What is the meaning of "modulated physical systems"?

[gobarriga]

In particular I'm studying the paper "Theory of dynamic response functions of periodically modulated physical systems" by Lovesey et al. and "modulated system" are mentioned many times.
My thesis advisor recommend to me reed this paper but is very confuse, any reference you can give me in relation to the title of this paper will be very helpful.

 

[RPinPA]

The title of the paper does not give enough information to answer this question. Most likely the concept is defined within the first few paragraphs, and the equations there will tell you what the model is. Alternately, sometimes an author will instead refer you to an earlier paper where the important terminology is described.

My guess is that "periodically modulated" means there is a periodic external driving force or input. But I am just guessing.

Can you provide an image of the first few paragraphs? That's not ideal, but it's better than nothing.