dx1/dt=- a1*(x1 - x2) - ka*vm*x1*x5;
dx2/dt=a2*(x1 - x2);
dx3/dt=- b1*(x3 - x4) - kc*vm*x3*x5;
dx4/dt=b2*(x3 - x4);
dx5/dt=ka*x5^2*(a1*(x1 - x2) + ka*vm*x1*x5) + kc*x5^2*(b1*(x3 - x4) + kc*vm*x3*x5);
y1=x1;
