Why the Brazil nuts are on top.Why the Brazil nuts Brazil nut, common name for the Lecythidaceae, a family of tropical trees. It includes the anchovy pear (Grias cauliflora), a West Indian species with edible fruit used for pickles, and several lumber trees of South America, e.g. are on top When a can of mixed nuts--or powders, balls or otherparticles--is shaken, why does the largest nut end up at the surface, even if it is much denser than the others? That is what researchers at Carnegie-Mellon University in Pittsburgh set out to discover with computerized computerized adapted for analysis, storage and retrieval on a computer. computerized axial tomography see computed tomography. Monte Carlo simulations Monte Carlo Simulation A problem solving technique used to approximate the probability of certain outcomes by running multiple trial runs, called simulations, using random variables. of a shaken can containing large and small balls. In the March 9 PHYSICAL REVIEW LETTERS Physical Review Letters is one of the most prestigious journals in physics.[1] Since 1958, it has been published by the American Physical Society as an outgrowth of The Physical Review. , Anthony Rosatoand his co-workers conclude that the size difference among balls makes it more likely that a small, rather than a large, ball will fill a void that may open during the shaking process; for a large ball to move down in the can, several small balls must simultaneously move out of the way, whereas it only takes the movement of one large ball to create a void that several small balls can fall into. The researchers write that the extent of this size-segregationdepends on the relative sizes of the balls and the distance the balls are lifted during shaking. Rosato, who is now at the New Jersey Institute of Technology in Newark, says these and other studies of size-segregation (SN: 5/3/86, p.282) may help settle some problems associated with powder mixing, which is an important part of the powder metallurgy powder metallurgy Fabrication of metal objects from a powder rather than casting from molten metal or forging at softening temperatures. In some cases the powder method is more economical, as in making metal parts such as gears for small machines, in which casting would , pharmaceutical, glass and paint industries. |
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