[tt] the physics arXiv blog

Tue Jul 1 19:34:34 UTC 2008

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From: the physics arXiv blog <howdy at arxivblog.com>
Date: Tue, 1 Jul 2008 14:32:18 -0500 (CDT)
To: eugen at leitl.org
Subject: the physics arXiv blog
Reply-To: the physics arXiv blog <howdy at arxivblog.com>

[1]the physics arXiv blog

   [2]Group theory and spinal injuries

   Posted: 01 Jul 2008 12:46 AM CDT

   [3]Spinal groups 

   Medical science is stuck in the middle ages when it comes to
   understanding the causes of back pain and how to prevent it. If you
   want advice, "bend your knees when lifting" is all you're likely to
   get.

   The standard theory describing spinal injuries is known as the
   principal loading hypothesis and assumes that any damage is caused by
   one of either tension, compression, bending or shear forces on the
   spine.

   But Vladimir Ivancevic from the Defence Science & Technology
   Organisation in Edinburgh, Australia, says this is a vast
   simplification of what is really going on and has developed a far more
   sophisticated model to describe spinal damage.

   In his model, each vertebrae is able to undergo a range of
   rotations-pitch, yaw and roll-as well as a range of translations. In
   the language of group theory, these can be described by the Special
   Euclidean group SE(3).

   (An element of SE(3) is a pair (A, a) where A (- SO(3), the special
   orthogonal group of rotations,  and a (- R3. The action of SE(3) on R3
   is the rotation A followed by translation by the vector a.)

   The overall motion of the spine can then be described by composing the
   SE(3) groups for all 19 vertebrae.

   The key to Ivancevic's theory is that it is not the ordinary motion of
   the vertebrae that causes injury or even their acceleration but the
   rate of change of acceleration, the second derivative of velocity
   which he calls an SE(3)-jolt. He says that a certain class of the
   SE(3)-jolts cause tissue damage which results in pain.

   His group theory method could be powerfully employed to determine what
   classes of SE(3)-jolts are unacceptable. It would then be relatively
   straightforward to design car seats, webbing for soldiers and office
   chairs specifically to prevent these movements.

   This paper doesn't go that far, however. And here's where I think
   Ivancevic is stuck. Not all vertebrae have the same range of movement:
   lumbar vertebrae movement at the base of the spine is much less
   pronounced than cervical vertebrae movement at the top, and obviously
   this has to be allowed for in the model. But measuring and
   incorporating these idiosyncrasies is going to be tricky.

   So although his model may capture the behaviour of a perfect spine
   made from ideal building blocks, I can't help wondering whether
   translating this in to a real world model will be much harder than
   even Ivancevic anticipates.

   Ref: [4]arxiv.org/abs/0806.3340: New Mechanics of Spinal Injury

   [5][arXivblog?i=tZx8XK] 
   [6][arXivblog?i=1eKhtJ] [7][arXivblog?i=Cws5gJ]
   [8][arXivblog?i=5b8Hgj] [9][arXivblog?i=DsVFzJ]
   [10][arXivblog?i=vdPpUj] [11][arXivblog?i=rGwouJ]
   [12][arXivblog?i=6urfcj] [13][arXivblog?i=TI7i0J] 
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References

   1. http://arxivblog.com/
   2. http://feeds.feedburner.com/~r/arXivblog/~3/323798693/
   3. http://arxivblog.com/wp-content/uploads/2008/06/spinal-groups.jpg
   4. http://arxiv.org/abs/0806.3340
   5. http://feeds.feedburner.com/~a/arXivblog?a=tZx8XK
   6. http://feeds.feedburner.com/~f/arXivblog?a=1eKhtJ
   7. http://feeds.feedburner.com/~f/arXivblog?a=Cws5gJ
   8. http://feeds.feedburner.com/~f/arXivblog?a=5b8Hgj
   9. http://feeds.feedburner.com/~f/arXivblog?a=DsVFzJ
  10. http://feeds.feedburner.com/~f/arXivblog?a=vdPpUj
  11. http://feeds.feedburner.com/~f/arXivblog?a=rGwouJ
  12. http://feeds.feedburner.com/~f/arXivblog?a=6urfcj
  13. http://feeds.feedburner.com/~f/arXivblog?a=TI7i0J
  14. http://arxivblog.com/
  15. http://www.feedburner.com/fb/a/emailunsub?id=8632699&key=kesJ612ZsV
  16. http://feeds.feedburner.com/arXivblog
  17. http://feeds.feedburner.com/arXivblog

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Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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