Wikipedia:Reference desk/Archives/Science/2011 January 25

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January 25

minerls

How is a mineral inoganic but yet found in natere?♠ — Preceding unsigned comment added by Dwight peru (talk • contribs) 01:52, 25 January 2011 (UTC)

There is no contradiction, maybe your difficulty is in the meanings of the words. Organic in this definition usually means either Organic compound or Organic matter while the definition of Nature can be found there. Vespine (talk) 02:15, 25 January 2011 (UTC)

To be a bit more precise, in the nomenclature of chemistry, "organic" means that it contains carbon as the key element. Inorganic means carbon is not a key component. Thus a "Mineral Acid" (a slightly archaic term) is an acid without carbon as a key component of its stoichiometry. Hydrochloric Acid (HCl) exists in nature but is a mineral acid based on the fact it contains no carbon. 65.29.47.55 (talk) 08:59, 25 January 2011 (UTC)

Furthermore, the "natural" sense of the word "organic" doesn't just mean "found in nature". Uranium is found in nature, after all, but you won't see "with 99.28% natural ²³⁸U!" on your granola bars anytime soon. --Sean 14:16, 25 January 2011 (UTC)

99.28% 238 would be a poor granola bar but an excellent kinetic penetrator for an antitank shell!

Organic food#Meaning and origin of the term states:

In 1939, Lord Northbourne coined the term organic farming in his book Look to the Land (1940), out of his conception of "the farm as organism," to describe a holistic, ecologically-balanced approach to farming—in contrast to what he called chemical farming, which relied on "imported fertility" and "cannot be self-sufficient nor an organic whole." This is different from the scientific use of the term "organic," to refer to a class of molecules that contain carbon, especially those involved in the chemistry of life.

A list of articles related to the various uses of the term organic is at our Organic disambiguation page. -- 119.31.126.68 (talk) 00:31, 26 January 2011 (UTC)

Minerals like calcite, however, can sometimes have an "organic" origin. Any sedimentary rock not considered organic is clastic, though even some new igneous rocks and minerals could have an ultimately organic origin when subducted limestone, coral or the fossil fuel substances return through volcanic activity. ~AH1^(TCU) 22:42, 26 January 2011 (UTC)

Lip cells

Hi. How often do the different layers of lip cells usually replace themselves through cellular division? Is this rate faster or slower than for regular skin epidermis? This is neither homework nor a request for medical/legal advice. Thanks. ~AH1^(TCU) 02:57, 25 January 2011 (UTC)

Epithelial surface cells, in general, will be replaced every 7-10 days. Lips can be divided into keratinized and unkeratinized sections (by the lip wet/dry line) and the unkeratinized (which is contiguous with the lining of the lips and cheeks inside the oral cavity) will be moist, decreasing friction and reducing cell shedding due to mechanical insult. Then again, a quick, sturdy rub of the lips against the teeth will remove cells at a much faster rate than normal -- it's like rubbing a dull knife over your skin. So if you do that 5 times a day every day, which most people do, and then you may bite or pick at the lips, even more cells will be removed. So I'd go for faster rate of superficial layer loss. This is all educated guess-timation, but a derm or dental textbook would likely not take into account the tooth scraping, and it seems as though that should play an overwhelming role. DRosenbach ^{(Talk | Contribs)} 07:00, 25 January 2011 (UTC)

Loss of cabin pressure / oxygen at high altitude flight

I looked at Effects of high altitude on humans, but I have some lingering questions. Obviously losing cabin pressure at high altitude is a problem, but it's my understanding that standard procedure is to descend quickly to a lower altitude. What altitude is that generally? My other question is whether or not this is a substantial problem or not. Obviously it's not beneficial, but humans have been known to survive at 26,000+ feet for hours at a time (mountain climbers of course) and for considerably longer at lesser altitudes. I guess I wonder if emergency oxygen systems are placed out of an abundance of caution, or if there's some other factor that exacerbates the problem when the loss of oxygen is quick... or something similar. Shadowjams (talk) 03:37, 25 January 2011 (UTC)

We have quite good articles on Cabin pressurization and Uncontrolled decompression. Vespine (talk) 03:43, 25 January 2011 (UTC)

Here's a topical answer - "A Qantas airliner carrying 99 passengers from Adelaide to Melbourne was forced rapidly to descend 26,000 feet after a sudden cabin depressurisation this morning... Oxygen masks dropped from the overhead consoles on the Boeing 737-400 as the pilots of flight QF670 announced that they would have to make a rapid descent from a cruising altitude of 36,000 feet to just 10,000 feet." From here. HiLo48 (talk) 03:53, 25 January 2011 (UTC)

Immediately after complete loss of cabin pressure the crew of a civil aircraft will descend quickly to an altitude around 10,000 to 12,000 feet. Trained athletes are capable of considerable exertion at altitudes above 20,000 feet, but the passengers of an airline aircraft are not trained athletes and it must be assumed some of them will be particularly vulnerable to inadequate pressure.

