an energy spectrum that rolls off as ...

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Mauricet

Senior Member
French - France
Dictionaries seem to ignore "to roll off" as used here (in a science article), without a complement (neither "rolls off (of) something" nor "rolls something off"): Here, Onsager predicted for velocity fluctuations an energy spectrum that rolls off as the -5/3 power of the wavenumber.

I guess it means the spectrum decreases as that power of the wavenumber, right? Is it usual to say it that way, is it kind of familiar, how would you rephrase it? Thanks!
 
  • entangledbank

    Senior Member
    English - South-East England
    It's not familiar - I hadn't heard of it - but that is what I would guess it means. In fact one dictionary at least does mention it: here is the OED's sense 2.a. for 'roll off':

    intr. Of audio or electronic equipment: to exhibit a frequency response that decreases smoothly at the end of its range; (of a response or property) to diminish gradually. Also in extended use.

    And it gives several examples going back to 1948.
     

    Mauricet

    Senior Member
    French - France
    Well, I didn't expect to fall on something so weird, in a text by two scientists, one of whom at least being a native US English speaker. If this usage of roll off is somewhat dated as you suggest, maybe they were influenced by their subject matter, a physicist who wrote in the 40s. Strangely I didn't find this usage in Onsager's writings, however. The modern authors seem to have chosen it on their own.

    Too bad the Oxford English Dictionary is not free. MerriamWebster and dictionary.com don't have it. I wonder if there might be another reference?
     

    JulianStuart

    Senior Member
    English (UK then US)
    It is in common use still in audio in particular and in other areas as well where the X axis is increasng frequency (digital photograpy is a more recent example where it is used). It is very technical, verging on jargon, and mainstream dictionaries may not try to cover such fields. The OED's citations going back to the 40's only mean it has been in use since then
     

    Mauricet

    Senior Member
    French - France
    That's the noun roll-off, and one could say "the roll-off of the energy spectrum is 5/3". The question was about to roll off, the usage of which doesn't seem that common, does it? Or is the phrasal verb derived from the noun?
     

    JulianStuart

    Senior Member
    English (UK then US)
    That's the noun roll-off, and one could say "the roll-off of the energy spectrum is 5/3". The question was about to roll off, the usage of which doesn't seem that common, does it? Or is the phrasal verb derived from the noun?
    Now the question (verb vs. noun) is clearer than it was in the first post! The noun came from the verb, not the other way round. The verb is still also in common use in its field often with a qualitative sense : ... rolls off smoothly, or gradually or abruptly. For quantitative descriptions the niun is used : the roll-off is third order, etc.
     

    Mauricet

    Senior Member
    French - France
    Now the question (verb vs. noun) is clearer than it was in the first post!
    The question there (in post #1) was about the verb, not the noun. The wikipedia article you referred to was about the noun roll-off. So there was nothing unclear, I think, but now we have a clear picture of a verb and a related noun. Thanks!
     

    JulianStuart

    Senior Member
    English (UK then US)
    The first post did not ask whether it can be used as a verb (that word does not occur in that post) it asked if it meant decreases. It was not clear to me (it may have been clear to you :D ) that you were asking about usage as a verb, rather it appeared that you were asking about its meaning, not a question related to parts of speech. Hence the explanation and reference to an article explaining its meaning without regard for which form/part of speech was referred to.

    "Can roll off be used as a(n intransitive) verb as in my example?" Yes, it can.
     
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