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A new convection scenario in granulates under geometrical restriction

Friday 9th January 2009 - 12:35 to 13:00
INI Seminar Room 1
An experiment is presented that extends the diversity of pattern forming phenomena found in granular media. A flat container (Hele-Shaw cell) is filled with a granular mixture and slowly rotated about its horizontal long axis. The filling fraction is crucial for the observed effects. At partial filling of the container, the material can be fluidised during rotation and patterns of axially segregated stripes appear which undergo slow coarsening. On longer timescales the onset of periodically travelling stripes are observed. This effect resembles stripe patterns commonly found in rotating drums. A novel interesting phenomenon emerges under geometrical restrictions when the container is nearly filled. Although the particles are on the brink of jamming, and their mobility is almost inhibited, we observe regular convection rolls that are accompanied by, and decorated by a conspicuous serpentine segregation pattern. In contrast to the loosely moving beads at partial filling, the particles move in collective clusters. Furthermore the number of convection rolls is long-term stable and only related to the container geometry. Even though there are some superficial similarities to well known convection rolls in vibrated granular systems, there are striking differences concerning driving forces, segregation patterns, and number of rolls. Our system complements convection phemonena found in agitated granulates and brings up new questions that are discussed in the study.
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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons