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November 8

Street lights, rain drops and windows

A few nights ago it was pouring down with rain. I looked out a window to take a look, and I noticed that really beautiful patterns of light appeared as I put my eyes right in front of rain drops that were in front of a street light. The rain drops had interesting 'arms' surrounding them, but the most important part I noticed was that there were so many black lines covering the entirety of the drops.

I was able to take a picture of them with my phone, but unfortunately most of the the lines do not appear in the photos. You can see some on the sides but most of them are missing.

What caused these lines to appear?

―Panamitsu (talk) 05:08, 8 November 2024 (UTC)[reply]

See Caustic (optics). --Lambiam 09:37, 8 November 2024 (UTC)[reply]

The repeating black lines are an example of Newton's rings. They occur due to internal reflections in a thin wedge of fluid and are most apparent when the source light is monochromatic e.g. yellow sodium light. The article shows a more reliable way to view the rings using a thin convex lens than relying on chance raindrop spreading. Philvoids (talk) 10:49, 8 November 2024 (UTC)[reply]

Yes, can confirm that this is what the lines looked like, although they were not as round as in the article's images. Thanks. ―Panamitsu (talk) 22:11, 8 November 2024 (UTC)[reply]

November 9

Black Body emissive power in medium

The black body emissive power in a medium $E_{m}$ is equal to the product of the square of its refractive index $n$ and the emissive power in vacuum $E_{v}$ with the formula:
$E_{m}=n^{2}E_{v}$ .
What does this mean in terms of the energy emitted, respecting the principle of conservation of energy and in the case where the energy is emitted in a vacuum, then enters a medium with refractive index $n$ ? Malypaet (talk) 23:16, 9 November 2024 (UTC)[reply]

Power is energy emitted over time. So energy is conserved as it is emitted more slowly. Heat energy turns into electromagnetic energy. Graeme Bartlett (talk) 10:15, 11 November 2024 (UTC)[reply]

Yes, but here, if you use the SI units in

Joules\cdot s^{-1}\cdot sr^{-1}\cdot m^{-2}

for emissive power as radiance, you have

E_{m}>E_{v}

. So, to conserve energy, you cannot use only the velocity for power, as you suggested. Malypaet (talk) 23:31, 12 November 2024 (UTC)[reply]

the most important unit is sr . In the vacuum the energy is distributed into all directions. In the medium it's too. But on entering the vacuum only certain directions are possible. In these directions the energy is concentrated. 176.3.66.65 (talk) 23:14, 22 November 2024 (UTC)[reply]

November 10

What is a pipehead dam?

I've seen various things described as a "pipehead dam" (common noun), as well as some specific instances of dams named "... Pipehead Dam", eg Serpentine Pipehead Dam, which is separate to Serpentine Dam. I gather from the text of Serpentine Pipehead Dam that a pipehead dam is a smaller dam fed from a larger dam, with the smaller (pipehead) dam then feeding water into the pipe into the water supply system - but I cannot find anything (including with a Google search) that specifically says that. Mitch Ames (talk) 01:03, 10 November 2024 (UTC)[reply]

Wow! This was hard to hunt down. Deep in the results for probably the same set of searches you did, I finally found on page 77 of [https://sitecore9-cm-prod.watercorporation.com.au/-/media/WaterCorp/Documents/Our-Water/Regional-Water-Supplies/water-forever-south-west-final-report.pdf]: "Pipe-head dam — a diversion dam that takes streamflow

from the catchment to another dam for storage." --jpgordon^{𝄢𝄆𝄐𝄇} 01:22, 10 November 2024 (UTC)[reply]

That definition appears to be the reverse of what the Serpentine articles say. The articles say water goes from main dam to pipehead dam, but the Water Corp definition suggest the water goes from pipehead to another (main?) dam. Mitch Ames (talk) 10:01, 10 November 2024 (UTC)[reply]

The point that might not necessarily come from the easy picking of the water authority or google online materials, is that in the history of the dams, the water can be moved either from the main dam to the pipehead, or vice versa - and in turn can also be distributed to other parts of the system, there is no one way only part of the system, maybe not easily found online but nevertheless the current water corp web space is very poor on the intracies of the dynamics of the water supply system. There could well be a range of security issues attached to the lack of information . JarrahTree 10:55, 10 November 2024 (UTC)[reply]

...for the over two centuries that pipe head dams have existed? --jpgordon^{𝄢𝄆𝄐𝄇} 16:37, 10 November 2024 (UTC)[reply]

The higher the pitch of the instrument the longer the bow: why?

