Scale-Free Vertical Tracking Microscopy, a.k.a. Gravity Machine | Hacker News Reader

Scale-Free Vertical Tracking Microscopy, a.k.a. Gravity Machine

gravitymachine.org

58 pointssohkamyung6 comments

There is one problem, though.

The water column the microorganism travels is not uniform and endless. As it travels, the conditions change. Some can be easily adjusted (for example lighting), some would be much more difficult to get (pressure, chemical composition).

So while the microorganism can travel it can't actually get anywhere.

True, but if you want to do microscopy on a moving subject for even a few seconds, a little treadmill will make a big difference!

They have a method for imitating natural chemical, temperature, and light gradients even in the otherwise sealed tube. So they can simulate a great deal of those conditions and have observed some interesting behaviors at boundary layers, if you check the gallery.

Ah, missed it.

I'm probably just misunderstanding the physics involved, but wouldn't moving the container only impart movement on the fluid inside in proportion to the viscosity of the liquid? And once the fluid is moving wouldn't stopping it require movement in the opposite direction or waiting for friction to reduce the inertia of the fluid?

I'm thinking of the behavior of the semicircular canals of the ear, and how the inertia of the endolymph can cause dizziness after spinning for a while.

Maybe the critical part I'm missing is that the organism is actually sinking in the fluid around it and the effect of fluid current if present is minimal compared to the effect of gravity.

As an aside, the homepage for this project is quite nicely illustrated.

I had this exact question, and the researchers said it was a serious consideration. Turns out the critters at this scale move quite slowly and so does the wheel. There's some effect certainly but it's small enough that they can track a single organism for quite a long time. It wouldn't work in other circumstances or scales for sure.

I wrote it up here, in case anyone would like to read about it in article form: https://techcrunch.com/2020/08/19/this-looping-aquatic-tread...

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