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September 3

valved n95 respirators

It's still very hard to get unvalved n95 respirators, but valved ones (not recommended for virus protection because the exhaust port spews virus if you are infected) are getting easier to find. Home Depot near here has some. 1) Does snipping out the valve and patching the hole with a rubber seal sound like a reasonable fix to this issue? The seal would probably be a bit of cut-up nitrile glove hot-glued into the mask. From the picture I think the hole would be maybe 15mm diameter. 2) Why after all this time are regular n95 still so hard to get? There's no toilet paper shortage any more, for example. Thanks. 2601:648:8202:96B0:0:0:0:DDAF (talk) 05:47, 3 September 2020 (UTC)[reply]

I once ordered and wore a valved N95 (FFP2 in the EU) mask during pandemic. The valve there is for a reason, presumably otherwise they would not be certified as N95 (FFP2). My understanding is that "spewing" is negligible compared to the issue of heating and excess moisture buildup in a valveless mask (particularly in hot summer). Any custom modification of a N95 mask may breach its integrity and resistance. Brandmeister^talk 08:19, 3 September 2020 (UTC)[reply]

For (2), the comparison does not make much sense. Toilet paper shortages were due to (a) panic buying resulting in a build-up of stock among consumers, (b) a change in the products consumed (toilet paper bought by companies, theaters etc. is not the same product as bought by private individuals). (a) takes care of itself within a few weeks because the demand spike is followed by a demand gap, (b) can be fixed by a (supposedly easy) retooling of existing machinery. On the other hand, the demand for masks has increased dramatically since February/March and will remain at a higher-than-before level for quite some time; it is not easy to expand production ten-fold at short notice, even with big price incentives. Tigraan^{Click here to contact me} 08:45, 3 September 2020 (UTC)[reply]
Most studies indicate such valved masks are not terrible in spreading the virus, as long as the valves are properly used. This is just one example of many articles on the subject. The valved mask is not as good as the full N-95, but it is, within error bars, comparable to, and in some cases better than, things like cotton masks and surgical masks. In short: The valved mask is not as good as the full N-95, but neither does it "spew virus", and it is comparable to the wide range of other kinds of masks on the market, and much better than things like bandanas and T-shirt material buffs. If you can't get the fitted N-95, the valved one may be among your next best options. --Jayron 32 11:47, 3 September 2020 (UTC)[reply]

Why is surgery done with only surgical masks? Sagittarian Milky Way (talk) 15:57, 3 September 2020 (UTC)[reply]

Sometimes they also use surgical knives. --Lambiam 21:13, 3 September 2020 (UTC)[reply]

It gets worse, i've heard some rogues even wear surgical gloves! Zindor (talk) 21:46, 3 September 2020 (UTC)[reply]

Some of them also wear surgical stockings. {The poster formerly known as 87.81.230.195} 2.122.2.158 (talk) 22:49, 3 September 2020 (UTC)[reply]

So why is it okay to do surgery with only a fancy cloth on your face but corona nurses need gas mask-looking things? Sagittarian Milky Way (talk) 01:49, 4 September 2020 (UTC)[reply]

I suspect your premise is flawed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:50, 4 September 2020 (UTC)[reply]

It looks like a serious question. Face masks during the COVID-19 pandemic is a good start to learn about the various masks. Medical prophylactic practices have to strike a balance between efficiency (protection against contamination by a given pathogen), cost, and side effects (a hazmat suit will block all pathogens, but it would be unwieldy to perform chirurgy from inside one); it is not surprising that the best option for a given context might not be best for another context. You should also note that handling yourself around an operating room requires nontrivial training ("operating room training" returns a bazillion hits for certification programs), so it seems possible to me (OR warning) that stringent procedures compensate for lower-protection equipment. Tigraan^{Click here to contact me} 15:22, 4 September 2020 (UTC)[reply]

Chemistry, Nitrogen and it's compounds form three

How is nitrogen gas prepared ? — Preceding unsigned comment added by Emmanuel ngetich (talk • contribs) 17:58, 3 September 2020 (UTC)[reply]

Mostly by taking it from the air, of which it is the overwhelmingly major constituent. The air separation article describes the major processes for doing it. DMacks (talk) 18:08, 3 September 2020 (UTC)[reply]