As everyone has probably noticed, the violin has a longer bow than the viola, which has a longer bow than the cello, which has a longer bow than the double-bass. Why? I'm guessing a given length of bow (irrespective of the instrument) takes the string through a given number of vibrations. Therefore to make the string vibrate for a given amount of time at a higher frequency requires more bow length. But is this correct? Another consequence would be that no matter what the instrument the bows make the string vibrate for roughly the same amount of time and that the violin requires a higher bow speed than the viola which requires a higher bow speed than the cello which requires a higher bow speed than the double bass. Again, is this correct? 178.51.16.158 (talk) 08:15, 10 November 2024 (UTC)[reply]

To make the string vibrate with a nice sound, there has to be sufficient (but not too much) friction between the bow and the string, which requires the bow to move at the same speed or just slightly faster than the top speed of the vibrating string, 2π times the product of amplitude and frequency. So higher frequencies at a given level of dynamics require a higher bow speed. --Lambiam 09:17, 10 November 2024 (UTC)[reply]

Ok. But leaving aside variations of the amplitude of the vibration, of the tension of the string, of the tightness or looseness of the bow (which the player can adjust), of the mass of the string and of the bow, of the thickness of the string and of the material it is made of, of the thickness of the bow, of the length of the string, of the force exercised by the hand, of how carefully the player has rubbed his bow with rosin, of the quality of the rosin, etc. etc. is it nevertheless the case that (things being roughly equal) to sustain a string's vibration at a higher frequency for a given unit of time requires more bow length? Clearly in practice there wouldn't be a linear relation between increase in frequency and increase in length. 178.51.16.158 (talk) 17:12, 11 November 2024 (UTC)[reply]

(Only) slightly pertinent to this query, you might be amused by Kingsley Amis's 1971 novel Girl, 20, in which a would-be avant-garde classical composer and violinist performs a controversial concert with rock musicians (an actual thing at the time, see for example Concerto for Group and Orchestra). Someone has secretly greased both his violin bows, but he impresses with his technical skills (though not with his actual music) by borrowing and using a double-bass bow. {The poster formerly known as 87.81.230.195} 94.7.95.48 (talk) 17:54, 10 November 2024 (UTC)[reply]

The articles about Bow (music) and the archetien who makes them say little about bow length. My survey below does not support the OP's observation. Lengthwise the bows for viola, violin and cello seem nearly interchangeable. The wide variation in longer bows for the double bass is due to the sitting players' preferences and arm lengths.


                |  Viola |   Violin |  Cello  |  Double bass
                |        |          |         |
bow    strings  |        |          |         |
cm   LOW    TOP |        |          |         |
----------------+--------+----------+---------+-------------
80   196    659 |   GE   |          |         |   x
79     .      . |        |          |         |   x
78     .      . |        |          |         |   x
77     .      . |        |    CA    |         |   x
76     .      . |        |   x      |         |   x
75     .      . |  x     |   x      |         |   x
74     .      . |  x     |          |   CA    |
73     .      . |        |          |  x      |
72    41     98 |        |          |  x      |    EG
 cm    Hz     Hz

Philvoids (talk) 12:15, 11 November 2024 (UTC)[reply]

Your chart would make the relationships clearer if Violin were in the first column, reflecting the order of relative sizes (hence string lengths and usual ranges) of the instruments. I can see a clear correlation between increasing size and decreasing bow length for the first three instruments. The double-bass may be anomalous because, unlike the other three, it is usually played standing.

I am also puzzled by your quoted figures, as my full-sized violin bow is only 65cm (ribbon length), and I am sure I have seen double-basses played with bows less than 50cm. {The poster formerly kown as 87.81.230.195} 94.7.95.48 (talk) 17:53, 11 November 2024 (UTC)[reply]

November 13

Light patterns

When I stare at a ceiling light and use my fingers to very slowly close my eye lids I see a weird pattern emerge. It looks like floaters that are covering my entire vision. I must also add that you can also see it (but with lesser detail) if you position your phone so that you can see the sun's reflection in the camera, and then you bring the reflection right in front of an eye.

What am I seeing? I'm guessing it is something inside my eyes because it looks so much like floaters. ―Panamitsu (talk) 10:38, 13 November 2024 (UTC)[reply]

It sounds like you should ask your eye doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:33, 13 November 2024 (UTC)[reply]

November 14

Tau propagation

Create redirect Tau propagation to ~~Tau_protein#Tau hypothesis of Alzheimer's disease~~ which section of Tau protein? ExclusiveEditor _{Notify Me!} 20:12, 14 November 2024 (UTC)[reply]

It is a controversial hypothesis that cannot be dealt with with a simple redirect. --Lambiam 05:38, 15 November 2024 (UTC)[reply]

November 15

Why are Koalas vulnerable to extinction

Hi. I was wondering why Koalas are vulnerable to extinction unlike Kangaroos, which are way more common, and both animals are found in Australia. Please let me know. Thanks. 2605:B100:142:A3B7:1D63:4EBE:694C:7BCA (talk) 04:22, 15 November 2024 (UTC)[reply]

The article has some information on it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:54, 15 November 2024 (UTC)[reply]

