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December 29

Absorption (skin) article

The article let's me wondering: why is the skin impermeable to water? How would absorption differ for seawater and fresh water? Does the lining of the mouth or intestine count as skin (that is, should this go into the article)? Do they behave differently? --Hofhof (talk) 11:54, 29 December 2017 (UTC)

It is not impermeable, it is simply already saturated, given the high amount of water our body keeps in every cell. Cells also have the ability to selectively take up, filter, throw out and keep an inner balance of chemicals, so it should not make a difference how much salt water contains that comes in contact with the skin. --Kharon (talk) 14:29, 29 December 2017 (UTC)

What? -165.234.252.11 (talk) 19:34, 29 December 2017 (UTC)

To actually answer this guy's questions: the impermeability of the skin is thanks to a layer of keratin that composes the outermost part of the skin (see e.g. keratin, human skin, epidermis, stratum corneum), and no, the lining of the mouth and intestine are not skin, they're mucous membranes, and they don't belong in that article. -165.234.252.11 (talk) 19:56, 29 December 2017 (UTC)

• Would the mucous membrane in the intestine absorb water? For example, if there's only seawater available, would pumping this water down there hydrate a human? Isn't that the same as a vodka-soaked tampons (aka Alcohol enema? Is a Seawater enema a thing?--Hofhof (talk) 22:41, 29 December 2017 (UTC)

Sea water is hypertonic compared to human blood, and pumping it into the intestine would suck water out of the body, causing dehydration, diarrhea, and death. μηδείς (talk) 02:23, 30 December 2017 (UTC)

See osmosis - to desalinate water requires the input of energy in some well engineered process. The body can do it to a limited degree (and does so in the loop of Henle for example) but is not evolved to be able to do it to the extent of being able to use seawater. Wnt (talk) 11:39, 30 December 2017 (UTC)

Year of description of a new species

Good morning/afternoon/evening. This article describes Varalphadon janetae sp. nov. As you can see, it is due to be published in the April 2018 issue of Cretaceous Research, but it has been available on ScienceDirect since last month.

Since the ICZN Code recognises electronic publication for species described after 1 January 2012, should the authority of this taxon be cited as "Carneiro, 2017" or "Carneiro, 2018"? In other words, should we use the date on which the journal carried the article or the actual date when it was published online? Thanks.--Leptictidium (mt) 12:49, 29 December 2017 (UTC)

Articles should not use commercial sources like Sciencedirect, Elsevier and alike, which are definitely not freely available, not even in university libraries. See WP:Identifying reliable sources#Vendor and e-commerce sources The journals from these companies usually are tho. So best use the journal reference. --Kharon (talk) 14:14, 29 December 2017 (UTC)

Neither Sciencedirect nor Elsevier are vendor and e-commerce sources and the guideline that you cited is not applicable to them. Ruslik_Zero 19:40, 29 December 2017 (UTC)

I don't know what you mean by 'not even in university'. Lots of universities have access to Elsevier. In the same way that Wikipedia editors have access to it: [1].--Hofhof (talk) 22:44, 29 December 2017 (UTC)

• The answer to the original question is that you should use the date assigned to the article by the journal, because any other approach would lead to unacceptable confusion. Looie496 (talk) 20:24, 29 December 2017 (UTC)

Sorry, but this is incorrect in general. Often the date printed in the journal predates when a journal was printed (because of publication delays), or may postdate when an author distributed reprints. The date of publication to be used is "the earliest day on which the work is demonstrated to be in existence as a published work". For that reason the library stamps on journal issues indicating when they were received can be important historical evidence about priority in taxonomy. For zoology, the relevant part of the ICZN code is Chapter 5 (http://www.iczn.org/iczn/index.jsp). Jmchutchinson (talk) 16:04, 30 December 2017 (UTC)

• It only took a moment to search out the ICZN rule change you mentioned at [2] - article 9.9 explicitly says that electronic pre-publication doesn't count. This is an arbitrary decision; however understandable the choice may be, there was no way to decide it from first principles. Wnt (talk) 11:36, 30 December 2017 (UTC)

• It is not quite that simple, but depends on whether the electronic pre-publication is the “version of record”, that is the final version, which will be identical to the printed version. If the electronic version may be updated prior to printing on paper, the rules are clear according to the ICZN: "21.8.3. Some works are accessible online in preliminary versions before the publication date of the final version. Such advance electronic access does not advance the date of publication of a work, as preliminary versions are not published (Article 9.9)." For the botanical code, the rules are very similar (http://www.iapt-taxon.org/nomen/main.php?page=art30).

However, if the electronic version is identical to the later printed version, and especially if the publisher designates it as the version of record, then my understanding is that the date of publication is that of this electronic version. I think to remember that it is not considered important whether an electronic version of record includes the page numbers of the printed version. For instance, the respected taxonomic journal ZooKeys writes (https://zookeys.pensoft.net/about): "The journal publishes electronic versions of the articles when these are ready to publish, without delays that might be caused by completion of an issue. These electronic versions are not "pre-prints" but final and immutable (Version of Record), hence available for the purposes of biological nomenclature. The date indicated on the electronic version is to be considered the actual publication date." Jmchutchinson (talk) 14:29, 30 December 2017 (UTC)

Good catch! I am more accustomed to sections like this, which I think are clearly excluded by the policy, but you give a perfect example to the contrary. Wnt (talk) 15:14, 30 December 2017 (UTC)

• Wikipedia is a tertiary source. We don't need to worry about establishing priority, etc. That is someone else's problem. In so far as we actually need to discuss disputes about priority that ought to be done by citing secondary sources that discuss the issue. However, that does not appear to be the crux of the question being asked. The OP seems to be asking what is the correct way to cite: [3]. Our goal is to provide a clear citation to allow others, including those without internet access, to find the paper. For that purpose, I agree with the comment above that using the date provided by the publisher as it appears on the paper is the only reasonable choice when writing out the citation since that is the natural way that someone would look up the paper. So, I would write the full citation as :

Carneiro, Leonardo M. (April 2018). "A new species of Varalphadon (Mammalia, Metatheria, Sparassodonta) from the upper Cenomanian of southern Utah, North America: Phylogenetic and biogeographic insights". Cretaceous Research. 84: 88–96. doi:10.1016/j.cretres.2017.11.004. Retrieved December 30, 2017. 

