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This paper presents a three-dimensional fluid-structure-coupled simulation of a flexible caudal fin with different trailing-edge shapes. The influences of caudal-fin shape on hydrodynamic performance are investigated by comparing the results of a simplified model of a square caudal fin with forked and deeply forked caudal fins under a wider range of non-dimensional flapping frequency, 0.6 < f* < 1.5, where f* is the ratio of flapping frequency to the natural frequency of each caudal fin, i.e., f* = f / f n . The leading edge of each caudal fin is forced to oscillate vertically in a water tank with zero free-stream conditions. The numerical results show that the amount of forking in the geometry of the caudal fin has significant effects on its hydrodynamic performance. A comparison of thrust coefficients shows that the square caudal fin has a greater thrust coefficient in the non-dimensional frequency range of 0.6 < f* < 1.2, while the deeply forked caudal fin generates higher thrust when 1.2 < f* < 1.5. In terms of propulsive efficiency, the square caudal fin is more efficient when 0.6 < f* < 0.9, while the propulsive efficiency of a deeply forked caudal fin is significantly enhanced when 0.9 < f* < 1.5. Based on our results, the deeply forked caudal fin has greater thrust coefficients and a higher propulsive efficiency in a higher frequency range than the natural frequency of each caudal fin. The thrust characteristics and flow fields around each caudal fin are investigated in detail.

The aim of this study was to investigate the effect of perfluorocarbon on the respiratory status of newborn mice with pulmonary hypoplasia without diaphragmatic defects, following intrauterine exposure to nitrofen. Three groups of newborn mice were compared: pups exposed to nitrofen antenatally without (group A) or with (group B) perfluorocarbon treatment and pups not exposed to nitrofen as a control (group C). Respiratory evaluation was performed by scoring, pressure-volume analysis, and histological examination. At 40 minutes after birth, the survival rates in groups A, B, and C were 51%, 94%, and 95%, respectively. The clinical scores of group B mice at 40 minutes were significantly better than those of group A mice in which pulmonary hypoplasia was induced. In group B, the hysteresis ratio was significantly higher than that in group A, and lung histology showed a significant increase in airspace. An immunohistochemical examination showed that perfluorocarbon did not alter the expression of mature surfactant protein B and surfactant proprotein C. This study demonstrated that treatment with perfluorocarbon was useful in stabilizing critically ill mice with primary pulmonary hypoplasia during the early phase of therapy.