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March 11

Why in USA it isn't recommended to put masks on?

Why in USA it isn't recommended to put masks on? (to avoid covid19) "As of February 26, 2020, face masks are not recommended for the general public in the US. Some health facilities require people to wear a mask under certain circumstances".ThePupil (talk) 02:28, 11 March 2020 (UTC)[reply]

The so-called experts are saying they are best used by the ones who are sick and by the ones closely caring for them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:20, 11 March 2020 (UTC)[reply]

There is some logic to that. Whether it is the truth is another matter. There's no doubt that if you are spraying droplets of virus infested spit and phlegm around the place that wearing a mask will tend to catch some of the droplets. But I suspect the claim that healthy people do not reduce risks to themselves by wearing masks is driven more by hope and a wish to preserve mask stocks, than actual evidence. Of course providing masks to those who definitely need them, as opposed to a healthy individual, does have a benefit for the healthy, but it is a second order effect. Greglocock (talk) 04:27, 11 March 2020 (UTC)[reply]

Hence my use of "so-called". ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:57, 11 March 2020 (UTC)[reply]

Health authorities in France, New Zealand, UK etc. all say there is no evidence that wearing a mask protects you (as in "there is no evidence that faith healing works" - "no evidence that" does not mean "we have not looked" but rather "we looked and found nothing but proving a negative is hard"). The possibility are hence

the advice is correct
the advice is wrong because scientific evidence is lacking
local health authorities are all incompetent and fell for WHO disinformation
local health authorities are all conspiring to lie to the public (and no journalist has found a whistleblower yet)

I have no idea how likely 1 or 2 are, but I am pretty damn sure that those are much more likely than 3 or 4. Tigraan^{Click here to contact me} 08:42, 11 March 2020 (UTC)[reply]

I think 3 also requires a vast overestimation of how much the US CDC cares about what the WHO says. As I said below, IMO this also requires that we make assumptions that they were doing this long before the COVID-19 outbreak since the advice is consistent with that for seasonal influenza, or that COVID-19 is different and this is known but being ignored. Nil Einne (talk) 09:12, 11 March 2020 (UTC)[reply]

(EC) This discussion reminds me somewhat of the discussion a few weeks ago about whether COVID-19 is airborne. While COVID-19 is new, and there's still a lot we don't understand about it, as I understand it the general assumption is spread is likely to be similar to other respiratory diseases, albeit one with likely very limited immunity and where a lot about when, who and how easily it infects etc is still fairly unknown. (See e.g. [1] for an example of uncertainty.)

Therefore the face mask stuff tends to come back to what we know about their use with other respiratory diseases. And there seems to be little evidence that surgical type face masks worn by health individuals in public helps with such diseases, seasonal influenza being the obvious example. To be clear, this means there is an absence of evidence not that there have been good studies demonstrating they are not effective.

Many epidemiologists and others who study how such diseases spread, how to protect against them and observe human behaviour tends to believe they will be of little benefit in healthy individuals especially when many people don't know how to wear them correctly, may not change them frequently enough, etc. One of the most common suggestions is that they may discourage people from touching their faces but the counterpoint is that with at least some people they may actually do it more to adjust the mask etc. I think there is also a concern such masks may give a false sense of security and reduce compliance with good hand hygiene, which is believe to be of significantly greater benefit.

There seems to be some limited evidence of a benefit for correctly wearing such masks by healthy individuals when living in a household with an infected person and combined with good handwashing. [2] [3] [4] [5] [6] Possibly also when people are living in a crowded setting in general [7]. Note AFAICT, such studies generally did not find benefit for masks alone without handwashing, and they also generally included instructions etc on mask use. These studies are also I think, taken as evidence that such masks may be of benefit to protect health care workers who may regularly be coming into contact with infected individuals. (And are already supposed to be practicing good hand hygiene.)

