The initial growth of vapor bubbles in various liquids produced by electric sparks is described. Because of the large rate of expansion observed, an assumption is made that the heat flow across the bubble boundary can be neglected during the initial stage, i.e., the bubble makes an adiabatic expansion. On this assumption it follows that the radius of the bubble, R, is given approximately by R=Kt0.4 where t is time, and K a constant. This radius-time relation has a significant feature compared with the results obtained by both Raileigh and Plesset. Experimental results obtained by the use of a high-speed cine-micrograph are in good agreement with the theoretical prediction, although, when the gap-length of electrodes is relatively large, some corrections regarding the shape of the bubble are required.
On the assumption that the motion of vibrating conveyor is linear sinusoidal and a conveyed material is a particle, mechanism of progression of a particle is analyzed and experimented. Analysis is made in consideration of D'Alembert force due to horizontal acceleration of the conveyor and frictional force between a particle and the conveyor surface. Even when maximum vertical acceleration of the conveyor is less than the gravity acceleration g, the particle moves forward due to the difference between forward and backward slides which arise between the particle and the conveyor surface. And when maximum vertical acceleration is greater than g, the particle moves forward due to forward and backward slides and jump in space. Path of progressive motion of the particle and progressive speed obtained from the experiment coinside with results of the analysis.
Trapping phenomenon of carriers in Ge at low temperature is studied by the method of photoconductivity decay time measurement on various crystals that contained Cu and dislocations. The carrier capture is considered to occur at many levels corresponding to multiple charged conditions. Crystals with no dislocation or with controlled concentration are used for the experiment. Cu, which is a recombination center in Ge at room temperature, becomes a full hole trap below -100°C and both the decay time and the photoconductivity increase markedly. Samples with higher Cu concentration show longer decay time at low temperature, and those with higher donor concentration show shorter decay time which shows that the shift of Fermi level is not the only cause for the appearence of trap at low temperature. Electron capture cross section of the third level of Cu in Ge is found to have a temperature dependence in the form σn3∞ exp (-ε/kT), ε=0.25 ev. As to the dislocations, both the decay time and photoconductivity decrease with falling temperature, which rather favors the 1-level model of recombination.
Intensity and energy spectrum of scattered gamma-rays in labyrinth of Co-60 3000c irradiation facilities are measured with chamber type detectors and a scintillation spectrometer. The problems involved are the difference between radiations in two sections of the labyrinth, the contribution of scattered-rays to spacial dose-rate, the estimation of dose-rate and so on. Scattered rays that come into the labyrinth are experimentally confirmed to be composed of photons produced by soft component of the energy; this soft component ranges 100_??_200 KeV and is multi-scattered within the shielding walls. Dose-rate in the labyrinth can be expressed approximately as the product of the amount of the source, specific gamma-ray emission, two geometrical factors determined by the shape of the labyrinth, and energy reflecting coefficient. On the assumption that the labyrinth is simple in shape, calculated results agree fairly well with observed.
Effect of moisture content on thermal conductivity of porous materials has been investigated. As the most ideal samples, calcarious sandstones of various kinds, different in porosity and small in content of water soluble matter, are chosen. For measuring the thermal conductivity, the comparison method was used. Temperature difference between two opposing faces of sample plate is kept as small as possible to lessen the influence of vapour diffusion in the sample caused by the difference in partial pressure of the vapour. The moisture content is represented by volume percentage of free water contained in the sample. The thermal conductivity is obtained as a function of moisture content with the temperature as parameter. This functional form is found the same in trend for all the samples, formulation of which is difficult because of three dimensional irregularity of the sample structure. The relation between thermal conductivity and porosity can be explained by a formula derived by the author if the empirical exponent n of the formula is taken as 2.
Activation energies for creep of zinc crystals are observed in a temperature range of 100-400°K. Above room temperature the creep of zinc is believed to be associated with dislocation climb since the experimentally determined activation energy for creep is about 26.0 Kcal per mol and is about equal to the energy for self diffusion. Below room temperature the activation energy for creep decreases with decreasing temperature. The diffusion at low temperatures is considered to be considerably less than that at high temperatures. Hence at low temperatures, the creep will not be associated with dislocation climb; some other model for creep should be considered. Suzuki suggested that creep of metals is controlled by the rate of nucleation of dislocation loops which are formed when the segments of dislocations pinned by solute impurity atoms moved, leaving the solute atoms behind. The values of activation energies for creep of zinc calculated by the author on the basis of Suzuki's model agreed with the observed values in low temperature range.
Permeation rate of gas through thin polymer membranes of high diffusion constant is often determined by not only the diffusion in the membrane but also the adsorption and desorption on the membrane surface. In such cases, if the measurement is made on membranes, one side of which is coated by evaporated metal film of “lake” structure, contribution of these three different processes to the total permeation resistance can be separately estimated. This paper presents the theoretical basis of the above method and the results of measurement made on cellophane of 50 microns in thickness which shows that the resistances to the three processes are of the same order of magnitude.
A practical gridded ionization chamber for spectroscopic identification of alpha-emitting nuclides has been constructed. The chamber is designed to use counting gas of 3.5 atm. pressure so that alpha energies of all natural alpha emitters (_??_10 MeV) can be measured. A new type sample changer which can be operated under such high pressure has been devised. With this device, five samples can be measured successively without opening the chamber. Commercially available PR gas as counting gas, model A-1 D amplifier and RF high voltage supply are used. The energy resolution of the chamber is about 1.1% for polonium alpha particles (5.3 MeV). The drift of pulse height is about 1% in a 24 hour measurement. Background counts are 5 to 6 counts/hour above 3.5 MeV.
Ceramic manganese-zinc ferrites which contain small amounts of SiO2 and CaO have high electrical resistivity as well as anomalously large dielectric constant. In these properties, however, considerable dispersions have been observed in radio-frequency range. The anomalies are considered to result from heterogeneous dielectric structure in which constituting grains are separated from one another by resistive layers. The resistivity and the thickness of the layer are estimated to be 105106 Ω-cm and 10-7-10-6cm, respectively.
An analog computor has been built for the analysis of crystal structure by the method of minimum function which was developed by M. J. Buerger. Intensity modulated map of the Patterson function is affixed on a cylinder which rotates and axially translates back and forth. Electric signals of the Patterson function as given by reflection of light are picked up by a set photocell. Thus the whole picture is scanned. Another photocell, set at a different position, picks up the signals of the same map, these signals differing in phase from the former by a constant amount. Selecting-out of weaker one of the two signals by a minimizer gives the M2 function on cathode ray display. M4 function can be obtained by simultaneous use of four photocells.