It is perfectly acceptable to develop a conference abstract into a full-fledged article and submit it to a journal. This will not be considered duplicate publication even if the abstract and full article are published in two different journals. However, when submitting the paper to the journal, you should clearly mention in your cover letter that the article is based on a conference presentation. You should also mention that the abstract presented at the conference will be published at the society's journal and provide a link to the abstract if it is published by the time you submit the article.
Additionally, you need to keep a few things in mind:
1. The title of the paper should be different from the title of the abstract that will be published.
2. The published abstract should be cited in the article. (If it is not yet published, you should still cite it mentioning the journal name and marking it as accepted for publication.)
3. The article submitted to the journal should have at least 30 percent new content compared to the conference presentation.
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