It's worth noting that while the current situation may be somewhat unprecedented, if we get back to the earlier point, it isn't completely unique. If health authorities had good reason to think healthy individuals wearing masks in the general public would have a significant benefit for regular seasonal influenza, there's a good chance it would have been recommended by at least some, since there's no reason why supply couldn't have been adapted to cope with the demand. Possibly even during something like the emergence of H1N1, supplies could have coped with demand. In addition, it's likely at least some working on pandemic planning would have recommended more massive stockpiling to to prepare for something such as this, if they felt their use among healthy individuals should be encouraged. Note that there are plenty who recommended, long before this outbreak, that people with symptoms of respiratory illnesses/flu should wear masks as is common in a number of Asian countries.

See e.g. [8] [9] [10] [11] [12] [13] [14] [15]

As a final point, having sort of an interest in medical and health topics for a while, one thing I feel a lot of people don't appreciate is that in reality, a lot of what we believe and is put into practice is not based on particularly strong evidence. The relationship between diet and acne is perhaps a classic example of this. A loosely related example is there's always been controversy and recently been a strong move against antibacterial soaps based on the lack of evidence of any real benefit, and fears of possible harm from their widespread use. But I also came across this interesting example when searching this answer [16].

Nil Einne (talk) 09:12, 11 March 2020 (UTC)[reply]

Off-topic but: a lot of what we believe and is put into practice is not based on particularly strong evidence - That is true of science in general. A standard experimental paper (at least in physics) will contain "methods", "results" and "analysis" sections; usually you can trust that if you follow the steps of the "methods" section you will end up with what was described in the "results" section, but "analysis" is often a pompous word for "we scratched our heads trying to figure it out, here goes the least crazy of our hunches". Of course in medicine there are additional ethical problems. If people are dying left and right from an epidemic, you might want to aggressively test highly-speculative remedies, whereas in physics, you can almost always wait for more confirmation.

The experimental method is still the best way we have found for figuring out things, but our state of knowledge about the world is a lot a shades of grey between "we know for sure that thing" and "we have no idea whatsoever to explain that thing". Tigraan^{Click here to contact me} 13:28, 11 March 2020 (UTC)[reply]

(EC) One additional point. It's possible that some feel based on available evidence and understanding, healthy people wearing masks has a greater chance of being beneficial than of causing harm. Even after consideration of the relative risks and level possible of harm and benefit. This evaluation would likely be based both on the possible benefits of reduced transmission to said healthy people, and also reducing transmission from people who think they are healthy but aren't. (But also considering the chance it may increase transmission due to people adjusting their masks, masks collecting contaminants, a false sense of security, distracting from hand-washing advice etc.)

So the precautionary principle would suggest healthy people should be encouraged to wear masks. But this isn't being happening due to a recognition supplies cannot cope with it and so they need to be reserved for those cases where the chance of benefits is far greater. (And it doesn't happen for seasonal influenza given factors like the low estimation of possible benefit, possible differences in number of carriers and people at risk of infection, limited number of people who may follow such advice and additional confusion and uncertainty that may result.)

However this is a fairly different issue from suggesting authorities are being misleading about the evidence. Although such views could be one the reasons why some authorities require mask wearing even for healthy individuals e.g. I believe in HK and some other countries it's required to ride on their mass transport systems. (But there are other factors that may be at play e.g. the difficulty of enforcing a requirement to wear masks on people who know they have symptoms of a respiratory illness, compared to simply requiring it from everyone.)

