“Arbitrary unit”的意思、由来-开放百科全书

In science and technology, an arbitrary unit (abbreviated arb. unit,^[1] see below)

is a relative unit of measurement to show the ratio of amount of substance, intensity, or other quantities, to a predetermined reference measurement. The reference measurement is typically defined by the local laboratories or dependent on individual measurement apparatus. It is therefore impossible to compare "1 arb. unit" by one measurer and "1000 arb. unit" by another measurer without detailed prior knowledge on how the respective "arbitrary units" were defined; thus, the unit is sometimes called an unknown unit.^[2] The unit only serves to compare multiple measurements performed in similar environment, since the ratio between the measurement and the reference is a consistent and dimensionless quantity independent of what actual units are used.

Units of such kind are commonly used in fields such as physiology to indicate substance concentration, and spectroscopy to express spectral intensity.

When the reference measurement is precisely defined and internationally agreed upon, arbitrary units can also be a unit capable of public comparison. One example of a publicly defined arbitrary unit is the WHO International Unit.^[2]

Abbreviations and nomenclature

Abbreviations for "arbitrary unit" include: arb. unit,^[1] arb. u., AU,^[3] and a.u.^[4]

Among these, "AU" and "a.u." are common abbreviations for astronomical units and atomic units.^[5] For this reason, Physical Review journals, the Japanese Journal of Applied Physics, and an increasing number of other academic journals, recommend against using "a.u." (Jpn. J. Appl. Phys recommends "arb. unit" instead).^[6]

While arbitrary unit is not a formally recognized unit,^[1] IUPAC and IFCC recognize the need to deal with "unknown units", and decided in 2008 to use the term "procedure defined unit" in their database.^[2]{{dead link|date=January 2013}} The decision forbids using factors or denominators in conjunction with p.d.u. (such as "p.d.u./L").

References

1. ^¹²{{cite journal |last1=Olesen |first1=H. |last2= |first2= |year=1995 |title=Properties and Units in the Clinical Laboratory Sciences: I. Syntax and Semantic Rules (IUPAC-IFCC Recommendations 1995) |journal=Pure Appl. Chem. |publisher=IUPAC |volume=87 |issue=8/9 |pages=1563–1574 |url=http://media.iupac.org/publications/labinfo/English/Documents/syntax%20and%20semantic.pdf |doi= 10.1351/pac199567081563}}
2. ^¹²³{{Cite report|url=http://www.iupac.org/divisions/VII/VII.C.1/C-NPU_Uppsala_081023_25_minutes_confirmed.pdf|title=Confirmed minutes for the meeting in Uppsala 2008-10-23 – 25|last=|first=|date=October 23, 2008|publisher=Committee and Subcommittee on Nomenclature, Properties and Units (SC-C-NPU), IUPAC–IFCC|issue=|doi=|volume=|pmid=|docket=|archive-url=https://web.archive.org/web/20110810201956/http://old.iupac.org/divisions/VII/VII.C.1/C-NPU_Uppsala_081023_25_minutes_confirmed.pdf|author=|coauthors=|accessdate=September 10, 2010|archive-date=August 10, 2011}}
3. ^{{cite web |url=http://www.jci.org/kiosk/publish/abbreviations |title=Standard abbreviations |date=January 2, 2008 |work=Journal of Clinical Investigation |publisher=American Society for Clinical Investigation |accessdate=September 10, 2010| archiveurl= https://web.archive.org/web/20100728115108/http://www.jci.org/kiosk/publish/abbreviations| archivedate= 28 July 2010 | deadurl= no}}
4. ^{{cite web |url=http://ep.physoc.org/site/misc/abbreviationslist.pdf |title=Abbreviations and Symbols List |work=Information and Guidance for Authors, Experimental Physiology |publisher=The Physiological Society |accessdate=September 10, 2010}}
5. ^{{cite book |title=AIP Style Manual |url=http://www.aip.org/pubservs/style/4thed/toc.html |accessdate=September 9, 2010 |edition=4th |year=1990 |publisher=American Institute of Physics |chapter=Appendix C: Units of Measure |chapterurl=http://www.aip.org/pubservs/style/4thed/appc.pdf| archiveurl= https://web.archive.org/web/20100915110256/http://www.aip.org/pubservs/style/4thed/toc.html| archivedate= 15 September 2010 | deadurl= no}}
6. ^{{cite web|title=Instructions for preparation of manuscript |url=http://jjap.ipap.jp/pdf/instruction_e.pdf |work=Japanese Journal of Applied Physics |publisher=The Japan Society of Applied Physics |accessdate=September 11, 2010 |deadurl=yes |archiveurl=https://web.archive.org/web/20090711021314/http://jjap.ipap.jp/pdf/instruction_e.pdf |archivedate=July 11, 2009 |df= }}
7. ^{{cite web|last=Schadow|first=Gunther|title=The Unified Code for Units of Measure §45 chemical and biochemical units|url=http://unitsofmeasure.org/ucum.html#para-45|accessdate=2018-01-15|date=2017-11-21}}