Scale instanced object according to particle lifespan?

[alcino-alves]

Hello guys.
I'm working on a project here which consists in a silhouette of an animated character. While this silhouette walks, many cubes follow it 'outlining the geometry'.
The closer these cubes are from the silhouette the smaller they are and the further they are the bigger they'll be.

I'm emitting the particles from the silhouette and I thought of creating cube instances from these emitted particles.
So here are my questions:

How do I make an expression to control the scale of these instanced cubes according to their lifespan?

I want to have a certain amount of particles and I don't want them to spread through space forever. I want them to be closer to the silhouette geometry border because I want them to follow the animation without spreading. How can I do such thing?

I'm not familiar with expressions in Maya, that's why I'm asking for your tips and help.

Sorry about my English, I hope you understood my questions.
Thanks in advance.

[joojaa]

make a new attripute call it scalePP or whatever really and when you create the isntacer choose allow all attributes and under the scale options chose that scalePP value this attribute now controlls scale.

[alcino-alves]

Thanks man, it worked fine.

and what about my second question?
"I want to have a certain amount of particles and I don't want them to spread through space forever. I want them to be closer to the silhouette geometry border because I want them to follow the animation without spreading. How can I do such thing?"