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July 8

Full face diving mask Vs mouth piece

Thinking about the Thai cave rescue I wondered which would use air quickest a full face mask or a mouthpiece. On one hand a full face mask would need air flow through all the time. On the other hand a mouthpiece means that air breathed out is used up even if there could be enough oxygen to breathe it again mixed with some fresh air. Intuitively I think you should be able to tune the flow of a full face mask to use air more slowly, though that might seem stale to the diver. -- Q Chris (talk) 16:27, 8 July 2018 (UTC)

Pure speculation but they may be using rebreathers since they have to stay underwater for a long time and supplying cylinders is difficult. This would mean they use up a large percentage of the oxygen in the cylinders. I found breathing in through my mouth rather than my nose difficult. Dmcq (talk) 17:07, 8 July 2018 (UTC)
(ec) Take a look at full face diving mask. Both mouthpieces and full face masks usually have on-demand air supply, i.e. you "suck" the air through a valve (more precisely, the equaliser valve opens when it detects underpressure). Both will normally also release the overpressure when you breathe out. You cannot create an over- or underpressure that would allow you to "store" air that you breathe out in the mask - neither would your lungs stand it, nor would the seal of the mask hold it. Low oxygen content is not a problem, as the partial pressure even of quite oxygen-depleted air under pressure is high. This allows experienced divers to reduce their rate of breathing to below normal - they still get plenty of oxygen, but you need to train the body to notice that. If you want maximum endurance, you can use a rebreather. These are available for full-face masks and for more normal mouth pieces. --Stephan Schulz (talk) 17:17, 8 July 2018 (UTC)
I suspect the issue might be that a conventional mouthpiece has to be held between the teeth - not fail-safe for an untrained kid liable to panic. "Wearing full-face masks, which are easier for novice divers than traditional respirators..." BBC News - Thailand cave rescue: Mission to save boys under wayAlansplodge (talk) 19:28, 8 July 2018 (UTC)
Officials Call for Donations of Small Diving Masks to Rescue Cave Boys
Full face diving mask
Amazon: Divers Full Face Mask
--Guy Macon (talk) 22:27, 8 July 2018 (UTC)
For what it's worth, PADI (one of the world's largest recreational SCUBA diving organizations) treats a full face mask as a specialized skill that requires extra training beyond the basic open-water SCUBA certificate. Rebreather Diver is a formal certificate, and before PADI will grant it, the diver must satisfy experience minima and obtain the enriched air training and certificate, also known as breathing NITROX. Other dive agencies have similar requirements.
Breathing an atmosphere other-than-air can feel very strange; it requires skill and discipline to avoid physiological harm; in the case of an emergency rescue, the rescue divers would have to weigh any benefits against these serious extra workloads and risks.
Of course, diving in a cavern (or any other confined space) is an extremely advanced skill; and it can be extremely dangerous even in recreational settings. This rescue operation certainly falls under extraordinary circumstances; no dive instructor would want to put novice divers into such conditions if it could be avoided. As in any emergency, standard rules and procedures take a backseat to making a safe and rapid egress.
Nimur (talk) 01:54, 9 July 2018 (UTC)
I did notice that the PADI training has a lot about setting up the mask properly (which someone experienced would do in this case), that there would be opportunity to take the children down in short test dives to see if they have any problems, and that they wouldn't have to swim but rather be dragged along. They might even administer a sedative. And of course there is no alternative. Clearly it worked with four kids so far. I wonder if they started with the sickest or with the most healthy (to work out any bugs in the system)? --Guy Macon (talk) 05:59, 9 July 2018 (UTC)
Media reports suggest the initial plan was possibly to bring out the strongest, but after an assessment by a doctor the decision was made to bring the weakest out first [1] [2] [3]. According to those reports, this may have been in part, other than greater urgency for them to leave, also because it was expected that the conditions could be the best they would ever have. Nil Einne (talk) 08:50, 9 July 2018 (UTC)

July 9

Puncture repair patches - what's the orange stuff?

Puncture repair patches typically have a black part and an orange part but I've also seen patches that are just a big piece of buytl rubber which you can cut pieces off and they don't have the orange stuff. So what is the orange stuff? --129.215.47.59 (talk) 14:12, 9 July 2018 (UTC)

The orange layer is cold-vulcanizing uncured rubber.[4] When you put it on a clean neoprene surface with cold-vulcanizing fluid (commonly -- and incorrectly - called "adhesive") it melts into the surface The black layer is neoprene, which is stronger than cold-vulcanized rubber and more resistant to blowouts. --Guy Macon (talk) 15:29, 9 July 2018 (UTC)
  • The black part is butyl rubber (not neoprene) and is filled with carbon. That makes it strong and stiffer, but also less elastic. If you join two pieces of this together with a glue, then it's an inelastic joint which stresses the glue layer and causes an early failure. The softer unvulcanised rubber acts as a mechanical interface and shoc absorber between the two. As it's then a sandwich between them, it doesn't need to be especially strong.
Butyl to butyl joints are fine when made carefully in the workshop (and they're glued right to the edges) - but for a quick repair on the road, the orange layers will do a better job. Andy Dingley (talk) 16:35, 9 July 2018 (UTC)
Thanks for the correction. --Guy Macon (talk) 14:50, 10 July 2018 (UTC)

July 10

Surviving a firenado

Could a person survive getting sucked into a “firenado”? The question was inspired when I watch Into the Storm where a man got sucked into a firenado and die. PlanetStar 00:40, 10 July 2018 (UTC)

Responders who want to tackle this one might want to peruse Into the Storm (2014 film) and Fire whirl. People occasionally survive all manner of seemingly unsurvivable events, but I'd think that being drawn into a tornado of essentially turbocharged gasses burning at 1,000°C would be quite hard to survive, as even if the victim was thrown clear quite quickly, a breath or two would likely cause fatal lung damage. I haven't myself been able to find any authoritative references specific to 'firenadoes', however. {The poster formerly known as 87.81.230.195} 90.212.98.167 (talk) 02:11, 10 July 2018 (UTC)

Why are the Great Plains of North America not considered to be a system of piedmont plateaus?

