Biomedical Engineering Reference
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(a)
(c)
(b)
(d)
FIGURE 14.11
Different states of bioconvection pattern. (a) Uniform initial state;
(b) diffusion state; (c) transient state; (d) steady state of the plumes. (Nguyen-
Quang, T., Nguyen, T.H., Guichard, F., Nicolau, A., Smatzari, G., LePalec,
et al., Zoo. Sci ., 26, 2009, doi:10.2108/zsj.26.54.)
10 4 to 1
10 5
Concentration values leading to this state range from 5
×
×
cells/cm 3 , depending on the dimensions of the Hele-Shaw cell.
14.3.4.2
The Stationary Convection Regime
When the concentration is higher than a certain critical value, the diffusion
state does not exist anymore and we observe the appearance of a station-
ary convection regime with many small plumes. Figure 14.11(d) illustrates
the steady convection patterns obtained with a concentration n =1 . 27
×
10 5
cells/cm 3
×
0 . 075 cm). The time t c required for the steady state to establish varied from
30 minutes to 3 hours, depending on each experimental parameter sets, but
mostly on the initial filling concentration and the health status of TP cells.
For this assay (Figure 14.11[d]) t c is around 30 minutes. Figure 14.11(c) shows
a transient state before reaching the stationary convection regime.
(the Hele-Shaw apparatus dimensions are H
×
L
×
b =4
×
15
14.3.4.3
Unsteady Convection Regime
As the concentration is increased to higher values than those leading to the
state described earlier (stationary convection), we observed an unsteady con-
vection regime characterized by a collection of cloudy plumes. These plumes
have nonstationary shapes, moving from side to side, dividing themselves into
small plumes and then reassembling again (Figure 14.12). The motion of these
plumes continues until the death of the Tetrahymena cells. The time for this
nonstationary regime to appear is about 15-30 min, depending mostly on the
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