Nil Einne (talk) 13:50, 11 March 2020 (UTC)[reply]

The advice not to touch your face and to wash your hands is probably also not based on experimental evidence of its efficacy, but nevertheless appears sound if contact transmission from touching contaminated surfaces is a major factor in spreading the infection. If it is the major pathway, then wearing a mask is probably not going to help much more in reducing the spread. It is also plausible enough that reusing masks may even increase the wearer's risk. I'd be surprised though if wearing proper and regularly changed masks would not prove to somewhat reduce the risk for someone who meticulously follows the other WHO advice. --Lambiam 14:01, 11 March 2020 (UTC)[reply]

Yes, this is important for such public health advice. Surgical masks only work when you wear them properly and change them regularly and properly. If people don't don't do this they're useless, and may be worse than useless because they may cause people to feel a false sense of security and hence not follow other advice (risk compensation). When evaluating interventions that people perform themselves we have to look at differences between "perfect use" and "typical use". (This is relevant for many interventions, for example birth control methods.) --47.146.63.87 (talk) 03:59, 12 March 2020 (UTC)[reply]

What I always heard about surgical masks is they help prevent you from infecting other people (e.g. by coughing: the mask stops the droplets). They don't stop the other people from infecting you, i.e. airborne viruses travel right through it. They help you stop touching your face with your hands though, something I do all the time out of habit. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 05:09, 12 March 2020 (UTC)[reply]

Short answer: They don't need it. There is a limited supply of masks, and we want them on the people who are coughing and sneezing. For all others, be careful and clean with your hands, and expect to get this cold eventually no matter what masks you are wearing, but be careful and clean so that those of us who must seek hospital care have space to do so. ~ R.T.G 18:22, 15 March 2020 (UTC)[reply]

COVID query

If this coronavirus spreads around the world, and it seems like it most certainly will, will it just disappear then? Is this virus set to be a new recurring incurable disease among humans as more familiar flus are?

This question doesn't seem to be asked a lot. People are more worried about dying today... However, influenza, which COVID is being called though it apparently is not, mutates at a rate which prevents it being cured by vaccination, or something like that, hence the new concoction yearly in the flu jab... I understand from reading about tundra that the deadly "Spanish Flu" has been detected in bodies thawed from the permafrost such that it is a concern among archaeologists and palaeontologists finding remains in the arctic circle. I also am led to believe that bubonic plague persists, even in America... So what is the outlook here? I'm not going to say "if" it is beyond our control. Will COVID persist as an irritant? As a deadly disease? Will it disappear? Expectedly, I cannot seem to find this enquiry in the new reports... without digging ten feet into muck which I've already turned over several times.

Any response appreciated, thank you, ~ R.T.G 16:45, 11 March 2020 (UTC)[reply]

Coronaviruses were first discovered in the 1960s, so they're obviously not going away anytime soon. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:00, 11 March 2020 (UTC)[reply]

To be clear, the virus that causes CoVID-19 is the same species as SARS, the same family as some common cold viruses but a completely different order from influenza virus. Not closely related. Rmhermen (talk) 18:05, 11 March 2020 (UTC)[reply]

~~You meant "group", not "species", which has a very specific meaning in biology.~~ (The concept of a species is not really well-defined for viruses anyway.) --47.146.63.87 (talk) 07:00, 12 March 2020 (UTC)[reply]

My apologies! I see from the article that it was recently classified as the same species. I had read earlier that it was simply classified as "related". --47.146.63.87 (talk) 19:27, 12 March 2020 (UTC)[reply]

Well, Wikipedia says there is a plague season in Madagascar! As often with texts about infectious diseases, the truth is a good bit less disturbing than the headline, but the headline is not wrong. I'll point out that we don't worry too much about the plague and that may not be a reckless judgment. If you're look for a book about this sort of thing, I recommend David Quammen's Spillover. 93.136.81.202 (talk) 03:07, 12 March 2020 (UTC)[reply]

Bubonic plague (caused by Yersinia pestis) is definitely still around, but it's not that big a public health problem today, since it can be slowed down with hygiene and treated with antibiotics, neither of which were available (much) back in the middle ages. Covid-19 does seem to be able to survive in air "up to 3 hours post aerosolization".[17] There are a bunch of temporary measures announced like closing schools for the next 2 weeks, but if anything the pandemic will be even worse 2 weeks from now than now. Better start stockpiling loved ones ahead of the outbreak. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 04:18, 12 March 2020 (UTC)[reply]

