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June 20

What is the nonmetallic liquid with the highest surface tension?

Specifically at around 20 °C. OrganoMetallurgy (talk) 20:55, 20 June 2017 (UTC)

There is a data table in the surface tension article - the only things with a higher surface tension than water (apart from mercury) are concentrated salt and sugar solutions. There is another list here - - but nothing beats water. This list is even longer - - but the answer is still water. Wymspen (talk) 21:53, 20 June 2017 (UTC)
As far I can tell hydrogen peroxide actually has a higher surface tension than water does. But is there anything else? OrganoMetallurgy (talk) 15:23, 21 June 2017 (UTC)

Are there any ionic liquids with a surface tension exceeding that of water? OrganoMetallurgy (talk) 20:48, 21 June 2017 (UTC)

No. Only Mercury (which is a metal) and strong inorganic salt solution have higher Surface tension than water. Blooteuth (talk) 23:44, 21 June 2017 (UTC)
I'm finding sources that say hydrogen peroxide's surface tension is higher. Abductive (reasoning) 04:58, 23 June 2017 (UTC)
I see a bunch of numbers at sites like this (though they'd have to be checked) - apparently platinum is higher than mercury at its melting point, and sulfur is higher than water. Near room temperature you can get anything from mercury-like surface tension to less than olive oil out of an indium-gallium alloy, I think it was in base, depending on applied charge. [1]
It would be interesting to see more of a theoretical overview of this. At a liquid's melting point, it almost has enough bonding to be locked into a solid. So why are some at a low surface tension and others at a high surface tension, based on different levels of cohesion between particles of the liquid? I assume there's some aspect of "flexibility" involved but I admit I have no clue on this one. Wnt (talk) 12:03, 23 June 2017 (UTC)

Can you make thiourea from urea?

Can urea be converted to thiourea? How? I know thiourea is usually synthesized using hydrogen sulfide. — Preceding unsigned comment added by (talk) 22:13, 20 June 2017 (UTC)

Yes. This page describes three different methods for converting carbonyls to thioketones. Although those methods are given in general terms, not for specific compounds. I don't know if the amide groups of urea would interact with the other compounds used in those methods. Someguy1221 (talk) 01:46, 21 June 2017 (UTC)
The examples on that page (two different reagents, two variations of the recipe for one of them) all say that certain amides are viable. But for the specific example of urea to thiourea (not regular amides, and not more complex structures containing these substructures), hydrogen sulfide can do it after an initial treatment with various metal oxides at a few hundred degrees celcius.[1] DMacks (talk) 03:31, 21 June 2017 (UTC)


  1. ^ CN patent 101602702, "A production method of thiourea from urea", issued 2009-16-12 

What mug material would make it hardest for soda bubbles to resist their buoyancy?

Teflon-coated diamond? Oil-coated glass? How would I know. The cup has vertical, smooth sides and is at sea level on Earth. Which material would make it easiest for the bubbles to resist their buoyancy? Sagittarian Milky Way (talk) 22:23, 20 June 2017 (UTC)

What does "resist their buoyancy" mean? You want them to stick to the side of the mug without rising? CodeTalker (talk) 23:44, 20 June 2017 (UTC)
Right. So one material would have the highest adhesion strength to bouyancy ratio and one would have the lowest. Sagittarian Milky Way (talk) 00:10, 21 June 2017 (UTC)
I suspect that if you gave the bubbles a charge, and the water was very pure they would stick to the side. Graeme Bartlett (talk) 04:16, 21 June 2017 (UTC)
I would suggest something that imitates Diving bell spider belly, that allow them to bring bubbles of air from the surface to their diving bell
that is, a "hairy" hydrophobic coating, so that, when the bubble detach from the hair, more water tries to touch it, which is resisted
Gem fr (talk) 09:34, 21 June 2017 (UTC)
The Q needs clarification:
1) If you just want to prevent bubbles from rising, then preventing them from forming is one way. A lack of nucleation sites is one way to accomplish this, with very smooth sides and a pure liquid.
2) If, on the other hand, your goal is to have lots of bubbles sticking to the sides, then the above approach won't work. Here a container with "pockets" to catch the bubbles might help. StuRat (talk) 13:23, 21 June 2017 (UTC)
2, where it takes the most force to dislodge the bubbles (i.e. banging it on the table) and the opposite of 2 - which would look cool if they rise fast without percussive help but otherwise have no practical use. Perhaps something hydrophobic and smooth but not so smooth that there's no nucleation sites? Would they rise still in contact with the sides even if adhesion could be zero (since it's perfectly vertical) or would they break contact with the side out of a desire for spherical shape or because of turbulence if the adhesion was low enough that it wouldn't have resisted their rise much? Sagittarian Milky Way (talk) 20:14, 21 June 2017 (UTC)
Turbulence is unlikely from just bubbles rising in soda. StuRat (talk) 01:24, 22 June 2017 (UTC)
Their mugmates burst sometimes though, as bubbles are prone to do. Sagittarian Milky Way (talk) 02:19, 22 June 2017 (UTC)

How much damage would an explosion at Trinity that barely destroyed New Mexico cause?

That's impossible but what effects would that cause? About how many gigatons is needed to do it? Sagittarian Milky Way (talk) 23:26, 20 June 2017 (UTC)

Trinity was the code name of the first detonation of a nuclear weapon conducted about 35 miles (56 km) southeast of Socorro, New Mexico. Its explosive yield was about 22 kilotons of TNT (92 TJ). The article Nuclear weapon yield may be of interest. Blooteuth (talk) 00:49, 21 June 2017 (UTC)
It may be noted that one of the things the physicists had to consider before the Trinity test was whether it might ignite a nuclear chain reaction in the atmosphere. They were able to rule this out, but as it says in the article, "Enrico Fermi offered to take wagers... on whether the atmosphere would ignite, and if so whether it would destroy just the state, or incinerate the entire planet." (Emphasis added.) -- (talk) 07:13, 21 June 2017 (UTC)
Fun times, the Manhattan Project! I can recommend this book if this arouses your interest. (talk) 23:19, 21 June 2017 (UTC) (different IP user)
You need something like this. Count Iblis (talk) 05:46, 21 June 2017 (UTC)

June 21

Tendons and ligaments are classified under muscular or bone system?

