bgc

@blockspins

readin and writin

Joined January 2010

Media

  1. 18 Oct 2019
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  2. 13 Oct 2019

    from Vincenzo Vitelli's group on "edge currents" and "odd viscosity" in active chiral systems like these! (movie from tweet above: ) (movie in this tweet: ) Conclusion: from toys to active fluids, soft matter physics rules the world!

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  3. 13 Oct 2019

    A difficult and eye-opening paper: you can model the "hydrodynamics" of just about anything if you list the degrees of freedom and symmetries (or at least Tom can!). Fast-forward to a few years ago and I was fortunate to be around to witness some of the exciting developments...

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  4. 13 Oct 2019

    After seeing the absolute delight on his face, I looked up his paper with Tsai, Rodriguez, Ye and Gollub on a "chiral granular gas" that was inspired by these toys: (more movies here )

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  5. 12 Oct 2019
  6. 20 Sep 2019

    A final picture: parametric_plot( (2*(27 - 18*t^2 - 8*t^3 - t^4)/(45 - 12*t + 22*t^2 + 4*t^3 + 5*t^4), -(63 + 84*t + 26*t^2 + 20*t^3 - t^4)/(45 - 12*t + 22*t^2 + 4*t^3 + 5*t^4) ), (t,-1e5,1e5), plot_points=1e6)

  7. 20 Sep 2019
    Replying to

    The other component arises if you "flip" the smallest rhombus, collapsing the blue point to one of the other joints.

  8. 20 Sep 2019

    ... and I forgot to point out that there are actually 2 of these gadgets. 🤦‍♂️

  9. 20 Sep 2019
    Replying to

    I suspect the equation you're missing is the one that constrains these 3 points to be collinear.

  10. 13 Sep 2019

    Long ago, I learned about range expansions from a talk about this paper: Hallatschek, Hersen, Ramanathan, and Nelson, PNAS 104, 19926-19930 (2007), . This paper showed that segregation can occur just from genetic drift (small population effects).

    Fig. 1 of Hallatschek et al, 2007.
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  11. 7 Sep 2019
    Replying to

    Indeed, see . The first comment, in particular, makes reference to this delightful image, "Six Circles" by Roger Vogeler.

  12. 1 Sep 2019

    As an aside, figuring out that "higher Ling soil" = kaolin clay was tricky: the patent reads 高砱土 but it should be 高岭土, after 高岭村 (Gaoling village, see ). A related oddity: in this screenshot from the scan, you can see 砱 written in by hand! 7/6

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  13. 1 Sep 2019

    I then found a Baidu article (google translation shown) explaining that there are indeed two types: those based on a "physical change" (fitting the Reddit description) and those based on "chemical reactions" (the ones I have seem to be of that type). 4/6

    https://translate.google.com/translate?hl=en&sl=zh-CN&u=https://baike.baidu.com/item/%25E6%25B0%25B4%25E5%2586%2599%25E7%25BA%25B8/5932571&prev=search
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  14. 1 Sep 2019

    Here are photos of our sheets (sorry for the poor lighting). The texture of the gray side reminds me of a blackboard, but it still feels like paper. When the gray side is wet, it turns black. It fades to gray again as it dries. Wetting the back side doesn't have any effect. 3/6

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  15. 26 Aug 2019
    Replying to

    In a similar vein, Bragg and Nye used "bubble rafts" to visualize grain boundaries and dislocations in metals back in 1952 (!). They made an amazing film, too: (paper: )

  16. 5 Aug 2019

    Just for fun, a juxtaposition: images from letters of Johnson's to Lamonte Young and Joan Birman (the former from the interview linked above and the latter from here: )

  17. 8 Jul 2019

    The above notebook (and the other members of its family & ) were inspired by the paper "The Limit Shape of Convex Hull Peeling" by Jeff Calder and Charles K Smart:

    Figure 1.1 from Calder & Smart, "The Limit Shape of Convex Hull Peeling"
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  18. 8 Jul 2019

    Suppose you place a bunch of random points in a region and then repeatedly remove the points on the boundary of the convex hull. Over time, the boundary of the region will shrink to a point. But where will that point be?

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  19. 25 Jun 2019
    Replying to

    i.e. pairs of 5- and 7-coordinated vertices, as in this figure. Images from a classic paper by Bowick, Nelson, and Travesset that popularized the idea of "grain boundary scars" on curved crystals.

  20. 25 Jun 2019
    Replying to

    Presumably they're the only vertices with only 5 triangles around them rather than 6? If so, what you're seeing is the concentration of Gaussian curvature at those 12 points - for a more round-looking result you'll need to spread out the curvature by adding "dislocation pairs"...

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