Maybe, maybe not. We don't do predictions on the ref desk, and predictions at this point are going to be very uncertain. If we can control its spread, we might be able to contain it eventually, and then it will just "burn out" if it's unable to infect anything new. Plague is an example of a "direct zoonosis". It can infect numerous species as-is, so it circulates in natural "reservoirs" of animals, and can infect humans from there. To eradicate it we would have to immunize, kill, etc. all infected animals. But there is no sustained human-to-human transmission. Influenza is a whole big family of viruses that circulate in numerous strains among different species and, as you noted, mutate rapidly (because they're RNA viruses), which is why it's such a nasty thing to get a handle on. Smallpox and rinderpest, the two diseases we've eradicated, were eradicated with mass vaccination; the latter only affected various large mammals, which can't travel long distances easily, another helpful factor. However, we're still cursed with the descendant of rinderpest: measles. --47.146.63.87 (talk) 07:00, 12 March 2020 (UTC)[reply]

There was a reddit ama yesterday by an NHS critical care doctor that has what looks like good info: [18] 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 09:51, 12 March 2020 (UTC)[reply]

flowers with 2 differnt sexes and with one sex

How do I find a list of flowers that have 2 different versions (male and female)? How do I a list of flowers that have only one versions (which is both male and female)? In the first case I want to find pictures of each of the versions.

Thanks a lot, Rami (talk) 19:33, 11 March 2020 (UTC)[reply]

Plant reproductive morphology looks like the starting place you want. Most flowers are "perfect", having both male and female sex organs, so a list of the latter will be most flowering plants. --47.146.63.87 (talk) 04:02, 12 March 2020 (UTC)[reply]

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)[reply]

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)[reply]

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 [19]. Bazza (talk) 12:12, 12 March 2020 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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. [20] [21] Even that UK supercarrier that got a lot of attention at one time only infected 11 that we know of [22] 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. [23]. Nil Einne (talk) 17:47, 12 March 2020 (UTC)[reply]

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. [24]. Nil Einne (talk) 18:13, 12 March 2020 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

Fish liver is rich in vitamin A; 15grams should provide enough for a day. LongHairedFop (talk) 22:21, 12 March 2020 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

Good point, the Dyson Sphere does indeed look like a much better approach! Earl of Arundel (talk) 21:35, 12 March 2020 (UTC)[reply]

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)[reply]

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)[reply]

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 T_eq absolute temperature by 2^1/4-1 = 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)[reply]

March 13

Psychological Research on Rules and Domain Expertise

I'm developing a presentation for a workshop on artificial intelligence. My presentation is an overview of knowledge representation in AI. One of the points I want to make is that one of the reasons that rule-based systems were first used was that there is empirical evidence that domain experts often represent their expertise in rule like forms. This is something I know I've heard several times and I think I've read but it's been a long time since I did work on expert systems and I can't remember where I read it (or if perhaps this was something that people often said even though there isn't good research to back it up). Any and all pointers would be appreciated. --MadScientistX11 (talk) 15:03, 13 March 2020 (UTC)[reply]

See the article Knowledge representation and reasoning and a tutorial about knowledge representation. DroneB (talk) 15:40, 13 March 2020 (UTC)[reply]

That goes way back to the early books on AI, like the one by Nilsson. The trick is what to do when multiple rules saying conflicting things apply to a situation. Deep learning seems to be the first thing pointing at a satisfactory answer. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 17:30, 13 March 2020 (UTC)[reply]

March 14

Viral infection transmission

1. suppose you are infected and you come in contact with someone else who is infected with the exact same virus. Can that make either or both of you *more* infected than you already were?

2. The virus is mutating quickly, so maybe the person you come in contact with has a slightly different strain. Same question as above.

