the min value between two peaks and index of zero-crossing point

Hi Experts, Please check these two graphs here: http://i45.tinypic.com/24pb240.gif In the graph at the top, I am interested in the percentage when the line cross the zero, in the graph below it I am interested in the value and index (in this case percentage) of the valley between two peaks. I appreciate your help Sobhan

[Thomas]

how do you generate the graphs? do you have the data points to generate it in Matlab?