A large-solid-angle X-ray Raman scattering spectrometer at ID20 of the European Synchrotron Radiation Facility

An end-station for X-ray Raman scattering spectroscopy at beamline ID20 of the European Synchrotron Radiation Facility is described. This end-station is dedicated to the study of shallow core electronic excitations using non-resonant inelastic X-ray scattering. The spectrometer has 72 spherically bent analyzer crystals arranged in six modular groups of 12 analyzer crystals each for a combined maximum flexibility and large solid angle of detection. Each of the six analyzer modules houses one pixelated area detector allowing for X-ray Raman scattering based imaging and efficient separation of the desired signal from the sample and spurious scattering from the often used complicated sample environments. This new end-station provides an unprecedented instrument for X-ray Raman scattering, which is a spectroscopic tool of great interest for the study of low-energy X-ray absorption spectra in materials under insitu conditions, such as inoperando batteries and fuel cells, insitu catalytic reactions, and extreme pressure and temperature conditions.Peer reviewe

Suivi archéologique des restaurations du théâtre d'Orange. Présentation du monument et de l'opération

National audienc

The simultaneous measurement of energy and linear polarization of the scattered radiation in resonant inelastic soft x-ray scattering

Resonant Inelastic X-ray Scattering (RIXS) in the soft x-ray range is an element-specific energy-loss spectroscopy used to probe the electronic and magnetic excitations in strongly correlated solids. In the recent years, RIXS has been progressing very quickly in terms of energy resolution and understanding of the experimental results, but the interpretation of spectra could further improve, sometimes decisively, from a full knowledge of the polarization of incident and scattered photons. Here we present the first implementation, in a high resolution RIXS spectrometer used to analyze the scattered radiation, of a device allowing the measurement of the degree of linear polarization. The system, based on a graded W/B4C multilayer mirror installed in proximity of the CCD detector, has been installed on the AXES spectrometer at the ESRF; it has been fully characterized and it has been used for a demonstration experiment at the Cu L3 edge on a high-Tc superconducting cuprate. The loss in efficiency suffered by the spectrometer equipped with this test facility was a factor 17.5. We propose also a more advanced version, suitable for a routine use on the next generation of RIXS spectrometers and with an overall efficiency up to 10%.Comment: 26 pages, 8 figure

Spin-orbit coupling in a half-filled t2gt_{2g} shell: the case of 5d35d^3 K2_2ReCl6_6

The half-filled $t_{2g}$ shell of the $t_{2g}^3$ configuration usually, in LS coupling, hosts a S = 3/2 ground state with quenched orbital moment. This state is not Jahn-Teller active. Sufficiently large spin-orbit coupling $\zeta$ has been predicted to change this picture by mixing in orbital moment, giving rise to a sizable Jahn-Teller distortion. In $5d^3$ K$_2$ReCl$_6$ we study the electronic excitations using resonant inelastic x-ray scattering (RIXS) and optical spectroscopy. We observe on-site intra-$t_{2g}$ excitations below 2 eV and corresponding overtones with two intra-$t_{2g}$ excitations on adjacent sites, the Mott gap at 2.7 eV, $t_{2g}$-to-$e_g$ excitations above 3 eV, and charge-transfer excitations at still higher energy. The intra-$t_{2g}$ excitation energies are a sensitive measure of $\zeta$ and Hund's coupling $J_H$. The sizable value of $\zeta \approx$ 0.29 eV places K$_2$ReCl$_6$ into the intermediate coupling regime, but $\zeta/J_H \approx 0.6$ is not sufficiently large to drive a pronounced Jahn-Teller effect. We discuss the ground state wavefunction in a Kanamori picture and find that the S = 3/2 multiplet still carries about 97 % of the weight. However, the finite admixture of orbital moment allows for subtle effects. We discuss small temperature-induced changes of the optical data and find evidence for a lowering of the ground state by about 3 meV below the structural phase transitions.Comment: 16 pages, 14 figure

Electronic excitations in 5d45d^4 J=0 Os4+^{4+} halides studied by RIXS and optical spectroscopy