Note: science question, not medical, though the current event inspiration is obvious. I trust we are all taking as many precautions as we can. Thanks. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 00:46, 14 March 2020 (UTC)[reply]

If the virus has started replicating already and you have a measurable viral load, the minute contribution from a second source will probably not make much of a difference. Viral superinfections do occur, and if the second strain is considerably more virulent, it may make a difference. If it is only slightly different, that is not impossible but somewhat unlikely. --Lambiam 04:41, 14 March 2020 (UTC)[reply]

Notably, if an organism is infected by multiple strains of influenza at once, this can result in antigenic shift, where daughter viruses are produced that combine genes from both strains. This basically creates a new strain, which can then spread rapidly because nothing has resistance to it. --47.146.63.87 (talk) 00:49, 15 March 2020 (UTC)[reply]

Microplastics in the oceans: Thermal load

Do microplastics in the world's oceans increase the capacity of those oceans to store heat?

The water in the oceans weighs about 1,400,000,000,000,000,000 tons. The combined mass of the microplastics in the oceans is estimated to be about 300 tons. The specific heat capacity of the materials making up that mass varies but is on the average about one quarter of that water. So it is about the same as a relative increase from 1,400,000,000,000,000,000 to 1,400,000,000,000,000,075, less than 0.000000000000006%. It should be clear that this is not going to make a measurable difference. --Lambiam 09:08, 14 March 2020 (UTC)[reply]

The argument holds, but I think the current estimate for Microplastics in the ocean is more around 300000 tons (with overall plastic load increasing by around 10 million tons per year, but most of the plastic is "macro"). See e.g. [25]. --Stephan Schulz (talk) 11:36, 14 March 2020 (UTC)[reply]

Thanks for the correction. I used a figure from our Microplastics article that said "270 tons", but I should have checked the source (which has "270.000 tones" [sic]). Now corrected. --Lambiam 17:58, 14 March 2020 (UTC)[reply]

March 15

COPD 2

What is COPD 2? I've seen some references to it but no clear explanation of what it is, and the COPD article says nothing at all. There are several types of COPD (emphasyma, bronchitis etc.) but they don't seem to have numbers connected with them. There are also severity levels 1 thru 4, but no indication that it refers to that either. Is this standard terminology? Thanks. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 01:41, 15 March 2020 (UTC)[reply]

Where did you see it? Some quick searching suggests that there are "2" main kinds of COPD, but it's not like they're numbered 1 and 2. Without further info, my guess would be that it's just short for COPD Stage 2 (i.e. "moderate" per this). Matt Deres (talk) 01:52, 15 March 2020 (UTC)[reply]

A friend of mine has it and was hospitalized for it, and then I did a web search and didn't find much. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 03:00, 15 March 2020 (UTC)[reply]

Are you sure there wasn't some miscommunication and it's not actually the pandemic virus going around? The official name for the disease is COVID-19, but the virus itself has been named SARS-CoV-2, which could get clipped to "CoV-2". Otherwise, yeah, I'd go with the above respondent that it might be a COPD exacerbation, which can require hospitalization. --47.146.63.87 (talk) 06:32, 15 March 2020 (UTC)[reply]

Thanks, COPD exacerbation sounds like it exactly it. The idea of a sudden attack of something chronic otherwise seemed paradoxical. She has been out of the hospital for a few weeks, so if she had a covid-19 infection I think it would have incubated by now. That makes me feel relieved that she probably doesn't have it. She said she was not tested for it, but is staying at home. 2601:648:8202:96B0:386A:A40C:EBB1:ACC0 (talk) 08:05, 15 March 2020 (UTC)[reply]

How does COVID-19 kill?

