Wikipedia:Reference desk/Archives/Science/2018 May 30

= May 30 =

Date of "power-is-over" ?
If you look at the picture after expanding itMost probably the lowest line printed on the box (i.e. 6.11.2002) is a date. Is it to warn that by this particular date the powder will loose (or start loosing) it's power as a propellant ? Jon Ascton   (talk)  08:31, 30 May 2018 (UTC)


 * Or is it the date it was packaged? --76.69.118.94 (talk) 10:14, 30 May 2018 (UTC)
 * The VihtaVuouri website advises "DO NOT KEEP OLD OR SALVAGED POWDERS. Check old powders for deterioration regularly. Destroy deteriorated powders immediately." without qualifying how long after the datestamp is regarded as "old". DroneB (talk) 10:48, 30 May 2018 (UTC)


 * Its power may even increase with storage. A powder with large grains can suffer from damage where the grains start to break up, thus increasing their surface area. Although their energy might reduce with age, their instantaneous power, and their initial chamber pressure, can be increased by the increased burning rate of their increased surface. Andy Dingley (talk) 11:03, 30 May 2018 (UTC)
 * Well, the OP did ask if it would loose its power... AndrewWTaylor (talk) 11:44, 30 May 2018 (UTC)

How important is sleep for being able to concentrate well?
Almost all sources will point to the importance of sleep to perform well in mentally demanding tasks. However, there are a few examples of people who didn't need much sleep:

John Wallis "Another aspect of Wallis's mathematical skills was his ability to do mental calculations. He slept badly and often did mental calculations as he lay awake in his bed. One night he calculated in his head the square root of a number with 53 digits. In the morning he dictated the 27-digit square root of the number, still entirely from memory. It was a feat that was considered remarkable, and Henry Oldenburg, the Secretary of the Royal Society, sent a colleague to investigate how Wallis did it. It was considered important enough to merit discussion in the Philosophical Transactions of the Royal Society of 1685."

Paul Erdős

"...he only needed three hours of sleep. He’d get up early and write letters, mathematical letters. He’d sleep downstairs. The first time he stayed, the clock was set wrong. It said 7:00, but it was really 4:30 A.M. He thought we should be up working, so he turned on the TV full blast. Later, when he knew me better, he’d come up at some early hour and tap on the bedroom door. ‘Ralph, do you exist?’ The pace was grueling. He’d want to work from 8:00 A.M. until 1:30 A.M. Sure we’d break for short meals but we’d write on napkins and talk math the whole time. He’d stay a week or two and you’d collapse at the end."

So, if quite a few people need just 3 hours of sleep to be able to concentrate well for about 19 hours a day, and they are able to keep that up for most of their lives, then why do most other people need 8 hours sleep and will only be able to concentrate well for about 6 hours before feeling drowsy at the end of the working day? Count Iblis (talk) 15:07, 30 May 2018 (UTC)
 * Very important for concentration, per this. You have confused two unrelated ideas "anecdotes" and "data."  Information about how a human works is basically useless for understanding how humans work.  That one person once did something wrong and didn't suffer for it does not mean that all of humanity should work that way.  There are two possibilities to consider here: 1) That these individuals would have been even more productive with more sleep and 2) These individuals are built in such a way as to be sui generis outliers for whom the normal rules of human health do not apply.  Trying to understand "is sleep necessary" is not understood by looking at the statistically insignificant individuals for whom it isn't, but rather for the billions for whom it is.  After all, you've only noted two data points. 2 divided by the population of the world is a number that is as close to zero as to basically be zero.  So if you're trying to decide how much weight to give to anecdotal information for a topic like this, that's your answer.  Count the number of anecdotes you have, divide by the total number of humans to have ever lived, and that will tell you how much weight to give it.  -- Jayron 32 16:20, 30 May 2018 (UTC)
 * There's also the possibility that the guy took cat-naps during the day. ←Baseball Bugs What's up, Doc? carrots→ 16:35, 30 May 2018 (UTC)
 * I'd also note that in both instances, it was remarked as to how exceptional those individuals were (i.e. it was understood that they were outside the norm). It would not be unlike using Usain Bolt to start a discussion of how fast people can run. Matt Deres (talk) 18:34, 30 May 2018 (UTC)
 * Well, it's more like someone who excels at some activity but who is also at the opposite end for the recommendations to improve on the skills for that activity. So, noting that Bolt is good at sprinting isn't a good analogy, it's more noting that a record breaker like Bolt has a lifestyle that according to experts is the exact opposite of what is needed to become an athlete. Count Iblis (talk) 13:11, 2 June 2018 (UTC)


