Vol. 20, No. 10 (1964)
1964-05-20
CONTENT
1964, 20 (10): 947-953.
doi: 10.7498/aps.20.947
Abstract +
For a class of nonlocal potentials, the S matrix element is proved to be analytic in the right half λ planeexcept at the poles.
1964, 20 (10): 954-969.
doi: 10.7498/aps.20.954
Abstract +
The semiclassical equations which describe the behaviours of three-level lasers were derived. The method of nonlinear mechanics was used to treat the electromagnetic oscillations coupled with the dipole moments of molecules. It is shown that when the pumping power is larger than the critical value, the amplitude of output oscillations is stable (corresponding to a stable equilibrium point in phase space), only if the homogeneous line width of molecules (1/T2) is larger than the damping width of the resonan-tor (q). The appearance of instability of output oscillations is due to the effect of coherence. Furthermore, a stable limit cycle was shown to appear when the above mentioned equilibrium point becomes unstable as qT2 increases. Therefore, it seems true that there is no limit cycle near the equilibrium point when it is stable. These results may account for the instability of amplitude of output oscillations observed by some authors in ruby lasers, and should be checked in detail with gas lasers.
1964, 20 (10): 970-990.
doi: 10.7498/aps.20.970
Abstract +
Based on the general methods for the reduction of direct products of space group irreducible representations developed by Birman, a simpler method of finding the wave vector selection rules is derived. The method is applied here to the hexagonal close-packed and the wurtzite space groups. The coupling coefficients for the reduction of the direct products of two space group irreducible representations are given explicitly.
1964, 20 (10): 1003-1018.
doi: 10.7498/aps.20.1003
Abstract +
On the basis of the general expression of the scattering matrix between two particles with spin, derived by Jocob and Wick, with certain approximations we have analysed the experimental data of the angular distribution of the fission fragments from Th230,Th232,U234,U236, and U238, bombarded by neutron whose energy is in the region near the fission threshold. The results of this analysis show: (1) The angular distribution of the fission fragments, in the region near the threshold, can be explained by a few rotational bands (every band has a definite parity) above the saddle point. (2) These rotational bands are consistent with the asymptotic energy levels of Nilsson.Furthermore, based on the idea that the barrier of the saddle point of the symmetric fission is higher than that of the asymmetric, we discussed the correlation between the anisotropy of the angular distribution of fission fragments and its mass ratio.
1964, 20 (10): 1019-1026.
doi: 10.7498/aps.20.1019
Abstract +
Effects of hydrostatic pressure up to 18000 kg/cm2 on the current-voltage characteristics of germanium Esaki diodes are reported. The pressure dependence of the peak currents IP, valley currents IV, peak voltages VP, valley voltages VV, and the exponential excess currents IX have been studied on sixteen germanium Esaki diodes. The results indicate that the semi-logarithmic plot of peak currents IP versus pressure P consists of two straight lines with different negative slopes. The intersecting point occurs in a pressure range from 5000 kg/cm2 to 9000 kg/cm2. The peak voltages VP change only slightly with pressure, while the valley voltages VV are independent of pressure within the limit of experimental errors. For most diodes the pressure dependence of the valley currents is the same as that of peak current. The onsets of the exponential excess currents move toward high voltages with pressure. The pressure dependences of the peak currents and exponential currents have been discussed. It is shown that the presence of two straight lines with different slopes may be related to different tunnelling processes. A pressure coefficiant of the energy gap Eg can be determined at a constant exponential excess current; the result is in good agreement with that given by other authors.
1964, 20 (10): 1027-1036.
doi: 10.7498/aps.20.1027
Abstract +
Some investigations on the titanium-containing (～5% Ti) and higher cobolt content (～34% Co) permanent magnet alloy recently developed upon the basis of the composition of Alnico 5 are reported in this paper. It is shown that superior permanent magnetic properties may be obtained by means of isothermal magnetic treatment as compared with those obtained by controlled cooling rate treatment, confirming the experience of Koch et al. It has been found that the coercive force is very sensitive to the temperature of isothermal magnetic treatment. The structural states of isothermally-magnetically treated specimens were investigated by means of electron microscopy and other means. The results indicate that different conditions of prior isothermal magnetic treatment lead to states of different dispersion and morphology of the a′-phase, and hence to different permanent magnetic properties. The experimentally determined C-curve of γ1-phase shows that the precipitation of the γ1-phase is very rapid. Careful metallographic examination has revealed that the so called ar-phase is actually heterogeneous. The experimentally established quantitative relationship between the permanent magnet properties of the alloy and the content of the "ar-phase" clearly demonstrates the detrimental effect of the latter on the former.
1964, 20 (10): 1037-1047.
doi: 10.7498/aps.20.1037
Abstract +
By means of the Laue X-ray diffraction method the distribution of polytypes, rule and characteristic features of syntaxic coalescence, and crystal perfection of 400 silicon carbide single crystals, which were taken from graphite furnace and induction furnace of 32 experimental runs and from industrial furnace, have been studied. Numerous observations demonstrate that parallel coalescence in plate silicon carbide single crystal is a very common phenomenon. The crystals with coalescence of more than two polytypes amount to about 2/3 of the crystals studied, whereas crystals of the single type amount to only 1/3. Sometimes coalescence consists of even above 4-5 polytypes.The analysis of polytype distribution in furnace indicates that the polytypes are distributed irregularly, and different polytypes may be found even at the same place of one furnace. The relations among polytype, colour, and etching figure in SiC are analysed. Finally, the different mechanisms of polytype formation in silicon carbide suggested up to date are discussed.