Giving any other date for the paper than the publisher's date of April 2018 seems likely to make it harder to find. Then, if one is giving a short reference to this citation, I would say "Carneiro, 2018" is the way to go. Dragons flight (talk) 21:44, 30 December 2017 (UTC)

You misinterpret the original question. The issue is not how to cite an article in Wikipedia or in another publication but how to write the "taxonomic authority". You will be familiar with the Latin binomial name given to every species, but the full scientific name includes a reference to the original description; for instance "Rattus norvegicus (Berkenhout, 1769)". See Author citation (botany) and Author citation (zoology). It is often a requirement to quote the name in full including the taxonomic authority (author and date) at the first mention of a species in a scientific article, so that readers can be sure which species is being referred to (another author, or even the same one, might later have used the same name to refer to another species). Except in some taxonomic papers, the full bibliographic details of such works are not routinely listed in the reference section. But it is important to follow the formal rules of which date to use for the taxonomic authority. One reason is so that everybody uses the same date in this context; otherwise it appears that two different species might have been described using the same name. A second reason is that this date is the criterion deciding what name has priority: if two publications described the same species, it is the one with the earlier date that is valid. You would be doing nobody any favours by writing a non-standard date here, even if it might make it easier to find the original publication. And according to the formal internationally agreed rules of scientific nomenclature, it is simply wrong.

In other situations when citing publications, cases of dates written in publications not matching their actual date of publication are often dealt with by writing both dates with one in square brackets, and perhaps using inverted commas. There seems to be considerable variation between journals in how this is done. But, to re-emphasise the main point, including both dates like this and using square brackets are explicitly not allowed when including the taxonomic authority in the formal name. Jmchutchinson (talk) 09:24, 31 December 2017 (UTC)

Perhaps Leptictidium would like to clarify. I agree the question is ambiguous, but the context still suggests to me that he is asking how "we" (as Wikipedians) should state the citation and taxonomic authority. If instead he is asking how he should state it in some other context (a journal article he is writing perhaps?), then the answer might be different. I stand by my answer as it comes to Wikipedia. I believe that a Wikipeidian who is citing this paper when referencing the creation of this species should also give the paper's corresponding date in any statement of authority (i.e. Carneiro, 2018). To be explicit, to the extent there is an interpretation of ICZN rules that might be read to give a different statement of authority, then in my opinion that should be ignored on Wikipedia as long as the only source is the paper itself. A) It is likely to create confusion if the full citation and the short authority statement disagree, B) it isn't Wikipedia's job to decide such issues of priority, and C) the interpretation of ICZN rules arguably requires original research. If some later review article or other source assigned a different taxonomic authority (e.g. "Carneiro 2017"), then Wikipedia could cite the later source when stating the authority. In the absence of such a third-party clarification though, and when the only source provided is the paper itself, I believe the reasonable course is for Wikipedia to treat the information as it would other citations and use the publisher's date. Dragons flight (talk) 19:21, 31 December 2017 (UTC)

Sorry for not making the question clear enough. Indeed, I am not asking how to cite the paper, but how to write the taxonomic authority. Based on the above answers, since the version available on Sciencedirect seems not to be the full article, merely a short advance extract, I'm inclined to go for "Carneiro, 2018". Thanks everyone for your valuable feedback.--Leptictidium (mt) 19:35, 31 December 2017 (UTC)

• The pdf of the full version of this particular article is behind a paywall, to which I have no free access. However, it does appear to be available. With reference to the issue in which this article appears, the journal web site (https://www.sciencedirect.com/science/journal/01956671/84/supp/C) states that "This issue is In Progress but contains articles that are final and fully citable." That implies that the electronic version is the version of record, and so the authority should be Carneiro 2017. My opinion is that there is here no freedom of choice about how to write the taxonomic authority correctly. But if you cite the article, you can write Carneiro (2017 [“2018”]), or something similar, to clarify the situation. I agree that this is an unfortunate circumstance, but presumably not such an unusual one nowadays. However, it is routine in old literature that printed publication dates do not reflect reality, and taxonomists are very used to dealing with that situation appropriately, so that the consequent mismatch of dates is thus not so surprising to professionals. Nowadays in some journals the final printed pdfs make clear the date of online publication, which is good practice. Jmchutchinson (talk) 21:16, 31 December 2017 (UTC)

December 30

Feynman Lectures. Exercises. Exercise 16-5 JPG

. .

...

The Berkeley "bevatron" was designed to accelerate protons to sufficiently high energy to produce proton-anti-proton pairs by the reactio

p + p --> p + p + (p + p)

The so-called threshold energy of this reaction corresponds to the situation when the four particles on the right move along together as a single particle of rest mass M = 4 m_p. If the target proton is at rest before the collision, what kinetic energy must be bombarding proton have at threshold?

