The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
I believe I am correct in asserting that sphere packing of unequal spheres can sometimes result in higher packing efficiency than equal sphere packing. If spheres are atoms, it seems plausible that alloys can be denser than either constituent metal. My question: does this ever happen?--Leon (talk) 17:12, 9 October 2016 (UTC)[reply]
See Sphere packing#Unequal sphere packing. It seems fairly obvious that after the closest possible packing of equal spheres has filled 74% of the volume, it must then be possible to add smaller spheres in the empty 26% volume. A demonstration of infinite accumulation in two dimensions of successively smaller circles is Ford circles. AllBestFaith (talk) 19:23, 9 October 2016 (UTC)[reply]
It would be interesting to see if StuRat's scenario actually occurs; in reality the addition of interstitials can cause expansion. Spot checking palladium hydride up to PdH.02 (where a phase change occurs), using a unit cell density calculation, I find that the addition of hydrogen actually reduces the density from 12.0179g/cc (Pd alone) to 11.9647g/cc (PdH.02). The expansion of the lattice parameter from 3.889 to 3.895 (from the palladium hydride article) overwhelms the additional mass of the hydrogen. Additional inputs: 4 atoms/cell and 106.42g/mol Pd, 0.08atoms/cell and 1.0079g/mol H, 6.022*10^23 atoms/mol.
There is a long list of alloys that have densities greater than the mean density of the constituents, including some rather common ones such as brass and bronze. But I don't know if there are any with a density greater than either constituent. SpinningSpark23:14, 9 October 2016 (UTC)[reply]
I haven't been able to find any examples for alloys. However, if we make the question more general, I think many ionic compounds qualify. For example, NaCl is significantly denser than either sodium metal or chlorine liquid. In this case though the change in density is because the exchange of electrons changes the size of the respective atoms. Whether or not that counts probably depends on why you are asking. Dragons flight (talk) 07:09, 10 October 2016 (UTC)[reply]
I'm giving a lesson on sphere packing to a non-technical class, essentially to illustrate how, in most cases, volume cannot be used with 100% efficiency. I was hoping to include a tangible example of how different sorts of packing are relevant to understanding common experience.--Leon (talk) 07:42, 10 October 2016 (UTC)[reply]
The common example I use for close-packing of equal spheres in that context is stacking fruit at the supermarket. Everyone can see that there are spaces among the apples or oranges. And one can carefully build a primitive cubic stack that is more "see-through" (lay language for "less dense", but technically also relates to the alignment of the spaces). But if one pulls out a mid-layer fruit, the local area collapses to face-centered cubic. It's still close-packed, but the layers become more compact vertically, suggesting more complete use of space. DMacks (talk) 14:19, 10 October 2016 (UTC)[reply]
Air pressure / volume graph
Hi, can anyone locate a graph of air pressure versus volume (at room temperature) that clearly shows the situation at extreme pressures when the air becomes no longer compressible? 109.148.99.203 (talk) 17:48, 9 October 2016 (UTC)[reply]
I wouldn't think you would call it air then, as at those pressures the constituents would become solid and/or liquid, unless very hot, then it would be a plasma. StuRat (talk) 17:55, 9 October 2016 (UTC)[reply]
It is that region that I want to see. I doubt it is exactly Boyle's law instantly turning exactly into a straight line. Also, I want to know at what pressure these effects occur at room temperature. 109.148.99.203 (talk) 19:43, 9 October 2016 (UTC)[reply]
Another thing I don't understand that someone can hopefully explain. Here it says "oxygen cannot be liquified above a temperature of -119 degrees Celsius (-182 degrees Fahrenheit), no matter how much you compress it". So what happens when you compress oxygen at room temperature until the molecules are as close together as they are in liquid oxygen? What is the essential difference between the resulting substance and actual liquid oxygen? 109.148.99.203 (talk) 00:20, 10 October 2016 (UTC)[reply]
Thanks for your reply. Despite the references, I still cannot visualise the key physical distinction between liquid oxygen below -119C and oxygen above -119C that is compressed to the point where the molecules are as close together as they are in liquid oxygen. On a molecular level, what is different? Also, here it says "For the cold liquids, adding more pressure would not increase the density very much because liquids are nearly incompressible. But the supercritical fluid in the cylinder is very compressible - to a first approximation you would get ten times as much gas in the cylinder at 3000 psi as you would at 300 psi". I don't understand this at all. Why would liquid oxygen below -119C be "nearly incompressible", and yet supercritical fluid oxygen above -119C compressed to the point at which the molecules are the same distance apart as in liquid oxygen still be "very compressible"? On a molecular level it seems not to make any sense. 86.129.206.211 (talk) 17:11, 11 October 2016 (UTC)[reply]
We're getting beyond what I really know, but I don't think that supercritical fluids are infinitely compressible, there's just no sudden change in volume with a small change in pressure as would happen between a gas and a liquid. I expect that the maximum density of a supercritical fluid would be close to that of the liquid. Supercritical liquid-gas boundaries and supercritical fluid extraction discuss some properties of supercritcical fluids. Some of the references appear to discuss the thermodynamic properties in some detail, but look fairly technical.--Wikimedes (talk) 21:21, 11 October 2016 (UTC)[reply]
This might be helpful: there is a stepwise change in density going the small distance from the gas to the liquid side of the line separating the gas and the liquid in the phase diagram. As temperature and pressure increase along the line, the gas gets denser (I don't think the liquid density changes much) so the change in density gets smaller, until at the critical point the gas and the liquid have the same density.--Wikimedes (talk) 21:37, 11 October 2016 (UTC)[reply]