Supplemental oxygen systems are provided in high-flying aircraft to provide support to the passengers during the descent from cruise altitude (typically 30,000 to 45,000 feet) down to below 20,000 feet. Pressurised propeller-driven aircraft, and other aircraft that don't fly higher than 20,000 feet, usually don't have supplemental oxygen systems for the passengers because they can descend to 12,000 feet quickly enough. All aircraft that fly above 10,000 feet have supplemental oxygen systems for the pilots. Dolphin (t) 04:01, 25 January 2011 (UTC)

It's interesting that the article said it took a full 10 minutes to go from 36,000 to 10,000 feet. That's a surprisingly long time. --Sean 14:21, 25 January 2011 (UTC)

Thank you all. I especially found the Time of useful consciousness article helpful, although again, I'm surprised that the TUC limit at Everest style heights is on the order of minutes, when clearly some individuals are able to withstand it for longer. I suppose it only highlights how remarkable a feat that is. Shadowjams (talk) 04:41, 25 January 2011 (UTC)

It does indeed, though it should be added that at such altitudes humans do suffer from effects of altitude, it is common practice for teams making a bid for very high peaks to carry and use oxygen, though at partial pressures not as their only breathing gas. Mishandling of such cylinders due to the effects of oxygen deprivation have been implicated in peak casualties and near-casualties. 65.29.47.55 (talk) 09:03, 25 January 2011 (UTC)

The TUC will be for someone that has not acclimatised. People climbing Everest will do so over several days and will be starting from a pretty high altitude (Everest Base Camp is at around 18,000ft) where they will have spent days, if not weeks, acclimatising before they even start their ascent. That makes a big difference compared with rapid decompression on a malfunctioning aeroplane. The body's abilty to acclimatise to high altitude is pretty remarkable, indeed. --Tango (talk) 23:49, 25 January 2011 (UTC)

As for "surprisingly long time", descending 2600 feet per minute at a forward speed of 800 km/h corresponds to a downwards slope of about 1:19. It appears believable that the 737's lift-to-drag ratio is in about that range, so that would be consistent with the pilots reducing thrust to idle and letting the plane glide downwards at constant speed. Going down faster than this would require some additional drag to avoid exceeding the maximal rated airspeed. It is probably SOP not to deploy spoilers in this situation unless particularly necessary. In the event of sudden trouble (and remember there's a problem of unknown nature unfolding somewhere on the aircraft) it would be preferable not to start dealing with it from a deliberate high-drag/low-lift configuration. –Henning Makholm (talk) 15:35, 25 January 2011 (UTC)

The problem is increasingly difficult to solve as the airplane's cruising altitude increases. The highest-flying airliner is (was) Concorde which cruised around 60,000 feet, almost twice as high as other types of jet airliner of the day. (Time of useful consciousness at 60,000 feet is not long enough for passengers to react and don their supplemental oxygen masks.) The maximum credible cause of sudden decompression was loss of one complete window in the passenger compartment. It was possible for Concorde's engines to supply sufficient compressed air into the cabin to maintain cabin pressure at a survivable level during the deceleration and descent to 10,000 feet, even with one complete passenger window missing and air pouring out the resulting hole. However, it necessitated smaller windows in the passenger cabin than windows in other types of jet airliner of the day. See Concorde#Cabin pressurisation. Dolphin (t) 06:14, 26 January 2011 (UTC)

Exoatmospheric Warefare

Hypothetically, would an airtight bulkhead be of any use when applied to an exoatmospheric vessel intended for warefare? Would the bulkhead be at all effective in minimising the loss of atmosphere due to explosive decompression, like what could result from an explosive ordinance strike?

Conditions:

1. The vessel has a large internal volume, approximately seven million cubic meters.
2. The bulkheads doors are normally in the open position, they take 3 seconds to seal.
3. The doors are approximately 14 square meters in area.

--Plasmic Physics (talk) 10:16, 27 January 2011 (UTC)

Independence Day

Hello.

  I refer to the 1996 film Independence Day, in which during a missile tipped with a nuclear warhead is used to destroy the alien mothership. The alien mothership is said to be 550 kilometers long, with a mass one-quarter that of the Moon; so how can a single nuclear warhead completely destroy such a huge vessel? I'm quite familiar with the scene where anti-ship Harpoon missiles were fired at a 15mi-wide destroyer ship floating in the air, but obliterating a 550km-long mothership with one single nuclear warhead would require new spans of imagination, as I estimate that the equivalent of around 14,600,000,000 tons of TNT would be needed to blow up something that big. Even the world's most powerful nuclear bomb ever made, the Soviet Tsar Bomba, had a maximum yield of 100,000,000 tons. So atleast 146 Tsar Bomba warheads would be needed to obliterate a 550km-long alien mothership. Are my calculations correct?

  Thanks, everyone. Rocketshiporion♫ 03:54, 25 January 2011 (UTC)

Maybe they hit the armory. APL (talk) 04:06, 25 January 2011 (UTC)

Could you share your calculations? Taking your numbers (which sound familiar, so I'll assume they're correct), the gravitational binding energy of the ship (which I further assume, incorrectly, to be spherical) is on the order of 9 x 10³¹ joules, or about 2 x 10¹⁶ megatons of TNT. You could certainly destroy a ship with less, but I'm assuming you're going for the "explodes into a million tiny pieces and leaves no large wreckage" level of destruction that was seen in the movie, which although it leaves Earth being pelted with a considerable amount of debris, is better than being pelted with a moon-sized spaceship. I'm willing to chalk up the epicness of that destruction to secondary explosions - maybe there was antimatter onboard. Someguy1221 (talk) 04:12, 25 January 2011 (UTC)

This really counts as an entertainment question rather than a science question - there's no doubt that such a ship could blow up, if designed in a highly unstable way. In the movie, as I recall, the big saucers over the cities could be blown up with a single 9/11 style attack on their main weapon, and the main ship was attacked with a bomb brought near to a central reactor. Wnt (talk) 04:24, 25 January 2011 (UTC)