We demonstrate that the cubic antifluorite-type halides K$_2$OsCl$_6$, K$_2$OsBr$_6$, and Rb$_2$OsBr$_6$ are excellent realizations of non-magnetic J=0 compounds. The magnetic susceptibility shows the corresponding Van-Vleck type behavior and no sign of defects. We investigate the electronic excitations with two complementary techniques, resonant inelastic x-ray scattering (RIXS) and optical spectroscopy. This powerful combination allows us to thoroughly study, e.g., on-site intra-$t_{2g}$ excitations and $t_{2g}$-to-$e_g$ excitations as well as inter-site excitations across the Mott gap and an exciton below the gap. In this way, we determine the electronic parameters with high accuracy, altogether yielding a comprehensive picture. In K$_2$OsCl$_6$, we find the spin-orbit coupling constant $\zeta$=0.34 eV, Hund's coupling $J_H$=0.43 eV, the onset of excitations across the Mott gap at $\Delta$=2.2 eV, the cubic crystal-field splitting 10Dq=3.3 eV, and the charge-transfer energy $\Delta_{CT}$=4.6 eV. With $J_H/\zeta$=1.3, K$_2$OsCl$_6$ is in the intermediate-coupling regime. In a $t_{2g}$-only Kanamori picture, the above values correspond to $\zeta^{eff}$=0.41 eV and $J_H^{eff}$=0.28 eV, which is very close to results reported for related $5d^4$ iridates. In the tetragonal phase at 5 K, the non-cubic crystal field causes a peak splitting of the J=1 state as small as 4 meV. Compared to K$_2$OsCl$_6$, the bromides K$_2$OsBr$_6$ and Rb$_2$OsBr$_6$ show about 12-14 % smaller values of 10Dq and $\Delta_{CT}$, while the spin-orbit-entangled intra-$t_{2g}$ excitations below 2 eV and hence $\zeta$ and $J_H$ are reduced by less than 4 %. Furthermore, the Mott gap in K$_2$OsBr$_6$ is reduced to about 1.8 eV.Comment: 14 pages, 14 figure

RIXS observation of bond-directional nearest-neighbor excitations in the Kitaev material Na2_2IrO3_3

Spin-orbit coupling locks spin direction and spatial orientation and generates, in semi-classical magnets, a local spin easy-axis and associated ordering. Quantum spin-1/2's defy this fate: rather than spins becoming locally anisotropic, the spin-spin interactions do. Consequently interactions become dependent on the spatial orientation of bonds between spins, prime theoretical examples of which are Kitaev magnets. Bond-directional interactions imply the existence of bond-directional magnetic modes, predicted spin excitations that render crystallographically equivalent bonds magnetically inequivalent, which yet have remained elusive experimentally. Here we show that resonant inelastic x-ray scattering allows us to explicitly probe the bond-directional character of magnetic excitations. To do so, we use a scattering plane spanned by one bond and the corresponding spin component and scan a range of momentum transfer that encompasses multiple Brillouin zones. Applying this approach to Na$_2$IrO$_3$ we establish the different bond-directional characters of magnetic excitations at 10 meV and 45 meV. Combined with the observation of spin-spin correlations that are confined to a single bond, this experimentally validates the Kitaev character of exchange interactions long proposed for this material.Comment: 6 pages, 5 figures, plus 4 pages Supplementary Information (incl. 5 figures

Direct Evidence for Dominant Bond-directional Interactions in a Honeycomb Lattice Iridate Na2IrO3

Heisenberg interactions are ubiquitous in magnetic materials and have been prevailing in modeling and designing quantum magnets. Bond-directional interactions offer a novel alternative to Heisenberg exchange and provide the building blocks of the Kitaev model, which has a quantum spin liquid (QSL) as its exact ground state. Honeycomb iridates, A2IrO3 (A=Na,Li), offer potential realizations of the Kitaev model, and their reported magnetic behaviors may be interpreted within the Kitaev framework. However, the extent of their relevance to the Kitaev model remains unclear, as evidence for bond-directional interactions remains indirect or conjectural. Here, we present direct evidence for dominant bond-directional interactions in antiferromagnetic Na2IrO3 and show that they lead to strong magnetic frustration. Diffuse magnetic x-ray scattering reveals broken spin-rotational symmetry even above Neel temperature, with the three spin components exhibiting nano-scale correlations along distinct crystallographic directions. This spin-space and real-space entanglement directly manifests the bond-directional interactions, provides the missing link to Kitaev physics in honeycomb iridates, and establishes a new design strategy toward frustrated magnetism.Comment: Nature Physics, accepted (2015

Extracorporeal shock waves down-regulate the expression of interleukin-10 and tumor necrosis factor-alpha in osteoarthritic chondrocytes