Where in the world did you find it? When did you collect it? What type of area was it growing in? The answers to these questions can help. If you don't get an answer here, you might try at reddit's What's this plant. SemanticMantis (talk) 14:15, 10 October 2016 (UTC)[reply]
Our electricity was out for a long time because of hurricane Mathew. I have a clock radio that runs on A/C and it says that it uses 3 watts. I put it on a UPS rated at 780 watts or 1300 VA. The battery capacity is 187 volt-amp-hours. There is a chart saying that it should provide 300 watts for 20 minutes. Since the clock radio uses 3 watts, I was figuring that it would last 2000 minutes, or over 33 hours. There is a counter on the UPS showing how many minutes of life it has with the current load and that was showing less than 6 hours. The UPS was nearly fully charged when I started using the radio and it is new - I bought it this year. Why was it lasting so much less than my calculation? Bubba73You talkin' to me?07:39, 10 October 2016 (UTC)[reply]
The UPS manufacture should take into account the inverter drain and publish the available power deliverable. That said, the inverter is going to consume some linear power regardless of the drain (OK I know that not exactly right but talking base-load here) . Most UPS's are used for short brownouts and thus prolong longtime power outages may mess up the long-term calculations based on the manufactures data sheets.. This (I think) backs up the previous comment by Greglocock . The other thing to remember, is even if the UPS is fresh out of the box. Those storage batteries may not be able to hold their indicated charge. You could consider a cheap purchase (or steal, borrow, etc,) some wire wound resistors to act as a dump for the UPS's full rated power for the purpose of which it was advertised for. Should the UPS still fall short, then return it under warranty. --Aspro (talk) 12:10, 10 October 2016 (UTC)[reply]
A clock with a cord always seemed like a truly terrible idea. By comparison, the all too clever folks at ISIS use the Nokia 105, which is cheap enough to afford in the Third World and is alleged to be able to stand by for 35 days on a single charge, and includes an AM radio. Wnt (talk) 14:36, 10 October 2016 (UTC)[reply]
The OP may be referring to a much loved and cherished Clock Radio Alarm of a style like they don't make anymore. Sure, he could get a modern, boring, equivalent that cuts to battery upon a power failure and a RRC chip to ensure that if he goes camping (off mains 60Hz grid) it will still wake him up with an accuracy of a couple of milliseconds.. But that is not what the OP is asking.--Aspro (talk) 16:14, 10 October 2016 (UTC)[reply]
Well, the way ISIS customizes them, one of those cheap little cell phones can wake you up many blocks away. :) :( Wnt (talk) 10:34, 11 October 2016 (UTC)[reply]
Aw. That's assume. They just don't make them like that any more! The modern ones are of poor build quality and all made in China now. Think yours, may have one of the National Semiconductor MM5314N series of clock chips inside (all made in the US), so consider passing it on to a grandchild as a family heirloom.--Aspro (talk) 17:59, 10 October 2016 (UTC)[reply]
Phase-locked loop digital tuning was only just being introduced at that time. My transceiver had it but is cost about £400 back then. Mind you my 1957 Pontiac Star Chief had a self-seeking radio. But there again, in bed, one doesn’t tend to move out of one local broadcast station area and into another. So there was no point in include this feature in a bed-side alarm clock. Also, even though it is a Sony, it still probably has this chip series as they were ubiquitous back then. They were duel standard. Outside North America, within a country with a 50 Hz main frequency one just shorted out pin 16 on the chip, on returning home, one simply broke the short. Unscrew the box and I bet, it has a MM5 n n n n n chip like one of these: [1] . Digital tuning … 60 years before, one had to fiddle for ages with the cat's whisker before even getting the chance to tune in. Oh, those were the halcyon days...--Aspro (talk) 21:07, 10 October 2016 (UTC)[reply]
I have two reasons for wanting digital tuning: (1) tune in more accurately to the station. Even though the one I have come on automatically is a local station, it isn't picked up very well in the house. I have to turn the radio a certain way to get it to come in at all. (It broadcasts with only 7,000 watts.) (2) during the power outage when stations were dropping off the air, I kept having to search for stations that were broadcasting information. It would have been a lot easier to find them if the tuner could scan. Bubba73You talkin' to me?02:56, 11 October 2016 (UTC)[reply]
See the problem. 7000 watts is actually quite strong and a external dipole aerial (even a cheap one that just tapes onto the wall above) works wonders for good reception. From memory though, I don't think these Sony Radios had any thing other than an internal ferrite rod. Not even a telescopic antenna. If it does, that’s easy, just hook the dipole aerial up-to that (unscrew it first and feed into the socket) . Failing that, the only other solution for a stronger signal would be to drill into the case and pass the the external aerial feed though. But at the minimum, you will need a capacitor or even a balun to match the arial to the radio. However, that dispenses with the need to turn the radio this way and that to get a strong signal. The other thing is: if your local station is broadcasting to mainly automobile audiences. The transmitters are probably vertically polarized. Domestics radios have their ferrite horizontal, so you might try standing it on edge for a stronger signal.--Aspro (talk) 13:57, 11 October 2016 (UTC)[reply]
