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June 27
Why doesn't everyone go into eachother's Roche limit when their in crowds?
I mean, they are really close together, maybe in eachother's Roche limit! AtomicSphere 19:59, 27 June 2022 (UTC)
- The simple computation of the Roche limit at Roche limit#Rigid-satellite calculation assumes that the satellite is in hydrostatic equilibrium, meaning in particular that it is held together only by its own self-gravity. That assumption is radically wrong for humans. Their self-gravity is completely negligible; they are held together by their tensile strength. --Trovatore (talk) 20:27, 27 June 2022 (UTC)
- By extensional metaphor, we could model complicated behaviors using some kind of effective potential, describing the crowd's behavior in aggregate "as if" it were controlled by attractive or repulsive forces between individuals...
- Such modeling methods are used in both practical- and artistic- applications. For example, big-budget motion pictures might use crowd simulation to animate large groups of people for visual effects in filmmaking. Some of these methods are specifically particle system models. If one were inclined, one could tease apart the equations and work the similarities- and differences- from an inverse-square-law model. Similar methods could be used for non-filmmaking purposes to model things like foot-traffic for architectural design, fire-safety, and so on.
- But the big caveat is that the dynamics of a crowd of people are more complicated - a simple inverse square law would make for a poor and unrealistic model of the crowd. Therefore, a Roche limit-like horizon - at least, one that is a consequence of an inverse square law - would probably not emerge from a well-designed model.
- Applied mathematics is full of techniques for studying complex systems - and equally so, it is full of attempts to extract simplified group-dynamics from diverse governing equations. A recurring theme is explored in chaos theory: even very simple governing equations lead to unpredictability. These emergent properties would make it hard, in any non-trivial system, to rigorously define any 'limit' analogous to the Roche limit we compute for an inverse-square-law system.
- Nimur (talk) 21:01, 27 June 2022 (UTC)
- Nimur, I'm not sure I've understood what you're getting at, but I don't think it's what the OP meant. As I understood it, the OP was asking why you don't get torn apart by tidal forces when you walk too close to another person. --Trovatore (talk) 21:49, 27 June 2022 (UTC)
- Obviously we're in agreement that the actual force of gravity is irrelevant in these scenarios ... gravity is very weak.
- But the point I was making is that we can make mathematical models for emergent behaviors - we can write relations to express whether characters walk toward- or away from each other. That is to say - we can model groups of people using methods that are normally used for particle-dynamics. Then, we can use these models to study how crowds form and dissipate. These kinds of approaches aren't (necessarily) tracking any "physical law" - the governing equations are purely synthetic, and usually selected because they make cool results. Anything we conclude from the results is only as good as our computer-model. Real human individuals don't obey simple mathematical laws governing their trajectories - but animated characters in a video-game or film might do!
- Here's an example - this is a tutorial for animating crowds using Unreal Engine. Around the 1 minute mark, the animator shows "traditional" crowd simulations using targets and collision dynamics; ... around the 19 minute mark, you can see the animator/programmer playing with a particle simulator by controlling parameters like effective collision radii, which is much more performant...
- These kinds of approaches can be used to model or simulate how a crowd forms (or disperses). If the collision radii is too small, the characters collide in an unrealistic way; but if that same parameter is too large, the crowd disperses!
- I sort of imagine you could describe a "Roche limit" metaphor to describe the circumstances that cause a group to "disperse"...
- In case it's not clear, I'll reiterate: these are not physically valid models of crowds - they're dramatic simplifications that follow simple programmed rules or equations. They're basically just simple equations that are useful for creating cool animations. If you were mathematically inclined, you could manipulate those equations ad infinitum to see how the emergent behaviors compare with other particle-dynamics models, like an n-body gravity simulation; and you could try to find analogous modalities.