I thought the big saucers over the cities were destroyed because the "9/11 style attack" damaged their one and only engine? (Or at least, their one and only glowing bit.) and they fell down onto the city. Not really the best strategy on the part of the saucers. Very intimidating, but it seems like an engines-on hover like that leaves them at their most vulnerable. APL (talk) 06:14, 25 January 2011 (UTC)

gravitational binding energy is not the right way to measure this since no ship would be held together this way. But lets ignore that. The ship massed 1/4 of earth's moon, i.e. 1.836×10^22 kg. The Tsar Bomba has an energy of 420PJ. Put those together and you can accelerate the ship to the amazing velocity of 6.8 mm/s! So yah, a nuclear bomb would do absolutely nothing to it. It would barely be able to move it much less destroy it. Ariel. (talk) 04:37, 25 January 2011 (UTC)

I used GBE not because it was what held the ship together, but because the level of destruction showed that GBE was probably exceeded. Someguy1221 (talk) 04:43, 25 January 2011 (UTC)

The writers and creative directors of Independence Day probably didn't worry too much about the technical merits of the plot. So, suspension of disbelief is called for. But anyway - the energy of explosion is not only from the bomb. Consider another issue: overpressure. The mothership was floating in space; its material construction (or energy beam shielding or whatever) had to keep the air inside in, across a pressure differential with the vacuum of space. A slight increase in the pressure (such as we'd expect, at least locally, when the bomb explodes) would increase the internal pressure, presumably above the yield strength of the ship's walls and superstructure, and boom. All that air - which was not gravitationally bound - serves as an energy reservoir of pressure-volume work. One slight disruption breaks the external containment, and boom. This is one reason why space combat is a very bad idea. You don't need to obliterate a ship - you just have to pop its pressure hull like a balloon. Nimur (talk) 05:31, 25 January 2011 (UTC)

of all the myriad issues with the rigors of science and Independence Day I find the question of how an off-the-shelf apple computer could hack an alien mainframe that might not even use binary logic far more pressing... however it is noted well above and I concur that it has been proven in real-life naval combat that a single blow to a vital section can destroy a ship, assuming an alien energy reactor was poorly designed in such a way it might release energy explosively if tampered with, the real cause of destruction would be the xenos own personal Chernobyl happening in the middle of the ship, not the bomb itself. 65.29.47.55 (talk) 09:07, 25 January 2011 (UTC)

The most unlikely part of that film was the RAF officers saying "Thank God for the Americans" - "It's the Americans - take cover!" is much more likely ;-) Alansplodge (talk) 09:56, 25 January 2011 (UTC)

IMO, destroying a 550km-long spaceship (really more like an artificial moon, given its sheer size and mass) with a single nuclear warhead would be equivalent in scale to blowing up an aircraft-carrier with a single hand-grenade. A well-aimed thermite hand-grenade tossed into one of the jet fuel reserves on an aircraft-carrier would cause the entire ship to explode, but the hull would still mostly be in one piece - there's still be a pretty large wreck. As for my calculations, they are quite crude. Using the Little Boy, which had a blast radius of around 3km, as a yardstick, I calculated as follows.

 3km blast radius - 20kT yield, hence 275km / 3km = 91.6666666667 and 20kT * 91.6666666667^3 = 15,405,092.592kT
 for simplicity (albeit not accuracy) I rounded it off to 20kT * 90^3 ≈ 14,600,000kT

Rocketshiporion♫ 11:31, 25 January 2011 (UTC)

A ship of that size and mass would have a density of about 65 times that of the Moon (and that's assuming the ship is spherical, any other shape would increase the density further). That's denser than the core of the sun! I don't know of any was of constructing a space ship that would give such a high density, so we must assume it is something completely beyond our science. In that case, we cannot predict how it would respond to a nuke. --Tango (talk) 00:07, 26 January 2011 (UTC)

In the very same movie, they use an old Apple Mac to upload a "virus" onto miraculously compatible alien mothership (the very same that was destroyed, I guess US government should review Apple's export activities) when in practice such hypothetical virus would not even be compatible with current Mac OS X. I think you are wasting your time trying to make sense of the logic behind it and maybe you should consider turning on your suspension of disbelief.--110.174.117.185 (talk) 06:33, 28 January 2011 (UTC)

Energy as a measure of damage?

Have there been any studies on how the kinetic energy of a bullet or the thermal energy of an explosive device relates to the number of shots or blasts it takes to kill a person or destroy a vehicle, if accuracy is held constant? NeonMerlin 04:22, 25 January 2011 (UTC)

You'll have to define "destroy". Or even kill. News reports demonstrate a properly aimed Q-tip can kill a man given the right circumstances. Now, as for vehicles, I'm certain you would clasify "hitting a tank so hard the turret comes off" as destroy, but what about simply taking the treads off the wheels? Or what about a weapon that burns a tiny hole through the armor and then incinerates everyone inside? You'd have to not only define destruction, but also hold constant the way the weapon works. Someguy1221 (talk) 04:38, 25 January 2011 (UTC)

You may find Impact depth interesting as it gives a direct relationship. Ariel. (talk) 04:43, 25 January 2011 (UTC)

Possibly the science used to answer this question would be Terminal ballistics. Vespine (talk) 05:37, 25 January 2011 (UTC)

