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Health effects of drinking human blood

Per OP's recommendation. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:29, 29 January 2020 (UTC)[reply]

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

If a person were to drink human blood, would that be fattening? Freeknowledgecreator (talk) 06:33, 26 January 2020 (UTC)[reply]

At this point I am getting a thirst for drinking troll blood. 67.164.113.165 (talk) 09:34, 26 January 2020 (UTC)[reply]

It is a serious, matter of fact question. I am looking for a serious, matter of fact answer. If you find a question offensive for some reason, you obviously do not have to respond to it. Indeed, it is probably better to make no response in such situations. Freeknowledgecreator (talk) 09:40, 26 January 2020 (UTC)[reply]

Please try google before asking further stupid questions here. Example. 67.164.113.165 (talk) 09:51, 26 January 2020 (UTC)[reply]

Insulting me really serves no purpose. If you don't like the question, don't respond. That should be simple enough, shouldn't it? As for those Google hits, none of them, at a quick look, address the specific question of whether drinking human blood would be fattening. Freeknowledgecreator (talk) 09:54, 26 January 2020 (UTC)[reply]

See Black pudding#Nutrition. Not about drinking it, but eating it. Seems like it depends on the recipe. HiLo48 (talk) 10:05, 26 January 2020 (UTC)[reply]

You Australians have some crazy black pudding recipes. Most other places use pork blood for their black pudding although some may use sheep or cow blood. Various other blood sausages exist but human blood sausages is a new one to me. (Discounting vampire fiction.) Nil Einne (talk) 10:41, 26 January 2020 (UTC)[reply]

Are we sure Mrs. Lovett never made sausages instead of pies? HiLo48 (talk) 10:50, 26 January 2020 (UTC)[reply]

As I have previously responded the level to which any food is fattening depends on how much you consume compared with the amount of effort used to burn the consumed calories (this is only part ot the complex problem of obesity) See Blood as food. Where would you propose to obtain the human blood, or is this a hypothetical question? Richard Avery (talk) 15:36, 26 January 2020 (UTC)[reply]

The question is, of course, entirely hypothetical. Freeknowledgecreator (talk) 23:30, 26 January 2020 (UTC)[reply]

(Singing) Use HiLo48, if you must watch your weight! Gråbergs Gråa Sång (talk) 17:08, 26 January 2020 (UTC)[reply]

(e/c) These questions are pointless, not because any one of them are "stupid" but because you don't seem to be getting the gist of the answer: NOTHING in and of itself can just be called fattening or healthful or thinning or good for reducing belly fat or any of the other tiresome variations you've raised. The dose makes the poison and no one eating event is going to change your body's fat content appreciably. You need to consider the entire diet, the body of the consumer, their level of exercise, their general fitness and metabolism, and other things. Matt Deres (talk) 15:45, 26 January 2020 (UTC)[reply]

You have a point, but it still serves some purpose to ask whether a given food or substance would be fattening. If necessary, interpret the question, "is x fattening?" to mean, "If a person consumes x on a regular basis, would that be fattening?" Freeknowledgecreator (talk) 23:04, 26 January 2020 (UTC)[reply]

What would be an average serving size? Bus stop (talk) 23:52, 26 January 2020 (UTC)[reply]

Irrelevant. I am simply noting that even if there is no food or substance that is automatically fattening in every situation, it is still legitimate to speak of a given food or substance as having a tendency to be fattening, hence the point of the questions I've been asking. Freeknowledgecreator (talk) 00:13, 27 January 2020 (UTC)[reply]

That's a valid point. My guess would be human blood would be similar to blood of some of the other creatures we eat. One exception might be Horseshoe crabs, which use Hemocyanin to carry oxygen instead of Hemoglobin, as used by humans. Would this be cooked or uncooked human blood? We also have to be concerned with blood-borne disease—"Since it is difficult to determine what pathogens any given sample of blood contains, and some bloodborne diseases are lethal, standard medical practice regards all blood (and any body fluid) as potentially infectious." Bus stop (talk) 00:22, 27 January 2020 (UTC)[reply]

No, the serving size is very relevant. If I eat 1 g of chocolate every day, the impact on my weight would be very different from what it would be if I ate 1 kg of chocolate every day. "On a regular basis" is also vague to the point of uselessness. Once every 10 years and every 10 minutes are both "on a regular basis". --Khajidha (talk) 14:01, 27 January 2020 (UTC)[reply]

What I had in mind by "on a regular basis" was daily. Freeknowledgecreator (talk) 22:46, 27 January 2020 (UTC)[reply]

1) Then say so. We can't read your mind. 2) The portion size would still be important. If I eat one potato chip every day that is different from eating one snack size pack of potato chips every day. Let alone eating one family sized pack of potato chips every day. For what seems to be the millionth time, how much of a food is eaten and how often it is eaten and how active the consumer is are much more important to your health and weight than what food is eaten. --Khajidha (talk) 15:26, 28 January 2020 (UTC)[reply]

For portion size, let's say, sufficient to satisfy the sort of hunger a person is likely to feel on waking up early in the morning, after having had three meals sufficient to meet normal physical needs the previous day. That's quite specific. Freeknowledgecreator (talk) 01:53, 29 January 2020 (UTC)[reply]

You would still have to account for whatever else the person ate that day. And for their activity level. And for their personal metabolic rate. There simply is no way to say if a particular food is "fattening" in an absolute sense. --Khajidha (talk) 12:28, 29 January 2020 (UTC)[reply]

I know. The question, is something fattening, should simply be understood to mean, does it have a tendency to be fattening? I'm not surprised that no one has been really been able to answer my question whether this would be true of human blood, and perhaps this whole discussion should be archived. Freeknowledgecreator (talk) 22:24, 29 January 2020 (UTC)[reply]

Just call him Drac. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:12, 27 January 2020 (UTC)[reply]

Please, I already noted the question was entirely hypothetical. Freeknowledgecreator (talk) 04:32, 28 January 2020 (UTC)[reply]

Whatever you say, Drac. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:45, 28 January 2020 (UTC)[reply]

January 27

Bransden and Joachain, Introduction to QM

Does anyone know this book? Do you recommend it as an introductory QM text for someone with a reasonable math background but not much physics beyond elementary mechanics? Thanks. 173.228.123.190 (talk) 09:46, 27 January 2020 (UTC)[reply]

And what is a reasonable math background? That is, does that mean first-year calculus, or something beyond that? I think it would be very difficult to deal with quantum mechanics without a knowledge of first-year calculus. Robert McClenon (talk) 20:46, 27 January 2020 (UTC)[reply]

Well, enough math for introductory QM ;). Question is more about the physics required for this specific book, and also whether it is a good book for self study, has good exercises, etc. Thanks. 173.228.123.190 (talk) 01:43, 28 January 2020 (UTC)[reply]

Oxford Electric Bell

How is the Oxford Electric Bell not a perpetual motion machine? Thanks. Anton 81.131.40.58 (talk) 11:29, 27 January 2020 (UTC)[reply]

To quote the article, "The Oxford Electric Bell does not demonstrate perpetual motion. The bell will eventually stop when the dry piles have distributed their charges equally if the clapper does not wear out first." Seems pretty clear. But besides that, a "perpetual motion machine is a hypothetical machine that can do work indefinitely without an energy source. This kind of machine is impossible, as it would violate the first or second law of thermodynamics". Freeknowledgecreator (talk) 11:36, 27 January 2020 (UTC)[reply]

It's battery powered. When the batteries run flat, it will stop. It's likely that it may wear out mechanically first. Andy Dingley (talk) 12:34, 27 January 2020 (UTC)[reply]

Here is a very lovely piece of light scholarly reading: The Methods of Modern Logic and the Conception of Infinity (1907), available at no cost on JSTOR. In this piece, Richard Haldane, 1st Viscount Haldane extolls the evolution of modern scientific and philosophical understandings of the truly absurd mathematical facts that pertain to the "conception of infinity." This is a paper that was read in front of a bunch of smart people at Oxford - "a long time" ago, but ... that was not "an infinite time" ago.

