on the critical characteristics of the superconductor are discussed in details.

Numerical exploration of spontaneous broken symmetries in multiorbital Hubbard models

We study three proposals for broken symmetry in the cuprate pseudogap - oxygen antiferromagnetism, $\Theta_{II}$ orbital loop currents, and circulating currents involving apex oxygens - through numerical exploration of multi-orbital Hubbard models. Our numerically exact results show no evidence for the existence of oxygen antiferromagnetic order or the $\Theta_{II}$ phase in the three-orbital Hubbard model. The model also fails to sustain an ordered current pattern even with the presence of additional apex oxygen orbitals. We thereby conclude that it is difficult to stabilize the aforementioned phases in the multi-orbital Hubbard models for parameters relevant to cuprate superconductors. However, the $\Theta_{II}$ phase might be stabilized through explicit flux terms. We find an enhanced propensity for circulating currents with such terms in calculations simulating applied stress or strain, which skew the copper-oxygen plane to resemble a kagome lattice. We propose an experimental viewpoint to shed additional light on this problem.

Band Structure and Quantum Oscillations in YBa2Cu3O7: A Local Spin Density Approximation with the On-Site Coulomb Interaction Study

First-principles calculations have been performed on the Bravais lattice, the density of states (DOS), the band structure (BS) and the Fermi Surface (FS) topology for high-Tc superconductor YBa2Cu3O7. We used the method of the Full-Potential non-orthogonal Local-Orbital Minimum-Basis Band-structure Scheme (FPLO) [in the local spin density approximation with the on-site Coulomb interaction (LSDA+U) and the coherent potential approximation (CPA)] coupled with the XFSF program. Our FPLO Fermi surface consists of four large quasi-2D cylinders centered on the Brillouin zone corners with mostly CuO2 plane character and two quasi-1D sheets with mostly Cu–O apex (or apical O) chain character. The main feature of this Fermi surface is that each CuO chain-sheet shows up in its center a small tubular pocket with a funnel-like shape (Fermi pockets) with mainly Ba–O apex character which could give rise to the quantum oscillations observed by Doiron-Leyraud et al. (Nature 447: 565, 2007). Our FPLO band structure (BS) shows that three flat bands cross the Fermi level (FL) which suggests that the two Fermi pockets could be produced by the conjunction near the Fermi level of two flat bands arising from the apex oxygen (BaO layer). This is consistent with the density of states (DOS) where the Fermi level is dominated by the two O apex (BaO) peaks (∼90 %). Moreover, the strong narrow peak exhibited in the DOS just below the Fermi level (FL) corresponds to the van Hove singularity (VHS) and originates from the hybridization of Cu 3d and apex O2p (BaO) orbitals. In other hand, the calculated value of the bare band-structure Sommerfeld constant γ0band=10.60 mJ/(mol K2) corresponds to a very high Fermi level density of states N(EF)=4.72 states/(eV×cell) and the electron–phonon coupling constant λ is found to be about 1.64 which implies that YBa2Cu3O7 compound is a strong-coupling superconductor and the cyclotron effective mass m∗ is enhanced in comparison with the band mass mb [m∗=(1+λ)mb]. Also, the discrepancy between our FPLO calculated Debye temperature (274.15 K) and that obtained experimentally (437 K) may originate from a phonon anisotropy likely generated by the antiferromagnetic spin fluctuations. Our results therefore provide evidence of changes in the topology of the Fermi surface materialized by the Ba–O apex small pockets formed in the center of the Cu–O apex Fermi surface sheets.

The fluctuations of the spin state of 3d-ions near the “triple point”

The spin states of 3d ions placed in an arbitrarily distorted coordination complex are investigated within the semiempirical modified crystal-field theory. A scheme for constructing spin-state diagrams is presented. Spin-state diagrams are obtained for transition metal ions with electron configurations 3d4, 3d5, and 3d6 placed in a pyramidal environment. The spin-state diagrams for all configurations studied display so-called “triple points”, i.e., regions where the spin states are mixed in equal proportions. The spin-state evolution of a five-coordinated Co3+ ion in the layered rare-earth cobaltite GdBaCo2O5.5 is studied. It is found that the intermediate spin state of the Co3+ ion is stabilized by the apex oxygen displacement along the pyramidal axis.

