Green with Complexity

Green with Complexity - PERSPECTIVES be designed into a...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
portion of the chute, thus thwarting demixing. The idea is reminiscent of droplets in zigzag- ging channels aimed at generating chaotic mixing in the drops ( 13 ). Extensions of the zigzagging idea have practical consequences. Baffles have long been used in mixing tumblers, but were designed by trial and error. Usually, short baffles were attached to the outer wall of the container (see the second figure, left). In fact, the best mixing is achieved with long internal baffles (see the second figure, right) ( 6 ). Physical understanding, computational and theoretical approaches ( 14 16 ), and experimental capabilities ( 17 ) are now suffi- ciently mature so that mixing or demixing can be designed into a system with a reasonable probability of success. The next challenge is extending the ideas to three dimensions. Recent theoretical work on mixing a single class of particles in three-dimensional tum- blers ( 18 )—a far simpler case than mixing two classes of particles—suggests an explosive increase in the richness of problems that may be encountered when tackling mixing and demixing of granular materials. References 1. J. B. Knight et al ., Phys. Rev. Lett. 70 , 3728 (1993). 2. M. E. Mobius et al ., Nature 414 , 270 ( 2001). 3. T. Shinbrot, F. J. Muzzio, Phys. Rev. Lett. 81 , 4365 (1998). 4. S. B. Savage, C. K. K. Lun, J. Fluid Mech. 189 , 311 (1988). 5. S. Ulrich et al ., Phys. Rev. E 76 , 042301 (2007). 6. D. Shi et al ., Phys. Rev. Lett. 99 , 148001 (2007). 7. K. M. Hill et al ., Complexity 10 , 79 (2005). 8. N. Jain et al ., Phys. Rev. Lett. 86 , 3771 (2001). 9. P. W. Anderson, Science 177 , 393 (1972). 10. A. Brucks et al ., Phys. Rev. E 75 , 032301 (2007). 11. G. D. R. MiDi, Eur. Phys. J. E 14 , 341 (2004). 12. H. Li, J. J. McCarthy, Phys. Rev. Lett. 90 , 184301 (2003). 13. M. R. Bringer et al ., Phil. Trans. Roy. Soc. London A 362 , 1087 (2004). 14. M. Moakher et al ., Powder Tech. 109 , 58 (2000). 15. D. C. Rapaport, Phys. Rev. E 75 , 031301 (2007). 16. S. W. Meier et al ., Adv. Phys. 56 , 757 (2007). 17. S. L. Conway et al ., Chem. Eng. Sci. 60 , 7091 (2005). 18. www.maths.leeds.ac.uk/~rsturman/pwi_mixing.html 19. S. J. Fiedor, J. M. Ottino, Phys. Rev. Lett. 91 , 244301 (2003). 20. S. W. Meier et al ., Phys. Rev. E 74 , 031310 (2006). 10.1126/science.1152849 www.sciencemag.org SCIENCE VOL 319 15 FEBRUARY 2008 913 CREDIT: ADAPTED FROM SHAHID NAEEM PERSPECTIVES W hy the sky is blue is a matter of basic physics, but why land is green is a much trickier question. The obvious response is that land is green because it is cov- ered with plants. This answer, however, raises the question of why land is covered with plants in the face of omnipresent herbivory, which in turn raises the question of why herbivory is omnipresent in the face of omnipresent car- nivory? Why land is green, or what governs pri- mary productivity, is one of the most basic yet astonishingly complex questions in ecological research. Like a Russian matryoshka doll, each answer uncovers another question. On page
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 2

Green with Complexity - PERSPECTIVES be designed into a...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online