Or thought of as one.... A plateau is a high plain. Piedmont plateaus are plateaus that are bordered on one side by mountains and on the other by a body of water or a plain as is the case with the Piedmont Plateau east of the Appalachian mountains and west of the Atlantic Plain, and the Appalachian Plateau on the west of these mountains and east of the Central Plains. That all sounds like the Great Plains. The high plains of the Great Plains are west of the lower Central Plains and east of the Rocky Mountains. The Great Plains reach heights higher than 6000 ft above sea level in some areas. For example, Colorado Springs is around 6035 ft above sea level and Cheyenne, Wyoming is around 6062 ft in elevation. The Continental Divide is around 11000 ft in elevation, but the peaks of the Rocky Mountains can reach above 13000 to 14000 ft in elevation. One can see the the land rising as one approaches the Great Plains in some areas. What characteristics do the Great Plains lack from a piedmont plateau or is it actually a system of piedmont plateaus? Willminator (talk) 03:35, 10 July 2018 (UTC)

Have you read Great Plains? ←Baseball Bugs What's up, Doc? carrots→ 04:54, 10 July 2018 (UTC)
It may be true that you can see the land rising as you approach them in some places but the part I crossed was very flat. It's a mile high drop but hundreds of miles wide and some elevation ranges of that mile are surely steeper than others. The Plains are mostly volcanic ash deposits from the Rocky Mountains erupting since before the range was the height of the Himalayas or Andes, the further east the less ash and the closer to sea level. Sagittarian Milky Way (talk) 05:30, 10 July 2018 (UTC)
"Mostly volcanic ash..."? That isn't how I learned my geology. The U.S. Geological Survey summary of the interior plains describes a great inland sea from which sediments accumulated and compressed.
Nimur (talk) 11:35, 10 July 2018 (UTC)
Huh, you are correct. How far west did the sea ever get? Sagittarian Milky Way (talk) 12:57, 10 July 2018 (UTC)
Well, that's a complicated question because over geological time-scales, the continents have moved and changed shape. For a start, here's the Wikipedia entry on the geologic timeline of Western North America and the main article on the geology of North America. If we go far back into ancient paleo-history, the areas that are now the great plains were underneath the western ocean abutting the continent of Laurentia; the far west parts of our continent (like California's Sierra Nevada mountains) didn't exist yet because the Nevadan orogeny didn't occur until the late Jurassic era... but this is all a vast simplification. Like all questions of science - how many years do we want to spend on the topic to refine and perfect our understanding?
When I used to teach geology for small kids, we gave a brief summary suitable for early elementary school: you can find fossils of seashells in the mountains of Colorado and Utah because a lot of that land used to be the bottom of the ocean. Once again, we're so severely oversimplifying that we run the risk of lie to children-style factual error.
A great book, for the interested reader: The Geology of North America: An Overview (1989); available at Amazon. One reviewer wrote, "...very dense and pretty dry..." Well, what can one expect from a book on rocks?!
If we want to get very precise about the exact farthest west extent, and so on, all I can say is that I am reminded of our discussion in March, quibbling on the details about the exact age of Earth. How shall we measure west-ness in paleo-Earth? Should we measure degrees of longitude, from the Greenwich meridian to the easternmost tidal high water mark? ... and where exactly was Greenwich, so many million years ago? These are, ultimately, issues that relate to false precision. Paleo-geology is a different kind of science than analytical chemistry; geologists have to accept an amount of intrinsic uncertainty; and so we accept that we must maintain the scientific method without any ability to conduct controlled experiment. But at the same time, we can hold ourselves to the highest standards of analytical investigative rigor.
Nimur (talk) 14:53, 10 July 2018 (UTC)
So in the case of the Great Plains, it matters how steep and long the slopes are from a plain or sea to the top of a piedmont plateau in order for it to be classified as a piedmont plateau and not just a high plain? Willminator (talk) 14:42, 10 July 2018 (UTC)
The U.S. Geological Survey's scheme for classification is centered around the idea of a "geological province," which is a concept they invented to group areas that have similar geological histories (and therefore, similar geological properties). But they use terminology fluidly: a region has specific areas that "exhibit the geology of the interior plains," even if there are counter-examples.
The term "piedmont" is used to refer to a specific, different area of the United States. In that sense, which is the canonical usage defined by the USGS, the word "Piedmont" is used as a locale, not as a generic description. For more information on this standardization of terminology, Wikipedia has an article on United States physiographic regions.
Nimur (talk) 14:53, 10 July 2018 (UTC)
I think the key thing that makes a plateau a plateau is that you can look up at it. According to the article, it is "raised significantly above the surrounding area". In the case of the Piedmont Plateau, there is an edge called the Atlantic Seaboard fall line. Though it's an obscure feature now, apparently at one point it meant a bunch of sweaty guys had to lug a canoe a long distance uphill practically any way they tried to boat inland, so it counted as a highly noticeable feature to them. The Great Plains don't have this AFAIK. Wnt (talk) 16:12, 10 July 2018 (UTC)
The Atlantic Fall Line can be quite dramatic in places and there's a clear delineation, for example, between the Atlantic Coastal Plain and the Piedmont all up and down the East Coast, from the Metacomet Ridge in Connecticut to the The Palisades in New Jersey. If you've ever crossed the George Washington Bridge, you're basically staring at the escarpment that marks the Eastern edge of the Piedmont. I live in Raleigh, NC which lies right on the fall line, and it's obvious when you're approaching it: South and East of Raleigh is flat: there's very little hills or elevation changes. In Raleigh, there are some fairly dramatic elevation changes in the area of the North Hills and the Crabtree Valley which clearly mark the transition to the Piedmont. There's also an even more dramatic transition from the Piedmont to the Appalachians, the Blue Ridge Escarpment, which you notice dramatically on any highway going west through the Carolinas or Virginia. By contrast, when traveling West across the Great Plains, there's no dramatic escarpments or changes in elevation. It's true that the great plains can get quite high as elevation gradually ramps up from East to West, but there's no clear boundary the way there is for the Piedmont.--Jayron32 23:47, 10 July 2018 (UTC)
Here's the Palisades. There's still ridges of ancient metamorphic rock east of them, only about half the height of the Palisades at the GWB though. Beyond West Bronx and the skyscraper district with the tallest non-Manhattan building there's still naked eye hills over 200 feet above sea level but they're just piles of glacial detritus like terminal moraines. Sagittarian Milky Way (talk) 02:57, 11 July 2018 (UTC)