In simple words: a machine can run for a long time, and that is different from running "perpetually." Great thinkers have studied the difference between "a long time" and "perpetuity" ... for ...a long time. (...But, even our best and greatest human scholars have not studied this philosophical precept for a perpetually long time). Over a long period of time, there has been a gradual change in the general philosophical consensus-understanding about the difference between these two concepts. In technical settings like physics and mathematics and thermodynamics, we now have very precise ways to distinguish "a long time" from an "infinite" amount of time. And we even use different words in common speech to distinguish these concepts. For example, we have a word, in the English language: "perpetual"; and in certain cases, we use this word; and in other cases, ... we do not apply that adjective.

In the case of the Oxford Electric Bell, ... intelligent people do not apply the adjective "perpetual" to describe the motion of the machine.

...So, where is your confusion? This is a machine that runs for a long time, and it is not a perpetual motion machine, and no reasonable person even says it is a perpetual motion machine.

Nimur (talk) 17:36, 27 January 2020 (UTC)[reply]

To try to get at what might be causing you confusion: I suspect you're thinking, how come this thing has run for over a century, but I need to get a new car battery every few years? The article on the bell says the batteries are probably Zamboni piles, and if you read that article you'll see that their current output is in the realm of nanoamperes. Zamboni piles are primary (non-rechargeable) cells, but their chemistry appears pretty stable, and the amount of power the bell uses is very tiny. But it would take a huge number of Zamboni piles connected in series to run something like a flashlight, which is why we don't use them for much. --47.146.63.87 (talk) 23:10, 27 January 2020 (UTC)[reply]

One could run a flashlight from just a few layers of a Zamboni pile - however the area needed would need huge discs. Andy Dingley (talk) 23:15, 27 January 2020 (UTC)[reply]

Ah, thanks for the correction. And of course they're not rechargeable, which makes them not terribly practical for most applications, though the article states they did find a few uses until recently. --47.146.63.87 (talk) 02:54, 30 January 2020 (UTC)[reply]

I have a couple here from 1st generation military night vision goggles. The photomultiplier tubes need a 1kV or so to power them, but with a tiny current, so Zambonis were ideal. My 1960s NV sets had already switched to electronic PSUs instead. Andy Dingley (talk) 02:27, 31 January 2020 (UTC)[reply]

January 29

Acupuncture injuries

Can acupuncture result in permanent damage or injury to the person who undergoes it? Freeknowledgecreator (talk) 03:34, 29 January 2020 (UTC)[reply]

Of course it can. Google "can acupuncture cause permanent damage" for more info. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:54, 29 January 2020 (UTC)[reply]

See Acupuncture#Adverse events. --Lambiam 08:21, 29 January 2020 (UTC)[reply]

Pretty much any medical intervention can. What we care about is: is the intervention superior to placebo, and what is the risk–benefit ratio? Related concepts: number needed to treat, number needed to harm. --47.146.63.87 (talk) 02:59, 30 January 2020 (UTC)[reply]

Do travel restrictions stop virus outbreaks spreading? Comment Reply Suggestion Reply

E.g. the 2020 Wuhan lockdown. An article in Vox by Julia Belluz and Steven Hoffman suggests it's just "political theater". -- Jeandré, 2020-01-29t07:55z

The sourced answer to that question might be worth including in our article(s) quarantine or/and cordon sanitaire, which do not discuss it at all. (Notice also that both "quarantine can work in general" and "the Wuhan lockdown in Chinese government theater" could be true.) Tigraan^{Click here to contact me} 08:18, 29 January 2020 (UTC)[reply]
The article in Vox states that travel restrictions may "delay the spread of disease but don’t impact the number of people who eventually get sick". It does not consider possible beneficial effects of such delay, in particular reducing the overload on medical support systems caused by massive amounts of people falling ill at the same time. --Lambiam 08:28, 29 January 2020 (UTC)[reply]
Indeed. One of the problems is in how "success" is defined here. If "success" is "no one else in the world will ever get sick ever", then we have an unrealistic measure of success. If "success" is some other standard, such as what you note, being the slowing of the spread to allow response systems to be better prepared for when it does eventually get there, then it can be successful. And, as noted, just because it is political theater doesn't mean it isn't also effective. Propaganda doesn't have to be untrue to be propaganda. --Jayron 32 13:01, 29 January 2020 (UTC)[reply]
I'm reminded of the leadup to the Mount Saint Helens eruption 30 years ago. The governor ordered the area evacuated, and some citizens griped about it. They didn't use the term "political theater", but they were skeptical that there was a real threat, calling it an overreaction, etc. Then the eruption came, killing everyone and everything for miles around, and the skeptics were never heard from again. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:17, 29 January 2020 (UTC)[reply]
Ex post.

One of those skeptics was Haroun Tazieff who had predicted that the 1976 Grande Soufrière eruption (yes, that's a red link - if you can read French, this is as good a wrap-up of the event/polemic as you will ever find; La_Grande_Soufrière contains a few sentences too) would be a mild event (there was some seismic activity but no dangerous magmatic phenomenon). Yet tens of thousands were evacuated for three months.

It does not mean either evacuation was wrong or right. It means that such judgement should be formed by analyzing what information was available/obtainable at the time of decision-taking, rather than the how the event actually turned out.

Hence: whether certain quarantine practices are efficient at achieving certain objectives should be evaluated from how the use of such practices turned out in the past, but whether the Wuhan lockdown is or is not a good idea could be evaluated now already (if one had perfect knowledge of internal government deliberations, that is). Tigraan^{Click here to contact me} 15:51, 29 January 2020 (UTC)[reply]

The idea is to prevent a pandemic. If you consider it unwise to travel to Wuhan right now, you might also want to arrange that Wuhan not travel to you. It doesn't make sense that the number of people infected somehow would stay constant. Also, there is a good chance of having vaccines available pretty soon, so slowing the spread helps. 173.228.123.190 (talk) 19:42, 29 January 2020 (UTC)[reply]

You appear to assume that the travel restrictions will prevent a pandemic. Is that assumption justified? --Lambiam 04:43, 30 January 2020 (UTC)[reply]

Compared with doing nothing? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:29, 30 January 2020 (UTC)[reply]

Everyone putting plugs in their noses beats doing nothing. Still, that does not warrant the assumption that it will stop a pandemic. --Lambiam 06:52, 30 January 2020 (UTC)[reply]

It's called containment. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:42, 30 January 2020 (UTC)[reply]