—  R. B. Leighton , Feynman Lectures on Physics. Exercises

${\begin{cases}m_{\text{pv1}}+m_{\text{p0}}=4m_{\text{pv2}}\\m_{\text{pv1}}v_{1}=4m_{\text{pv2}}v_{2}\\m_{\text{pv1}}={\tfrac {m_{\text{p0}}}{\sqrt {1-v_{1}^{2}/c^{2}}}}\\m_{\text{pv2}}={\tfrac {m_{\text{p0}}}{\sqrt {1-v_{2}^{2}/c^{2}}}}\end{cases}}$

${\begin{cases}v_{1}={\tfrac {4{\sqrt {3}}}{7}}c\\v_{2}={\tfrac {\sqrt {3}}{2}}c\\m_{\text{pv1}}=7m_{\text{p0}}\\m_{\text{pv2}}=2m_{\text{p0}}\end{cases}}$

So I got $0.5m_{\text{pv1}}v_{1}^{2}={\tfrac {24}{7}}m_{\text{p0}}c^{2}$

But Feynman answer is $6m_{\text{p0}}c^{2}$.

Why?

Username160611000000 (talk) 12:55, 30 December 2017 (UTC)

It seems Feynman has used a formula $T=(m_{\text{pv1}}-m_{\text{p0}})c^{2}$. Username160611000000 (talk) 15:45, 30 December 2017 (UTC)

Suppose that the full 4D momentum of the 4 resulting particles is $u$. Since at the threshold it behaves like a single particle with mass $4m_{p}$ we have $u^{2}=16m_{p}^{2}c^{2}$. On the other hand the 4D momentum of initial proton at rest is $u_{1}=(m_{p}c,0)$ and that of the moving initial proton $u_{2}=(m_{p}c+K/c,\mathbf {p} )$ where $K$ is its kinetic energy and $\mathbf {p}$ its 3D momentum. So, we have $(u_{1}+u_{2})^{2}=2m_{p}^{2}c^{2}+2m_{p}c(m_{p}c+K/c)=u^{2}=16m_{p}^{2}c^{2}$. Quite obvious that $K=6m_{p}c^{2}$. Ruslik_Zero 20:57, 30 December 2017 (UTC)

@Ruslik0: That's a great derivation, except ... aren't you saying that the four resulting particles are at rest? If they're at rest, they should be in the frame where the two colliding protons have equal and opposite velocities. Wnt (talk) 17:05, 31 December 2017 (UTC)

Yes, it is true that they are at rest in the reference frame of their center of mass (at the threshold). In the laboratory reference frame they have exactly the same 4d momentums. You can easily understand why: in the center of mass frame two initial protons have the same energy and momentum but move in opposite directions towards each other. So, their total 3d momentum is zero. If we are at threshold of the reaction, all kinetic energy of both moving protons is spent to create a proton-antiproton pair. Therefore in the final state all four particles are at rest in the center of mass frame. When we transform the reference frame back to the laboratory frame, 4d momentums of the final four particles remain equal to each other. So, if $u'$ is the 4d momentum of one of those four particles, then their total momentum is $u=4u'$ and $u^{2}=16u'^{2}=16m_{p}^{2}c^{2}$. Ruslik_Zero 17:34, 31 December 2017 (UTC)

Momentum and energy is conserved, not momentum and inertial mass. So your first equation is the one that is wrong. Dragons flight (talk) 22:30, 30 December 2017 (UTC)

I feel like an idiot when I try to do this, but hopefully it is, by definition, a method any idiot can follow. Looking at the system in the final frame of the four proton masses, we need two proton masses of mass + two proton masses of energy to begin with, so each proton has a relativistic mass twice that of its rest mass. Actually that just lets us directly set gamma = 2 = 1/sqrt(1-v^2/c^2). So v = sqrt(3)/2 c. Now using the velocity-addition formula I get that if one of the initial moving protons is set at v=0, the other (with twice the speed) is now at sqrt(3) c / (1 + 3/4) = 4 sqrt(3)/7 c. Taking that gamma formula, that gets 1/sqrt(49) i.e. gamma=7. One mc^2 of that is actual rest mass and 6mc^2 is kinetic energy. Double checking with the energy-momentum relation and saying that E^2 = (m c^2)^2 + (p c)^2, we first use p = gamma m v with the two sets of gamma and v values to get 2 * m * sqrt(3)/2 c = sqrt(3) m c and 7 * m * 4 sqrt(3)/7 c = 4 sqrt(3) m c. Then we put that into the formula and we have E = 2 m c^2 and E = 7 m c^2 respectively. So we do indeed have 4 m c^2 on two protons with equal speed in the final frame and 7 m c^2 on one proton moving + 1 m c^2 on one proton at rest in the lab frame. In the lab frame we know that all the protons have 2 m c^2 total energy after the collision x 4 so this energy is properly conserved. And the 4 sqrt(3) m c value for p on one proton in the lab frame allows all the protons coming out to end up moving with momentum sqrt(3) m c.

I will admit, however, that I am having a very hard time following anyone else's calculation above, and I fear the same may be true here. :( Wnt (talk) 02:42, 1 January 2018 (UTC)

Your derivation is correct but it can be done much simpler as I showed above. Ruslik_Zero 17:13, 1 January 2018 (UTC)

If you can lead me to some background on how to use 4D momentum as you are, I'd welcome it. Our offering on four-momentum seems more mysterious than useful to me at present. I was fiddling about on my own and derived a way to add gamma factors directly: "g1+g2" (by which I really mean, the gamma factor of something with gamma factor g1 viewed from a frame at a velocity in the same direction that would impose gamma factor g2) works out to be g1*g2 + sqrt(g1^2*g2^2-g1^2-g2^2+1). There is probably some way to make that more concise and to make it into a vector result to boot, but it is already an improvement for this problem: knowing that each proton has to have gamma factor = 2 to carry the extra relativistic mass to make a new proton, I can then shift the frame and calculate directly the gamma on the moving proton is 2*2 + sqrt(4*4-4-4+1) = 7, meaning it carries 6 proton masses of kinetic energy plus its rest mass. Wnt (talk) 18:35, 1 January 2018 (UTC)

