Wikipedia:Reference desk/Archives/Science/2015 January 7

= January 7 =

Habitability of Alpha Centauri Bb
If it exists, Alpha Centauri Bb is not really a good candidate for life by the numbers - after all, it is at 0.04 AU from its star with a predicted surface temperature over 1100 K. However.... it is that close to its star, which means that it is tidally locked. Which means that the planet should have a dark side that (like Mercury's) is extremely cold. Unless... it has an atmosphere that spreads the heat to the dark side. That is, unless the hotside atmosphere has condensed on the dark side, either quantitatively removing all of it, or building up some kind of dike of frozen material that confines the superheated material to the near side.

Of course, the planet might have a moon, and even a tiny moon would bring bright warm day to the far side. Conceivably even the heat coming through the planet could warm the far side, though I assume by analogy with Mercury it basically doesn't; yet if the far side had deep crevices containing some atmosphere of gas that has escaped from the near side, it might build up more than on Mercury. Or a minor remnant of gas might warm it by any degree. It seems to me it should not be impossible for this planet to have Earthlike temperatures on its far side, and conceivably even places where there is a potentially Earthlike atmosphere.

Anyway, I'm wondering whether there is any real sourced discussion of the potential fates of darksides of tidally locked hot planets in general, or of the most "optimistic" scenarios for this planet in particular. Wnt (talk) 00:45, 7 January 2015 (UTC)


 * We have Hypothetical types of biochemistry and the categories to which it belongs, and there is the tidally-locked (albeit colder) 'Aurelia' from Aurelia and Blue Moon which gives a tidally locked scenario that works with some tweaking. The huge unknown is what sort of metabolisms in cells with heavier cell membranes and some solvent other than water might support. I suspect any body with a permanent and impure ocean of some sort will originate life as specualted in Origins of Order. μηδείς (talk) 01:23, 7 January 2015 (UTC)


 * Note in passing that Mercury has no permanent dark side; its rotation is tide-locked, but because of orbital eccentricity it's not 1:1. The sun appears to stand nearly still at perihelion, when the tide is strongest. —Tamfang (talk) 10:48, 7 January 2015 (UTC)

Clarification: For now I was looking to focus on habitability by Earth life or at least human colonists, i.e. supposing a scenario such as: the darkside is cold and therefore the light side has little atmosphere, but deep pools of atmosphere exist somewhere on the dark side, and some energy source exists such as a satellite to provide some 'sunlight' (apparently the Roche sphere should be 1/25 of Earth's, but 1.5 million km / 25 is still 60,000 km, allowing orbits up to "geostationary" (for Earth, not Bb) and slower, so the satellite could sort of mimic an Earthly day and night cycle, I think) Wnt (talk) 02:34, 7 January 2015 (UTC)


 * One worry would be things like stellar flares and coronal mass ejections. At that range they might wipe out any life on the planet, even the dark side. StuRat (talk) 02:40, 7 January 2015 (UTC)


 * In light of Wnt's clarification, I'd ask WikiProject Astronomical objects what the temperature given in the template actually means. If the dark side (assuming tidal locking) is frozen and digging under the surface is an option, stellar falres shouldn't matter.  It seems the mass implies sheltered human habitations should be possible if there are areas with temperatures closer to the frozen/liquid water interface at STP.  The given temperature in the template may be a high or an average based on the brightest spectrum, and really doesn't say anything about the dark side. μηδείς (talk) 02:49, 7 January 2015 (UTC)


 * I'm thinking of the stellar flares that don't quite escape the star's gravity, and drop back down, potentially hitting the far side of the planet as they do so. StuRat (talk) 03:14, 7 January 2015 (UTC)


 * I'm not sure if Wnt wants his colonists to be able to walk freely in the atmosphere, in which case that would obviously be a huge issue, or whetehr they can just live underground, which should be possible with high technology and a suitable way to vent heat. μηδείς (talk) 18:20, 7 January 2015 (UTC)


 * I don't think having them locked underground in a refrigerator counts. But I'm skeptical that solar flares actually heat the dark side of a planet this way.  I would blindly guess that radiation has a fair chance of being corralled by some magnetic field, or at least, not descending vertically to the bottom of deep canyons on the dark side, but I don't really know. Wnt (talk) 21:42, 7 January 2015 (UTC)