Absolutely yes. Conservation of energy is widely used in the study of weaponry, in both design and operation. If you peruse our various articles on military firearms and heavy artillery, you'll see the term muzzle energy pop up very often. This energy term has huge impact on the stopping power of a handheld firearm, and on the damage of an artillery, cannon, or other heavy weapon; energy can be a more useful parameter than muzzle velocity because it also accounts for the mass of the projectile. Downrange energy is a little harder to be precise about, because it depends on how far down range your projectile ends up; how much air resistance, and the trajectory it took. Have a start at our ballistics article, and our terminal ballistics article, and let us know if you need help finding anything more specific. Nimur (talk) 05:38, 25 January 2011 (UTC)

h (home depot)

does home depot have a basement — Preceding unsigned comment added by Tommy35750 (talk • contribs) 04:27, 25 January 2011 (UTC)

The one near me doesn't. Unless you find a home depot with a second story, it's pretty safe to assume it doesn't have a basement. Why do you ask? Ariel. (talk) 04:41, 25 January 2011 (UTC)

A basement is generally opposed to the idea of a "big box store" (hmmm, that's an American sense - apparently the UK has two story "big box stores", but having to take everything up an elevator is just the sort of labor that an American big box store is trying to cut out), but I would be surprised if they don't have at least some sort of crawlspace for their plumbing, and a "penthouse" on the roof for some of their HVAC equipment. Wnt (talk) 05:46, 25 January 2011 (UTC)

We are lazy, aren't we? My own observation is that the big box stores (not Walmart, but Target and such) have second floors where land is too expensive to have a profitable one-floor outlet. But then high land prices tend to ruin the whole "low low prices" strategy, which is why they're still pretty rare. Someguy1221 (talk) 09:21, 25 January 2011 (UTC)

They put all the plumbing around the sides, and nothing in the middle. It would be too expensive to make a strong elevated floor (the loading levels are much higher than in a residence or office) rather than just placing in on grade. And even if they put something in the middle it would just be a buried pipe without a crawlspace. Ariel. (talk) 07:07, 25 January 2011 (UTC)

Home Depot in Manhattan is the lower levels of a large building. I can't remember if anything except the entrance is as high as ground level--just a small space to get to the escalators/elevators, and I think most of the major actual store floorspace is on the lowest below-ground level (at least among those open to the public). It was built into an existing building IIRC, so this is definitely a large store in a multilevel construction, not "expand exoskeleton to fill the land" as typical "big-box". DMacks (talk) 09:28, 25 January 2011 (UTC)

• I think that everyone has missed the OP's question completely. I think they are trying to ask if the Home Depot runs a bargain basement; which is the term for a store which sells damaged/old/out of style items for a main store. In the past, the "bargain basement" used to literally be in the basement of large, multistory downtown department stores; though they eventually got spun off as independent chains for selling remainders from the main store. In the U.S. northeast, prior to the 1990's department store consolidation, many people will remember Filene's Basement, which was spun off from the higher-end Filene's. I take the OP's question to mean "Does the Home Depot maintain any 'bargain basement' stores for selling its damaged/old/remaindered items." I don't know the answer, per se, but it does give us an extra place to search... --Jayron32 15:47, 25 January 2011 (UTC)

what I wanted no is why A does in the concrete not crack. in my basement there are cracks in flour — Preceding unsigned comment added by Tommy35750 (talk • contribs) 21:58, 25 January 2011 (UTC)

If there are cracks in your foundation, you need to contact a business that repairs them or ameliorates their effects. Look up "foundation repair" to find someone to come out and inspect your situation. If you live in an area with a high water table you may also need to install a sump pump to keep your basement dry. Cracked foundation is generally not a good thing. --Jayron32 04:10, 26 January 2011 (UTC)

The Target store nearest me has two full shopping floors. It has a amusing four-lane escalator. The outer lanes are, as usual, for customers, while the center two are fitted to handle shopping carts. PhGustaf (talk) 22:43, 26 January 2011 (UTC)

Genomic DNA in northern blot

Ummm... is it necessary to remove genomic DNA before performing a northern blotty blot blot? --129.215.47.59 (talk) 10:47, 25 January 2011 (UTC)

According to Northern_blot#Procedure - yes. SmartSE (talk) 10:54, 25 January 2011 (UTC)

You probably should consider a more technical how-to forum like this one (there are many others). In general what you would usually like (though it could be different for specialized situations) is a known amount of polyadenylated RNA in each well, pure as the driven snow. If you have genomic DNA mixed in with your samples, for example, who knows how much you're really loading? And of course there is always the dread of RNAse in less-pure preparations (though then again there's also the dread of contaminating the RNA or letting it get chopped up while you're messing with it).

That said, at least in theory, the emphasis on doing Northerns with poly(A) rather than total RNA does impose a certain bias, because who knows if the RNA you're interested in really follows all the standard rules about how RNA is supposed to be processed in the cell? For all you know, for example, the removal of the last intron is a crucial regulatory step for your gene. Wnt (talk) 20:12, 25 January 2011 (UTC)

What comes after Blu-ray?

There was VHS --> DVD --> HD-DVD --> Blu-ray. What's after? --70.179.181.251 (talk) 14:08, 25 January 2011 (UTC)

Internet TV? I know we already have it, but it does seem as though the time will come when having a physical copy of something will be a bit pointless. If everywhere was to have a high speed broadband connection then you could hire/buy an electronic film in HD and have it streamed to you as and when you want. (Oh and the HD-DVD --> Blu-ray isn't quite accurate as both are the same step, it's just that Blu-ray won the format war, like the VHS over Betamax.) SmartSE (talk) 14:27, 25 January 2011 (UTC)

Blu-ray#Ongoing_development covers some future directions. --Sean 14:29, 25 January 2011 (UTC)

