Re:

[TRAORE Abdoulaye <Abdoulaye.Traore@xxxxxxxxxxxxxxx>]

So i think you have guessed that i'm not a chimist. 
I'm a senegalese student in french and preparing a thesis of applied mathematic, probability. 
The subject of the Ph.D is, in general, the stabilisation of stochastic differential systems.
We interest stability in probability, exponential stability, stability in lyapunov sense, 
lyapunov exponent.
The idea is when you've a stochastic differential equation, you calculate its lyapunov 
exponent and with the sign of this, you know if your systhem is stable or not. Now, a 
interesting problem draws my attention, optimal control. I explain to you.
In the case where your system isn't stable (its lyapunov exponent is positive), you can put 
a control on it , i choice a feedback control, and with the new system, you search a algorithm 
which permits to find a optimal control which stabilizes the system.

Abdou