Should I use present or past tense when referring to a (scientific) paper? [duplicate]

Possible Duplicate:
What (grammatical) tense to use when doing reference in a paper?

In the two examples below, which tense is preferred?

"Smith (2001) noted that ..." or
"Smith (2001) notes that ..."

"The paper established ..." or
"The paper establishes ..."

If both forms are equally valid, is it customary to use both forms within a text, or should I stick to one form?

MLA style and others recommend using present tense when citing published sources. Their explanation is that "Smith notes that" is a signal phrase, and that signal phrases should have present tense verbs.

The lone exception seems to be APA style, which "dictates that writers use the past or present past tense when citing previous research," i.e. "Smith (2001) noted" or "Smith (2001) has noted."

If you're governed by APA style, follow their guidelines and use past or present past tense. Otherwise, use present tense.

"APA style requires authors to use the past tense or present perfect tense when using signal phrases to describe earlier research, for example, Jones (1998) found or Jones (1998) has found."