Tendons and ligaments are classified under muscular system or bone system? Basically they are not bones or muscles and that's why I have doubt. (talk) 02:17, 21 June 2017 (UTC)

Neither. They're connective tissue. Rojomoke (talk) 06:30, 21 June 2017 (UTC)

Death = last thing seen gets imprinted in the eye

This sounds like a urban legend or fictional thing, but I guess it won't hurt to ask. Is it true that when a person dies, the last thing they see gets imprinted in the eye and the image can be retrieved somehow?

This was used as a plot point in Saint Seiya (manga only, the eye thing does not appear in the anime) by the character Black Swan.

(I tried to Google this, but keywords like "... image eye last thing seen death ..." got mostly pages about the completely unrelated notion that we see our whole lives past our eyes when we die.) --Daniel Carrero (talk) 07:32, 21 June 2017 (UTC)

Your hunch was right. The opsins in photoreceptor cells are degraded rapidly after being photoactivated by incoming light. This makes sense if you think about it. Your eye has to "refresh" in order to update what it's seeing. The membrane potential of the cell also rapidly resets to its resting state; furthermore, following death, the cell will deplete its energy reserves, the cell's ion pumps will stop working, and its membrane potential will dissipate. -- (talk) 08:12, 21 June 2017 (UTC)
Wikipedia has an article on Optography.--Shantavira|feed me 08:16, 21 June 2017 (UTC)
An interesting read. The idea is not false after all. But its usefulness as a forensic tool is pretty near zero. It would be interesting to see if this Gary Larson item could be accurate.[2]Baseball Bugs What's up, Doc? carrots→ 10:40, 21 June 2017 (UTC)
Almost all organic cells keep functioning for a while after an Organism is regarded dead. Else organ transplantation operations, from victims of accidents that subscribed to be donor in case of death, would not work. So this imprint theory is completely made up nonsense as usual in movies and shurely much more so in japaneese ones. --Kharon (talk) 07:00, 22 June 2017 (UTC)
The article disagrees. ←Baseball Bugs What's up, Doc? carrots→ 10:56, 22 June 2017 (UTC)
  • Optography is a smelly article. The whole scientific literature seems to boil down to Wilhelm Kühne; a GScholar search for "optography" returns a whopping 35 results, most of them false positives, and zero of them are recent research purporting that to be true (this, assuming it went through a relatively thorough search of the available literature, is certainly discouraging). I am going to put this on the fringe theory noticeboard. TigraanClick here to contact me 11:22, 22 June 2017 (UTC)
The article Optography is already categorized in Category:Pseudoscience. So its hardly allowed to cite this here in Wikipedia:Reference desk/Science ;D. --Kharon (talk) 17:28, 22 June 2017 (UTC)
But we don't have Wikipedia:Reference desk/Pseudoscience! Plus, if the answer were "Yes, this is true. Eyes do work like that in real life." it would be science. (thanks for the answers!) --Daniel Carrero (talk) 19:43, 22 June 2017 (UTC)

Dicotyledonous wood

What on earth is dicotyledonous wood? I came across the term while researching for draft:Akal Wood Fossil Park. There's no WP article about it and Google search mostly yields research papers only which are largely unintelligible to lay readers. A book search also failed to turn up any explanation for what it is. (talk) 13:53, 21 June 2017 (UTC)

  • Obviously it's wood from a dicot, rather than a monocot. However, is it a term in any sort of use?
I checked my usual source for all such, R. Bruce Hoadley's Understanding Wood. It's not in there. A thorough check might also cover the US Forest Products Handbook. So although woodworkers are deeply interested in wood structure and distinguish between species, let alone hardwood and softwood, there's no evident distinction for dicots and monocots. Timber species are almost all dicots, the only monocots I can think of for commercial timber production would be the woody palms and bamboo.
From the context, I think that this is a palaeontological question, not a timber question. The point is that monocots are seen as "early" plant in a geological context and the dicots as "later". Their fossils are also identifiable by species, thus then (indirectly) categorizable as either dicot or monocot.
AFAIK (I may be wrong here, I'm no botanist, just a carpenter), there is no specific timber or fossil structure that shouts out "dicot", any more than other differences between species (there are some common differences between softwood and hardwood as groups). So a botanist still has to identify down to a finer detail than "monocot", such as "a palm" or "a bamboo" before identifying to the group level. But if the distinction is interesting as a fossil one, then they might be doing just that. Certainly identifying fossil species from structure, seeds or pollen grains is an important discipline. Andy Dingley (talk) 14:34, 21 June 2017 (UTC)
I think, most xylologists and foresters and botanists would not consider e.g. bamboo to be be true wood anyway. While our article doesn't call normal wood, dicotyledonous wood, it does have section on monocot wood, indicating its sort-of-wood status. So I suspect dicotyledonous wood is being used here as sort of equivalent to "true wood", and this is useful verbiage (Edit,see below) to distinguish from monocot fossils that may also be woody. SemanticMantis (talk) 16:56, 21 June 2017 (UTC)
And to clarify further: " there is no specific timber or fossil structure that shouts out "dicot", any more than other differences between species ", I don't think that's true. I think if a paleontologist had a small bit of bamboo fossil and a small bit of coinfer dicot fossil, they could immediately distinguish the two. The growth of monocot "wood" is very different, they don't have the same tissue structures. See here [3] for some discussion of differences, and e.g. here [4]. One easy detail is that monocots won't have growth rings. SemanticMantis (talk) 17:22, 21 June 2017 (UTC)
  • Monocots (for the most part) don't produce wood. Nor are monocots the most primitive angiosperms, the claim above is not even close. The Magnoliids are usually called dicots, and they along with a few other minor groups are the oldest angiosperm clades. They produce wood, unless they are herbaceous. The two crown clades of Angiosperms are the monocots and the Eudicots which are equally recent. Conifers also produce wood, so it is not unique to Angiosperms.
Basically, dicot wood in the broad sense is what we think of as hardwood, and include wood from the Magnoliids and the Eudicots, but excludes wood from the conifers and monocots. It's a taxonomically invalid (polyphyletic--like calling whales fish) grouping, but it is useful in forestry and woodworking.
Of course there are the articles wood and secondary growth. There's also Plant Biology, Raven, Evert, and Eichorn which gives an encyclopedic view of the biology of the Plantae proper as well as other organisms such as fungi and protists historically treated as part of botany from an evolutionary and physiological standpoint.
μηδείς (talk) 01:46, 22 June 2017 (UTC)
Nobody said monocots were primitive, so I'm not sure what or whose claim you're referring to. But I do think you're right that coniferous wood would be excluded from "dicot wood", so I've stricken the "true wood" bit above, because it's confusing. For the rare occurrence where it comes up, "dicot wood" is basically synonymous with "hardwood" SemanticMantis (talk) 15:02, 22 June 2017 (UTC)

