In your examples, you are trying to attach specific information (the creators/inventors/etc.) to their subjects. Specific things are identified using the definite article,
So, there is only one Scottish professor name John Dudgeon. Therefore, it would be correct to say "written by the Scottish professor John Dudgeon."
an are indefinite articles and communicate the the following noun is indefinite; that is, that the speaker acknowledges that there could be more than one such noun.
Saying "The paper was written by a Scottish professor John Dudgeon" communicates that "Scottish professor John Dudgeon" is non-specific or indefinite. This isn't actually incorrect, but the usage is less common. If the speaker makes no claims to knowing that there is only one Scottish professor names John Dudgeon, he might use the article "a" to emphasize that he isn't being specific. "John Dudgeon" seems like an uncommon name, so the example is quirky; consider instead the dialogue:
"Who sold you the car?"
"I bought it from some guy - a John Smith".
Here, the speaker uses the article "a" to communicate that there could be many "John Smith's".
Finally, you can communicate definite information using the indefinite article by including a comma:
Written by a Scottish professor, John Dudgeon
In this case, the sentence structure communicates that "John Dudgeon" is specific information about the more general "Scottish professor".