Wikipedia:Reference desk/Archives/Science/2020 March 12

= March 12 =

COVID 19, again
1.	Does the self-isolation of two weeks really work? If man A shows symptoms and was in contact with man B. Man B is asked to self-quarantine for 14 days but has already been exposed for a week, his family in his home then become carriers and as they too are self-isolating for two weeks they too are prevented from spreading it, but in the week that man A and man B were in contact each could have been in contact with thousands of people on trains, busses and other. SO by the time they self-isolate, thousand are already carriers and don’t know and go on to spread the virus to thousands, I can’t see how the cycle is broken with self-isolation. Please let me know what I am missing.

2.	If I am a possible carrier and self-isolating, when I start to show symptoms, how do I treat the illness? I understand that I should not leave home and should not go to hospital unless vital, so how do I treat this at home? Some may not show such bad symptoms. Thanks. Anton 94.198.187.35 (talk) 11:40, 12 March 2020 (UTC)


 * You should look at the reddit thread that I linked further up. 1) yeah it's tricky, and this stuff of shutting down events with more than 100 people seems to miss that transit stations have that many people in them all the time during commute hours.  If you take a train to work you are probably in a 100+ person "event" twice a day.  BART (commuter train here in California) traffic has apparently dropped significantly in the past few weeks.  2) The Dr. in the reddit ama above addressed this question but if I paste what he said (tldr: nothing too surprising), the "medical advice" police here on RD will go berserk.  So it's best to just look there yourself, since it's an informative thread. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 12:03, 12 March 2020 (UTC)
 * The OP looks like they're in the UK. Rather than follow random social media contributors, the advice here is to use NHS 111, by phone or . Bazza (talk) 12:12, 12 March 2020 (UTC)
 * For the UK, if you may have symptoms and can access the Internet, go directly to https://111.nhs.uk/covid-19. --Lambiam 14:49, 12 March 2020 (UTC)
 * The person doing the FAQ is an NHS acute care doctor treating covid-19 cases, and there is discussion about the 111 system in the thread. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 17:12, 12 March 2020 (UTC)


 * There is no proven treatment, and therefore there is little patients can do by way of self-treatment. We cannot give medical advice here, but perhaps it is allowed to relate the common-sense advice that generally applies to other virus-based illnesses such as the common cold and the flu: make sure to rest well and stay warm (also if you have a fever); breathe fresh air; eat and drink well enough but do not overindulge. Basically, allow your body to use its energy on fighting the infection. All other advice you find on the web is quackery and may even be harmful. Self-isolation as recommended will not bring the transmission rate down all the way to zero, but it will help reduce the spread of infection. If we can get the R0 down to below 1, the pandemic will peter out. --Lambiam 14:49, 12 March 2020 (UTC)