Smartse is probably correct in that the future is fully digital (i.e. physical-copy-less) media. Music is already going that way. Future advances will go towards speeding delivery methods and improving resolution and quality of digital streaming, but given the trends in other media (cloud computing, MP3 and iTunes, etc.) the days of maintaining a hardcopy of anything are fading. In fact, given the trend towards cloud computing, you may not even have a locally stored copy of your media. You simply buy the rights to play a song/movie/video game and then you have the ability to listen/view/play the media anywhere you want, using any of your connected devices. We're already almost there now, there's just the inertia attached to the old media and attitudes. Give it a few decades, and we'll all be wondering why people in past generations felt the need to keep a personal copy of anything... --Jayron32 15:05, 25 January 2011 (UTC)

Your list conflates physical formats with resolution upgrades. You need to split them. I agree that it's likely that the next physical format won't exist, and it will be internet. But a resolution upgrade is certainly possible, and is likely to be 4K resolution, after that comes Ultra High Definition Television (but given how technology works we may skip 4K and go directly to UHDT). Ariel. (talk) 15:16, 25 January 2011 (UTC)

Stereo blu-rays may be "next". They're not a new media, but they're a reason to buy all your movies again if you're into that. It'll be a hard sell, though. 5-10% of the market is stereo blind, (or stereo-blind enough that they don't care about 3d) and the most of rest aren't going to want it until someone invents an auto-stereo TV that can be seen from any angle.

Personally, I'd like to see movies at a higher frame-rate, but I believe that blu-ray disks could handle that as well.

Blu-ray may be the end for a while. Physical collections of movies may become the domain of a small market of enthusiasts and collectors. That's probably not enough of a market to support a new standard every decade. APL (talk) 15:40, 25 January 2011 (UTC)

I stream high definition TV from the internet via Netflix and "Hulu plus" using a Roku wireless connection box. It is a much more satisfying experience than watching Netflix discs or discs from the library or rental place, since most discs which have circulated a few times have scratches causing the program to skip ahead or back, with some bits utterly unwatchable. Only new CDs seem to play reliably without the need to clean the disc and polish out scratches. The only benefit for physical media right now is the larger selection: Netflix still has far more titles on CD than on Internet. I suppose that in the future one might rent or borrow from the library a video program stored on a solid state memory chip. That would get past the problems of a device trying to read a spinning disc optically through jammy thumbprints and deep scratches. Moving media belong in the scrapheap of technology. Edison (talk) 16:33, 25 January 2011 (UTC)

I would like to suggest that your disk player has a problem. Over the years I have rented literally hundreds of disks from Netflix, both DVDs and Blu-rays and I have received exactly two that were damaged in any way that had the slightest impact on my viewing experience. (They were both snapped in half by the postal service.) Not once has a scratch caused even the slightest problem for me. Nor have I ever felt the need to "clean" a disk before putting it in my player, because I know from experience that any number of thumbprints will not effect playback.

On the other hand I find that compression artifacts are very noticeable in Netflix's streaming service, especially since they changed it about two years back. And that's if you have as much bandwidth as Netflix is willing to give you. If your network connection has problems that day (For example, if it's a school snowday and your local cable-provider is over-stressed.) then you'll get even worse quality and the skipping and stuttering you're so afraid of.

(I'll grant that my sensitivity to compression artifacts may be because I watch movies through a projector that lights up my entire wall, and not a small computer screen.)

I'm not complaining, I love both halves of Netflix's service, but for movies that are a "visual feast", there's still no substitute for a blu-ray. Or even a DVD if there's no blu-ray available. APL (talk) 17:14, 25 January 2011 (UTC)

Sadly, the problem is scuffs and scratches on the DVD, (as well as sometimes dirt) since 2 DVD players and a computer DVD drive all have problems with the same DVDs. I would rather have compression artifacts I cannot see rather than have the playback stop, the skip back or forward several minutes. Then I try cleaning the disc, with a soft cloth, which usually does not fix the problem. Then I spend some time cleaning the disc with a device sold for that purpose, if I still want to watch it at that point. Sometimes I try reversing back to as close to the scratched sport as I can, but it always takes out part of some scene I would like to watch without all the fiddling around. You might have a more modern or sophisticated player with more error correction. Edison (talk) 01:00, 26 January 2011 (UTC)

Well, OK, I believe you, but I have rented huge number of Netflix disks (In the three digits) and have honestly never had that problem. I pop the disk into my Playstation3 and it works every single time. I mean that literally. This is not an exaggeration. APL (talk) 03:46, 26 January 2011 (UTC)

Maybe the number of my bad experiences stands out in disproportion to its mathematical exactitude, and the good disc experiences fade into the background. Edison (talk) 18:36, 26 January 2011 (UTC)

I think that the rumors of the death of physical media in the way you are predicting are greatly exaggerated. There will always be people who want to hold physical copies of something, if nothing else, to have possession of it once its DRM authentication server gives up the ghost. Titoxd^{(?!? - cool stuff)} 17:17, 25 January 2011 (UTC)

Based on reports that Blu-ray requires censorship from anyone allowed to mass-produce the disks [1] I would say that it is not actually a storage medium at all, but a publisher with some proprietary format. But it appears that the company is creating some ambiguity on the issue, and I can't say for sure what the full truth is. Wnt (talk) 20:24, 25 January 2011 (UTC)

