Request for: Einstein
huberrob opened this issue · comments
Please provide the following a literature reference (or attachment) which provides a scientific definition. A scientific definition is a quantitative one, not just words "unit for the amount of XYZ." A scientific definition will also give some way of converting or inferencing something with the values expressed using that unit. You can include document URLs or drag/drop attachments to accompany your request.
In Biology and Environmental Sciences the 'Einstein' unit is frequently used and is defined and while it is not recommended to be used, a large amount of data still is produced which is using 'Einstein' abbreviated as 'E'.
Consequently some large environmental data archives still use this unit .
Definitions: https://en.wikipedia.org/wiki/Einstein_(unit)
Examples are:
- At vocabulary level: https://vocab.nerc.ac.uk/collection/P06/current/UMES/
- At dataset level: https://doi.pangaea.de/10.1594/PANGAEA.948489
Note the scope of UCUM is science, healthcare, engineering, and business (not including currencies). Units outside this context are discouraged.
Be certain to include the unit in the issue title above.
Initially I was sympathetic until I opened the Wikipedia article. The Wikipedia article discusses why it should not be used. It says the kind of quantity is not quite clear. Is it for Energy? There is no precedence for having mol of anything as a special unit.
The NERC UMES entry shows there is a huge problem with the wavelength parameter.
The second reference (PANGAEA) seems to be evidence against Einstein, because that word is not found in the page, instead "light intensity (55 vs. 160 μmol photons m-2 s-1)" which means that those authors agree with the caution expressed in the Wikipedia link.
I would request that we look at 3 pieces of examples which show measurement data communicated in scientific articles where the Einstein is used by itself not doubled up with it's meaning. This is IMO the litmus test: is there significant independent use?
Unfortunately the unit is frequently used by biologists in the context of photosynthesis in the recent literature and associated data.
Here some recent literature examples:
https://doi.org/10.1117/12.2575469
https://doi.org/10.3389%2Ffpls.2021.758213
https://doi.org/10.1016/j.biteb.2022.101152
https://ui.adsabs.harvard.edu/abs/2022cosp...44.2842F/abstract
https://doi.org/10.3390/su12166610
etc..
In PANGAEA the term 'Einstein' does not appear but the unit is used abbreviated as 'E' in e.g. 'µE/m2/s'
I can't see the text of some of those papers. But I do see it on others, used as unit E without explanation, this is an indicator for it being widely recognized. So I shift my vote to become in favor of this proposal.
Now can we have a single definition (remembering that the Wikipedia was somewhat ambiguous), ideally a definition that shows some consideration of (a) the possible ambiguity, (b) a solid understanding of coherence with SI, (c) a clear specification of the kind of quantity that this unit has.
Don't want to get into the "is cycle a dimensionless number or an angle of 360 degree?" after we have integrated the Einstein.
As for symbol, giving it the plain symbol E is a privilege that must be reserved to only units very well defined for use with the SI. The E is available, and I am inclined to vote for granting the E to this Einstein after we have checked whether there are other units deserving the E more, because they are more well defined to be harmonious with the SI.
Maybe this article is useful:
I think it is accessible but just in case, here is the section which might be relevant (sorry for the copy/paste errors):
Photosynthetic radiation
Most crops are sensitive to radiation with wavelengths between 400 and 700 nm. The eye is most sensitive to radiation of wavelength 555 nm and becomes less sensitive for wavelengths less than or greater than this value (25). Because of the tremendous difference between the sensitivity of the crop and of the eye, it is meaningless to use light measurements for
plant research. Later, the term radiant flux density will be defined, a term which does not take into account this “peak” wavelength of the crop.
It is for this reason that the einstein unit (E) was introduced. This unit is defined by the Einstein-Stark equation (24):
ξ=nhc/λ
where ξ is the energy absorbed per unit mole of photon (in einstein units), and n is Avogadro’s constant (6.02 x
1023 mol-1), h is Planck’s constant (6.63 x 10"34J s), c is the speed of light (3.00 x 10*m s'1) and λ is the wavelength
of the radiation.
The einstein is not an SI unit, but since it is used fairly extensively in the plant sciences, there may be merit for
its inclusion into the SI.
It is important to note then that the einstein is the energy in Avogadro’s number of photons. Dybing (7) and
Shibles (21) have suggested the term “photosynthetic photon flux density” (symbol PPFD) with unit µE s'1 m'2
and “photosynthetic photon density” (unit µE m '2). Incoll et al. (11) use the term photon flux density. Recently,
some changes to the definition, or the unit of PPFD have been proposed ( 11, 20).
We are getting somewhere. Trying to boil it down to simply "what is the Einstein"
1 E = .... ?
The Einstein-Stark equation is given as
ξ=nhc/λ
and the underlying idea is photons being absorbed cause the (photo-)synthesis reaction to take place. And the ratio of reaction speed (mol product formed / s) over photon flux (mol photon absorbed / s) is a constant Φ, called quantum yield. Like an efficiency coefficient. The mol (just Avogadro's constant) cancels out over the fraction, as does the unit of time (here seconds). So this constant is dimensionless. You could give it in % like people do with thermodynamic efficiency.
Trying to understand that ξ equation now. Underlying this is the photon energy:
E = 1/2 m v2 = hf
the unit of h is J.Hz, or eV.Hz, with Hz being 1/s, so h has unit J.s and c being m/s, or rather c/λ is just f. So a unit of ξ would be just J. What is the point of that?
To wit: the Avogadro constant n comes in only because of the mol. ξ=nhc/λ, and c/λ is just Hz. So ξ/n = hf, which means ξ is just again the energy (strange they use xi and not epsilon, looks like an "e" but is not an e).