 * For the dire consequences of total sleep deprivation, see Fatal insomnia. ←Baseball Bugs What's up, Doc? carrots→ 19:13, 30 May 2018 (UTC)
 * In that disease, caused by a prion infection arising from a mutated gene, insomnia is merely one of the several resulting symptoms, not the cause. Notwithstanding that, prolonged sleep deprivation due to external factors can indeed likely result in highly deleterious health effects, insanity, and death (as has been demonstrated using experimental animals). Published scientific descriptions of the most serious human outcomes will be hard to find because of the obvious unethicality of experimentation on human subjects. {The poster formerly known as 87.81.230.195} 90.202.160.23 (talk) 20:27, 31 May 2018 (UTC)
 * Yes. All they can do is report incidents. A few years ago National Geographic had an article which discussed it to some extent. Fatal familial insomnia is much more than simply sleep deprivation, as you indicate. But it is kind of the extreme case of what happens when you don't sleep. ←Baseball Bugs What's up, Doc? carrots→ 20:39, 31 May 2018 (UTC)
 * Note that I emphasised published because there have undoubtably been deaths from sleep deprivation used as punishment or torture by police, military, security or intelligence personnel, but those instances would have ranged from merely morally reprehensible through locally criminal on up to international war crimes (depending on the milieux), so there details have been concealed rather than studied. {The poster formerly known as 87.81.230.195} 90.202.160.23 (talk) 21:37, 1 June 2018 (UTC)


 * if someone sleeps less than you, it's difficult to estimate how much less that is, since you'll probably be at sleep when they go to sleep, and at sleep when they wake-up, but let's assume the observation is right.
 * Just because someone saw them getting only 3 hours of sleep and working 19 hours in one day, that does not mean that happened every night. They could have an extremely irregular sleep pattern. And when inspiration struck, they spent the night working like mad men.
 * Getting 3 hours of sleep is not that though and it's common for many professions. Doroletho (talk) 00:01, 2 June 2018 (UTC)


 * I think the responses you are hearing here expressing skepticism of such anecdotes bear taking to heart. Without a question, the need for sleep (and the detrimental effects when one does not get enough) will vary noticeably between individuals.  But impressionistic observations about gifted individuals are bound to suffer the same kinds of empirical defects of any anecdotes; they often get subjectively tweaked in the recollection and then further exaggerated in later re-communication.  And even if we could rely upon them as accurate testimony to the events, remember that they often present a window into a very small period of time; the effects of sleep deprivation grow markedly, the longer the habit is sustained.  Also, even if somebody was operating with above-average or even super-ordinary cognitive function in a specific task while under-slept does not mean that they would not be performing even better if they were well rested. Some people are so gifted at certain tasks (as in your Erdős example) that they are going to be quite capable of wowing the average well-rested person, or even their average well-rested colleague, even when they are not operating at peak ability (be that from exhaustion or any other cause).


 * In any event, both objectively as someone with background in the neurophysiology of cognition and anecdotally as someone who has suffered from periods of severe sleep deprivation in parts of their life, I can assure you, the impact upon focus is considerable. Unfortunately, it is impossible to quantify said impact in one figure (or even a discrete number of figures) such as your inquiry seems to contemplate, because focus, being in some respects qualia, has no direct measures or strong experimental correlates.  The best we can do is test performance on certain kinds of tasks while a subject is in a sleep deprived state and compare it against well-rested performance by the same individual (or against established baselines).  There has been a large amount of research in this area for specific tasks, but answering your question of "how much does limited sleep impact concentration" in a straightforward and general fashion is basically impossible, as you are always going to need specific context and appropriate testable proxies for the subjective experience of concentration. Snow let's rap 11:00, 3 June 2018 (UTC)