High index lenses

Are there any disadvantages to a 1.74 high index lens compared to one of lower index such as 1.67? I.e. Why doesn’t everyone with strong prescriptions get 1.74 instead of 1.67? Clover345 (talk) 07:52, 10 July 2018 (UTC)

  • Agreed. I have terribly myopic eyesight and shell out the extra for the high index lenses. When it comes time to pick out lenses, my optician and I typically have to sift through several pages of various strengths and coatings to get some reasonable trade-off between price and utility (fashion falling a distant third). People requiring the higher index lenses also typically require other modifications as well, driving up the price again. For example, my optician makes several modifications to the grinding of the edges to reduce glare simply because there's more lens there to cause it. Matt Deres (talk) 12:20, 10 July 2018 (UTC)
  • I have one of each. My eyes are strongly asymmetrical and although my prescription for one eye is strong enough to justify high index lenses anyway, I get a more mechanically balanced pair of lenses if the thicker lens is made thinner, but not the thinner one, so they end up matching more closely. It also has an effect on opacity for sunglasses.
Of course, graded index lenses would be even more interesting. Andy Dingley (talk) 13:28, 10 July 2018 (UTC)
While cost is a big factor, it isn't the only disadvantage. Coatings was mentioned above, but not clearly mentioned is one reason for coatings is because of the lenses. Higher index lenses generally mean more reflections, hence why nearly all high index lenses come with AR coatings. (And that can lead to other things like scratch resistance.) This is mentioned in the above linked source about cost but is also discussed here [5]. As mentioned there you also tend to get more chromatic aberrations, or other distortions of peripheral vision with high index lenses. (Also mentioned here [6] [7].) Although as mentioned, this tends to be a bigger problem for those with low powered prescriptions because those with higher powered ones are often more used to limitations of their peripheral vision. As sort of hinted there and also mentioned above, it also depends on the skills of the optometrist or whoever is designing the glasses/dispensing the prescription, along with choosing the best option, working with the patient. See e.g. [8] [9]. As mentioned in a the second source, a notable advance is using computerised tools to give a more precise individualised solution generally called digital, HD or free-form lenses [10] [11]. Nil Einne (talk) 15:47, 10 July 2018 (UTC)

How do Voltage converters deal with Hz?

Do voltage converters from 220/240 to 110/120 or from 110/120 to 220/240, normally also convert the between 50 and 60 Hz? I know most devices won't need a converter anymore and that this might be indifferent for most appliances, but sometimes it matters. --Doroletho (talk) 18:34, 10 July 2018 (UTC)

No. It's rarely necessary to do this. When it is, it's usually easier to replace the 60Hz motor with a 50Hz one (it's almost never necessary to do it the other way). For US machine tools imported to Europe, it's sometimes necessary to do this because poorly designed motors overheat on 50Hz as their design was marginal in the first place. Andy Dingley (talk) 20:30, 10 July 2018 (UTC)
And besides motors, are other devices affected by the 'wrong' Hz? Some devices set their internal clock through the electric power. Wouldn't these be heavily affected, specially if they run on a timer and require exact running times? --Doroletho (talk) 21:12, 10 July 2018 (UTC)
A timer or synchronous clock doesn't just require conversion, it needs accurate conversion. Such a thing is possible, but I've never seen anyone bother to do it. We do already have clocks in Europe - it's cheaper to just use a local one. Andy Dingley (talk) 21:19, 10 July 2018 (UTC)
Some clocks do use grid frequency to synchronize (at least in Europe). Of course, a 50/60Hz mismatch would make the clock completely useless, not "slightly missing on the precise time". TigraanClick here to contact me 08:57, 11 July 2018 (UTC)
Another device that the frequency affects is a transformer, though 50 and 60 Hz are close enough that I don't think it's likely to matter. See Transformer#Effect of frequency. --76.69.47.228 (talk) 09:40, 11 July 2018 (UTC)
Not true. A transformer designed for 50 Hz will run well at 60, but a 60 Hz transformer may overheat when run at 50. Akld guy (talk) 22:05, 14 July 2018 (UTC)
Most converters don't change the frequency. It is possible to get "inverters" or "frequency converters" that do this, though even the cheap ones are generally hundreds of dollars. Most electronics don't care about the frequency very much, and of those that do (e.g. things with motors or cheap timing circuits), it is often easier/cheaper to buy a version that is designed for the local frequency than it is to import a foreign version and buy an inverter. Dragons flight (talk) 08:20, 11 July 2018 (UTC)