If all forms of travel are effectively prevented, it will stop the further spreading of the disease. Such containment is only possible by draconic measures and may have side effects (e.g. worldwide famines) that are worse than the problem they are meant to solve. But no one has proposed or is going to implement this. The thesis of the referenced publication is that (lesser) travel restrictions merely slow down the speed at which the disease spreads, like a film in slow motion. One may disagree with this thesis, but it is not absurd and does make sense. Plugging the larger holes of a leaky container will not keep it from eventually being emptied; it just takes longer, but in the end it is just as empty. --Lambiam 20:48, 30 January 2020 (UTC)[reply]

On a side note, an amazing film is "La Soufrière" by Werner Herzog. Bus stop (talk) 01:37, 30 January 2020 (UTC)[reply]

Taste of food

Why is it that food which is good for you tastes bad, and vice versa? — Preceding unsigned comment added by 2600:1000:B160:9CC8:2D34:DDFE:8A95:EFCD (talk) 16:49, 29 January 2020 (UTC)[reply]

This article has some good information which may help drive your research in this area. --Jayron 32 16:56, 29 January 2020 (UTC)[reply]

It depends on the food. Liver is supposed to be good for you, and apparently some people actually like it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:23, 29 January 2020 (UTC)[reply]

It is generally agreed that fruit is a healthy food and most fruit is delicious. Richard Avery (talk) 19:39, 29 January 2020 (UTC)[reply]

I think the OP might be suggesting that fruit, delicious as it is, still doesn't compare to, err, bacon double cheeseburgers or chicken chow mein :) ——SN 54129 14:11, 30 January 2020 (UTC) [reply]

Because you wouldn't eat bad food otherwise. So if food is bad (sausages made of the infamous 'all lips and arseholes' recipe), you add salt or sugar or MSG or herbs or something to make it tasty. Or at least, crudely tasty (sweet or salty) to an unsophisticated palate.

There's also the problem of vanished scarcity. At one time, sugar was rare. So a dense source of energy from it (wild fruit, maybe honey) would be appreciated by a forager and consumed. It was good for you (stopped you starving). Now we've learned to produce enough sugar to kill us, but we still like it, and will (mostly) keep on choosing to eat it. Andy Dingley (talk) 16:55, 30 January 2020 (UTC)[reply]

There is a broad misunderstanding behind the question and many of the replies. When speak of foods as "bad" that typically means that they're full of fat, salt, and/or sugar. However, those things are all vital to our health. Without salt we would die and sugar and fat supply the calories we need to walk/talk/move/etc. So, we evolved in such a way that those things taste freaking great to us. Taste is an ongoing area of study, but we basically only recognize a handful of tastes directly (as opposed to flavour, which is mixed with aroma/smell). Saltiness and sweetness are signs we should eat a thing, while sourness and bitterness are signs we should not, as they indicate unripeness and poison, respectively. That's how important saltiness and sweetness are to us. So what's wrong? Well, our desires for those tastes have been exploited by food producers - what started as a keen enjoyment of some sweet fruit has become weaponized into an addiction to refined sugar. Our desire to eat the fatty parts of animals to extract the much-needed calories has been co-opted into eating meat that is much more saturated in fats than what we'd ever be exposed to "naturally". That is to say, the things we desperately required thousands of years ago are now in a superabundance at the local quick service restaurant and that abundance has developed much faster than our tastes possibly could, so we still keenly desire then as if they were still rarities. Matt Deres (talk) 19:41, 31 January 2020 (UTC)[reply]

Supernova

Considering that full moon is bright enough to cast shadows in a city night, I'm wondering how close would a supernova have to be to cast shadows on a clear moonless night in a low light pollution area? 89.172.78.189 (talk) 16:51, 29 January 2020 (UTC)[reply]

What your asking is how to calculate the apparent magnitude of a supernova, and at what distance from earth would a typical supernova need to be in order to have an apparent magnitude equal to that of the moon. There are equations in that article which may help you work that out. --Jayron 32 16:58, 29 January 2020 (UTC)[reply]

Well - almost.... Jayron is absolutely correct that we do want to know the apparent magnitude. This is sort of "step zero", or maybe "step one", in setting up the problem. This number is easy-ish to compute, and it tells us how much light there will be - using units that are easy to compare to all the other sources of light. If we want to be very approximate, we can just say "it will cast a shadow if..." the apparent magnitude is bigger than some arbitrary reference value - let's say, maybe, the brightness of the moon. That's not very precise, but it might be all you're looking for.

The challenge is that "casting a shadow," used as a plain english phrase, actually has a pretty ill-defined technical meaning in the context of optical imagery. We have an article - shadow - that at least introduces the subject, and talks about its use in astronomy. To throw some technical jargon at the problem: we want to know what brightness will provide a sufficiently large contrast between a shadowed area and an unshadowed area - which means that we need to carefully define the imaging condition. Basically, we want to know how large the object is, and on what surface is it "casting" a shadow, and the precise geometries of those items (e.g. we need to fill out the extrinsics matrix for the object casting the light and the object casting the shadow and the object on which the shadow shall be observed)... and we need to define a statistical "confidence interval" in which the absence-of-an-observed-photon is strong evidence of the existence-of-a-shadow, for all regions where we expected to see a shadow based on geometry and the simplification of photons-that-travel-in-straight-lines... which is not actually what photons do!

The point is, though, the ordinary day-to-day use of the word "shadow" is a little too informal for these kinds of astronomical objects. Even in the simple common case of "sun/earth/moon" shadowing, we have to worry about the umbra and penumbra - and that's just because the relevant objects have non-zero size!

In the absolute simplest case, consider a two-pixel camera - a pair of photodiodes. Place the two pixels so that one is blocked by a box, and one is ... not blocked by the same box.

If this one of these diodes captures any light at all - in other words, if it images anything - the box is "casting a shadow" on to a very low resolution image: a 1x2 pixel digital photograph.

Because we really literally truthfully cannot know where the photon came from, we really literally truthfully can't tell you whether that photon came from the supernova. All we can do is present a statistical likelihood - which means we need to use lots of math and physics - and the name of this is "to solve for the imaging condition", estimate a resolution, and compute a signal-to-noise ratio.

Nimur (talk) 17:36, 29 January 2020 (UTC)[reply]

It wouldn't have to be as bright as moon but anyhow I was wondering if anyone else has done those calculations. Surely I'm not the first person to think of this. 89.172.78.189 (talk) 17:08, 29 January 2020 (UTC)[reply]

... no, ... no, there is a long legacy of optical physicists whose tenure extends for centuries; and they have thought about this problem and many variations on the theme, for a long, ... long time.

We don't need to look much farther than the writings of Isaac Newton or Christiaan Huygens to see that they considered the problem of shadow-casting: Huygens' wave principle is a surprisingly modern take on the problem, treating every point in the illuminated area as point-propagators of a new wave of illumination; and every shadowed, un-illuminated point as ... not a point-propagator. And Kepler's Supernova was studied by none other than Johannes Kepler in 1604 - as well as many other scientific observers around the entire world; many of the recorded observations were mathematical and quantitative. All of these old dead guys were really big into their telescopes, and they tended to point them at the interesting weird dots they spotted in the night-sky. Then, they'd spend hours and hours inventing new kinds of mathematics to explain what they saw and figure out new ways to see things differently.