The Sony clock radio has no external antenna and no screws for a dipole antenna. The station's transmitter is less than 10 miles away, but I can pick up stations 70 miles away better (probably a lot more powerful). We have a lot of electronic stuff in our house which may interfere with the reception. It is FM, BTW. Bubba73You talkin' to me?16:20, 11 October 2016 (UTC)[reply]
Are you thinking of the right phone? The article you linked to mentions use for making IEDs, but doesn't say anything about including an AM radio and a search also finds nothing. An AM radio is extremely rare in a mobile phone primarily I think because of antenna difficulties. By comparison FM radios are somewhat common in phones, both smart phones and classical phones, especially those targetting the developing market. Smart phones commonly rely on the earphone cord for the antenna as do some classical phones although some have a built in antenna that is sufficient. However I suspect the FM radio isn't a big selling point for IED makers. While nominally you could use that perhaps as a backup trigger AFAIK most simply rely on the mobile phone network for trigger. Nil Einne (talk) 03:08, 11 October 2016 (UTC)[reply]
BTW, the two fluorescent lights I tried on the UPS didn't work right, probably because that the output is a stepped approximation to the sine wave. Would an LED work on such a UPS? Bubba73You talkin' to me?15:33, 10 October 2016 (UTC)[reply]
USP's of the type referred to, are designed to power computers. Computers have smoothing capacitors in the internal power supply to smooth out spikes. So not surprised if your tubes “didn't work right”. If the tubes didn't work right, then it can be assumed that LED's (depending on their drivers) may also strobe. Solution: Place a electrolytic capacitor before the LED (or LED chain) and a resistor after.--Aspro (talk) 16:14, 10 October 2016 (UTC)[reply]
As the above, a UPS is really just to stop your computer suddenly and unexpectedly losing power (and data) during a power "interruption" or a brown out, it's not really a complete power "replacement" device. If you do have a full power outage, a UPS gives you enough time to startup a backup generator OR at least perform a graceful shutdown, it's not really designed to just keep running your computer "as normal". Vespine (talk) 22:22, 10 October 2016 (UTC)[reply]
Yes, I know, I've used them for years. I shut all of the computers down as soon as the power went out. I have five UPSs that I used for the radio and charging devices. We drained the three smallest ones. I used up about half of the battery on the largest one. Bubba73You talkin' to me?23:15, 10 October 2016 (UTC)[reply]
We were without electricity for 47 hours because of Hurricane Mathew (starting 6 hours before it hit). I was trying to keep the radio going to get news reports and get some lights. (I have a battery-powered radio with a telescoping antenna, but it would not turn on, even though the batteries are good.) Bubba73You talkin' to me?20:44, 11 October 2016 (UTC)[reply]
In most common installation scenarios UPS are intended to be used like that. However UPSes installed for alarms and home fibre connections are often intended to be used for most power failures and many people don't even have any provision for generators. (When it comes to home fibre connections, depending on the country I think many people don't even have UPSes.) However this is more commonly for the more routine (power cuts lasting several hours rather than those extremely rare events (at least in the developed world) lasting several days. Of course you commonly don't really need a UPS, a quick acting battery backup will do at least for the fibre system but it's often easier just to use a UPS of some times. (Alarms systems may not like any loss of power.) Ideally a DC to DC may be better, but some do use 240V UPSes. I believe some roadside telecommunications cabinet also rely on UPSes or battery backups (more commonly the former although sometimes a UPS may simply be called a battery backup even if it designed like a UPS) exclusively as they lack a connection for power to the telecommunications exchange and while it may be possible, it's generally fairly unlikely except in special circumstances that anyone is going to attach a generator to each cabinet. Nil Einne (talk) 03:35, 11 October 2016 (UTC)[reply]
Sounds like its time to think out side the box. Depending on a UPS is like putting all ones eggs in one basket. Don't know what your financial situation is like but LED lanterns are inexpensive today and last for days. An auto battery with a inexpensive DC-to-DC converter bought from (say) eBay will keep a cheap (£4.00) Raspberry Pi (that can maintain internet connection) going for days and days, plus a cheap FM/MW transistor radio with a proper arial. The car battery will also (via the DC-to-DC converter) recharge your phone many times. Start preparing now and you will be prepared before Hurricane Nicole and Otto hits, (Otto hasn't got going yet but it may be coming your way when it does).--Aspro (talk) 23:39, 11 October 2016 (UTC)[reply]
Note that sparks, having a high surface-area-to-volume ratio, cool quickly as they shoot through the air, so they are not molten when they land, they are solid. StuRat (talk) 21:17, 10 October 2016 (UTC)[reply]
I worked in a tool shop for a while that had a manual welding "production line" with several people using MIG welder pretty much all day. Those definitely DID constantly spit out little balls of metal, and yes there were little balls of metal everywhere, but they are so small and most of the time if they build up to more than one "layer" on anything (jig, frame, table, etc) they just brush off. I think very very rarely, someone would get a grinder out if some build up happened in an inconvenient place. Vespine (talk) 21:57, 10 October 2016 (UTC)[reply]
Spatter builds up, but doesn't fly all that far (it's dense). So anywhere exposed to it is usually covered by something non-metallic to which it won't stick. For wire-feed welding, spatter does build up around the gas shield nozzle and has to be cleaned off periodically. It can also be a problem around fume extraction vents (if the atmosphere is kept human-friendly), where the airflow can be enough to draw light spatter into it, where it accumulates.
