Characteristics of cavities trailing different projectiles penetrating water.
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Biomedical subjects
Publications and source records attributed to D T Wang.
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The characteristics of the soft-tissue wounds of the hind legs of 155 dogs produced by stainless steel spheres with four different masses and at various impact velocities were observed. It was found that when the mass of the spheres was identical, the velocity became the main factor to determine the severity of the damage; when the mass of the spheres was different but their kinetic energy was similar, then a smaller but faster sphere produced more severe damage than a larger but slower one. Shallow but wide and severe wounds usually resulted. The rate of disability of extremities with such wounds was very high. These wounding properties of steel spheres have caused some new problems in the treatment of war injuries.
The wounding effects of small fragments of the same weight (0.44 gm) but different shapes and at different impact velocities (708-1,560 m/s) on the soft tissues of the hind legs of 156 dogs were studied. The experiments showed that velocity was the major factor in causing wounds. For fragments of the same shape, the energy transmission, volume of wound cavity, sectional areas at entrance and exit, and amount of tissue that had to be excised increased rapidly with increasing velocity. In particular, as the velocity reached about 1,500 m/s, a shallow and wide wound tract was liable to occur, peripheral tissue lesion was relatively apparent, even extended to the whole leg, and the rate of occurrence of bone fracture was high. The wounding effect of the shape of the fragment closely related to its sectional specific weight (W) and drag coefficient (CD). Given the weight of the projectile and the density and thickness of the tissue, the energy transmission (delta E) was directly proportional to the square of the velocity and to the drag coefficient, and inversely proportional to the sectional specific weight of the fragment. Therefore, under certain conditions, reducing the sectional specific weight often increased the drag coefficient, in favour of causing a wound. In this experiment, the extent of wounds caused by the triangular, the square, and the cylindrical, and the spherical fragments decreased in that order, in agreement with their values of sectional specific weight and drag coefficient.
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To better understand why some mothers talk to their children about sex and others do not, we examined the role of two social cognitive variables--self-efficacy and outcome expectancies--in explaining sex-based communication. The present study was part of a larger study to test the efficacy of two HIV prevention programs for mothers and their adolescents. Mothers and their adolescents were recruited from a large community organization that serves youth who live in disadvantaged circumstances. The sample for the present study included 486 mothers who averaged 38.4 years of age (SD = 6.73). The majority were African American (97.7%), not married (66.7%), and had a high school degree (89.5%). Their adolescents ranged in age from 11 through 14 years of age and most were male (61.3%). The results of the analysis revealed that mothers who expressed higher levels of self-efficacy and more favorable outcomes associated with talking to their children about sex were more likely to do so. In a regression analysis, we learned that the mother's degree of efficacy beliefs, along with her expected outcomes associated with talking about sex, the importance of religious beliefs to her, and the age and sex of her adolescents were important factors associated with talking with them about sex.
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