Habitat loss, especially lack of connected habitats, chlamidia, overcrowding, dogs. I doubt they are anywhere near extinct. Greglocock (talk) 05:17, 15 November 2024 (UTC)[reply]

It might have been quicker to Google your question - this was one of the first results; Threats To The Koala. Alansplodge (talk) 11:44, 15 November 2024 (UTC)[reply]

Kangaroos are more flexible in what they eat, and can move large distances faster. But koalas are cuter and so have more public awareness and are used as the poster animal, like giant pandas. Graeme Bartlett (talk) 23:52, 15 November 2024 (UTC)[reply]

More generally, the more specialised an organism is, the less likely it is to go extinct as a result of competition from other species but the more likely it is to be affected by environmental changes. So Koalas aren't going to have to worry about some other similar animal taking over its territory and taking all the eucalyptus for themselves. But they would be vulnerable to anything that killed off the eucalyptus. Iapetus (talk) 12:42, 19 November 2024 (UTC)[reply]

Admiral Nakhimov

In the time leading up to the shipwreck in late August 1986, is it known whether Captain Victor Tkachenko of the Petr Vasev had been transferred there from a smaller ship? Because I've read an article a while ago in Science et Vie (the Russian version) about the human factors in that disaster, and this would be the only conclusion which would make any sense! 2601:646:8082:BA0:CD5E:73B7:6DF6:2CF6 (talk) 14:50, 15 November 2024 (UTC)[reply]

I think the question is better suited at WP:RDH. ExclusiveEditor _{Notify Me!} 20:56, 16 November 2024 (UTC)[reply]

Why don't plants photosynthesize efficiently?

Photosynthesis is 6% efficient in green plants, 20% in solar panels. I see hints that it's more efficient in red algae, but I can't find a figure. They need to be efficient because they live in low light environments. There's a note here at Artificial_photosynthesis#Some_advantages,_disadvantages,_and_efficiency which says photosynthesis is typically 1% efficient! What's up with that? Something about not having enough CO2 around in the air to have any use for the energy? I found this article which says For the cell, a steady input of electrical energy coupled to a steady output of chemical energy is best: Too few electrons reaching the reaction center can cause an energy failure, while “too much energy will cause free radicals and all sorts of overcharging effects” that damage tissues, but that seems to boil down to "the cells can't do it". Card Zero (talk) 20:54, 15 November 2024 (UTC)[reply]

Evolution doesn't necessarily aim for perfection, just for survival. If that 6 percent is good enough for survival, there would likely be no evolutionary pressure to do it "better". ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:55, 15 November 2024 (UTC)[reply]

Trees compete for light, so there's some pressure to grow faster, isn't there? Card Zero (talk) 23:15, 15 November 2024 (UTC)[reply]

If you want to compare solar panel effiency, you should compare production of a chemical like glucose from carbon dioxide using electricity. Or should we allow any other reduced and useful carbon compound. As plants do not just produce electricity. Graeme Bartlett (talk) 23:23, 15 November 2024 (UTC)[reply]

Photosynthesis in plants can be very efficient under the right conditions. For instance, from photon to hydrogen/ATP it is nearly 100%,because the difference to really 100% is what destroys the chlorophyll. And replacing destroyed chlorophyll is costly, energywise and sometimes it even costs magnesium. Therefore that part is developed to maximize efficiency. Another goal is in the development of the carbon dioxide capture. For this one must know that chemical reactions with gases are very dependent on the pressure of the gases. Even the direction, that is if it's exothermic or endothermic, depends highly on the pressure. If RuBisCo would be faster the carbon dioxide could not come fast enough onto the site of enzymatic activity and would therefore drop in pressure there. Which in turn would drive the demand for energy up in this pathway. To overcome the RuBisCo-limit the C4 plants were developed. But they have other deficiencies, where they additionally spend energy to capture carbon dioxide for storage, and don't get it back at the RuBisCo.

Generally plants have too much energy for the amount of water and, most important, carbon dioxide, to synthesize sugar. Some hydrogen has to be dumped into the production of Ethen and Latex or other hydrocarbons. Of course, the energy for this is typically not counted towards the efficiency of photosynthesis. Moreover some ATP is simply hydrolysed for heating. Or for regeneration of ADP. Whichever is needed where this takes place.

For comparison there exist bacteria where chemical reactions are driven by 1/16th of a proton, that is 1/64 ATP-Unit. That only works with a large Quantum state in a superposition. If someone would want to maximise the efficiency of the photosynthesis, the recipe is there for the taking. But think of the side effects! 176.2.78.14 (talk) 06:02, 16 November 2024 (UTC)[reply]

For this one must know that chemical reactions with gases are very dependent on the pressure of the gases. Even the direction, that is if it's exothermic or endothermic, depends highly on the pressure. If RuBisCo would be faster the carbon dioxide could not come fast enough onto the site of enzymatic activity and would therefore drop in pressure there.

