"Il n'y a pas de vent."
Translation:It is not windy.
These articles are changed to "de" when the sentence is in the negative:
J'ai des chats
BUT Je n'ai pas de chats.
Il fait du cafe BUT Il ne fait pas de cafe.
**Edit: I have just looked it up and while the above rule is true when using the partitive, it is not always true in other cases. For example, generally the verb "etre" will not see the change to "de" in the negative. There are other rules where this doesn't occur, of course, but that must be for advanced study.