Wikipedia:Reference desk/Archives/Science/2021 April 27

= April 27 =

E2 (in real life)
A few questions about the arguably most famous switch engine of all (completely out of proportion to its actual role in rail transport), the LB&SCR E2 Class: (1) How far could it go before it had to take on water? (2) How far could it go before it had to take on coal? (3) What was its top speed under its own power (on the level with a light train)? And (4) if it was being dragged by a faster train (like in "Thomas Gets Tricked"), or pushed downhill by a heavy unbraked freight train (like in "Trouble for Thomas"), how fast could it go without derailing? 2601:646:8A01:B180:CDB1:68B7:A1BD:8384 (talk) 05:53, 27 April 2021 (UTC)


 * There's not a lot of technical detail in our articles, but I can make a few educated guesses. The E2 used the same boiler and cylinders as the I2, so it would have about the same coal and water consumption per unit of time. It had smaller wheels, so would do so at lower speed, hauling a heavier train. The I2 was in turn a stretched version of the I1 (few other modifications), with the same, undersized firebox. The same cylinders and pressure mean the same peak power, the same firebox means the same sustained power, larger boiler means it could hold peak power for a bit longer. The boiler acts as a buffer, where energy from the fire is temporarily stored. The small firebox means it had low performance, but also low consumption of water and coal.
 * The I1 and I2 where meant for suburban passenger trains. Typically, one would design the water tanks large enough to run from one end of the line to the other, which would be less than an hour on these suburban lines. Water capacity of the E2 was about half the capacity of the I2, so, when working hard, I guess it could consume all its water in half an hour. But most of the time it wouldn't be working hard. Real-life driving would be with frequent stops and quick acceleration to about 40 km/h, but at constant speed the water supply would last much longer.
 * In a typical steam locomotive of that age, 1 ton of coal could make 7 tons of steam. The E2 carried 5 tons of water and 2.5 tons of coal, so its coal supply would last 3.5 times as long as its water supply.
 * At high speed, steam locomotives suffer from large, unbalanced reciprocating masses. This causes the locomotive to flex, bounce on its springs and ultimately jump off the track. The effect mostly depends on the rpm of the driving wheels, not on speed directly (which is why express locos had such large driving wheels). Further, at high rpm it gets harder to get the steam in and out of the cylinders quickly enough without excessive loss of pressure, limiting power. Anything over 5 revolutions per second would be called fast, some locomotives reached around 10 revolutions per second. On an E2, 5 revolutions per second means 78 km/h. I don't know how well balanced it was, but as it was designed for low speed, probably not very well. PiusImpavidus (talk) 12:02, 27 April 2021 (UTC)
 * On second thought, it's possible the water tanks of the I2 were oversized, for some extra reserve. In that case it could run for longer before the water supply was exhausted. Without details like actual water/coal consumption or at least grate area it's impossble to say. PiusImpavidus (talk) 08:36, 28 April 2021 (UTC)

About Covid 19 and Covishield vaccine
Q1, I am a bit confused regarding 14 day quarantine/isolation. If someone comes in contact with a positive patient then he is(/was earlier) advised for 14 day quarantine to check if he developes covid symptoms as 14 days is believed to be max. incubation period. If no symptoms after 14 days then roam freely(with mask) But, what about one who is positive. Is there a guideline that if you are home quarantined for being positive then what?? Does the person's quarantine ends automatically after 14 days or should he get tested again for negative report ? Where am I thinking wrong? -- Parnaval (talk) 06:07, 27 April 2021 (UTC)
 * It varies but usually until two successive test are negative. Ruslik_ Zero 12:00, 27 April 2021 (UTC)

Q2, In India there is vaccine named Covishield. I am searching for guideline about what to do if we currently have covid or have just recovered. Should there be a time delay (of, say, a month or a week) before we take a 1st or 2nd dose. Not for personal advice, just because I am curious -- Parnaval (talk) 06:07, 27 April 2021 (UTC)
 * For those who have had COVID-19 vaccination against it is not indicated at least for 6 months after it. Ruslik_ Zero 11:59, 27 April 2021 (UTC)
 * Thanks for answer 1, but is the protocol of two negatives really followed. And answer 2 is not clear to me. Can you elaborate. I think you misunderstood question 2. I was asking about potential negative effects(if any) of the vaccine if taken during or just after recovering from infection -- Parnaval (talk) 16:45, 27 April 2021 (UTC)
 * There will be no negative effects. Ruslik_ Zero 16:54, 27 April 2021 (UTC)
 * We should be careful about giving medical advice this way, even if it isn't "personal advice," without sources. I personally wouldn't have guessed that vaccines could give someone blood clots, but in a very very small percentage of individuals, they can. I don't think we should say "there will be no negative effects" of taking the vaccine just after recovering from infection without some source to back that up. Even if the incidence is low, maybe that causes some sort of autoimmune response, especially in compromised individuals. Again, I'm not saying it does, just that we should probably provide sources before saying, unequivocally, that there will be no negative effects. --OuroborosCobra (talk) 18:39, 27 April 2021 (UTC)
 * That blood clot problem is very rare. But I am asking about a bigger risk. I mean, there has to be a guideline about taking(or not) vaccine during or after covid infection because on any day, there are millions of people who are positive and as everyone is pushing on more vaccination what about those who are infected, should the people be stopped -- Parnaval (talk) 09:06, 28 April 2021 (UTC)
 * Of the millions who have taken a vaccination, many thousands must have been asymptomatic or presymptomatic carriers. Nothing special regarding this contingency has been reported. There is no advice to get tested prior to being vaccinated, which there would be if there was a known associated risk. Of course, people who are symptomatic or known to be carriers should not visit a vaccination site but stay home. --Lambiam 09:32, 28 April 2021 (UTC)
 * I actually meant that there will be no negative effects specifically related to the previous COVID-19 disease - the question was about them. At least nothing known about them and as has been already noted many millions people, who had had COVID-19, have been already vaccinated. Ruslik_ Zero 20:04, 28 April 2021 (UTC)

