1,300 research outputs found
Magnetic properties of Yb2Mo2O7 and Gd2Mo2O7 from rare earth Mossbauer measurements
Using 170-Yb and 155-Gd Mossbauer measurements down to 0.03K, we have
examined the semiconducting pyrochlore Yb2Mo2O7 where the Mo intra-sublattice
interaction is anti-ferromagnetic and the metallic pyrochlore Gd2Mo2O7 where
this interaction is ferromagnetic. Additional information was obtained from
susceptibility, magnetisation and 172-Yb perturbed angular correlation
measurements. The microscopic measurements evidence lattice disorder which is
important in Yb2Mo2O7 and modest in Gd2Mo2O7. Magnetic irreversibilities occur
at 17K in Yb2Mo2O7 and at 75K in Gd2Mo2O7 and below these temperatures the rare
earths carry magnetic moments which are induced through couplings with the Mo
sublattice. In Gd2Mo2O7, we observe the steady state Gd hyperfine populations
at 0.027K are out of thermal equilibrium, indicating that Gd and Mo spin
fluctuations persist at very low temperatures. Frustration is thus operative in
this essentially isotropic pyrochlore where the dominant Mo intra-sublattice
interaction is ferromagnetic.Comment: 9 pages, 9 figure
Is the neutrophil-to-lymphocyte ratio more correlated than C-reactive protein with postoperative complications after major abdominal surgery?
Peer reviewedPublisher PD
Spin Dynamics in Cuprates: Optical Conductivity of HgBa2CuO4
The electron-boson spectral density function I^2ChiOmega responsible for
carrier scattering of the high temperature superconductor HgBa2CuO4 (Tc = 90 K)
is calculated from new data on the optical scattering rate. A maximum entropy
technique is used. Published data on HgBa2Ca2Cu3O8 (Tc = 130 K) are also
inverted and these new results are put in the context of other known cases. All
spectra (with two notable exceptions) show a peak at an energy (Omega_r)
proportional to the superconducting transition temperature Omega_r ~= 6.3
kB.Tc. This charge channel relationship follows closely the magnetic resonance
seen by polarized neutron scattering, Omega_r^{neutron} ~= 5.4 kB.Tc. The
amplitudes of both peaks decrease strongly with increasing temperature. In some
cases, the peak at Omega_r is weak and the spectrum can have additional maxima
and a background extending up to several hundred meV
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Modeling of the general circulation with the LMD-AOPP-IAA GCM: Update on model design and comparison with observations
The LMD-AOPP GCM is developed conjointly by LMD in Paris and AOPP in Oxford, with the collaboration of
IAA in Granada for the physical processes specific to the upper atmosphere. The collaboration between the
two teams is based on the use of two different dynamical core (gridpoint at LMD, spectral at AOPP), which
allow us to estimate the likely uncertainty arising from certain types of modeling errors. Similarly, we use
different schemes to compute tracer transport, etc. The work has benefited from support from ESA (since 1995)
and CNES (since 2000). Within that context, the GCMs are used to produce a Martian climate 'database' which
is used by more than 30 teams around the world for mission design and scientific studies (see Bingham et al.,
this issue and Lewis et al., 1999). The baseline version of the GCM is described in detail in Forget et al. (1999). Here we describe the recent improvement and design changes since this publication. Compared to this previous version, the new GCM covers a wider range of altitude, from 0 to 120km in the vertical, it uses improved topography and thermal inertia surface
maps from Mars Global Surveyor (MGS), and includes a new 'dust scenario' to describe the distribution of airborne dust in the atmosphere
Angle-resolved photoemission study of the role of nesting and orbital orderings in the antiferromagnetic phase of BaFe2As2
We present a detailed comparison of the electronic structure of BaFe2As2 in
its paramagnetic and antiferromagnetic (AFM) phases, through angle-resolved
photoemission studies. Using different experimental geometries, we resolve the
full elliptic shape of the electron pockets, including parts of dxy symmetry
along its major axis that are usually missing. This allows us to define
precisely how the hole and electron pockets are nested and how the different
orbitals evolve at the transition. We conclude that the imperfect nesting
between hole and electron pockets explains rather well the formation of gaps
and residual metallic droplets in the AFM phase, provided the relative parity
of the different bands is taken into account. Beyond this nesting picture, we
observe shifts and splittings of numerous bands at the transition. We show that
the splittings are surface sensitive and probably not a reliable signature of
the magnetic order. On the other hand, the shifts indicate a significant
