how to find whether this paper is already available or not, if authors just changed the Paper title & author name?
There are several software available for checking plagiarism, which would also fit the problem you are investigating. The journal (actually the publisher) for which I am editor use iThenticate. I am not in a position to compare the numerous software and services around, some free, some commercial. However, a simple check that can easily be made is to to a Google search on bits of text. I have personally used this to check on similarities between manuscripts and earlier published articles to check on the degree of overlap and it works fine. It will give you a first indication at which stage you can decide on continuing with a more advanced analysis. 

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