High-field superconducting materials such as Nb-(25%) Zr and Nb3Sn have prompted the ex-ploration of applications, including superconducting magnets, energy storage and production of homogeneous fields. These high-field superconductors belong to non-ideal Type II superconductors, which exhibit irreversible magnetic behavior and sustain high critical current density. The major disappointment has been the poor ac characteristics. In this report the magnetization process and the influence of external current on it are explained with a model based on the GLAG theory. The model makes it clear that the hysteresis of magnetization and high-current carrying capacity are caused by the pinning effect of crystal lattice imperfections on the quantized flux line in the mixed state. Next theexperimental results of ac properties are surveyed. It is shown that a model proposed by H. London has revealed the hysteresis mechanism of ac loss and explainsthe experimental data quantitatively.
The cold-work damping peak in α-iron is studied with a torsionpendulum. Some significant-results obtained are: (i) the dependence of cold-workpeak height on interstitial impurity content is weaker than given by the linear relation reported in some previous papers, (ii) the peak height depends on thedeformation temperature, (iii) the cold-work peak has various activation energies (1.4_??_1.9eV), and (iv) the recovery of cold-work peak is not by a single activation energy and is of very complicated behavior. A proposed model pictured by taking the relaxation caused directly by anelastic motion of dislocation and the effects of dislocation interaction and clustering of interstitial impurities into account is considered to elucidate the above expeimental results.
A method of measuring the average transparence of aggregation of small columnar crystals, such as gultamic acid soda (0.2_??_0.5mm thick and 0.5_??_2.2mm long) is introduced. The trans-parence is defined by the normal transmittance, T*, of closely distributed one layer crystals Since this is difficult to be realized, T* is calculated from measured transmittance values at two given acceptance angles obtained on a crystal layer discretely formed over a definite area on a glass plate by virtue of the transmittance being in linear relations with the weight of the crystals and the acceptance angle of less than 12 degrees, the latter relation being experimental. The value of T* is found nearly independent of the weight of the crystals provided they are in one layer, but depends slightly on the mean crystal size. With two kinds of samples apparently different in transparency, values of T* differ by 50% for crystals of the same size. The estimated weight of closely distributed crystals is found to be proportional to the mean thickness of crystals.
For improvement of accuracy of measurement by the pulsed neutron method in the nuclear reactor physics, a sequentially delayed sampling time analyzer has been developed. The analyzer has 256 channels with a minimum channel width of 0.1 μs; it measures the time variation of thermal neutron flux by sampling the flux every 15 μs. The sampling times are made to delay by 1.6 μs increment every burst of fast neutron, whereby an effective sampling rate of 1.6 μs is obtained and measurement of rapid variations of the flux is attained. This device is uesd as a, plug-in unit in connection with a pulse analyzer of 1024-channel, 16-bits/ch magnetic memory cores. In a diffusion test with graphite moderator in a semihomogeneous critical assembly of the Japan Atomic Energy Research Institute, the time resolution of the analyzer was confirmed to be about 10 times of that of conventional ones.
As a continuation of previous work by E. Ikeno on analysis of current wave form in non-linear parametric oscillator circuits with varying capacitance, an analysis is made on the current of one half of the frequency of a parametric oscillator circuit which has a saturation coil whose number of turns varies in continuous and periodic manner. When the characteristics of the circuit was examined by the phase plane method, there were found, independently of the initialconditions, three types of oscillation according to the codenser capacity, namely, steady oscillation, occational oscillation and no oscillation, and computation of transient wave form revealed the cases of occur-rance and non-occurrance ofoscillation: when the oscillation occurred, distortion of wave form was more than that of parametric oscillation caused by variation of condenser capacity.
Electrical resistance of Ni films evaporated in a magnetic field is measured along the direction of the applied field (ρ||) and perpendicular to it (ρ⊥). The dependence of the value of (ρ⊥/ρ||) uponthe film thickness is investigated. The value of ρ⊥/ρ|| is found to be between 2 and 3 for films thinner than 200Å and between 0.70 and 0.93 for films thicker than 600Å. The value fluctuates between 0.6 and 1.2 for films of the thickness between 200 and 600Å. The dependence of the valueof ρ⊥/ρ|| upon the magnetic field strength applied during deposition was not observed in the range between 200 Oe and 1000 Oe.