[en] MR imaging was performed in patients with compressive lesions of the cervical cord. High signal intensity was observed within the spinal cord on T2-weighted images in approximately 25% of the patients, the incidence being higher in patients with herniated disk, atlantoaxial dislocation, ossification of the posterior longitudinal ligament, and degenerative osteoarthritis. The degree of subarachnoid compression and high signal intensity was proportionally related to the degree of myelopathy. There was contrast enhancement with Gd-DTPA in a small number of these patients. The finding of high signal intensity was important in determining the management of these patients

[en] Twenty-nine patients with atlantoaxial subluxation (18 with rheumatoid arthritis, 2 due to trauma, 4 with os odontoideum, and one each with polyarteritis nodosa, rheumatic fever, Klippel-Feil syndrome, achondroplasia, and cause unknown) were evaluated using a 0.22 tesla resistive MRI unit. Cord compression was classified into four grades according to the degree on magnetic resonance imaging. There were 7 patients with no thecal sac compression (grade 0), 10 with a minimal degree of subarachnoid space compression without cord compression (grade 1), 7 with mild cord compression (grade 2), and 5 with severe cord compression or cord atrophy (grade 3). Although the severity of myelopathy showed poor correlation with the atlantodental interval on conventional radiography, high correlation was observed between MR grading and the degree of myelopathy. The high signal intensity foci were observed in 7 or 12 patients with cord compression (grades 2 and 3) on T2 weighted images. Other frequently observed findings in rheumatoid arthritis included soft tissue masses of low to intermediate signal intensity in the paraodontoid space, erosions of the odontoid processes, and atlanto-axial impaction on T1 and T2 weighted images. (orig.)

[en] Carrier transported liquid CO₂ at 55 ^oC is denser than ambient seawater at mid-ocean depths. We have investigated whether this property effectively enables sinking of injected CO₂ from mid-depth to the ocean floor, >3500 m depth, where CO₂ is gravitationally stable as a lake on the dented sea floor. In order to obtain basic data for the realization of this idea, the National Maritime Research Institute, and the Monterey Bay Aquarium Research Institute, conducted three joint in situ experiments of CO₂ sending method for the ocean storage (COSMOS), to release cold CO₂ at the mid-ocean depths. The experiments were carried out in Monterey Bay from October 1999 to February 2002 using remotely operated vehicle (ROV) techniques to effect the controlled release and subsequent imaging. From the data obtained, it was clear that a cold CO₂ mass, released as a large unit, was apt to be broken up into small droplets by a Taylor type interface instability. Even for a unit of sufficient heat capacity for formation of a significant ice layer, break up into droplets due to liquid instabilities occurred in a short time. However, in experiments with a CO₂ slurry mass (a mixture of dry ice and liquid CO₂) of 8 cm size we observed that the released material could keep its shape and sink even further until the covering ice layer melted. The behavior of the CO₂ slurry mass strongly suggests that this technique offers the potential for effective transfer of released CO₂ from mid-depth to the ocean floor, and our experiments provide numerical constraints on the required design goals for this. (author)

[en] Raman scattering spectra of single crystalline PrRu₄P₁₂ have been measured in the temperature region between 4.6 K and 300 K. Additional peaks appear below metal-insulator transition temperature. Among these peaks, CEF excitations for two different Pr ion sites can be assigned from the results of magnetic field (H≤8T) dependence and polarization dependence. From the energy of CEF excitations in Raman spectra, we have re-determined CEF energy levels for Pr1 and Pr2 ions. From the result of CEF level schemes and the different atomic displacement of Ru around Pr1 and Pr2, Pr1 ion is affected by a strong positive point charge potential of Ru, and Pr2 ion feels strong p-f hybridization.