July 11

copper pitchers for storing drinking water

The alleged beneficent results of drinking water stored in copper pitchers have caused great demand for them and they are selling hot on Amazon India and other online stores. Numerous sites display pages describing such benefits. Are there chances of copper poisoning from drinking water stored in a copper pitcher? — Preceding unsigned comment added by 2405:204:D00C:7689:5D99:8D01:C88E:2E5D (talk) 16:28, 11 July 2018 (UTC)

This study says that storing drinking water in copper vessels has clear benefits in killing off bacteria in the water and that "Safety of leached copper does not appear to be an issue since studies have shown that the current WHO guideline of 2 mg Cu/L is safe ...., and the levels leached in the study were 1/20th of the permissible limits." Mikenorton (talk) 16:38, 11 July 2018 (UTC)
It's noted in hospitals the spread of infection has greatly increased after copper worktops (which killed bacteria) were replaced by plastic ones. 46.208.78.215 (talk) 18:41, 11 July 2018 (UTC)
Who says so? ←Baseball Bugs What's up, Doc? carrots→ 18:45, 11 July 2018 (UTC)
I don't know about any historic changes but Antimicrobial copper-alloy touch surfaces mentions clinical trials on new products. BTW we also have articles on Antimicrobial properties of copper and Copper alloys in aquaculture. Nil Einne (talk) 19:03, 11 July 2018 (UTC)
Copper is a poor choice, as it has toxicity risks. Although it also has antibacterial benefits, these are shared equally well (possibly better) by brass or monel fittings, which avoid the risks.
Copper is a risk depending on the water inside it. Hard water is fine, but something more acidic is a risk. Some contents - such as vinegar, pickles etc. involving acetic or lactic acid are downright dangerous. Andy Dingley (talk) 19:36, 11 July 2018 (UTC)

The above two articles for touch surfaces (which focuses a lot on in healthcare settings) and aquaculture at first glance seem to mostly deal with alloys given the titles.

However if you check the touch surfaces one, sometimes it simply refers to copper. Most of the time it's unclear if this specifically means near pure copper or just a simplification of copper containing alloys. However they do mention C11000 foil which seems to be basically a form of pure copper (see Oxygen-free copper, [12] [13] although note as mentioned in those sources silver is counted as copper) is used for cladding bed rails in one hospital. The EPA also has a group which seems to cover pure copper group I 95.2% to 99.99% 82012-1 although of course it doesn't necessarily mean these products are used in hospitals. Note that from reading all these sources, it seems one complication is probably that from what I've seen in the earlier articles, is what you count as an alloy e.g. C11000 may be called a copper-alloy although from what I understand as said earlier it's basically pure copper. (While you don't have to have much of something else to reasonably be called an alloy e.g. steel, from the earlier sources it seems like C11000 often does not intentionally include anything else. In other words, other components are impurities rather than add to make an alloy.)

Anyway point being, while the reasons for the various choices isn't really mentioned at least with some healthcare surfaces I'm not sure whether it's true that copper alloys are always definitely better than what may reasonable be called copper. (And I'm also not convinced that the reason for choosing an alloy rather than simple copper is because of toxicity concerns.)

BTW that earlier article for touch surfaces mentions brass. However it does not mention monel and at least for EPA approved surfaces, it seems monel isn't suitable or at least hasn't yet been demonstrated as it says all of the registered ones have over 60% copper. They do have other Cupronickel alloys with a significantly higher percentage of copper e.g. C70600 [14] is one mentioned for the same hospital mentioned earlier.

Nil Einne (talk) 04:28, 12 July 2018 (UTC)

Here in Australia there has been some recent media hype about old "copper" plumbing fittings actually containing some lead, and hence being a potential source of lead poisoning. Being slightly technical, this is an area where I don't trust journalists in the mass media at the best of times. Most have no scientific training. But it struck me as possible. HiLo48 (talk) 23:44, 11 July 2018 (UTC)
The lead is more likely to come from the solder used to join the pipes. Make sure the water container is not soldered with lead containing solder. Graeme Bartlett (talk) 00:50, 12 July 2018 (UTC)
For greater clarity: read "lead-containing solder" or "solder containing lead". --76.69.47.228 (talk) 10:03, 12 July 2018 (UTC)
Ah yes, old solder. That makes sense. HiLo48 (talk) 07:54, 12 July 2018 (UTC)
  • European practice for some years now is that soldered joints for potable water need to be made with lead-free solder.
There's still plenty of short stubs of lead pipe around in old houses, usually the main water supply into the house. In most water conditions, this isn't a problem (the pipe interior is coated with a layer of deposited minerals). In places where the water will corrode the lead, more of such pipes have been replaced by now. To connect modern piping to old lead it's necessary to use a mechanical pipe fitting, not a soldered joint. The specific type of soldered joint used to connect to old lead requires a leaded solder, so can no longer be used on potable water (by the regulations), even though it's still permissible to leave the old lead pipe in use. Andy Dingley (talk) 10:03, 12 July 2018 (UTC)
Regulations will vary widely around the world. The OP is presumably in India. HiLo48 (talk) 10:06, 12 July 2018 (UTC)
Metallic copper probably has little or no toxicity. It's the copper salts, such as copper sulfate, that are toxic. But you'd need to ingest about 10 to 20 grams copper sulfate in order to die. Copper sulfate ingestion is relatively popular for committing suicide in India. Acidic foods such as vinegar, pickles etc. are already preserved by the acid, so there's no further benefit from putting them into copper vessels. --46.189.28.77 (talk) —Preceding undated comment added 10:32, 12 July 2018 (UTC)
Wilson's disease is an inherited genetic disorder in about 1 in 30,000 people in which copper builds up in the body, named after neurologist Samuel Alexander Kinnier Wilson 1878 - 1937. Some of the signs of copper sulphate poisoning after swallowing 1-12 grams include a metallic taste in the mouth, burning pain in the chest and abdomen, intense nausea, vomiting, diarrhea, headache, sweating, shock and discontinued urination leading to yellowing of the skin. DroneB (talk) 14:57, 12 July 2018 (UTC)