Does this mean that plants photosynthesize more efficiently in environments with elevated air pressure? Can you recommend any resources for learning more about that? Thank you! -- Avocado (talk) 14:21, 16 November 2024 (UTC)[reply]

@Avocado Not air pressure but partial pressure of carbon dioxide. That's standard in greenhouses. See Greenhouse#Carbon dioxide enrichment for details. Mike Turnbull (talk) 12:57, 20 November 2024 (UTC)[reply]

Thank you! Is there any research about elevated air pressure, too? IIRC, humans absorb oxygen more efficiently at higher air pressures (up to a point), so it seems like it might make sense (based on both that and what little I know about gas exchange across membranes) for plants to absorb CO2 better at higher air pressures as well. -- Avocado (talk) 21:02, 20 November 2024 (UTC)[reply]

humans are developed to an oxygen pressure of 0,22 atm. Over it there are many reactions that disturb the physiology, under it there is to over 0,17 atm no difference as long as no (not the least amount) Carbon monoxide comes into play. But even 0,11 atm is sufficient for up to 2 hours. At this low pressure of oxygen no normal combustion is possible but nobody needs an oxygen mask immediately. In case of a fire that is a great advantage for fire fighting. 176.3.66.65 (talk) 23:04, 22 November 2024 (UTC)[reply]

What about near volcanos?

Are there specialized plants growing in carbon dioxide rich environments that photosynthesize faster? Card Zero (talk) 12:42, 16 November 2024 (UTC)[reply]

No. I heard there are only a few places where there is consistent outgassing of CO₂ and yes, plants grow faster there. The thing is, plants are so starved for CO₂ that increasing CO₂ concentration instantaneously leads to increased sugar production. We think that the current photosynthesis evolved in a time when the atmosphere was like Venus's with perhaps 100 times the partial pressure of CO₂. Even now, you can put a houseplant in a pure CO₂ atmosphere in a glass vessel, and it does great. Another way of putting this is that there can be no natural selection for specialization in growing in a "carbon dioxide rich environment" since that would entail getting worse at using CO₂. Abductive (reasoning) 21:07, 16 November 2024 (UTC)[reply]

Thermometer thermal mass

I'd like to measure the air temperature in a room, outdoors, etc. Ideally by bringing the thermometer, turning it on if it is electronic, and looking at it. All thermometers that I've tried take several minutes to settle, which is annoyingly long. Is that inherent? Are there quicker ones? Don't want to spend a fortune, but "premium" is ok. Thanks. 2601:644:8581:75B0:0:0:0:2CDE (talk) 22:12, 15 November 2024 (UTC)[reply]

For an expensive high-tech solution use tunable diode laser absorption spectroscopy which should measure the temperature in the gas, rather than waiting for it to conduct into a detector. see https://www.yokogawa.com/solutions/products-and-services/measurement/analyzers/gas-analyzers/tunable-diode-laser-spectrometer/#Overview for a product. Graeme Bartlett (talk) 23:45, 15 November 2024 (UTC)[reply]

a really cheap way to go at it would be Resistance thermometer of course in Four-wire configuration. If the coil is very short, which is possible in four wires, then it will get the temperature in under a second. 176.2.78.14 (talk) 01:36, 16 November 2024 (UTC)[reply]

Thanks both, the resistance thermometer approach sounds promising. The tunable laser page says "request a quote" which means "too expensive for me to think about". 2601:644:8581:75B0:0:0:0:2CDE (talk) 02:45, 16 November 2024 (UTC)[reply]

An infrared thermometer retails at around USD 10, and reacts in less than a second from when you press the button. It doesn't measure air temperature but if you can assume your walls/floors/furniture/etc are about the same temp, it'll work. 85.76.117.61 (talk) 15:45, 16 November 2024 (UTC)[reply]

I have one but it is not very consistent between surfaces, and the air temperature can change faster than the furniture temperature. I guess it is better than nothing. Thanks. 2601:644:8581:75B0:0:0:0:2CDE (talk) 02:13, 17 November 2024 (UTC)[reply]

November 17

A lead zeppelin is your stairway to heaven?

In terms of fatalities per passenger-mile, and excluding combat losses during World War 1 (but including accidental losses during the same time period), which airships were more dangerous to fly in, those filled with hydrogen or with helium? I'm aware of the argument that helium-filled airships have a narrower flight envelope, which causes them to crash more often -- but, on the other hand, the flammability of hydrogen often had the effect of turning an otherwise survivable crash into one which is fatal for everyone on board, and also created the danger of explosion from lightning strike -- so between these two dangers, which one was the greatest? 2601:646:8082:BA0:CD5E:73B7:6DF6:2CF6 (talk) 03:41, 17 November 2024 (UTC)[reply]

Is there a source for the claimed explosion? It is not plausible, scientifically. --Lambiam 08:48, 17 November 2024 (UTC)[reply]