 * The dr. in the reddit thread says basically they have given up hope of stopping the pandemic. They are trying to slow its spread to take some load off treatment facilities, and allow for more supplies and drugs and test kits to be made (plus vaccine development).  The US and UK both seem to be using the time badly, unfortunately.  Places like Hong Kong with memories of SARS are acting a lot faster and have done a better job containing the spread.  Warmer weather as summer arrives in the northern hemisphere will supposedly also slow it down. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 17:12, 12 March 2020 (UTC)
 * I think the basic reproduction number is an important point here. Just because someone is in contact with 500+ other people (which in many cases probably isn't true anyway), doesn't mean everyone of those people will get infected. The OP's assumption that 2 people will by themselves infect 1000 other people is not supported by anything I'm aware of. Most studies I've seen suggest a median of around 3. [//www.ijidonline.com/article/S1201-9712(20)30091-6/fulltext] [//www.ijidonline.com/action/showPdf?pii=S1201-9712%2820%2930083-7] Even that UK supercarrier that got a lot of attention at one time only infected 11 that we know of [//www.bbc.co.uk/news/uk-51459210] which even assuming there a bunch undiagnosed is very, very far off from 500+. The chance of a single person infecting 500+ others by themselves doesn't seem very high unless they're intentionally trying to spread the disease. Of course you don't need a single person to infect 500 other people for rapid spread. Even 3 can lead to rapid spread if those 3 people then go one to infect 3 other people etc. Note that there is plenty of modeling of such things e.g. [//www.thelancet.com/journals/langlo/article/PIIS2214-109X(20)30074-7/fulltext]. Nil Einne (talk) 17:47, 12 March 2020 (UTC)
 * More generally, that's why authorities in some areas are doing contact tracing. If there really are 1000 people these 2 people came into contact with, they need to be traced and asked to self-isolate as well. If you catch them early enough, they hopefully haven't infected anyone else yet so you could theoretically stop the spread. If any of these people test positive for COVID-19, you do the same for their contacts etc. Note that per my earlier point, it's quite likely many of these people will never test positive. And there's general debate about what level of contact before you should suggest self isolation or require quarantine. (E.g. if someone was in the same train but a different carriage, or the same carriage but almost the other end etc.) Of course, successfully tracing everyone, and getting to them in time is tricky and you run into a whole host of issues like privacy considerations e.g. [//www.theguardian.com/world/2020/mar/06/more-scary-than-coronavirus-south-koreas-health-alerts-expose-private-lives]. Nil Einne (talk) 18:13, 12 March 2020 (UTC)
 * If person A comes into contact with person B (each might or might not already be infected), call that a "transmission opportunity". If A, B, and C are in a room, that's three opportunities (AB, BC, and AC).  If N people are in a room, that's N*(N-1)/2 = O(N2) opportunities, so if N=1000 that's 100x more opportunity than N=100, at least in the simplistic model where they all contact each other.  I'd guess in a large crowd the diffusion equation might model the spread better, but I have no idea if it works that way in practice. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 19:25, 12 March 2020 (UTC)

This article is very interesting. It's not an academic publication but it's well researched and has been cited by some pretty smart people around the interwebz. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 04:36, 13 March 2020 (UTC)

Nutrition
Can I survive on just rice, ground soy and fish? — Preceding unsigned comment added by 193.64.221.25 (talk) 14:33, 12 March 2020 (UTC)
 * For a short time yes, but not indefinitely. You will also need water.


 * The fish should include a sufficient amount of fatty fish. The rice should be whole-grain brown rice or else fortified rice. You may survive for quite some time, but I have the impression this diet does not provide enough vitamin A or provitamin A carotenoids. It will take a considerable effort to research if such an unvaried diet will not also eventually lead to malnutrition due to a deficiency in some other essential nutrients. --Lambiam 15:32, 12 March 2020 (UTC)
 * Golden rice would help with the vitamin A concerns, sadly you have almost zero chance of getting it. Nil Einne (talk) 18:18, 12 March 2020 (UTC)
 * Multivitamin pills are probably a good idea with such a diet. You might add some more kinds of beans, and with some kind of vegetable fat you can do without the fish.  Rice and beans are a popular pairing: see protein combining.  2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 19:29, 12 March 2020 (UTC)
 * Fish liver is rich in vitamin A; 15grams should provide enough for a day. LongHairedFop (talk) 22:21, 12 March 2020 (UTC)


 * Vitamin C deficiency may also be a problem. Thing is that if you're on a very restrictive diet then all sorts of complications can happen that you can sometimes deal with by making your diet even more restrictive. For example there are people who stick to a zero carb, 100% meat diet, see e.g. here. There is almost no vitamin C in this diet. This works (some people have been on this diet for a decade without getting scurvy) because the requirement for vitamin C goes down sharply if you don't eat any carbs at all. If you would eat just a small amount of rice on such a diet, then your vitamin C requirement would become much larger and you would get scurvy. Count Iblis (talk) 04:13, 13 March 2020 (UTC)

Emergence of seasonal flu and common cold
After any given wave of flu or common cold subsides, how and where does patient zero pick up the virus yet again, making it recurring? Thanks. 212.180.235.46 (talk) 15:30, 12 March 2020 (UTC)


 * Flu season on the northern and southern hemisphere alternates, so a late patient arriving from one half of the globe may reignite the other half. In reality, the flu activity never gets really to zero everywhere in summer; it is just low. Quite a few infected people are asymptomatic, and perhaps some of these are long-time asymptomatic carriers. This is a relevant article. --Lambiam 15:47, 12 March 2020 (UTC)
 * The tropics don't really have the classical "four seasons". And as stated by the previous respondent, transmission even in temperate regions never drops totally to zero. I recall getting a cold in summer once. --47.146.63.87 (talk) 19:41, 12 March 2020 (UTC)
 * When I rode public transport every day, I got a fever every few months, winter or summer. —Tamfang (talk) 03:37, 19 March 2020 (UTC)