How is that inferred? We can say a body's mass is consistent with the presence of such a core, but it's also consistent with a bigger core of ice. Can its moment of inertia be measured? —Tamfang (talk) 00:41, 11 October 2016 (UTC)[reply]
I don't fully understand the math behind it, but many observations feed into the model. Specifically: surface spectroscopy, mass, radius, gravitational dipole moment, gravitational quadrupole moment, and modeling of the behavior of different materials under high temperature/pressure. As far as I can tell from reading papers on Uranus' core that I don't fully understand, you can't make a model agree with all of this without having a rocky core. Someguy1221 (talk) 00:57, 11 October 2016 (UTC)[reply]
Also I dare say evolution of the solar system might have a few things to say about what is likely and unlikely to be found at the center of a gas giant. I strongly suspect there are very good reasons why no one expects to find solid ice in the middle of any planet, let alone a gas giant. Vespine (talk) 03:06, 11 October 2016 (UTC)[reply]
Yes, there are reasons to think most planetary cores are primarily iron and nickel. Iron and nickel are the most common "heavy" elements in the universe because their nuclei are the most stable. Denser elements tend to sink to the center of a planet, so iron and nickel, along with any denser elements, "want" to sink to the core. --47.138.165.200 (talk) 10:34, 11 October 2016 (UTC)[reply]
But, Uranus is rather unique in that there is much evidence of a major collision in the early formation. It is further away than models show it should be. It is rotating on its side. It radiates almost no heat. That last one fits with a collision that would have kicked out most of the rocky or metallic core, leaving a sparse icy ball behind. The magnetic field, which was traditionally thought to be solely created by cores may not come from the core. It is off by about 60 degrees, but so is Neptune's. Therefore, the theory that it comes from movement in the core may be wrong. It may come from another source. In the end, our current models and expectations make us believe that Uranus has a rocky/metallic core. However, it is strange and as we learn more about it, we may very well discover that it has a core of loosely compressed ice. 209.149.113.4 (talk) 14:07, 11 October 2016 (UTC)[reply]
I don't see how you'd get a core of ice. The successful models of Uranus inner structure all assume a core density of ~10g/cc, which as far as I know is way higher than you could achieve with water/ammonia ice, even under extreme pressure. Someguy1221 (talk) 21:51, 11 October 2016 (UTC)[reply]
I would have loved to prove you wrong, but [2] says that you need pressures in the ballpark of 100 GPa (one million times the atmospheric pressure) to even reach 2g/cm^3 in water. So yeah, 10 sounds hard. TigraanClick here to contact me08:05, 12 October 2016 (UTC)[reply]
The "we may very well" is used to indicate that the following statement is unlikely. However, it is used in this case because currently accepted models of the core of Uranus indicate that the inner core of rock/metal is very small and very cold. The outer core (mantle) is vary large made of ice. The interesting part isn't that it is made of ice. The really interesting part is that this ice exists in high pressure and high temperature (relatively - you have to note that Uranus is much colder than any of the other planets). So, the icy mantle of Uranus is a very unique and unexpected feature - if it actually exists. 209.149.113.4 (talk) 17:53, 12 October 2016 (UTC)[reply]
October 11
Nights are loud
Why are background noises from cars louder at night than during the day? It is because nights are quieter as there aren't as many people outside. When people are outside making sounds like voices, machines, etc.; those sounds are effective at blocking background noises from cars, but don't travel as far, that's a reason why days are often quieter, that's my opinion. Upon hearing cars loudly at night, I can picture the outdoor as a giant dome! At the time of this writing, I had a window opened next to me at night and heard those background noises somewhat loudly. PlanetStar02:28, 11 October 2016 (UTC)[reply]
I think you definitely have at least "part" of the answer. Our ears are very good at attenuating sounds and a clue is that decibels are a logarithmic scale. This means you roughly need ten times the sound energy to make something sound twice as loud. Without "loud" sounds to drown them out, you can hear the quiet sounds a lot better. I've noticed pretty much the same effect when I listen to music or a podcast on the train, I don't listen to it loud, just a comfortable level like someone speaking to me, when the doors open and I step out of the train it easily gets drowned out by the noises outside of the train in particular as the train takes off. Even though without headphones at all the train doesn't actually sound that loud at all, subjectively one at a time the train sounds doesn't seem nearly loud enough to drown out what's coming out of my headphones, but in actual fact when you have both sounds at the same time, I have to increase the volume substantially on my headphones to be able to hear over the sounds of the train. Vespine (talk) 02:57, 11 October 2016 (UTC)[reply]
There is also another effect called sound refraction, when there is a layer of cold air above or below a layer of hot air, (which typically happens at night as the earth cools and the warm air rises, but also happens on hot days when the earth heats up but the air above is still cool) sounds do actually travel further and therefore would seem louder from farther than normal. So cars on a road nearby could be heard from further away, for example. Vespine (talk) 03:02, 11 October 2016 (UTC)[reply]
In my above opinion, quieter IS louder would be a paradox. Sound behaves like light that there is refraction you mentioned as well as reflection. There is also sound fog, sound glare, and even colors of sound. So sound have all the characteristics that light has, except that sound does not travel in outer space like light. Also hearing background car sounds is often louder on rainy days. Sometimes though, car noises are only slightly audible at night, possibly due to minimal air temperature differences by layer, don't you think? PlanetStar04:39, 11 October 2016 (UTC)[reply]
The first part is believable, after all, splashing water makes a lot of noise. But I don't buy that wet roads reflect sound better than dry roads. Please provide a source for that. StuRat (talk) 22:21, 11 October 2016 (UTC)[reply]
It's often very evident that it's currently raining or has been raining, as you can hear the splashing as the cars plow through the layer of water on the roadway. Whether the roadway is otherwise "reflecting" more sound than a dry road could be hard to measure. ←Baseball BugsWhat's up, Doc?carrots→ 07:33, 12 October 2016 (UTC)[reply]
I believe for awhile that we hear sounds more loudly in the dark than in the light because light interacts with sound. I looked up in Yahoo Answers and reported to be true. The darkness of night may have minutely contributed to cars heard more loudly than during the light of day. PlanetStar04:39, 11 October 2016 (UTC)[reply]
I'm going to assume good faith here but the above answers are nonsense. Sound and light do not interact at all, one is a physical propagation of vibrations through a medium (like air) and the other is electromagnetic radiation. That yahoo answer is preposterous, I very strongly suspect it's only got "up votes" by people who think it's "so ridiculous it's funny", not because anyone has verified it as true. It would be trivially easy to prove, does the sound of ANYTHING change when a cloud blocks out the sun? Clouds block 50%-80% of the photons reaching the earth but nothing gets quieter louder when a cloud goes overhead. Vespine (talk) 06:13, 11 October 2016 (UTC)[reply]
Also, color of sound is purely a metaphor, you can just as validly call it "flavor of sound" it does not mean you can literally "taste it" with your tongue. Vespine (talk) 06:20, 11 October 2016 (UTC)[reply]
Sound and light are both waves. Both are described by the physics equations for wave propagation, which describe how waves are reflected or refracted when their speed changes depending on the medium where they move. That's about all they have in common. Light is an electromagnetic wave, sound a pressure wave.
