The heat conduction involving a change of phase such as that of a slab melting from its surface is a problem mathematically nonlinear-Therefore, if specified boundary-ondifiunss are not given., exact solution is yet to be found. In this report, an approximate solutionn which gives the location of the boundary between solid and liquid (melt line) is derived by the “heat balance integral” method when the surface tempeaat d on time and the slab melts from its surface. The relation between the distance of the melt line from the surface and the time required for the melt line to cover this distance is repreiented by a differential equation. Fsecially when the is a linear function of time, solution of this iequation can be obtained. An approximate solution of this equation is applied to the problem of drying mold. In order to find the degree of dryness of mold, temperature distribution in the sample mold placed in a drying furnace is measured. The results of numerical calculation agree with the results of this experiment.
In a previous work, skimmed milk powder containing moisture from 6 to 7% was found to. show an anomalous property relating to the heat of sorption of water, which was considered attri-butable to particular hygroscopicity of lactose. To confirm this postulation, dielectric properties and gravimetric isotherms of samples of powder moistened in various degrees are investigated. Investigations are further made on the surface and crystallinity of the powder particle under elec-tron microscope and by X-ray diffraction method respectively. Apparent dielectric constant of the powder particle in air, ε', decreases steadily with the increase of frequency of applied potential; in a low frequency region, it increases greatly with the moisture content. The linear relation known to exist between (ε' -1)/(ε' + 2) and moisture content shows an abrupt discontinuity at about 8% of moisture content which is above the amount of monolayer adsorption. This is due to the amorphous lactose becoming crystallized by hydration as evidenced by X-ray spectrum. Minute hollows on the particle surface with outlets of capillaries are about 100Å in depth; in all probability, they trap water in the form of capillary condensation.
Faculty of Engineering, Osaka University, Higashinoda, Miyakojima, Osaka The rise of surface temperature of a glass substrate during vacuum deposition is measured from the variation of electric conductivity of deposited germanium thin film with temperature. The temperature rise is considered to be caused by (1) the heat radiation from evaporator which, is heated at a high temperature, (2) the kinetic energy of atoms that come flying from the evapo-rator to the substrate, and (3) the heat of condensation which is generated on the film when the deposited atoms occupy the stable lattice points. Results of calculations and measurements show that, if the temperature of the evaporator is high, (1) plays the predominant role, but, if the tem-perature of the evaporator is low, (3) becomes important, and (2) is always negligible. And the increase of resistance of germanium film observed in a few minutes immediately after the deposi-tion is found attributed to the fall of film temperature.
Solarization of various kinds of glass-hard glass of mercury lamp for copying, soda glass, quartz glass etc. -by exposure to ultra-violet rays from a quartz tube mercury lamp is measured and their cut-off characteristic in ultra-violet region is examined with the following results. (1) Some solarization is caused in every sample of glass during the first 20 hours of alto-gether 100 hour exposure to strong ultra-violet rays; during the rest 80 hours, the solarization remains practically unchanged. (2) On the surface of soda glass, a thin white film is formed by 20 hours exposure to the rays, lowering the transmittance because of the film which can be wiped off, leaving the glass not much affected. (3) One way of representing the solarization is to use a diagramatized model of cut-off characteristic of glass.
Volume dilatometric, dynamic mechanical and dielectric measurements and creep test are made on seven kinds of asphalt differing in the extent how far the blowing is processed. With the in-crease of asphaltene content, the glass transition point shifts to a higher temperature and the in-tensity of glass transition becomes weaker, and, at the same time, both the viscosity and retardation time of elastic deformation undergo a conspicuous increase, while the equilibrium elastic compliance remains almost unaffected. Such behavior is interpreted as indicating that the viscoelasticity of asphalt is essentially due to Brownian motion of maltene molecules, on which asphaltene molecules have a suppressing effect. Both the free carrier of electric charge and the electric dipole increase in number with increas-ing asphaltene content. The dipoles are believed to be mostly ester groups as proved by infrared absorption.
Some improvement made on the procedure of measuring the resistivity of semiconductor ma-terial by two- or four- point probe a. c. method is described. In the a. c. measurement, elimination of the current probe stray capacitance to ground is important, and for this purpose a differential amplifier is used in the input circuit. To obtain the accuracy of 2% in error over the whole range, the amplifier must have a good common mode rejection ratio, a linear characteristic over the range of 80 db, and an input resistance greater than 50 megohms, which also reduce the error due to the parasitic ground capacitance of the voltage probe to become less than 0.01 per cent. The measurable range of resistivity is from 0.001 to 10, 000 ohm-cm. The V-I characteristic at each point contact differs depending upon whether the surface is mechanically polished or chemically etched. As the surface becomes cleaner, the rectification becomes remarkably appeared. Measured resistivity of a smooth specimen is always lower than its bulk resistivity because of injection of minority carriers. To minimize such an error, a sandpaper-polished rough surface is to be used and also the output waveform is to be monitored by an oscilloscope. Thus, the reduction of error on contact potential and the raising of sensitivity become easier by the a. c. method than by the d. c. method.
The accuracy of a multi-channel pulse height analyzer (M. C. P. H. A.) rests on its component parts concerning their characteristics, among which the linearity of A-D conversion, the stability of digital computer, the linearity of linear amplifier and the linearity of D-A conversion are important, the first two in particular because of large influences they have on the over-all characteristics of the M. C. P. H. A., especially on the linearity and resolving time with respect to radiation energy, the durable stability of channels, the dead time and the number of available channels. The 100 channel pulse height analyzer and 400 channel pulse height analyzer reported in the previous paper were examined for these characteristics. The result assures their practicability.
The variation of photoelastic and mechanical behavior of cross-linked polymers, such as, phenolic, epoxy resins, diallylphthalate (DAP) polymer, styrene-divinylbenzene (S-DVB) copolymers, and methylmethacrylate (MMA)-DAP copolymers, has been studied between 20°and 200°C. A large change of the stress-optical coefficient is observed in the glass transition region. At temperatures above this region, suitably cross-linked polymers show photoelastic behavior corresponding to entropy elasticity, but too much cross-linked ones do not show it perfectly. The effect of copoly-merization ratio on the stress-optical coefficient has been studied in S-DVB and MMA-DAP copoly-mers. The DVB content affects the coefficient considerably in the entropy elasticity region but negligibly in the glassy state. The value of Δn/σ extrapolated to zero degree of cross-linkage agrees well with that of the linear polymer. The reversal of the sign of stress-optical coefficient in the glass transition region is observed for S-DVB copolymers but not for the others. The stress-optical coefficient of MMA-DAP copolymers in both glassy and rubbery states and the stress-optical coefficients of respective monomors are not additively related. Generally the degree of cross-linkage affects remarkably the stress-optical coefficient in rubbery state, differing from the result of statis-tical theory of rubbery photoelasticity. From photoelastic data, the values of the optical anisotropy (αl-α2) are derived. The photoelastic behavior of polymers can be explained by applying a model in which two photoelastic effects corresponding to glassy and rubbery elasticities are considered.