What exactly does COVID-19 do to a person's body that causes them to die? Freeknowledgecreator (talk) 02:47, 15 March 2020 (UTC)[reply]

Basically blocks and damages the lungs til the person suffocates, thus the treatments with medical ventilators and ECMO. 2601:648:8202:96B0:54D9:2ABB:1EDB:CEE3 (talk) 02:59, 15 March 2020 (UTC)[reply]

This BBC website article from yesterday (14 March) is to the point, if fairly basic. {The poster formerly known as 87.81.230.195} 90.197.27.39 (talk) 07:39, 15 March 2020 (UTC)[reply]

COVID-19: typically death results from pneumonia, ARDS, and/or septic shock. It's likely in some cases coinfections like bacterial pneumonia contribute—this often occurs in influenza deaths—but we can't definitely say right now because of course everyone is running around trying to get a handle on things. Once things are more under control people will start reviewing case reports. Most deaths have occurred in people with preexisting conditions like hypertension. --47.146.63.87 (talk) 08:59, 15 March 2020 (UTC)[reply]

It's mostly collateral damage due to the body's own immune system. In older people the immune response tends to react more with an inflammatory response which then can cause damage to the lungs. This lung damage and the extra strain on the heart that now needs to pump more blood can then lead to acute respiratory distress syndrome (ARDS). A significant fraction of people over 80 already have heart failure to begin with. Even many "healthy" 80-year-olds who have not been diagnosed with heart failure, do have heart failure to some degree. They are at risk to get acute heart failure when the heart would be strained without any lung damage. In that case fluids builds up in the body, also in the lungs which then leads to ARDS without any lung damage. Also, people older than 80 often have impaired kidney function. If (additional) fluid builds up in the lungs due to heart failure, diuretics to remove all that excess fluids won't work well. And dialysis can at best only replace about 20% of a healthy kidney function. Count Iblis (talk) 21:13, 15 March 2020 (UTC)[reply]

There has been significant discussion/suggestion that the virus attacks heart muscle tissue as well. A number of patients have died of myocarditis after apparently weathering the respiratory storm, so to speak. NorthBySouthBaranof (talk) 21:43, 15 March 2020 (UTC)[reply]

G-force in a head-on collision

Suppose a 1-ton automobile runs head-on into a 2-ton automobile. Can you calculate the G-forces of people in each auto? It is an elastic collision, so the conservation of momentum doesn't apply. Does it depend on the details of the cars? Bubba73 ^{You talkin' to me?} 20:26, 15 March 2020 (UTC)[reply]

The G-forces on the people is independent from the relative mass of the cars involved. It depends on the time vs. distance for the people to go from speed-on-impact to zero -- which might differ for each vehicle, depending on a variety of factors (including mass). 107.15.157.44 (talk) 21:01, 15 March 2020 (UTC)[reply]

Indeed, this is the whole purpose of crumple zones. Someguy1221 (talk) 21:52, 15 March 2020 (UTC)[reply]

The G-loading cannot be calculated for any collision, using the basic principles of physics. (Contrary to the original question, momentum IS conserved in any collision but that doesn’t help with calculating the G-loading.) The reason is that the distance involved in decelerating the bodies varies from one body to the next. In a vehicle collision this distance is closely related to the crumple zone of each vehicle. Dolphin (t) 21:59, 15 March 2020 (UTC)[reply]

Some of the energy goes into deforming the automobiles. Bubba73 ^{You talkin' to me?} 23:54, 15 March 2020 (UTC)[reply]

It is not an elastic collission. Momentum is conserved. No you can't calculate the G forces on the occupants, that's what supercomputers are for. The accelerations in general in the 1 tonne car will be around twice those in the two tonne car, independent of the distribution of structural properties of the two cars, because of Newton's laws F1=-F2 and F=ma.Greglocock (talk) 00:21, 16 March 2020 (UTC)[reply]

To make it a little bit clearer: Momentum is a vector property (it has size and direction). The total momentum is the (vector) sum of the two individual momentums of the cars, both before and after the crash. Momentum is always conserved in a closed system. See Momentum#Conservation. What is not conserved in an inelastic collision is kinetic energy (which is a scalar property, not a vector property. --Stephan Schulz (talk) 02:13, 16 March 2020 (UTC)[reply]