- Nimur (talk) 00:39, 28 June 2022 (UTC)
- I 100% agree with Nimur. -- Charlesreid1 (talk) 06:12, 30 June 2022 (UTC)
- Nimur, I'm not sure I've understood what you're getting at, but I don't think it's what the OP meant. As I understood it, the OP was asking why you don't get torn apart by tidal forces when you walk too close to another person. --Trovatore (talk) 21:49, 27 June 2022 (UTC)
- We stand on planet Earth, and it doesn't tear us apart (does it?) so it's unlikely standing next to a way much smaller-mass object, such as another human, would tear us apart (physically, anyway). --←Baseball Bugs What's up, Doc? carrots→ 11:41, 30 June 2022 (UTC)
- I 90% agree that Baseball Bugs' self attraction will hold. Philvoids (talk) 15:46, 30 June 2022 (UTC)
- You lost me at the bakery. --←Baseball Bugs What's up, Doc? carrots→ 22:56, 30 June 2022 (UTC)
- I 90% agree that Baseball Bugs' self attraction will hold. Philvoids (talk) 15:46, 30 June 2022 (UTC)
June 30
Origin of blue eyes
Hans Eiberg has claimed that blue eyes occurred between 6,000 and 10,000 years ago. "Before then, there were no blue eyes." However, for instance, here it says: Homo sapiens arrived in Europe from Near East some 42 000 years ago. Like in their African origin, these humans had dark skin but due to variations of their OCA2 gene (causing iris depigmentation) many of them had blue eyes (cf. the diagram below). Now which is correct? Hildeoc (talk) 00:44, 30 June 2022 (UTC)
- It is difficult to determine when a particular mutation first appeared in history. So, I would take the claim that it happened 6,000-10,000 years ago with grain of salt. I think that the later work is correct. Ruslik_Zero 04:45, 30 June 2022 (UTC)
- Given that this Wiley Book you referenced was a peer-reviewed and edited and published book in 2020, very recently, and this article on livescience.com you referenced was based on a paper published in 2008, a loooong time ago in biological terms, I would state definitively that the Wiley book is more reliable with no further review required. As for determining when mutations occurred in history, it's not a simple question, but there are portions of the genome that evolve more slowly than others and can thus be used to follow populations over places and time (see Mitochondrial_DNA#Use_in_evolutionary_biology_and_systematic_biology) and that is an important technique in population genetics - determining parts of the genome that evolve slowly, and using those to determine an organism's genetic past. -- Charlesreid1 (talk) 06:27, 30 June 2022 (UTC)
- Agreed. I'll also add that blanket statements like "Before then, there were no blue eyes." should be treated with suspicion. Our eye color article notes that "Blue eyes are common in northern and eastern Europe, particularly around the Baltic Sea. Blue eyes are also found in southern Europe, Central Asia, South Asia, North Africa and West Asia." and having a single source for blue eyes that recently would mean that all those disparate groups came had a common origin, or at least intersection. Matt Deres (talk) 15:49, 30 June 2022 (UTC)
- All those people did interbreed, for thousands of years. Shocker. Abductive (reasoning) 18:30, 30 June 2022 (UTC)
- Oh indeed. But my point was more that it means that either there were mass migrations of blue-eyed people or multiple mutations causing blue eyes to come into existence or that they all shared a common ancestor 6-10 kya. Those aren't impossible, but you'd want something independently corroborating them before declaring anything. Matt Deres (talk) 20:03, 30 June 2022 (UTC)
- I would say that all those things are true. Abductive (reasoning) 10:17, 1 July 2022 (UTC)
- Is there any speculation that Neanderthals had blue eyes? --←Baseball Bugs What's up, Doc? carrots→ 13:44, 1 July 2022 (UTC)
- Yes, and red hair. Abductive (reasoning) 14:29, 1 July 2022 (UTC)
- But not (I have read) due to the same mutation that results in red hair in the Scots, or the different one that does so amongst Jews – or, for that matter, the one that did so in Mammoths (some of which were also blonde, apparently).
- We have to remember that most obvious phenotypical characteristic`s, such as hair, eye and skin colour, result from complex interactions of numerous alleles, and there isn't just one "gene (allele) for blue eyes" despite the simplified example most of us were taught in secondary (high) school biology class (see Lie-to-children). {The poster formerly known as 87.81.230.195} 90.195.174.88 (talk) 17:00, 1 July 2022 (UTC)
- @Abductive: But is there actual evidence that Neanderthal genes for blue eyes were successfully passed on to Homo sapiens?
