Contribution to the Willowsia species having body scales of the long basal rib type: four new species and a redescription of W. qui (Collembola: Entomobryidae)

Four new species of the genus Willowsia Shoebotham, 1917 are described from China: W. fascia Zhang & Pan sp. nov., W. pseudoplatani Zhang & Pan sp. nov., W. pseudobuskii sp. nov., and W. similis sp. nov. Willowsia qui Zhang, Chen & Deharveng, 2011 is re-described based on types and fresh material. All five species possess the pointed body scales with basal ribs longer than distal ones. These scales are absent on antennae, legs, ventral tube and furca. Colour pattern and dorsal chaetotaxy are the main diagnostic characters for these species. DNA barcodes of four species are also provided, with genetic distances compared. A key to the Willowsia species having scales of the long basal rib type is given.

The Effect of Nose Blunting on the Wave Drag of Ogive Forebodies

SummaryA theoretical method is used to predict the surface pressure distribution and drag-rise characteristics of blunted ogive forebodies. The results confirm the observation that a moderate degree of nose blunting can reduce wave drag relative to that of a pointed body of the same fineness ratio. An analysis of the theoretical data provides a simple explanation of this phenomenon.

Linearized theory of axisymmetric hypersonic source flow past bodies of revolution

The linearized theory of axisymmetric hypersonic source flow past a slender pointed body is treated by using linearized potential theory, assuming that the hypersonic parameter is less than unity. The governing equation in the transformed co-ordinates with the ratio of specific heats γ = 1.5 shows a modified form relative to the equation for parallel flow, whereas that with γ = 2 shows essentially the same form. Some numerical calculations for a cone and a cone-cylinder are presented, and the surface pressure distributions obtained for both γ = 1.5 and 2 show that there is a considerable pressure-distribution difference between source flow and parallel flow. The pressure on a cone in hypersonic source flow approaches zero downstream, while, if the cone has a cylindrical afterbody, the pressure recovers to the free-stream value quickly. This suggests that the static pressure probe for supersonic parallel flow is useful also in source flow.

On optimum profiles in Stokes flow

In this paper, we obtain the first-order necessary optimality conditions of an optimal control problem for a distributed parameter system with geometric control, namely, the minimum-drag problem in Stokes flow (flow at a very low Reynolds number). We find that the unit-volume body with smallest drag must be such that the magnitude of the normal derivative of the velocity of the fluid is constant on the boundary of the body. In a three-dimensional uniform flow, this condition implies that the body with minimum drag has the shape of a pointed body similar in general shape to a prolate spheroid but with some differences including conical front and rear ends of angle 120°.