Tiny metal rods can behave like a flock of birds, physicists in India report. Just like flocking birds, the half-centimeter-long tapered brass rods will orient themselves in the same direction and move en masse when sprinkled randomly onto a vibrating bed of millimeter-sized aluminum beads. But unlike, say, logs floating down a river, the rods align themselves without physically touching. Instead, the rods influence one another indirectly, the researchers reported last month in Nature Communications. - Model bird flocks that go with the flow news.sciencemag.org/physics/2014/10/model-bird-flocks-go-flow Tiny metal rods can behave like a flock of birds, physicists in India report. Just like flocking birds, the half-centimeter-long tapered brass rods will orient themselves in the same direction and move en masse when sprinkled randomly onto a vibrating bed of millimeter-sized aluminum beads. But unlike, say, logs floating down a river, the rods align themselves without physically touching. Instead, the rods influence one another indirectly, the researchers reported last month in Nature Communications. Each rod takes up energy from the vibration and begins to move. But the jiggling rod then disturbs the surrounding beads and drags them along with it. The motion of the beads then reorients nearby rods, which get dragged along in the flow like weathervanes in the wind, leading to the overall flocklike behavior. The finding could suggest an alternative to the conventional model of flocks, in which a bird aligns itself with its nearest neighbors and not through the surrounding medium. Video: Model bird flocks that go with the flow video.sciencemag.org/News/3816234233001/1 - Flocking behaviour of the non-living natureasia/en/nindia/article/10.1038/nindia.2014.133 Non-living things can also organise themselves and move in a group if rendered motile, just like formations of flying birds, according to new research on small metal beads and rods1. The insight might lead to possible new method for cellular matter transportation in the human body. Researchers at the Indian Institute of Science (IISc), Bangalore and TIFR Center for Interdisciplinary Sciences, Hyderabad dispersed millimetre-sized tapered brass rods among spherical aluminium beads on a gently vibrating surface. They were interested in studying the collective behaviour of such moving rods. They found that the motile rods dragged the beads along, and neighbouring rods reoriented themselves to move in a circle. The researchers call this phenomenon a ‘flocking transition’ where the rods go into a state of spontaneous alignment.“We were expecting the rods to show cooperative behaviour as seen in living objects”, says Ajay Sood, one of the authors.The study shows that particles far apart can influence self-organisation as opposed to the conventional thinking that they just follow their nearest neighbours. The researchers claim that their work demonstrates for the first time the ‘formation of a true flock in a collection of dry grains’. The discovery that a small concentration of motile particles can transport a large non-motile cargo might have wide applications in biological systems as well as industry, they say. Reference Flocking at a distance in active granular matter Nature Communications 5, Article number: 4688 doi:10.1038/ncomms5688 nature/ncomms/2014/140903/ncomms5688/full/ncomms5688.html PDF: arxiv.org/pdf/1402.4262v2.pdf Abstract The self-organized motion of vast numbers of creatures in a single direction is a spectacular example of emergent order. Here, we recreate this phenomenon using actuated nonliving components. We report here that millimetre-sized tapered rods, rendered motile by contact with an underlying vibrated surface and interacting through a medium of spherical beads, undergo a phase transition to a state of spontaneous alignment of velocities and orientations above a threshold bead area fraction. Guided by a detailed simulation model, we construct an analytical theory of this flocking transition, with two ingredients: a moving rod drags beads; neighbouring rods reorient in the resulting flow like a weathercock in the wind. Theory and experiment agree on the structure of our phase diagram in the plane of rod and bead concentrations and power-law spatial correlations near the phase boundary. Our discovery suggests possible new mechanisms for the collective transport of particulate or cellular matter. Supplementary information nature/ncomms/2014/140903/ncomms5688/extref/ncomms5688-s1.pdf Movies Supplementary Movie 1 nature/ncomms/2014/140903/ncomms5688/extref/ncomms5688-s2.avi A typical disordered state seen in experiments. Φb = 0.52 and Φr = 0.06. Video plays at four times the real speed. Supplementary Movie 2 nature/ncomms/2014/140903/ncomms5688/extref/ncomms5688-s3.avi A typical ordered state observed in experiments. Φb = 0.63 and Φr = 0.08. Video plays at four times the real speed. Supplementary Movie 3 nature/ncomms/2014/140903/ncomms5688/extref/ncomms5688-s4.avi A typical disordered state in bounded simulation. Φb = 0.57 and Φr = 0.06. Video plays at four times the real speed. Supplementary Movie 4 nature/ncomms/2014/140903/ncomms5688/extref/ncomms5688-s5.avi An ordered state in bounded simulation. Φb = 0.67 and Φr = 0.11. Video plays at four times the real speed. Supplementary Movie 5 nature/ncomms/2014/140903/ncomms5688/extref/ncomms5688-s6.avi A typical disordered state in simulations in a periodic box. Φb = 0.57 and Φr = 0.03. Video plays at four times the real speed. The system size is 24.2 rod lengths. Supplementary Movie 6 nature/ncomms/2014/140903/ncomms5688/extref/ncomms5688-s7.avi A typical ordered state in simulations in a periodic box. Φb = 0.61 and Φr = 0.10. Video plays at four times the real speed. The system size is 24.2 rod lengths. Supplementary Movie 7 nature/ncomms/2014/140903/ncomms5688/extref/ncomms5688-s8.avi Turning of a single polar rod in a uniform bead flow. Φb = 0.60. The video plays at real speed.
Posted on: Sun, 05 Oct 2014 00:26:11 +0000
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