It's not easy to come up with a truly new idea in optical physics...

Nimur (talk) 17:50, 29 January 2020 (UTC)[reply]

I have seen a shadow from a crescent moon so low it was orange from a suburb where I couldn't see the Milky Way. It was shadow-producing as fuck when higher up and the faint shadow faded to nothing by the time the sand couldn't see the 25% phase or less crescent anymore (half a half moon or less, almost 90 degrees from the zenith). This was because I was almost in a cocoon with only a few square degrees of light polluted sky visible and almost zero other artificial light like being able to see a light bulb or a patch of ground lit by a light bulb or a patch of ground lit by a patch of ground lit by a light bulb. It couldn't have been more than magnitude minus 6 when that low. Some people say Jupiter is a shadow-producing object when it's dark enough, that would be magnitude minus 2. Sagittarian Milky Way (talk) 00:54, 30 January 2020 (UTC)[reply]

A supernova can be absolute magnitude minus 20 so 18 magnitudes would be "9 magnitudes further away" or 4,000 times 10 parsecs which is too close for a Magellanic Cloud and too far for the furthest part of the young star disc which you can't see anyway due to dozens of magnitudes of interstellar extinction. The sample size is very low but our list of supernovae gives some idea of what is realistic as sightlines with less galactic dust tend to have less supernovae. Sagittarian Milky Way (talk) 01:40, 30 January 2020 (UTC)[reply]

To explicitly state something for clarity's sake, a supernova's naked-eye brightness from Earth depends not only on its distance but its intrinsic brightness—which astronomers describe as absolute magnitude—in the visible spectrum. This is of course the case for all astronomical objects. There isn't one fixed distance. This is why apparent magnitude is used to describe an object's brightness as observed from Earth. Shadow helpfully tells you that an object has to have an apparent magnitude equal to or less than -4 to cast shadows. --47.146.63.87 (talk) 02:49, 30 January 2020 (UTC)[reply]

-4 seems about right (eagle eyed freaks excepted) Sagittarian Milky Way (talk) 04:24, 30 January 2020 (UTC)[reply]

We can ask an analogous question that does not need a definition of shadow casting: at what distance would a nova be as bright as the full moon? The apparent magnitude of Betelgeuse going supernova is estimated to be −12.40, at a distance of 700 ly. The apparent magnitude of the full moon is, under ideal circumstances, −12.90. A value of −11 may be more realistic. So a Betelgeuse supernova will be slightly dimmer than an ideal full moon, but brighter than a more typical full moon. --Lambiam 06:46, 30 January 2020 (UTC)[reply]

Interesting! 40,000 pc even in unrealistic conditions is quite a bit more than I expected. 89.172.78.189 (talk) 08:12, 30 January 2020 (UTC)[reply]

1 ly = 0.3066 pc. 700 ly = 214.62 pc. --Lambiam 19:49, 30 January 2020 (UTC)[reply]

January 30

Car rolling down slope

If I park my car on a slope and don't apply the handbrake, if the gradient is steep enough, it will eventually start rolling because (as I understand it, but correct me, I'm no scientist) the forces exerted by gravity overcome friction/inertia.

However, if I park on a slope that's fairly gentle, there seems to be a delay before the rolling kicks in.

What is it that is happening during the interlude that turns lack of movement into movement? Why doesn't it start rolling immediately? Presumably gravity and friction are constant during that time. Let's exclude outside factors like wind. --Dweller (talk) Become old fashioned! 13:58, 30 January 2020 (UTC)[reply]

If we exclude outside factors like wind, then there is no movement. Wind is often the culprit in such situations, as if there is a stable equilibrium between static friction and gravity, there would need to be some outside force (wind, a cat rubbing up against it, a bird landing on it, etc.) to upset that equilibrium. Be aware that static friction is always greater than moving friction (such as rolling friction or sliding friction), so there only needs to be just enough force to get it moving, from that point gravity is sufficient to do the rest. Simply put, if a stationary car starts moving, it is absolute proof that there IS some "outside factor like wind." that got it started. --Jayron 32 15:01, 30 January 2020 (UTC)[reply]

If the slope is steep enough, a wheeled device without brakes is likely to start rolling immediately. The next question might be, what is the threshold for sufficient steepness for that rolling to start? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:08, 30 January 2020 (UTC)[reply]

It's hypothetically calculable, but there's a LOT of variables to consider, including (but not limited to) size and type of tires, mass and shape of car, type of pavement, is it wet or dry, if it is windy or not, how much friction there is in the car axles, etc. etc. --Jayron 32 15:28, 30 January 2020 (UTC)[reply]

So various friction components, assuming stability otherwise, could be enough to keep it from going anywhere when there's only a shallow slope. Analogous to a shopping cart. If the pavement is sufficiently close to being level, the cart will stay put during unloading. If it's steep enough (even a few degrees), it will start rolling unless you constrain it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:40, 30 January 2020 (UTC)[reply]

That's true, but it is true of any object, not just a car. If you were standing on the ground, and the slope suddenly started to increase, you could maintain your position until the force of gravity overcame the friction between your shoes and the ground, and which point you'd start sliding down the hill. --Jayron 32 15:45, 30 January 2020 (UTC)[reply]

For sure. The difference is that you can adjust your posture to try to keep from sliding. An inanimate object can't do that. The OP's original statement that "the forces exerted by gravity overcome friction/inertia" is not blanketly accurate. It's only true when the slope is sufficient for the force of gravity to take over. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:49, 30 January 2020 (UTC)[reply]

Not really, You can adjust your posture to keep from falling over, but no amount of posture adjustment will have a significant impact on the friction between your shoes and the slope, and once you start sliding, you ain't stopping. --Jayron 32 15:51, 30 January 2020 (UTC)[reply]

That would again depend on the steepness angle. Although if you insist on trying to stay on your feet in that situation, as opposed to falling backward and changing your situation, it's probably as you said. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:59, 30 January 2020 (UTC)[reply]

The tires don't immediately deform if the tendency to roll is slight. It may take a moment for tire deformation to take place, and once tire tire deformation has taken place, inertia may now become a force favoring motion whereas inertia when the car was first stopped would tend to favor a body remaining at rest. Deformation of the tires is an important prerequisite of a rolling automobile. When you initially brought the car to a stop you used the normal foot brakes to bring the car to a stop. At that point the deformed tires are essentially a wheel chock, if the forces favoring a rolling motion are slight. "[A] rubber tire will have higher rolling resistance on a paved road than a steel railroad wheel on a steel rail." Bus stop (talk) 16:40, 30 January 2020 (UTC)[reply]

Let's not fall into the trap of assuming that a modern manufactured road-legal automobile is made of four simple wheels that are rigidly connected to simple axles... these machines are complicated.

Among the factors to consider, we have a suspension, a complex axle and/or independent suspension, the differential, ... not to mention the drive coupling stuff like the clutch and the transmission ... and we have bearings and automotive-grade lubricants... and nowadays there are active control systems ... if we were to try to model the torque or the transient response of the wheels, it would not be a simple curve like the ones you see in our articles on friction.

