Ok, I have a site I'm building. All of my content is original, however, i want to also have research articles that have been written about my topic. Will my entire site get penalized if i put the article on my site (with sources of course)?
Duplicate content is just that. Reposting something that is on other sites has less benefit (in the eyes of google) than something original. That doesn't mean if you reprint a portion of an article that your site is automatically hit with a penalty, but no one outside of google can tell you exactly how their algorithm works. Since you need permission to reprint an article anyway, why not just write a summary of the article and cite the source? Then you wouldn't need to worry about duplicate content.
There is no penalty for duplicate content, it just gets filtered out of the SERPs. The rest of the site remains unaffected. It doesn't make sense to list 10 versions of the same content in the SERPs when a user performs a search (it doesn't make for a good user experience) so SE's make efforts filter duplicate content out.
Their is a lot of speculation about duplicant content. Duplicant content REALLY effects sites that only use the content verbatim. I've scraped content and then put it on sites that had really nice designs, other original content on them and a few other ways to get original content and the pages were getting ranking within a week. On some instances, they were rankings above the original....and my site was newer. So, bottom line? If it is good for the users of your site, go for it. All the suggestions I mention are keeping in mind of Copyright laws...of course.