Doctors that refuse abortions

is there a name for a doctor who refuses to perform an abortion (in a country where abortion is legal), based on personal beliefs? The source I have checked calls it a "Conscientious objector", but I'm not sure if we should use that term in Wikipedia's voice, as it seems to be specific to the military. The source probably uses it simply because it conveys a similar idea.

NOTE: I'm not asking for help or medical advise about abortions, just a name. I'm writing an article about a proposed abortion law, and I want to make sure that I'm using the right terms. Cambalachero (talk) 19:07, 11 July 2018 (UTC)

Maybe see Hippocratic Oath. ←Baseball Bugs What's up, Doc? carrots→ 19:37, 11 July 2018 (UTC)
"Conscientious objection" does appear to be the commonly used term. Searching google for "Conscientious objection abortion" finds many relevant hits.-gadfium 20:07, 11 July 2018 (UTC)
"Conscientious objection" is the term used in the Abortion Act 1967, Section 4. See also [15], [16]. --46.189.28.77 (talk) 20:14, 11 July 2018 (UTC)
And it's the term used by newspapers like The Guardian, but others refers to them as "abortion refuseniks" like The Spektator which is a misnomer, since refuseniks were the object of a denial, and not denied something actively themselves. --Doroletho (talk) 21:21, 11 July 2018 (UTC)
Perhaps we should update the article on Conscientious objector then, to include the non-military usage? Cambalachero (talk) 12:08, 12 July 2018 (UTC)
See Talk:Conscientious objector #Limited definition for previous discussion. hydnjo (talk) 18:50, 12 July 2018 (UTC)

Japanese home appliances in a country split between a 50 Hz and 60 Hz power grid?

Japan, as a very rare exception (Brazil is another, don't know about others), has a power grid split between a 50 Hz and a 60 Hz area. Are there home appliances versions for each area? Are home appliances designed upfront with the idea in mind that they might be used in one or the other area (and therefore made to be tolerant of deviations)?--Doroletho (talk) 21:35, 11 July 2018 (UTC)

Virtually all this list of home appliances, consumer electronics and AC adapters tolerate the difference between 50 Hz and 60 Hz mains frequency with only a minor exception of older electric clocks, tape recorders and record players that employ synchronous motors whose rotation period is an integral number of AC cycles. West Japan uses 60 Hz and east Japan uses 50 Hz; on the boundary between the regions there are back-to-back HVDC sustations that convert the frequency. DroneB (talk) 22:48, 11 July 2018 (UTC)
Note that some home appliances which are affected by mains frequency e.g. clock radios have a 50/60 Hz switch. These devices don't generally have synchronous motors of course and developing a product with one which can easily cope with both frequencies is I imagine difficult enough that it is basically very rarely if ever done. Nil Einne (talk) 04:35, 12 July 2018 (UTC)
The one device which both depended upon frequency and couldn't easily be changed was the synchronous motor. I've some industrial cam timer switches here which run on 50Hz, but they're designed for the US market too. As their motors are standardised, it's a two-screw operation to swap the motors. Motor makers for these just make them in two forms, with the same final speed. I've even got old (unusued) spares of 60Hz US motors for them, taken off US-built equipment and swapped over when it was imported. The motors run fine on 50Hz, they just run slow.
My woodworking machinery (the large fixed stuff) runs on induction motors, rather than the brushed universal motors that a smaller or cheaper power tool tends to use. These are also related to line speed, so my machines here run more slowly than they would in the US. These motors run at fixed speeds (either a nominal 1500 / 1800 rpm or 3000 / 3600 rpm, depending on their 4 pole vs. 2 pole design, and the 50Hz / 60Hz line frequency), so they often have a pulley and belt drive to change the speed to what suits the machine. If I wanted to, I could change the pulley by a small amount to bring the speed back to the original speed - but it's rarely needed. Andy Dingley (talk) 10:16, 12 July 2018 (UTC)

July 12

Glandular fever not found in a blood test, even though it's supposed to remain in the body for life

Somebody is saying that they had Infectious mononucleosis (glandular fever) and when they recovered, had a blood test and the virus was not found. But the glandular fever virus is supposed to remain in the body for life right? Is it possible a blood test wouldn't find it or some other explanation? — Preceding unsigned comment added by 2001:8000:1A4F:C500:2169:E3AB:DAE4:2459 (talk) 02:24, 12 July 2018 (UTC)

Depends on which test was done. As you can read further at Infectious_mononucleosis#Serology and its sources, most blood tests for Epstein-Barr are actually for the antibodies your body raises against the virus. Once it has been in the latent phase for a while, most of those antibodies become undetectable. There is also the possibility of a false-negative. Someguy1221 (talk) 02:57, 12 July 2018 (UTC)
In latency the virus is tightly controlled by the immune system and it is usually undetectable because it is present in the blood only in very low numbers. Ruslik_Zero 06:40, 12 July 2018 (UTC)

Spatial memory

What games (video games, traditional games, etc) are scientifically proven to enhance spatial memory? — Preceding unsigned comment added by 149.129.219.94 (talk) 07:14, 12 July 2018 (UTC)

"Playing “Tetris” on Nintendo DS develops the ability to imagine rotations of objects in 2D and 3D (spatial relations) to a greater extent than playing Tetris on a PC."