There are indeed reasons why sound seems louder at night. In the dark you see less, so you pay more attention to what you hear. At night, the air close to the ground cools. This leads to a warm layer on top of the surface layer, known as an inversion, and this warm layer refracts sound back to the ground. And at night, there's less background noise. PiusImpavidus (talk) 10:02, 11 October 2016 (UTC)[reply]
1) One obvious reason is that you have a window open at night, and presumably not during the day.
2) Another could be rush hour, with more cars on the road from around 5 or 6 AM, which could still be called "night".
3) As for the effect of darkness, that brings lower temperatures, and potentially fog. Both effect sound propagation. I think sound travels better in cold air, but high frequencies are blocked by fog (hence low frequency fog horns). So, if cars make more low frequency sounds, they may then stand out better, due to a lack of competing high frequency sounds. StuRat (talk) 12:42, 11 October 2016 (UTC)[reply]
[3] says, on page 156: "...the maximum value of absorption increases with increasing temperature". Therefore, sound is absorbed less at lower temps. StuRat (talk) 22:17, 11 October 2016 (UTC)[reply]
See Psychoacoustics, especially the subsection titled "Auditory masking" and the article titled Auditory masking. To wit "Auditory masking occurs when the perception of one sound is affected by the presence of another sound." Also very relevant is the article titled Loudness, again to quote the relevant part "loudness is a subjective measure, often confused with physical measures of sound strength such as sound pressure, sound pressure level (in decibels), sound intensity or sound power." --Jayron3213:20, 11 October 2016 (UTC)[reply]
The speed of sound link isn't relevant, but the second link is. Also note that my foghorn link does state that low frequencies travel better through fog. StuRat (talk) 15:09, 11 October 2016 (UTC)[reply]
not references or answers
Shall I box this up as a non-answer? Speed of sound most certainly talks about effects of temperature. Maybe you're having some problems with reading comprehension, in addition to having problems with scientific facts and references? SemanticMantis (talk) 15:43, 11 October 2016 (UTC)[reply]
"Sounds travels better" could mean speed, in which case it goes up with temperature (at constant pressure though, methinks), or attenuation factor, in which case it goes down with temperature (at least for some non-irrealistic range).
I'm not sure I know what you're talking about. I have never pretended not to understand anything on these pages. I make it a point to provide as little as possible other than the references I cite. I admit my (now removed) sarcastic confrontation was not ideal. However, since I cannot delete Stu's misleading and incorrect posts, and he adamantly refuses to properly cite references, I have little recourse other than posting correct information, and challenging his guesswork. SemanticMantis (talk) 16:51, 11 October 2016 (UTC)[reply]
I was hoping you were just pretending not to understand, but, just in case you really don't understand, I will patiently explain. This Q is about why cars seem louder at night. Loudness is volume, and attenuation of that volume is therefore the issue here. Loudness is not related to the speed at which sound travels (unless you are talking about sonic booms). Frequency and wavelength are related to the speed at which sound travels, but this Q is not about that.
As for references, my fog horn ref was good one, and I've added another good one, while you had some good refs, some bad refs, and some missing refs, so don't get all "holier than thou" on me. StuRat (talk) 22:05, 11 October 2016 (UTC)[reply]
I'll stop criticizing you when you learn how to properly reference your claims. I'm fucking thrilled that you managed to find a decent ref to support your claim above. Good job. Next time, do it without being asked, and you'll be on the path to being useful here. SemanticMantis (talk) 13:38, 12 October 2016 (UTC)[reply]
I did provide a useful ref, the fog horn one. You provided at least one USELESS ref, about the speed of sound, wasting the OP's time, and failed to provide any ref for your claim that wet roads reflect sound better. Stop criticizing others and try to do better with your own refs. StuRat (talk) 16:45, 12 October 2016 (UTC)[reply]
This is not exactly rocket science. Atmospheric conditions could be a factor, but keep in mind that what you can hear often depends on what other noises there are. Vespine's original answer pretty well explains that part of it. As a simple example, when you're driving in your car with your radio at what seems like an optimal level, if you stop the car and turn off the engine, the radio will seem louder, even though you have not increased the volume of it. Why? Because the engine noise is no longer there. Another practical example is attending a game in a domed stadium filled to capacity with spectators. When your team scores, the crowd's roar is very loud and that's about all you can hear. But when there's nothing going on, you can hear a lot more of the "quieter" sounds that Vespine points out. ←Baseball BugsWhat's up, Doc?carrots→ 06:40, 12 October 2016 (UTC)[reply]
What plants are these (the ones in the foreground)?