Synthesis, structural and thermal studies of Pu(VO3)4: A new vanadate in PuO2–V2O5 system

A new phase Pu(VO3)4 in PuO2–V2O5 system was prepared by heating an appropriate amount of pre-dried PuO2 and V2O5 at 640°C. The structural and thermal properties of Pu(VO3)4 were investigated by powder X-ray diffraction and thermogravimetry (TG). Structural analyses revealed that Pu(VO3)4 crystallizes in tetragonal (space group: I41/a) lattice with unit cell parameters, a=8.4528(2)Å and c=28.6644(9)Å and is isostructural to metavanadates of thorium and neptunium. Structure shows crystallographically two distinct vanadium atoms V(1) and V(2), one plutonium atom (Pu1) and seven oxygen atoms in the unit cell of Pu(VO3)4. Vanadium atoms form VO4 tetrahedra while plutonium forms PuO8 polyhedra with oxygen atoms. The VO4 units are linked together by sharing apex oxygen atoms and form infinite spiral chains of (VO3)n. Along c-axis, the plutonium atoms are sandwiched between the two layers of (VO3)n chains. TG of Pu(VO3)4 showed thermal stability of the compound up to 700°C.

Metal–insulator transition in V1−xWxO2: structural and electronic origin

The driving mechanism of the metal-insulator transition (MIT) in VO(2) has always attracted attention, in particular with regards to understanding if and how the doping mechanism may tune the MIT transition temperature. However, due to the lack of detailed local structural information, in this oxide the underlying MIT mechanism is still matter of debate. In this contribution on the V(1-x)W(x)O(2) system, we attempt to clarify the origin of the MIT induced by tungsten doping. Combining W L(3)-edge and V K-edge extended X-ray absorption fine-structure (EXAFS) spectroscopy, the local structures around both V and W have been obtained. The data point out the occurrence of internal stress along the V-V chains induced by doping. It reaches a critical value that remains constant during the transition. The main effect of the internal stress on the vanadium local structure has also been identified. Actually, upon increasing the dopant concentration, the tilt of the V-V pairs towards the apex oxygen atoms in the VO(6) octahedron decreases while the V-V bond lengths remain unchanged. The electronic structure has also been investigated by O K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Actually, at high doping concentrations the interaction of O(2p) and the V d(∥) state increases, while the hybridization of O(2p) and V π* decreases. The O(2p)-V(3d) hybridization is therefore an essential parameter correlated with the decreasing transition temperature in the V(1-x)W(x)O(2) system.

Superconducting Condensation Energy of the Two-Dimensional Hubbard Model in the Large-Negative-t' Region

We compute the superconducting condensation energies Econd of Hg1201 and Tl2201 cuprates by applying the variational Monte Carlo method to the two-dimensional Hubbard model, first, with the specific band parameters t' = -2t" = -0.25t appropriate for these highest-Tc single-CuO2-layer cuprates; t, t' and t" are the first-, second- and third-neighbor transfer energies, respectively. In the range of on-site Coulomb energy U of (7\sim10)t with optimal doping, we succeed in obtaining the bulk-limit Econd values by extrapolating the results. They sharply increase with increasing U and become comparable to experimental values when U \approx 9t. Next, Econd values at t' = -2t" = -0.18t demonstrate that with a fixed U the bulk-limit Econd quickly increases with a decrease in |t'| = 2t" in the large-|t'| region. Finally, we argue that the remoteness of the apex oxygen from the planar Cu in the two cuprates is considered to increase U and bring about the experimental magnitude of Econd. The present scheme explains the observed correlation between Tc and t' among cuprates.

Femtosecond Response of Quasiparticles and Phonons in SuperconductingYBa2Cu3O7−δStudied by Wideband Terahertz Spectroscopy

We measure the anisotropic midinfrared response of electrons and phonons in bulk YBa(2)Cu(3)O(7-δ) 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.

Phonon dispersion and anomalies in one-layer high-temperature superconductors

Phonon dynamics, charge response and the phonon density ofstates are calculated for the high-temperature superconductorsHgBa2CuO4 andBi2Sr2CuO6 within amicroscopic model for the electronic density response. The results are compared with previous calculationsfor La2CuO4 and Nd2CuO4. Our main focus is on the phonon anomalies which are connected with the high-frequencyoxygen bond-stretching modes (OBSM) found before in our calculations for p-dopedLa2CuO4 andn-doped Nd2CuO4. We investigate the question if the characteristic softening of the OBSMand the related strong coupling to the electrons is also present inHgBa2CuO4 andBi2Sr2CuO6. In particular, the importance of the contribution of the more delocalized Cu 4s statebesides the localized Cu 3d state on the softening is investigated and the differentanticrossing behavior due to the presence of several phonon modes with the same symmetryas the OBSM is studied. This makes the identification of the anomalies quitecomplicated. Furthermore, the influence of electronic polarization processes at ionsout of the CuO plane in the ionic layers on the phonon dynamics is calculated.In this context the qualitative type of charge response, i.e. the presence or notof possible metallic charge fluctuations at the Hg or Bi ion, respectively, linkedvia the apex oxygen to the CuO plane, proves to be very sensitive for certainphonon modes. All the calculations are compared to the experimental resultsavailable so far. The latter, however, are rather incomplete for the Hg and Bicompounds.