 * If you are assuming they live on the surface, but our article says the surface temperature averages 1100K, there's a contradiction somewhere. Regardless of irradiation, which I do think would be an insuperable problem on the dark-side surface, there would still have to be some way of keeping the heat down.  Given the boiling point of water is 373K, even Venus should be more hospitable. μηδείς (talk) 21:37, 8 January 2015 (UTC)
 * Well, the nighttime surface of Mercury is one of the coldest places in the Solar System, so it seems like there should be some room to work in there. As for the radiation, I don't really pretend to understand  well, but my take is that a really strong solar wind sort of "pushes in" the magnetosphere of Mercury to the interior of the planet.  This sounds like a bad thing, but what it means is that there are no Van Allen belts, no fancy loops of particles floating around; so far as I get it, the charged particles that would generate radiation pound the front side of the planet and ought to leave the rear side alone because there's nothing strong enough to loop it around to hit there. Wnt (talk) 23:02, 8 January 2015 (UTC)

What happens when the helium balloon enters the atmosphere ?
I have many thoughts about this question when I usually buy this balloon and left on. This will float in air after I don't know what happens to it. So I asked this question. Arvind asia (talk) 01:50, 7 January 2015 (UTC)
 * It may rise till it pops, or else the helium slowly leaks out and the balloon comes down somewhere. Releasing balloons is a form of littering. Graeme Bartlett (talk) 01:55, 7 January 2015 (UTC)
 * The balloon is already in the atmosphere when you are holding it; we all are, but here is scientist's answer: http://www.thenakedscientists.com/HTML/questions/question/2030/ Mingmingla (talk) 02:14, 7 January 2015 (UTC)
 * Helium balloons sold as novelties leak, shrink, and sink. Even metallically coated ones don't tend to stay afloat more than a week.  Keep in mind also that buoyancy decreases as altitude increases.  So the easy answer is no for the standard party balloon. μηδείς (talk) 02:56, 7 January 2015 (UTC)
 * ‘no’ what? —Tamfang (talk) 10:43, 7 January 2015 (UTC)
 * No, it won't just (indefinitely) float in the air. μηδείς (talk) 18:17, 7 January 2015 (UTC)
 * Further to Graeme Bartlett's comment above, released balloons can cause suffering or death to wildlife and even to farm animals. See here for a "BirdGuides" opinion.    D b f i r s   08:26, 7 January 2015 (UTC)

Can I flatten a thick magnetic stripe card with a microwave?
It was in a dryer. The Internet says use iron or hairdryer. I don't have one. (don't try without Googling it!) Maybe there's a microwave setting. Sagittarian Milky Way (talk) 03:32, 7 January 2015 (UTC)


 * I wouldn't count on it. Is there a T-shirt near you? They use a big square iron to press on letters and images and such. However, before doing that, I recommend you call the credit card company and see what advice they have, if any. If you're lucky, maybe they'll send you a replacement for free. ←Baseball Bugs What's up, Doc? carrots→ 03:36, 7 January 2015 (UTC)


 * Yea. A microwave oven is almost certain to ruin it. I take it it's warped ?  Maybe you can force it through a card reader as is, until your replacement card arrives. StuRat (talk) 04:25, 7 January 2015 (UTC)


 * I assume you're trying to straighten a crooked magnetic stripe card. If an iron or a hairdryer is the right solution but you don't own one, can you borrow one? A "hack" that I read about on the Internet for ironing clothes without an iron is to use the bottom of a heated pan. I'm not recommending it, just mentioning it as an idea that I read about. Here's another idea for your consideration: bathe the card in hot water; if it softens, maybe you can bend it back into shape. (I've not tried it and can't vouch for its effectiveness or safety. If you decide to try it, you're doing it at your own risk.) I doubt the microwave would work. --98.114.98.174 (talk) 04:28, 7 January 2015 (UTC)


 * I say again that your best bet is to call the credit card company for advice. But one thing you could do, which seems like it would be potential less destructive than an iron or anything hot, is to place it on a table with the concave side down, and stack a bunch of heavy books on. Leave that for a few days and see if it makes any difference. ←Baseball Bugs What's up, Doc? carrots→ 04:37, 7 January 2015 (UTC)


 * Although it could well be the case, the OP didn't say it was a credit card. --98.114.98.174 (talk) 05:06, 7 January 2015 (UTC)


