Vol. 25, No. 1 (1976)
1976, 147 (1): 1-9. doi: 10.7498/aps.25.1
With LiH as additive and Mg/Mg3N2 as catalyst hexagonal boron nitride is transformed into the cubic form, pressure and temperature being maintained at 55-64 Kb and 1700-2100℃ respectively. The structure and related properties of crystals thus obtained are identified and tested. Microseopie examination of impurities, defects, growth centers and steps on crystal surfaces indicates that this cubic BN possesses the common features of crystals grown under ordinary conditions. The results of the synthesis which depends closely upon the P-T condition, catalyst composition and catalyst assembly are analysed and discussed. The remarkable effect of the presence of a small amount of LiH in the catalyst on the grain growth is particularly described. Cubic BN crystals larger than 1mm. have been obtained.
1976, 147 (1): 10-22. doi: 10.7498/aps.25.10
The switching process of transistor Schmitt circuit was studied in this paper. Concrete analytical expressions of the switching process have been derived. Using these expressions numerical calculations were carried out for two types of commonly used transistor Schmitt circuit. Experiments were carried out to check the theoretical calculations. Experimental results fit the theoretical calculations quite well. From this study, some rules for selection of the transistors and circuit elements were obtained. The results of calculation in this paper may be used to estimate the switching speed of Schmitt eircuit in the early design stage.
1976, 147 (1): 23-30. doi: 10.7498/aps.25.23
A dynamical surface emission center model which can explain all observed phenomena in thermionic cathodes is proposed. The emission comes from such an aggregate of atoms that the moving electrons may have momentarily highest energy and/or the attraction from the nuclei to these electrons is momentarily least. Excess barium is the source for supplying high energy electrons, while the oxygen may play a favorable or unfavorable role to emission depending upon its relative quantity and relative position in the aggregate. Although strontium, calcium, aluminate, tungstate, etc. are minor factors to emission, yet they may have some effect on the evaporation, migration, and transition of electrons etc.. The non-uniformity of emission in practical cathodes proves the existence of such centers, while their dynamical character exhibits instability of emission e.g. flicker noise.
UNITARY TRANSFORMATION AND GENERAL LINEAR TRANSFORMATION BY AN OPTICAL METHOD (Ⅱ)——THE ITERATIVE METHOD OF SOLUTION
1976, 147 (1): 31-46. doi: 10.7498/aps.25.31
An important problem in applied optics is the design of an optical processing system composed of a series of holographic lenses for the purpose of realizing an arbitrary transformation. In this paper, we give an iterative method of computation to resolve this problem. The convergence of the method and the problem in relation to finite dimension approximation are discussed. Some problems which emerged in the course of numerical calculation are analysed by means of several simple examples.
1976, 147 (1): 47-52. doi: 10.7498/aps.25.47
In this paper starting with the general expression of the reverberation intensity for short pulses Ir(t,τ)=Kτt-me-βt, the corresponding exact expressions of the reverberation intensity for longer pulses are derived. The corresponding approximate formulae are also presented under the assumption that the exponential attenuation loss over the pulselength can be neglected. It is shown that, at short ranges, the reverberation intensity tends to saturation and decays inversely with the (m-l)st-power of the time t when the exponential attenuation coefficient β is small enough and the pulselength τ longer than the effective pulselength τm=amt(am decreases as m increases, and m is a real number greater than 2). Experimental results agree well with the theory.
1976, 147 (1): 53-57. doi: 10.7498/aps.25.53
We investigate the contributions of W-meson intermediate states to photon-photon scattering in SU(2)L×U(1) model. Because the spontaneously broken gauge theories are renormalizable and the electromagnetic gauge invariance remains valid under symmetry-breaking, the infinities in the scattering amplitude of one loop approximation must cancel each other. We show the finiteness of the photon-photon scattering amplitude by calculation. We give the effective nonlinear interaction Lagrangian of the electromagnetic field and the scattering cross section at low energies. At low energies the leptonic intermediate states dominate the scattering amplitude, but at high energy limits the contributions of W-meson intermediate states are comparable with the contributions of leptonic intermediate states.