- And regarding the source referenced by me above, claiming that many of the Homo sapiens arriving in Europe from the Near East had blue eyes, why – in terms of the logic of evolutionary adaptation – would their iris color have depigmented that long before their skin color? Hildeoc (talk) 17:44, 2 July 2022 (UTC)
- I was giving the mathematician's answer that yes, there was speculation. Wikipedia's articles Neanderthal genetics and Interbreeding between archaic and modern humans says they did not give us anything fun. The speculation about eye colors is that the change to lighter colors preceded the skin color changes due to sexual selection. Abductive (reasoning) 18:37, 2 July 2022 (UTC)
- Yes, and red hair. Abductive (reasoning) 14:29, 1 July 2022 (UTC)
- Is there any speculation that Neanderthals had blue eyes? --←Baseball Bugs What's up, Doc? carrots→ 13:44, 1 July 2022 (UTC)
- I would say that all those things are true. Abductive (reasoning) 10:17, 1 July 2022 (UTC)
- Oh indeed. But my point was more that it means that either there were mass migrations of blue-eyed people or multiple mutations causing blue eyes to come into existence or that they all shared a common ancestor 6-10 kya. Those aren't impossible, but you'd want something independently corroborating them before declaring anything. Matt Deres (talk) 20:03, 30 June 2022 (UTC)
- All those people did interbreed, for thousands of years. Shocker. Abductive (reasoning) 18:30, 30 June 2022 (UTC)
- Agreed. I'll also add that blanket statements like "Before then, there were no blue eyes." should be treated with suspicion. Our eye color article notes that "Blue eyes are common in northern and eastern Europe, particularly around the Baltic Sea. Blue eyes are also found in southern Europe, Central Asia, South Asia, North Africa and West Asia." and having a single source for blue eyes that recently would mean that all those disparate groups came had a common origin, or at least intersection. Matt Deres (talk) 15:49, 30 June 2022 (UTC)
- Given that this Wiley Book you referenced was a peer-reviewed and edited and published book in 2020, very recently, and this article on livescience.com you referenced was based on a paper published in 2008, a loooong time ago in biological terms, I would state definitively that the Wiley book is more reliable with no further review required. As for determining when mutations occurred in history, it's not a simple question, but there are portions of the genome that evolve more slowly than others and can thus be used to follow populations over places and time (see Mitochondrial_DNA#Use_in_evolutionary_biology_and_systematic_biology) and that is an important technique in population genetics - determining parts of the genome that evolve slowly, and using those to determine an organism's genetic past. -- Charlesreid1 (talk) 06:27, 30 June 2022 (UTC)
Any electrical engineers here?
Ok I am 1 to never thought of to ask this question here. But today at work, I was to train someone in my lab. Later I noticed, when he was on the laptop, it was unplugged. And I talked to him about it. He said he did it on purpose. And told me to not plug it back in, because it hurts the battery when the laptop is fully charged. So I said, "so let it discharge until it's, 5%?" And he said "No, 20%." (Then charge it to 100% and unplug it back to 20%.). And so, I'm at a lost of words here. To not make this a parenting question, and more of a science question, who's in the wrong here? Because, I feel the burden of proof is on him, that this is common sense, but now I realize I only how to think only the way I think and not others, maybe there are others who feel this way? If I am in the right, any electrical engineers can provide a relatively good explanation for this? Note that this is not a question about recharging. 67.165.185.178 (talk) 22:52, 30 June 2022 (UTC).