From the context, I think that this is a palaeontological question, not a timber question. The point is that monocots are seen as "early" plant in a geological context and the dicots as "later".

could be intepreted that way, whether or not it was the intention. I personally did intepret it that way. Nil Einne (talk) 16:33, 22 June 2017 (UTC)
"*Monocots (for the most part) don't produce wood" but see Coconut timber. Alansplodge (talk) 09:53, 23 June 2017 (UTC)
That's why it's called timber. True wood is a form of secondary growth, where new layers grow over old ones yearly from secondary meristem. Monocots do not increase in girth this way, having lost the ability, hence coconut timber is a granular pithy material, not true wood. Functionally it can replace wood, and has some excellent qualities, as can bamboo. But biologically neither is true wood, with annual rings, as found in the gymnosperms, magnoliids, and eudicots. μηδείς (talk) 18:22, 23 June 2017 (UTC)

Solar eclipse hype

Today on the CBS Morning News Charlie Rose said "A total solar eclipse will cross the United States for the first time in 99 years." That would at first blush seem to mean no "total eclipse" in any US state since about August 1918. I have seen this August 2017 eclipse similarly hyped elsewhere. It seems like every decade the newscasters tell us there is about to be the first such eclipse in umpty-ump years and there won't be another one in our lifetimes, as if we have no memory of previous eclipses. The article List of solar eclipses visible from the United States lists "total eclipses" which crosses the US.Neglecting annular and partial eclipses, it lists the most recent one as the Solar eclipse of July 11, 1991 and says Hawaii (by then long since a US state) saw a total eclipse. It lists Solar eclipse of February 26, 1979 whose article says there was a total eclipse in five US states. It lists Solar eclipse of March 7, 1970, whose article's map appears to show totality across several east coast states. It lists Solar eclipse of July 20, 1963 whose map appears to show totality crossing at least Maine. It includes the Solar eclipse of June 30, 1954 which had totality over several northwest states. It says about the Solar eclipse of July 9, 1945 that "The path of totality crossed northern North America, ..." and a semi-legible map shows the path crossing several northwest US states. It says the Solar eclipse of August 31, 1932 hit the NE US and the map seems to show a couple of NE states in the path. The Solar eclipse of April 28, 1930 hit the northwest US states. The Solar eclipse of January 24, 1925 produced a total eclipse viewable in New York City. The list claims the Solar eclipse of September 10, 1923 hit the SW US, but the fuzzy map and the article about the eclipse imply the totality missed the US. Then we get to the 99 year eclipse: The Solar eclipse of June 8, 1918, which crossed many states from the northwest to the southeast. But how can they dismiss the eclipses of 1991, 1979,1970, 1963, 1954, 1945, 1932, 1930, and 1925? From 1918 to 2017 inclusive, there have apparently been 11 total eclipses visible in one or more US states, for an average of 8.9 years. What am I missing here? That is more often than some people trade cars. Do astronomers endorse this hype? Edison (talk) 14:25, 21 June 2017 (UTC)

