Nolinear least squares regression

This is the research written by Joshua Aizenman Yi Sun. I have some question about the function on page 9 and on table .it is nonlinear least squares regression.

First, how can i make it simple ? (put it on the linear squares regression)

second, how can i compute t ?. in this page, you see b1 +b2*t=0, but t value on table 5 have negative before it. i can understand how can they have this result ?

finally, can you show what ways to run this regression ?

This is link of this research :attachments_19_01_2010.zip

and my nickname on gmail:

robinthanh89@gmail.com