Hello! 

I would say you're very clear on your motivation for continuing your studies--you give a good, detailed history of your passions and the evolution of your interests in the field. I would, however, say that the committee might want to see more information on your plans for the future--right now you only touch base for a sentence or two on what you want to do after you graduate from UCLA, and UCLA in particular is always concerned with what its alumni do after they leave the institution. Hope this helps! =)