Before you dive into any analysis, it might be good to start with an introduction to modern automobile design. Here's a book you might find at your local library: Automotive Technology: A Systems Approach.

Nimur (talk) 16:43, 30 January 2020 (UTC)[reply]

You're not on a flat slope, you're on a tiny mountain range. It's lumps and bumps.

If you roll an infinitesimal amount on a smooth slope, you're going to the bottom (however slowly).

However if you wobble a bit on a rough slope (and with deformable tyres) you might have the momentum to roll a bit further (i.e. to potentially go all the way), except that this might not be enough to get past the next minor lump of gravel, or tyre tread block. So you stop. Wobble a bit harder (even just bouncing vertically up and down, as many kids left in cars have found) can be enough to get over that step. If you've the momentum to get over the first representative hump, and there's a slope to gain a little bit more, then you've probably got enough to get over the next. Then the next (unless it's appreciably bigger) and on it goes. Andy Dingley (talk) 16:51, 30 January 2020 (UTC)[reply]

The questioner is no doubt aware of the greater complexities involved. But they only mention parking the car, which means bringing it to a stop, and not applying the handbrake. They are asking why, if it eventually rolls, does it sometimes not start rolling immediately. Yes, wind may be a contributory factor, as Jayron32 says, but I find that Rolling resistance gets more to the heart of the matter on a theoretic level. An inflated tire is deformed when the car is at rest. It doesn't have the minimized rolling resistance of "a steel railroad wheel on a steel rail." Bus stop (talk) 16:58, 30 January 2020 (UTC)[reply]

"Parking doesn't mean the handbrake" is only in North America (and influences). It would be a specific fail on the UK driving test to do that, even for relatively short stops, much shorter than parking. Andy Dingley (talk) 17:03, 30 January 2020 (UTC)[reply]

But nobody said "Parking doesn't mean the handbrake". To bring the car to a stop they used some sort of brake. Maybe in some parts of the world they use differently-activated braking systems than in my dysfunctional part of the world. We are known to use antiquated inertia resistors. But the point is that after bringing the car to a stop, no permanent or long-lasting braking system was applied. Therefore this question is essentially about a delayed reaction and what could cause that delayed reaction. If rolling eventually transpired but was not immediate, we need to look for factors that can lie dormant for awhile. Bus stop (talk) 17:19, 30 January 2020 (UTC)[reply]

The OP said "If I park my car on a slope and don't apply the handbrake" which seems a clear enough statement that they're referring to a situation where someone parks the car but whether by accident or intention does not apply the handbrake and there is no suggestion this is normal or acceptable. You said "But they only mention parking the car, which means bringing it to a stop, and not applying the handbrake." which is fairly confusingly worded. It can easily be read to suggest you think applying the handbrake is not a normal part of parking the car. But Andy Dingley is correct in a lot of of the world applying the hand brake is a part of parking the car. Not doing so would for example, generally be a fail in a driving test. It doesn't matter if the car is an automatic or manual. Nil Einne (talk) 05:43, 31 January 2020 (UTC)[reply]

P.S. Although I stick by my above comments, in NZ at least I think it's rare you'd fail from not applying the hand brake for parking since there's no real opportunity to assess it. When start your test, you get into the car first so the instructor can check the lights etc. So even if you forgot to apply the hand brake, the testing officer will probably simply consider it's possible you've been a bit too enthusiastic and taken off the hand brake already. (And you aren't necessarily the person who parked the car anyway.) Likewise while a reverse parallel park is generally a standard part of the modern restricted test, I don't think it's the norm to penalise you for not applying the hand brake at the end of it. Since it's understood you'll be driving off soon, I think they won't care if you don't apply it, although it's probably a good idea. (Also if the officer asks you if you've completed your parking manoeuvre, I would make sure the hand break is applied and even put the car on park for an automatic or an appropriate gear for a manual.) During the test, I think you're generally asked to park after the first stage of the test while the officer checks if you're eligible to proceed onto the next portion. But again, since you're going to move on I think they won't care if you don't apply the handbrake although again, it's probably a good idea. Especially since I think this is when they'll also tell you if you failed the first portion and you don't want to accidentally move if you're emotional and release the footbrake a bit too much, especially in an auto. At the end of the test, you'll drive back to the centre and park. This is again where you'll be told if you passed or failed. But AFAIK, this is generally done from within the car. I'm not totally sure if these sort of things [1] means they sometimes get out of the car. But even so, by this stage they've basically already passed or failed you. So considering the stress of the situation, I wonder if even if you get out of the car without applying the hand brake before they told you you've passed, they'll actually let you off if the car isn't likely to roll off (e.g. an automatic on park or a manual with wheels facing the curb and gear in the opposite direction of any slope). I mean possibly they won't even notice. During the test, if you don't use the hand brake during a hill start especially in a manual and roll backwards this generally be enough for a fail, but that's a specific problem and often not related to parking per se. I had a quick look for comments and couldn't actually find any suggesting the UK is that different. I.E. it's accepted as standard part of parking the car, but simply not really assessed. Nil Einne (talk) 07:14, 31 January 2020 (UTC) [reply]

As a UK driver, let me assure you that failing to apply the handbrake when stopping the car, either at traffic lights, in 'stop-start' traffic conditions, when parking temporarily before and after the "reverse round a corner" exercise, or at the end of the test, will result in or at least contribute towards a failure. Driving itself is inherently stressful (as is taking a test of any kind), especially for a novice, and demonstrating that one can competently and reliably do so without creating potential or actual hazards for other road users (including pedestrians) is the main purpose of the test. Examiners actively look for the evidence of one's competence, and the fact that some experienced drivers know when they can safely deviate from driving-test protocols does not excuse the testee from having to demonstrate all the required skills and knowledge. {The poster formerly known as 87.81.230.195} 90.205.58.107 (talk) 10:35, 31 January 2020 (UTC)[reply]

The thing which is stopping the car from accelerating is friction ; if the friction is greater than the net force the car will not move at all. However, the friction is not a constant: it may start high enough to prevent acceleration but then start to drop due to, for example tyre deformation or cooling. As soon as it drops below the critical threshold acceleration can start and the previously stationary car will move. 2A01:E34:EF5E:4640:2C0A:BBF1:8583:7297 (talk) 18:38, 30 January 2020 (UTC)[reply]

Inertia is not a force and does not play a role in the car remaining stationary or starting to roll. As indicated by several earlier posters, we have the gravitational force, static friction, and possible outside forces such as wind force. If the car was initially stationary (at rest for more than an infinitesimal period) and then starts rolling, an initial equilibrium most have been disturbed. ("I sense a disturbance in the Force.") Leaving loading/unloading the car and earthquakes and such out of the considerations, a change in the gravitational component is unlikely. Either the static friction has decreased or the net outside force has increased. Lacking such changes, the car will remain at rest. What may happen is that the motion of the car in the first few seconds, although not zero, is so low that it is not perceived. --Lambiam 20:22, 30 January 2020 (UTC)[reply]

There are other factors that could dampen incipient motion but the most obvious one is the necessary deformation of the tires for rolling under the weight of the car. Bus stop (talk) 21:38, 30 January 2020 (UTC)[reply]

I agree with Bus stop. The element missing from the earlier analyses was the time-dependent properties of rubber tires. The phenomenon under discussion is not observed in vehicles with steel wheels, operating on steel rails. Dolphin (t) 08:54, 31 January 2020 (UTC)[reply]