In what way not plausible? If your objection is to do with needing oxygen, that airship probably leaked: six months previously, "many small tears appeared". Card Zero (talk) 09:39, 17 November 2024 (UTC)[reply]

It would leak hydrogen out, not oxygen in. --Lambiam 10:16, 17 November 2024 (UTC)[reply]

So if a leak of hydrogen into air is hit by lightning, on top of a balloon made from sausage skin that's filled with more hydrogen, how do you imagine events would unfold after that? Hindenburg_disaster#Lightning_hypothesis says that airship fires have been observed under these kind of circumstances. I'm surprised that they were only fires, it makes the outcome sound mild, like lighting a gas stove. Card Zero (talk) 10:52, 17 November 2024 (UTC)[reply]

If there's a leak in the gas bags, it's plausible you may get an explosive mixture in the space between the gas bags and the outer hull. What exactly happened to Dixmude may never be known, but whether it was an explosion or rapid burning, too rapid for an orderly emergency landing (Hindenburg burned all its lifting gas in about half a minute), doesn't matter; all on board would be dead anyway. PiusImpavidus (talk) 14:00, 17 November 2024 (UTC)[reply]

That would indeed explain it. Without prior mixing with oxygen-containing air, hydrogen burns fiercely in a rapidly advancing front, as seen in the Hindenburg disaster, but not so rapid that there is an explosion. --Lambiam 16:46, 17 November 2024 (UTC)[reply]

I found a source, but no explanation. --Lambiam 10:30, 17 November 2024 (UTC)[reply]

According to the footnote in this republished 1923 article, there was an inquiry in January 1924, so maybe there is a report out there somewhere. Sean.hoyland (talk) 10:38, 17 November 2024 (UTC)[reply]

This is hard to say...

A helium-filled airship has less lift for the same volume, so it has to compensate somehow: fewer passengers and passenger-kilometres, giving more accidents per passenger-kilometre, or lighter skin, frame or engines or less fuel, all increasing accident rate.

A helium-filled airship is less likely to burn. The hydrogen fire itself isn't very lethal (except for those sitting high up in the envelope), but it can accelerate the destruction of the airship, leading to a faster crash, and set the skin and fuel on fire, leaving burning wreckage, which can kill passengers.

A third effect, which you didn't mention, is the heat capacity ratio. Helium has a heat capacity ratio of 1.66, hydrogen of 1.41, just like dry air, and moist air has an even lower heat capacity ratio. This means that on descent, helium heats up by adiabatic compression faster than hydrogen or the surrounding air, increasing the stability of the airship. When flying in slightly superadiabatic dry air, a hydrogen-filled airship is unstable in altitude. If it descends, the lifting gas heats up slower than the surrounding air, decreasing lift and accelerating the descent. This is no problem for helium-filled airships. Those have difficulty changing altitude faster than the time needed to equalise inside and outside temperature.

When looking at fatalities per passenger-kilometre, it's best to look only at passenger flights. Including military flights, test flights and accidents on the ground will increase the number of accidents without adding passenger-kilometres, making the airship appear more dangerous. Worse, those were the most dangerous occasions for airships. Ground accidents happened when the airship was grounded for bad weather, test flights were obviously more dangerous than regular flights and even when excluding combat damage, military flights were more dangerous as the airship was flown in weather and through manoeuvres that no captain would attempt on a civilian flight. However, excluding all military flights will exclude all helium-filled rigid airships, so no useful statistics are left. The safety record of those four helium-filled rigid airships of the US Navy doesn't appear too good though: three fatal crashes in only a third of the flight hours of Graf Zeppelin. PiusImpavidus (talk) 16:50, 17 November 2024 (UTC)[reply]

As noted in List of airship accidents, there is a variety of causes, a number of them being weather-related. The most successful airship was the Graf Zeppelin, which was filled with hydrogen, but never burned up or crashed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:55, 17 November 2024 (UTC)[reply]

There were no helium-filled passenger airships - they were all operated for naval reconnaisance. Alansplodge (talk) 15:56, 19 November 2024 (UTC)[reply]

There are some modern helium-filled non-rigid or semi-rigid passenger airships, used for sightseeing, but there are no hydrogen-filled modern airships, so there's no useful comparison possible. There are both helium-filled and hydrogen-filled gas balloons, but that isn't really the same thing. PiusImpavidus (talk) 09:57, 21 November 2024 (UTC)[reply]