Impact of dynamical screening on the phonon dynamics of metallicLa2CuO4

It is shown within a quantitative calculation that poor dynamical screening of the long-ranged Coulomb interaction due to the slow charge dynamics around the $c$ axis leads in metallic ${\text{La}}_{2}{\text{CuO}}_{4}$ to low-energy electronic collective excitations in a small region around this axis, strongly mixing with certain interlayer phonons. The manifestation of such a phonon-plasmon scenario in layered systems based on a nonadiabatic charge response recently proposed on a qualitative level is quantitatively investigated by a realistic calculation of the frequency and wave-vector-dependent irreducible polarization part of the density response function. Our calculation corrects for a generic deficit of LDA calculations which as a rule predict a too large electronic $c$-axis dispersion insufficient to describe the $c$-axis charge response in general and in particular the phonons along this axis in the cuprates. As shown in this work, the latter are highly sensitive with respect to the interlayer coupling and thus a very accurate electronic dispersion along the $c$ axis is crucial. Linear response theory is used to calculate the coupled mode dispersion in the main symmetry directions of the Brillouin zone and the charge-density redistributions excited by certain strongly coupling phononlike and plasmonlike modes. The corresponding mode induced orbital averaged changes in the self-consistent potential felt by the electrons are assessed. Our analysis should be representative for the optimally to overdoped state of the cuprates where experimental evidence of a coherent three-dimensional Fermi surface and a coherent $c$-axis charge transport is given. It is demonstrated that modes from the outside of a small region around the $c$ axis can reliably be calculated within the adiabatic limit. On the other hand, modes inside this sector have to be determined nonadiabatically. In particular, the relevance of a strongly coupling nonadiabatic phononlike apex oxygen $Z$-point breathing mode ${\text{O}}_{z}^{Z}$ at about 40 meV is emphasized whose mode energy decreases with less doping.

Raman study of twin-free ortho-IIYBa2Cu3O6.5single crystals

The polarized Raman scattering spectra from freshly cleaved ab, ac, and bc surfaces of high quality twin-free YBa2Cu3O6.5 ortho-II single crystals Tc=57.5 K and T=0.6 K were studied between 80 and 300 K. All 11 Ag Raman modes expected for the ortho-II structure as well as some modes of B2g and B3g symmetries were identified in close comparison to predictions of lattice dynamical calculations. The electronic scattering from the ab planes is strongly anisotropic and decreases between 200 and 100 K within the temperature range of a previously reported pseudogap opening. The coupling of phonons to Raman active electronic excitations manifested by asymmetric Fano profiles of several modes also decreases within the same range. Among the findings that distinguish the Raman scattering of the ortho-II phase from that of the ortho-I phase is the unusual relationship xx − yy between the elements of the Raman tensor of the apex oxygen Ag mode.

Hydrostatic pressure induced lattice effects in La2-xSrxCuO4

Micro-Raman measurements under hydrostatic pressures up to ~6 GPa have been carried out on high-quality La2-xSrxCuO4 polycrystalline compounds with Sr concentration up to x = 0.24. The zz scattering polarization has been investigated at room temperature, where two strong modes due to La/Sr and the apex oxygen atoms are observed. The energy of the strong modes increases almost linearly with pressure for the Sr concentrations studied. Modifications in the increment rate dω/dp have been detected depending on the amount of doping. Finally, measurements at low temperatures denote that the application of pressure minimizes the distortions of the CuO6 octahedra.

Local Environment of Fluorine Atoms in Sr[sub 2]Ca[sub n][sub – 1]Cu[sub n]O[sub 2][sub n][sub + δ]F[sub 2 ± ][sub y] (n = 2, 3) High-Temperature Superconductors Grown under High Pressure

The local environment of fluorine atoms in Sr2Can − 1CunO2n + δF2 ± y (n = 2, 3) high-temperature superconductors (Tc = 99 and 111 K) is studied using soft x-ray emission and absorption spectroscopy. The fluorine spectra of the samples studied are found to be similar to those of SrF2, which supports the conjecture that fluorine atoms substitute for apex oxygen atoms and form double SrF layers.