Though, pertaining to the section title, nitrogen compounds are rarely if ever prepared from nitrogen gas, because the dinitrogen triple bond is very strong and takes a lot of energy to break apart. Instead, ammonia or other nitrogen compounds are used as the nitrogen source. Ammonia is produced today with the Haber–Bosch process, one of the most important inventions of the 20th century and a major industrial process. --47.146.63.87 (talk) 22:14, 3 September 2020 (UTC)[reply]

Which of course it is important to note that the Haber-Bosch process uses nitrogen derived from the air as it's feedstock, so ultimately most industrially-derived sources of nitrogen compounds do indeed come from nitrogen in the air. Before the Haber-Bosch process, nitrogenous compounds were primarily obtains through old-fashioned biosynthetic means: we used plants and animals to produce them, and we got it from there. This includes things like guano deposits (basically bird shit and bat shit) and nitrogen-fixing microorganisms in the soil and plant roots known as Diazotrophs. Bird shit used to be so important to the world economy that global conflicts have been started over access to it. See Guano Islands Act, Chincha Islands War, War of the Pacific, etc. all of which were significantly about control of guano. The Haber-Bosch process changed a lot of that. --Jayron 32 15:22, 4 September 2020 (UTC)[reply]

Right, Haber–Bosch catalyzes the breaking of the dinitrogen bond so it can be done at scale. Non-synthetic nitrogen compounds get their nitrogen ultimately from nitrogen fixation by microbes, which have nitrogenase enzymes that accomplish the same trick. --47.146.63.87 (talk) 02:11, 5 September 2020 (UTC)[reply]

September 4

Covid?

This is regarding someone who died recently from as-yet unannounced causes. You can probably figure out who, but the question is about the illness rather than the person, so I omit his name. A news article said:

"However, [person] posted on Twitter in August that he had “been sick for a month.” He maintained that the illness caused him “z exhaustion, stomach [and] lung-ache.”

He was up and about until a few days ago, then entered hospital and died rather quickly. Do those symptoms sound like covid, or anything else particularly? Thanks. 2601:648:8202:96B0:0:0:0:DDAF (talk) 08:57, 4 September 2020 (UTC)[reply]

Per the instructions at the top of the page "We don't answer requests for opinions, predictions or debate." This would require respondants to give opinions about whether or not the patient in question had Covid. No one here examined that patient. Instead, if you want to form your own opinion, you can read Coronavirus disease 2019#Signs and symptoms. --Jayron 32 14:40, 4 September 2020 (UTC)[reply]

Not a diagnosis and hardly an opinion, but each of these symptoms has been reported for COVID-19. Each individually could have any number of causes. --Lambiam 14:50, 4 September 2020 (UTC)[reply]

The OP is capable of reading the linked article and learning that themselves. He doesn't need us to tell him that. --Jayron 32 15:12, 4 September 2020 (UTC)[reply]

Notice that "disease X causes set of symptoms Y with high probability" does not entail "symptom set Y is caused by disease X in most (or even many) cases". It is therefore not sufficient to know whether someone's symptoms are compatible with a given disease to deduce that they likely have that disease. For instance, blue mucus is a symptom of infection by Pseudomonas aeruginosa, but blue mucus reports are likely to be caused by hallucinogen abuse (source (fr)). Tigraan^{Click here to contact me} 15:33, 4 September 2020 (UTC)[reply]

[Damn, it's no longer possible to recover an unsaved edit from an edit conflict, so I have to rewrite this response]. I carefully tried to not make this about the patient, but rather about whether those symptoms match what has been observed about Covid and other possible causes. That's not a matter of speculation, but of trying to identify Bayesian priors, grounded in sources (maybe indirectly) if you like to think of it that way. E.g. this mentions toxins as a cause of soapy taste in the mouth, suggesting he was exposed to something, while "lung-ache" immediately evokes covid. "Speculation" on the other hand would be e.g. "maybe Putin poisoned him with Novichok".

Note that Wikipedia's treatment of this type of topic is almost useless, because MEDRS makes it exclude an enormous amount of sourcing that a reasonable person would consider informative. I mentioned that the person is dead to make it clear that this is not about a medical decision. Plus, a Covid article would say nothing about other possible causes.

