Vol. 13, No. 5 (1957)
1957, 38 (5): 357-364. doi: 10.7498/aps.13.357
From the analysis of the experimental results (high energy electron scattering, X-ray spectra of μ-mesonic atoms), it is pointed out that the radius of nuclear charge distribution, Rp, is very nearly proportional to the cubic root of the atomic number z1/3, ins tead of the usually accepted relation Rp∝A1/3. Under this assumption, we have modified the semi-empirical mass formula. The Coulomb energy term is now assummed to be of the form 3/5 (z2e2)/ropz1/3).The aagreement of the nuclear binding energies calculated fromthe new fomula with the experimental data is definitely better than that of the old Bethe-Weizsacker formula. Also the mass numbers of the most beta-stable nuclei are very correctly predicated by the new formula.
A PRELIMINARY REPORT ON MEASUREMENTS OF SOUND ABSORPTION COEFFICIENTS OF CHINESE ACOUSTICAL MATERIALS
1957, 38 (5): 365-387. doi: 10.7498/aps.13.365
Normal sound absorption coefficients of some Chinese acoustical materials as measured by the tube method were tabulated and problem of conversion to random coefficients was discussed. Our results: most of the prefabricated units showed low absorption efficiency especially at low frequencies.In order to clarify the feasibility of these acoustical materials and to throw some light on the development of our future acoustical material industry, test data and relevant theoretical interpretations were presented for the effects of paint, thickness, flow resistance, and perforations etc. on absorption characteristics, and also for the functions of panel and perforated-panel absorbers. Emphasis was made for the last type for its versatile acoustical applications and insufficient use in this country. A conclusion was drawn with several suggestions both for the improvement of the existing products and for the manufacture of new ones.
SEDIMENTATION MOTION OF SAND PARTICLES IN MOVING WATER (Ⅰ)——THE RESISTANCE OK A SMALL SPHERE MOVING IN NON-UNIFORM FLOW
1957, 38 (5): 389-398. doi: 10.7498/aps.13.389
In hydraulics, when we deal with the problem of sand particles moving relative to the surrounding water, Stokes' formula of resistance has usually been used to render the velocity of sedimentation of the particles. But such an approach has not been proved rigorously, and its accuracy must be carefully considered. In this paper, we discuss the problem of a sphere moving in a non-uniform flow field, on the basis of the fundamental theory of hydrodynamics. We introduce two assumptions: i)the diameter of the sphere is much smaller than the linear dimension of the flow field, ii) the velocity of the sphere relative to surrounding water is very small. Usnig these two assumptions, we solve the linearized Navier-Stokes' equations and equations of continuity by the method of Laplace transform, and finally we obtain a formula for the resistance acting on a, sphere moving in a non-uniform flow field.
SEDIMENTATION MOTION OF SAND PARTICLES IN MOVING WATER (Ⅱ)——SEDIMENTATION OF SAND PARTICLES IN LAMINAR FLOW
1957, 38 (5): 399-408. doi: 10.7498/aps.13.399
In dealing with the problem of sand particles moving relative to the surrounding water, Stokes' formula of resistance has usually been used to render the velocity of sedimentation of the particles. But such an approach has not been proved rigorously, and its accuracy must be carefully examined. In the previous paper, we gave the resistance acting on a sphere moving in a non-uniform flow field. In this paper, we assume the concentration of sand particles to be very small, and using the previously obtained formula for the resistance, we establish the general equations of motion of laminar flow of sand particles and water. Then, we discuss the sedimentation motion of sand particles for laminar flow in an open channel.Finally, we find that the component of relative velocity parallel to the main stream is not equal to zero. Thereby, we obtain the error in the position of sedimentation as calculated by means of the usual simplified assumption. This error in position is proportional to the depth of water, and is independent of the size of sand particles. In general, it is not a negligible quantity.
1957, 38 (5): 409-416. doi: 10.7498/aps.13.409
In γ-iron (containing 1.7% of Mn) an internal friction peak was observed around 240℃with a frequency of vibration of about 2 cycles per second. The height of the peak was found to increase with an increase of the carbon content and was found to decrease when the specimen was annealed at an elevated temperature. The activation energy associated with this peak was found to be 34,000±2,000 calories permole which is close to the activation energy of diffusion of carbon in y-iron determined in macro-diffusion experiments. It is concluded, thus, the observed internal frictionpeak is associated with the stress-induced diffusion of carbon in y-iron.The coefficient of diffusion D of carbon in y-iron in the temperature range of 200-260℃ was calculated according to data given by internal friction measurements. When plotted with logD against 1/T, these values of D were found to lie on the same straight line with those values of D in the temperature range of 1000-1200℃ determined in macro-diffusion experiments.The height of internal friction peak appeared to vary with the square of the carbon content in the specimen. This seems to indicate that two carbon atoms are participating in the elementary act associated with the stress-induced diffusion. A preliminary model for the observed internal friction peak was suggested thereupon: Owing to the presence of holes (vacancies) in the crystal lattice, two carbon atoms are apt to form an atomic-pair and this pair produces lattice distortions which are different along three crystallographic directions. Rotation of such an atomic-pair under the action of stress gives rise to internal friction.
DIE TEMPERATURABHANGIGKEIT DES PHOTOEFFEKTES DER Sb-Cs PHOTOKATHODEN IM TEMPERATURBEREICH-170℃—+ 20℃
1957, 38 (5): 417-420. doi: 10.7498/aps.13.417
Es wurde die Temperaturabh?ngigkeit des Photoeffektes der Sb-Cs Photoka-thoden im Temperaturbereich -170℃-+20℃ untersucht. In der Nahe derGrenzwellenlange wurde ein monotoner Abfall der Empfindlichkeit mit abnehmen-den Temperaturen gefunden. Bei kurzeren Wellenlangen ist die Empfindlichkeit in einem weiten Temperaturbereieh unabhangig von der Temperatur und erst bei den tiefsten Temperaturen ergab sich ein steiler Abfall der Empfindlichkeit.
1957, 38 (5): 421-427. doi: 10.7498/aps.13.421
A method of measuring photoconductive spectra is described in detail, and results of measurement made on n-type germanium are presented. It is found that the shape of the photoconductive spectra is dependent on the surface treatment of the sample.
1957, 38 (5): 428-442. doi: 10.7498/aps.13.428
The continuity equation of minority carriers in n-type germanium is solved for the stationary case, in which the volume recombination is assumed to be of the recombination-center type and the surface recombination is introduced in the boundary condition. An expression for the photoconductivity is obtained from this solution.By substituting the known absorption data and the volume lifetime of minority carrier in the sample into the expression of photoconductivity and by choosing suitable values of surface recombination velocity, photoconductive spectra are calculated and are compared with the experimental curves. The agreement is satisfactory for wave-lengths greater than 1.2 μ. Below 1.2 μ, the experimental curves fall well below the calculated curves. It is thought that other types of volume recombination may exist.The photoconductive spectra usually have a maximum outside the absorption edge. By measuring the relative height of the maximum, the surface recombination velocity can be obtained. This method is suitable for medium and large values of surface recombination velocity.The photoconductivity drops sharply on both sides of the maximum in case of large values of recombination velocity. In such cases, the energy gap of the semiconductor can be obtained in a simple way. For germanium the energy gap is 0.83 eV for direct transition and 0.635 eV for indirect transition.From this investigation, the energy gap of CdS is reestimated to be 2.53 eV and that of Cu2O greater than 2.10 eV.