Hi I remember asking a question about mind uploading a few weeks back. If mind uploading were not possible, would there be other possible ways for humans to become immortal?Uncle dan is home (talk) 08:12, 11 October 2016 (UTC)[reply]
Immortality is a philosophical problem, not a physical one. The atoms that make up the body endure. The fundamental essence of consciousness (Atman) is arguably universal and immortal. Even the information learned in a lifetime accumulates in some sense, whether transmitted recognizably as text or whether it disperses and affects future events in unpredictable ways. Even particular aspects of the genome are long-lived - though the precise combination of genes may not occur again, the individual alleles likely remain present in the gene pool for a very long time. And this is even before we broach such issues as parallel universes and whether they contain copies of ourselves, or the related quantum immortality. And then there are creepy misgivings regarding qualia, such as Nietschze's notion of "eternal return". Now all these things are uncertain, but is it certain that who you were five minutes ago was you, rather than just a memory? Let alone a robotic effigy or an imperfectly cell-printed copy! So outside the very narrow sense of trying to put off disease a little longer, the fundamental issue of what the human being is and whether or how long he remains is a far voyage beyond all we understand. Wnt (talk) 10:30, 11 October 2016 (UTC)[reply]
Wave some philosophy at it. When you're dead, you don't exist. At the moment of death, you're dead. Therefore, you never experience the moment of death; hence, you never die. Q.E.D. :) Wnt (talk) 12:34, 11 October 2016 (UTC)[reply]
There's the possibility of some type of suspended animation, like being frozen. Of course, there's not much point in living forever if you aren't aware of any of it. But the hope is that eventually mind uploading will be possible, then you could be revived and live again. Other life extension techniques, like replacing failing organs with those cloned from your own stem cells, may also keep you alive until that time. StuRat (talk) 12:29, 11 October 2016 (UTC)[reply]
There are only a finite number of physically distinguishable states your brain can be in. This means that an immortal brain would eventually have to experience the same things over and over again, ad infinitum. Anything that this brain experiences will involve only a finite recollection of a "past" (which in most cases will be an artifact of false memories). The more you try to evade these limitations by using a system that can access larger and larger number of states, the more different persons with different experiences you'll end up producing. Count Iblis (talk) 17:19, 11 October 2016 (UTC)[reply]
Radiation is such a vast, complex idea, you can't make general statements about "radiation" as though it were some tiny little thing that always does the same thing. It's like asking "Is eating good"? Eating what? When? How much? --Jayron3216:35, 11 October 2016 (UTC)[reply]
Okay. Thank you for your exteremely helpful comment. Radiation is not "some tiny little thing that always does the same thing." Glad we cleared that up. Can any of the kinds of radiation you would be exposed to in outer space cure cancer?--Captain Breakfast (talk) 16:41, 11 October 2016 (UTC)[reply]
Jayron32 is helpfully pointing out that this topic is incredibly broad. It might take weeks of reading background science to bring you up to the point where you are phrasing your question in a way that a scientist could actually answer. But here at the reference desk, we aren't here to provide you with a definitive "yes" or "no" to your question: our role is just to point you in the right direction towards great encyclopedic resources.
Proper medical professionals rarely talk about curing cancer; they use words like "treatment," "prevention," "remediation," "remission." Even our encyclopedia editors have decided that cure for cancer ought to redirect to our article on cancer research - because this is how well-informed individuals actually speak about cancer.
So - where do you want to begin? Jayron32's advice was much briefer than mine - but he's making the exact same point: your question, as it is worded, cannot be answered with scientific rigor.
Radiation therapy works by focusing a beam of ionizing radiation onto a localized area of cancer, to kill the cancer cells. The radiation must be carefully directed so that it hits the intended target (the cancer) without affecting very much of the surrounding noncancerous tissue. Exposing the entire body to radiation at a level that would kill cancer cells would most likely kill the patient, by killing large amounts of normally functioning cells. Exposing the body to lower, non-lethal, levels of radiation would be more likely to cause cancer than to cure it. CodeTalker (talk) 16:44, 11 October 2016 (UTC)[reply]
(edit conflict) Radiation can kill cell, even cancerous ones. Dead cells don't reproduce. So yes, it "can".
Now, either the probability of that happening without killing the patient is ridiculously small, or radiotherapists with access to precise levels of radiation and focusing the rays at some places are desperately incompetent.
What Jayron32 said is actually very relevant, because (to take his example) your answer amounts to "glad that we cleared up that the safety of food depends on its type" - if you ask an imprecise question, people are not going to assume you are an expert in the subject. In addition to "it depends on radiation", I would add "it depends on cancer", because there are plenty of "cancers" out there and some of them are completely different. TigraanClick here to contact me16:53, 11 October 2016 (UTC)[reply]
"Treat" also implies survival of the patient generally. A shotgun cures cancer quite effectively otherwise. Likewise radiation - it may well stop the cancer, the tricky bit is not making the side-effects worse than the initial disease. Marvel Comics are not a competent guide to medical physics and the therapeutic uses of radiation, even when administered via the spider-bite mechanism. Chemotherapy is already a matter of deliberately poisoning the patient and hoping that the cancer is slightly more poisoned than the rest of the patient. We have some hope that the next generation of cancer treatments will be more self-targeted themselves.
