Loosely packed spheres.Loosely packed spheres Uniform ball bearings ball bearings n → roulement m à billes poured into a large pitcher would most likely fill between 60 and 63 percent of the space inside the container. Those limits, originally determined by experiment, represent the range over which random packings of uniform spheres can rest in stable arrangements. Such random packings have long been of interest as models for the arrangement of atoms in simple liquids and glasses. George Y. Onoda and Eric G. Liniger of the IBM (International Business Machines Corporation, Armonk, NY, www.ibm.com) The world's largest computer company. IBM's product lines include the S/390 mainframes (zSeries), AS/400 midrange business systems (iSeries), RS/6000 workstations and servers (pSeries), Intel-based servers (xSeries) Thomas J. Watson Research Center The Thomas J. Watson Research Center is the headquarters for the IBM Research Division. The center is on three sites, with the main laboratory in Yorktown Heights, New York, 45 miles north of New York City, a building in Hawthorne, New York, and offices in Cambridge, in Yorktown Heights, N.Y., have now taken a closer look at the lower limit on packing density. Their experiments show that the fraction of space occupied by randomly packed spheres in arrangements that can still support a load can be as low as 55.5 percent -- if the gravitational grav·i·ta·tion n. 1. Physics a. The natural phenomenon of attraction between physical objects with mass or energy. b. The act or process of moving under the influence of this attraction. 2. force acting on the spheres is in effect zero. Their results appear in the May 28 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. . To minimize the effects of gravity. Onoda and Liniger immersed glass spheres, about 250 microns in diameter, in a liquid with a density close to that of the spheres. After letting the spheres settle gently in the liquid-filled, 500-milliliter graduated cylinder, they measured the fraction of space that the randomly placed spheres took up within the container. The fraction they obtained corresponds to a continuous, rigid network of touching spheres. The researchers also demonstrated that this packing fraction seems to determine the onset of dilatancy di·la·tan·cy n. pl. di·la·tan·cies 1. The increase in volume of a granular substance when its shape is changed, because of greater distance between its component particles. 2. , an important property of granular materials such as sand. Dilatancy occurs when particles must spread apart in order to move past each other in response to a shear force applied to the material. That causes the overall volume occupied by packed particles to increase. The research results show that the packing fraction must be higher than 0.555 for dilatancy to occur. |
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