74 research outputs found
Orbital order in NaTiO : A first principles study
The debate over the orbital order in layered triangular lattice system
NaTiO has been rekindled by the recent experiments of McQueen, et al.
\cite{cava} on NaVO ({\em Phys. Rev. Lett.} {\bf 101}, 166402 (2008)). In
view of this, the nature of orbital ordering, in both high and low temperature
states, is studied using an ab-initio electronic structure calculation. The
orbital order observed in our calculations in the low temperature structure of
NaTiO is consistent with the predictions of McQueen, et. al. An LDA plus
dynamical mean-field calculation shows considerable transfer of spectral weight
from the Fermi level but no metal- insulator transition, confirming the poor
metallic behaviour observed in transport measurements.Comment: 6 pages, 6 figure
Trimer Formation and Metal-Insulator Transition in Orbital Degenerate Systems on a Triangular Lattice
As a prototypical self-organization in the system with orbital degeneracy, we
theoretically investigate trimer formation on a triangular lattice, as observed
in LiVO2. From the analysis of an effective spin-orbital coupled model in the
strong correlation limit, we show that the previously-proposed orbital-ordered
trimer state is not the lowest-energy state for a finite Hund's-rule coupling.
Instead, exploring the ground state in a wide range of parameters for a
multiorbital Hubbard model, we find an instability toward a different
orbital-ordered trimer state in the intermediately correlated regime in the
presence of trigonal crystal field. The trimer phase appears in the competing
region among a paramagnetic metal, band insulator, and Mott insulator. The
underlying mechanism is nesting instability of the Fermi surface by a
synergetic effect of Coulomb interactions and trigonal-field splitting. The
results are compared with experiments in triangularlattice compounds, LiVX2
(X=O, S, Se) and NaVO2.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp
Description of an aerodynamic levitation apparatus with applications in Earth sciences
<p>Abstract</p> <p>Background</p> <p>In aerodynamic levitation, solids and liquids are floated in a vertical gas stream. In combination with CO<sub>2</sub>-laser heating, containerless melting at high temperature of oxides and silicates is possible. We apply aerodynamic levitation to bulk rocks in preparation for microchemical analyses, and for evaporation and reduction experiments.</p> <p>Results</p> <p>Liquid silicate droplets (~2 mm) were maintained stable in levitation using a nozzle with a 0.8 mm bore and an opening angle of 60°. The gas flow was ~250 ml min<sup>-1</sup>. Rock powders were melted and homogenized for microchemcial analyses. Laser melting produced chemically homogeneous glass spheres. Only highly (e.g. H<sub>2</sub>O) and moderately volatile components (Na, K) were partially lost. The composition of evaporated materials was determined by directly combining levitation and inductively coupled plasma mass spectrometry. It is shown that the evaporated material is composed of Na > K >> Si. Levitation of metal oxide-rich material in a mixture of H<sub>2 </sub>and Ar resulted in the exsolution of liquid metal.</p> <p>Conclusions</p> <p>Levitation melting is a rapid technique or for the preparation of bulk rock powders for major, minor and trace element analysis. With exception of moderately volatile elements Na and K, bulk rock analyses can be performed with an uncertainty of ± 5% relative. The technique has great potential for the quantitative determination of evaporated materials from silicate melts. Reduction of oxides to metal is a means for the extraction and analysis of siderophile elements from silicates and can be used to better understand the origin of chondritic metal.</p
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HIBISCUS: Hydroxychloroquine for the secondary prevention of thrombotic and obstetrical events in primary antiphospholipid syndrome
The relapse rate in antiphospholipid syndrome (APS) remains high, i.e. around 20%-21% at 5 years in thrombotic APS and 20-28% in obstetrical APS [2, 3]. Hydroxychloroquine (HCQ) appears as an additional therapy, as it possesses immunomodulatory and anti-thrombotic various effects [4-16]. Our group recently obtained the orphan designation of HCQ in antiphospholipid syndrome by the European Medicine Agency. Furthermore, the leaders of the project made the proposal of an international project, HIBISCUS, about the use of Hydroxychloroquine in secondary prevention of obstetrical and thrombotic events in primary APS. This study has been launched in several countries and at now, 53 centers from 16 countries participate to this international trial. This trial consists in two parts: a retrospective and a prospective study. The French part of the trial in thrombosis has been granted by the French Minister of Health in December 2015 (the academic trial independent of the pharmaceutical industry PHRC N PAPIRUS) and is coordinated by one of the members of the leading consortium of HIBISCUS
Vers la construction d’un corpus commun de français langue étrangère : pour une étude phonétique des productions de locuteurs de langues maternelles plurielles
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