- He's mostly right although not about the 100% bit, it would likely be better to cut off charging at 80% or something if you don't need that extra life and aren't going to let it get too low because you didn't charge it enough. Most types of lithium ion batteries in common use, especially those generally used in smart devices have increased capacity loss when charged to or kept at 100% or a high level of state of charge (whatever the manufacturer defines that). This is mentioned in our article under Lithium-ion battery#Lifespan. The general recommendation if you're just storing a lithium-ion battery is to keep it at something like 50% (although it varies depending on how long you plan to store it and the level of discharge expected since you don't want to let it get too low either). The same if discharged to whatever the manufacturer defines as 0%. Although this isn't so clearly mentioned in our article, it mentions depth of discharge but doesn't really explain how this affects cycle life, however depth of discharge does mention this. Most guides which talk about how to take care of lithium ion batteries will also mention this see e.g. [1] [2] (although doesn't clearly mention the disadvantage of charging to 100% SoC) batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries. Some devices let you limit the maximum charging voltage or "state of charge" and/or allow you to adjust the discharge cut off point for this reason. Note that lithium ion cells can sustain dangerous damage making the prone to combusting when recharged if they are over discharged so as a safety measure manufacturers do their best to ensure they never get to such a level and may not allow them to be recharged if they do. And likewise overcharging is dangerous. Note also while some electrical engineers will be able to explain in depth why this is the case, I would not assume all, or even most would. Electrical engineering is a wide field, and even with the rapid rise of battery powered devices, I'm sure there are many who only have minimal dealings with batteries and so may only have minimal understanding of their characteristics, further well many lithium-ion batteries are affected, not all batteries are especially when it comes to how maximum charging voltage affects capacity loss. They may be better able to understand some of the papers dealing with it, but OTOH, I'm guessing a lot of people who are not electrical engineers probably have a better existing understanding than many of these electrical engineers who don't know do or maybe even want to. Nil Einne (talk) 23:51, 30 June 2022 (UTC)
- Official guidance from one major manufacturer of battery-powered portable computers:
- One takeaway is that many modern devices are able to self-control and self-regulate their battery charging behavior cycles. The engineers and designers who make the product put effort into maximizing both the battery "life" and "lifespan".
- Whether the "optimal" battery discharge levels for each cycle are 20%-to-80%, or 5%-to-100%, or any other cycle values, depends entirely on the product. It's unlikely that an end-user can meaningfully guess which values are "best" without reference to the specific product documentation - in fact, the end-user probably doesn't meaningfully have any visibility into what these numbers even measure. (These numbers express a "percentage" of which parameter, exactly? Volts? Amps? Volt-Amps? Volt-Amp-Hours? Amp-hours? Just plain old hours? One really cannot know without an engineering specification, and consumer devices don't usually publish one!) Modern batteries are a bit more complex than a AA-cell: the batteries inside many consumer computers have ...their own separate computer inside the battery (!), complete with custom circuitry, software, and complicated behavior. Golly, it's 2022: most computer power cables have their own computer inside the power cable, complete with custom circuitry, software, and complicated behavior. (Here's an official presentation on the USB Power Delivery specification - there's more than copper wire in that cable, and it takes a hundred slides to introduce the subject!) Seriously, I read a lot about of the history of computing, and the inventors of VLSI and electronics miniaturization — for all their prescience and forward-thinking — really did not ever talk about this inevitable reality consequent to their efforts).
- So - refer to your exact product's specification or instructions to get the best performance. The real engineering answer is that we should discourage guessing about the inner workings of a hyper-complex system, and point the user to reference their product documentation, and we shouldn't promulgate hearsay or rumors that are based on "approximate" understanding of the engineering principles of complicated battery design.
- Nimur (talk) 04:44, 1 July 2022 (UTC)
- I never really looked at battery life or lifespan optimisation of my laptop. I just let it charge to somewhere between 95–100% (or whatever the battery calls 100%) and when I use it, not so often, I don't let it drop below 15%. The battery is now 11 years old and performance drop isn't really noticable (no more than 15%). It looks like not worrying was the right strategy. PiusImpavidus (talk) 09:09, 1 July 2022 (UTC)
- The earliest generation of rechargeable batteries for digital computers and electronic equipment (Ni-Cd batteries?) suffered from developing a memory that eventually reduced their effective life. Various strategies evolved for extending the lives of these batteries. I think the strategy described in the original question is a legacy of that era of Ni-Cd batteries. Newer types of batteries do not suffer from a memory and those early strategies are no longer of much value. Dolphin (t) 10:50, 1 July 2022 (UTC)
- For lithium-ion batteries in mobile devices, the purpose of discharging fully and then charging fully is to calibrate the 'full' and 'empty' battery points so that the device's onboard software is able to display a meaningful battery level. (Anecdotally, I ran into a particularly acute example of this when I purchased a USB 'power bank' a few years ago. The first time I used it, I charged it fully and then used it to charge some of my devices on an airline flight. Its seven-segment display fell from 100 to 0% within half an hour, and then it kept charging my devices for another three or four hours with its display pegged at 0% the entire time. After fully discharging it once and recharging it, the charge-level display began to work normally.)