P.S. when g=g1=g2 this reduces to 2*g^2 - 1, so repeatedly "doubling velocity" should get gamma factors of 2, 7, 97, 18817, 708158977... all apparently numerators of diophantine approximations to the square root of 3,[4] if that means anything. ...Actually, if g(n) is 1,2,7,26,97,362,1351,5042,18817,70226,262087,978122 for n=0,1,2,3,4... then viewing g(n1) from a frame with g(n2) seems to yield an integral gamma value g(n1+n2). Wnt (talk) 20:32, 1 January 2018 (UTC)

PP.S. Actually those diophantine approximations seem relevant -- the velocities for those gamma values are the inverse of the diophantine approximations * sqrt(3) * c: 0, sqrt(3)/2, 4*sqrt(3)/7, 15*sqrt(3)/26, 56*sqrt(3)/97 etc. Each velocity is reached from the preceding by shifting the frame by a velocity of sqrt(3)/2 c. (the momenta are thus 0,1,4,15,56... * m * sqrt(3) * c), appearing here as the numerator, with gamma as the denominator of each speed) Wnt (talk) 03:21, 2 January 2018 (UTC)

Writ, I agree that all these maths can be really hard to follow... and the required gamma factor is 2 as you determined above from considering the center-of-mass frame, a factor that fixes the final kinetic energy of the proton accelerated from rest, so in the lab frame it is $m_{p}c^{2}$ (since their kinetic energies are given by $(m-m_{0})c^{2}$ or $(gamma-1)m_{0}c^{2}$). The total energy of the four protons (which I've assumed behave as a single particle at the threshold as pointed out by Ruslik0) is thus 4*(rest energy + kinetic energy) or $8m_{p}c^{2}$. Given that the energy of the rest masses of the initial two protons are $m_{p}c^{2}$ each, by energy conservation, the additional kinetic energy of the initial bombarding proton is $6m_{p}c^{2}$. This is a simpler derivation, if I'm not mistaken and implied by your double check above, that doesn't mess around with the velocity-addition formula or the four-momentum with this particular problem. -Modocc (talk) 03:34, 2 January 2018 (UTC)

Simply put, bring the 4-momentum you want to eliminate to one side of the equation and square it, as the square of the 4-momentum yields the known mass and thereby indeed eliminates the variables (energy and momentum) you want to get rid of. Count Iblis (talk) 16:08, 2 January 2018 (UTC)

I should mention that I took a sidetrack of this to the Math Desk and eventually learned that a key concept here is rapidity, which is $ln{\sqrt {\frac {1+x}{1-x}}}$, with x = c/v, or $1/2ln{\frac {c+v}{c-v}}$ if you prefer. Unlike velocity, rapidity is additive between frames, so it seems worth learning more about to solve this sort of problem. Wnt (talk) 12:49, 3 January 2018 (UTC)

December 31

How many of a 100 year old's atoms have been in their body their whole adult life?

Which elements are these atoms most likely to be? Atoms of which elements are most likely to stay? (not necessarily the same since they could be rare)

Do weight changes or yo-yo dieting affect this or is lipid storage an unlikely place for atoms that don't leave the body for decades to have been?

2. Could their body at this instant have an atom that has spent at least 1/2 continuous centuries outside and came back? Well of course it can but is this almost certain, almost certainly false or in between? How is such an atom most likely to leave and return? (i.e exhalation, food, water) Sagittarian Milky Way (talk) 01:00, 31 December 2017 (UTC)

Seriously, SMW, this is the sort of nonsense that made User:Floquenbeam suggest that you might be a candidate for a topic ban. We don't do predictions or debate. This is not a forum. I suggest you do with this what you did with your enquiry on the Klingon word for diaper. μηδείς (talk) 01:07, 31 December 2017 (UTC)

When did I ask about Klingon? I've never asked about Klingon. Sagittarian Milky Way (talk) 01:13, 31 December 2017 (UTC)

Medeis might have been thinking of this, which was posed by a 140 IP. Floq's comment came in reference to SMW's Muzak question.[5] ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:10, 31 December 2017 (UTC)

Oh, my. I think the question speaks for itself μηδείς (talk) 17:22, 31 December 2017 (UTC)

I would say virtually none remain. Cells die, even fat cells. Cells respirate. It's hard to imagine that a cell lives without exchanging atoms. --DHeyward (talk) 02:34, 31 December 2017 (UTC)

Exhalation is the dominant effect here, you can use the information in this article to calculate the exhaled body mass per unit time for some given metabolic rate. This is the same as the absorbed body mass from carbs and fats in food for someone who has a stable body weight. If you then assume that the exhaled CO2 mixes with the atmosphere, then it's easy to compute the fraction of the carbon that comes back later from the food you eat. Count Iblis (talk) 02:37, 31 December 2017 (UTC)

User:Sagittarian Milky Way is not asking about that. He is interested in turnover time. For example, collagen molecules in cartilage have a 400 year median turnover time. So some of them remain in your body for your whole life. Abductive (reasoning) 05:45, 31 December 2017 (UTC)

The question as posed is meaningless. All atoms of the same sort are identical to each other. Therefore one can not distinguish "old atoms" from "new atoms". On the hand complex molecules can be "old" as they can carry some defects which can be used to distinguish them from other molecules of the same sort. Please, see this. Ruslik_Zero 17:15, 31 December 2017 (UTC)