Anyway, stop freaking out. We have a big article about possible causes of the death of Mozart since how Mozart died is still uncertain centuries later. What's left is to match up Mozart's symptoms with possible causes, as that article shows is a perfectly reasonable thing to do. The only thing really different about the case I'm thinking about is that it is much more recent. 2601:648:8202:96B0:0:0:0:DDAF (talk) 15:52, 4 September 2020 (UTC)[reply]

No one has freaked out. What people have done is told you where to find the answer to your question. That's what we do here: tell people where to find answers to their questions. If you have more questions, please ask them, and we will tell you where to find those answers. --Jayron 32 16:21, 4 September 2020 (UTC)[reply]

You mischaracterized a reasonable factual question (what identifiable causes do these symptoms match) with "request for opinions, speculation, or debate". I consider that response to be freaking out. I rather carefully constructed the question to avoid the issues that trigger some people here (medical advice => nope, the person is dead; BLP/BDP => avoided naming the deceased person, etc.) but you seem to have gotten triggered anyway. Obviously the cause of death can't be identified with certainty with the info available (at least as of yesterday) but I'm not seeking certainty. As the Mozart article shows, it's perfectly reasonable to look for informative priors even though reaching anything like certainty is impossible. That's all I'm trying to do here. I really don't understand what set you off. It's certainly a less consequential question (since the guy is dead) than "what could cause my washing machine to make a squealing noise during its spin cycle" (might be a belt, might be a problem with the motor, etc.) and nobody would complain about that question here, I hope. 2601:648:8202:96B0:0:0:0:DDAF (talk) 16:38, 4 September 2020 (UTC)[reply]

Also, "people" did not tell me where to find answers. You are the only one who did that, in an unhelpful and bureaucratic way. Two other regulars, Lambiam and Tigraan, gave actual useful answers, for which I thank them. (Tigraan's answer was basically advice to beware of confounders when reasoning about conditional probability and causation, something we all have to be reminded of sometimes). 2601:648:8202:96B0:0:0:0:DDAF (talk) 17:35, 4 September 2020 (UTC)[reply]

In case there's some confusion, BLP including BDP apply to living persons and recently deceased regardless of whether you "avoid naming them" when it's extremely obvious who you are referring to. The question of what level of obviousness may be debated, but if you were to open a discussion at WP:BLP/N I'm sure you'll find this affirmed. Otherwise I could sat "according to my contacts, the president of X is a paedophile who enjoys raping kids" (where I specify X), and it's fine since I didn't actually name the person. That's clearly nonsense. If you want to try and argue semantics that "president of X" is equivalent to naming them, you could easily substitute world leader who talked about injecting disinfectants, world leader actively promoting Covid-Organics, former world leader who said "we don't have homosexuals, like in your country" etc.

P.S. As a further example of why your question was so incredibly flawed, you seem to have completely ignored that person you're referring to also said they tested negative in response to a question about COVID at the time of the post you referred to. You also ignored the fact the post referred to a tooth infection and root canal. Such details are surely important when considering the symptoms but of course are difficult to consider when we are analysing random parts of someone's post where you think avoiding mentioning their name or directly linking to them somehow gets around BLP concerns. If you didn't mention such details because they weren't explicitly mentioned in whatever RS you read, that again, the obvious question is why it matters unless you too recognise that there are indeed still BDP concerns. (I think it also raises the question of how reliable this source actually if is they would neglect to mention such details.)

Nil Einne (talk) 08:09, 6 September 2020 (UTC)[reply]

There is a difference between article space, like the Mozart article, and reference desk space, where we are now, and different rules apply to those different spaces. We have specific rules against answering the type of question you have asked here. In an article space, with proper reliable sources (rather than speculation of editors), something could be said (in conjunction with rules regarding biographical articles). Not here, though. --OuroborosCobra (talk) 18:20, 4 September 2020 (UTC)[reply]

