How to set properties for material.

I simulated the insulator model in 2D-axial symmetric in AC/DC Module. i use com sol 4.3. i have some doubts related to that.
How to set (or) apply a switch threshold value for particular (my model) material in COM SOL software?
How can we apply a conductivity of the material as a function of electric filed?
How can we merge the different graphs (Two graph) in COM SOL?
How to apply an Impulse signal to model in COM SOL (For that purpose wither need COM SOL with MAT LAB interface)?
Please any one help me.