Note that if you read the linked article carefully, it's only Sony who refused to work with porn. And while Sony may have been a key part of Blu-ray, the Blu-ray group themselves said they would work with anyone. And even before they won the format wars (and everyone else who wasn't part of Blu-ray joined so Sony's influence diminished even more) people were already making Blu-ray porn [2] and there is plenty of porn on Blu-ray porn now [3] (store link, if you are at work and they aren't extremely liberal with what you can do you may want to consider what we're discussing and look at the link name before clicking on it) including of course 3D porn [4] (discussion of a specific title, again think of what we're discussing). On the other hand even while the format wars were ongoing plenty of people mentioned that it didn't really matter much unlike it allegedly was in the Betamax-VHS fight since the porn market was moving on from physical mediums which was what would happen with other movies and shows, and that hasn't died down [5]. Nil Einne (talk) 21:55, 25 January 2011 (UTC)

In fact, the fact the LA porn industry endorsed blu-ray and not HD-DVD was a major deciding factor in the format war. 65.29.47.55 (talk) 01:46, 26 January 2011 (UTC)

I know the Porn-Drives-All-Media has a grain of truth to it, but it can't claim credit this time. Blu-ray's success was almost entirely due to Sony's efforts. Both their strong advertising campaign (Much stronger than the HDDVD one), movies from Sony Pictures were big factors, but most importantly the Playstation3 solved the chicken-egg adoption issue by putting millions of blu-ray players into the homes of people who weren't necessarily looking for a new movie player. APL (talk) 03:58, 26 January 2011 (UTC)

All true I will admit, but the choice by the LA-based porn industry to back blu-ray was a significant coup for the format. If porn decided to back HD-DVD it would have made HD-DVD a potent contender instead of a distant also-ran 65.29.47.55 (talk) 09:10, 27 January 2011 (UTC)

Jupiter," Posibly a furter STAR ?"

I have heard that the core of Jupter is a metalic Hydrygen , posible because of the extreme presure,not posible here on Earth. When our Sun novas and explodes is it posible the core of metalic Hydrgen will ignite and start a new star? ( If you have seen Magneseum burn and the brightness of that, and know the explosive forces of Hydrogen ,with the Sun as a flame or catalist to ignite the metalic hydrogen I wonder if it could become a new Star?" My questioncomes from the artical on Nova posible from Hydogen —Preceding unsigned comment added by 71.190.254.93 (talk) 17:15, 25 January 2011 (UTC)

It already happened in 2010. Staecker (talk) 17:27, 25 January 2011 (UTC)

Most planetary scientists do not believe that the pressures and conditions inside Jupiter are anywhere close to sufficient to sustain nuclear fusion - so the short answer is "no." If you're interested, I recommend this article, Formation of Giant Planets and Brown Dwarfs, written by a leading NASA planetary scientist, that explores the practical observational facts that we have collected on the formation of large planets - there are many similarities and differences from small stars. For the slightly less technical reader, here is a 2002 Nature article, Extrasolar planets, by the same author, that discusses Jupiter structure, comparatively to other celestial observations of stars and star-like objects. That article also states that Jupiter is about 13x too small for deuterium fusion to occur. Nimur (talk) 17:37, 25 January 2011 (UTC)

Stars are not on fire. See fusion. --Sean 18:08, 25 January 2011 (UTC)

Our Jupiter article, in the section "Mass", says that Jupiter might ignite if it were 75 times its current mass. Comet Tuttle (talk) 19:08, 25 January 2011 (UTC)

The chemical reaction of magnesium with oxygen, or hydrogen with oxygen, is completely unrelated to proton-proton fusion. What is more surprising is that fusion is actually a very weak energy source, which our article on the Sun compares to the amount of heat generated by a compost heap! What is difficult to grasp is that the Sun is very, very, very big, and all the heat from the core of the Sun has to come out of the surface. It's as if a "compost pile" the diameter of the Earth were perfectly insulated except for the very top and all the heat just adds up. (See square-cube law if you want a really technical description of that) The funny thing is, hydrogen in the Sun wouldn't even burn with oxygen - in stars that are big enough, just before supernova, the oxygen sinks to the core instead of forming water. That's because the Sun is so hot that it is made up of a "plasma (physics)" where all the electrons are stripped away from the atoms - they're transcended beyond burning. Wnt (talk) 20:35, 25 January 2011 (UTC)

I thought our sun wasn't the right size to even qualify for a supernova death? TomorrowTime (talk) 20:37, 25 January 2011 (UTC)

Sorry about the confusion, I wasn't saying it was - just if it were. Wnt (talk) 20:46, 25 January 2011 (UTC)

This post does pose an interesting question, though: how much matter could Jupiter be expected to capture and accrete while the Sun is shedding its outer layers into a planetary nebula? Titoxd^{(?!? - cool stuff)} 21:13, 25 January 2011 (UTC)

Apply the inverted formula of Jean's Escape to compute a rate of gravitational-capture. The answer depends on the gas temperature. You can estimate an effective "capture cross section" for Jupiter to describe the percentage of gas particles that will pass close enough to Jupiter to be captured (assuming they are ejected from the sun isotropically - a zeroth-order model that you could improve on as you so desire). Over astronomical time-scales, I doubt it even matters which direction or trajectory an individual ejected gas particle follows - eventually, the nebula will reach thermal/gravitational equilibrium; and angular momentum will be conserved. Nimur (talk) 23:15, 25 January 2011 (UTC)

To order of magnitude, if Jupiter captures everything that comes within a few Jupiter radii and the sun ejects matter isotropically then you have a factor that is ((radius of Jupiter) / (orbital distance of Jupiter))^2 = 8×10⁻⁹. Which basically guarantees it won't make a big difference in Jupiter's life cycle. Dragons flight (talk) 23:27, 25 January 2011 (UTC)

