Mechanism Of Ring Formation Research Articles

Ring formation of Kirkendall voids in Pb-alloy thin-film diffusion couples

Ring formation has been observed in thin-film diffusion couples consisting of a 400-nm-thick Pb0.71Bi0.29 (in weight fraction) or Pb layer above a 200-nm-thick Pb0.84In0.12Au0.04 layer with a very thin (∼6 nm) rf-grown oxide diffusion barrier in between. When interdiffusion was initiated by a rupture in the oxide barrier, concentric rings were observed to form in Pb-Bi or Pb layer centering at the rupture site as interdiffusion proceeded. Rings were found to be a string of voids resulting from Kirkendall interdiffusion. In addition, relatively high concentrations of indium and oxygen were found at rings. Although the mechanism for ring formation is not clear at present, factors which influence ring formation are discussed.

A vortex theory of animal flight. Part 1. The vortex wake of a hovering animal

The distribution of vorticity in the wake of a hovering bird or insect is considered. The wake is modelled by a chain of coaxial small-cored circular vortex rings stacked one upon another; each member of the chain is generated by a single wing-stroke. Circulation is determined by the animal's weight and the time for which a single ring must provide lift; ring size is calculated from the circulation distribution on the animal's wing. The theory is equally applicable to birds and insects, although the mechanism of ring formation differs. This approach avoids the use of lift and drag coefficients and is not bound by the constraints of steady-state aerodynamics; it gives a wake configuration in agreement with experimental observations. The classical momentum jet approach has steady momentum flux in the wake, and is difficult to relate to the wing motions of a hovering bird or insect; the vortex wake can be related to the momentum jet, but adjacent vortex elements are disjoint and momentum flux is periodic.The evolution of the wake starting from rest is considered by releasing vortex rings at appropriate time intervals and allowing them to interact in their own velocity fields. The resulting configuration depends on the feathering parameterf(which depends on the animal's morphology);fincreases with body size. At the lower end of the wake rings coalesce to form a single large vortex, which breaks away from the rest of the wake at intervals. Wake contraction depends onf; the minimum areal contraction of one-half (as in momentum-jet theory) occurs only in the limitf→ 0, but values calculated for smaller insects of just over one-half suggest that the momentum jet may be a good approximation to the wake whenfis small.Induced power in hovering is calculated as the limit of the mean rate of increase of wake kinetic energy as time progresses. It can be related to the classical momentum-jet induced power by a simple conversion factor. For an insect or hummingbird the usual momentum-jet estimate may be between 10 and 15% too low, but for a bird it may be as much as 50% too low. This suggests that few, if any, birds are able to sustain aerobic hovering, and that as small a value offas possible would be necessary if the bird were to hover.Tip losses (energy cost of the vortex-ring wake compared with the equivalent momentum jet) are negligible for insects, but can be in the range 15–20% for birds.

河ますの成長及び死亡

1. Effect of variations of water temperature on the growth rate. It is believed that the rings on the scale, otolith and centrum of vertebral bone are formed annualy by the cyclic variation of water temperature. Then, if we culture fishes in water of constant temperature, scale rings will not be formed. In order to ascertain this point, I kept trouts at Oizumi experimental station of Tokyo College of Fisheries (Long. 138°24' Lat. 35°50', Height 1000m) from April, 1943 to June, 1945. The result is shown in Table 1 and Fig. 2. From these results we can conclude that growth rate is not constant even if water temperature is constant. Consequently we can not assume that mechanism of ring formation are due to the variation of water only. II. On the determination of death rate. Few results of the determination of death rate of fish by rearing experiments are published. We can get the death rate of traut from the above experiment. I counted dead fish one by one every day and I got a 10 days total of them. The result is shown in Table 2 and Fig. 3-4.