Historically radiotherapy has largely been a matter of three dimensional geometry and cooking the patient along a line through their body, repeating treatments at different angles to repeatedly dose the cancer site whilst irradiating other parts only once. This relies on radiation as narrow collimated beams, and accurate positioning relative to the patient. Neither of these would arise from the "cook in space" approach. Andy Dingley (talk) 17:17, 11 October 2016 (UTC)[reply]
Adding to what the others have said, there are many ways radiation is used in oncology. Its almost always used to cook the cancer more than the tissue we don't want to kill. The typical question is how you concentrate the radiation. Chemotherapy generally assumes that tumors get more blood flow that healthy tissue so adding a bit of radioactive material to the blood will hurt the tumor more than the rest of the body. Beams of radiation (Cyberknife) where you fire from many directions at one point are another way to get the local concentration. Yet another way is via radioactive seals (brachytherapy) placed near/around the tumor. This is common for prostate surgery. Springee (talk) 17:57, 11 October 2016 (UTC)[reply]
Nothing personal, but your terminology is incorrect. Chemotherapy refers to the use of cytotoxic drugs. Administering radioisotopes is known as radioisotope therapy. Also chemotherapy isn't really based on tumors having increased blood flow, though that does help. Rather, it's based on the tendency of cancer cells to divide rapidly. Most chemotherapy drugs interfere with cell replication, and thus affect rapidly-dividing cells more. This also accounts for their most common side effects. --47.138.165.200 (talk) 19:44, 11 October 2016 (UTC)[reply]
Total body irradiation generally involves 10-12 Gray given in "fractions" so the patient can recover from shorter term effects in between. Honestly I have not bothered to learn the exact protocol which sounds like some kind of semi-fictional horror story about the Dark Ages. The Apollo astronauts received 0.86 Gray during the outbound transit through the Van Allen belts, according to [9]; the inbound was much less though, presumably since they could use the atmosphere to slow down more at the end? So it seems plausible that a nice leisurely orbit through the Van Allen belts can deliver the same total radiation dose in as many fractions as desired, though the profile of how long each treatment takes will be forced to be longer. I don't know if that matters. I would presume there is no FDA approval or Cochrane review about doing total body irradiation using a space capsule, so there is a certain level of guesswork here. :) One good thing is that potentially the capsule may have been very well disinfected prior to launch, making recovery safer from infection. The astronaut might shield his lungs per the current irradiation protocol, and of course you'd best shield the bone marrow to be transplanted afterward! You might cure leukemia with something like this. Wnt (talk) 20:24, 11 October 2016 (UTC)[reply]
Feynman Lectures. Lecture 30. 30–1The resultant amplitude due to n equal oscillators [10]
I'm trying to check formulae 30.1 and 30.2 in Mathcad:
PNG xmcd
So according the image we see that two formulae give different graphs. But it looks like the derivation of 30.2 is correct. How is it possible?
The density of air at ordinary temperatures and pressures is around 1.2 kg/m3, or about 830 times less dense than liquid water. Something a trillion times more dense than air would be about 1.2 billion times more dense than water, which is denser than the core of the sun (150x that of water). In fact, the only place in the universe you find material this dense is inside a neutron star. Someguy1221 (talk) 21:58, 11 October 2016 (UTC)[reply]
October 12
Knew Earth Like Planets
General question, The knew possible earth like planet reported in the news could be covered in water, with the current scientific methodology if this is so could we also assume it would have an oxygen rich environment or can water exist in fluid form with out producing any oxygen? 5.175.72.42 (talk) 09:19, 12 October 2016 (UTC)[reply]
We can't assume it has oxygen rich environment just because it has water. Our atmosphere is oxygen rich because early life on earth produced lots of oxygen. Fuortu (talk) 10:06, 12 October 2016 (UTC)[reply]
Is it possible through current scientific methods to see the makeup of the environment...as we do with in our solar system or is the exo-planet to far away? an aded question i know sorry. — Preceding unsigned comment added by 5.175.72.42 (talk) 11:14, 12 October 2016 (UTC)[reply]
We can often estimate an exoplanet's mass and orbit size by observing the motions of its host star. That, plus the brightness of its host star is enough to get a rough idea about its surface temperature (if one assumes it is a rocky planet). That gives us a clue about whether it might possibly be habitable for earth-like life. If the planet happens to pass directly in front of the star from our point of view, it is also possible to estimate the composition of the atmosphere by the nature of the small changes observed in the star's light during the time the planet is passing in front. Most planets don't happen to have orbits that pass in front of their host star. As far as I know there is no feasible way right now to learn about an exoplanet's composition if it doesn't happen to pass in front of host star. Dragons flight (talk) 12:09, 12 October 2016 (UTC)[reply]
Regenerating a li-ion battery?
Is it possible to regenerate a li-ion battery that has degraded due to normal use (that is, several cycles of charging and discharging)? I suppose the wikihow solution of putting the battery in the freezer does not help. However, is there an industrial scale refurbishing of old batteries? Maybe not for small smartphone batteries, but for hybrid/electric vehicles. --Llaanngg (talk) 10:23, 12 October 2016 (UTC)[reply]
Battery recycling generally involves taking the battery apart, melting down the components to separate out the valuable metals, and then using the resulting materials to build new batteries. At industrial scales, such recycling is often cheaper than buying freshly mined raw materials. However, that's not really a "refurbishment". As far as I know there is no simple process to restore the longevity of a li-ion battery. They degrade due to chemical and physical changes in the battery itself and I am unaware of any method of reversing those processes that doesn't involve scraping the battery. Dragons flight (talk) 12:17, 12 October 2016 (UTC)[reply]
(ec) The article Li-Ion#Battery life describes a variety of different ways that these batteries can degrade and there is no way to reverse them all. It is true that their life is longer if kept at low temperature and if a battery management system prevents operation outside each cell's safe operating area (max-charge, min-charge, safe temperature range). Experiments in reviving Li-Ion batteries by methods that have been suggested, such as "zapping crystal dendrites away with an electric welder" (that has been proposed to treat Nicad batteries that have an unrelated chemistry) are too dangerous due to the documented liability of Li-Ion batteries to explode. Thus the only option is to replace degraded Li-Ion battery cells with newly manufactured ones. Ideally old Li-Ion batteries should be recycled to recover their elements including iron, copper, nickel and cobalt but not much has been invested into recycling Li-ion batteries due to costs, complexities and low yield. AllBestFaith (talk) 14:28, 12 October 2016 (UTC)[reply]
"Several" discharge cycles should have no effect on the battery; it should take several hundred cycles at least for any noticeable loss of charging capacity. If you were being literal, and you have a battery that is new, it's defective and you should return it if it's under warranty. --47.138.165.200 (talk) 19:43, 12 October 2016 (UTC)[reply]
What's the Maximum cruise speed for Boeing 767 at 5000 ft?