The question was "Do those symptoms sound like covid, or anything else particularly?" and why should it be forbidden to answer something like "No, they don't. If 'exhaustion, stomach [and] lung-ache' are compatible with covid, they are also compatible with a lot of other things. But so far as I know "beeing sick for a month" is not compatible with covid, which if it kills it does so in one to two weeks. And beside that several common symptoms are missing in the description like high fever, headache and insistent cough, which would have probably been mentioned had they been present." ? 2003:F5:6F00:ED00:D3A:2C30:3941:92C6 (talk) 14:57, 8 September 2020 (UTC) Marco PB[reply]

If you are unsatisfied, we can refund you all of the money you spent getting these answers. If you prefer, you can ask at other places on the internet where people are happy to pretend to know more than they do and give free medical advice. We're just not going to do that here. --Jayron 32 15:39, 8 September 2020 (UTC)[reply]

River proximity and groundwater levels

Am I right in thinking that groundwater levels are higher the closer the place is to a river bank? Would that mean that dams reduce groundwater levels downstream by making rivers smaller? Is there any place I can read more about this? Wikipedia does not provide answers, unfortunately. Surtsicna (talk) 22:51, 4 September 2020 (UTC)[reply]

Usually the water table is higher than a river, and there will be springs and seepage coming into the river. However in a desert, you could expect the water table to be lower, and that the river recharges the water table. However if much of that happens the river will dry up. A dam will likely raise the water table around the dam, but since a dam is designed to retain water, it should not be in a place where much water leaks out. Graeme Bartlett (talk) 23:49, 4 September 2020 (UTC)[reply]

And if you aren't busy, Geological structure as a control on floodplain groundwater dynamics tells all. Alansplodge (talk) 11:33, 5 September 2020 (UTC)[reply]

September 6

Brown bear vs. human

I read that brown bear species (Ursus arctos) is divided into sixteen subspecies, due to morphological/genetical differences and habitat. My question is: from a strict biological perspective, would be ncecessary to divide humans (Homo sapiens) into subspecies, again due to morphological/genetical differences? Notice that I reject the social construct of "race", any kind of racial discrimination, the concept of one "race" being "superior" or "inferior", racial laws and historical definitions such as "Nordic race", Mediterranean race" and so on. I know that dividing humans into three or five or seven "subspecies" is not the same of brown bears, but I read biological differences exist and that's what I ask. Thanks in advance.--Carnby (talk) 07:51, 6 September 2020 (UTC)[reply]

Looking at Subspecies, I don't think it applies to humans. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:36, 6 September 2020 (UTC)[reply]

[Edit Conflict] The current consensus is that all living humans are members either of the species Homo sapiens which has no recognised subspecies, or of the single subspecies Homo sapiens sapiens, most often contrasted with the now extinct sister subspecies Homo sapiens idaltu.

Neanderthals have sometimes been classified as the subspecies H. sapiens neanderthalensis and sometimes as the species H. neanderthalensis: Denisovans have not yet been given a formal taxonomic status to my knowledge (which may well be outdated), as too little physical material representing them has been identified: one could argue for them being part of H.Neanderthalensis, a subspecies "H. neanderthalensis denisova", "H. sapiens denisova", or something else. The problem is that in biology there is no objective agreement on exact definitions of and distinctions between species and subspecies: different definitions (over 30 for "species") are used in different contexts. At least one prominent paleoanthropologist has expressed the opinion that there has never been more than one human species extant at any one time, given the evident willingness of various named 'varieties' of humans to interbreed when the opportunity arose.

There is also a model currently emerging within paleoanthropology of African Homo sapiens being an amalgam of several African regional populations somewhat physically and genetically differentiated through temporary geographical isolation prior to their subsequent re-merging, before their subsequent interbreeding outside of Africa with Neanderthals, Denisovans and possibly other groups as yet unknown.