- Discharging to full depletion is not recommended for lithium-ion batteries (except infrequently for calibration purposes) and does shorten their lifespan. https://news.umich.edu/tips-for-extending-the-lifetime-of-lithium-ion-batteries/
- Lithium-ion batteries are also stressed somewhat by being charged fully. (This is, incidentally, different from some other battery chemistries. Lead-acid batteries, for instance, are happiest when floated at full charge.) Fully charging isn't nearly as damaging as fully discharging, however. The maximum lifespan of a li-ion battery is obtained by bouncing between a medium-high and medium-low level of charge, never fully charging or discharging the battery. The Asus laptop I'm typing on right now has a battery health tool that lets me cap the maximum charge level of the onboard battery at 80% or even 60% if I want to prolong my battery's life (at the expense of unplugged working time). https://www.asus.com/us/support/FAQ/1032726/
- If you can plug in, you should--if you're using the wall outlet for power, you're not using the battery at all. TenOfAllTrades(talk) 14:43, 3 July 2022 (UTC)
July 1
BTUs and air conditioning
We are getting a new 3.5-ton air conditioner for a 1946-square foot house with 8-foot ceilings. Is this reasoning right:
(1) 3.5 tons of A/C, 1 ton = 12,000 BTU per hour. So 3.5 tons of A/C cools 42,000 pounds of water 1 degree Farenheit in 1 hour.
(2) 1946 square feet x 8 feet = 15,568 cubit feet of air in the house.
(3) Water has 4.23 times more specific heat capacity of air.
(4) A cubic foot of air weighs 0.08 lbs.
(5) So there are 1,245 pounds of air in the house. Air's specific heat is 4.23x less than that of water, so that is equivalent to 294 pounds of water.
(6) If the A/C can cool 42,000 pounds of water 1 degree F in 1 hour, it can cool 294 pounds of water (or all of the air in the house) 1 degree F in 25 seconds. Bubba73 You talkin' to me? 16:33, 1 July 2022 (UTC)
- I'm not familiar with those units, but that appears to be correct (haven't checked the first line). However, the heat capacity of your house is much larger than the heat capacity of the air in your house. All those solids and liquids matter: walls, floors, ceilings, furniture, jars of peanut butter, whatever. Then, a change in temperature will affect the rate at which heat is produced in the house and the rate at which it leaks in or out. PiusImpavidus (talk) 18:18, 1 July 2022 (UTC)
- British thermal unit: The amount of joules it takes to warm a pound of water by 1° Fahrenheit.