The 1925 eclipse was pretty cool. A scientist asked people what street they were on and whether they saw totality and 100% saw it above 96th Street and 0% saw it below 94th Street (or something similar). 1 street is only 264 feet. Sagittarian Milky Way (talk) 21:06, 21 June 2017 (UTC)
One news story added the qualifiers "first total solar eclipse to cross the United States from coast to coast in nearly a hundred years" which seems accurate, but so far as one's personal experience, you just see it in one place (absent pacing it from inside a Concorde as was once done)., and the sense of wonder is not much greater to know that many others can see it too. Yet Rose said he had "never seen one, and little wonder, since there hasn't been one in a hundred years" which seems to be nonsense. Edison (talk) 14:48, 21 June 2017 (UTC)
Correct, that's the big thing here. coast to coast, more states, more 'potential observers within reasonable travel distance' than in a long while. 1918 was somewhat comparable to this event in terms of the track. So 'for the first time in 100 years' is somewhat accurate in that regard, but it should be noted that the 2045 event will be similar (longer even). So yeah, it's a bit of hyperbole, but then, that's the news. For anyone outside Hawaii, NYC, or the North West, there is a big chance that you have not had this good an option to observe a full eclipse in your lifetime before. Esp. because modern times has made travel this cheap. —TheDJ (talkcontribs) 15:17, 21 June 2017 (UTC)
It's ignorance, more than anything else. Here's a report of an eclipse which never happened:[5] (talk) 15:23, 21 June 2017 (UTC)
BTW, as having personally observed a total eclipse in France when I was in my teens, I would advise any and everyone to take any opportunity you can to observe it. It's one of the strangest experiences I ever had. Will never forget it. —TheDJ (talkcontribs) 15:28, 21 June 2017 (UTC)
Solar eclipse of February 15, 1961. I remember it as a deep partial eclipse. My mother saw a total one - for practically everyone in Britain 11 August 1999 was clouded out, and the one before that was 30 June 1954 (also visible as total in the United States). Our article Solar eclipse of August 11, 1999 could do with some work - it claims it was "the first visible in the United Kingdom since 29 June 1927". (talk) 16:11, 21 June 2017 (UTC)
Few saw the '91 umbra in America because the average July sunniness of Baja vs Hawaii made many people plan to fly or drive to the tip of the Baja desert to see it and by the time the weather report showed it was more likely to be seen in Hawaii than Mexico flights to Hawaii were probably pretty expensive. In the end the desert of Baja California had lots of cloud and the tropical rainforest of Hawaii saw the eclipse. Sagittarian Milky Way (talk) 16:17, 21 June 2017 (UTC)

What plane is this

What plane is this[6]? I've never seen anything with that kind of a belly before. The screenshot is from 0:40 of this video[7]. Scala Cats (talk) 20:45, 21 June 2017 (UTC)

C17 Globemaster? Someguy1221 (talk) 21:11, 21 June 2017 (UTC)
That's it. Thanks! Scala Cats (talk) 21:32, 21 June 2017 (UTC)

Can acetic acid in aqueous solution alone pickle foods?

Is it safe enough to be consumed? (talk) 22:51, 21 June 2017 (UTC)

Yes, if suitably manufactured. In the UK it has long been sold as "Non-brewed condiment", diluted and coloured with caramel, as a substitute for malt vinegar. "Vinegar", if sold under that name, must be made by brewing (or at least fermentation). NBC uses industrial acetic acid. It is cheapest (if you're buying acetic acid for industrial workshop use) to buy these "acetic acid pickling vinegars" in gallon jars, rather than a chemical reagent-grade acid.
Note though that glacial acetic acid is fairly easily available but warrants all the care in handling of any concentrated acid. Andy Dingley (talk) 23:03, 21 June 2017 (UTC)
This sounds like normal "white vinegar" we use in the U.S. It is the most common vinegar and apparently can use either foodstuffs or petroleum as a starting material although the industry claims not to be aware of any company making food-grade vinegar from petroleum.[8] It seems in the UK, malt vinegar may be the main type in use and laws do not allow certain other products to be labeled as vinegar: non-brewed condiment. Rmhermen (talk) 17:24, 22 June 2017 (UTC)
Yes, and you could pickle with it, but it would be a bit nasty if used "alone" (emphasis in title). A typical pickling solution would include salt and other seasonings. Matt Deres (talk) 20:08, 22 June 2017 (UTC)

June 22

anal sex & hygiene

a. What measures (or cleaning routine) are taken to keep the rectal region clean ? How sexually engaged couple makes sure that there are no remaining excretions behind ? Is an enema required each time they commence love-making ? b. Is the issue of remainings age dependent ? Namely, natural cleaning processes are more efficient when we're younger ? c. A few years ago, as I remember, I saw somewhere in Wikipedia (through 'external' or 'see also' ?) some guide regarding this issue, medically & hygienically. Any ellaboration is welcome. בנצי (talk) 15:07, 22 June 2017 (UTC)

Here's a guide from Cosmo [9], here's one from Men's Health [10]. Dan Savage also has plenty to say on the topic, see e.g. here [11] or search The Stranger archives for related content. SemanticMantis (talk) 15:13, 22 June 2017 (UTC)
Also see under point 3 in this Article in the cosmopolitan. Seems google thinks cosmopolitan-readers practice this allot :D. Doubtfull if "amateurs" always take as much care and you can be shure todays media would reveal if both ever did any seriouse harm to anyone - i remember reading about people needing surgery after "working" themselves up with big objects in that area so anything alike oddly ironic would have made headlines too. I also read there are far worse (medically & hygienically) frequently practiced kinks in human sexuality. --Kharon (talk) 17:15, 22 June 2017 (UTC)

The Wikipedia article about Anal sex has general information but it is not a how-to guide. However it links to an external guide that concludes "The most important pieces of advice anyone can give on anal sex are: lubricants, condoms, and patience." Blooteuth (talk) 07:56, 23 June 2017 (UTC)

There are a lot of things I've seen written about this topic that don't seem to add up. For example, I have no idea how the logistics of prison rape are supposed to work when it is done this way (and certainly I've seen sources that say it is). Are the victims forced to prepare in advance, or do the guards see one guy crying with a soiled uniform in the rear, and another with a soiled uniform in front, and just smile and keep going about a good day at work? And there are authors like Norman Mailer who seem to engage in flights of fancy, or at least, fantasies that omit anything unappealing. Wnt (talk) 11:57, 23 June 2017 (UTC)
Preparing is not mandatory at all, and I confirm it does not get messy very often, even without any preparing. But many people like to prepare. Here is a very detailed description with drawings of how to thoroughly prepare (not safe for work) : [12] --Lgriot (talk) 15:50, 23 June 2017 (UTC)