[en] Since 2002, researchers from Japan, the United States and Norway have been collaborating on the Ocean Abyssal Carbon Experiment (OACE) project. This paper presented information on the three year project. It presented a discussion of the high-pressure laboratory work, instrument development and theoretical and numerical modelling associated with field experiments. The purpose of the project is to conduct groundbreaking and challenging experiments to determine of the fate of carbon dioxide (CO₂) disposed onto the ocean floor. Several observations from small-scale CO₂ experiments at different depths conducted off the coast of California were presented. In the experiments, when the seawater velocity was sufficiently strong, parcels of liquid CO₂ were torn off and transported away as discrete units by the turbulent water current. Newly formed frazil hydrate was observed at the interface, occasionally including sediment particles in the deep experiment. In addition, hydrate collected and created a floating consolidated solid consisting of ice in the downstream end of the trough, dissolving slowly from one day to the next. It was concluded that these observations have significant implications for understanding and modelling of larger scale anthropogenic CO₂ disposal at the seafloor. 15 refs., 3 figs

[en] Deuteron inelastic scattering (d, d') provides a promising spectroscopic tool to study nuclear incompressibility. In studies of deuteron inelastic scattering of unstable nuclei, measurements of low-energy recoiled particles is very important. In order to perform these measurements, we are developing a GEM-TPC based gaseous active target, called CAT (Center for nuclear study Active Target), operated with pure deuterium gas. The CAT has been tested with deuterium gas at 1 atm and 100-μm-thick GEMs. The low-pressure operation of CAT is planned in order to improve the detection capability for lower-energy recoil particles. A 400 μm-thick gas electron multiplier (THGEM) was chosen for the low-pressure operation of CAT. However, the properties of THGEM in low-pressure deuterium are currently undocumented. In this work, the performance of THGEM with low-pressure pure deuterium gas has been investigated. The effective gas gain of THGEM has been measured in various conditions using a 5.5-MeV ²⁴¹Am alpha source. The effective gas gain was measured for 0.2-, 0.3- and 0.4-atm deuterium gas and a gas gain of about 10³ was achieved by a double THGEM structure at 0.2 atm. The maximum achieved gain decreased with increasing gas pressure. The dependences of the effective gas gain on the electric field strengths of the drift, transfer and induction regions were investigated. The gain stability as a function of time in hydrogen gas was also tested and a relaxation time of THGEM of about 60 hours was observed with a continuous irradiation of alpha particles, which is significantly longer than previous studies have reported. We have tried to evaluate the gas gain of THGEM in deuterium gas by considering only the Townsend ionization process; however, it turned out that more phenomenological aspects, such as transfer efficiency, should be included in the evaluation. The basic properties of THGEM in low-pressure deuterium have been investigated for the first time

[en] Raman scattering of skutterudite compounds RT₄X₁₂ (R=La, Ce, Pr, Nd, Sm and Yb, T=Fe, Ru and Os, X=P and Sb) have been measured. All first-order Raman active phonons are observed and are assigned as the pnicogen vibrations. At the low energy region, the second-order phonons, due to the vibration of the rare earth ions with a flat phonon dispersion, are observed in the spectra of RRu₄P₁₂ (R=La and Sm) and ROs₄Sb₁₂ (R=La, Ce, Pr, Nd, and Sm). The appearance of the second-order phonons in the spectra is caused by an anharmonic vibrations of rare earth ions in large cage space and a large density of state due to the flat phonon dispersion. However, in spite of the similar cage space, the 2nd-order phonons are hardly observed for RFe₄Sb₁₂ and RRu₄Sb₁₂. Thus, these results suggest that the dynamics of the rare earth ion is closely related to not only the cage size but also the electronic state due to the transition metals. Raman spectra of PrRu₄P₁₂ show the drastic spectral change due to the metal-insulator transition. The phonon spectra and crystal field excitations due to the structural change have been assigned above and below the transition temperature

[en] Raman scattering of skutterudite compounds RT₄X₁₂ (R=La, Ce, Pr, Nd, Sm and Yb, T=Fe, Ru and Os, X=P and Sb) have been measured. All first-order Raman active phonons are observed and are assigned as the pnictogen vibrations. At the low energy region, the second-order phonons, including the vibration of the rare-earth ions with a flat phonon dispersion, are observed in the spectra of SmRu₄P₁₂ and ROs₄Sb₁₂. The second-order phonons can be observed for the sample with the larger cage space. The large displacement in the large cage space and the large density of state due to the flat phonon dispersion increase the intensity of the second-order Raman scattering process. The intensity of the second-order phonon are also affected by the valence of the rare-earth ions