Dielectric strength of transformer insulation at DC polarityreversal

Among special insulation tests for DC power converter transformers, polarity reversal tests can be substituted by applied AC voltage tests from a stress similarity in oil ducts. In order to investigate equivalent levels of other insulation tests to polarity reversal tests, the dielectric strength of a transformer at polarity reversals was examined by use of a model of typical oil/paper composite insulation. From the comparison of polarity reversal and other insulation tests, it was found that dielectric strength of transformer insulation at polarity reversals is phenomenally similar to that under switching impulse stresses. Equivalent AC test voltage to polarity reversal test was also estimated from the experimental results. The breakdown characteristics of polarity reversal tests showed that partial discharges at polarity reversals impose less harmful stress on insulation barriers than those at usual AC or impulse tests     

Characteristics of two-phase condensing flow by visualization using computed image processing

The mechanics of the condensing behavior of vapor bubbles in a subcooled bulk flow is complicated and influenced by both heat and mass transfer. To examine the characteristics of such thermal-nonequilibrium two-phase flow, experimental and analytical researches have been made. In the experiment, the movement of each vapor bubble in a flowing channel was recorded on video tapes and analyzed by an image processing system. As result, the distributions of void fraction along the test section were obtained. In the analysis, a simple analytical model was introduced to predict the distributions of void fraction and liquid subcooling temperature. By considering the rate of vapor condensation along the flow direction, the differential equation of energy balance between two phases was obtained. Integration of this equation yielded the void fraction and bulk liquid subcooling at any position. The condensation rate was estimated as a function of the local liquid subcooling, interfacial area and mass velocity. Finally, a close fit between calculated results and experimental data was obtained.     

Application of a Two-Dimensional Computer Simulation to Cake Growth in Slip Casting with Complicated-Shape Gypsum Molds

A two-dimensional computer simulation method, developed by the authors using the method of finite differences, was applied to estimate the cake growth in slip casting of alumina with a triangular gypsum mold and a box-type gypsum mold with a convex bottom. The cake growth patterns, water penetration patterns, water flow rate distributions, and pressure distributions were simulated in the molds and/or cakes. The simulated cake growth patterns were in good agreement with those observed experimentally in both molds. Moreover, the cake growths could be well understood from the results of the water flow rate distributions in each case. The present method is applicable to cake growth simulation in slip casting with complicated-shape gypsum molds.     

Blocking Probability in Link-Frame Systems from the Viewpoint of Overflow Processes

From the development of the work concerning the overflow processes due to Palm and Taḱcs, we consider the blocking probability in four-stage type systems which are used for telephone services as speech-path connecting networks in central systems. First, the events causing failure in channel matching in the system and the stochastic properties in the system are considered. After that distribution of interval-times between the instants at which the link blocking occurs is considered from the viewpoint of overflow processes, taking into consideration the above obtained results, and finally this distribution and the blocking probability are determined.     

Noncontact transverse scan rotating head recording device

A new transverse scan rotating head recording device was investigated which is capable of high speed tracking and noncontact recording. Small tracking time less than 1 ms was obtained in a reel-to-reel tape transport by the circuit technology improving the effective resolution of a reel motor tachometer. Noncontact recording capable of more than 10⁷head scans without tape wear was achieved by the development of both a pressurized air bearing female guide and a spherical monolithic head. High track density of 12 tracks/mm was also obtained by this monolithic head.     

Parallel multipliers with NOR gates based on G-minimum adders

Based on the adders with a minimum number of NOR gates discussed in Ref. 1, parallel multiplers are designed in Ref. 2, using fewer gates, fewer connections, and faster operation than conventional multipliers based on carry-save adders. In this paper, parallel multipliers of NOR gates are designed, by expressing two numbers to be multiplied in the sign and magnitude representation unlike those in Ref. 2. The multipliers in this paper are advantageous over the carry-save adder-type multipliers known to date, in terms of the number of gates and connections.This work is supported in part by the National Science Foundation under Grant No. MCS77-09744 and MCS81-08505.     

Simultaneous manifestation of squamous cell carcinoma in identical twins with epidermolysis bullosa

We report a case of identical twins with recessive dystrophic epidermolysis bullosa, who developed squamous cell carcinoma in the hand at the latter half of their third decade. To our knowledge, this is the first case of manifestation of squamous cell carcinoma in identical twins and may contribute to the understanding of oncogenesis in such patients.