Given the potentially fraught outcomes that might result from defining any living human population as a different subspecies from the rest of humanity, I suspect that all responsible scientists are very unlikely to discuss even the theoretical possibility of doing so. {The poster formerly known as 87.81.230.195} 2.122.2.158 (talk) 08:59, 6 September 2020 (UTC)[reply]

I echo the explanation by I.P above. Also you might find our article on Homo floresiensis interesting, who were described as the 'hobbit' people. Populations in the Nazca region and beyond (Easter Island) may have possibly been influenced by the Paracas culture; who are theorized as having naturally elongated skulls that predated and influenced Artificial cranial deformation. That's all a bit fringe though, and isn't well-covered on Wikipedia. Zindor (talk) 09:38, 6 September 2020 (UTC)[reply]

Correct me if I'm wrong but didn't I read somewhere that human races are more genetically similar to each other than different parts of an animal subspecies' range? Cause genetic mixing caused by humans exploring and falling in love or lust. Presumably in low tech eras the skin colors and nose shapes wouldn't mix quite as much as other genes as they were slowly selected by the sunlight and temperature of where they originated. So the races have mixed more than racists think. Also they like to show that Equatorial Guinea has the lowest IQ and don't say it was a small country where the crazy dictator killed anyone who might be smart and even anyone with glasses and they were the Dachau of Africa for awhile with massive population loss and brain drain from purges and people braving the minefields and boat ban to flee. Sagittarian Milky Way (talk) 13:53, 6 September 2020 (UTC)[reply]

Squirrels are able to produce subspecies. Potatoes are able to produce cultivars. Is H. Sapiens indeed the only magical life form totally unable to produce subspecies? I strongly suspect this is a very dangerous question to utter. People have been cancelled for far lesser crimes than asking this question. Tread carefully, as you are walking on politically correct eggshells here. 85.76.78.82 (talk) 16:57, 6 September 2020 (UTC)[reply]

Read what it is that causes subspecies, and it should become clear why humans don't qualify. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:29, 6 September 2020 (UTC)[reply]

We're all awfully closely related for a species with our numbers. Probably mostly due to recent bottlenecks, only a few thousand generations, in evolutionary times. There's a concept in population biology which I can't remember the name of - being the size of the population you would guess from a given amount of genetic variation. Well, humans have the genetic variability you would expect in a species of 100,000 or so, not billions. If that's missing from our relevant articles, it is probably because they were written by humans. :-)John Z (talk) 06:20, 7 September 2020 (UTC)[reply]

I think the answer to my question is this (from subspecies): "The variation among individuals is noticeable and follows a pattern, but there are no clear dividing lines among separate groups: they fade imperceptibly into one another. Such clinal variation always indicates substantial gene flow among the apparently separate groups that make up the population(s). Populations that have a steady, substantial gene flow among them are likely to represent a monotypic species, even when a fair degree of genetic variation is obvious."--Carnby (talk) 11:25, 7 September 2020 (UTC)[reply]

If a convenient asteroid is modeled as x% gold and platinum atoms and the rest rubbish how high does x need to be to mine it soon?

All mixed together homogenously.Sagittarian Milky Way (talk) 13:18, 6 September 2020 (UTC)[reply]

Gold and platinum are native metals so i would imagine they'd be available fairly easily in their elemental form. I'm assuming the 'rubbish' would be carbonaceous chondrite such as found in a C-type asteroid. How to deal with that chemically i don't know, it might be easier to physically mine it. Zindor (talk) 13:34, 6 September 2020 (UTC)[reply]

So when I hear of people mining rocks with invisible gold content it just means the easy stuff is gone and they're scraping the bottom of barrel. So I might find gold nuggets walking around (jetpacking around?) a NEO and just pick them up? Sagittarian Milky Way (talk) 14:04, 6 September 2020 (UTC)[reply]

I doubt they'd exist alone as a sizeable nugget, as space debris would be constantly wearing away at them. As far as i'm aware, these companies mining precious metals out of low% sediment do turn over a profit. I'd suggest that panning in a river for nuggets might be a more viable option that jetpacking around an NEO. Zindor (talk) 14:24, 6 September 2020 (UTC)[reply]

Of course they make profit or they wouldn't do it, I'm wondering how many percent you'd need to scoop up the regolith or whatever and choose which atoms you want to take (maybe vibrating the grains in a centrifuge and taking the dense ones?) and still make profit. No one can be sure an asteroid is profitable without going there probably so it'd be a very expensive risk. Maybe one of our tech billionaires will try one day lol. And one wonders who gets to mine where if other billionaire(s) suddenly want to try the same asteroid if the first one makes high profit. Sagittarian Milky Way (talk) 15:37, 6 September 2020 (UTC)[reply]