- Ton: A ton is the cooling power of ice melting at a steady pace of 1 ton per day. Sagittarian Milky Way (talk) 04:45, 3 July 2022 (UTC)
- I think that is right too. I got the 12,000 BTU per hour figure from Ton of refrigeration. Bubba73 You talkin' to me? 02:30, 4 July 2022 (UTC)
- The cooling is not instantaneous. The temperature will not go down from 90°F to 32°F in (90 − 32) × 25 seconds = 24 minutes and 10 seconds. The cool air that is blown in is probably warmer than 32°F anyway, and it does not simply replace the hot air but mixes until equilibrium is reached. This may take a long time. The equilibrium temperature also depends critically on the outside temperature and the isolation. --Lambiam 21:10, 1 July 2022 (UTC)
- Oh, yes, I see. Bubba73 You talkin' to me? 19:06, 2 July 2022 (UTC)
July 2
Butterfly picture ID's
Hello all, I have questions regarding several pictures of butterflies (and because they are pictures, I have no information regarding size of these species or which parts of the world they're native to): (1) For those who play Lily's Garden, what species are the three swallowtail butterflies on the first loading screen? (The yellow one on the right looks somewhat like Papilio zelicaon, and the blue one on the left just might be Papilio ulysses, but I'm not sure about either of them, and I have no clue what the green one might be, except that it's probably not Papilio palinurus.) (2) I would also like to know the species of a butterfly I recently saw on a mural -- this one is also a swallowtail, with black markings almost exactly like the aforementioned P. ulysses, but the background color is not, repeat not, electric blue but ruby red or maybe beet red. (3) And last but not least, I'd like to know about a butterfly which I saw in large numbers in a Train Simulator ad -- this one is not a swallowtail but is probably a nymphalid or lycaenid (or maybe, but less likely, a metalmark), and it has black reticulations like Danaus plexippus, but the background color is not orange but a bright blue (this one was in the ad for the Frankfurt to Koblence route pack, but I checked the list of butterflies of Germany and that list has nothing of the sort). Oh, and I am 100% positive that none, repeat none, of the above species have a tiger-striped pattern similar to that of Papilio glaucus (which is the only pattern which can scare me -- note no link to the article on this last species), so pictures are OK (as long as they're not super huge). 2601:646:8A81:6070:618C:4412:5EAA:BD36 (talk) 03:31, 2 July 2022 (UTC)
- Without having seen any of these depictions, it's impossible to be sure, but I think it's very likely that few or none of these (assuming they're not photographs or videos of live specimens) are intended to be accurate depictions of actual species, merely artistic creations utilising the approximate form and appearance of swallowtail butterflies.
- Butterflies in general are a popular theme in art, and in advertising, perhaps because of their associations with the natural outdoors and their supposedly carefree, random motions (an illusion, they're fighting for survival just like any other wild creature). As a sometime amateur lepidopterist, I notice butterfly depictions and have lost count of how many inaccurate, fanciful or plain imaginary renditions I've seen. {The poster formerly known as 87.81.230.195} 90.195.174.88 (talk) 23:38, 2 July 2022 (UTC)
- Oh, BTW, for the Lily's Garden loading screen, the yellow one that looks like P. zelicaon is on the lower left, not the right -- my mistake! (I actually tried to show you, but I couldn't upload the screenshot!) 2601:646:8A81:6070:E183:DDBB:407C:6CF8 (talk) 02:30, 3 July 2022 (UTC)
July 3
Breastfeeding Indio
During the Amazon Synod, a controversial picture of an Indio woman breastfeeding an animal was shown inside Santa Maria in Traspontina. What kind of animal is it? Here an image of it: https://www.aciprensa.com/images/IMG_2415_2019-10-09.jpg Thank you! 79.33.51.111 (talk) 14:17, 3 July 2022 (UTC)
- Out of all the small brown short-haired tailless mammals of South America, my guess is Azara's agouti, because of the location and environment and longish snout and legs. Then again, it's drinking milk, which implies a juvenile, so maybe it grows into something larger. Card Zero (talk) 14:57, 3 July 2022 (UTC)
July 4
Ironman vs. The Martian
At the end of The Martian, Mark Watney makes a hole in his glove (an implausibility on its own, as I assume spacesuits aren't really that easy to puncture) to reach the height of his passing ride. It seems to me that the escaping air wouldn't give a grown man+suit all that much thrust. Roughly how much would it actually impart? Clarityfiend (talk) 04:12, 4 July 2022 (UTC)
- First a generic formula. Let m be the mass of the astronaut+spacesuit, V the volume of the escaping air and v the speed at which it escapes. The mass of the escaping air, using 1.2 kg/m3 as its specific density, is then 1.2 V kg/m3, and if all escapes in the same direction, its total momentum equals 1.2 Vv kg/m3. By the conservation of momentum, the speed of the astronaut is then 1.2 Vv/m kg/m3. For the rest we can only do ballpark calculations. NASA gives the weight of a spacesuit as approximately 280 pounds.[3] Let us assume dramatically improved technology and put m = 120 kg. If V = 0.1 m3, which seems high, and the air escapes at 10 m/s, the resulting speed for the astronaut equals 0.01 m/s. --Lambiam 08:40, 4 July 2022 (UTC)
- I've only seen the movie once and it's some time ago. Spacesuits are normally filled with pure oxygen at around 30 kPa of pressure, so that density is a bit lower. Estimating the velocity of the escaping gas is a bit hard. I don't expect Bernoulli will give us a very accurate number, but it suggests speeds on the order of 100 m/s are energetically allowed. Still, with such a poor nozzle, 10 m/s seems more plausible. The hero could only use part of the gas in his spacesuit, or he would loose consciousness due to oxygen deprivation.