If the vehicles involved are traveling with a speed of one inch a year, the g-force will be low. Supposing the movement of the passengers is suitably constrained (safety belt; air bag) there are three things that can be used for a back-of-the-envelope calculation, assuming a constant deceleration from the moment of contact to a complete halt: (1) the speed v of the vehicle; (2) the time t it takes to come to a halt; (3) the distance s traveled by the passenger from the moment of collision to a halt. Any two out of these three will suffice, since they are connected by the relationship s = ¹/₂vt. {See Kinematics#Particle trajectories under constant acceleration.) Then the experienced deceleration a is given by a = v/t = ¹/₂v²/s = 2s/t². Since the passengers are also subject to the force of gravity g, the combined force is the square root of a² + g². To convert to the correct magnitude when using g-force as the unit, divide by g. --Lambiam 04:06, 16 March 2020 (UTC)[reply]

Of course it varies based on vehicle and crash conditions, but realistic deceleration curves tend to be rather pointy. From the examples here, especially for what looks like car vs. concrete wall, peak head acceleration is about double the average value.[26] Someguy1221 (talk) 05:49, 16 March 2020 (UTC)[reply]

White scar removal question

We are not supposed to answer questions calling for medical advice. Talk to a doctor.

The following discussion has been closed. Please do not modify it.

Is there any way to permanently get rid of a decade-old white scar that is about 1.0-1.5 inches long and 0.05-0.10 inches wide? For instance, with some kind of laser? Futurist110 (talk) 21:41, 15 March 2020 (UTC)[reply]

Wait another 10 years? Or go to a really good plastic surgeon. Greglocock (talk) 00:22, 16 March 2020 (UTC)[reply]

First talk to your family doctor, and see who they can refer you to - maybe a dermatologist. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:24, 16 March 2020 (UTC)[reply]

March 16

So what's with governments response to the corona virus?

Are some countries trying to stop it completely and have as few infected as possible while others are trying to have the populace gradually infected to build up immunity (UK)? What does the WHO want? 137.205.1.87 (talk) 00:45, 16 March 2020 (UTC)[reply]

This is a public policy question, and not a scientific one. --OuroborosCobra (talk) 01:12, 16 March 2020 (UTC)[reply]

From the science (or maybe math) angle, it is hoped that the many closures will delay enough cases so as to not overwhelm the health care systems, i.e. to "flatten the curve". ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:22, 16 March 2020 (UTC)[reply]

For more on "flatten the curve", see:

"These simulations show how to flatten the coronavirus growth curve". Washington Post.
Wilson, Mark (13 March 2020). "The story behind 'flatten the curve,' the defining chart of the coronavirus". Fast Company.

(etc.) 2606:A000:1126:28D:9CD1:2A09:62D0:11F5 (talk) 04:12, 16 March 2020 (UTC)[reply]

Chinese intervention let do a drop in R_0 from 3.9 to 0.32. Count Iblis (talk) 06:04, 16 March 2020 (UTC)[reply]

Given the nature of their organisation and international politics, the WHO is generally going to be circumspect about what they say about another country, especially a large powerful one, is doing. However IMO if you read what the WHO have said in the past e.g. when they confirmed that this was a pandemic, it seems likely they don't really agree with the UK approach. See e.g. this non RS [27]. The UK approach has of course received a lot of criticism from some others e.g. [28].

More generally though, while there seems to be almost universal agreement on the need to flatten the curve and ensure health care services don't become overwhelmed by the number of cases, there seems to be somewhat less agreement on whether the pandemic can still be contained. The WHO seems to think it can, and of course China, South Korea and also Singapore, Taiwan, Hong Kong are suggested as examples of that. Success with some previous cases, SARS-CoV-1, and to a lesser extent other outbreaks like EMC/2012 and Ebola other exampls. But the alternative view is that the given the nature of how the virus spreads, and that SARS-CoV-2 is now so widespread including having reached countries with poor health care systems that it's too late.