Mineral/precious metal deposit speculation is a real business and sometimes money gets thrown at non-profitable mining projects, keeping it afloat, in the hope that they 'strike gold/the motherload' so-to-speak. The key is to invest early, let uninformed investors pile in and raise the share price, then sell your shares just before the project goes bust. It'll be a free-for-all once humanity gets into space; the UN Space Treaty that currently exists will just be ignored for sure. Zindor (talk) 20:19, 6 September 2020 (UTC)[reply]

Per Outer Space Treaty#Key points there is apparently some ambiguity about whether the treaty prohibits space mining, and many space-faring nations have decided it does not. Tigraan^{Click here to contact me} 09:13, 9 September 2020 (UTC)[reply]

Our page asteroid mining cites [1] which does more or less that calculation. It assumes 150ppm platinum (0.015%) and would be deemed too unprofitable for the amount of risk taken. It also assumes between 700 and 70,000 tonnes of platinum are hauled back to Earth; the lower figure is already four times the yearly Earthly production (see [2], table 4) so it seems probable that the market price of platinum would decrease significantly if such a project happened (whereas the article assumes a fixed price). Tigraan^{Click here to contact me} 09:38, 7 September 2020 (UTC)[reply]

A genetic cause for sex height differences?

Is there a genetic cause for height differences between men and women? Futurist110 (talk) 21:33, 6 September 2020 (UTC)[reply]

See Sexual dimorphism in primates, Sexual dimorphism in non-human primates. Zindor (talk) 21:59, 6 September 2020 (UTC)[reply]

Puberty covers it. The pubertal "growth spurt" is both initiated and terminated by rising estradiol levels. After the onset of puberty, males have lower levels than females, so they generally start the "growth spurt" later, and it lasts longer, resulting in greater average adult height. --47.146.63.87 (talk) 04:47, 8 September 2020 (UTC)[reply]

September 7

Iguanas and snakes: Where was this filmed? What type of iguana and snake?

This YouTube BBC video [3] shows some type of iguanas and snakes, which are not identified. However, there is a longer clip from the original programme, which was broadcast on France 2, and has a complete voice-over narration, in French. I cannot understand spoken French, so I wonder if anyone here can do so, or otherwise identify the species of reptiles being filmed, and the location. I am not sure if it is allowed to post the second YouTube clip here, on WP. It can be found on YouTube by searching for "iguane vs serpents" and choosing the "ZAPPING SAUVAGE" clip, which runs for 5:13 minutes. Absolutely amazing! And if you like wildlife videos, well-worth the five minutes. (A secondary question...would a link to the second video be allowed here? I wished to err on the side of safety, and not post the link.) Thanks, Tribe of Tiger ^{Let's Purrfect!} 21:34, 7 September 2020 (UTC)[reply]

You can turn on English subtitles. However the clip does not say where or exactly what animals these are. Someone in the comments also asked exactly your questions without answer. Graeme Bartlett (talk) 00:29, 8 September 2020 (UTC)[reply]

The BBC site says this is Galapagos Islands.[4] Graeme Bartlett (talk) 01:24, 8 September 2020 (UTC)[reply]

The animals are Amblyrhynchus cristatus and Galapagos racer. Graeme Bartlett (talk) 01:25, 8 September 2020 (UTC)[reply]

@Graeme Bartlett: I did not know about the option for English subtitles, will try this. For some reason, I thought about the Galapagos, based on the volcanic terrain. Lucky guess! I will look at/follow your BBC link, so that in future, I can find such information for myself. Thanks so much for answering my question, and also for describing your method of obtaining it. You are a helpful editor and a good educator. Best wishes, Tribe of Tiger ^{Let's Purrfect!} 03:19, 8 September 2020 (UTC)[reply]

@Graeme Bartlett: I see that our WP article on the Galapagos racer has a reference to this excellent video. Because the terrain seemed so barren, I wondered how the iguanas found food...and WP provides the answer! Thanks again, Tribe of Tiger ^{Let's Purrfect!} 03:34, 8 September 2020 (UTC)[reply]