Free Neutrons making dark matter

I have a doubt. Please clear it. Can neutrons interact with electromagnetic radiation or electromagnetic fields? I am thinking that as neutrons have no net charge, they don't interact (I may be wrong). So I have a thought that free neutrons (like a diffuse gas) may contribute to majority of dark matter. (The reason for my doubt is that neutron stars can produce radio waves). So my major question is that can slow and diffuse free neutrons interact with electromagnetism considerably? Please help me.--G.Kiruthikan (talk) 17:51, 22 June 2017 (UTC)

The origin of this doubt : Majority of normal matter is Hydrogen. Hydrogen's majority don't have neutrons. If neutrons were produced in roughly same number as protons, I think the rest of the neutrons could not make a nucleus and may be diffuse forming the dark matter.--G.Kiruthikan (talk) 17:58, 22 June 2017 (UTC)

Neutrons are not elementary particles. The net charge is practically zero, but it is made up of charged particles. It does interact with electromagnetic fields. A simple experiment shows this. Shoot a beam of neutrons through a strong electromagnetic field and it will separate into two beams. (talk) 18:34, 22 June 2017 (UTC)
Neutrons are not stable. With the half life of ~882 seconds they would decay very fast emitting in process copious amounts of energetic electrons. Ruslik_Zero 19:59, 22 June 2017 (UTC)
The charge on a neutron is zero within the limits of experimental accuracy, so it is not affected at all by an electric field. The magnetic component of an electromagnetic field is what affects the path of the neutron. Dbfirs 20:05, 22 June 2017 (UTC)
Some of the above might be confusing, so I should emphasize that as far as I know nobody expects to see any small amounts of charge on a particle - it is believed that all free particles have multiples of the elementary charge and quarks have multiples of 1/3 that amount. The charge does not vary with reference frame like other parameters in special relativity, so you can't get partial charges at a point in space by shooting things past each other either. I have no idea what kind of awesome mathematics can be invoked to explain that quantization, but I think no one expects to find a fractional charge on a neutron if they look really hard. Wnt (talk) 20:21, 22 June 2017 (UTC)
Neutrons and protons were indeed formed in similar quantities at the Big Bang, but most of the neutrons all quickly got mopped up by Big Bang nucleosynthesis into helium-4; the unlucky ones that didn't decayed away. Double sharp (talk) 23:42, 22 June 2017 (UTC)
Only neutrons traveling at super relativistic speeds could survive for a long time. But even these will be turning into high energy protons and electrons that would be easily detectable. However it is quite easy to make dark matter from matter contains neutrons. If there were many free floating Earth or moon like objects floating between the stars they would be dark. However these might be detected by gravitational lensing or eclipsing stars. Graeme Bartlett (talk) 08:56, 23 June 2017 (UTC)

Why is this seal used on buzzers ?

Why do we need to remove this seal after washing etc.[[13]] (talk) 19:27, 22 June 2017 (UTC)

This seal is there to cover the hole that is underneath. When a PCB has been assembled the soldering flux is washed off and the seal prevents this fluid from getting into the hole and damaging the buzzer. The seal also mutes the loudness, which in some applications may be desirable. The innards of these devises are also affected by moister etc., and thus its life can be prolonged by leaving the seal in place (at the expense that it operates more quietly). Also note, the circle with the + sign within it, aids quick identification of the positive terminal; although this should be obvious from the length of the leads. Aspro (talk) 22:28, 22 June 2017 (UTC)
Whoops... Completely missed answering your question. One does not need to remove it. The manufacturer of the buzzer leaves the choice to its customers – but only after washing. Aspro (talk) 23:00, 22 June 2017 (UTC)

June 23

Random chance, probability, and predictability

In chemistry, I once learned that the exact locations of the electrons are not known (and probably not important anyway), but the probability of finding the electron at a particular point can explain why something bonds with another. Then in statistics, I learned about probabilities, which then made me think of randomness. In a realistic setting, what is randomness? While in theory "random" means "everything is equally likely", how is this practically possible? If one writes a personal name on an index card and repeats the process for 50 index cards, each having an unique name, and then puts all the cards in a Black Box and shakes the Black Box, then it may seem random that a random card will be drawn, but in reality, the card at the top may be more likely to be drawn than the card at the bottom. Maybe "randomness" is the "unknown"? If one doesn't know or expect something, then it's "random"? Another case is when a teacher lists the students "randomly". Practically, the students may race to the teacher and line up. Whoever's first in line may just happen to be closest to the teacher to begin with or be the fastest person in the room. The last student in line may be the slowest person, or because he/she can't find any open spots, may be forced to be the last in line. At what point is something "random"? At what point is something "biased" or has some sort of tendency/correlation? (talk) 00:37, 23 June 2017 (UTC)