(PDF) Do Video Games Improve Spatial Abilities of Engineering Students?. Available from: [17]. See also: [18] Richerman (talk) 13:15, 12 July 2018 (UTC)

Rubik developed his cube to help students understand 3D rotations. Don't know if there's any studies on whether it helps though. Dmcq (talk) 15:31, 12 July 2018 (UTC)


July 13

Millipede legs; restriction on total number

Centipedes always have an odd number of pairs of legs, meaning that their number of legs is always divisible by 2 but not by 4. But is there any restriction on how many legs a millipede can have?? Georgia guy (talk) 00:49, 13 July 2018 (UTC)

This article,[19] among others, says millipedes have four legs per segment. ←Baseball Bugs What's up, Doc? carrots→ 01:18, 13 July 2018 (UTC)
Which means that millipedes could never have the same number of legs as centipedes. --Jayron32 00:16, 14 July 2018 (UTC)
One Internet site talks about 394 as a common number of legs; another says that millipedes always have an even number of pairs (meaning a number that is divisible by 4.) These 2 sources clearly contradict each other. Georgia guy (talk) 00:22, 14 July 2018 (UTC)
Sometimes a source won't have a leg to stand on. ←Baseball Bugs What's up, Doc? carrots→ 00:33, 14 July 2018 (UTC)
Encyclopedia of the Animal World, Elsevier 1972, calls the segments "rings" and says that most rings have 2 pairs of legs, while the first few rings only have 1 pair of legs. So it looks like the number of millipede legs could be divisible by four or two, depending on whether the number of segments with 1 pair of legs is even or odd.--Wikimedes (talk) 16:46, 14 July 2018 (UTC)
Discounting "common species have between 34 and 400 legs" in our millipede article, I haven't found a specific example of a millipede with the number of legs divisible by 4. From the 2nd paragraph of Millipede#Body: "The second, third, and fourth body segments bear a single pair of legs each and are known as "haplosegments"", which would indicate that the number of legs is never divisible by four. This [20] site says there are "often 3" haplosegments.--Wikimedes (talk) 17:18, 14 July 2018 (UTC)

And again I know nothing about birds

cheep cheep

So, saw these little guys while boating. Didn’t see any larger birds that looked like adults of the same species. This was right on the waterline of a small island in a freshwater lake in the Kenai National Wildlife Refuge. They certainly acted like chicks, making little “cheep cheep” noises, staying right on the apparent nesting site, making no attempt to fly or swim. Anyone know what they might be? Beeblebrox (talk) 02:30, 13 July 2018 (UTC)

I certainly know nothing about birds too, but they look a bit like greater sage-grouse chicks to me. Alex Shih (talk) 02:46, 13 July 2018 (UTC)
Here is a website for Alaskan birds. Of course it is a big state with lots of avians so it might take some searching. To my untrained eye this is a bit like your pic - especially if you allow for variation in coloring for young chicks. I could be way off though. MarnetteD|Talk 04:30, 13 July 2018 (UTC)
Rats I missed where it stated that the turnstone is a coastal bird. Good luck in tracking it down. MarnetteD|Talk 04:33, 13 July 2018 (UTC)
The beaks are too substantial for turnstones, they're probably some kind of young gulls, which are notoriously hard to identify. Acroterion (talk) 00:36, 14 July 2018 (UTC)
The fact that this is a freshwater lake may narrow the field. I’m beginning to think they are maybe Arctic Terns. Most images I can find show a orangish-yellow beak, but some of juveniles show a duller beak as these have. Beeblebrox (talk) 17:19, 15 July 2018 (UTC)

Vitamin B11

I can't find the chemical formula for Vitamin B11 (pteryl-hepta-glutamic acid). Can you help? 121.44.187.6 (talk) 03:57, 13 July 2018 (UTC)

There isn't one in this list B vitamins#List of B vitamins. Hopefully someone else can help. MarnetteD|Talk 04:22, 13 July 2018 (UTC)
A google search bring up this. MarnetteD|Talk 04:24, 13 July 2018 (UTC)
BTW, although it's one of the few to be unsourced I'm fairly sure our article is right. There's no longer such a thing as a recognised Vitamin B11 in humans. Any source which still calls pteryl-hepta-glutamic acid (or PHGA or chick growth factor) as a human vitamin B11, or which says there is such a thing as a human vitamin B11, is either outdated or unreliable. Or maybe both. If someone is trying to sell you something with vitamin B11 for human consumption, run away. Nil Einne (talk) 08:46, 13 July 2018 (UTC) 09:53, 13 July 2018 (UTC)
This is the original poster. I am well aware it has no value for humans. It happens that I am in a family of chicken ranchers. 121.44.187.228 (talk) 08:53, 13 July 2018 (UTC)

This one was a head-scratcher. The problem is that references to Vitamin B11 basically end in the 1950s as far as the scientific literature goes (though the papers that studied it continue to be cited later). Many of the papers on the subject are behind paywalls even my library can't get past, and those that I can read predate the chemical identification of the molecule. The first clue I had that something was wayyy off was seeing articles much much later that cited these B11 papers while discussing folic acid! Indeed, NCBI's pubchem lists "vitamin B11" as one of the 200+ synonyms for folic acid[21]. Unfortunately, it's specifically listed in vendor synonyms. Which means, at some ponit, somewhere, folic acid has been sold as B11. Which does not mean that scientists consider it the same. Anyway, what I conclude, but can't be 100% sure of, is that it was identified as an essential vitamin for chicks, and later found to be a known compound, and the name was never used again. Someguy1221 (talk) 10:32, 13 July 2018 (UTC)

