In vacuum molding process, the plastic film covering the surface of the mold peels sometime during pouring. This causes defects in the casting. It was thought that factors affecting stripping off the film were the force of heat contraction of the film, the elastic force of contraction retained in the film after formation and the vacuum force on the mold.
  The main factor causing stripping of the film was the elastic force of contraction that arised on forming and retained in the film. The force of heat contraction of the film little affected the stripping of the film, and just after the film strip, caused it to rapidly contract. When pressure in the mold was higher, the film stripping tendency became greater. The pressure in the mold increased during pouring, however, the pressure difference between the mold and the mold cavity was maintained when the film was not stripped, and it was not kept when the film was stripped.

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In this essay, on the investigation of the scale of peasant mulberry tree plantation during China's Ritsuryo period, the author states that about 50 trees constituted the average amount per household, whereas 100-200 indicated a fairly large landowner, and a 1000 level plantation was considerably rare. From these results the author concludes that the item of the Agricultural Law (田令) of 731 contained in the T'ung-tien (通典) which states that one row (畝) of mulberry trees on the land held in perpetuity (永業田) contained over 50 trees, is not at all realistic, and therefore that the unit, "per row" (毎畝), is not applicable in this case. For the peasants working equally apportioned lands (均田) which had very low rates of kubunden (公分田) apportionment, it was the general practice to grow various grains and beans between the mulberry trees on the land held in perpetuity which had a higher percentage of kubunden apportionment. For this reason, the alleged scarcity of mulberry trees on lands held in perpetuity really poses no problem for such peasants. With respect to sericulture, spring sericulture was the established custom during this period, whereas summer silkworms, even though seen here and there in the Chiangnam (江南) region, were generally not raised. Summer sericulture is not an easy task in itself and, even though silk floss can be produced from the cocoons, the threads obtained are so brittle and weak that they could probably be used only for personal consumption in the weaver's household. For this reason, the assertion that summer sericulture was not only widespread but also the object of taxation cannot be proven. In the Southern Sung (南宋 1127-1279), summer sericulture became more popular to a certain degree in the regions of Chiangnam and Liangche (両浙). In contrast to this, in northern China under the Chin (金) Court (1115-1234), autumn sericulture began to be carried out, and this breakthrough may be considered as one important factor in the growth of sericulture-mulberry planting and silk-cotton weaving during China's later periods.

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