Vol. 27, No. 6 (1978)
1978-03-20
CONTENT
1978, 27 (6): 615-630.
doi: 10.7498/aps.27.615
Abstract +
Theoretical calculations and experimental measurements of the basic parameters of coated small dipole antenna were carried out in the short wave range. It was concluded that the resonance frequency of the dipole could be lowered and the radiative resistance could be improved by magnetic coating at the price of some loss in band width and efficiency. The radii ratio of the coating and the inner conductor played a primary role as compared to the absolute size of the magnetic material. In addition, the characteristics of the magnetic coated antenna was explained within the framework of an approximate theory based on surface wave transmission line concepts. The design procedure of such antennas was also discussed.
1978, 27 (6): 631-644.
doi: 10.7498/aps.27.631
Abstract +
Porous diffusers, a distinguished group of silencers, have been developed in the last years, and are used widely in foreign countries. They are preeminent in their small volume, simple structure and high noise reduction. Unfortunately, there are lack of theoretical discussions as yet. In this work, the aerodynamics of flow through porous materials is discused in detail and the authors suggest that the outflow through porous material can be characterized by an effective area and an effective stagnation pressure reduction. Furthermore, the principle of noise reduction of porous diffusers has been studied in some detail, to facilitate the design and the estimation of porous diffusers. Some of the porous diffusers are studied in the light of the present theory.
1978, 27 (6): 645-650.
doi: 10.7498/aps.27.645
Abstract +
In this work, the expressions of molecular dissociation rate and isotope enrichment coefficient in an strong IR field, as the functions of the laser energy per pulse, the focal length of lens, the number of laser pulses, and etc., were derived by using the kinetic theory. The theoretical expression of isotope enrichment coefficient was compared with the experimental results for SF6, and good agreement was found. In addition, the theoretical expressions compared with experiments would provide some useful informations of the molecular dissociation in the strong IR field.
1978, 27 (6): 651-663.
doi: 10.7498/aps.27.651
Abstract +
The scattering of laser beam by a rough plane surface with one-dimensionally random fluctuations is treated by a simplified statistical method. The real surface is replaced by a series of taps of width λ along the direction of scores. The height hn, of the n-th tap is the average of the heights of real surface over the interval corresponding to the n-th tap. All the random variables hn are assumed to be independent and every one of them varies in the same inteval [-h,h] with the same probability distribution, h being the scale of roughness of surface. The problem thus becomes one of seeking the expected value of the light intensity produced by the interference of a series of element sources with certain random phases. This probabilistic problem can be solved strictly only with difficulty. With an approximate simplification it reduces to the problem of seeking the position of center of gravity of an arc and a simple "random walk" problem.The expression of the expected value of light intensity distribution I(θ) in the recording plane is deduced. The expression of the ratio R of the total energy in the central region to that in the two side wings in the recieving plane is very simple.The numerical results are given. Several methods of measurement are discussed. It is pointed out that the generalization of this model to the cases of surface with two-dimensionally random fluctuations and surfaces of other shape (non planar) is not difficult.
THEORY OF MULTI-PHOTON PHOTO-DISSOCIATION OF POLYATOMIC MOLECULES IN AN INTENSE INFRARED LASER FIELD
1978, 27 (6): 664-680.
doi: 10.7498/aps.27.664
Abstract +
Based on the theory of non-linear vibration and conception of uni-molecular reaction, we suggest in this article a physical model to describe the phenomena of instantaneous dissociation of polyatomic molecules interacting with an intense ir laser field. It is shown that there exists close and internal relationship between the dissociation threshold usually observed and the "jumping" processes occured inherently in nonlinear vibration. Taking the SF6 molecule as an example, the dissociation threshold, frequency "red shift" and the rotational compansation etc. are analyzed and evaluated. Good quantitative agreement between theoretical results and experimental observations is found.
1978, 27 (6): 681-690.
doi: 10.7498/aps.27.681
Abstract +
The self-consistent integral equation for the field distribution of the resonant modes in a concave (plane) grating-mirror stable resonator is solved in the limit of infinite Fresnel numbers and under Littrow (collimate) configuration. Under the conditions above mentioned the field distribution is approximately independent of the blazing angles of the grating. In the direction parrallel to the grooves of the grating (y direction) the inclined grating can be equivalent to the concave mirror which has the radius of curvature ry-r1·cosθ and is perpendicular to the axis of the resonator (z axis). In the x direction the field distribution can be described in terms of Hermit-Gaussian function and the perturbation term. The perturbation term which is proportional to tangent of the incline of the grating introduces astigmatism to the field. When the perturbation can be neglected, the inclined grating would be equivalent to a concave mirror of radius rx=r1-cos3θ, which is also perpendicular to the axes of the resonator.The resonant condition, the stabilty condition, the field distribution and other charecteristies of the field distribution are obtained.
