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Old 01-29-2007, 06:03 PM   #281
Erick Mead
 
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Dojo: Big Green Drum (W. Florida Aikikai)
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Re: Baseline skillset

Quote:
Ignatius Teo wrote:
If you're talking about this study: http://arxiv.org/PS_cache/cond-mat/pdf/9908/9908185.pdf, I bowed out then because I could not fathom how you arrived at a conclusion of "dual eccentric hip gyrating the center of mass in a chaotic orbit shaped roughly like a warped figure-eight".

If you're referring to Figure 1. in that study, which plots the upper body's random meandering path in the plane of the anteroposterior (front-to-back) coordinate and mediolateral (side-to-side) coordinate over one minute.... I still don't see how you inferred that such a random chaotic front-to-back and side-to-side swaying (as in like a pendulum) as gyrational motion (i.e rotation on an axis) - much less a "figure of eight".
It is not random, it is clearly chaotic, which is just a very, very complex order. Kinda like this -- different system -- same family of chaotic attractor:
http://www.exploratorium.edu/complex...va/lorenz.html

In the phase space diagram (just go with it, really), the whorls you see in the linked Lorenz attractor and the rough radius of them, equate to the linear 2D depiction of the study I showed you (you are correct about figure 1) in the phase space. It would be (very roughly) as if you looked at that Figure 1 diagram edge on from the top of the page downward, in a plane that is horizontal to the page itself. Then you would see the repetitive, and dual ecccentric tendencies of the excursions shown in a shape very much like the Lorenz attractor.

You can see the realtionship between the two types of depictions in this link: The "X(t)" applet (the second one) shows what Figure 1 in the study shows, linear with respect to time. The first applet on the page (X-Z) shows the Lorenz attractor in the phase space. You should run the graphing applets at a fast speed to get the idea.
Quote:
Ignatius Teo wrote:
From what I've read and understand, the human balance system uses strategies based on simple harmonics - linear oscillations - not rotational oscillation.
Sorry, but that is one of the points of the study, that it does not fit that. One of the other studies that I linked in an ealier discussion showed that the assumption of linear "spring-like" actuation by the leg muscles was actaully the reverse of the linear spring model. The hip orbit dynamic stability model fits with that, the linear static stability model does not.
Quote:
Ignatius Teo wrote:
But then again, we're talking about baseline skills and how to develop these baseline skills. So to me, anything discussing balance coping strategies, reeling silk, and gyrational motion are way off-base.
More basic than balance. I am essentially saying that kokyu is just the extension of my balance control system into the other guy's balance system. Not as metaphor -- as physical reality.

Really, that is all I am saying.

Admittedly -- in too many words, but I try to back up my arguments.
Quote:
Ignatius Teo wrote:
I believe Nick Gudge frequents Aikiweb, and it would be interesting to hear his opinion.
Look forward to it.

Cordially,

Erick Mead
一隻狗可久里馬房但他也不是馬的.
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