Hi Hernan - Here are my entries. I noticed the samples you provided were all pretty stylized, I tried to match that distinctiveness and character in my design. I've used a lot of bright colors because teens and kids love colors. Even though the colors aren't natural to a real Chihuahua, they are very fun and stylish and eye catching. Your logo will really stand out. I've given him a bow-tie to make him more like a professor. Please don't hesitate to communicate with me, we can work together to come up with a design you like.
-melinda