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 | Tuesday, May 6, 1997
Lecture 9 |
WRITTEN #2 DUE
TRANSFERING STRATEGIES FROM EXCEL INTO STELLA
Flip-flop, "all or nothing" model
- Our basic STELLA model has a flip flop strategy. See lecture 9 for a full description.
- We are going to modify this to have a variable light input
- change the light from a single value to:
- if sin(Pi*mod(time,24)/12)>0 then 1000*sin(Pi*mod(time,24)/12) else 0
- this will give a sin curve for light that is dark at night
Fixed ratio model
In Excel we had a strategy that just invested a fixed amount into Pmemb and the rest into Penz. You can build this version in STELLA by:
- nuke the indicator box, the reinvestment will not depend on any factor
- make the two following changes to existing flows controls
| Component | name | initial value or equation |
| flow | reinvest_in_Pmemb | .3*carbon_production |
| flow | reinvest_in_Penz | .7*carbon_production |
NADPH feedback model
We discussed making the control of the model depend on the concentration of NADPH relative to the total cell carbon. This value would be relative to the total volume of the cell.
This model is a little bit more complex to modify. See the diagram below and the equations that are different between the original model and this one in the table.
| Component | name | initial value or equation |
| converter | relative_amount_of_NADPH | NADPH/total_carbon |
| flow | reinvest_Pmemb | if relative_amount_of_NADPH <.1 then 0.7*carbon_production else 0.3*carbon_production |
| flow | reinvest_Penz | if relative_amount_of_NADPH <.1 then 0.3*carbon_production else 0.7*carbon_production |
COMPETITION
Pick a favorite adaptation strategy and build a model that incorporates that strategy. The input to the light reaction needs to be called "light". We will have a little competition between models to see who wins and who looses.
The light environments that we will use will be based on a diel light cycle and mixing with depth. Light is attenuated with depth according to the general equation Iz=I010-z/f
where:
z is the depth in meters
I0 is the light hitting the surface of the water
Iz is the amount of light availble at depth z
f is the depth at which only 10% of the light is getting through
The general shapes of light attenuation curves are exponential.
The equation that we will use to simulate this will be:
light = (10^-(10+random(-10,10,5))/10)
where the depth of the 10% light level is 10 meters
and the alga moves up and down in the water between the surface and 20 meters