Land surveying

Does modern land surveying (such as placement of streets after another, width of roads and blocks etc.) in take place using metric units in countries such as Canada, Australia and New Zealand, which have used metric distances for many decades now? Is there any English-speaking country that had already metricated when first surveys for 19th-century cities were done? Are there any downtown grids in English-speaking areas where streets are placed exactly 100 metres apart, and there are ten streets per one kilometre? In grids that place 16 streets per mile, the number of metres passed eventually deviates from number of 100 metres (hectometres) passed, since one mile is not exactly 1,600 metres. Placing ten streets per mile indicates number of miles passed by fourth-to last digit of house numbers, but does not indicate number of feet (or any other imperial unit) passed by whole number. By contrast, placing ten streets per kilometre indicates both number of kilometres passed by fourt-to last digit of house numbers and number of metres passed by whole house numbers. This placing is common in Argentina, but does it occur in any English-speaking country? --40bus (talk) 16:01, 17 November 2024 (UTC)[reply]

There are 100 meter blocks in Melbourne, Australia if I remember correctly. Mile/km/block-based addresses is not the original England way which was to count plots or buildings and call an unexpected new building in between the address of its neighbor suffixed with a letter or fraction. Manhattan's a hybrid: 1 address pair per 20ft plot of ownable (non-street) distance except 1 axis is 100 per block causing gaps like 153, 155, 201 except 3LPM5's 100 per 2 blocks cause Lex+Mad are new. Sagittarian Milky Way (talk) 05:48, 18 November 2024 (UTC)[reply]

The Melbourne blocks are 200 metres and then only by a coincidence; they are actually 10 chains or 660 feet, which happily converts to 201.17 metres. See Hoddle Grid for the details. Alansplodge (talk) 15:38, 19 November 2024 (UTC)[reply]

This is a new South Australian development near to where I live and the blocks are measured in metres, but not in nice whole metres. Zoom in and move the map to see details of the blocks. https://villawoodproperties.com.au/community/oakden-rise/find-buy/interactive-masterplan/ TrogWoolley (talk) 09:41, 18 November 2024 (UTC)[reply]

The same inaccuracy as 16 per mile then. Sagittarian Milky Way (talk) 01:29, 20 November 2024 (UTC)[reply]

Just to note that Australia, South Africa, New Zealand and Canada all began metrication in the 1960s or very early 1970s, so using metric measurements for any official purposes in the 19th-century would be highly improbable. Alansplodge (talk) 15:54, 19 November 2024 (UTC)[reply]

Is the any English-speaking country that already used metric measurement for official purposes in the 19th century? Was there anything that was measured in metric during Victorian times in the UK? --40bus (talk) 21:20, 19 November 2024 (UTC)[reply]

There was apparently a 6 mm government cartridge specification, the 6mm Lee Navy. I haven't dug up a contemporary source using mm, but it looks like it was so named even in 1895. (Note though the alternate .236 name.) Card Zero (talk) 06:26, 20 November 2024 (UTC)[reply]

The Abridgment: Containing Messages of the President of the United States to the Two Houses of Congress (1898) p. 480:

"Ten thousand 6 mm. Lee straight pull rifles have been supplied..." Alansplodge (talk) 12:44, 20 November 2024 (UTC)[reply]

On the subject of weapons, the QF 2-pounder naval gun of 1915 was made by the very British firm of Vickers and had a calibre of exactly 40 mm, but was known in British service by the weight of its shell in Imperial measure. The use of metric units here may be connected with the acquisition by Vickers of the Maxim Nordenfelt Guns and Ammunition Company in 1897, which although a British company, had its origin in the company owned by Thorsten Nordenfelt, a Swedish inventor. Alansplodge (talk) 12:33, 20 November 2024 (UTC)[reply]

A near miss though. Québec was a French colony using French units until 1763, switched to Imperial units after that, which was only 32 years before France metricated.

South Africa is an even nearer miss. It (or at least, the Cape Colony) was a Dutch colony until 1795, which is the year when the Netherlands metricated. The British then introduced Imperial units as they took over. Dutch rule was briefly restored in 1803–1806, but it appears this was too short to make the switch to metric. The Boers went their own way, continuing the use of traditional Dutch units (no longer used in the Netherlands) until Imperial units were made the standard in 1922: one of the last countries to switch to Imperial units. PiusImpavidus (talk) 19:31, 19 November 2024 (UTC)[reply]

How sampling rate in ADC adjusted or set ?

I am interested to learn how sampling rate in Analog-to-digital converter adjusted or set ? This page: Sampling (signal processing) didn't explain how it was adjusted. HarryOrange (talk) 18:36, 17 November 2024 (UTC)[reply]

Do you mean on a black box ADC (the sort of thing you have in a lab), or do you mean on an adc chip? Greglocock (talk) 22:00, 17 November 2024 (UTC)[reply]

@Greglocock I mean any typical ADC chip. How Sampling rate is adjusted? HarryOrange (talk) 05:03, 18 November 2024 (UTC)[reply]

I guess you read the data sheet for the chip. eg p41 and 42 here https://www.analog.com/media/en/technical-documentation/data-sheets/ad7768-7768-4.pdf Greglocock (talk) 06:04, 18 November 2024 (UTC)[reply]

