Observation of local atomic displacements intrinsic to the double zigzag chain structure of 1T-MTe2 (M = V, Nb, Ta)

We describe the existence of local distortion discovered in the synchrotron x-ray single-crystal structure analysis of layered ditelluride 1T-MTe2 (M = V, Nb, Ta). In 1T-TaTe2, the double zigzag chain structure of Ta is deformed at about 170 K, and heptamer molecules are formed periodically at low temperatures. We found that some of the Ta atoms that compose the double zigzag chain structure appearing at high temperatures are locally displaced, resulting in local dimerization. This tendency weakens when Ta is replaced by V or Nb. Our results indicate that the local distortion persistently survives in these ditellurides, where the electronic degrees of freedom, including orbitals, are weakened. We further discuss the origin of local distortion in these ditellurides, which is different from many usual material systems where molecular formation occurs at low temperatures.Comment: 11 pages, 4 figures, 18 tables, To be published in Phys. Rev.

Radial volumetric imaging breath-hold examination (VIBE) with k-space weighted image contrast (KWIC) for dynamic gadoxetic acid (Gd-EOB-DTPA)-enhanced MRI of the liver: advantages over Cartesian VIBE in the arterial phase

To compare radial volumetric imaging breath-hold examination with k-space weighted image contrast reconstruction (r-VIBE-KWIC) to Cartesian VIBE (c-VIBE) in arterial phase dynamic gadoxetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (DCE-MRI) of the liver. We reviewed 53 consecutive DCE-MRI studies performed on a 3-T unit using c-VIBE and 53 consecutive cases performed using r-VIBE-KWIC with full-frame image subset (r-VIBEfull) and sub-frame image subsets (r-VIBEsub; temporal resolution, 2.5-3 s). All arterial phase images were scored by two readers on: (1) contrast-enhancement ratio (CER) in the abdominal aorta; (2) scan timing; (3) artefacts; (4) visualisation of the common, right, and left hepatic arteries. Mean abdominal aortic CERs for c-VIBE, r-VIBEfull, and r-VIBEsub were 3.2, 4.3 and 6.5, respectively. There were significant differences between each group (P < 0.0001). The mean score for c-VIBE was significantly lower than that for r-VIBEfull and r-VIBEsub in all factors except for visualisation of the common hepatic artery (P < 0.05). The mean score of all factors except for scan timing for r-VIBEsub was not significantly different from that for r-VIBEfull. Radial VIBE-KWIC provides higher image quality than c-VIBE, and r-VIBEsub features high temporal resolution without image degradation in arterial phase DCE-MRI. aEuro cent Radial VIBE-KWIC minimised artefact and produced high-quality and high-temporal-resolution images. aEuro cent Maximum abdominal aortic enhancement was observed on sub-frame images of r-VIBE-KWIC. aEuro cent Using r-VIBE-KWIC, optimal arterial phase images were obtained in over 90 %. aEuro cent Using r-VIBE-KWIC, visualisation of the hepatic arteries was improved. aEuro cent A two-reader study revealed r-VIBE-KWIC's advantages over Cartesian VIBE.ArticleEUROPEAN RADIOLOGY. 24(6):1290-1299 (2014)journal articl

OVSG's instrumental networks

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Les risques volcaniques au XXIe siècle : surveiller et prévoir ; l’exemple de l’OVSG

L’unrest volcanique est une déviation du niveaud’activité d’un volcan par rapport à son comportementde base, ce qui est préoccupant à court terme (quelquesheures à quelques mois), car il pourrait être le préluded’une éruption. L’unrest volcanique est un phénomènecomplexe comportant plusieurs aléas. Le fait que l’unrestpuisse conduire à une éruption imminente contribue àgénérer une incertitude importante pour l’évaluation, àcourt terme, des dangers de l’activité volcanique. Bienqu’il soit raisonnable de supposer que toutes les érup-tions sont associées à une activité précurseure, la connais-sance des liens de causalité entre les processus souter-rains, les signaux d’unrest qui en résultent et l’éruptionimminente est aujourd’hui encore insuffisante. Cela résul-te principalement des incertitudes liées à l’identificationdes processus causatifs de l’unrest et, par conséquent, dela prévision de leur évolution à court terme. Cependant,la clé pour une atténuation et une gestion efficace desrisques lors de l’unrest est l’identification précoce et fiabledes changements dans la dynamique souterraine d’unvolcan et de leur évaluation en tant que précurseurs d’uneéruption imminent