Vol. 27, No. 2 (1978)
1978-01-20
CONTENT
1978, 27 (2): 121-125.
doi: 10.7498/aps.27.121
Abstract +
Ever since the fifties, profound theoretical and experimental investigations were spent on the noise production of subsonic and supersonic jets, but little has been done on the turbulent noise of a choked jet. In a previous paper the authors derived the pressure dependence of the latter. In this paper it is shown that a slight modifica-tion of the formula in the above-mentioned paper will make it applicable to subsonic jets too, and an interpretation is obtained for turbulent jet noise in general. From this it is inferred that turbulent jet noise has its origin in the quadrapole radiation of turbulent eddies, the only difference in that, for a choked jet, the turbulence velocity further increases with the stagnation pressure, although the mean jet velocity does not. From this point of view, the rule of increase of the turbulent velocity with increasing stagnation pressure is predicted. This interpretation seems plausible and the noise relations thus derived agree with experiment.
1978, 27 (2): 126-136.
doi: 10.7498/aps.27.126
Abstract +
The changes of maximum reflection coefficient, half maximum line breadth and integrated reflection power of double-crystal reflection curves in some planes of the α-LiIO3 single crystal have been investigated under the action of the electrostatic field along the z-axis and x-axis.Based upon the Experimental fact that kB(0) is dependent on the applied voltage and the charging time and there exists a maximun value, a possible explanation is suggested by supposing the displacement and rotation of the IO3- group along and around the z-axis under the action of the electrostatic field.
1978, 27 (2): 137-145.
doi: 10.7498/aps.27.137
Abstract +
In this paper the lifetime of the terminal energy level has been considered in the rate equations of the fast Q-Switched four-level laser. Computer solutions are pre-sented. The effects of the terminal energy level lifetime, the initial inversion popula-tion density, the stimulated emission cross-section and the cavity length on the behavior of giant laser pulses and multipulses have been studied in detail. The optimization and miniaturization of electro-optically Q-Switched lasers are discussed.
1978, 27 (2): 146-159.
doi: 10.7498/aps.27.146
Abstract +
The temperature coefficient of resonant frequency Tkf is obtained from the degree of ferroelectric domains alignment in piezoelectric ceramics and the adiabatic. piezoelec-tric equations. It is expressed as a function of the temperature expansion coefficients of the crystal lattice, their remanent polarization and other parameters. When the experi-mental data of "pure" Pb(ZrxTi1-x)O3 are substituted in the theoretical expressions, curves showing Tkf as a function of the Zr/Ti composition near the morphotropic phase boundary are obtained, and the theoretical results are found to be in close agreement with experiment. Thus the effects of different poling and heat treatment processes upon Tkf have been explained successfully. A discussion is given concerning the ways and means by which the resonant frequency temperature stability of piezoelectric ceramic vibrators can be improved.
1978, 27 (2): 160-168.
doi: 10.7498/aps.27.160
Abstract +
Corresponding to the 14 Bravais lattices there are 44 different types of reduced cells whose base vectors are unique, therefore it is possible to deduce the Bravaislattice type from the scalar products of reduced cell vectors(a·a b·b c·c b·c c·a a·b). If the crystal lattice is already known, the plane reduced cells in the reciprocal space are first calculated from the lattice parameters and then the electron diffraction patterns can be indexed by comparing them with the calculated plane reduced cells. If the crystal lattice is unkown, three diffraction spots are selected from two electron diffraction patterns taken one before and the other after tilting the crystal through an angle ψ, the spots being chosen so that they lie close to the center, corresponding to three reciprocal lattice vectors with low indices. These vectors constitute a primitive cell in reciprocal space which is first transformed to a primitive cell then further to a reduced cell in the crystal space. The lattice type and parameters of the Bravais lattice are then deduced and the indices of diffraction spots fixed. Computer pro-grams of the above indexing procedures have been written in Fortran for the purpose of phase analysis and the direct determination of the Bravais lattice of unknown crystals.
1978, 27 (2): 169-174.
doi: 10.7498/aps.27.169
Abstract +
In crystal structure determination with presence of heavy atoms, Patterson method and methods based on it, i.e. the heary atom method, the isomorphous replacement method and the anomalous scattering method are conventionally employed. When applying these methods ambiguities in results often arise. It had been suggested by one of the present authors in 1965 that the ambiguities can be eliminated by using the direct method. In recent years, similar investigations are continued abroad. These methods not only present their distinctive feathures in the work of structure analysis of crystals of small molecules, but their further developements will be effec-tive in extension the field of application of direct methods in structure analysis of biological macro-molecular crystals, making contribution on improving the state of art of these studies. The application of the method in the case of centric symmetry have been demonstrated in the published work of one of the present authors. Another successful example on the case of non-centric symmetry is given here. Although only the problem of ambiguity of Patterson method is treated in this example, but the same approach can be applied to that of the isomorphous replacement method and the anomalous scattering method.
1978, 27 (2): 175-180.
doi: 10.7498/aps.27.175
Abstract +
An analytical treatment is given for the scattering of light, neutron and electron beams in the presence and absence of an external applied electro-static field by a system for which the charge transport can be described by the D-H equation. The resulting scatterings are shown to be quasi-elastic, i.e., Rayleigh scattering. When there is no external field, the spectral distribution of the Rayleigll scattering consists of two superposed central peaks of different widths, their shapes being assymmetric. The application of an external static electric field would give rise to variation of width and location of these Rayleigh peaks. The possibility of observing the above mentioned phenomena is also discussed.
1978, 27 (2): 181-186.
doi: 10.7498/aps.27.181
Abstract +
Using an exact cosmological solution of a simple model it is shown that the break-ing of symmetry in the vacuum state may be due to cosmological effects.
1978, 27 (2): 187-202.
doi: 10.7498/aps.27.187
Abstract +
A new integral equation for current distribution of a cylindrical antenna is de-rived. This is a one-dimensional Predholm equation of the second kind, and is different from the conventional Hallen equation in antenna theory. Emphasis is laid on the analysis of the current and magnetic field for an infinitely long antenna. It is found that our equation is more suitable for describing an actual antenna than the Hallen equation. Preliminary numerical computations for a finite antenna have been carried out. The results show that numerical computation using our equation is practical.
1978, 27 (2): 203-218.
doi: 10.7498/aps.27.203
Abstract +
It is proved that the CG coefficient of the permutation group and the outer-product reduction coefficient are just the coupling coefficient which couple the irreduci-ble basis of any SU(m) and SU(n), to those of SU(mn)?SU(m)× SU(n) and SU(m+n)?SU(m)?SU(n) respectively. Several simple methods are given for the calculation of the irreducible bases of SU(mn)?SU(m) × SU(n) and SU(m+n) ?SU(m)?SU(n) when using the Gelfand representation of SU(mn) and SU(m+n). The SU(6)?SU(3) × SU(2) and SU(8)?SU(4) × SU(2) baryon wave functions commonly used in elementary particle models are given in detail.
