Vol. 30, No. 5 (1981)
1981-03-05
CONTENT
1981, 30 (5): 573-583.
doi: 10.7498/aps.30.573
Abstract +
MHD instability of the noncircular cross-section plasma is investigated by using a step current profile model. A new criterion for the instability is obtained. It is a generalization of Zakharov's criterion for circular cross-section plasma. The effects of elliptical and triangular distortion, current gradient and the value of safety factor q on β value are indicated. The optimistic value of q for achieving the largest β value is also given.The critical β value for various plasma parameters is calculated and compared with the numerical results from the local instability and ballooning modes criteria. It is noted here that the current gradient affects the β value seriously. The noncircular cross-section plasma has advantage for obtaining higher β value.
1981, 30 (5): 584-593.
doi: 10.7498/aps.30.584
Abstract +
In this papar, a theory of the average propagator U for the plasma turbulence is established on the basis of the Gaussian process. The group properties of U is showed, its physical meaning and the fundamental applications are analyzed. It is pointed out that the theory is a better description for the plasma turbulence compared to the weak coupling EQL theory given by Misguich and Balescu.
1981, 30 (5): 594-601.
doi: 10.7498/aps.30.594
Abstract +
A serious problem in the application of direct methods is the problem of phase degeneration. That is the phases of structure factors of a non-centrosymmetric crystal converge to a set of centrosymmetric phases. This would occur frequently in case of space groups P21, P41 etc. Phase degeneration gives rise to an additional centre of symmetry and hence a considerable number of spurious peaks in the resulting E-map leading often to the failure of direct methods. In this paper, a two step procedure of solving this ambiguity is proposed. In the first step, the crystal is treated as a centrosymmetric one and a mised image including both enantiomorphs is obtained, while in the second step, the actual structure is then derived from the mixed image by making use of the so-called "component relations". This method has been verified with a known structure and proved to be effective.
1981, 30 (5): 602-609.
doi: 10.7498/aps.30.602
Abstract +
Phase degeneration occured during the solution of crystal structure of asosarmen-tosin by using symbolic addition procedure. This led to an E-map containing simultaneously both enantiomorphs. By making use of the component relation, this E-map has successfully been retrieved leading to an E-map containing only one of the enantiomorphs. It turns out that, with the help of component relation there is no need to modify the starting set even though phase degeneration occurs during the solution of noncentrosymmetric crystal structures by symbolic addition method. Hence the efficiency of the symbolic addition procedure can be improved.
1981, 30 (5): 610-617.
doi: 10.7498/aps.30.610
Abstract +
During the determination of three unknown structures, the method of optimal selection on the distribution of index among the starting reflections was incorporated with the symbolic addition and the MULTAN procedures respectively. It is proved that the optimal selection method provides a better starting set which in the case of MULTAN leads to increase of the figure of merit corresponding to the correct solution. An example is given that structure which had failed to be solved by MULTAN 78 can be solved successfully by incorporating with the optimal selection method.
1981, 30 (5): 618-623.
doi: 10.7498/aps.30.618
Abstract +
The problem of multiple solution is frequently a result of Patterson analysis. This problem can be solved by making use of the component relations or the phase relations of the multiple-solution type. A pseudo structure model containing simultaneously the actual structure and its symmetrical equivalents is in turn the basis for the application of the component relations or the phase relations of the multiple-solution type. The so-called Multiple-solution Fourier Syntheses is the Fourier syntheses based on the whole or partial pseudo structure model. This model can be developed and improved by this type of Fourier syntheses. A practical example is given.
1981, 30 (5): 624-632.
doi: 10.7498/aps.30.624
Abstract +
Temperature dependences of multiphonon relaxation rates for 4F3/2 states in Nd3+-glasses were determined by measuring fluorescence intensity and lifetime in the range of 300-600 K. According to the theory of multiphonon relaxation and vibrational spectrum we made a theoretical fitting of curves. Multiphonone processes of 4F3/2 states have been investigated in five Nd3+-glasses. The phonon energy and number involved in the process were determined and the relation between matrix property and phonon relaxation was analysed. Further examination of multiphonon relaxation theory was conducted in this material.
1981, 30 (5): 633-641.
doi: 10.7498/aps.30.633
Abstract +
A "rectangular" phenomenological model of interaction between ms pulses of laser beam and metals has been set up. When power density is greater than the damage threshold, the metal possesses a constant ablation rate. A differential equation has been obtained by combining propagation of a Gaussian beam. Through numerical calculation, relations of the dependence of depth and shape of hole on the target position, lens focal length, directionality and energy of laser beam have been discussed.