Fundamental particles are identical, yet the ways they are assembled are not - which includes atoms, since there are isotopes. Count Iblis gave an excellent example above -- the amount of carbon-14 in hippocampus DNA depends on date of birth, even though there is some turnover. Wnt (talk) 17:50, 31 December 2017 (UTC)

Note: the excellent answer was given by User:Fgf10 and promptly removed by some drama asshole with nothing to contribute ([6]). Here it is: Another possibility for long lived atoms is in the DNA of non-dividing cells, such as neurons. This has been used to carbon date cells, and see here for an example of cells with DNA containing carbon incorporated well before the onset of atmospheric nuclear testing. Fgf10 (talk) 15:09, 31 December 2017 (UTC)

See the Biology section of the Bomb pulse article --catslash (talk) 19:20, 31 December 2017 (UTC)

Ruslik is correct, the question as posed is rambling and meaningless. We have no way of determining how many of the atoms of you are born with will last over any period, or especially whether "their body at this instant have an atom that has spent at least 1/2 continuous centuries outside and came back?" Iblis hasn't addressed that by pointing out that people born at certain times have more or less of certain isotopes, it doesn't generalize into anything other than a sophomore bullshit session. μηδείς (talk) 00:56, 1 January 2018 (UTC)

I'm not sure I understand the hostility to the question. Carbon dating is based on the exchange of atoms. How close the body and its parts resemble natural radioisotopes is very meaningful. Radioisotopes are also not chemically identical to each other as carbon uptake by plants is different for different carbon isotopes. --DHeyward (talk) 01:12, 1 January 2018 (UTC)

I apologize for inadvertently deleting FGF's comment when I reverted his busy-body hatting.

":Another possibility for long lived atoms is in the DNA of non-dividing cells, such as neurons. This has been used to carbon date cells, and see here for an example of cells with DNA containing carbon incorporated well before the onset of atmospheric nuclear testing. Fgf10 (talk) 15:09, 31 December 2017 (UTC)"

Thankfully, I am not inclined to sink to his level of arrogance and low-life chatter. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:14, 1 January 2018 (UTC)

Lest there be any confusion, this is my level of annoyance, expressed before I quoted his posting above. We do not need trolls who don't answer the questions and do destroy the good answers to the questions while waving bogus administrative claims against people who asked good questions; people who win every debate on what gets "hatted" and one doesn't according to one simple policy, namely that the race goes not to the swift nor the strong but to him that edit-wars unto the end. This is a classic good question, asked fairly often in biological circles and answered with varying degrees of persuasiveness, and Fgf10 provided a decent example. Wnt (talk) 04:51, 1 January 2018 (UTC)

No one is stopping you, Wnt. Please do answer "How many of a 100 year old's atoms have been in their body their whole adult life" and whether "their body at this instant have an atom that has spent at least 1/2 continuous centuries outside and came back?" μηδείς (talk) 05:14, 1 January 2018 (UTC)

Just because you lack to knowledge to awnser the question doesn't mean everybody else does. Please don't troll. Thank you! Fgf10 (talk) 10:15, 1 January 2018 (UTC)

Just because a question is difficult to answer does not mean that it should not be asked. I've learned a lot about neurons and collagen reading this debate and it's possible that others might contribute further insights. Someone might post an approximate answer or be able to answer a different but related question. It was a perfectly sensible question (to which I don't know the answer). Robinh (talk) 07:31, 1 January 2018 (UTC)

The question about atoms leaving and returning is harder to answer, but we can certainly lay down some approximations. If we suppose that products leaving the body are perfectly mixed into the rest of the world, then we can say that people take about 9 kilograms of nitrogen gas into their body daily (promptly expelling it again) [7] and release about 1 kg of CO2 daily [8] and drink about 3 liters = 3 kg of water a day [9]. These are all very approximate figures, but for reasons we'll see below even an order of magnitude is more accuracy than we need. The global carbon pool in the atmosphere is 750 Pg (that's petagram, x 10^15 g) [10]; obviously there's some exchange out of that to the oceans and crust but again, order of magnitude argument here. The pool of water is 1,338,000,000 km^3 = 1.3 x 10^18 m^3 = 1.3 x 10^21 dm^3 = 1.3 x 10^21 kg. [11] for the first. And Earth's atmosphere should have about 4 x 10^18 kg of nitrogen. (see atmosphere of Earth, multiply by 78% or so - also confirmed here) Now taking each of these dilutions, we see that the water is diluted 3 kg in 1.3 x 10^21 kg is about 1 in 2 x 10^21, the CO2 is diluted 1 kg in (7.5 x 10^17 g C = 7.5 x 10^14 kg C x (48 g CO2/12 g C) = 3 x 10^15 kg CO2) or 1 in 3 x 10^15, the nitrogen is diluted 9 kg in 4 x 10^18 kg is about 1 in 5 x 10^17. Now Avogadro's number is 6.022 x 10^23 atoms per mol; a mol of water is 18 g, a mol of CO2 is 48 g, a mol of nitrogen is 28 g. So 9 kg of nitrogen contains about 300 mol, which means it has 1.8 x 10^26 molecules (multiplying by Avogadro's number). If these are perfectly diluted into the nitrogen of the atmosphere and rebreathed, you get that diluted by a factor of 5x10^17, which means you're still breathing in, oh, close to 4 x 10^8 = 400,000,000 molecules that you breathed on some day in the distant past; double that for atoms. (For this purpose it doesn't really matter if they've found new partners in the meanwhile). Likewise you're breathing that many atoms breathed by Jesus on the day of the Sermon on the Mount or whatever, because according to [12] all the other non-geologic nitrogen pools are pretty small compared to atmosphere. I'll leave the others as an exercise, though tracing the CO2 involves some more figuring since so much of the carbon and oxygen end up in other forms.