I did discover that some naturopaths & homeopaths sell what they call "Vitamin B11" as folate. What they are actually selling could be anything - particularly homeopaths, homeopathy being essentially 100% quackery, and B11 being useless for humans as noted. Can any nice chemist tell me how to arrive at a formula for pteryl-hepta-glutamic acid? OP 121.44.185.44 (talk) 13:55, 13 July 2018 (UTC)
It does apear to be a folate derivative. Here's a ref (I don't have time to chase the cited refs right now): doi:10.1021/jo00837a600. DMacks (talk) 14:15, 13 July 2018 (UTC)
Here's another one. Ok, so part of the problem was that it's actually pteroylhepta-γ-L-glutamic acid. Also explains the history. When people started purifying folic acid and identifying its chemical structure around the 1940s, it was found that there were many forms, some of which only differed in the length of the glutamate chain (as a name of a chemical rather than a class of chemicals, "folic acid" only has one glutamate). It was further found that the length of the glutamate chain affected the molecules bioavailability in a species-specific manner. That's it. That's all, nothing else magical or special. Different organisms like to get their folate while it's attached to different things. Someguy1221 (talk) 00:09, 14 July 2018 (UTC)

July 14

Mass of earth over time

This article discussing a meteorite impact 3 Ga ago claims that "when this asteroid hit, Earth was only a third its current size". I've interpreted that as meaning that the earth was 1/3 of it's current mass at that time, which I find very, very hard to believe. An alternative interpretation is not occurring to me either. I've been trying to find something like a graph of the mass of earth over time, but I can't find such a thing. I imagine it's because the mass of the earth only substantially changed in the period up to and during the formation of the moon (4.5 Ga ago), and that since then changes to the earth's total mass have been negligible. The late heavy bombardment (4.1 to 3.8 Ga ago) consisted of around 22,000 objects large enough to leave craters at least 20km in diameter on earth. Even if we assume all 22,000 of them were the size of 5 Astraea (which would leave a crater far larger than only 20km in diameter) and no ejecta escapes the earth's gravity, the event only would have increased the earth's mass by around 1%. Since the LHB, I don't think there have been any major sources of additional mass, and the slow accretion of additional mass which is negligible anyway has been opposed by the gradual loss of hydrogen and helium. Is there any possibility that the claim in this article is correct? Also, does anyone know if a graph of the estimated mass of the earth over time, even if it just covers the accretion and moon formation stages exists anywhere? 2A0D:5600:3:9:201:200:0:10B3 (talk) 08:26, 14 July 2018 (UTC)

Yeah, that's nonsense. I suspect what someone intended to say was that at 3 Ga, the earth was 1/3 it's present age, but somehow that got miscommunicated as "size". Dragons flight (talk) 08:34, 14 July 2018 (UTC)
(EC) Several of the comments under the article say that this should read "a third its current age". That is numerically correct, and presumably also what the author intended to write. If Earth had indeed tripled in size by whatever process, there would be no way that any traces of this crater would be detectable now. --Wrongfilter (talk) 08:36, 14 July 2018 (UTC)
(ECx2) Yeah I was right about to post the same, after "lulwhat?" I did check the the original paper to make sure, and no, it doesn't make this statement anywhere. Someguy1221 (talk) 08:36, 14 July 2018 (UTC)
Pfft. This is clearly a clever set-up for a geologically based "Yo mama..." joke. Matt Deres (talk) 02:49, 15 July 2018 (UTC)
See, they just admitted expanding Earth is true! Wake up sheeple! --47.146.63.87 (talk) 07:52, 15 July 2018 (UTC)
Note that Earth gains mass from meteors and loses mass from gasses stripped by solar wind and by radioactive decay -- at nearly identical rates [22] (estimates vary).2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 18:04, 15 July 2018 (UTC)

July 15

Photography - tracking fast moving subjects

In professional filmmaking, how are cameras stabilised when they are following a fast moving subject close up? For example of an actor is sprinting and the cameras is right next to them following, how is the camera stabilised? Assuming that it’s not possible to use a guide rail. Let’s say the actor is sprinting over many obstacles and turning a lot and the filming is done in a public area. — Preceding unsigned comment added by 90.206.71.55 (talk) 12:15, 15 July 2018 (UTC)

Wildlife photographer Roger N. Clark explains The key to fast autofocus and focus tracking is the use of phase detection focus. The link shows examples. DroneB (talk) 12:55, 15 July 2018 (UTC)
SteadiCam, and many similar products, provide smooth video of motion using mechanical stabilization and a trained operator. Nimur (talk) 14:43, 15 July 2018 (UTC)
Steadicam's introduction was apparently a really big deal. I came across this recently and there's a couple interesting historical pages from the current manufacturer.[23][24] The "art museum steps" scene from Rocky was inspired by a very similar shot in the original Steadicam demo reel. The full sized ones (made for Hollywood movie cameras) are huge and expensive but they now have some small handheld ones for smartphone/gopro sized cameras that are pretty affordable I do not need another gadget.... Interestingly only a very recent (phone sized) model has a gyroscope: I had expected they all did, but apparently the traditional one is just an elastic mount on some gimbals, completely inertial. 173.228.123.166 (talk) 16:54, 15 July 2018 (UTC)
Also there is a Hollywood profession of focus puller, someone whose sole duty is to focus the lens while the shot is in progress. That is not so easy to do automatically. The focus puller has to understand exactly how stuff will be moving in the shot and what parts are supposed to be kept in focus, so that the focus movements are pre-planned/choreographed but done in real time as the shot proceeds. 173.228.123.166 (talk) 16:58, 15 July 2018 (UTC)
A little web research shows bigger gyroscope stabilizers are a thing. ken-lab.com apparently originated them in the 1950s. There are other brands and some DIY ones now[25] (even one using old hard disk drives as gyros![26]) but it all seems cumbersome and low tech. I tried some stabilized binoculars in a store once (they have little piezo actuators that wiggle the prisms in the binocular to compensate for wobble) and they worked amazingly well, and optical image stabilization in camera lenses is similar, so I guess this gyro stuff is for heavier gear, higher amplitude vibration etc. 173.228.123.166 (talk) 19:16, 15 July 2018 (UTC)

