I would like to if publishing articles on domain.com and domain.com/blog (in both places same articles) is considered duplicate content. Logically speaking, it is duplicate content but is the search engine penalizing me for this ?
Yes.. it's definitely duplicate content.. and whether Search Engines penalizes you or not depends on your luck..
Yes, that's a duplicate content and your site might be penalized for that. According to googlewebmastercentral.blogspot.com
Of course that's duplicate content ... talking about Google penalizing or not? it's very much possible especially if you start doing it repeatedly. Besides, what's the idea behind posting the same article at your website and blog (that's on the same domain) at the same time?