Movements through switches
What are the typical speed limits for the following types of railroad switches: (1) variable switch or spring/weighted switch; (2) double slip or single slip switch; (3) outside slip switch; (4) scissors crossover; (5) three-way switch; (6) interlaced turnout; (7) wye switch; (8) dual-gauge switch; (9) dual-gauge swish (spelling is correct); and (10) switch diamond? 2601:646:8A01:B180:CDB1:68B7:A1BD:8384 (talk) 06:22, 27 April 2021 (UTC)


 * As I understand it, it is not so much the type of switch as the curvature of the track. On a straight track there is no need for a limit. The article you linked to discusses this in some detail, but says "As a general rule, the smaller the crossing angle of a turnout, the higher the turnout speed." See Railroad_switch.--Shantavira|feed me 09:19, 27 April 2021 (UTC)


 * I was aware that for standard switches, the curvature of the track is the limiting factor -- but I was wondering, maybe for these unusual types, there could be additional factors which further limit the maximum speed of the train (for example, an increased danger of splitting the switch at higher speeds)? 2601:646:8A01:B180:28A4:780E:CE56:DB62 (talk) 11:52, 27 April 2021 (UTC)


 * Types 1, 2, 3, 4, 5, 6, 8 and 9 are usually found in yards, where speed is already limited to about 40 km/h. All switches would normally have the same radius of curvature and speed limit. It doesn't depend on the type. An outside slip has a longer arc and therefore larger radius of curvature at the same angle than an inside slip, so could have a higher speed limit, but this is not practical as speed is already limited by other nearby switches. Outside slips make some sense if the angle is a bit courser than normal. On wye switches practices vary between countries. In Germany they're only common in yards, where speed is low anyway, but in the neighbouring Netherlands they're frequently used away from stations, where the speed limit is much higher (120 km/h). The wye switches are used there because they allow a higher speed limit. The switch diamond tends to have a high speed limit, as at low speeds a non-switching diamond is usually sufficient as one can arrange the angle to be course enough. PiusImpavidus (talk) 12:36, 27 April 2021 (UTC)

J70 steam tram
Did the J70 steam tram have sandboxes? If not, how did they deal with slippery tracks? 2601:646:8A01:B180:28A4:780E:CE56:DB62 (talk) 11:55, 27 April 2021 (UTC)


 * I don't know where you got the idea that a Sandbox (locomotive) is required to deal with slippery tracks. It is far more convenient, but older locomotives sometimes used a man with a shovel to sand the tracks (often needed only on startup and on steep grades). On some newer locomotives the Wheel slide protection is good enough that sand is rarely needed, and in some places a special train applies Sandite. --Guy Macon (talk) 12:52, 27 April 2021 (UTC)
 * As far as being required on steep grades/inclines, goes, the lines for which these locomotives were designed and were later used didn't (to my partial personal knowledge) have any to speak of. {The poster formerly known as 87.81.230.195} 90.200.135.95 (talk) 11:34, 28 April 2021 (UTC)

Why do humans feel their skin crawlwhen they saw disgusting images?
Why do humans feel their skin crawl when they saw disgusting images? Is there any reason for this? There is also a [https://www.merriam-webster.com/dictionary/make%20someone%27s%20skin%20crawl%2Fcreep#:~:text=%3A%20to%20make%20someone%20feel%20disgusted,made%20my%20skin%20crawl%2Fcreep. idiom] exist in English language. Rizosome (talk) 13:05, 27 April 2021 (UTC)
 * See Goose bumps. ←Baseball Bugs What's up, Doc? carrots→ 13:10, 27 April 2021 (UTC)
 * We also say "It made my skin crawl", whatever that is supposed to feel like. Richard Avery (talk) 14:53, 27 April 2021 (UTC)