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
