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Bacterial aggregates formed by coagulation are not spheres, but rather fractals. This aggregate was stained with acridine orange and fluoresces green.

This is a photograph of a floc formed from red latex microspheres that has captured yellow-green microspheres during coagulation. The microspheres are latex particles. By counting the number of yellow-green beads in the red floc, we can determine collision efficiencies of fractal particles with other particles. This photograph was modified and used for the cover of my textbook, Environmental Transport Processes (published by Wiley)
This is a similar photograph to the one above, but here we are examining red aggregates composed of only a very few particles.
Many large aggregates formed in the ocean are held together by transparent exopolymer particles (TEP). The polymeric material is essentially invisible until stained with alcian blue dye. This particular aggregate was formed from a pure culture of Chatoceros, a green algae that exudes copious amounts of polymer in culture.
This is an example of how a photograph of a fractal aggregate can be analyzed. The photograph of a marine snow aggregate (below) is converted to a binary image (right) and then the size, area and perimeter of the object can be analyzed.




 

Bruce E. Logan |  Department of Civil and Environmental Engineering | 231Q Sackett Building
Phone: 814-863-7908 | Fax: 814-863-7304 
The Pennsylvania State University, University Park, PA 16802