 * Whatever purpose the card serves the best thing to do would be to seek a replacement from the issuer. Why wouldn't you? Richard Avery (talk) 08:08, 7 January 2015 (UTC)
 * ... however, having said that I've just tried a simple experiment with boiling water which works very well. After deforming the card I laid it on a flat chopping board, on the sink drainer, and gently poured boiling water over it. Perfectly flat. Leave it for a minute or so to cool and harden. I can't guarantee what happens with your card but it worked with a standard plastic credit card. Richard Avery (talk) 11:32, 7 January 2015 (UTC)
 * Does the magnetic stripe still work? ←Baseball Bugs What's up, Doc? carrots→ 13:11, 7 January 2015 (UTC)
 * Good question that I can't answer because the card is out of date so I can't check, but I doubt that 212°F is going to demagnetize it, but I'd be pleased to know. Richard Avery (talk) 16:25, 7 January 2015 (UTC)
 * So you're basically conducting an experiment? In any case, the next time you go to the store you could take the expired card, explain the situation, and ask them to run it through their scanner - just to see if it works. ←Baseball Bugs What's up, Doc? carrots→ 16:47, 7 January 2015 (UTC)
 * Buy a gift card, warp it, fix it and then see. They will key it in by hand if it fails to read so no way to lose money or waste a real credit card.  --DHeyward (talk) 10:48, 8 January 2015 (UTC)
 * Which they can likewise do with a regular credit card, assuming you have proper ID. ←Baseball Bugs What's up, Doc? carrots→ 12:13, 8 January 2015 (UTC)

What's an incident infection and what's a persistent infection>
What's an incident infection and what's a persistent infection? — Preceding unsigned comment added by 199.119.235.169 (talk) 05:12, 7 January 2015 (UTC)


 * You might want to look at acute infection versus chronic infection. Accute infections are things like the cold virus, which infects the mid respiratory tact, and which the body normally eliminates quickly because the area is will infused with antibodies and blood vessels.  Chronic infections like toe-nail fungus, tuberculosis, and leprosy tend to sequester themselves in areas away from blood flow.  AIDS and retroviruses actually sequester themselves within nuclear DNA, where a normal antibody response won't eliminate them. μηδείς (talk) 18:12, 7 January 2015 (UTC)

If helium balloon goes on
When the balloon stops or pops ? If it goes on reaches the corona of sun or it will burst in atmosphere. Arvind asia (talk) 11:35, 7 January 2015 (UTC)
 * The balloon certainly won't reach the sun, and it will not leave the atmosphere of the earth. This is because the air gets less buoyant as it thins out with height, and the volume of the balloon cannot support the weight of the balloon envelope. If it pops it will be inside the atmosphere somewhere. The wind will blow it around though. Graeme Bartlett (talk) 11:47, 7 January 2015 (UTC)
 * A typical but often illegal application, due conflicts with and danger for air traffic was to use multiple baloons to lift equipment like radio transceivers or cameras into the air. One of the balloons was filled more than all others. When it bursts, the other balloons make the equipment falling down slower, but can not keep it in the air. Do not try this! -- Hans Haase (有问题吗) 13:40, 7 January 2015 (UTC)


 * I'm actually more disturbed by the atmosphere vs. corona of the sun as some sort of boundary. There is very basic knowledge that is missed by even posing the question.  For what it's worth, helium is a very good heat conductor.  It would interesting to see how expansion from the pressure difference compares to the temperature fall at altitude.  --DHeyward (talk) 10:56, 8 January 2015 (UTC)

the balloon into Pacific Ocean
If the balloon with carbon dioxide gets to deepest part (mariana trench). It will be burst that's my guess or what happens to it. Arvind asia (talk) 11:44, 7 January 2015 (UTC) or if I filled with my mouth exertion this will also Sinks?


 * Balloons float on the surface if the sea, and would not sink. Graeme Bartlett (talk) 11:47, 7 January 2015 (UTC)


 * However if you did fill come some container with carbon dioxide and then forced it down the carbon dioxide would turn into a liquid, as it would be colder than supercritical carbon dioxide. The container / balloon would be crushed or crumpled. This would happen at depths deeper than 720 meters. I believe that this liquid is denser than water and so would then sink. Some people think that unwanted carbon dioxide can be disposed of by pumping it deep in the ocean. However it would lead to ocean acidification. Graeme Bartlett (talk) 11:52, 7 January 2015 (UTC)


 * It might be time to change your "come container". StuRat (talk) 05:12, 8 January 2015 (UTC)


 * Probably before it liquified, the balloon displacement would be less than its own weight and would sink..  As a practical matter, this is done when snorkeling with weight belts (or scuba when holding breath during descent.  The weight belt goal is that a few feet below the surface, the lungs compress enough to reduce volume and the diver changes from floating to sinking (when ascending, never hold breath with scuba).  --DHeyward (talk) 11:19, 8 January 2015 (UTC)

balloon with exertion
Then the balloon is filled with mouth exertion taken into deep sea what will happen to it ? Arvind asia (talk) 13:01, 7 January 2015 (UTC)


