86 research outputs found
Influence of crystallographic orientation of biogenic calcite on <i>in situ</i> Mg XANES analyses
Micro X-ray absorption near-edge spectroscopy at the Mg <i>K</i>-edge is a useful technique for acquiring information about the environment of Mg<sup>2+</sup> in biogenic calcite. These analyses can be applied to shell powders or intact shell structures. The advantage of the latter is that the XANES analyses can be applied to specific areas, at high (e.g. micrometre) spatial resolution, to determine the environment of Mg<sup>2+</sup> in a biomineral context. Such in situ synchrotron analysis has to take into account the potential effect of crystallographic orientation given the anisotropy of calcite crystals and the polarized nature of X-rays. Brachiopod shells of species with different crystallographic orientations are used to assess this crystallographic effect on <i>in situ</i> synchrotron measurements at the Mg <i>K</i>-edge. Results show that, owing to the anisotropy of calcite, <i>in situ</i> X-ray absorption spectra (XAS) are influenced by the crystallographic orientation of calcite crystals with a subsequent potentially erroneous interpretation of Mg<sup>2+</sup> data. Thus, this study demonstrates the importance of crystallography for XAS analyses and, therefore, the necessity to obtain crystallographic information at high spatial resolution prior to spectroscopic analysis
Role of magnetic and orbital ordering at the metal-insulator transition in NdNiO3
Soft x-ray resonant scattering at the Ni L2,3 edges is used to test models of
magnetic and orbital-ordering below the metal-insulator transition in NdNiO3.
The large branching ratio of the L3 to L2 intensities of the (1/2,0,1/2)
reflection and the observed azimuthal angle and polarization dependence
originates from a non collinear magnetic structure. The absence of an orbital
signal and the non collinear magnetic structure show that the nickelates are
materials for which orbital ordering is absent at the metal-insulator
transition.Comment: 10 pages, 4 figures, Physical Review B rapid communication, to be
publishe
Magnetic and electronic Co states in layered cobaltate GdBaCo2O5.5-x
We have performed non-resonant x-ray diffraction, resonant soft and hard
x-ray magnetic diffraction, soft x-ray absorption and x-ray magnetic circular
dichroism measurements to clarify the electronic and magnetic states of the
Co3+ ions in GdBaCo2O5.5. Our data are consistent with a 3+ Py Co HS state at
the pyramidal sites and a 3+ Oc Co LS state at the octahedral sites. The
structural distortion, with a doubling of the a axis (2ap x 2ap x 2ap cell),
shows alternating elongations and contractions of the pyramids and indicates
that the metal-insulator transition is associated with orbital order in the t2g
orbitals of the 3+ Py Co HS state. This distortion corresponds to an
alternating ordering of xz and yz orbitals along the a and c axes for the 3+ Py
Co . The orbital ordering and pyramidal distortion lead to deformation of the
octahedra, but the 3+ Oc Co LS state does not allow an orbital order to occur
for the 3+ Oc Co ions. The soft x-ray magnetic diffraction results indicate
that the magnetic moments are aligned in the ab plane but are not parallel to
the crystallographic a or b axes. The orbital order and the doubling of the
magnetic unit cell along the c axis support a non-collinear magnetic structure.
The x-ray magnetic circular dichroism data indicate that there is a large
orbital magnetic contribution to the total ordered Co moment
Pionic charge exchange on the proton from 40 to 250 MeV
The total cross sections for pionic charge exchange on hydrogen were measured
using a transmission technique on thin CH2 and C targets. Data were taken for
pi- lab energies from 39 to 247 MeV with total errors of typically 2% over the
Delta-resonance and up to 10% at the lowest energies. Deviations from the
predictions of the SAID phase shift analysis in the 60 to 80 MeV region are
interpreted as evidence for isospin-symmetry breaking in the s-wave amplitudes.
The charge dependence of the Delta-resonance properties appears to be smaller
than previously reported
The KARMEN Time Anomaly: Search for a Neutral Particle of Mass 33.9 MeV in Pion Decay
We have searched for the pion decay pi^+ --> mu^+ X, where X is a neutral
particle of mass 33.905 MeV. This process was suggested by the KARMEN
Collaboration to explain an anomaly in their observed time distribution of
neutrino induced reactions. Having measured the muon momentum spectrum of
charged pions decaying in flight, we find no evidence for this process and
place an upper limit on the branching fraction eta leq 6.0 * 10^{-10} of such a
decay at a 95% confidence level.Comment: 17 pages including 4 for figure
Study on Resistance Switching Properties of Na0.5Bi0.5TiO3Thin Films Using Impedance Spectroscopy
The Na0.5Bi0.5TiO3(NBT) thin films sandwiched between Au electrodes and fluorine-doped tin oxide (FTO) conducting glass were deposited using a sol–gel method. Based on electrochemical workstation measurements, reproducible resistance switching characteristics and negative differential resistances were obtained at room temperature. A local impedance spectroscopy measurement of Au/NBT was performed to reveal the interface-related electrical characteristics. The DC-bias-dependent impedance spectra suggested the occurrence of charge and mass transfer at the interface of the Au/NBT/FTO device. It was proposed that the first and the second ionization of oxygen vacancies are responsible for the conduction in the low- and high-resistance states, respectively. The experimental results showed high potential for nonvolatile memory applications in NBT thin films
High precision measurements of the ground state hyperfine structure interval of muonium and of the muon magnetic moment
No description supplie
A compact and cost-effective hard X-ray free-electron laser driven by a high-brightness and low-energy electron beam
We present the first lasing results of SwissFEL, a hard X-ray free-electron laser (FEL) that recently came into operation at the Paul Scherrer Institute in Switzerland. SwissFEL is a very stable, compact and cost-effective X-ray FEL facility driven by a low-energy and ultra-low-emittance electron beam travelling through short-period undulators. It delivers stable hard X-ray FEL radiation at 1-Ă… wavelength with pulse energies of more than 500 ÎĽJ, pulse durations of ~30 fs (root mean square) and spectral bandwidth below the per-mil level. Using special configurations, we have produced pulses shorter than 1 fs and, in a different set-up, broadband radiation with an unprecedented bandwidth of ~2%. The extremely small emittance demonstrated at SwissFEL paves the way for even more compact and affordable hard X-ray FELs, potentially boosting the number of facilities worldwide and thereby expanding the population of the scientific community that has access to X-ray FEL radiation
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