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to investigate the effects of extra corporeal shock waves (ESW) therapy on the metabolism of healthy and osteoarthritic human chondrocytes, and particularly on the expression of IL-10, TNF-alpha and beta1 integrin.</p> <p>Methods</p> <p>Human adult articular cartilage was obtained from 9 patients (6 male and 3 females), with primary knee osteoarthritis (OA), undergoing total joint replacement and from 3 young healthy donors (HD) (2 males, 1 female) with joint traumatic fracture. After isolation, chondrocytes underwent ESW treatment (electromagnetic generator system, MINILITH SL1, STORZ MEDICAL) at different parameters of impulses, energy levels and energy flux density. After that, chondrocytes were cultured in 24-well plate in DMEM supplemented with 10% FCS for 48 hours and then beta₁integrin surface expression and intracellular IL-10 and TNF-alpha levels were evaluated by flow-cytometry.</p> <p>Results</p> <p>At baseline, osteoarthritic chondrocytes expressed significantly lower levels of beta1 integrin and higher levels and IL-10 and TNF-alpha levels. Following ESW application, while beta1 integrin expression remain unchanged, a significant decrease of IL-10 and TNF-alpha intracellular levels was observed both in osteoarthritic and healthy chondrocytes. IL-10 levels decreased at any impulses and energy levels, while a significant reduction of TNF-alpha was mainly found at middle energies.</p> <p>Conclusion</p> <p>Our study confirmed that osteoarthritic chondrocytes express low beta₁integrin and high TNF-alpha and IL-10 levels. Nonetheless, ESW treatment application down-regulate the intracellular levels of TNF-alpha and IL-10 by chondrocytes, suggesting that ESW might restore TNF-alpha and IL-10 production by osteoarthritic chondrocytes at normal levels. However, further in vivo and in vitro studies are necessary to establish if ESW can represent a viable option in the treatment of OA.</p

Conservative treatment of fractures of the clavicle

Background: In the treatment of clavicle fractures, the choice of procedure depends on the possibility of restoring the anatomical functional integrity of the shoulder. Methods: We examined 71 patients (51 males and 20 females, mean age 38.9 years) who were affected by clavicle fracture sequelae. Demographic and clinical data and the site of the lesion were recorded for each partecipant. The dissatisfaction of the patient was determined by the presence of 1 or more affirmative answers on the Simple Shoulder Test. The Constant Shoulder Score was also included in the functional and clinical exams. We measured the length of the healthy clavicle and the previously fractured clavicle, and we expressed the difference in length in mm and in percentage shortening. We then examined the correlations between the shortening of the bone and the clinical and functional outcomes of the patients. Results: Sixty patients had a lesion of the diaphysis, 8 patients had a lesion of the lateral third of the clavicle, and 3 patients had a lesion of the medial third of the clavicle. The mean Constant Shoulder Score was 77.9, and 51 of the 71 patients were satisfied with their treatment. Radiography showed a mean clavicle shortening of 10 mm (mean percentage 6.5%). In the 20 dissatisfied patients, the mean clavicle shortening was 15.2 mm (9.7%). In these patients, we found a highly significant association between dissatisfaction with treatment and the amount of bone shortening, (p &lt; 0.0001), as well as with a diaphyseal location (p &lt; 0.05) and with the female sex (p = 0.004). No other variable related to the patient, the type of treatment or the fracture characteristics correlated with the treatment outcome. Conclusions: In the literature, measurements of the shortening of the bone segment following a fracture range between 15 and 23 mm, and marked shortening is correlated with the failure of conservative treatment. However, these data need to be reinterpreted in light of the physiological variability of the clavicle length, which ranges from 140 to 158 mm in the healthy population. Shortening of the bone by more than 9.7% should be the cut-off for predicting failure of conservative treatment

Strong Double Higgs Production at the LHC

The hierarchy problem and the electroweak data, together, provide a plausible motivation for considering a light Higgs emerging as a pseudo-Goldstone boson from a strongly-coupled sector. In that scenario, the rates for Higgs production and decay differ significantly from those in the Standard Model. However, one genuine strong coupling signature is the growth with energy of the scattering amplitudes among the Goldstone bosons, the longitudinally polarized vector bosons as well as the Higgs boson itself. The rate for double Higgs production in vector boson fusion is thus enhanced with respect to its negligible rate in the SM. We study that reaction in pp collisions, where the production of two Higgs bosons at high pT is associated with the emission of two forward jets. We concentrate on the decay mode hh -> WW^(*)WW^(*) and study the semi-leptonic decay chains of the W's with 2, 3 or 4 leptons in the final states. While the 3 lepton final states are the most relevant and can lead to a 3 sigma signal significance with 300 fb^{-1} collected at a 14 TeV LHC, the two same-sign lepton final states provide complementary information. We also comment on the prospects for improving the detectability of double Higgs production at the foreseen LHC energy and luminosity upgrades.Comment: 54 pages, 26 figures. v2: typos corrected, a few comments and one table added. Version published in JHE