In order to study the effect of aging on the mechanical strength of thermoformed thermoplastics, we carried out uniaxial tensile test of thermoformed poly(methyl-methacrylate) (PMMA). Thermoformed and aged specimens were generally much more ductile in its longitudinal direction in comparison with the unstretched ones. The ductility of longitudinal specimens was reduced by aging. Sheets aged at a temperature of 50°C for an aging time of 50h had quite high ductility in the longitudinal direction. Yet, ductility of specimens cut in the transverse direction was little affected by aging. These data bring us to predict toughness for aging in the thermoformed PMMA sheet.

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To study the effect of aging on the mechanical strength of uniaxially thermoformed thermoplastics, we carried out uniaxial tensile test of thermoformed poly (vinyl chloride) (PVC) aged for varios time periods. The ductility of thermoformed specimens in the direction transverse to that of stretching was reduced by aging. At a high elongation ratio, the ductility in the direction of stretching was not reduced by aging. Thus, the ductility is probably dominated by not only the relaxation from the quenched structure but also the relaxation of strongly stretched polymer chains. These data bring us to predict the thermoforming condition avoiding the reduction of ductility for aging.

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ラッピング加工は，仕上げ面の精度や品質が極めて高く，精密加工の最終仕上げ法として多用されている．しかし，研削に比べ単位時間あたりの加工量が小さいため，電子部品用基板や高精度機械部品の量産分野では，ラッピングの加工量向上に関する要望が強い．本研究では，模擬ラッピング装置を使用し，ラッピング加工中の遊離砥粒の挙動を可視化し，加工にあずかる砥粒量を増加させる方法を見出している．定盤上の砥粒保持用小穴（ピット）の上端部のバリを除去することによって，加工に関与する砥粒量を増やすことができると予測し，これを検証している．得られた結果を実用に供するため，細粒の砥粒と軟質の結合材を用いたラップ定盤能力向上用修正砥石（Conditioner）を開発している．当該砥石を用いて修正した定盤を使用し研磨加工試験を実施した結果，ラップ定盤上のピットのバリが除去されるとともに，加工物には必要な表面粗さや歩留まりを維持したまま，4割程度の定盤寿命の増加を実現している．Conditionerは従来のラッピング工程中においても簡単に使用できるため，ラッピング加工の生産性向上に寄与できる．

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In order to examine the effect of thermoforming process on the fracture behavior of thermoplastics, uniaxial tensile tests and deformation recovery measurements at heating were carried out for uniaxially stretched poly(methyl methacrylate)(PMMA). In spite of the development of tensile stress during rapid cooling processes, stretched specimens were much more ductile than undeformed ones. Plastic strain frozen in the thermoformed specimens was recovered at heating only in the glass transition range. Thus, the molecular structure of the stretched PMMA was supposedly free from the localization of strain energy which is probably a key factor reducing the static strength of thermoplastics. The smoothness of the specimen surface probably improved by stretching was also likely to contribute to the increase of ductility for the PMMA.

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Optimum strength of polyvinyl-chloride (PVC) sheet thermoformed by uniaxial stretching was studied by mechanical test, thermally stimulated deformation recovery and structural observation using polarized light. In spite of tensile stress evolution during rapid cooling of thermoformed sheets, their deformation recovery behavior at reheating showed no evidence of storage of strain energy probably lessening static strength of thermoformed sheets. Sheets thermoformed at 100°C had quite high ductility presumably due to the peculiar crystalline structure still left in PVC after thermoforming. Sheets thermoformed at 130°C showed much less ductility and was found to have no crystalline structure.

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In a shallow lake, the interaction between convective circulation and biological activities are important for material circulation. The purpose of this paper is to estimate the effect of nocturnal cooling on convective circulation and purification activities in a shallow lake. We have conducted a measurement of temperature and water quality in a littoral zone of a brackish lake, Lake Shinji, where filter-feeding bivalves (Corbicula japonica) are densely populated. To confirm the mechanism of convective circulation, numerical simulation was also carried out. Results showed that diurnal heating and nocturnal cooling created density gradients that drove strong horizontal mass exchange. Those phenomena contribute the promotion of purification.

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大阪の若年者の歯周疾患罹患状態を調べることを目的として1469名の高校生を対象とし, 61/61|16/16の pocket depth (PD) を測定し, 歯肉の炎症状態は Löe (1963) のGIで評価した。その結果, 4mm以上のPDの出現率は2.4%で5mm以上のPDの出現率は0.3%であった。各学年間にPDの分布に有意差は認められなかったが, 男子の方が女子より有意に深い値を示した。部位別の平均PD値は大臼歯部の方が中切歯部より大きく, 中切歯唇側においては隣接面部の方が中央部より大きかった。高いGI値の出現は2年生>1年生, 隣接面>頬舌面, 男子>女子であった。1ケ所でも5mm以上のPDを有する44名についてさらに口腔内精査を行い, 全身所見に異常なく, 5mm以上のPDを示す歯が3歯以上存在するにもかかわらず肉眼的に著明なプラークや歯石の認められなかった2名について1/1|1/1デンタルおよびパノラマ X-ray 撮影を行ったが, 若年性歯周炎と診断できる患者は存在しなかった。

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