- With such a low thrust, controllability doesn't look like a very serious problem. There's enough time to compensate by moving your hand around. PiusImpavidus (talk) 09:24, 4 July 2022 (UTC)
- About what I figured. Watney asphyxiates in orbit to the tune of "Don't Leave Me This Way" ("I can't survive, can't stay alive ..."). Clarityfiend (talk) 10:13, 4 July 2022 (UTC)
Millipede and centipede gaits
Millipedes walk with a gait characterized by waves of legs propagating from the back to the front, as can be seen in this 30-second video: https://www.youtube.com/watch?v=rlIwoiO24XI
Centipedes I've run across walk this way also.
However, some centipedes (such as those from the scolopendra genus) walk with a gait having leg waves propagating from front to back.
Here are simulations I made of both gaits. I modeled these with OpenSCAD. Each foot spends 50% of the time on the ground and each segment is 45° out of phase from the adjacent segment. The only difference between the two animations is the sign of the phase shift.
I'm curious how these gaits evolved. I notice that even 4-legged creatures walk with the hind legs leading the front legs on the same side, as can be seen in the animations in the gait article. If I crawl on my hands and knees, I can crawl in either manner if I think about it, but it feels more natural for my legs to lead my arms on the same side, just like a four-legged animal.
I can see an advantage to each centipede gait:
- The back-to-front gait has the feet more evenly distributed on the ground.
- On the other hand, the front-to-back gait has feet more or less touching the same place, which would be useful for traversing over small obstructions.
An explanation I found in this paper from Nature, which studied scolopendra centipedes, suggests that neural impulses travel from the head to the tail, which makes intuitive sense to explain the front-to-back waves, but not the back-to-front waves. That paper also found that cutting the nerve connection between two segments impeded the propagation of impulses for a wriggling swimming motion but the legs still figured out walking from mechanical contacts in spite of being severed from the brain.
Has anybody seen any explanation for the difference? Unfortunately I was unable to find anything about this on Wikipedia. The gait article is good, but its main focus is on tetrapods. ~Anachronist (talk) 03:20, 4 July 2022 (UTC)
Wouldn't back-to-front be easiest to implement with a nerve to the rear and back that transmits at the speed of the wave? Then if it wants to stop it can't even start trying till an entire brain-to-butt signal has travelled while in front-to-back all the legs would've got the message already.My bad you mentioned that already. I've always wondered what gait cockroaches run. And if the milder waddlers hit some sort of vibrational resonance or something or maybe just didn't get enough copies of the evasive maneuvers gene. Which probably doesn't hurt it much vs no evasive maneuvers gene as a line doesn't have to be very straight to be almost as short. Sagittarian Milky Way (talk) 14:48, 4 July 2022 (UTC)
- Web-searching "Centipede gait" throws up a number of references, the first one being here.
- Perhaps this and other hits will have some insight on the question, but finding evolutionary explanations for complex anatomical details and especially behaviours (which do not fossilise well) run the risk of approaching 'Just-so stories.' {The poster formerly known as 87.81.230.195} 90.195.174.88 (talk) 17:53, 4 July 2022 (UTC)
- Thanks. I had done the same search and found many papers about robotic walking applications, which wasn't really what I was looking for, but it seems I didn't look carefully enough because that paper you reference seems to derive the two gaits from sensory inputs rather than simply coming up with a way to reproduce the gaits mechanically. ~Anachronist (talk) 20:44, 4 July 2022 (UTC)
Catalogued stars that went supernovae
Other than typical SN designations which are assigned after explosions, List of supernovae and a quick look into related category doesn't mention any catalogue names of related stars, including Bayer and Flamsteed designation. Why is that? 212.180.235.46 (talk) 19:39, 4 July 2022 (UTC)