Thypher #2: Solve the Equations

Solve the following equations to guess the word based on the common variables with which they are associated.

r_{0} A^{1/3}

λ N

- \frac{α}{r}

I_{0} e^{- μ x}

N_{0} e^{- λ t}

\frac{2 J + 1}{(2 s_{a} + 1) (2 s_{b} + 1)}