The normal cruising height for a large jet is above 30,000 feet. At 5,000 feet the plane will have difficulty reaching its normal cruising speed. Wymspen (talk) 13:24, 12 October 2016 (UTC)[reply]
14 C.F.R. §91.117 (a) Aircraft Speed states: "Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.)." (These rules apply in the United States, but generally, almost all other nations have similar or stricter requirements).
If you happened to be near San Francisco this week, you might have seen a United Airlines 747-400 operating low and slow - here's a video of Saturday's show. The aircraft maneuvered below 5000 feet MSL at speeds between 145 mph and 300 mph (with special approval from the FAA).
A large airliner like a 747 or 767 is not designed to operate efficiently at cruise configuration at 5000 feet MSL - but it is capable of flying in that configuration.
In normal cruise flight, a 767 is operating at or below VNO. That means its flaps are up, its gear is up, and its multiple engines are configured for long-term, efficient flight; and it is not making any abrupt control surface deflections.
Sorry, but... [citation needed] ? Do you make this claim because a reliable source - like the post-crash investigation report - indicated that the accident would have been survivable if the pilot(s) had done something differently? Because... if not, you probably shouldn't repeat that kind of a ludicrous claim on our encyclopedia, especially if you aren't an expert in the detailed analysis of 747 accidents.
After a major aviation accident that involves such great loss-of-life, experts study the event in great detail and publish their findings. If it is determined that different pilot-decision-makingcould have saved lives, that type of important detail gets published, and usually gets incorporated into training material. I do not believe any reputable accident-investigator believes that El Al Flight 1862 could have been made survivable if the pilots had made different decisions.
A detailed analysis of crew decision making is included in Chapter 2.5 of the Nederlands Aviation Safety Board AIRCRAFT ACCIDENT REPORT 92-11, available in English from archive.org. There is no mention whatsoever that Count Iblis' proposal - which does not even comply with the emergency-operations procedures for a 747 - could possibly have made the situation work out any better. Specifically quoting the accident report: "the possibility for a safe landing was highly improbable, if not virtually impossible" - even if the pilots had done something differently. That's the official, published opinion from a team of aviation experts - who specifically studied the accident - and know far more than you and I about 747 operations.
This is Wikipedia - the free encyclopedia that anyone can edit - but we have a standard for sourcing our claims. Just like you can't make up random numbers and facts about general science and post them in our articles, you should not post procedures, airspeeds, or analyses, if you don't know them and can't cite sources for them.
See here: "The analysis indicates that the accident aircraft was recoverable from a technical point of view. However, the required procedures to perform such a recovery are not part of current industry training practices for complex in-flight emergencies or handling qualities in degraded modes. It is therefore understandable that a successful recovery of the aircraft was highly improbable." Count Iblis (talk) 19:10, 12 October 2016 (UTC)[reply]
Caterpillars and butterflies
Here it says that butterflies are "able to remember the solution to a puzzle that they were taught how to solve when they were a caterpillar". How can you teach a caterpillar how to solve a puzzle? How can you even teach ANYTHING to an animal as inferior as a caterpillar? --Qnowledge (talk) 16:13, 12 October 2016 (UTC)[reply]
Note that the "puzzle" could be quite basic, like remembering that the red leaves are bitter and the green leaves are good. StuRat (talk) 16:39, 12 October 2016 (UTC)[reply]
These scientists. When volunteering to help at a reference desk, it's a good idea to look for references before posting. It can be hard, so I'll tell you how I did it. I remember reading the work, but forgot who published it and where. So I went to google and typed /caterpillar learn butterfly/ [12]. The top hit is this Wired article [13], and a quick skim of that gave me an author name, Weiss. Now it's just another click over to google scholar, where I typed /weiss caterpillar learn/ [14], where the mentioned PLoS ONE article is the second hit. That's how you can help provide references on the reference desk. It took me longer to type this up (~3 minutes) than it did to find the answer for OP (<1 minute), but I hope that helps. SemanticMantis (talk) 17:42, 12 October 2016 (UTC)[reply]
The famous recent work on butterfliesLepidopterans remembering what was learnt as a caterpillar is Blackiston et al. (2008) "Retention of Memory through Metamorphosis: Can a Moth Remember What It Learned As a Caterpillar?" [15] It explains in the abstract:
“
Fifth instar Manduca sexta caterpillars received an electrical shock associatively paired with a specific odor in order to create a conditioned odor aversion, and were assayed for learning in a Y choice apparatus as larvae and again as adult moths.
I came across this recently which appears to boast that their car can run on ordinary sea water. It sounds bogus but I wanted to confirm with the experts here. This is bs right? ScienceApe (talk) 18:53, 12 October 2016 (UTC)[reply]
Yep, total bs, more precisely some mix of pseudoscience, hoax, and fraud. We have a pretty good article on water-fueled cars that explains the problems and some history, Snopes is also always a good place to check for this kind of thing. They don't seem to have a full article but their discussion thread on the topic is here [16]. SemanticMantis (talk) 18:58, 12 October 2016 (UTC)[reply]