When would today's temperature in Kelvin be relevant?
In looking at Google News, it displays the daily weather in the top right corner. It defaults to Fahrenheit (probably because of the location it's displaying), but it gives me options to view it in Celsius.. and Kelvin? My understanding is Kelvin is a unit of temperature that mostly has a place in a lab setting. Why would one want/need to know the daily weather in Kelvin? Thank you for your time! RedLinkJ (talk) 15:44, 30 May 2018 (UTC)
 * When... one is in a lab? Surtsicna (talk) 15:48, 30 May 2018 (UTC)
 * Thank you for your answer! I'll try to clarify my question.  My understanding is Kelvin is useful for extreme temperatures; approaching absolute zero, for example, and that those temperatures are generally *not* reached in a natural setting where humans live.  I understand those temperatures are created in a lab setting, so how is it relevant to know it's 303 Kelvin outside when I'm working inside lab conditions, where outside temperature seems largely irrelevant? RedLinkJ (talk) 16:03, 30 May 2018 (UTC)
 * Google are a bunch of nerds. Also see furlongs per fortnight and smoots. Andy Dingley (talk) 16:11, 30 May 2018 (UTC)
 * Thank you! That was my first thought, but I admit I'm a pretty ignorant guy (but not willfully so), so I thought I'd ask folks likely smarter than me. RedLinkJ (talk) 16:20, 30 May 2018 (UTC)
 * Although I have just remembered that one of my workshop thermometers is in Kelvin. It's a K type thermocouple, typical lab thing, and it's stuck on a heated drying cabinet that I rarely use. So mostly it shows the workshop temperature. As a Brit, I use Celsius and it's something I just don't think about to convert the two. Andy Dingley (talk) 16:34, 30 May 2018 (UTC)
 * Which temperature scale you are "comfortable" with is largely a symptom of acculturation; that you find Celsius or Fahrenheit (or for that matter Kelvin) more useful is largely only a factor of the fact that you are accustomed to using that scale. Kelvin feels useless in your day-to-day life, only because you're not using it.  It's a self-fulfilling principle that any arbitrary measurement scale is only useful only insofar as it is used.  Try a thought experiment: Imagine you were only every exposed to the Kelvin scale from birth, so that was the only temperature scale you worked with on a day-to-day basis.  You would know what 300 Kelvin meant to you (what does it feel like?  How do I dress?  etc.) so you would have internalized its meaning in a personal, and non-academic, way.  Then it wouldn't feel odd to you that the weather website had a Kelvin option.  The only reason Kelvin feels awkward is its unfamiliarity.  For day-to-day use, no one scale has any inherent benefit in terms of "comfort" that a person may feel using it (benefits of one system over another are only apparent in specialized applications, which is outside of the experience of someone who just wants to know what kind of coat to wear that day).  So the answer is that Kelvin only feels unimportant to you because you haven't used it for those purposes you've used the other scales.  Fahrenheit (for example) feels "natural" to you only because it is what you are used to.  If you had learned that 300 degrees "feels" natural to humans, you wouldn't have thought to question it.  The answer is nothing inherent to humanity or nature; it is purely cultural.  -- Jayron 32 16:13, 30 May 2018 (UTC)
 * You're absolutely right, and that's the heart of my question. It isn't comfortable to me, whereas it likely is to others.  I guess another way to rephrase my question is, who would feel comfortable expressing the daily weather outside of those who use it in lab settings in Kelvin?  Kelvin doesn't indicate if there are any locations/cultures that use it in their day-to-day lives, so I believe Andy Dingley's answer above of "Google are a bunch of nerds" seems to hit the nail on the head.  RedLinkJ (talk) 16:20, 30 May 2018 (UTC)
 * That's basically it. Who could is a different question than who does.  In this case the answer to the first question is "anyone who had been so raised" and the answer to the second question is "no one".  -- Jayron 32 16:29, 30 May 2018 (UTC)
 * My understanding is Kelvin is useful for extreme temperatures (...) and that those temperatures are generally *not* reached in a natural setting where humans live. Yes, but Kelvin is still used for settings close to human temperatures. The concept of absolute zero is critical in thermodynamics; according to Thermodynamic temperature the emergence of the concept is strongly linked to the ideal gas law, which does not make sense in Celsius or Farenheit or any other scale that does not start at the "real" zero. For instance, if you want to compute the variation of pressure of a closed volume of air that you heat from (say) 20°C to 50°C (which is close-to-human bounds), the calculation makes much more sense in Kelvin; same if you want to compute the efficiency of a thermodynamic process (e.g. the Carnot cycle). Even outside the lab, this has obvious practical implications (e.g. for steam machines during the Industrial Revolution).