The catch to all this though is that the mixing isn't random, especially with non-nitrogen elements that can more readily react close to the site of production. If you end up living in the same house after 50 years somehow, a drop of boyhood pee on the floor may have combined with some calcium in grout or cement or something, to release countless billions of oxygen atoms on a warm day fifty years later. Seems absurd, but think of the levels of dilution we're talking about here! You can release billions of atoms from a spot on a floor and not notice *any* difference in what is left. As a result, the non-random flows seem likely, by idiosyncratic and bizarre means, to swamp the smaller random flows. Wnt (talk) 16:52, 1 January 2018 (UTC)

• It is precisely because I do know the absurd number of variables involved in this arbitrary question with so many undefined parameters, (I majored in biology as an undergrad, did the air Jesus breathed calculation four decades ago, tested out of Chemistry 101 & 102, having gotten a 5 on AP chem, and understand the conservation of DNA molecules versus the recycling of red blood cells) and the fact that not a single RS is going to answer it, that I am closing this bullshit session as a request for prediction and debate. μηδείς (talk) 17:08, 1 January 2018 (UTC)

Stop your disruptive behaviour or I will be forced to take this to ANI. Several people have provided partial answers, something you have neglected to do. The vendetta you and BB have against Sagittarian is ridiculous. Fgf10 (talk) 18:23, 1 January 2018 (UTC)

You have jumped to a false conclusion. And you need to fix your own vendettas before worrying about someone else's alleged vendettas. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:44, 4 January 2018 (UTC)

Earth science not biology might be the biggest problem with 2. for water. Most of the industrialized world doesn't fertilize their food with their waste or drink their recycled pee and breath but flushes it far away so if rebreathing your own water vapor isn't considered becoming part of the body if it doesn't reenter the blood then perhaps random mixing isn't so far off for them. Then the chance of ~10³⁰ water atoms/decade shuffling between pools of ~10⁴⁷ and ~10^27.2 water atoms causing at least one of them to be in the smaller one now and the bigger one for at least 50 contiguous years of the last 100 seems possible to estimate with mathematics. The worldwide tropospheric mixing time is only about a year but most water is sea and the thermohaline circulation takes a millennium so even if that calculation showed a high probability 2. is true it'd require more earth science than I know to know to see if that answer isn't bullshit. Sagittarian Milky Way (talk) 20:17, 2 January 2018 (UTC)

If it is so obvious that this is an unanswerable question, then presumably there will be reliable sources stating that it is an unanswerable question. In which case surely the appropriate way to treat this question is to link to the source that states it is unanswerable. Iapetus (talk) 14:40, 3 January 2018 (UTC)

January 1

sanding/filing/grinding stainless steel

I have some stainless steel parts[13] with burbs and burn marks on them that I want to clean up. Googling around I found three ways of accomplishing this easily at home without any heavy power tools:

1. Sand with sandpaper

2. File with a file

3. Grind it with a grinding attachment on a dremel

Cost wise all three are about the same (I have a dremel already, just no grinding tools). Which of these three methods is the least time consuming? Which produces the best results? Mũeller (talk) 03:15, 1 January 2018 (UTC)

For an professional a file is the fastest because there is not need for any tool preparation. The result depend on your skills in every case, especially with a file, which needs allot of practice for best results. For an amateur i would recommend sand paper and i would not, no matter what tool, expect "best results". In case of some "hidden skills" the result may end up being ok ofcourse. --Kharon (talk) 05:33, 1 January 2018 (UTC)

Once you have the equipment, a dremel will almost certainly provide the quickest execution. However, it is also the most prone to accidentally removing more material than you intended. It takes a fair amount of skill to handle a dremel with precision. A small metal file is likely to be the most precise approach. Professionals can use a file in a manner that is both fast and precise; however, I generally find that even amateurs can do a decent job with a file if they take it slow. I'm not a fan of using sandpaper for removing large imperfections on metal (e.g. burrs), though very fine sandpaper may be appropriate for cleaning / polishing. Dragons flight (talk) 08:45, 1 January 2018 (UTC)

Agreed. In particular, it seems that cleaning up the holes with a dremel would lead to unwanted beveling unless great care was taken. Matt Deres (talk) 16:52, 1 January 2018 (UTC)

• I do a lot of this. I would usually polish it with a Garryflex block - a rubber block impregnated with abrasive powder. Several grades are produced, colour coded, and they're produced worldwide under several different brands. As usual, start coarse and work through to fine.

If it's too discoloured or damaged to start with these hand tools, smooth it first by machine, using a foam-backed flap disc on an angle grinder. Use a foam-supported one, to avoid making more machine facets.

If you have the equipment, and especially for many small parts that are mostly corners, then the best way could be to grit blast it.

Stainless steel should be passivated after finishing, to avoid it self-passivating naturally and possibly discolouring in blotches. This can be done by wiping it with citric acid, or even just lemon juice. Andy Dingley (talk) 20:51, 1 January 2018 (UTC)

The best and most used method was not mentioned: Sandblasting! The results are usually superior and you dont have to worry about overdoing or doing it wrong. Its like painting with airbrush, actually a very satisfying, fun task to do. And economical and fast aswell.

In case you count yourself proud member of the Do it yourself-club and do all sorts of work, you may even want to check out how easy it is to build your own little sandblasing cabinet. There are many videos on youtube unter "sandblasting DIY". --Kharon (talk) 12:59, 2 January 2018 (UTC)

Of course it was already mentioned.