Wouldn't deformation of the tyres tend to increase friction? --Lambiam 09:29, 31 January 2020 (UTC)[reply]

@Lambiam: Friction is a force and most forces are instantaneous responses to their drivers, and remain of constant magnitude whenever the driver is constant. My reply is alluding to time-dependent properties of some materials, where the force exerted by the material is not constant over time even though the driver is. This is an inadequate explanation, I know, but I don’t see an article that goes directly to the matter. Hysterisis hints at material properties that are time-dependent or non-linear so it might be helpful. Another illustration is to contemplate crunching a sheet of paper into a compact ball and then watch it over the next few minutes. Over time, the compact ball of paper will slowly open up and expand in volume even though no external force is forcing it to do so. As the paper ball opens it may do so asymmetrically so that it suddenly topples and rolls a short distance until it finds a new equilibrium position. I hope this helps. Dolphin (t) 00:46, 1 February 2020 (UTC)[reply]

Thanks all, interesting stuff. So it seems that the factor(s) I was looking for was tyres deforming (possibly around lumps and bumps on the road surface). Thank you. And thanks to my invisible friend who emailed. --Dweller (talk) Become old fashioned! 09:15, 31 January 2020 (UTC)[reply]

Looking for a chemist who has seen Dark Waters

One day ago, I undid this addition because of WP:V and WP:OR. The user logged out and reverted me and made some minor modifications. As the film is not yet running in Swiss cinemas, I can't verify the doubted claims. Is there any chemist (or natural scientist) around who has seen Dark Waters (2019 film)? --Leyo 21:18, 30 January 2020 (UTC)[reply]

I haven't seen the film, but I suspect that what you reverted was mostly right. However I have not checked references to see if this is original research or others commented this about the film. Certainly the statement "perfluorooctanoic acid (PFOA-C8) is ... also known as Teflon" is wrong, but if it is in the film as stated then it is OK to include. However I think it would be important to have a statement in that article that points out the errors in the film. Otherwise readers of our article may believe it is true, and take inappropriate personal actions. The reference [2] points out some errors in the film, but that does not mean that it identified all of them! Graeme Bartlett (talk) 21:58, 30 January 2020 (UTC)[reply]

PFOA certainly isn't Teflon!

It's on the list of "Well of course you wouldn't want any exposure to that!" chemicals, so there's relatively little studied about it, because of course no one would dump it into the environment. But then the US standards are so lax, du Pont went and did so. Andy Dingley (talk) 00:03, 31 January 2020 (UTC)[reply]

I am well informed about the case (I've seen The Devil We Know, read the NYT feature etc.) and very well about PFOA. I'm asking about the actual content of the film. It is likely that certain simplifications are made in the film, as the target audience are not chemists. This might have been done with more or less factual errors. BTW: I had mentioned the reference linked by Graeme Bartlett in my edit summary. --Leyo 09:58, 31 January 2020 (UTC)[reply]

Have a quick look round the auditorium and see of they're all wearing lab coats and protective glasses? Martinevans123 (talk) 10:20, 31 January 2020 (UTC) [reply]

Muscle twitches before sleep

A person who is trying to get to sleep may experience an involuntary muscular twitch or spasm of varying intensity before nodding off. Is this a scientifically recognized phenomenon and if so what is the term for it? Freeknowledgecreator (talk) 22:27, 30 January 2020 (UTC)e[reply]

Hypnic jerk. Although yes, that does sound like a dance from the 1960s. Martinevans123 (talk) 22:33, 30 January 2020 (UTC)[reply]

Also check out Exploding head syndrome, which is fortunately not quite so alarming as it sounds (I speak from experience). {The poster formerly known as 87.81.230.195} 90.205.58.107 (talk) 10:39, 31 January 2020 (UTC)[reply]

Almost as nice as a goodnight kiss. Martinevans123 (talk) 10:49, 31 January 2020 (UTC) [reply]

January 31

Triple point of water

Is a slush of ice in water an example of water at it's triple point? We clearly have both solid and liquid water present, and the vapor pressure of water will certainly be non-zero, so doesn't that fulfill the criteria of being at the triple point (having 3 phases present together)? Am I correct to assume that the temperature of the slush and the vapor pressure will tend to the triple point values for water (0.01°C and 0.006atm)? 139.194.157.157 (talk) 11:11, 31 January 2020 (UTC)[reply]

Your example demonstrates the coexistence of solid and liquid phases at 1 atmosphere pressure, and a temperature slightly lower than that of the triple point. Dolphin (t) 11:24, 31 January 2020 (UTC)[reply]

No, to be at the triple point, the phases have to be more than just coexisting at the time. They need to be in equilibrium, which is to say that if left alone, they need to remain at the same relative amounts. If you leave your mixture for an extended period of time, if the water is evaporating or if the ice is melting in the slush, it is not at equilibrium. If you come back in an hour, and some of the ice has melted, you were not at equilibrium and you were thus not at the triple point. The triple point is defined by this behavior, so you actually have to have a temperature of exactly 0.01 deg C and 0.006 atm. You also need to have a system which is at thermodynamic equilibrium, which is to say it is a closed system with no internal temperature or pressure gradients, thus the entire container holding the ice, water, and vapor would need to be at 0.01 degrees C and 0.006 atm, and well insulated from its surroundings. At room pressure and room temperature, you are NOT at those conditions. --Jayron 32 14:31, 31 January 2020 (UTC)[reply]

The above is correct except for if the water is evaporating. There is a subtle difference between evaporation and boiling. Evaporation: for any condition (temperature/pressure/etc.) where liquid is present, there will be a small but nonzero amount of gas phase; at equilibrium its partial pressure is equal to the vapor pressure. Boiling: the liquid phase can be less stable from an enthalpy point of view, and completely transform into the gas phase, depending on the temperature and (total, not partial) pressure. Boiling is what defines the triple point. Tigraan^{Click here to contact me} 14:52, 31 January 2020 (UTC)[reply]

Yes, of course. Thanks for the correction. --Jayron 32 17:40, 31 January 2020 (UTC)[reply]

Boiling happens when the vapour pressure equals that of the ambient atmosphere. So, there is no connection between the boiling of water and the triple point. Ruslik_Zero 19:53, 1 February 2020 (UTC)[reply]

See Triple point of water which is a stable equilibrium that occurs only at 0.0075 °C and 0.00603659 atm. That is the minimum pressure at which liquid water can exist. DroneB (talk) 15:53, 31 January 2020 (UTC)[reply]

String vibratio

A string is stretched between two supports such as the bridge and nut of a guitar. If the fundamental frequency sting is f, ant what frequncy doesc the bridge (or nit) vibrate, and why?86.8.201.66 (talk) 14:36, 31 January 2020 (UTC)

The diagram shows the string vibration frequency components. Their relative amplitudes vary depending on where the string was plucked: for a clear musical note pluck at the center of the string, for a "tinny" sound that is mostly high harmonics pluck near either end of the string. On a Guitar (see article) the upper end support is either the nut (open string) or a fret chosen by the player's finger. The lower end support is the bridge which on an acoustic guitar is mounted on a flexible soundboard that couples the string vibrations to the surrounding air, producing sound. An electric guitar instead relies on one or more magnetic pickup(s) to convert the vibrations of its steel strings via electronic amplification to sound. Different pickup positions along the strings give sounds with different harmonic content. The initial "attack" sound of a plucked guitar string is a burst of many frequency components as the mechanical impulse travels away from the pluck position and it is subsequent reflection of the impulse from the end supports that augments the standing wave frequencies shown. DroneB (talk) 15:33, 31 January 2020 (UTC)[reply]

no I'm interested in the cyclical variation in forces on the bridge, by which the sound is transmitted to the body. At what frequency are these forces?

