x_{1} = \left(1 - 1 / \left(k_{1} \cdot \left(\exp\left(k_{2} \cdot t\right) - 1\right) + 1\right)\right) \cdot k_{3} \cdot k_{4} \cdot k_{5} \cdot \left(k_{8} - k_{5}\right) / k_{5}