A light emitting diode with superconducting Nb electrodes was fabricated to investigate the contribution of cooper pairs to radiative recombination in a semiconductor. Electroluminescence observed from the active layer in which electron cooper pairs and normal holes are injected was drastically enhanced at the temperature lower than the superconducting transition temperature of the Nb electrodes. This is the first experimental evidence that cooper pairs enhance radiative recombinations by the superradiance effect.
In conventional solidification of multicomponent mixtures, a mushy zone appears between the pure solid and liquid regions and promotes stable solidification by accepting the rejected solute regionally. From the standpoint that the fineness of inhomogeneity influences the mechanical properties in material processing, the linking of macro heat transfer and microsolidification in the mushy zone was studied. First, the crystal growth and its accompanying concentration field near the advancing front of the mushy zone were observed precisely by using the light absorption method. It was clarified that the mushy zone consisted of the leading front in which the frame structure formed with an accompanying concentration boundary layer and a growing region where the solidification proceeds by fattening of the crystals. Second, the mechanism of side-branch evolution was studied in conjunction with interfacial instability due to constitutional supercooling and curvature supercooling around the primary arm surface. Summarizing these results, the microsolidification process is discussed quantitatively in relation to macro heat transfer.
Triple-crystal X-ray diffractometry has been combined with time-resolved measurement techniques. A simple time-resolved technique was employed by using a digital storage oscilloscope and a fast X-ray detector. The time dependence of the deformation tensor was determined for a gallium arsenide wafer after a flash of a 130 fs laser pulse. The laser pulse produced instantaneous expansion resulting in a localized convex surface. Time-resolved measurements showed that a flexural standing wave, explained well by the classical elasticity theory for thin plates, appeared in the relaxation process.
Most of the vehicle components have a variety of materials, such as fine- and/or coarse-grained polycrystalline alloys, and resins. Since they and their jointed components are often surrendered under severe fatigue conditions, we would like to evaluate their integrity, hopefully non-destructively. From such points of view we have developed and introduced some techniques on three-dimensional non-destructive mechanical analysis methods with at SPring-8:BL33XU (Toyota beamline). The first one is a conventional diffraction for depth resolved stress and strain measurement but with area detector and our-developed rotating spiral slit. This technique enables us to measure space-resolved strain distribution of arbitrary materials. The next one is a scanning three-dimensional x-ray diffraction (scanning 3DXRD) microscopy with a high-energy x-ray microbeam. By this technique we can measure inter- and intra-granular distribution of crystal orientation. We also tried the corresponding crystal plasticity finite element (CPFE) analysis to understand the plastic behaviour for polycrystalline iron and interaction between the grains. The third one is a synchrotron laminography for three-dimensional material analysis. The digital volume correlation is also applied to visualise not only the internal morphology but also its strain distribution non-destructively. These three individual or integrated methods are helpful for developing and analysing electric-powered mobilities’.
This study has been conducted to pursue the enhancement of forced-convection heat transfer by applying an electric field. Experiments were performed in an air channel flow where a series of wire-electrodes were installed in parallel with the primary flow direction, or installed at right angle to the primary flow direction. By applying the electric field, secondary flow was electro-hydrodynamically induced by the Coulomb force. The visualization of flow patters and measurement of heat transfer coefficient and consuming power were carried out. The theoretical analysis on electric, flow and temperature field was also performed taking account of momentum transfer between ions and neutral fluid molecules. On the basis of these results, fundamental characteristics of the EHD combined flow and the heat transfer were clarified in conjunction with applied voltage, primary velocity and wire-electrode arrangement. And, the possibility of the practical applications of the ionic wind are discussed.
