5. Results and discussion
5.1. Brazil nuts
In Fig. 2 we show results for a shaken polydisperse system of nuts.We observe that the system reaches a statistical steady “final” statewhere around 22%±2.8% of the Brazil nuts are on the surface. In thissystem there are enough Brazil nuts to saturate the top surface of thebed. However we observe that only a small fraction of the top surfaceis occupied by Brazil nuts. The percentage of Brazil nuts on the surfacewas calculated by dividing the number discernable on the surface bythe total number of Brazil nuts in the system. Fig. 2 shows a side viewof the same system for perspective of the bed depth. For comparison, we also purchased a sample of 10 cans of standard mixed nuts, whichpresumably segregated during transportation and handling, openedthe cans and counted the Brazil nuts on the surface. We observed that,on average, a similar percentage of Brazil nuts – in this case 26%±7% –are found on the surface. This is in contrast with single intrudershaking experiments with materials of similar density where thesystem reaches a final state with the large intruder on top.To identify why so few Brazil nuts are on the surface in a classicsystem that has been associated with the term the “Brazil-nut effect”,further experiments were carried out with more controlled binaryand ternary nut mixtures. We examined a binary mixture of thesmallest species (½ peanuts) and largest (Brazil nuts) from the mixednut system (Fig. 3a), and a ternary mixture of small (½ peanuts), large(Brazil nuts) and intermediate (almonds) (Fig. 3b). In the binarysystem, 30.5±2 or 39%±2.7% of all Brazil Nuts are on top. For theternary system, 18.5±0.7 or 36%±1.4% of all the Brazil nuts are ontop. The results demonstrate that as the number of species in themixture increases from binary to ternary to a mixed nut system, thepercentage of Brazil nuts on the top decreases in the “final” statisticalsteady state demonstrating the reduction in segregation. Fig. 4 is a bargraph quantifying the trend in the snapshots from Figs. 2 and 3 (bluebars). These values are also presented in Table 4 where we presentboth the number and percentage of large particles on the surface.Standard deviations from the average are presented for two points atsteady state.