@Tribe of Tiger: if you mean this video [5] then yes I think linking to it is fine. I'm not entirely sure what Zapping Sauvage is, but the tick is a positive sign. The about page isn't as clear as I would like (at least based on a machine translation) [6] but Matthieu Briere seems to be associated with France TV. I think it's reasonable to assume the channel is in some way associated with France TV and therefore concerns about linking to known or suspected external copyright violation do not apply. Nil Einne (talk) 19:24, 8 September 2020 (UTC)[reply]

@Nil Einne: Yes, this is the video! I did not know about the "tick", as an attribute/attribution, etc,, per copyright, on YT. I did remember, from a year or two ago, some discussions regarding YouTube links, and wished to be careful, per your reference to external copyright violation. Thanks so much, very helpful. I will save your useful cmts for future references to articles. Sincere thanks, Tribe of Tiger ^{Let's Purrfect!} 22:31, 8 September 2020 (UTC)[reply]

September 8

Red squirrels

where are red squirrels native to in North America? — Preceding unsigned comment added by 47.156.108.52 (talk) 22:22, 8 September 2020 (UTC)[reply]

Our article on the American red squirrel has a map with its distribution. --OuroborosCobra (talk) 23:30, 8 September 2020 (UTC)[reply]

Although the OP probably knows this, casual readers should be aware that this is not the same species as the Eurasian red squirrel, which is not native to North America although there may well have been past attempts to introduce it. {The poster formerly known as 87.81.20.195} 2.122.2.158 (talk) 08:56, 9 September 2020 (UTC)[reply]

September 9

Normal reading distance

A figure often given for "normal reading distance" is 40 cm (16 in).^[7][8][9] But K.-K. Shieh and D.-S. Lee (2007) (doi:10.1016/j.apergo.2006.06.008) cite the book Human Factors in Engineering and Design (1992 edition) for the statement that "when reading a book or paper-like material, the normal reading distance is usually somewhere between 305 and 406 mm, with a mean of 355 mm." That is awfully precise for something that is quite variable, made vague by "usually". It makes a considerable difference whether the distance of 5 cm between the reported mean and the upper/lower bound is the estimated statistical dispersion, or the 2 sigma associated with the two-sided p = 0.05], or something else. If the latter, 40 cm is somewhat unusual. The uncanny 1 mm precision suggests that this is based on a large number of measurements, but given the general character of the book, covering a wide range of issues, it seems unlikely that the authors performed the measurements themselves. My question is: where did the data come from and how should the spread be interpreted? (Using Google Books I only see unhelpful snippets.) Also, are there other (authoritative) sources that do not just parrot what everyone else is saying? --Lambiam 17:38, 9 September 2020 (UTC)[reply]

Are we looking for a normal in the sense of "the average human" (for any given definition of "average") or are we looking for normal in the sense of "established standard for the purpose of having an agreed-upon value just so we can cut down on variables"? The first will be necessarily fuzzy and imprecise, but closer to actual human usage, the second will be more precise (and thus useful as a standard) but arbitrary and only coincidentally close to a real human average. Which sort of value are you looking for? Because both are useful in different situations. --Jayron 32 17:52, 9 September 2020 (UTC)[reply]

And me with 20/60 vision reads everything at 10 inches cause it degrades after 12 without squinting or optics (I got to 20/15 with optometrist thingy before she stopped, could've done 20/12 probably). Why wouldn't you want your book to be full Quatro HD anyway? 16 inches is wasted resolution. Sagittarian Milky Way (talk) 18:19, 9 September 2020 (UTC)[reply]

Who is the "we" who is looking for a normal in some sense? Personally I'm satisfied with my customary reading distance without comparing it to a supposed norm. But it would be nice to have an authoritative source for linking to in articles that mention the concept (Naked eye, Optics, Visual system). If the source is any good, they'll surely also define what they mean by "normal" in the context. I'm not happy with citing just any odd source; although 40 cm; is frequently mentioned, equally "reliable" sources give sometimes considerably different values. I also think the concept is sufficiently notable that it should actually deserve an article of its own – or perhaps a dedicated section of an article with a wider scope and less normative title, such as "Viewing distance". --Lambiam 19:42, 9 September 2020 (UTC)[reply]

