From: jmfbahciv@aol.com Subject: Re: Packing Density of Bricks Date: Thu, 23 Mar 00 12:24:28 GMT Newsgroups: sci.physics,sci.math Summary: [missing] In article , meron@cars3.uchicago.edu wrote: >In article <8bad3c$icm$10@bob.news.rcn.net>, jmfbahciv@aol.com writes: >>In article , meron@cars3.uchicago.edu wrote: >>>In article <8b88dk$m0q$1@news.panix.com>, erg@panix.com (Edward Green) >>writes: >>> >>>>Suppose I have a dump truck full of bricks, which I dump into a random >>>>heap. What is the packing density of the resulting pile? How might I >>>>intelligently estimate such a thing? >>> >>>As I recall, the above problem for spheres is still not solved (though >>>it has been around for a long time). Now you're asking about >>>bricks?:-) Hmm... well, assuming point bricks .... >> >>I thought that the hexogonal stacking was proved. There was >>an article about it in Science News but you're going have to >>pay me to go look for it :-). >> >That's just what I was referring to. There was a claim that it is >solved, then some faults were found with the proof and then ... I lost >track. I tried to look for the article but couldn't find it. One of my pasttimes is to solve the forward-referencing problem but I haven't been able to eliminate the human factor...yet. :-). >> >>Also, maybe 1-1/2 years ago, there was an article in the same >>mag about about some guys who figured out this stuff about >>sand. Their goal was to figure out how to adjust the flow >>such that a pile of sand won't cave in on itself. >> >Was it by a guy named Bak? You're asking someone who occasionally forgets her own name :-). I found this article. It's called "Dry Sand, Wet Sand: Digging into the physics of sandpiles and sand castles" by Ivars Peterson, Science News, Vol. 152, September 20, 1997, pp. 186, 187. The article cites other publications: Science News: 7/14/89, p. 40 October 1996 _Reviews of Modern Physics_, H.M. Jaeger and S. R. Nagel of UofChicago and R.P. Behringer of Duke U. These guys worked with glass beads and used polarized light (interesting method) to measure stress, finding that the walls carry much of the weight. S.N. Coppersmith of UofC tried to build a model but seems to have found problems with "formulating equations embodying the observation that the particles rest against each other without sticking". I don't know what that means but it seems to have to do with 3-dimensional forces between grains. I don't understand this. She [Coppersmith] is quoted to say "you have too many unknowns and not enough equations". There seems to be an article investigating geometric aspects of granular packing, J.H. Herrman of U. of Stuttgart, describing a model in Aug. 25 Physical Review Letters (I'm assuming the year is 1997). They got ispired by the Tetris game and then the article talks about a notion called geometric frustration. This must be Ed's bricks. Then the article slues back to Nagel, talking about jamming and mentioning a program organized by Nagel September, 1997 at the Ins. for Theoretical Physics at U.of California, Santa Barbara. Then this Sci. News article talks about an experiment described by Peter Schiffer, Albert-Laszlo Barabasi at Notre Dame to study differences between wet and dry sand in June 19 Nature (I'm again assuming that the year is 1997). But I don't see a mention of anyone named Bak. There's a lot more stuff in the article that I don't mention. /BAH Subtract a hundred and four for e-mail.