Don't use sand for this though, use an abrasive grit, manufactured for the task - probably a silicon carbide grit, maybe glass beads, depending on the grade of stainless, the dirt to be removed and the amount of edge rounding that's acceptable. Sand has very few appropriate uses left for literal sand blasting, as it's not the best medium to work with and it also has safety hazards (the dust hazard from sand blasting is far worse than grit blasting). Andy Dingley (talk) 13:07, 2 January 2018 (UTC)

Oh sorry, i oversaw you mentioned "grid blast". Regarding the hazards was why i mentioned building a cabinet for that. Most professional shops have one and if build and handled right it is very save work. --Kharon (talk) 13:22, 2 January 2018 (UTC)

Most grit blasting cabinets can't be used for sand (if you're bothering to follow the appropriate regs). The exhaust air needs filtering too. You can't allow sand-shard-laden air into a workshop. Andy Dingley (talk) 20:36, 2 January 2018 (UTC)

Some even use glass perls and good cabinets have a circular system where the abrasive is reused. A vacuum cleaner needs a filter too. Never heard that kept anyone from using one in a workshop. --Kharon (talk) 04:37, 3 January 2018 (UTC)

They all need an air outlet (if they don't, or it's not enough, the door can fly open and whack you in the face!). If the interior air is full of silica shards, that air outlet needs to be filtered.

Sand isn't re-used. It's cheap and it wears out too quickly. One of the few things sand is still used for is when it can't be captured and recycled like this.

If you're cleaning up some hazardous powder materials, like silica dust or asbestos, your vacuum cleaner filters need to be maintained, with change schedules and records keeping, as much as your breathing gear does. Andy Dingley (talk) 11:36, 3 January 2018 (UTC)

Split rocks on Theodore Roosevelt Island

I am wondering if anyone might shed light on these three rocks that were photographed on Theodore Roosevelt Island? Is this splitting possibly the result of a natural process? If so, please describe ... Many thanks in advance -- P999 (talk) 18:29, 1 January 2018 (UTC)

By definition it is the result of a natural process. ;) The question is which. What I know is that the description given of gneiss and schist doesn't obviously match with the basalt of the most dramatic formation with this appearance I can think of, which is Giant's Causeway. On the other hand, they are metamorphic rocks, which raises a bit of a question of how metamorphic and metamorphed from what ... I wish I could say more, but I certainly don't know presently. Wnt (talk) 19:03, 1 January 2018 (UTC) Sorry, I realize the dramatic top photo on that site probably is just a bannerhead and not about this location at all. Though List of places with columnar jointed volcanics does list a site in Virginia not too far from the Potamac. Wnt (talk) 19:11, 1 January 2018 (UTC)

Such "erratic" rocks were certainly carried by glaciers. Ruslik_Zero 19:08, 1 January 2018 (UTC)

I regret that I was unable to provide a link directly to the photograph of the split rocks in question, but the website where it resides, being a blog, does not seem to allow individual links to the images; however, I have tried to improve the description of the rocks to which I am referring in my query. Thank you very much for your responses, Users Wnt and Ruslik. These rocks are of particular interest to me because they are either on, or a short distance from, the eastern limit of the Atlantic Fall Line which passes through the southern tip of TR Island ... P999 (talk) 20:11, 1 January 2018 (UTC)

You mean this link to these rocks? --76.69.117.217 (talk) 20:54, 1 January 2018 (UTC)

Yes, thank you very much! I will change my query to include it.

Yes, it's likely a glacial erratic, but that doesn't explain the breakage. My guess would be frost weathering; if you check out the photo in that article, the broken rock there is quite similar to the one in question. Matt Deres (talk) 02:38, 2 January 2018 (UTC)

I find it very hard to believe that it is a glacial erratic. The last glacial maximum did not reach as far south as the Roosevelt Island . (Great Falls is a few miles upstream) — Preceding unsigned comment added by Addisnog (talk • contribs) 04:34, 2 January 2018 (UTC)

Much more likely to be a boulder carried down by the river, but I agree about the frost shattering as the likely explanation for the splitting. Mikenorton (talk) 11:11, 2 January 2018 (UTC)

It may not be the last maximum. Ruslik_Zero 13:24, 2 January 2018 (UTC)

Fixed your confusing typo. --76.69.117.217 (talk) 21:26, 2 January 2018 (UTC)

For a simple explanation of the process, see Frost Wedging. Alansplodge (talk) 11:43, 2 January 2018 (UTC)