86.8.201.66 (talk) 18:06, 31 January 2020 (UTC)[reply]

They are at the same frequencies as the vibrating string. --Lambiam 18:38, 31 January 2020 (UTC)[reply]

Show me how and why please.86.8.201.66 (talk) 21:04, 31 January 2020 (UTC)[reply]

If you look at the shape of the vibrating string you'll see near the bridge it is operating at an angle. The string has a tension in it, so it is applying a force at that frequency to the bridge. The vertical component will be T*sin(theta) where theta is the angle of the string to the bridge, zero being flat. There may be other effects. Greglocock (talk) 05:08, 1 February 2020 (UTC)[reply]

For the how and why, see Vibration#Forced vibration with damping: "The result states that the mass [that is, the body. --L.] will oscillate at the same frequency, f, of the applied force [by the vibrating string. --L.], but with a phase shift

\phi .

" This is a somewhat simplistic model, but if you look at the section Multiple degrees of freedom systems and mode shapes further down, the generic solution

{\begin{Bmatrix}x\end{Bmatrix}}={\begin{Bmatrix}X\end{Bmatrix}}e^{i\omega t}

implies that all components vibrate with a combination of vibrations at the same set of frequencies (found by the eigenvalues of the equation). If the string vibrates at a combination of multiples of some fundamental, the harmonics, then so will the neck, bridge and soundboards, with the same fundamental. The higher partials need in fact not be perfect harmonics, but if the guitar has a nice sound to it, they are apparently close. --Lambiam 09:55, 1 February 2020 (UTC)[reply]

February 1

Hydrogen peroxide and white fingers

Goodmorning. Why the common disinfectant hydrogen peroxide 3% make temporarily the fingers white? What happened in our skin, is it a chemical reaction?

Thank you very much for the attention--87.7.92.114 (talk) 12:11, 1 February 2020 (UTC)[reply]

This is complicated, as a lot depends on the concentration, the exposure time and the state of the skin (oily skin resists better).

Hydrogen peroxide is a powerful oxidiser, even in a weak 3% solution. It has several effects, some of which aren't oxidation. It also acts as a dewatering agent (water in a substance will preferentially bond to the H₂O₂, rather than the previous substance). Much of the oxidation is seen as a 'bleaching' effect.

By 'skin' here, you may mean the epidermis of the skin, rather than the dermis beneath. This is sometimes described as a 'dead' layer, but that's wrong - what it means is that there's no blood supply within it (the dermis has a blood supply), and the layer must be nourished just by permeability through it. The very outer layer of this is the stratum corneum, made of corneocytes - skin cells which have lost much of their normal cell contents and have also become keratinised (I'm simplifying a lot). They do though still contain a lot of water (if they lose this, you get dry, cracked skin).

Many substances, including skin, are transparent in close up, because they are water-filled cells which have a similar refractive index all the way through. There are many cell boundaries, but these aren't visible. Microscopy might need to use phase-contrast microscopy to see them. If they lose this consistency though, they stop being transparent and become translucent or opaque, usually white (there's nothing to colour them) because light can no longer pass through an optically consistent medium, but it starts to get scattered on the boundaries. Physically, the first effect we see from weak hydrogen peroxide on clean skin is no more than a dewatering effect. Just like dry skin otherwise, the epidermis now becomes white and opaque. If you expose skin in some places (the palms, finger tip pads, or sometimes the soles of the feet), that skin also has a layer, the stratum lucidum, beneath the corneum which displays this effect even more obviously. This effect is mostly reversible with a skin moisturiser, or just washing with water. The effect here is mostly physical, rather than a chemical reaction (it's removing free water, not reacting with the skin).

If you have a longer exposure, more concentrated hydrogen peroxide, or a deeper exposure (such as an abraded or cut surface) then you might see its effects on the dermis. The effects here can start to become more serious, especially if the peroxide is concentrated. it may cause permanent effects (which may heal over time, or may even form permanent scars, like a burn). 30% peroxide (hairdresser grade) is enough to do this. The physical effects can be supplanted by real chemistry. Anything which involves oxidation within the dermis counts as a chemical burn, won't be reversible within minutes and would need to heal long-term, if it can.

It can be nasty stuff, if you go over the 3% region! Andy Dingley (talk) 14:41, 1 February 2020 (UTC)[reply]

(edit conflict) "Many workers have noted that inadvertent skin contact to the more concentrated solutions [of hydrogen peroxide] causes white spots which spontaneously disappear within some hours; the change of colour is due to formation of oxygen microbubbles in the skin". [3] Alansplodge (talk) 14:46, 1 February 2020 (UTC)[reply]

I've had this happen to me (with 50%). But in terms of WP and RS, Hydrogen peroxide#Adverse effects on wounds concurs. Its cited website sounds more WP:SECONDARY than the case study you mention, but the archived content of its link does not mention this idea and the current target of the link only goes to a list of documents (uncertain which if any would be relevant). Seems like a ripe chance for WP:RD to lead to an article improvement:) DMacks (talk) 19:03, 2 February 2020 (UTC)[reply]

diagnosed without symptoms

I don't understand. "A 10-year old boy was diagnosed with the coronavirus despite showing no symptoms." How could the "10-year old boy [be] diagnosed with the coronavirus despite showing no symptoms"? Bus stop (talk) 18:44, 1 February 2020 (UTC)[reply]

More detail. He was tested because his relatives showed symptoms. --Wrongfilter (talk) 19:13, 1 February 2020 (UTC)[reply]

"The 10-year-old boy’s lungs were also scanned 'on the insistence by the nervous parents' and showed signs of infection, which was confirmed by swabs of the back of his nose and throat. That meant he was capable of transmitting the virus even though the kind of tests used in airport screening for the virus would not identify him as a carrier." So then why is a 14-day quarantine necessary for all Americans traveling from Wuhan to the US, beginning February 2 2020 at 5 pm eastern time? If there is a test—lung scans plus swabs of the nose and throat—wouldn't that obviate the need for all travelers to be quarantined? ("The United States government declares a public health emergency due to the coronavirus, and is closing its borders to all foreign nationals 'who pose a threat of transmitting the virus from entering the country and would quarantine U.S. citizens returning from Hubei province in China, the epicenter of the outbreak, for up to 14 days,' starting Sunday, Feb. 2 at 5 p.m.") Bus stop (talk) 19:27, 1 February 2020 (UTC)[reply]

The test would obviate the need for a quarantine only if it were (close to) 100 per cent reliable and never showed any false negative. Presumably that is not the case. --Wrongfilter (talk) 19:42, 1 February 2020 (UTC)[reply]

