A literal analysis of the sentences reveals that the subject, in both cases, is singular, and thus the verbs "to have" and "to be" would be used in the singular.
However, common American English usage, especially in conversation, is to use the plural in both cases. This represents another battle between literal grammatical forms and what has become common language usage. It has likely developed this way because the verb comes immediately after a word that is in the plural; in your example, the word "scientists," even though this is not the subject of the verb.
So, they mean the same thing. In writing, I would say that it is more proper to use the singular of the verbs, but in conversation you will sound more natural if you use the plural. You will be understood regardless of your choice.