4,559 research outputs found
Influence of static Jahn-Teller distortion on the magnetic excitation spectrum of PrO2: A synchrotron x-ray and neutron inelastic scattering study
A synchrotron x-ray diffraction study of the crystallographic structure of
PrO2 in the Jahn-Teller distorted phase is reported. The distortion of the
oxygen sublattice, which was previously ambiguous, is shown to be a chiral
structure in which neighbouring oxygen chains have opposite chiralities. A
temperature dependent study of the magnetic excitation spectrum, probed by
neutron inelastic scattering, is also reported. Changes in the energies and
relative intensities of the crystal field transitions provide an insight into
the interplay between the static and dynamic Jahn-Teller effects.Comment: 7 pages, 6 figure
Soft X-ray resonant scattering study of single-crystal LaSrMnO
Soft X-ray resonant scattering studies at the Mn - and
the La - edges of single-crystal LaSrMnO are
reported. At low temperatures, below K, energy scans
with a fixed momentum transfer at the \emph{A}-type antiferromagnetic (0 0 1)
reflection around the Mn -edges with incident linear
and polarizations show strong resonant enhancements. The
splitting of the energy spectra around the Mn -edges may
indicate the presence of a mixed valence state, e.g., Mn/Mn. The
relative intensities of the resonance and the clear shoulder-feature as well as
the strong incident and polarization dependences strongly
indicate its complex electronic origin. Unexpected enhancement of the charge
Bragg (0 0 2) reflection at the La -edges with
polarization has been observed up to 300 K, with an anomaly appearing around
the orbital-ordering transition temperature, K,
suggesting a strong coupling (competition) between them.Comment: Accepted by European Physical Journal
Universal subgap optical conductivity in quasi-one-dimensional Peierls systems
Quasi-one-dimensional Peierls systems with quantum and thermal lattice
fluctuations can be modeled by a Dirac-type equation with a Gaussian-correlated
off-diagonal disorder. A powerful new method gives the exact disorder-averaged
Green function used to compute the optical conductivity. The strong subgap tail
of the conductivity has a universal scaling form. The frequency and temperature
dependence of the calculated spectrum agrees with experiments on KCP(Br) and
trans-polyacetylene.Comment: 11 pages (+ 3 figures), LATEX (REVTEX 3.0
Using data insertion with the NAME model to simulate the 8 May 2010 Eyjafjallajökull volcanic ash cloud
A data insertion method, where a dispersion model is initialized from ash properties derived from a series of satellite observations, is used to model the 8 May 2010 Eyjafjallajökull volcanic ash cloud which extended from Iceland to northern Spain. We also briefly discuss the application of this method to the April 2010 phase of the Eyjafjallajökull eruption and the May 2011 Grímsvötn eruption. An advantage of this method is that very little knowledge about the eruption itself is required because some of the usual eruption source parameters are not used. The method may therefore be useful for remote volcanoes where good satellite observations of the erupted material are available, but little is known about the properties of the actual eruption. It does, however, have a number of limitations related to the quality and availability of the observations. We demonstrate that, using certain configurations, the data insertion method is able to capture the structure of a thin filament of ash extending over northern Spain that is not fully captured by other modeling methods. It also verifies well against the satellite observations according to the quantitative
object-based quality metric, SAL—structure, amplitude, location, and the spatial coverage metric, Figure of
Merit in Space
Accurate theoretical determination of the ionization potentials of CaF, SrF, and BaF
We present a comprehensive theoretical study of the ionization potentials of
the MF (M= Ca, Sr, Ba) molecules using the state-of-the-art relativistic
coupled cluster approach with single, double, and perturbative triple
excitations (CCSD(T)). We have further corrected our results for the higher
order excitations (up to full triples) and the QED self energy and vacuum
polarisation contributions. We have performed an extensive investigation of the
effect of the various computational parameters on the calculated ionisation
potentials, which allowed us to assign realistic uncertainties on our
predictions. For CaF and BaF, where precise experiments are available, our
predictions are in excellent agreement with the measured values. In case of
SrF, we provide a new accurate prediction of the ionisation potential that
deviates from the available experimental data, motivating further experimental
investigations.Comment: 7 pages, before paper submission (references will be added
additionally
TRANSONIC PASSAGE TURBINE BLADE TIP CLEARANCE WITH SCALLOPED SHROUD: PART III -HEAT TRANSFER IN ENGINE CONFIGURATION
ABSTRACT This work presents a numerical study that was done to investigate the heat transfer characteristics of a transonic turbine blade with a scalloped shroud operating at realistic engine conditions typical of those found in a large scale, land-based gas turbine. The geometry under investigation was an infinite, linear cascade composed of the same blade and shroud design used in an experimental test rig by the research sponsor. This simulation was run for varying nominal tip clearances of 20, 80, and 5.08 mm. For each of these clearances, the simulation was run with and without the scrubbing effects of the outer casing, resulting in a total of six cases that could be used to determine the influence of tip clearance and relative casing motion on heat transfer. A high quality grid (ranging from approximately 10-12 million finite volumes depending on tip clearance) with y + for first layer cells at or below 1.0 everywhere was used to resolve the flow down to the viscous sublayer. The "realizable" k-ε turbulence model was used for all cases. A constant wall heat flux was imposed on all the surrounding surfaces to obtain heat transfer data. Results produced include a full map of heat transfer coefficients for the suction and pressure surfaces of the blade as well as the tip, shroud, and outer casing for every case. Physical mechanisms responsible for the final heat transfer outcome for all six cases are documented
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