Monday, May 19, 2014

feedback systems and damping

a hn response to this

Our bodies have what the engineer in me might call a "control system" for blood sugar. When you're talking about control systems in engineering you look at the step response and that's what tells you everything you need to know. You have a "plant" which is the thing you're controlling and you have the "control system" which is the thing that provides negative feedback and thus controls the "plant".

If the control system responds faster than the plant you've got a decent shot at keeping things under control and your system is said to be critically damped or overdamped. Both of these are pretty acceptable solutions for process control. If your system doesn't respond fast enough, it's said to be underdamped and shit is real bad. We're talking the kind of runaway shit that you see in the Tacoma Narrows bridge video. Here's a nice picture of various control systems:

Our bodies have a control system for hunger, I'm sure of that. But we don't get to choose how fast that control system reacts; that's fixed. For a lot of foods, our control system responds faster than our blood sugar and things are fine. But some foods can cause our blood sugar to go up faster than we can store it or otherwise react to it. Then eventually enough insulin gets dumped into the blood stream that blood sugar starts to crash. So then you get really hungry and start eating again. The more you eat large amounts of easily digestible sugars, the further you go from the critical damping of (zeta = 1) to horrifically underdamped (zeta = 0).

I wonder when the engineers and the scientists are going to get together and hammer this stuff out formally.

from Lizard's Ghost

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