The gases that produce a planetary nebula at the end of the Sun's life would be ejected from the outer layers of the red giant sun with enough force to blow away most of Jupiter's atmosphere, leaving perhaps only its metallic core and possibly an outer layer of metallic hydrogen cooling over time despite the core's incredible density. Even to produce a brown dwarf, Jupiter would need to be roughly the same size it is now but at least 13 times more massive, which still is not enough to initiate nuclear fusion. See also formation and evolution of the solar system. ~AH1^(TCU) 22:37, 26 January 2011 (UTC)

I swear we used to have an article on Lucifer project. Vespine (talk) 00:11, 27 January 2011 (UTC)

I think human can do so ...... look that if we add one of jupiters moon mass to it it will be a star , we can send all earth nucleic bombs and explod IO or ganymide or metis then bring it to roche limit and fall on jupiter .then the human will release of that bombs .(INSHALLAH) dont think about that our sun is here for several billion years dont worry

--78.38.28.3 (talk) 16:06, 9 April 2011 (UTC)

  == for more information ==

akbarmohammadzade any interstellar object with mass (Jupiter +moon) will have especial condition and inner pressure and heat for beginning fusion and carbon cycle for nucleic reactivity , my meaning is not that our uranium can case Jupiter to be star , my plan is this (for Imagine only): this is my forecasting of such event 1)first we send nucleic bombs toward one of Jupiter moons (for example Métis or Io) 2)if we bombard it with bombs it will EXPLOD(If all nucleic bombs explode they can explode 5 times earth ) 3)METIS is closer moon to roche limit , and will fall on Jupiter 4)Jupiter mass will Increase (the IO and Ganymede have more mass)with adding it 5)fusion nucleic reaction will began and JUPITER will be a star 6)the magnitude of Jupiter will be first in sky after moon and sun 7) it can create a shadow of objects 8)some nights it will reduce the visibility of other stars and mars in conjunction

9)the radius angle of it remain stable 

10 )it will send poor energy 11)we will see it at day 12)IT can case creating shdow of moon on earth 13)it will send light on unvisible part of moon and we will see it wonder ful 14 )it will has hot winds and storm 16)it will effect on our radio relations --78.38.28.3 (talk) 10:27, 11 April 2011 (UTC) April 2011 (IUST)......

Orbit

What is the name of the object a satellite orbits around? Our article on Kepler's Laws just uses the phrase "sun", but obviously one would not refer to a planet or a black hole as a "sun". --T H F S W (T · C · E) 20:05, 25 January 2011 (UTC)

Perhaps "focus" (of the orbit) or "barycentre" or "centre of mass"? Dbfirs 20:12, 25 January 2011 (UTC)

Focus_(geometry) seems appropriate, but Barycenter seems incorrect, i.e. the focus around which an object rotates is not the center of mass of the system. From our article on Kepler's laws "The Sun is not in the center but in a focal point". The focal point is the abstract point in space though, not the object. SemanticMantis (talk) 20:18, 25 January 2011 (UTC)

... but the focus of the orbit is the barycentre (and the centre of mass of the two objects). The centre of mass is not at the centre of the ellipse, and the rotation is not around the centre of the ellipse. Dbfirs 00:03, 26 January 2011 (UTC)

I would use primary, although the article says that it has yet to obtain currency for extrasolar orbits. --Tardis (talk) 21:51, 25 January 2011 (UTC)

Yes, that's a better answer to the question, since it does ask for the object, and the focus is not necessarily within the object. Dbfirs 01:09, 26 January 2011 (UTC)

I agree that "primary" is a good term, and another description could be that the satellite orbits the centre of a Hill sphere. ~AH1^(TCU) 22:31, 26 January 2011 (UTC)

Autoclaving a bottle of liquid

Suppose you want to autoclave a bottle of medium, to make it sterile, and suppose the medium actually contains bacteria or bacterial spores at the beginning. If I understand correctly, the autoclave's mode of action is to utilise the latent heat of vapourisation of water to sterilise by subjecting things to steam. However, the liquid medium, whose primary component is water, will not benefit from this because steam will not permeate the liquid - it would be no more sterile than if it were boiled, and if any spores remain after boiling, then they would surely remain after autoclaving? Also, how loose should a lid be? Completely, and just resting on top, or..? --129.215.5.255 (talk) 20:24, 25 January 2011 (UTC)

The heat of vaporization has little to do with it. The main point of autoclaving liquids is that it makes them hotter than boiling them under typical room air pressure. For example, the typical lab autoclave will bring liquids to 121 C instead of 100 C. Now in order to do this, you need to do two things:

• Pressurize the chamber. Because water not under pressure boils at 100C, and it would boil out entirely.
• Saturate the chamber with water. Because if boiling water is not in equilibrium with steam, it still loses volume, and you have things in the chamber a fairly long time. (In practice the volume of solutions coming out of an autoclave still tends to be reduced a little, because the air isn't perfectly flushed out, etc.)

The easiest way to do these two things is with highly pressurized steam.

