A dangling modifier is a modifying phrase whose implicit subject does not match the explicit subject of the clause it modifies. Here’s an example of a dangling modifier (in bold):
The introductory clause (Using sarkosyl…) has an implied subject: a researcher. But the explicit subject of the sentence turns out to be the transcriptionally inactive b-globin gene. This means that the modifier (Using sarkosyl) is dangling, because its subject is not the same as the subject of the clause it modifies (the transcriptionally inactive…).
In modern English usage, dangling modifiers are considered errors. Unfortunately, they are rampant in scientific writing. I believe this is a result of religious reliance on passive voice. This seems to be the case in the above example.
Joseph Williams has this to say about dangling modifiers [Em. added]:
In my opinion, we should consider this not a license to make mistakes, but a rebuke of the scientific community. Just because everyone does it, it doesn’t make it the best thing to do. I think we should make the effort to avoid dangling modifiers because they confuse readers.