"Presumably" that is ruling out governmental overreach. Bus stop (talk) 19:44, 1 February 2020 (UTC)[reply]

Better safe than sorry. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:56, 1 February 2020 (UTC)[reply]

Symptoms = coughing, fever, that sort of thing. Test positive = the virus is detected by a throat culture, blood test, or whatever, showing that the person is infected. Incubation period = time between infection and when symptoms appear. For coronavirus this appears to be around 5 days according to news reports I saw yesterday. For HIV it can be months or maybe years before seroconversion. There isn't any contradiction between being infected and not showing symptoms. Just like there is no contradiction between a fire in your house (a cigarette butt is smouldering in the wastebasket) and it not yet being big enough to see flames coming out the windows from outside. 2601:648:8202:96B0:0:0:0:E118 (talk) 01:31, 2 February 2020 (UTC)[reply]

I asked How could the "10-year old boy [be] diagnosed with the coronavirus despite showing no symptoms"? but I didn't say there was a "contradiction". Bus stop (talk) 01:43, 2 February 2020 (UTC)[reply]

There are lots of ways to do diagnostics. I was recently diagnosed with strep even though I didn't have a sore through a rapid test. My wife had a rapid influenza A test positive, even though her symptoms didn't match standard flu. In both cases, we had rapid antigen tests. There are also antibody tests, and various forms of nucleic acid tests, such as PCR. None of these tests require the expression of standard symptoms (or symptoms at all) for positive diagnosis of infection, including viral. According to the CDC, coronavirus testing is currently a form of nucleic acid test called a Real-Time PCR test. This essentially confirms the presence of coronavirus by detecting its genome within a sample. This is a pretty accurate methodology, and as with all NAT testing, is not at all dependent upon symptom expression. --OuroborosCobra (talk) 01:52, 2 February 2020 (UTC)[reply]

If it is a "a pretty accurate methodology" why quarantine people for 14 days? Bus stop (talk) 02:00, 2 February 2020 (UTC)[reply]

It depends what "pretty accurate" means. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:36, 2 February 2020 (UTC)[reply]

Well, first off, you need quarantine for those that test positive. The 10-year old you started this conversation about tested positive even though they were asymptomatic. That would seem to be the point, we cannot quarantine based just on symptom expression or field tests at airports. RT-PCR is an intensive lab based testing technique and cannot be done at airports as passengers come off of planes. It can take hours or even days to get results. If we wait for the RT-PCR result before doing a quarantine, we are going to lose people to the general population and expose people in the general population while waiting for a test result. That doesn't sound terribly effective to me. Additionally, while NAT techniques are generally quite accurate, that accuracy is dependent upon access to genetic primers for the testing, and the quality of those primers. They need to be unique enough that non-coronavirus DNA sequences won't give a false positive, but generalized enough that small mutations in coronavirus won't result in false negatives. This actually isn't as easy as it sounds. The way to reduce the chance of mutations resulting in primers not working is to use conserved sequences of DNA, or, sequences that are so vital for function that small mutations generally result in organism non-viability and death, and so natural selection tends to preserve the conserved sections of DNA. This is a double-edged sword, however. Use a conserved genome for, say, an enzyme that is part of the citric acid in one bacteria, and you may find that your primer gives you false-positives for almost any bacteria outside of e Coli. It is not a simple task to find a primer that is both generalized and unique enough for NAT testing. We are dealing with a 2-month old outbreak, so the quality of our primers (we hope) is good enough, but with this short a time for testing, we have to be open to the possibility that our NAT testing method is currently insufficient. --OuroborosCobra (talk) 18:09, 2 February 2020 (UTC)[reply]

Maybe it's also worth remembering that while the time between exposure and when the virus can be reliably detected with RT-PCR is likely to be shorter than when symptoms show, it's not going to be instantaneous either. So if you concerned the people might have been exposed a few hours ago, you're still likely to want quarantines even if you had a test which gave instant results. (If you're concerned because someone just came from China and you fear they could have been exposed somewhere in China these concerns may apply up until their flight, and probably even on their flight.) And given our current state of knowledge of the virus, any estimates of when you can expect reliable detection are likely to be on the conservative side. Also, while I think testing facilities in most developed countries aren't stretched at the moment, they may not be able to easily cope with a significant increase. And even if they could, you may still want to consider the utility of who you choose to test. Remembering also that for the reasons mentioned before, you're probably going to need to collect specimens from people while they are self-quarantined, rather than simply at the airport or whatever. (While the techniques are something quite a few labs could perform, the number you trust to do it is often small, e.g. in the US it's only CDC Atlanta [4] [5]. In the event of a nationwide outbreak, together will likely need significant testing capability but this doesn't mean it makes sense to start doing it already, instead of just planning and preparing.) Self quarantine may be somewhat disruptive to the people affected, but it may very well be that doing 14 days of self-quarantine rather than 5 days (random estimate) but with all the costs for testing etc is seen as the best solution. (In the US, I've seen reports the self-quarantine will be 'monitored' [6] but I'm not sure if this means people visiting, it may simply be phone calls etc with visits only if there are concerns.) Nil Einne (talk) 02:06, 3 February 2020 (UTC)[reply]

Here's an interview with a virologist some might find informative. One point they make is that self-reporting of symptoms is far from 100% reliable. Mild symptoms especially can easily be ignored or assumed to be from allergies, lack of sleep, etc. --47.146.63.87 (talk) 09:39, 2 February 2020 (UTC)[reply]

February 2

What is a jumbo octopus?

I couldn't find a Wikipedia article that used the term. Here is where I saw the term.— Vchimpanzee • talk • contributions • 18:52, 2 February 2020 (UTC)[reply]

You misread the cartoon lettering. The term is "Dumbo octopus" and the article is Grimpoteuthis. Cullen³²⁸ Let's discuss it 18:58, 2 February 2020 (UTC)[reply]

Thanks. There's something wrong and the letters are hard to read.— Vchimpanzee • talk • contributions • 19:22, 2 February 2020 (UTC)[reply]

Finally had to resort to CTRL+. I don't know what the problem is today.— Vchimpanzee • talk • contributions • 20:21, 2 February 2020 (UTC)[reply]

(ec)Dumbo octopus. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:59, 2 February 2020 (UTC)[reply]

And Dumbo was inspired semi-indirectly by the famous elephant Jumbo. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:03, 2 February 2020 (UTC)[reply]

February 3

HIV antivirals kill coronavirus?

What is your opinion of [7]? EllenCT (talk) 05:56, 3 February 2020 (UTC)[reply]

This desk is not for opinions, especially not on medical issues. --142.112.159.101 (talk) 07:01, 3 February 2020 (UTC)[reply]

Without giving opinions, there is a fair amount of data indicating cross-effectiveness of antiviral drugs. That's just statistical though: they may have gotten lucky with that one patient. I even saw something about HIV antivirals helping against drug-resistant bacterial infections, which seemed bizarre to me (I'll see if I can find the reference later). 2601:648:8202:96B0:0:0:0:E118 (talk) 11:31, 3 February 2020 (UTC)[reply]

Fortune also has something about that Thai treatment, mentioning that an RCT has started.[8] 2601:648:8202:96B0:0:0:0:E118 (talk) 12:05, 3 February 2020 (UTC)[reply]