The lid has to be loose enough that there is no way, despite expansion/contraction, that it can possibly stick and form a tight seal, or else SOMETHING is going to give when the pressure changes. Wnt (talk) 20:43, 25 January 2011 (UTC)

(edit conflict) No, autoclaves usually use high pressure steam. I'm not sure what pressure is typical, but I recall autoclaves that were labeled for 2 atmospheres total pressure. The advantage of the high pressure when autoclaving water-based liquids is that it allows the liquid to be heated above 100 C without boiling away. So the media will reach an elevated temperature (e.g. 120-135 C) that is more effective at killing organisms than boiling (at 100 C) would be. Autoclaves intended for this purpose generally have a "liquid-cycle" that controls the pressure in a way that minimizes boiling during the cool-down phase. One also generally needs to run the cycle longer to ensure the whole volume of the liquid is effectively heated when compared with sterilizing empty containers. A rule of thumb with caps is that if you fill the bottle with water then the cap should be loose enough that the water will flow quickly past it and continue flowing easily even if you press down or pull up on the cap. One way to accomplish this is to simply leave the cap resting on top (and that's pretty common), though it is also common to see caps partially threaded, provided they don't create an effective seal. With liquids most of the heat will be conducted through the walls of the container (rather than through the top), but you need to avoid creating a seal that would lead the container to be at a different pressure than the outside since that could lead the container to explode (or implode). Dragons flight (talk) 20:56, 25 January 2011 (UTC)

The science classic "Microbe Hunters" (1926) says that Lazzaro Spallanzani, in the 18th century, sealed flasks of water or broth and left them in containers of boiling water for hours to kill off microorganisms. How was he able to do that without the flasks exploding? There is no mention of using a pressure cooker, and they were glass flasks of thin enough material he could pull the neck down to a thin tube and flame seal it. I have tried boiling a container full of water in a boiling water bath, and the water in the smaller vessel turned to steam. I have no idea how to calculate the pressure which would have resulted had the small vessel been sealed in an open bath of boiling water, but I expect there could have been an extreme pressure rise. Edison (talk) 00:54, 26 January 2011 (UTC)

I don't understand why there should be an extreme pressure rise in the sealed vessel. Provided that the vessel is surrounded by water at 100 degrees, the very slight pressure rise inside the sealed vessel will increase the boiling point of the water it contains above 100 degrees, so only a limited amount of steam can form and the water in the sealed vessel will stop boiling. Of course, if the sealed vessel contains alcohol or some liquid with a boiling point below that of the surrounding water, then pressure will rise higher. In an autoclave, a sealed vessel will perhaps need to be slightly stronger to withstand pressures both ways during heating and cooling, but, with a small expansion space, I still don't see how there will be extremes of pressure, because, once equilibrium is reached, the pressure (up to two atmospheres?) will be the same inside and out. The best way to test this would be to try it with a sealed aluminium can which will show the deformation either way.Dbfirs 08:24, 26 January 2011 (UTC)

In water bath canning, where the water bath boils at atmospheric pressure, a lid with a rubber ring is screwed onto the jar to be canned, which is filled with any fruit, veg, or juice, some of which would be so watery (low in salt, sugar or other solute as to have about the same boiling point as water. Other recipes would have enough salt or sugar that the boiling point would be elevated a bit. (One could always can distilled water, I suppose, for experiment's sake). Only a small airspace is left. Although the lid is on fairly tight, secured by a screw ring, the steam pressure from within forces out steam, and the water level may drop a cm or two more with normal processing times due to steam production. When the boiling stops, pressure drop inside causes the lid to "pop" downward and stay indented. I have always wondered how high the pressure inside would rise if the lid were very tightly shut, and conjectured that the jar might explode. Would higher pressure inside somehow mean higher temperature inside the jar? There has to be higher pressure for the steam to escape during the processing. Edison (talk) 18:32, 26 January 2011 (UTC)

This mostly has to do with the partial pressure of water vapor. Consider if you have a can of liquid water inside a container of boiling water. You wouldn't expect the water to squirt out of the can, or generate steam, just because you have some of it inside a can. (Excepting minor thermal expansion of liquid water) But when you have a can with an air pocket at the top, the water (which after all is at the boiling point) dissolves into the air pocket. The added vapor exerts extra pressure, and makes the air pocket larger or under more pressure. Wnt (talk) 18:43, 26 January 2011 (UTC)

All that seems clear, but could the pressure rise significantly in a sealed jar in a boiling water bath, if no steam at all could escape, assuming some air space to allow for thermal expansion of the water, like to several atmospheres, or only to a small percentage above atmospheric? (If the water bath boiled away, then a steam explosion would be assured after a bit, so don't try this experiment at home). Edison (talk) 22:24, 26 January 2011 (UTC)

Yes, I'm not sure whether a mixture of gases will exert a higher pressure than either of the gases separately. My intuition says that when the pressure rises just slightly, the water will stop boiling and some of the water vapour will condense back into the water, maintaining equilibrium at marginally above the pressure outside, but I haven't tested this out. It should be easy to test safely with just basic equipment, even in a school lab, using a manometer. Dbfirs 08:39, 27 January 2011 (UTC)

For a sealed jar of water, wouldn't a thermometer provide the same information as a pressure gauge or a mercury manometer? I seem to recall, from "chemical thermodynamics" class, tables of pressure versus temperature for water. Should I conclude that a sealed flask of water at 100C would not go wild producing steam with a large pressure increase, given enough "headspace" to allow for volume expansion of the water at the higher temperature? So that the Spallanzani microbioloigy experiments in the late 1700's are credible? Edison (talk) 05:05, 28 January 2011 (UTC)

Well in the experiment that I was imagining (without the autoclave), the thermometer would always read 100 degrees, since heat cannot flow from a cooler to a hotter region. There seemed to be some claim of increase in pressure from formation of steam, independent of an increase in temperature, hence my suggestion of a (simple water) manometer. I can't imagine that it would happen, but it would be reassuring to confirm my intuition with an experiment because sometimes my intuition is wrong. In the autoclave, a couple of maximum thermometers would subsequently confirm equal pressures inside and out (if we can confirm that boiling temperature and pressure are closely correlated). Dbfirs 08:28, 28 January 2011 (UTC)