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Vol. 23, No. 6 (1974)

1974-03-20
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CONTENT
PREPARATION AND MAGNETIC PROPERTIES OF HOT-PRESSED FERRITES
THE HOT-PRESSED FERrITE RESEARCH GROUP, DEPARTMENT OF PHYSIOS
1974, 140 (6): 1-12. doi: 10.7498/aps.23.1
Abstract +
Experimental studies have been carried out on the effects of raw material preparation and hot-pressed conditions on the density, microstructure and magnetic properties of hot-pressed Mn-Zn ferrites and Ni-Zn ferrites which are used for magnetic head application. Hot-pressed ferrites have been prepared by two different technologies: the co-precipitation method and the ball-milling method. It was observed that the co-precipitation method is better than the ball-milling method for preparation of hot-pressed ferrites. The microstructure can be controlled by varying the hot-pressed conditions. Dense ferrites of different grain sizes (average grain size 10 μm-300 μm) can be made. For example, dense Mn-Zn ferrites with μ0 = 7420 and Bm = 4950 Gs and dense Ni-Zn ferrites with different μ0(μ0= 100-2500) can be made by hot-pressing.
DYSPROSIUM IODIDE LAMP AND ITS USE IN PHOTOENGRAVING
YANG YONG-XIANG, WANG GUO-FU
1974, 140 (6): 13-16. doi: 10.7498/aps.23.13
Abstract +
The working principle, structure and characteristics of a dysprosium iodide lamp are described. It is a vapour discharge lamp containing a mixture of dysprosium iodide and halmium iodide. With a lifetime of 200 hours, its luminous efficiency is above 70 lumen/watt and its colour temperature 6000 K. Trial applications in photoengraving show that the dysprasium-iodide lamp, as compared with the carbon-arc lamp, has the virtues of higher brightness, smaller dimensions, and greater stability and cleanness. As a new type of light source it is expected to improve the art of photoengraving.
OCCURRENCE OF LOCALIZED SLIP REGIONS IN ALUMINUM-MAGNESIUM ALLOYS UNDER FATIGUE LOADING
HUANG Y. S., WANG C. K., HSIA Y. P., Kg T. S.
1974, 140 (6): 17-29. doi: 10.7498/aps.23.17
Abstract +
Previous studies on aluminum and aluminum-copper alloys have shown that the change of energy loss (△E) under fatigue loading can be divided into two stages. The first stage corresponds to the pinning of dislocations and the rise of △E in the second stage is associated with the occurrence of localized slip regions in the specimen. In order to confirm this viewpoint, torsional fatigue experiments were carried out on aluminum-magnesium alloys containing 0.52, 0.91, 3.46 and 5.15% of magnesium, and the area of the hysteresis loop (stress versus strain) after various stress cycles N was determined, from which the energy loss △E in each cycle was calculated. Results of metallographic observations on the specimen surface after various stress cycles show that for all the alloys used, the change of slip marks exhibits two distinctly different stages. In the first stage, several systems of fine and straight slip lines are often observed, and the slip lines are found to be distributed uniformly over a grain. In the second stage, some of these slip lines are thickened up to form localized slip regions. In general, such localized slip regions occur earlier in alloys with lower magnesium contents (0.52, 0.91%) and under higher applied maximum torsion strains.A comparison was made between the observed changes of the △E-N curves and the occurrence of the localized slip regions. After proper account is taken of the possible superposition of the△E's occurring in the first and second stages, it is shown that the occurrence of localized slip regions in the specimen can give rise to an increase of △E in the later stage of fatigue loading. This agrees with the results previously obtained in the case of aluminum and aluminum-copper alloys.The correlation between the state of the pinning of dislocations in the first stage of fatigue loading and the subsequent occurrence of localized slip regions is discussed.
COMPOSITE FIELD THEORY AND VECTOR MESON DOMINANCE (VMD), PARTIAL CONSERVATION OF AXIAL VECTOR CURRENT (PCAC), FIELD-CURRENT IDENTITY AND SOME PROBLEMS OF CURRENT ALGEBRA
HE ZUO-XIU, HUANG TAO
1974, 140 (6): 30-40. doi: 10.7498/aps.23.30
Abstract +
We derive the theory of vector meson dominance, partial conservation of axial vector current, field-current identity and the combined algebra of field and current with the application of the composite field theory. It can be shown that an unified theoretical foundation can be given by the composite field theory for these various theories.
DIRECTIVITY PATTERNS OF ANGLE PROBES FOR ULTRASONIC BULK WAVES AND SURFACE WAVES
YAN REN-BO
1974, 140 (6): 41-50. doi: 10.7498/aps.23.41
Abstract +
The directivity patterns of angle probes commonly used in ultrasonic material-testing are studied both theoretically and experimentally. Expressions are obtained for longitudinal waves and transverse waves radiating into the body under test and for surface waves propagating over the surface of the body, treated as a semi-infinite isotropic medium. Numerical computations are given in all three cases for a steel object. The theoretical deductions are partially checked by experiments for the case of longitudinal and surface waves. Some problems to be considered in ultrasonic testing are pointed out.
THEORY OF THIN PYROELECTRIC FILM DETECTORS
CHEN JI-SHU
1974, 140 (6): 51-58. doi: 10.7498/aps.23.51
Abstract +
The pyroelectric response and NEP of pyroelectric detectors with and without a substrate are calculated as functions of detector thickness and working frequency, using the one-dimensional diffusion theory. It is found that in order for a thin pyroelectric film detector to have better low frequency performance, it is essential that the substrate should be effectively free-bearing and very thin, preferably less than 0.1μ thick. The pyroelectric layer should also be thin, preferably as thin as the substrate. As concerns the substrate material, the product of its specific heat and density should be as small as possible.
ANALYSIS OF LENSLIKE EFFECTS IN GAS LASERS
ZHANG RUI-LIN
1974, 140 (6): 59-68. doi: 10.7498/aps.23.59
Abstract +
The optical cavities of general curved-mirrors with a negative lenslike medium are discussed, and used to analyze the thermal lensing effects in gas lasers. The mode analysis is made for a CW CO2 laser of a plane-concave cavity. It is shown that the thermal lensing effects have considerable influence on the output and resonance frequencies, particularly for the fundamental mode lasers. Finally, possible thermal lensing effects in ion gas lasers and other lasers are briefly discussed.