Satoaki Arai

Ferrimagnetic Particles in the Lung Part II: The Relaxation; Process

After ferrimagnetic particles in the lung have been magnetized and aligned by an external magnetic field which is then removed, they undergo relaxation. In this process the remanent magnetic field at the chest produced by the aligned particles decreases in time, typically by a factor of five in the first hour; this is the result of misalignments of the particles caused by random, physiological impulses. The purpose here is to consolidate previous and new relaxation curves (the decreasing field versus time), due to Fe3O4 particles in the human lung, and to interpret the curves. They are shown as a function of the magnetizing field strength, of the dust residence time in the lung, of smoking, and of the breathing pattern. Curves of ¿Fe2O3 in the hamster lung are also presented, showing the change due to death. The curves are qualitatively explained by the same physics model used in Part I, where single-domain and multidomain particles residing in a viscous fluid are subjected to random impulses. Although the physiological sources of the impulses are not directly considered here, the curves suggest that one cause of relaxation is elasticity of the fluid. Also, the curves indirectly support the findings by others that the physiological sources of the impulses are within macrophages.

Effect of the parallel circuit parameters on the instability of a low current vacuum arc

In order to clarify the instability phenomena of a low current vacuum arc, the authors observed the phenomena by changing the parallel circuit parameters. They measured instability initiation current, chopping current, arc voltage, arc voltage oscillation peak and the transient recovery voltage by using copper, copper chromium and silver tungsten carbide electrodes. It was found that the chopping current, the arc voltage oscillation peak and the transient recovery voltage are dependent on the parallel circuit parameters, but the instability initiation current and arc voltage is not dependent on them. They also found that the instability phenomena depend first of all on the cathode material.

Post-arc Current and Re-ignition after Many Interruptions by MCCB and the Endurance

The purpose of this investigation is experimental research of many interruption performance for Molded Case Circuit Breaker (MCCB) currently used for the protection of a low voltage circuit. It is anticipated by interruption especially by high current many interruptions that the interruption performance will decrease. In order to investigate the performance change by many interruptions, it is important to grasp an interruption characteristic.The interruption experiment was conducted in large current for many times, and phenomena which are one of factors of the successes or failure of interruption, were observed. By carrying out the numbers of interruption it is shown that post-arc current begins to flow and duration of the arc is ten to a few hundred micro seconds. In order to explore relation between post-arc current and a decrease of an interruption characteristics, experiment conditions of post-arc current was investigated.

STM Inestigations of the Grain Surface of Bi0.8PbxSr1Ca1Cu1.6O8+y Superconductors

Scanning tunneling microscopy was used to investigate the surface topographs of bared crystal grain in Pb-free or Pb-dopped Bi0.8PbxSr1Ca1Cu1.6O8+y, x=0.0~0.5, bulk superconductors. Images with a scanning electron microscopy resolution revealed that the profiles of grain surface was in the form of periodic rugged wavelet with the amplitude of 10 nm and the length of 20 nm. This result was considered to provide direct proof for the percolation processes between randomly oriented grains and grain boundaries in bulk superconductor.