Study of YBaCuO quasi-two-dimensional crystalline structure by light scattering

The following is a study of light scattering by C-oscillations of the apical oxygen O(4) ion, which has a specific role since the superconductive pairing mechanism is due to the fluctuation of O(4) positions in YBa 2Cu 3O 7− x -type crystals. The schema for estimation of the apex oxygen content and a number of consequences resulting from the mixing of the electromagnetic g- and u-modes in a YBa 2Cu 3O 7− x quasi-two-dimensional layer has been obtained. When oxygen vacancies are in the O(4)–Cu(1)–O(4) bridges (or another distortion of lattice symmetry), the C-vibrations of O(4) result in initiation of a dipole moment. At the same time they are associated with the Cu(1)–O(4) bond deformation. The latter one causes Raman scattering by dipole-active O(4)–oscillations. In the framework of the anharmonic oscillator model we have obtained the intensity of the second harmonic scattered signal, and sum and difference frequencies generated by YBa 2Cu 3O 7− x nano-crystalline film as well.

Study of YBaCuO quasi-two-dimensional crystalline structure by light scattering

The following is a study of light scattering by C-oscillations of the apical oxygen O(4) ion, which has a specific role since the superconductive pairing mechanism is due to the fluctuation of O(4) positions in YBa2Cu3O7−x-type crystals. The schema for estimation of the apex oxygen content and a number of consequences resulting from the mixing of the electromagnetic g- and u-modes in a YBa2Cu3O7−x quasi-two-dimensional layer has been obtained. When oxygen vacancies are in the O(4)–Cu(1)–O(4) bridges (or another distortion of lattice symmetry), the C-vibrations of O(4) result in initiation of a dipole moment. At the same time they are associated with the Cu(1)–O(4) bond deformation. The latter one causes Raman scattering by dipole-active O(4)–oscillations. In the framework of the anharmonic oscillator model we have obtained the intensity of the second harmonic scattered signal, and sum and difference frequencies generated by YBa2Cu3O7−x nano-crystalline film as well.

Magnetic interactions in calcium and sodium ladder vanadates.

Magnetic interactions in ladder vanadates are determined with quantum chemical computational schemes using the embedded cluster model approach to represent the material. The available experimental data for calcium vanadate is accurately reproduced and the nature of the interladder interaction is established to be ferromagnetic. An analysis of the main contributions to the magnetic couplings is presented and the role of the covalently bonded apex oxygen is elucidated. In the sodium vanadate, the ground state configuration of the rungs is V-3d1-O-2p5-V-3d1. We show that with this configuration good intrachain coupling constants are obtained for the high-temperature phase. The interchain coupling in NaV2O5 is predicted to be approximately 34 K, ferromagnetic in nature.

High pressure raman study of Y-124

In this work, a micro-Raman study under high hydrostatic pressure (up to ∼5.5 GPa) has been carried on YBa2Cu4O8 and Y(Ba, Sr)2Cu4O8 single crystals at room temperature. In both samples, seven strong modes, of Ag symmetry, and one weak, of B3g symmetry, have been observed and examined in connection with previously published results concerning YBa2Cu4O8. With the Sr substitution for Ba, the ambient pressure measurements show an upward shift in energy for all modes, except those that involve vibrations of the plane and apex oxygen atoms. With increasing hydrostatic pressure all phonons shift to higher energies. Anomalous nonlinear pressure behaviour has been observed for three phonons, which is correlated with the pressure dependence of T c of these compounds.

High pressure raman study of Bi-2212

The hydrostatic pressure dependence of the Raman spectra of Bi2Sr2CaCu2O8 single crystals has been investigated. The energy of the A g and B 1g modes was found to increase with pressure in agreement with previously reported measurements, except the strong mode at ∼465 cm−1, which softens with pressure, while another peak at ∼458 cm−1 appears more pronounced at low temperatures and high pressures. The energy of both modes does not seem to change with increasing pressure, up to ∼5 GPa, although the average energy of the wide band has been found to soften, which is in disagreement with previously published results. Based on the modifications observed in some phonons at ∼1.8 GPa, which correlate with the reduction of T c and the deformations of the CuO5 pyramids, we attribute the mode at ∼465 cm−1 to the vibrations of the apex oxygen atoms. All modes due to the oxygen atoms were found to be strongly anharmonic.