There are smartphone and tablet distance standards which are further for tablet or maybe I'm misremembering something where a corporation really pushes "typical distance" to make their minutes of arc look better. There's also a desktop computer rule of thumb that I can't focus at and it's too close for myopia glasses without slow eye damage. 19 to 24 inches according to this probably trustworthy image I've downloaded from god-knows where. Sagittarian Milky Way (talk) 22:03, 9 September 2020 (UTC)[reply]

If you can touch the screen with your arm without moving your head and shoulders closer, it's too close.^{[citation needed]} 93.136.121.193 (talk) 01:58, 10 September 2020 (UTC)[reply]

^{If I can't touch it it's at least 3 times too far. Sagittarian Milky Way (talk) 03:06, 10 September 2020 (UTC)}[reply]

The 305, 406 numbers would have been derived from 1 foot and 1 foot 4 inches, which does not have so many significant figures. But if a scientist or serious medical practitioner has been using feet, they must have been doing this measurement long-long ago, and so is likely seriously out of date, from the pre-computer/mobile phone era. Graeme Bartlett (talk) 22:08, 9 September 2020 (UTC)[reply]

Considering the near point of a healthy eye is at 25 cm, I'd say choosing to read at 30 cm is a little far-fetched unless the study wasn't limited to people with healthy eyes. 93.136.121.193 (talk) 01:56, 10 September 2020 (UTC)[reply]

I could focus 4 inches from my eyeball when I was 18. Now it's more like 5. God I'm getting old. Sagittarian Milky Way (talk) 03:04, 10 September 2020 (UTC)[reply]

Presbyopia --47.146.63.87 (talk) 09:22, 10 September 2020 (UTC)[reply]

September 10

What is the over/under for the closest a planet has been to Earth in the Phanerozoic? What about any planet pair?

2. Is the probabilistically most likely value for "what was the biggest Phanerozoic perturbation?" enough to cause detectable climate change if it magically happened now?

Planet means the kind we have 8 of. Sagittarian Milky Way (talk) 03:41, 10 September 2020 (UTC)[reply]

It is generally thought that the Solar System as a whole is unstable (see the article on Stability of the Solar System) and that the system of equations is is chaotic in the technical sense of mathematical chaos theory. On a time scale of a few million years nothing dramatic is to be expected, and the effects are too small to have been observed since Homo sapiens gazed up to the skies. But even the most precise long-term models for the orbital motion of the Solar System are not valid over more than a few tens of millions of years, let lone over the 500+ million years the Phanerozoic has lasted. Numerical integration of the differential equations on supercomputers suggests the possibility of collisions of Mercury, Mars or Venus with the Earth some 3.34 billion years into the future, but not sooner than within one billion years. Since the equations are time-symmetric, the models can equally be used to postdict the past planetary motions. I don't know if anyone has actually done that. It seems that for a time scale below a billion years into the past the result is likewise not likely to be dramatically different from the current orbits. But the lack of major upheaval for a long future time span is no guarantee of the same for the past. Until someone runs that simulation backwards the best answer to the question in the heading is that we don't know. As to the second question, current climate models have no contingency for a direct collision of Mars with Earth, but I think it is a fair bet the climate change would be detectable. --Lambiam 08:05, 10 September 2020 (UTC)[reply]

@@ Line 128: / Line 128: @@
 :Considering the [[near point]] of a healthy eye is at 25 cm, I'd say choosing to read at 30 cm is a little far-fetched unless the study wasn't limited to people with healthy eyes. [[Special:Contributions/93.136.121.193|93.136.121.193]] ([[User talk:93.136.121.193|talk]]) 01:56, 10 September 2020 (UTC)
 ::I could focus 4 inches from my eyeball when I was 18. Now it's more like 5. God I'm getting old. [[User:Sagittarian Milky Way|Sagittarian Milky Way]] ([[User talk:Sagittarian Milky Way|talk]]) 03:04, 10 September 2020 (UTC)
+:::[[Presbyopia]] --[[Special:Contributions/47.146.63.87|47.146.63.87]] ([[User talk:47.146.63.87|talk]]) 09:22, 10 September 2020 (UTC)
 = September 10 =