You can make use of the same article per site. You can post the same article in top 15 to 20 article submission sites for your site promotion. If two site having the same article with different author name, it will affected. Most probably you need to avoid duplicate content in your site.

yes duplicate content more effects on link value

I think duplicate content with different author's names but linked to same website won't considered as duplicate content. I think!

every duplicat content not accpted to google must effect on your site ranking

I don’t think there would be any penalty, but Google simply discounts one of the two backlinks. Because only one backlink will serve the purpose and backlinks from copied content will appear some sort of manipulation for search result rankings.

It's harmful for your both website it may drop down your keywords ranking too.

It is a duplicate content but Google won't ban your site for it. Google will only rank one article over the other as it sees them as the same. You can do some little alterations to the original to make it unique on your blog.

I agree with Alloviroid. After the recent penguin update I think duplicate articles on another website will harm your sites rankings. If it is an article directory site then it might not be so bad - I don't know. However the problem is that people are allowed to use contect on article directories and then you end up with your article being duplicated all over the web (if its that good!). I would say have unique content only on your own website. If you want to use an article directory write a different article for that - something that is not on your own site.

duplicate content reduces the quality of the search results, this problem also affects the search engine results..

yes duplicate content effect your site . You became spammer.

Duplicate content is not valuable,because Google copy scape is identified all duplicate content. So please reduced to post original article.please see the page
yoast.com/articles/duplicate-content/