Density dependences of NMR signal shifts and widths for 129Xe adsorbed on NaX, NaY, HY, CaY, and CaA zeolites are observed. At zero density, shifts upfield relative to Xe gas are 58±4 ppm for NaX, NaY, and HY, and 83±2 ppm for CaA. Shift/Xe density gradients are 46±2 ppm/1021 atoms/g for NaX, NaY, and HY, 58±2 ppm/1021 atoms/g for CaA. These shifts are explained mainly in terms of collisions between Xe atoms and cage walls and other Xe atoms. They correspond to a very high apparent Xe density (several hundred amagats).

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A series of metalfbimetal catalysts has been prepared from molecular car-bony1 clusters such as Rh6-yIr, (CO),,(x = 0-6) and Rh,Fe,(CO):, which were synthesized inside NaY zeolite supercages. Nay-entrapped Rh,, Ir, , Rh41r2, Rh,Ir, and Rh,Ir4 crystallites derived from the precursor carbonyl clusters have been well characterized by f.t.i.r., EXAFS, '29Xe n.m.r. and CO/ H chemisorption on their metallic structures and electronic states. The results suggested that the reduced crystallites inside NaY zeolite consist of cluster ensembles < 10 8, in size with controlled metal compositions. These

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Anterior decompression and fusion for treating ossification of the posterior longitudinal ligament of the cervical spine was performed in 12 patients. The central part of the vertebral body and the ossified area of the posterior longitudinal ligament were removed by means of a microrongeur and an air drill. The defect was filled with a long bone graft taken from the ilium. The operative results were excellent. Marked improvement of radicular and spinal cord signs was seen in all 12 cases. Three vertebral bodies were fused in one case, four in nine cases, and five in two cases. The highest level of fusion was C-2 and the lowest was T-1. It is considered that any ossification of the ligament below the C-2 level can be removed via an anterior approach as long as no more than five vertebral bodies are involved. Spinal computerized tomography was valuable in providing more detailed information about the stenotic spinal canal and the shape of the ossified ligament.

Four cases of calcification of the cervical ligamentum flavum are reported, all in women over 60 years of age. Neurological findings were not significantly different from those of other cervical compressive diseases. Among radiological examinations, computerized tomography was the most valuable diagnostic tool. Calcification might have been induced by the degeneration or abnormal nutritional state of the ligamentum flavum. Endocrine abnormalities and inflammatory processes might also have been contributory factors.

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International audienceA nuclear magnetic resonance study of xenon adsorbed on Pt-NaY zeolites, with or without pre-chemisorbed hydrogen, has made it possible, first, to prove that chemisorption of hydrogen occurs homogeneously on all particles of similar size, and, secondly, to determine the number of platinum particules and therefore their mean size. This technique seems highly useful when particles contain very few atoms and cannot be detected by electron microscopy