References

January 3

That's enough. Matt Deres (talk) 21:21, 3 January 2018 (UTC)
The following discussion has been closed. Please do not modify it.
Does Social Peer Pressure prevent people from stating the obvious? "up" If everyone is walking upside down on the south pole, does the social peer pressure from the scientific community which lives there in the south pole, prevent a good scientist from mentioning that they are all walking upside down? Perhaps the reason they do not know that they are walking upside down is because if everyone is walking upside down then from their point of view, they seems to be walking the right side up. 110.22.20.252 (talk) 06:11, 3 January 2018 (UTC) On Earth, "up" is the normal vector from the (spherical) surface, therefor anybody walking on the surface is doing so "right-side-up" (unless they're walking on their hands, of course). 2606:A000:4C0C:E200:3410:B2CC:5D3A:A0AC (talk) 06:58, 3 January 2018 (UTC) If the OP is serious with this question, he should sue his educational system for fraud. ←Baseball Bugs What's up, Doc? carrots→ 07:55, 3 January 2018 (UTC) It would only be upside down relative to the north pole. Even though it is still normal for whoever is standing there, the Moon and sky will appear to have been turned around. When I travelled to Alaska recently, I noticed that the Moon was sideways on there. Graeme Bartlett (talk) 09:24, 3 January 2018 (UTC) Simply adapt the old divers trick. Get a glass of water and a straw, make some bubbles and watch where they go. Thats "up"! --Kharon (talk) 09:51, 3 January 2018 (UTC) Answering the title question rather than the post: see our article about Asch conformity experiments. On a side note: a look at OP's contributions makes me suspect the question is serious, although either scientific reasoning or English language is an issue. TigraanClick here to contact me 10:02, 3 January 2018 (UTC) At the South Pole. It is not obvious here why the UK's flag flies upside-down while its facsimiles are correct on the flags of Australia and New Zealand. SdrawkcaB99 (talk) 20:35, 3 January 2018 (UTC) Here's a picture of someone at the South Pole. As you can see they are not doing anything unexpected. Since you're on to this how about pondering that other strange thing - how is it that people know the name of the star Betelgeuse when it is 640 light years away and nobody could ever have been there? ;-) Dmcq (talk) 10:11, 3 January 2018 (UTC) Easy! The Betelgeusians send a light-speed message around 170 CE, which Muhammad ibn Musa al-Khwarizmi captured with an early version of the radio telescope, and introduced into the scientific literature of the time. Need proof? There is no earlier recorded use of the name - how else can you explain that?!?!?!11! --Stephan Schulz (talk) 15:23, 3 January 2018 (UTC) (edit conflict)Do people near to the equator realise that they are walking horizontally, and spinning slowly tumbling head-over-heels? Slightly more seriously, if map-making had been first developed by a civilisation in the southern hemisphere, then the south pole would probably have been at the top, and it would be us northerners who walk upside down without realising it. Dbfirs 15:49, 3 January 2018 (UTC) Some old maps had east at the top.Greglocock (talk) 17:34, 3 January 2018 (UTC) See South-up map orientation. I knew an Aussie GR prof at an American uni who kept one on his door in a show of Down Under pride. -- ToE 18:14, 3 January 2018 (UTC) And in premodern China south was more important than north despite being in the Northern Hemisphere. Hence the south pointing chariot. Sagittarian Milky Way (talk) 18:25, 3 January 2018 (UTC) What really gets to me is why my questions are deleted from Science desk, I ask "attracting women" questions and people lay me as a troll or sociopath. But questions like these don't get deleted. Bummers. 12.130.157.65 (talk) 15:42, 3 January 2018 (UTC). Lots of your questions here have been answered. I think the misconception amused people. Dbfirs 15:49, 3 January 2018 (UTC)

human skeletal muscles

I have found your page that lists the human skeletal muscles. I would like to know the relative size of a muscle compared to other muscles in the body. I am a woman, so where there is a difference between male and female bodies, I'd be more interested in the female body data. Why? I have used resistance/weights exercises for years, and the usual advice is to exercise larger muscles before smaller muscles, but where is the data about muscle size/mass?---- — Preceding unsigned comment added by 156.99.40.14 (talk) 22:29, 3 January 2018 (UTC)

I did a bit of searching around, but didn't find anything useful (and didn't expect to). The size of individual muscles - however you'd want to measure it without performing an autopsy - is going to vary a lot from person to person and even side to side (the muscles on my right arm are slightly larger than the ones on my left; probably because I'm right-handed and therefore use it more). You'll occasionally see claims of longest/largest/smallest muscles (example here) but beyond that, it gets difficult to specify things. A quick look around the gym confirms that it's possible to train the body into many different forms, leading to very different muscle size ratios. Matt Deres (talk) 14:30, 4 January 2018 (UTC)

Which skeletal muscle? Your gluteus maximus is far larger than your pinky toe extensor. LongHairedFop (talk) 19:23, 4 January 2018 (UTC)

Human females have 20% less body mass on average, plus a higher fat content. But they are also shorter and have shorter limbs. So their muscles are going to be somewhat smaller than the average male's. One wonders about their proportions... And how much is cultural... Abductive (reasoning) 21:34, 4 January 2018 (UTC)

January 4

22° halos

I know that 22° halos are supposed to be very common, but I have never seen one. I have seen rainbows every now and then. I want to know how I can easily spot 22° halos. I assume that if I spot a halo, it will be a 22° halo, as other types are much more rare.

• I live in northeastern Massachusetts. Based on what I've read, this part of the world seems like a good spot to find halos. Is it?
• Do time of day, time of year, and temperature matter?
• In an open sky, seeing the halo means looking close to the sun, which causes a reflex to immediately look away. However, can I position myself so that the sun itself is blocked by a building, and I can still see the halo?
• How long do halos last? If I was to go outside tomorrow (there is a blizzard today), how likely am I to see a halo, and how many hours should I wait before checking again if there isn't one?

HotdogPi 15:18, 4 January 2018 (UTC)

It's all about the weather. I don't know about MA (or how close you are to the coast), but the dry winters of the continental US are generally good. Our article here even shows one from Salem. You need to have the right sort of high altitude ice crystals, with cold, nearly still, clear skies. I've only ever seen them really well when high in the Alps. As being cold helps, they're sometimes more easily seen at night, around the Moon. All the UK ones I've seen have been Moon halos. Andy Dingley (talk) 15:59, 4 January 2018 (UTC)

This way cool site has an explanation. Be careful, you could spend hours looking at these pics!--TammyMoet (talk) 18:17, 4 January 2018 (UTC)

I've only seen a few true 22° halos, but sun dogs are more plentiful and, as 22° optical phenomena themselves, frequently are associated with halos. You can still see the halo if the sun is blocked by a building, but that is probably not necessary; they're not as close as photos suggest. Matt Deres (talk) 18:29, 4 January 2018 (UTC)