Maybe I am talking inane basic things, just trying to wrap my head around it. Still searching for the Einstein unit
1 E = ...?
Somehow I am not getting to this point. Note all this text never has the E alone, it's always "µE s'1 m'2" and some such.
So back to Wikipedia:
the einstein (symbol E) is defined as one mol of photons.
woops? How is that a unit? Why don't we have a unit for "one mol of hydrogen" different from "one mol of water"? How would UCUM define 1 E? How would any SI unit table define the E?
As such, photosynthetically active radiation (PAR) may be reported in microeinsteins per second per square meter (μE⋅m−2⋅s−1).
see, again, it's not the E itself, it is some marker where E essentially stands for Avogadro's number.
The einstein is not part of the International System of Units (SI) and is redundant with the mole.
so UCUM would define 1 E = 1 mol, since indeed our mol is equivalent to Avogadro's number. But to what benefit now?
The einstein may have been originally defined as the energy in one mole of photons. Since the energy of a photon is proportional to its frequency, this definition would make this ill-defined as a unit of energy.
And there was our nhf or nhc/λ again. But none of that is useful, because in the end 1 E = 1 mol. Whatever the intention of this Einstein unit is, it always slips out of our hand right the moment we are trying to grasp it. Like a fish.
Now I came from resistance to it, to accepting it, trying to make a useful UCUM definition and then just coming back to not seeing any value.
At this point I am really skeptical about granting this awesome privilege of being a single letter non-bracketed UCUM symbol E. I am not sure enough that there isn't some other unit, let's call it the "elmer" that's used in the vibrational shear energy in material sciences. I am making that up of course, but since I don't know all sciences and their jargons and idiosyncratic units, I am just saying that if there was a niche in science where the "elmer" was alive and well, defined as a real unit with dimensionality and in conversation with SI folks to consider gaining some status, if we now rush to grant the E for this "mol of pair of shoes" unit, then we would regret that.
The maximum I can go for right now would be to grant [E] to the Einstein, still defining it as 1 mol.
I even don't think that making effort to encode the "of photons" in "mol of photons" into the unit would even be appreciated in any way, because in the end, when you make computations on photosynthesis, you are going to want to relate the mol of photons mol of product synthesized in reaction. If you defined the E strictly as mol of photons you could not then get to mol of reaction product without using some ever so trivial "constant" of 1 [E]/mol, which is just 1.
Finally, since ultimately the application of this is connected to reaction enthalpies, where J/mol is a common unit to see, the presence of this einstein seems to just obfuscate that.
Thanks for this excellent analysis! Defining Einstein as [E] in UCUM would be a pragmatic solution. Or can Einstein alternatively simply be expressed as : mol{Einstein} ?
I just tried to find out why this unit is still so frequently used despite its clearly discouraged by individual communities and I am almost sure the only reason is that the unit is still used my some manufacturers producing PAR sensors such as this one:
https://www.bodc.ac.uk/data/documents/nodb/pdf/Biospherical_QCP2300_QCP2350_Apr2014.pdf
researchers using these sensors simply use and publish the data as it is delivered by the sensor which causes problems when data e.g. needs to be compared with recommended, SI units and here it would be very helpful to have this unit available as UCUM
Related discussions probably here at this event:
I propose to add the einstein in Table 19 as follows:
Table 19: Units used in Chemical and Biomedical Laboratories
| name | kind of quantity | c/s | c/i | M | definition value | definition unit | |
|---|---|---|---|---|---|---|---|
| equivalents | amount of substance | eq | eq | EQ | yes | 1 | mol |
| osmole | amount of substance (dissolved particles) | osm | osm | OSM | yes | 1 | mol |
| einstein | amount of substance (photons) | E | [E] | [E] | yes | 1 | mol |
...
The unit osmol as the amount of dissolved particles is to be used with caution because it interferes with “osmolar” which is the amount of dissolved particles per liter.
The unit einstein is used in plant biology in conjunction with the Stark-Einstein law and it's meaning is now mostly for one mole of photons (regardless of wave length). Originally it may have been defined as the energy of 1 J contained in one mole of photons and as such would be equivalent with the J. But that would make the unit wavelength dependent. The use of this unit is discouraged but it is still widely in use practically with the meaning of 1 mol of photons (regardless of wavelength).
The gram-percent (g%) is a metric unit that has the same origin as %vol. Originally it was a dimensionless quanitiy expressing a ratio of two masses
I wondered if we need to change the caption of the table and section, to include Biology instead of subsuming that under Biomedical. Started doing it, then undid.
Reason I put it here is that the precedence of osmole really provides the ultimate justification.
The text I added would need a couple of references, not Wikipedia.
- the deprecation statement in Wikipedia links to Incoll, L. D., S. P. Long, and M. A. Ashmore. 1981. "SI units in publications in plant science". Commentaries in Plant Science. 2: pp. 83–96., but I can't confirm as I don't have access.
- the reference to the equipment manual for wide use might work, of course it would be better if there was a reference to an authority that affirms such widespread use.
Regarding the references,
Incoll et al. 1981 can be found at Google Books here: https://books.google.de/books?hl=en&lr=&id=vAbLBAAAQBAJ&oi=fnd&pg=PA83&dq=Incoll,+L.+D.,+S.+P.+Long,+and+M.+A.+Ashmore.+1981.+%22SI+units+in+publications+in+plant+science&ots=kbT6B0FDX1&sig=uDoAa6MPzV0ASmneZ-RtqMlq7vQ#v=onepage&q&f=false
And there is a similar publication here:
https://www.agronomy.org/files/publications/jnrlse/pdfs/jnr010/010-01-0070.pdf
Interesting, this author would definitely not like to say the einstein is a mol of photons because the energy was first.