1978, 27 (6): 691-699.
doi: 10.7498/aps.27.691
Abstract +
The visibility aurve and the spectral energy distribution curve of light emitted by semiconductor diodes are approximated by Gaussian functions with appropriate parameters. The buminous efficiency and both power and quantum efficiencies of luminescence of LED can then be evaluated by direct integration when the total luminous flux was measured. Comparison of the calculated values with those obtained by means of planimeter shows fairly good agreement for three kinds of LED: GaP. GaAs0.62P0.38 and Ga0.68Al0.32As.
1978, 27 (6): 700-709.
doi: 10.7498/aps.27.700
Abstract +
In this article, the mechanism of the enhancement of neutron diffraction from KDP and TGS crystals under the action of an electrostatic field is proposed. KDP and TGS are both proton conducting crystals. In the presence of an applied static voltage, an electric field is set up within the crystal with a certain spatial distribution. Because of the piezoelectric effect, the spacing of the reflecting crystallographic planes depends upon the spatial coordinates, thus the restriction for the angular range of neutron diffraction should be relaxed, and enhancement of neutron diffraction results. Treating the spacings of the crystallographie planes as a function of spatial coordinates, we have derived expressions for the neutron diffraction intensity in both the laue case and the Bragg case, and estimated the order of magnitude of enhancement of the neutron diffraction resulted from inhomogeneous piezoelectric effects. Good agreement with experiment is found. New experiments for further verification of this mechanism are suggested. By the way, we remark that the above mentioned mechanism is not the dominant one responsible for neutron diffraction enhancement observed in a-LiIO3 under the action of an electrostatic field. A possible micro-mechanism for a-LiIO3 may be that under the action of an inhomogeneous field, the defects assume a spatial distribution which results in inhomogeneity of spacing between the crystallographic planes and hence enhancement of neutron diffraction.
1978, 27 (6): 710-722.
doi: 10.7498/aps.27.710
Abstract +
The phase transitions of Mg(IO3)2·4H2O crystals in the heating process have been investigated by means of thermal analyses and X-ray diffraction at high and room temperatures. The results may be exhibited in the following diagram:no thermal effect observed on beating or coolingThe crystal structure of Mg(IO3)2·4H2O has been determined by means of the method of single crystal diffraction, it has been found that the space group of Mg(IO3)2·4H2O is P2 or Pm. There are two formula units per unit cell. Lattice parameters are: a=8.307?, b=6.627?, c=8.541?, β=100°5′. The crystal structure of α-Mg(IO3)2 has been determined by X-ray powder method. The unit cell of α-Mg(IO3)2 is hexagonal, with a=5.4777?, c=5.1282?, c/a= 0.9362 at 14℃. There is one formula unit per unit cell. The space group is P63. 60II are situated at the 6(c) positions, 2IV are situated at 2(b) positions, and Mg++-ion is disorderly distributed at half of 2(a) positions, the atomic parameters being Xc=0.096, Yc=0.344, Zc=0.162, Zb=0, Za=0.981. The crystal structure of α-Mg(IO3)2 is isomorphic with a-LiIO3. α-Mg(IO3)2 is different from a-LiIO3 only in that the Mg++-ion is disorderly distributed at one-half of 2(a) positions and the other half is vacant.
1978, 27 (6): 723-728.
doi: 10.7498/aps.27.723
Abstract +
In this article, a hew method of color holography is suggested. Only a single wavelength laser is needed as light source, and any monochromatic holographic plate for photographic recording. The hologram obtained is then reconstructed by means of white light transmission. Experiments have been carried out using flower and three color circles as objects, the reconstructed pictures are presented here.
1978, 27 (6): 729-745.
doi: 10.7498/aps.27.729
Abstract +
Interactions of dislocations, especially under dynamic conditions, on a single glide plane or from two crossing glide planes were studied in general, and certain dislocation configurations in particular, by means of transmission electron microscopy and diffraction contrast methods. The main findings are:1. Hexagonal dislocation networks are mainly formed by the interaction of dislocations on a single glide plane with Burgers vectors at 120°.2. Like screw dislocations, edge and mixed dislocations can also cross-slip between two glide planes.3. Interactions of dislocations from two crossing glide planes sometimes form long, straight, non-mobile dislocations at the intersections, e.g., Lomer-Cottrell dislocations. However, this non-mobile dislocation does not block, as it is generally accepted, the movement of dislocations on these two glide planes.4: In nickel-chromium alloys containing aluminum and titanium, interactions of superlattice dislocations are more or less similar to those observed in Al-and Ti-free alloys or in disordered solid solutions.
1978, 27 (6): 746-751.
doi: 10.7498/aps.27.746
Abstract +
We suggest that the superconductors should be divided into two types, type A and type B, for the former, λΛ. The meaning of Λ is given in this paper. Our analysis shows that the influence of effective phonon spectrum on the transition temperature of these two type superconductors are different and the ways for raising their transition temperature are different also. For type A superconductors, the most effective way for raising Tc is to increase λ, whereas for type B superconductors, is to increase λ (ω2).