An ADC sampling rate is determined by the data rate of the desired digital audio format. This article gives many examples of which 44.1 kHz, 48 kHz, 88.2 kHz and 96 kHz are typical. A designer simply ensures that an ADC chip receives a digital clock signal at appropriate frequency. Philvoids (talk) 20:17, 19 November 2024 (UTC)[reply]

Which is almost irrelevant to the question. An ADC chip or lab instrument can sample at many different rates. Greglocock (talk) 21:55, 19 November 2024 (UTC)[reply]

November 18

Open-air dust explosions

Dust explosion#Conditions required says There are five necessary conditions for a dust explosion. It even has a pointless diagram that arranges the five conditions in a pentagon with "dust explosion" in the middle. Condition 5 is confinement. But further down the page, Dust_explosion#Mechanism has a series of photographs demonstrating a dust explosion in open air. And thermobaric weapons, although more effective at killing people in confined spaces, seem to explode just fine in the open. So is condition 5, as a "necessary condition", plain wrong, perhaps an exaggeration of the fact that confinement makes a dust explosion more likely?

Supplementary question: I hear residents of Lahore and Delhi are wondering if their very sooty smog might one day explode. Is this at all plausible? Card Zero (talk) 00:09, 18 November 2024 (UTC)[reply]

Pointless? It is a five-pointed diagram. --Lambiam 06:53, 18 November 2024 (UTC)[reply]

In general, not only for dust, for detonation to occur, a mix of fuel and oxygen within the explosive limits has to be present in a compact largish volume. Upon detonation, the pressure in this volume will rapidly increase tremendously within (typically) microseconds. If the volume is not confined by an enclosure, the gases resulting from the combustion will expand supersonically with a shock wave that may or may not cause damage, depending on the power released and the environment. If the volume is confined by an enclosure, the enclosure may be able to withstand the pressure and contain the gases – possibly with controlled release through safety valves. (See e.g. Pyréolophore.) Otherwise, if the enclosure is broached, the gases will also expand explosively.

The OSHA fact sheet that is the source of our five-pointed list of conditions is actually about another scenario. It considers the case in which ignition merely leads to deflagration, which is much more likely to occur – the mix only has to be within inflammability limits. The combustion is much slower and does by itself not cause a shock wave. However, although the pressure rises less rapidly, the rise is still dramatic, especially if the volume is contained by an enclosure. If the enclosure cannot withstand the pressure, the gases will also expand explosively, as before.

So I think a fuel–oxygen explosion can occur in open air, but for this to be an explosion in the strict sense of causing shock waves, the right conditions will only very rarely be fulfilled accidentally. (In thermobaric weapons, they are fulfilled by design.) --Lambiam 09:05, 18 November 2024 (UTC)[reply]

But in the conditions there is no requirement of an accidental event?! 176.3.66.65 (talk) 15:10, 22 November 2024 (UTC)[reply]

Delayed onset muscle soreness

How long does it last and how to recover from it? CometVolcano (talk) 16:53, 18 November 2024 (UTC)[reply]

According to the article: "It peaks from 24 to 72 hours, then subsides and disappears up to seven days after exercise." --Amble (talk) 17:11, 18 November 2024 (UTC)[reply]

From the top of this page: We don't answer (and may remove) questions that require medical diagnosis... AndrewWTaylor (talk) 14:15, 19 November 2024 (UTC)[reply]

It is said that the soreness is helped by consuming protein. Abductive (reasoning) 10:27, 20 November 2024 (UTC)[reply]

November 20

John Balbus and Steven Balbus

Are Steven Balbus (Oxford University astrophysicist) and John Balbus (Head of Office of Climate Change and Health Equity in Biden's HHS) related? 178.51.16.158 (talk) 19:43, 20 November 2024 (UTC)[reply]

Given their mutual association with Philadelphia and their strong physical resemblance, it seems very likely, but I haven't been able to find any source confirming it with a cursory web search, so this might take some deep digging (better suited to someone in the USA, not Europe). John Balbus, incidentally, seems to me to be a good candidate for a Wikipedia article. {The poster formerly known as 87.812.230.195} 94.1.211.243 (talk) 02:13, 21 November 2024 (UTC)[reply]

They are brothers, with a third brother named Peter.^[1] Here on p. 33 is a photo of Steven en John side by side. Their father was Theodore G. Balbus,^[2] a radiologist, and their mother Rita S. Frucht.^[3] A bio of the father is found here, where you can also find that Peter runs a consulting firm called Pragmaxis. --Lambiam 10:09, 21 November 2024 (UTC)[reply]

November 21

Griffiths in math and physics

There's something called the Griffiths phase. If you search for griffiths phase activity so, you'll find things with similar names. A Griffiths singularity, Griffiths effects, there's probably more than one thing people call Griffiths' formula since there's a physicist called Phillip and two named David J. Griffiths. How many things are we dealing with under this name? Is there a book where they're all listed right next to each other? Gongula Spring (talk) 19:37, 21 November 2024 (UTC)[reply]