 * Of course, the answer to "why Google does this" is still probably "it's cheap and they are a bunch of nerds". Tigraan <span title="Send me a silicium letter!" style="color:">Click here to contact me 11:49, 31 May 2018 (UTC)
 * ...but if the hosts of that website are temperature-unit-nerds, they're temperature-unit-nerd-dilettantes at best. Kelvins are a great way to simplify certain calculations, but they're sort of ... mundane.  True thermodynamics nerds - and there are a great diversity among that group! - use a variety of units to measure temperature and heat and related properties. Steam engine nerds use Fahrenheit temperature scales, and percentages, to measure heat capacity; cloud nerds use celsius and Fahrenheit and altitude, and re-scale relative to the adiabat or to the standard atmosphere; proof testers measure heat with extraordinary precision by carefully counting individual grains of powder of number or charcoal briquettes before setting them on fire; the artful Skew-T log-P diagram demonstrates how we use units on the x-axis that are not exactly temperature in any unit scale, but are in fact a mathematical combination of the physical properties we care about, with isotherms usually splayed at a jaunty angle to make it easier to linearize the math.  And if you're tuning an internal combustion engine for performance, some of the gauges are unit-less: here's an article on Cylinder Head Temperatures and Exhaust Gas Temperatures; note that the EGT is in units of Fahrenheit, calibrated without specific numeric markings!  I'm inclined to link back to our September 2010 discussion on the physics, theory, and practice relating to measurement and units.  Sometimes, when we're using a unit-scale for practical purposes - and even if we are very concerned with the theoretical equations that model the practical behavior - our best choice for a unit-scale is "how much" the needle deflects on the gauge or dial!
 * Nimur (talk) 16:54, 31 May 2018 (UTC)
 * The EGT meter illustrated in that article is an Alcor Type K; possibly Part Number 46150 that has been calibrated at 1,600 °F. While not displayed numerically (because absolute readings in isolation are not useful) that calibration is presumably at the dot on the scale. Another version no. 46244 of the EGT meter does have a calibrated display range of 12 to 17 times °F x 100 with all values acceptable (marked green) up to a red line at 1650 °F. Such a high EGT is very unusual and can damage the turbine of a turbocharged engine. DroneB (talk) 14:20, 1 June 2018 (UTC)
 * It seems necessary to post this, assuming no one already has. --Trovatore (talk) 17:58, 31 May 2018 (UTC)
 * Ha@User:Trovatore. DMacks (talk) 04:57, 4 June 2018 (UTC)
 * In simple terms, Temperature is a measure of the thermal energy contained in an object. If you are using an absolute temperature scale, like Kelvin, the energy is proportional to the temperature in that scale.  For example, all else being equal, something at 546K (273C, 523F) has twice as much thermal energy in it as an identical object at 273K (0C, 32F).  But obviously 273C is not twice 0C, and 523F is not twice 32F.  Which is why Kelvin gets used in science - because it makes energy calculations easier.  So I guess the answer to the original question would be in "any situation where someone wants to do energy calculations based relating to the weather".  Iapetus (talk) 09:20, 4 June 2018 (UTC)
 * It is not generally true that energy is proportional to temperature, even in Kelvin. The relationship between temperature and energy is actually quite complex. In statistical mechanics, temperature is defined as the slope of the curve that relates energy to entropy. Looie496 (talk) 14:48, 4 June 2018 (UTC)
 * Science-history nerdiness: the drop in thermal capacity at low temperatures was one of the three big yet-to-solve problems of physics in Kelvin's 1900 lecture Nineteenth-Century Clouds over the Dynamical Theory of Heat and Light (the other two being the medium of light propagation and the ultraviolet catastrophe). I can find no citation but I remember that Kelvin's tone was that all these were minor problems and some effort would allow to solve all of physics once and for good. (It wasn't.) Tigraan <span title="Send me a silicium letter!" style="color:">Click here to contact me 17:00, 4 June 2018 (UTC)
 * THe natural scale of temperatures is relative to zero on the Kelvin scale. The temperature of the Earth is a balance between different effects and the change due to global warming is a quite small secondary effect on that scale though it is of course extremely important to us. A very large increase in global temperatures of 3°C would be only a 1% change on that scale. This is one of the reasons why figuring out the precise effects is difficult. Dmcq (talk) 11:19, 4 June 2018 (UTC)