While China may be having success in stopping the spread, it's just going to come back as they relax their controls. And it's not realistic for these controls to last indefinitely since they're so disruptive to everyday life and society, and people are eventually going to start rioting as they start to run out of food etc. [29] [30] Even holding out for a vaccine, which at best is probably in 18 months, is not realistic.

There are additional concerns. For example, we don't know how effective any immunity will be long term. It could be this the new SARS-CoV-2 will have enough antigenic shift that it becomes endemic, i.e. more like seasonal influenza and some other coronaviruses, continually spreading. [31] What that means is unclear, does it and will it have a greater mortality rate and treatment cost long term? That risk is an added reason to try and stop this, beyond the deaths this initial outbreak will cause.

Given there are still so many unknowns (including the infamous unknown unknowns), the differences between the current situation and anything we have dealt with in recent times, and the nature of science, there is going to be strong amount of disagreement even among experts. As I mentioned at the beginning, the WHO public stance still seems to be strongly of the view that the outbreak can be contained. The UK's view seems to be that it cannot be. Although to be clear, there are still some who adopt that view, but view the UK's plans as flawed.

Then there are the non experts. For example, in NZ a group has been calling for school closures. [32] However AFAWK, there is no ongoing community spread in NZ. It could be it's simply undetected, as has happened in plenty of countries besides NZ, in which cases maybe the proposals are sensible. But assuming there is indeed no ongoing community spread, shutting down schools is incredible disruptive so the long term plan with such a proposal seems somewhat unclear.

Nil Einne (talk) 11:41, 16 March 2020 (UTC)[reply]

In the latest WHO press conference, one of the key messages was "test test test" and that testing of suspected cases was the "backbone of stopping the spread", along with contact tracing and isolation of contactees of anyone who tested positive. [33] [34] I'm sure sources will emerge comparing this advice to what the UK suggested they will do. Nil Einne (talk) 16:37, 16 March 2020 (UTC)[reply]

Grauniad "When I first heard about this [UK plan], I could not believe it. I research and teach the evolution and epidemiology of infectious disease at Harvard’s Chan School of Public Health. My colleagues here in the US, even as they are reeling from the stumbling response of the Donald Trump administration to the crisis, assumed that reports of the UK policy were satire – an example of the wry humour for which the country is famed. But they are all too real." 2601:648:8202:96B0:386A:A40C:EBB1:ACC0 (talk) 19:34, 16 March 2020 (UTC)[reply]

March 17

What would the spermatogenesis process look like without the epididymis?

Is a man surgically gets rid of both of his epididymeses (epididymi?) and his vas deferens subsequently grow and attach themselves to the place/spot on his testicles where his epididymises (epididymi?) used to be, what are the sperm that are going to come out of this man's body going to look like? As in, how would the process of spermatogenesis be affected if everything else was done for this man's sperm other than a passage through the epididymis (on account of there no longer actually being any epididymises)? I know that testicular sperm cannot naturally achieve pregnancy and instead requires IVF, but I was wondering if the same was also true for sperm that went directly from the testicles to the vas deferens (again, due to there no longer actually being any epididymises) and then came out of a man's body the normal way. I was also wondering just how fertile this man is actually going to be in this scenario after his vas deferens would have regenerated and attached themselves to the place/spot on his testicles where his epididymises used to be. Is this man actually going to be capable of causing any unplanned pregnancies? Or are the sperm that are going to come out of this man's body simply going to be too immotile for him to ever actually cause any unplanned pregnancies regardless of which women he will ever have penis-in-vagina sex with due to his sperm not actually having any epididymis to mature in? 68.96.93.207 (talk) 00:14, 17 March 2020 (UTC)[reply]