1981, 30 (5): 642-649.
doi: 10.7498/aps.30.642
Abstract +
Co-absorbed γ-Fe2O3 magnetic powder is divided into two sorts: Co-doped γ-Fe2O3 (known as Co-γ-Fe2O3) and Co-ferrite epitaxial γ-Fe2O3 (known as CoFe-γ-Fe2O3). The coercivity of Co-absorbed γ-Fe2O3 is 100 to 400 (Oe) greater than the coercivity of γ-Fe2O3.The causes of the increasing coercivity of Co-absorbed γ-Fe2O3 were studied. The mechanism of increasing coercivity is different between the two sorts of powder: Co (OH)2 formed on the surface of γ-Fe2O3 raised its surface anisotrpy and the coercivity of Co-γ-Fe2O3 is increased. The cause of increasing coercivity of CoFe-γ-Fe2O3 is the coupling effect between the Co-ferrite epitaxial layer and γ-Fe2O3.
1981, 30 (5): 650-660.
doi: 10.7498/aps.30.650
Abstract +
In this paper, a method which can directly measure the thickness of compound thin films is given and the underlying principles are discussed. In the first approximation, the conclusion can be extended to the film with more layers. In order to increase the accuray of measurement, we obtained a more accurate equation and a set of data from electrinic computer. For the convenience of application, we set down all these data in the form of a handbook and express them with some diagrams.This direct method of measuring compound thin films on the substrate does not need any advanced equipment but only a ordinary ellipsometry. In principle, a PCSA optical system is to be used to solve the four-phase problem.
1981, 30 (5): 661-670.
doi: 10.7498/aps.30.661
Abstract +
The influence of the earth's curvature on calculation of ionosphere reflection coefficients at LF and VLF bands is discussed. By developping Maxwell equations in the spherical coordinate, a differential equation system for transverse components of electromagnetic waves has been achieved. The value of admittance matrix A at the bottom of ionosphere is able to be countted with the similar method given by Budden.Then the ionosphere reflection coefficients is able to be countted with the spherical stratified model.
1981, 30 (5): 671-678.
doi: 10.7498/aps.30.671
Abstract +
By means of perturbation and decoupled calculations, we obtained the following conclusion: In Kerr spacetime, all components of massless particle field of arbitrary spin can be decoupled. Using Kinnersley null tetrad, we proved that only two components of neutrino field and two components of electromagnetic field can be seperated with respect to its variables (r,θ) and the other decoupled equation cannot be separated.
1981, 30 (5): 679-685.
doi: 10.7498/aps.30.679
Abstract +
In this article, theoral formulas expressing the temperature dependence of thermal expansion coifficent, bulk modulus and Grüneisen paramentrs of solids are derived from generel thermodynamic relations. We apply the formulas in calulating the properties of MgO, the results obtained are in good agreement with experimental data.
BRIEF REPORT
1981, 30 (5): 686-689.
doi: 10.7498/aps.30.686
Abstract +
The formulas deduced in reference [6] for the electrical resistivity of substitu-tional alloys are applied to binary stoichiometric and completely ordered A-15 compounds. The comparison between theoretical expressions and experimental data shows that the main characteristics in the temperature dependence of resistivity in various types of A-15 compounds at low temperatures could be understood within the framework of [6], in spite of that there are remarkable differences between these two cases.
1981, 30 (5): 690-693.
doi: 10.7498/aps.30.690
Abstract +
According to the theory presented in reference [1] and the relationship between the electron cloud deformation of V atom and the electric charge which transfers from d‖ to d⊥ energy levels, a relation of the superconducting critical temperature Tc and lattice constant a in V3B compounds with A-15 structure is obtained, the theoretical curve is roughly in agreement with experimental data.
1981, 30 (5): 694-699.
doi: 10.7498/aps.30.694
Abstract +
According to the model of the relative displacement of the d subbands in reference [1], the paramagnetic susceptibility and its temperature dependence of V3B type of A-15 superconducting compounds are calculated. The results are roughly in agreement with experimental data.
1981, 30 (5): 700-704.
doi: 10.7498/aps.30.700
Abstract +
The proximity effect of superconducting multilayer films consisting of different metals is considered. Using Silvert and Cooper's method, an approximate relationship between the critical temperature of a multilayered heterogeneous film and its structure is given under the Cooper limit.
EFFECT OF ELECTRON-PHONON INTERACTION ON THE BINDING ENERGY OF A WANNIER EXCITON IN THALLIUM HALIDES
1981, 30 (5): 705-708.
doi: 10.7498/aps.30.705
Abstract +
The values of the binding energy of a Wannier exciton in thallium halides calculaled by some authors are about an order of magnitude large than the experimental values. Using the electron-hole effective potential derived by the present author, a binding energy of a Wannier exciton in thallium halides are calculated. We find that the values. calculated here are obviously better than that of other authors.