The concept of a Griffiths phase is named after theoretical physicist Robert B. Griffiths, who was the first to describe the appearance of such phases in an Ising model of ferromagnetism.^[4] He is also the eponym of the Griffiths inequality. Most uses of Griffiths singularity and Griffiths effect appear to be related. "Griffiths' formula" is a very general name that may refer to various formulas found by mathematicians with the surname Griffiths, such as Griffiths' integral formula for the Milnor number of an isolated hypersurface singularity, found by pure mathematician Philip A. Griffiths, also the eponym of the Griffiths group. See also Griffiths' theorem, named after yet another Griffiths. --Lambiam 23:43, 21 November 2024 (UTC)[reply]

That formulation seems at least superficially be leading to references to Alan Arnold Griffith. Formulas like ohmic or non ohmic dissipation in metallic griffiths phases used at the National High Magnetic Field Laboratory then tend to appear ambiguous to that effect too. Most other examples are deeply plunging into statistical quanta states thus unambiguously associated with Robert B. Griffiths instead. --Askedonty (talk) 00:13, 22 November 2024 (UTC)[reply]

The bracketing is not as in ((Griffith phase) field theory) but like (Griffith ((phase field) theory)), a theory of fracture, based on a phase-field model, developed by Griffith. --Lambiam 08:47, 22 November 2024 (UTC)[reply]

The interesting thing is that those approaches are leading us very near of a (a least to me ) finally rather satisfying view of the problematics induced by the idea of Action at a distance. --Askedonty (talk) 10:51, 22 November 2024 (UTC)[reply]

So much that you only have to think about it and what do you get? Long distances in apparent contradiction to.. --Askedonty (talk) 11:00, 22 November 2024 (UTC)[reply]

I'm not sure if these long distances anticipate my next question, which is what does "long-range" mean in the search results above?

Gongula Spring (talk) 15:54, 22 November 2024 (UTC)[reply]

Perhaps, as in #16 from that request as I get it "Temporal disorder in discontinuous non-equilibrium phase transitions: general results". The "long distances" discussion above being from 2002 by contrast. --Askedonty (talk) 16:39, 22 November 2024 (UTC)[reply]

Number 16 uses "temporal" and "critical" terms, are we getting toward ideas about long-range temporal correlations in critical brain dynamics? Are they spooky?

Gongula Spring (talk) 17:05, 22 November 2024 (UTC)[reply]

November 22

Heat of chillies

How hot, in terms of Scovilles, does a chilli need to be before a parrot can feel the burn? I just saw a video on Facebook of a macaw eating a ghost pepper without the slightest care. From what I read, parrots are extremely resistant to the capsicum from chillies. Or is it because we have thousands of taste buds and parrots have tens, which is also true. 146.90.140.99 (talk) 01:27, 22 November 2024 (UTC)[reply]

“The seeds of Capsicum plants are dispersed predominantly by birds. In birds, the TRPV1 channel does not respond to capsaicin or related chemicals but mammalian TRPV1 is very sensitive to it. This is advantageous to the plant, as chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, whereas mammals have molar teeth which destroy such seeds and prevent them from germinating.” Card Zero (talk) 03:22, 22 November 2024 (UTC)[reply]

Yes, as Card Zero says, birds have different TRPV receptors (for vanilloids like capsaicin) than mammals. I guess chillis want their seeds distributed far and wide by birds. On the other hand, I've never seen anything eat the chillis that accidentally grow in my garden. Interestingly, my dog appears to have different TRPV receptors than me as they don't seem to notice very spicy chilli seeds on food and they won't be damaging the seeds. Sean.hoyland (talk) 03:32, 22 November 2024 (UTC)[reply]

Indeed, one of the most effective ways to keep squirrels off my bird feeder is to sprinkle the birdseed with chilli powder. Shantavira|^{feed me} 09:23, 22 November 2024 (UTC)[reply]

My entire home crop of capsicums (bell peppers to Americans), and some chillis disappeared in one night last summer right after a colony of fruit bats arrived in my local park. Fruit bats, of course, are mammals. HiLo48 (talk) 10:08, 22 November 2024 (UTC)[reply]

That's interesting because there are many bats here. They often sleep individually or in small groups inside young banana leaves that haven't unfurled yet. They sometimes crash into me at night if I'm moving. I guess in bat-world tree-like things don't move. They seem to have a chilli-free diet but might eat some of the other fruit. Plenty of insects to eat. Bat teeth seem to be quite diverse molar-wise. Chilli is the only thing that survives the wildlife. It's a multi-belligerent fruit-based forever war over resources with the birds, squirrels, rats, countless insects, fungi, bacteria and viruses. Sean.hoyland (talk) 15:50, 22 November 2024 (UTC)[reply]

November 23