Dear madams/sirs,
I personally can tell you this: I am interested in the fields you need me to write about. Thery are part of my personal background and my girlfriend's university background. I know the topic, and I love writing about it.
Other than that, I can offer you one "free" article to help you decide if I am the person you are looking for, or not. I think telling you I am a good writer is pointless, for I could be lying. Let me try, you'll decide.
Most thankfully,
Stefano Tamiozzo
P.S.: I had to put 300 as a milestone, for the site wouldn't let me do otherwise. I am actually willing to write the article for free.