redistribution of the orbital occupations at the transition, especially within
the dxz/dyz system, which we discuss
Incommensurate spin density wave in Co-doped BaFe2As2
57Fe Mossbauer spectroscopy measurements are presented in the underdoped
Ba(Fe{1-x}Cox)2As2 series for x=0.014 (T_c < 1.4K) and x=0.03 and 0.045 (T_c ~
2 and 12K respectively). The spectral shapes in the so-called spin-density wave
(SDW) phase are interpreted in terms of incommensurate modulation of the
magnetic structure, and allow the shape of the modulation to be determined. In
undoped BaFe2As2, the magnetic structure is commensurate, and we find that
incommensurability is present at the lowest doping level (x=0.014). As Co
doping increases, the low temperature modulation progressively loses its
"squaredness" and tends to a sine-wave. The same trend occurs for a given
doping level, as temperature increases. We find that a magnetic hyperfine
component persists far above the SDW transition, its intensity being
progressively tranferred to a paramagnetic component on heating.Comment: 7 pages, 8 figures, published in EP
Highly efficient multilayer organic pure-blue-light emitting diodes with substituted carbazoles compounds in the emitting layer
Bright blue organic light-emitting diodes (OLEDs) based on
1,4,5,8,N-pentamethylcarbazole (PMC) and on dimer of N-ethylcarbazole
(N,N'-diethyl-3,3'-bicarbazyl) (DEC) as emitting layers or as dopants in a
4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl (DPVBi) matrix are described. Pure
blue-light with the C.I.E. coordinates x = 0.153 y = 0.100, electroluminescence
efficiency \eta_{EL} of 0.4 cd/A, external quantum efficiency \eta_{ext.} of
0.6% and luminance L of 236 cd/m2 (at 60 mA/cm2) were obtained with PMC as an
emitter and the 2,9-dimethyl-4,7-diphenyl-1,10-phenantroline (BCP) as a
hole-blocking material in five-layer emitting devices. The highest efficiencies
\eta_{EL.} of 4.7 cd/A, and \eta_{ext} = 3.3% were obtained with a four-layer
structure and a DPVBi DEC-doped active layer (CIE coordinates x = 0.158,
y=0.169, \lambda_{peak} = 456 nm). The \eta_{ext.} value is one the highest
reported at this wavelength for blue OLEDs and is related to an internal
quantum efficiency up to 20%
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The Mars Climate Database
The Mars Climate Database (MCD) [1] is a database of statistics describing the climate and environment of the Martian atmosphere. It was constructed directly on the basis of output from mulitannual integrations of two general circulation models (GCMs)developed by Laboratoire de Météorologie Dynamique du CNRS, France, the University of Oxford, UK, and Instituto de Astrofisica de Andalucia, Spain, with support from the European Space Agency (ESA) and Centre National d–Etudes Spatiales (CNES). A description of the MCD is given along with a comparison between spacecraft observations of Mars and results predicted at similar locations and times in the MCD.
The MCD can be used as a tool for mission planning and has been applied to prepare for several missions in Europe and the USA. It also provides information for mission design specialists on the mean state and variability of the Martian environment from the surface to above 120km. The GCMs on which the database is founded, include a set of physical parameterizations (radiative transfer in the visible and thermal infrared ranges, turbulent mixing, condensation-sublimation of CO2, thermal conduction in
the soil and representation of gravity waves) and two
different codes for the representation of large scale
dynamics: a spectral code for the AOPP version and
a grid-point code for the LMD version. The GCMs correctly reproduce the main meteorological features of Mars, as observed by the Mariner 9 and Viking orbiters, the Viking landers, and Mars Global Surveyor (MGS). As well as the standard statistical measures for mission design studies, the MCD includes a novel representation of large-scale variability, using empirical eigenfunctions derived from an
analysis of the full simulations, and small-scale variability based on parameterizations of processes such
as gravity wave propagation. The database allows the user to choose from 5 dust storm scenarios including a best guess, default scenario, deduced from recent MGS observations, an upper boundary for an atmosphere without dust storms, as observed by Viking the landers, and a clear, cold, lower boundary scenario, as observed by Phobos 2 and from Earth. The full version of the MCD is available on CDROM (for UNIX systems and PCs) and is also
accessible through an interactive WWW interface at
http://www-mars.lmd.jussieu.fr/
Use of the neutrophil-to-lymphocyte ratio as a component of a score to predict postoperative mortality after surgery for hip fracture in elderly subjects
Peer reviewedPublisher PD
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