 * The weight of the air inside the balloon will force the balloon to reach the sea surface. The skin of the balloon needs to resist this this force. As the pressure in the sea increases by depth, the air in the balloon will be compressed as well. The stretched skin of the balloon forces itself into its original condition. -- Hans Haase (有问题吗) 13:18, 7 January 2015 (UTC)
 * The balloon, filled with air at the surface, will get smaller the deeper you take it. At 10 m depth it will be half the volume it was at the surface.  This is shown in the second half of this video. -- ToE 13:13, 7 January 2015 (UTC)


 * If you can somehow get the balloon down to some small depth, then the pressure would indeed start to crush it - so it'll rapidly become a rather limp bag and then we can forget about it being a balloon and just consider how the contents fare.  Consider the reverse experiment done with high altitude weather balloons.  When they are launched, they are very limp bags that gradually swell to spherical shape at altitude...being at ground level is akin to your balloon being at the bottom of a swimming pool.   It's less and less likely to burst as the skin gets less and less taut as it's pushed to the bottom.


 * The problem is with how you get it down to that kind of depth. Just below the surface, the upward force on the balloon is rather high - it could easily displace a couple of liters of water - so the upward force would be a couple of kilograms at one g.   So pushing it down to a sufficient depth to relieve the pressure on the skin is going to be hard.   If you try to push a fully inflated balloon underwater with your hands, it invariably bursts before you get it even completely submerged because the forces involved aren't evenly distributed over the surface - and that causes it to tear.    Tying a string around the knot at the bottom of the balloon and pulling it under that way causes other strains on it.   The problem is that until the balloon is at a depth that significantly larger than it's own diameter, you're getting this differential pressure that's going to push it past breaking point before the air inside is compressed enough to relieve the tension on the skin.   If you could take the balloon down to a depth of a few feet in a water-tight pressure vessel, then slowly and uniformly increase the pressure inside until it equalled the pressure outside - then released the balloon, I'm pretty sure it would survive.  It would of course continue to try to rise to the surface until you lowered it to a depth where most of the the air would liquify...and (depending on the original size and weight of the balloon itself) might even start to sink.  But I don't think it would burst.   Of course there are other issues here.  The temperature of the water might drop sufficiently to embrittle the rubber...or extreme pressure might promote ordinarily slow chemical reactions to happen more rapidly and thereby degrade the balloon...but those things are harder to describe without knowing lots more about the overall situation and the chemistry of the rubber. SteveBaker (talk) 14:48, 7 January 2015 (UTC)

If "mouth exertion" means air that you exhale, note that it's nothing like pure CO2. Normal air is roundly 78% nitrogen, 21% oxygen, and 1% argon, usually with some water vapor mixed into that. When you breathe, some of the oxygen gets replaced with CO2 and there may be some water vapor added, but the nitrogen is still 78% (before accounting for water vapor); and there still is more oxygen than CO2, which is why mouth-to-mouth resuscitation works. --65.94.50.4 (talk) 04:58, 8 January 2015 (UTC)

Design code factor of safety in prestressed concrete design
If a design code specifies that 0.9 should be used as a factor of safety for prestressed concrete design, I'm aware that this should be used when calculating the prestressed strain. However, should it also be used when calculating the tensile force in the process of calculating the ultimate moment of a prestressed concrete beam? I.e. Should the equation be 0.9*(prestress/1.15)* area? 94.3.137.225 (talk) 21:15, 7 January 2015 (UTC)


 * A US-centric answer, based on ACI 318:


 * Some pedantry, first. I think you're talking about a "strength reduction factor" of 0.9, not a "factor of safety".  A factor of safety would normally (a) be larger than one, and (b) would compare the capacity to the expected demand.  You multiple the "nominal strength" by the "strength reduction factor" to get the "design strength". You then compare this to the "required strength" due to the applied loads multiplied by "load factors".


 * A strength reduction factor is applied to the overall strength of the member, not to the prestress strain used to evaluate internal strains and forces. The adjustment to prestress strain you would make would be a reduction for prestress loss, but not a factor of safety or a strength reduction factor. Indeed, somewhat counter-intuitively, the prestress strain (that is, the strain induced in the prestressing steel due to the prestressing force, prior to loading the beam) has no effect on the ultimate strength of the beam.  So I can think of no time when you would multiply the strain or tensile force by a strength reduction factor.


 * If you're asking about a non-US code, I can't help you. If you make a note of that here, maybe someone else can help.  --Floquenbeam (talk) 21:41, 7 January 2015 (UTC)