A numerical study of bifurcation in laminar flow in curved ducts

The bifurcation phenomenon whereby multiple-vortex secondary flow occurs in place of the normal two-vortex flow in laminar flow in curved ducts has previously been studied numerically by several researchers. However, the various results have been conflicting on many points. The present paper describes a set of numerical experiments conducted to study the effect of numerical accuracy on the solution. The results show that the transition from two- to four-vortex structure depends strongly on the differencing scheme and to a lesser extent on the grid size. The study also shows that as the Reynolds number of the flow increases, a two-vortex structure is re-established via a path which involves strongly asymmetric secondary flow patterns. These results are in agreement, at least qualitatively, with recent experimental theoretical and numerical results.     

Analysis of three-component soil structures

Impregnated soil blocks were collected from a tillage trial at Condobolin, New South Wales. The object of the trial was to examine the consequences of performing the first tillage operation of the season on different dates. It was apparent that the soil broke up on tillage into the usual range of aggregate sizes plus a dust which was presumably composed of micro-aggregates. This was apparent on sections through the blocks which showed three components: voids, aggregates and dust.A statistical method for quantifying soil structure, developed earlier, is extended to include three components. Since this involves a large number of transition probabilities, two approximate simplified methods were tested. One of these, here called the ‘grey-state method’, could be widely applied in structure studies using automatic scanning devices where features brighter or darker than some adjustable threshold level are detected.The results show that the most recently tilled plot had the coarsest structure, but that the earlier two treatments were not significantly different from each other. The usual trend of decreasing aggregate size and decreasing porosity with increasing depth was not observed. Instead, there appeared to be some inversion of the usual layering of tilled soil which is attributed to the use of a motor-driven rod-weeder.     

Densely mapping the phase diagram of cuprate superconductors using a spatial composition spread approach

A novel spatial composition spread approach was used successfully to deposit a 52-member library of La_2?xSr_xCuO₄ (0 ? x ? 0.18) using magnetron sputtering combined with physical masking techniques. Two homemade targets of La₂CuO₄ and La_1.82Sr_0.18CuO₄ were sputtered at a power of 41 W RF and 42 W DC, respectively, in a process gas of 15 mTorr argon. The libraries were sputtered onto LaSrAlO₄ (0 0 1), SrTiO₃ (1 0 0) and MgO (1 0 0) substrates through a 52-slot shadow mask for which a ?20 V substrate bias was applied to prevent resputtering. The resulting amorphous films were post-annealed (800 °C for 1 h then at 950 °C for 2 h) in a tube sealed with oxygen gas. Wavelength Dispersive Spectroscopy (WDS) analysis revealed the expected linear variation of Sr content from 0 to 0.18 with an approximate change of 0.003 per library member. Transport measurements revealed superconducting transitions as well as changes in the quasiparticle scattering rate. These transitions and scattering rate changes were mapped to produce the T-hole concentration phase diagram.