Differences between hydrogen and most elements

Why do isotopes of hydrogen make such a big difference?? If all carbon on earth were C14 instead of the standard C12, it wouldn't affect life very much. But if all hydrogen on earth were H2 instead of the more common H1, we would die. Why do isotopes of hydrogen affect the element's behavior more strongly than isotopes of other elements?? Georgia guy (talk) 18:29, 15 July 2018 (UTC)

What are the bases of your two premises? ←Baseball Bugs What's up, Doc? carrots→ 18:43, 15 July 2018 (UTC)
Bugs, this is kind of a well-known fact, except that the choice of C14 is unfortunate. C14 is very radioactive, with a half-life of only 6K years or so. If all carbon on Earth were C14, we would die promptly from radiation poisoning. But from a chemical point of view, I think GG is correct (the choice of C13 instead of C14 would probably have made the question correct).
I think the answer is that the extra neutron just makes a lot more difference when there's only one nucleon to start with. For example deuterium has double the mass of ordinary hydrogen. That affects the energetics of chemical reactions. Someone who knows more about quantum chemistry can probably elaborate, but I think this is the main point. --Trovatore (talk) 18:53, 15 July 2018 (UTC)
I guess this is also to do with energetics of reactions, just not chemical ones...but since the mass will effect the average velocity of the particles in solution, it would also have an effect on rates of diffusion. 61.247.39.121 (talk) 23:09, 15 July 2018 (UTC)
The Heavy water#Effect on biological systems says

The larger chemical isotope-effects seen between protium (light hydrogen) versus deuterium and tritium manifest because bond energies in chemistry are determined in quantum mechanics by equations in which the quantity of reduced mass of the nucleus and electrons appears. This quantity is altered in heavy-hydrogen compounds (of which deuterium oxide is the most common) more than for heavy-isotope substitution in other chemical elements.

BTW it also mentions the, I agree well known, problems organisms have with heavy water. It's perhaps worth remembering that while it's sometimes worth challenging a statement made in a question where you have good reason to be uncertain if it's true, it's not necessary to challenge every single statement made especially ones you know nothing about. If you just wish to know more about something said, it would be better to phrase it as a question. Nil Einne (talk) 19:55, 15 July 2018 (UTC)
Which is what I did. And Trovatore immediately shot down the first of the two premises. And thank you for providing a source for the second premise. ←Baseball Bugs What's up, Doc? carrots→ 00:14, 16 July 2018 (UTC)

Rinsing out a vessel

You have a 1 litre vessel full of soapy water. You want to rinse it until 0% soap remains (or nearly 0%). Which is most efficient?

  1. Pour out the soapy water. Fill it 10% full of clean water. Swish it around. Pour it out. Repeat until 0% soap remains.
  2. Pour out the soapy water. Fill it 50% full of clean water. Swish it around. Pour it out. Repeat until 0% soap remains.
  3. Pour out the soapy water. Fill it 90% full of clean water. Swish it around. Pour it out. Repeat until 0% soap remains.

Anna Frodesiak (talk) 20:44, 15 July 2018 (UTC)

Strictly OR, but when camping (with limited potable water), I use something most similar to 1 for washing dishes, etc. However, I too, would be interested in a "scientific" answer. 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 21:17, 15 July 2018 (UTC)
I think the answer is going to vary a lot depending on what sort of "efficiency" Anna has in mind, and a little bit on what "0%" means. Of course you're never going to get to literally zero percent by any practically feasible method. But if you have a threshold in mind, you can optimize the procedure for getting to that threshold based on things like the amount of time spent, the amount of water used, how difficult it is to "swish". I don't think we can really come up with a definitive answer here. --Trovatore (talk) 21:18, 15 July 2018 (UTC)
I assumed "efficient" meant least amount of water used (and "nearly 0%" meant undetectable for ordinary use). 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 21:36, 15 July 2018 (UTC)

I guess by efficient I mean time and effort. Anna Frodesiak (talk) 21:41, 15 July 2018 (UTC)

In that case, I'd go with 3 (more intuitive than scientific answer). 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 21:45, 15 July 2018 (UTC)

(ec) Too complicated for a once-and-for-all a priori solution, I think. We'd need to have a model that incorporated the rate at which the soap diffuses into the clean water, the characteristics of the pot as regards "swishing", et cetera. Probably best to just try it a few different ways and see what works for you. --Trovatore (talk) 21:48, 15 July 2018 (UTC)
If the contaminant is just soap, a few quick rinses with small amounts of water is easiest and saves water. Say dumping out the vessel's contents leaves 1 ml of solution in it by surface tension (probably too high a guess). If you started out with 1ml even of pure soap and treat the rinsing as pure mixing into a solution, 3 rinses of 100ml each would get to 1/1003 or 10-6 concentration, same as 2 rinses of 1000ml each, but probably quicker. See homeopathic dilution if you want to get silly. 173.228.123.166 (talk) 23:43, 15 July 2018 (UTC)
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