Implications of using multiple solar reflectors to create artificial "suns"?
Suppose we were to surround the earth with huge parabolic mirrors whose purpose was to reflect back the energy to solar panels on the ground. Also assume the requirement that the apparent size of each mirror must be that of the sun itself. What might be the implications of having the world exposed to daylight from all sides? I guess it just depends on how big they are and how far away. I wonder, would it throw the world out of balance, a planet without (much) night? Earl of Arundel (talk) 17:04, 12 March 2020 (UTC)


 * Nightfall (Asimov novelette and novel). 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 17:14, 12 March 2020 (UTC)


 * If the mirrors are parabolic, you can focus the reflected light to small areas; outside these areas the night sky will be as dark as usual. Such focusing will be needed anyway; you cannot build a continuous belt of solar panels around the equator. The problem might more with the shadow of these mirrors on the day side of the Earth: each causes a solar eclipse (without contributing energy to the ground; in fact, taking out direct solar energy). That might be solved by turning them sideways while between Sun and Earth. Also, there is no good reason for requiring the mirrors to have the apparent size of the Sun; one hundred mirrors, each one-hundredth the size in area, can together provide the same energy as one huge mirror but may be much easier to realize and manage from an engineering perspective. --Lambiam 19:17, 12 March 2020 (UTC)


 * If you really did this all over the world (basically doubling the Earth's total solar irradiance) and kept it up for long, that would presumably cause out-of-control warming even worse than what we have now. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 19:31, 12 March 2020 (UTC)
 * Nothing wrong with thought experiments, but practically speaking there'd be no point to this. If we're building orbital structures we would want to just build space-based solar power arrays, because that avoids the losses from the atmosphere as sunlight passes through it. Then we could use these to power things in orbit as well as transferring energy to the ground. --47.146.63.87 (talk) 19:37, 12 March 2020 (UTC)
 * Or perhaps someday when humans start colonizing space they could use such an approach with planets that are only semi-habitable. The inhabitants might live in an artificial city for example and as a result wouldn't care much about what's going on on the surface of the planet. All of the additional starlight could help ensure the colony's self-sufficiency (eg no fossil fuels). But true, probably not such a good idea for our planet...Earl of Arundel (talk) 19:59, 12 March 2020 (UTC)
 * I don't think any proposals for space-based solar power involve covering the whole earth with it, which as mentioned would throw the heat balance way off. The idea is just to replace conventional power plants, which add a tiny amount of energy compared to sunlight.  Global heating is from carbon emissions trapping solar irradiance, not from heat emitted by power plants.  Once you've got space colonization, of course, the next step is a Dyson sphere.  I mean why stop with surrounding the earth with solar collection, when you can surround the whole sun. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 20:03, 12 March 2020 (UTC)
 * Good point, the Dyson Sphere does indeed look like a much better approach! Earl of Arundel (talk) 21:35, 12 March 2020 (UTC)
 * If your budget allows it, you could also consider running your stuff with a relativistic jet. After that, though, I'm out of ideas. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 00:45, 13 March 2020 (UTC)
 * Well, a full "shell" enclosing the star will cause the rest of the solar system to freeze, though a Type II civilization building one might have decided to disassemble the solar system for the needed materials, so that might not matter. More likely is something like the "Dyson swarm" variant, which doesn't fully enclose the star. --47.146.63.87 (talk) 09:10, 15 March 2020 (UTC)
 * See Planetary equilibrium temperature, but note that it does not take into account atmosphere effects. The doubling of Earth's total solar irradiance mentioned above would increase the Teq absolute temperature by 21/4-1 = 19% -- an increase of 48 C (an increase of 87 F).  The massive resulting changes in atmospheric composition would presumably increase the strength of the greenhouse efect, but greater cloud cover compensate to some degree by increasing albedo. -- ToE 22:36, 13 March 2020 (UTC)