This is trickier than it may appear. Probability and statistics of discrete events (i.e. probability of a 2 dice roll being a seven (1 in 6) verses a 2 (1 in 36)) is different than quantum location where the distribution is a fundamental construct of the particle. Temperature of a gas is the mean of the temperature of individual particles and processes like evaporative cooling and sublimation work on the principle that particles are discrete. An electron in the orbital is a completely different construct that is described in models as a distribution and probability but lacks discrete components that can be separated to define the distribution. It is not a collection of random individuals but the distribution is a fundamental part of the particle. --DHeyward (talk) 01:05, 23 June 2017 (UTC)
Randomness doesn't mean all results are equally likely. It means the next result can't be predicted from the previous result. Iapetus (talk) 11:59, 23 June 2017 (UTC)
There several definition of randomness, yours is one of them. "all results are equally likely" is another definition, perfectly legit provided (big caveat!) you have a correct definition of "result" (ie: equal chance for a dice to produce 1-6, which is correct, vs equal chance for a dice to produce 1 or not, which is not). Unfortunately those 2 definition do not means exactly the same. Gem fr (talk) 14:00, 23 June 2017 (UTC)
Your question is hard, and not solved. There are different definitions of randomness, that do not exactly overlap. A system perfectly deterministic, but chaotic and hence unpredictable ( n-body problem or Double pendulum for instance), can be said random because unpredictable, or NOT random because prefectly determinist.
I would recommend determinism and Bohr–Einstein debates for the famous "god don't play dice" quote and implications. Also maybe Hidden variable theory: obviously in your student example, there are hidden variables (proximity and sprinting abilities), so the order is not random, but pseudorandom. It could however be argued that those variable are themselves randomly distributed, meaning the result is random. But it is no longer, if the teacher is well aware of these abilities, meaning he actually choose the result, hence it is not random. When you think of all the things that make you shift back and forth between "it's random" and "it's not random", you end up at classical Antoine Augustin Cournot's definition of randomness (i just wonder why it is neither in his article nor randomness) « Encounter of two independent causal series ».
for instance : a first series of causes made you arrive somewhere, sometime; an other series made a bus arrive at the same place at the same time. The more common causes there are, the less random (the more biased) your encounter with the bus is. With enough knowledge of the causes, your encounter could be perfectly predicted (or explained afterward and then appear it HAD to happen), but would nonetheless stay random (according to this definition) provided they stay independent.
hope it helped, although it may rise more question than it answered Gem fr (talk) 14:00, 23 June 2017 (UTC)

Can wine and beer be used to clean stuff?

Rubbing alcohol is isopropyl alcohol. Drinking alcohol contains ethanol. What happens if flour (with added water) is left fermented on the kitchen counter for a very time and then the fermented liquid is used to make beer, which is then used to clean stuff? Will ethanol still work as effectively as isopropyl alcohol? Is it safer to use ethanol than isopropyl alcohol simply because you can ingest it safely? If you add a lemon wedge or slice to the ethanol solution, then will it smell like lemons too? (talk) 00:53, 23 June 2017 (UTC)

  • Ethanol does make a good cleaner, beer and wine is usually only between 4-15% ethanol. The other stuff in beer and wine will make whatever you want to clean dirtier than before you started, defeating the purpose. Neutral spirits, such as vodka or moonshine can be used to clean things, though: [14]--Jayron32 01:05, 23 June 2017 (UTC)
Even so, rubbing alcohol is usually 70% which is stronger than most vodkas, whiskeys, rums and so on.Sagittarian Milky Way (talk) 02:03, 23 June 2017 (UTC)
Isopropyl alcohol is more toxic to humans' central nervous system than ethanol but it's not that toxic. It'd take about a half shot to be toxic. Methanol is more toxic. Now that's some dangerous stuff. Even so, if the thing being cleaned is 50.4's mouth, using 70% isopropyl alcohol is a bad idea even if you spit it out immediately. The mouth will instantly desiccate and take days to heal. Alcoholic mouthwash is designed to not do that. Sagittarian Milky Way (talk) 02:03, 23 June 2017 (UTC)
"The mouth will instantly desiccate and take days to heal." Some people actually tried that before? (talk) 03:50, 23 June 2017 (UTC)
Well at least the hard palate. Sagittarian Milky Way (talk) 03:55, 23 June 2017 (UTC)
"IPA causes rapid intoxication, so people sometimes drink it to get drunk. Other people use it to attempt suicide". What Is Isopropyl Alcohol Poisoning? Alansplodge (talk) 09:48, 23 June 2017 (UTC)
Some Russians told me it had been popular during Gorbachev's anti-alcohol campaign. Wnt (talk) 11:51, 23 June 2017 (UTC)
Sounds like you're describing this IPA. ←Baseball Bugs What's up, Doc? carrots→ 14:52, 23 June 2017 (UTC)
I'm surprised no-one has mentioned Deglazing (cooking) where wine is used to dissolve the gunge off the pan after frying some meat, especially if the meat has been coated in a seasoning with flour. Dmcq (talk) 10:41, 23 June 2017 (UTC)
The ethanol I'm the wine had nothing to do with that process. You can deglaze with chicken broth or even straight water. It's simply the action of hot water the removes the brown bits. Being wine had nothing to do with the deglazing bit, you use wine because it tastes good.--Jayron32 22:12, 23 June 2017 (UTC)
My experience is that a wine or something like it is much faster at the job than just water. Dmcq (talk) 23:31, 23 June 2017 (UTC)
And my experience is there is no difference. So we both lose.--Jayron32 02:53, 24 June 2017 (UTC)

Pinhole Camera

1. (Just to double check) Can a pinhole camera contain a lens element?

Assuming the answer is no, then:

2. Are these[15] really pinhole cameras? I can see a little glass-like reflection from little hole. And this site[16] sells what appears to be the cone-like tip of the camera, and it clearly contains a very large lens element.

Note that I'm not suggesting the seller is misrepresenting his product. Linguistically "pinhole camera" certainly covers all miniature cameras, regardless of operating principle. He has every right to sell it as a "pinhole camera". I'm just interested in learning about the operating principle behind these cameras. If they're not true (scientifically speaking) pinhole cameras then how come the front lens elements can be made so small? Is there a limit to how small the front lens elements can be before performance is unacceptably degraded? Scala Cats (talk) 01:16, 23 June 2017 (UTC)

Yes, diffraction. This is the same reason why a telescope lens has to be at least 115.8 millimeters wide to look as sharp as 20/20 vision at 60x magnification. Almost certainly not coincidentally, this is almost 60 times the width of the human pupil in the daytime. Sagittarian Milky Way (talk) 02:09, 23 June 2017 (UTC)


There are two completely different things that are called "pinhole cameras".

