What is a second order exponential decay function?

Can you explain what is a second order exponential decay function: $$y(x) = y_0+A_{1}e^{-\frac{x}{t_1}}+A_{2}e^{-\frac{x}{t_2}}$$

(the $t_i$, $A_i$, and $y_0$ are constants and, presumably, the "decay constants" $t_i$ are positive)?

• Qualitatively, what is the difference between "first order" and "second order"? (A first order exponential function has the form $y(t)=y_0 + A_1 e^{-\frac{x}{t}}$.)

• How can we estimate $t_1$ and $t_2$ from data?

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This is also known as a biexponential function: see google.com/search?btnG=1&pws=0&q=biexponential+model –  StasK Oct 16 '12 at 20:23
Please consult; en.wikipedia.org/wiki/Exponential_decay In order to find decay constants, fit the data with 2nd order exponential decay NLfit (Non-linear curve fit) using originlab 8.5 or higher. Good Luck –  Muhammad Azeem Arshad Aug 21 at 17:56