Hydrothermal synthesis of hydroxyapatite whiskers with sharp faceted hexagonal morphology

We report an effective method for the synthesis of hydroxyapatite whiskers with sharp faceted hexagonal shape employing a low temperature (90 °C) hydrothermal route with calcium nitrate tetrahydrate, diammonium phosphate and urea as starting materials. The key parameters of the synthesis process i.e. duration, temperature cycle of the treatment and starting pH value are carefully varied and the end products are investigated using powder X-ray diffraction (XRD), Raman-scattering, infrared spectroscopy (IR), elemental analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution TEM (HRTEM) in order to find the optimal reaction conditions that lead to the desired hexagonal morphology of HA whiskers. The results demonstrate that gradual and greater increase in solution pH during the hydrothermal process favors large quantity of the single-crystalline hydroxyapatite whiskers with well defined hexagonal morphology.     

Instability of the Solid-Liquid Interface of 4He during a Large Transformation

We report an instability of ⁴He crystal surface during a large modification of its shape observed by schlieren photography. ⁴He crystal was nucleated on an ultrasound transducer which was placed in the upper part of the sample cell facing the bottom. The crystal was grown on the transducer and the lowest part of it eventually touched the bottom of the cell. Almost immediately, the crystal started to change shape very quickly to adjust itself to the new boundary condition. During this large deformation, the hexagonal shape of the crystal surrounded by facets became unstable and the surface became corrugated. The corrugation pattern during the deformation was observed by a high-speed camera. The results were compared with Kelvin-Helmholtz type instability which Uwaha and Nozières predicted.      

Temperature control for the expansion of artificial DNA motif

The DNA, which forms a double helical conformation by the highly selective base-pairing rule with the width of 2 nm, is one of the polymers utilized as a template for nanoparticle assembly. Then, holiday junction structure, where two different DNA double strands intersect and replace each complement strand, is an important artificial motif for forming two-dimensional mesh-like DNA morphology. In this study, the two-dimensional sheet with the mesh-like conformation is formed and the growth of the DNA morphology is controlled by changing the temperature in the formation process. The influence of the cooling procedure on the formation process of the two-dimensional DNA sheet is observed by atomic force microscope, and the formation of double strands in the process is traced by absorption spectra. The spectroscopic results demonstrate that the two-dimensional DNA sheet is strongly dependent on the correlation between the applied cooling process and the melting temperature of double helical conformation, and that the growth of the two-dimensional DNA sheet can be manipulated by the cooling procedure. Further, we will show the size control of the DNA sheet by mixing the designed DNA which inhibits the growth of the DNA sheet.     

Photoluminescence and photoconductivity studies of oriented polyfluorene thin films

Photoluminescence and photoconductive properties of poly(9,9-dioctylfluorene) (F8) on rubbed polyimide (PI) alignment layers have been studied. The F8 thin films are highly oriented, which is manifested from polarized absorption, fluorescence, and photoconductivity spectra (the order parameter of F8 is 0.86). The ratio of photocurrent parallel to perpendicular directions to the rubbing direction (photoconductivity anisotropy) is 18 at 2.9 eV for F8. Effects of C₆₀ addition to F8 on the optical properties are also studied. C₆₀ addition to F8 significantly increases photoconductivity but decreases the order parameter (0.67) and the photoconductivity anisotropy (7 at 2.9 eV). Both F8 and C₆₀ doped F8 thin films exhibit similar photoconductive response and similar photoconductivity anisotropy (3-4) above 3.8 eV.     

Preparation and optical properties of polymer films having lamellar structure and cylindrical air bubbles

Polymer films displaying lustrous, iridescent colors were obtained by irradiation of poly(methyl methacrylate) films containing 1,4-benzoquinone with a medium pressure mercury lamp followed by solvent treatment. The colors were not produced by visible light-absorbing species in the polymer films because the color seen in reflection was complementary to that seen in transmission. It was found from optical and scanning electron microscopic studies of the polymer films that they have two characteristic optical structures; a great number of microcylindrical air bubbles oriented perpendicularly to the film surface and periodic lamellas with planes parallel to the film surface. The colors of the polymer films were thought to be produced by this periodic lamellar structure which would act as a three dimensional optical reflection grating. Continuous color change on tilting the sample could also be explained by the Bragg equation.     

Packed Powder as Superleak for Spin Pump Experiments in Superfluid 3He A1

Experimental exploration of highly spin-polarized states of liquid ³He by applying external magnetic field is limited by the availability of static magnetic field. In the “ferromagnetic” superfluid A₁ phase of liquid ³He there is an alternate method for boosting spin-polarization by the process of spin pumping without requiring such high magnetic field. The spin pumping in the A₁ phase takes advantage of a superleak (SL) acting simultaneously as a filter for both entropy and spin. The spin pump technique that uses the SL-spin filter and a mechanical actuator enables us to directly boost polarization of ³He. The amount of enhancement of spin polarization has been limited so far. We are now developing a new type of SL filter made of packed aluminum oxide powder (referred as PAP-SL), in order to achieve greater enhancement of spin polarization. Several kinds of the PAP-SL filter were constructed by pressing aluminum oxide powders into a cylinder holder. The packed structures were carefully characterized by a flow-rate-measurement, X-ray tomography, and mercury intrusion porosimetry. The preliminary result shows that the PAP-SL works as SL filter for the superfluid ³He.     

Design and manufacturing of JT-60SA vacuum vessel

JT-60 is planned to be upgraded to JT-60SA tokamak machine with fully superconducting coils, which is a project of the JA-EU satellite tokamak program under both Broader Approach program and Japanese domestic program. The JT-60SA vacuum vessel (VV) has a D-shape poloidal cross section and a toroidal configuration with 10° facet segmented in toroidal direction. The material of the VV is 316L stainless steel with low cobalt content of <0.05 wt%. A double wall structure is adopted for the VV to ensure high rigidity and high toroidal one-turn resistance simultaneously.Fundamental welding R&D and a trial manufacturing of the 20° upper half of the VV have been performed to study the manufacturing procedure. After the confirmation of the quality of the mock-up, manufacturing of the actual VV started in November 2009.