User:Brian P. Josey/Notebook/2010/05/24

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Thursday's Forces

I've calculated the forces acting on ferritin from the data that I collected on Thursday. I then carried this forward and calculated the average terminal velocity that the ferritin would be traveling at in water for the corresponding areas. Here is my data in a Google Spreadsheet:

View/Edit Spreadsheet

All forces are in fN, 10-12 N, and velocities are in μm/s, 10-6 m/s. In both cases, the force and velocity is pointed towards the magnet.

For reference, vertical from tip or saddle, means the points going away from the magnets at either the cone tip, or the edge of the magnets flanking at the side of the saddle. For these data points, this includes the points nearest the magnet, with in a flow cell placed up against the magnet, and those in a microcentrifuge tube.

Assuming that my calculations are correct, this would explain the bizarre patterns that I got from my experiments on Friday. It appears that nearest to the cylinder magnets on the side of the saddle, there is a much greater force than the near the tip of the cones in the center. This results in the ferritin being more attracted to the sides of the saddle, giving the volcano plum pattern that appears on the left and right of the image.

A while ago, Koch noticed that some stainless steel tweezers we had were more attracted to the cylinder magnets than the cone. I didn't think my of it, because the cylinder magnets were larger, and I assumed that on the scale of proteins the greater gradient from the cone's tip would compensate, but now I'm not so sure. So prompted by this new data, where the force near the tip of the cylinders is about twice that in the neodymium yoke, I need to check different orientations and shapes of the magnets, and see if the model and yoke that I've been using this whole time is not necessarily the best one.


I created a couple of simulations representing several different ideas that I've had for mounting the magnets on to the microscope's stage, and I ran them for most of the day today. I however wasn't able to finish, they take a while to run, and I will include the forces that I calculate in tomorrow's notebook entry.

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