Yuuji Horie

Photo-rechargeable battery with TiO2/carbon fiber electrodes prepared by laser deposition

Abstract A photo-rechargeable battery which has two functions of the opto-electric conversion and the storage of the electrochemical energy was investigated for TiO 2 /carbon fibers (CFs) compound electrodes. The laser deposition method was used to produce TiO 2 fine particles on the surface of CFs to improve the photo-rechargeable performances. Some of the electrodes prepared in He gas had the photo-charged quantity 10–100 times as large as those in vacuum and those prepared by the sintering method. The difference of the mechanism of the charge was discussed.

Hysteresis in magnetic field and field-direction dependence of critical current in Bi2Sr2CaCu2O8+y

Abstract We measured the dependence of the critical current density J c ( T,H ) on angles o and θ, the magnetic field H and the temperature T for Bi 2 Sr 2 CaCu 2 O 8+ y films with the preferred c -axis orientation prepared by a laser ablation technique, where o is an between H and the basal plane for the current density J ⊥ H , and θ an angle between H and J in the plane comprising the c -axis and J . Characteristic features were as follows. (1) J c ( T,H ) versus o and J c ( T,H ) versus θ had a characteristic hysteresis due to a characteristic pinning of the flux lines parallel to the c -axis. (2) When J c ( T,H ) versus o, J c ( T,H ) versus θ and J c ( T,H ) versus T were replotted with J c ( T,H ) versus the c -axis component of the magnetic fields, these dependences were almost identical. (3) This hysteresis was reduced if the magnetic field was applied by a special procedure.

New ultrasonic method to investigate flux pinning properties of superconducting thin films

A new ultrasonic method has been proposed for the investigation of flux pinning properties of superconducting thin films. In the method, pinned flux lines are excited by the ultrasonic vibration of pinning centers, and depinned flux lines are detected in terms of the flow voltage generated by the Lorentz force due to transport current. By applying a parallel magnetic field and propagating AM ultrasound perpendicularly to the surface of YBa2Cu3O7-δ films, a maximum of AC voltage was observed below the onset temperature of the superconducting transition. From its dependence on the ultrasonic amplitude and the transport current, the observed voltage is found to be induced by flux flow normal to the surface raised by ultrasound.

Flux creep and magnetic field direction dependence of critical current density in Bi2Sr1.7La0.3CuO6+y films prepared by laser ablation

Abstract Using Bi 2 Sr 1.7 La 0.3 CuO 6+ y thin films, prepared by the laser ablation technique, the resistivity was measured as a function of the temperature in the mixed state and the critical current density in different magnetic field directions. The temperature dependence of the resistivity was analyzed using an activation type formula. The magnetic field direction dependence of the critical current density was discussed on the basis of the two-dimensional property of magnetic flux lines.

Flux flow excited by ultrasonic deformation of flux line lattice in high temperature superconducting ceramics

Abstract To investigate the flux pinning behavior in HTSC against various kinds of deformation of flux line lattice (FLL), the flux flow excited by ultrasonic deformation of FLL was measured for bulk sintered samples of Bi2Sr2Ca2Cu3Oy. The compressional, tilt and shear ultrasonic deformations, which are associated with the elastic moduli of C11, C44 and C66 of FLL in isotopic superconductors, were applied to FLL. A peak of the flux flow resistivity was observed at a temperature Tp at which the dissipation of ultrasonic energy became the maximum. The differences in Tp and the peak height obtained for the three kinds of deformation were small, against the theoretical prediction with the model of thermally assisted flux flow. The results suggest that most flux lines are bent due to the pinning at insulating layers and/or grain boundaries.

Ultralow frequency oscillator composed of three switched-capacitor phase shifters

An ultralow frequency oscillator is discussed in which switched capacitors (SC) are used instead of resistors in CR phase shifters. The oscillation was stable down to the order of 10 /spl mu/Hz. The oscillation frequency varied linearly with the clock frequency of SC. An automatic gain controller is also discussed.

Ultralow-frequency design of the Wien bridge oscillator using switched capacitors

An ultralow-frequency oscillator and automatic gain controller circuitry are proposed in which switched capacitors (SC) are used in place of resistors of the frequency-determining arm in the Wien bridge oscillator. The oscillation frequency f is widely varied only by adjusting the SC clock frequency f/sub c/. Experimental results show that the oscillator is stable over the oscillation frequency range from 10 /spl mu/Hz to 100 Hz and that f is proportional to f/sub c/, which agrees with theoretical results. The oscillation voltage distortion is estimated to be less than -35 dB within the oscillation frequency range from 100 /spl mu/Hz to 100 Hz. The distortion increases at frequencies below 100 /spl mu/Hz, where an increase of output offset voltage has been observed. The very short rise time of the stable oscillation has been achieved by changing the clock frequency to a lower value after getting the stable oscillation at a higher clock frequency.

Magnetic field-direction dependence of critical current density in c-axis oriented Bi2Sr1.7La0.3CuO6+y films

Abstract The magnetic field-direction dependence of the critical current density is studied for the copper oxide superconducting Bi 2 Sr 2−x La x CuO 6+y films prepared by the laser ablation technique. Experimental results are discussed on the basis of the two dimensional properties of magnetic flux lines.

Ultrasonic studies of crystal structure dependence of flux pinning in Bi2Sr2Can − 1CunOy (n = 1, 2 and 3)

Abstract The changes in ultrasound velocity ΔVs(T, H) with magnetic field were measured for three kinds of Bi-based oxide superconductors, Bi2Sr2Can − 1CunOy (n = 1, 2 and 3) with a dopant of La or Pb. For n = 2 and 3, steps were observed in ΔVs versus T curves at a depinning temperature. However, no step was observed for n = 1, suggesting a small flux pinning force compared with n = 2 and 3. The correlation among crystal structure, coherence length and intrinsic pinning was discussed.