The first uses a pinhole instead of a lens. It is characterized by having everything in focus no matter how close or far it is, and by requiring a huge amount of light (typically full sunlight, fast film, and long exposures). Example:

The second uses lenses, but configured in such a way that you can drill a pin-sized hole in a wall with a cone-shaped space behind it (there is a tool for that) and then take pictures of the inside of the room, hopefully without anyone noticing the pinhole your camera is looking through. Example:

--Guy Macon (talk) 03:10, 23 June 2017 (UTC)

"The second uses lenses" That's what my first question is getting at. Do those tiny cameras that use lenses actually qualify, scientifically speaking, as a pinhole camera? Because the article starts off by saying "A pinhole camera is a simple camera without a lens". I not sure whether that means "A pinhole camera is commonly constrction without a lens" or "A pinhole camera is defined as a camera that uses a pinhole instead of lens" Scala Cats (talk) 17:44, 23 June 2017 (UTC)
  • Yes, we have dual meanings here. I have the same problem with herbal tea, which both means tea leaves plus herbs, and herbs alone (tisane). StuRat (talk) 17:55, 23 June 2017 (UTC)
Ah, gotacha. Thanks, that clarifies it. Scala Cats (talk) 18:36, 23 June 2017 (UTC)
Also note that the type of pinhole camera lacking a lens might still have a glass cover over the pinhole, to prevent dust from getting in. StuRat (talk) 17:55, 23 June 2017 (UTC)
Really? In the very unlikely circumstance of dust being a problem, wouldn't the shutter adequately serve that purpose?--Mrs Wibble-Wobble (talk) 18:37, 23 June 2017 (UTC)
No, because pinhole cameras need to keep the shutter open a long time, since very little light is let in through the pinhole, to gather enough photons for full exposure. Also, there could be a subtle breeze into the pinhole, to equalize pressure, due to temperature changes, and this could draw dust in. StuRat (talk) 18:48, 23 June 2017 (UTC)

Blocking gravity waves?

(My apologies if I missed this in the article gravitational wave.) Suppose a planet is near enough to its star that the view of a distant source of gravitational waves behind the star is completely blocked everywhere on the planet.

  1. Is the planet affected by gravity from the distant objects?
  2. Could detectors on the planet detect the gravitational waves from the distant objects?
  3. If either of the answers is yes, then how? Can gravitational waves go through solid light-blocking objects like the nearby star?

Loraof (talk) 16:43, 23 June 2017 (UTC)

No the waves are not blocked so the waves are still detected, and I can think of a number of reasons why gravity and its waves don't interact and disperse like other interactions. But you mustn't take my word for it today though... for I looked and found this to be asserted on the APS website here: [17]. As to how, I'd would just assume that the changes in local curvatures are accrued at the speed of light regardless of the source. --Modocc (talk) 18:35, 23 June 2017 (UTC)
Note that, even assuming gravitational waves pass through stars unmolested, that doesn't automatically mean they would be detectable on the far side. This is because the signal-to-noise ratio may be too low, with all the gravitational perturbations of the nearby star (created by non-symmetric mass movements, like coronal mass ejections, solar flares, etc.), swamping the subtle gravitational waves created perhaps billions of years ago and billions of light years away. StuRat (talk) 18:44, 23 June 2017 (UTC)
The detectors would have to be really really close to the star to create any significant noise however of any kind (not by waves per se). Presently, our Sun can briefly eclipse black hole events (putting them out of telescopic view), but that would not effect our gravitational wave detection. To put this another way, the magnitude of change in curvature produced by the blackhole events are clearly on a different scale than those caused by local perturbations. -Modocc (talk) 19:22, 23 June 2017 (UTC)
I looked for refraction of gravity waves and found some apparently relevant papers. [18][19] Thanks to Sci-Hub, Springer no longer means checkmate, but I haven't gone there because I doubt I'm going to try to make serious sense out of this anytime soon. I would *guess* that very heavy masses might be able to distort the waves away from a given viewer... Wnt (talk) 18:53, 23 June 2017 (UTC)
The effect is under normal conditions negligible, but the fact that it does exist is a simple consequence of conservation of energy. The fact that matter couples to the gravitational field (which is why you can have gravitational waves in the first place), also means that gravitational waves can interact with matter and be detected. But that means that energy can be extracted from gravitational waves (Thought experiment originally proposed by Feynman to argue that gravitational waves carry energy involves test masses that move due to a passing gravitational wave, Feynman argued that you could use masses with a hole and put a stick through the holes such that the masses would now slide with some friction against the sticks, thereby dissipating energy. Where does the energy come from if gravitational waved do not carry energy?). Then if energy is extracted from passing gravitational waves, the waves that move on will carry less energy than they would otherwise have carried. The difference is caused by the emission of gravitational waves due to extracting energy from the gravitational waves, these are opposite in phase such that the transmitted gravitational waves will have a lower amplitude. Count Iblis (talk) 19:48, 23 June 2017 (UTC)
True. But that is a big if ("if energy is extracted from passing gravitational waves") and neglected by that APS webpage. Bummer. Maybe there are sources predicting the significance/insignificance of such extractions that would be useful for the OP. --Modocc (talk) 20:28, 23 June 2017 (UTC)
Gravitational waves will be stopped by an event horizon. But that is not something that you could fabricate to any shape you like, such as a sheet. Spacetime is really stiff, and all known matter will be soft and deformable compared to space. So it is hard to couple something made from matter to moving spacetime to extract the energy and lose it. Perhaps if your gravitational wave has a tiny wavelength, such as that of an X-ray, you would stand a better chance of making it lose energy in solid matter. Graeme Bartlett (talk) 02:34, 24 June 2017 (UTC)

Can a leaning tower be built in a stable way ?

This Q comes up specifically regarding the leaning minaret in Mosul which ISIL recently destroyed, along with the rest of the mosque: [20]. I assume that at some point they would want to rebuild both, but this might also come up if the Leaning Tower of Pisa collapses, etc. So, is there a way to make a tower which appears to lean, but which is stable, as opposed to leaning further with each passing year and finally collapsing ? One thought is to give it a narrower width at the top, as this would allow one edge to slope, while the other remains vertical. Not quite "leaning" but might give that effect from certain angles:

  /    | 
 /     | 
/      | 

Also, there could be a cantilevered portion, made of a lightweight material, extending past the vertical wall:

  /    |///
 /     |//
/      |/ 

Do we have an article on such a construction technique ? StuRat (talk) 19:11, 23 June 2017 (UTC)

Are you old enough to remember the 1976 Olympics? Tower was finished in the late 80s. Sagittarian Milky Way (talk) 19:32, 23 June 2017 (UTC)
Interesting. Do we have a link for the pictured structure ? Is it still standing ? Could it stand for 100 years ? 1000 ? StuRat (talk) 19:52, 23 June 2017 (UTC)
Olympic Stadium (Montreal). Sagittarian Milky Way (talk) 19:55, 23 June 2017 (UTC)
Thanks. Looks like inclined tower is the general article, but it doesn't address the stability issue. StuRat (talk) 19:58, 23 June 2017 (UTC)
Apparently the tower wasn't finished in time for the 1976 Olympics, or even 1986. Maybe it was too short to impress in summer '76 so it's not as famous as it could've been. Sagittarian Milky Way (talk) 20:12, 23 June 2017 (UTC)
A structure is stable if its center of mass lies within its "footprint" (our support polygon article refers to this). So a tower can lean arbitrarily as long as the base of the tower reaches over to cover the vertical projection of its center of mass, as can be seen in the stadium picture above. Of course in extreme cases, the material of the tower may not be strong enough to handle the stress required if the base juts out at an extreme angle. CodeTalker (talk) 20:48, 23 June 2017 (UTC)
Figuring it out in terms of center of mass gets a bit hairy when you have something leaning with a cable anchoring it from the back. Does one include the chunk of earth between where the cable is anchored to the base of the leaning object? DMacks (talk) 21:07, 23 June 2017 (UTC)
I would say yes. Talking about whether a building tips over based on its center of gravity is assuming that it's been left lying flat on the ground like a toy block. Once you start digging cables into the ground, then it depends on how much of the ground has to come out with the cables in order for it to tip. Wnt (talk) 23:09, 23 June 2017 (UTC)
Rigid cables? Sagittarian Milky Way (talk) 21:29, 23 June 2017 (UTC)
Is the stadium part of the mass even though the tower is supporting the white thing with the cables instead of the other way around? Sagittarian Milky Way (talk) 21:29, 23 June 2017 (UTC)
Burj Al Arab-Modocc (talk) 22:02, 23 June 2017 (UTC)

Burj Al Arab is a luxury hotel located in Dubai, United Arab Emirates that takes the form of a sail, so it is essentially the world's tallest lean-to (and consistent with your first example of "leaning"). It's very stable for it doesn't have much in the way of any mass that actually leans. --Modocc (talk) 22:02, 23 June 2017 (UTC)

See Block-stacking problem, the tower can lean over as much as one likes with each layer being just as wide and heavy as any other. Dmcq (talk) 23:36, 23 June 2017 (UTC)
Obviously, there are going to be some very real lower limits to any tower's slope (total rises over runs) since overhangs of blocks are limited by the blocks' compressive and tensile strengths. For example, for walking on they must be stiff and not thin like cardboard.. The uppermost block/floor can only be so long for any given thickness of material and the loads placed on them. Even really thin materials have to rise above the horizontal as they are stacked. -Modocc (talk) 02:15, 24 June 2017 (UTC)

I should clarify my Q a bit. As I'm talking about replicating ancient structures, they shouldn't rely on steel cables to keep them from toppling over. Steel beams, inside the structure, might be acceptable, so long as they could be hidden. However, I'm skeptical of how good of a building material steel is in the long term. That is, it's seems to require constant maintenance to keep it from rusting, like repainting it every few years. So, if there's a way to build an inclined tower out of stone, in a stable way, I'd have more faith in it lasting for centuries. StuRat (talk) 00:51, 24 June 2017 (UTC)

It may be harder to make a forever pure stone and mortar tower that imitates an ancient one that was never intended to lean but did anyway. The blocks of the block thing don't lean but the stones of the leaning tower of Pisa do. Also, if it leaned unintentionally the soil on that site might be crap. Sagittarian Milky Way (talk) 01:13, 24 June 2017 (UTC)
I must be clueless, but if the stones are not tilted like the ancient structure you wish to replicate, its not really a replica is it? I mean people do notice their alignments and it is near impossible to hide anything that is too substantial. I venture that carbon fiber cables might eventually be a superior alternative but that's just an educated guess. --Modocc (talk) 02:15, 24 June 2017 (UTC)
Well, you could create angled lines on the structure to make it look like each block is leaning, but you would need to do something at the top or it being level would give away the whole deception. StuRat (talk) 02:33, 24 June 2017 (UTC)
Well, fakes of just about anything anywhere can substitute for the real thing certainly, whether or not the original is preserved. Many structures can be stabilized one way or another, and the one's that can't are usually condemned and demolished. For example, our government recently relocated a tall brick lighthouse further inland away from the shoreline. --Modocc (talk) 03:12, 24 June 2017 (UTC)

June 24

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