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August 15

Binary star systems and their planets

In sci-fi shows, planets with multiple suns are often shown. Are the distances between binary systems really small enough to allow a planet to be significantly affected by both stars, to the point where they can be seriously seen to have "two suns" by an observer on the surface? 2.223.230.86 (talk) 01:32, 15 August 2013 (UTC)[reply]

For some binary systems, yes. See Alpha_Centauri_B#Theoretical_planets for some discussion, as well as an artist's rendition of what such a sky would look like. However, in this case the planet would be in the ballpark of 10 times closer to one star than the other to be in a habitable zone, so you would never see two huge suns in the sky. Someguy1221 (talk) 01:39, 15 August 2013 (UTC)[reply]

The OP didn't specify that it has to be a habitable planet. Also, sometimes one star is more than 10X the diameter of another. I wonder if a planet can exist at the barycenter between the two stars, or at Lagrange points between them. StuRat (talk) 07:43, 15 August 2013 (UTC)[reply]

Planets have been discovered orbiting close binary stars at a larger distance, like at Kepler-47.

A planet placed (with 0 velocity) at the barycenter the planet would start falling towards the heavier star, and wouldn't have a stable orbit; and the Lagrange point L1 isn't the place for a stable orbit either. There are stable orbit around the Lagrange points L4 and L5 if one star is a lot more massive than the other (like the Trojan asteroids of Jupiter), and also around both of them (horseshoe orbit). Icek (talk) 08:36, 15 August 2013 (UTC)[reply]

One star has to be at least about 25 times heavier than the other in order for some of the Trojan orbits to be stable. Other stable orbit possibilities are, as Someguy1221 pointed out, when the planet is much closer to one of the stars, or, as Icek pointed out, when the stars are much closer to each other than to the planet. Dauto (talk) 15:08, 15 August 2013 (UTC)[reply]

See circumbinary. Wnt (talk) 15:42, 15 August 2013 (UTC)[reply]

Thank you. 2.223.230.86 (talk) 00:31, 16 August 2013 (UTC)[reply]

nipples

Why do men have nipples — Preceding unsigned comment added by 67.197.49.21 (talk) 04:46, 15 August 2013 (UTC)[reply]

See Nipple#In_male_mammals. Someguy1221 (talk) 04:49, 15 August 2013 (UTC)[reply]

Men don't have nipples in South Carolina. It's against their religion. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:07, 15 August 2013 (UTC)[reply]

But opossums have a baker's dozen, so it evens out. Sadly, it is still far too few overall nipples, if you're a baby opossum. InedibleHulk (talk) 05:32, 15 August 2013 (UTC)[reply]

Basically, if there is no evolutionary advantage to not having them, it is more efficient to use the same DNA for males and females. For men to have nipples doesn't cause us any problems whatever in daily life - so there is no natural selection pressure that would eventually eliminate them. Evolution tends to put as little information as possible on the sex chromosomes for reasons of efficiency - so men and women tend to be identical in ways that don't matter to the perpetuation of our species. Even the organs that we do have that are visibly different are often relatively simple modifications of the same underlying design. Another example of that would be facial hair. Men typically grow full beards and mustaches - women still have hair in those places - it's just fine and short so it's (usually) barely noticeable. SteveBaker (talk) 12:04, 15 August 2013 (UTC)[reply]

It's a little more complex than that - there actually is a phenomenon of male lactation, and however insignificant it may be at this point in history, who knows how often natural selection calls on it on a geologic time scale? And, they're unarguably pretty, i.e. there's sexual selection, which maintains many a useless structure. Wnt (talk) 15:32, 15 August 2013 (UTC)[reply]

There is also male breast cancer, despite the "pinkness" the disease has in pop culture. Though rare (about 1% of breast cancer cases), it can strike even as "manly" a name as Rod Roddy. InedibleHulk (talk) 17:41, 15 August 2013 (UTC)[reply]

Butterfly Wings

I understand that a caterpillar turns into a butterfly after time- so here is my question: If I cut the wings of a butterfly, does it 'revert' back into a caterpillar? Why is it that when a butterflies wings are cut off, it flaps around and dies, instead of living it's old life as a caterpillar? Thank you. --Howdalikya eggsdone (talk) 15:05, 15 August 2013 (UTC)[reply]

It's programmed to behave like a butterfly, also it can't eat anymore. Count Iblis (talk) 15:11, 15 August 2013 (UTC)[reply]

Every part of the butterfly is made anew from imaginal discs - pupation is more than just popping out a pair of wings. The legs are different from those of the caterpillar and the prolegs it used to help hold on are just gone, and the mouthparts are also changed for new foods. Wnt (talk) 15:28, 15 August 2013 (UTC)[reply]

I'm not an expert, but the way I understand it, the caterpillar can be viewed roughly like a highly evolved "egg". The butterfly actually hatches out of it. Vespine (talk) 22:54, 15 August 2013 (UTC)[reply]

No, that's not really accurate. Maybe the transition from caterpillar to adult has a certain amount in common with the stage at which mammalian embryos develop a stratum granulosum (the start of the thickened stratified epidermis) based on the arguable homology of T3 and ecdysone. But understand that adult tissues in many species begin with simple diploid 2n nuclei and develop into more "industrialized" cells with 4n, 8n, etc. nuclei that are big, highly functional, but not meant to replicate. For us, this transition is usually quite gradual and continuous, like liver cells that have a gradual gradient within the liver acinus. Many of our fastest replicating epithelial tissues never get the chance to go polyploid. But in insects there's a huge distinction between the fast-replicating imaginal disc, which is dividing for future use, and the polyploid and nondividing (and indeed rigid) external tissues, which are fully differentiated and finished growing. Still, it is an exaggeration of our more steady cell turnover, I would say. Wnt (talk) 03:59, 16 August 2013 (UTC)[reply]

I have no idea what the following was about. Wnt (talk) 03:59, 16 August 2013 (UTC) :[reply]

Please read the two questions together before answering. CambridgeBayWeather (talk) 01:16, 16 August 2013 (UTC)[reply]
The following discussion has been closed. Please do not modify it.

Is the daytime aurora visible in Northern Norway?

Or isn't it dark enough at Noon in Winter and you would need to go farther North to Svalbard to see it? Count Iblis (talk) 15:07, 15 August 2013 (UTC)[reply]

If you are north of the Polar Circle, it is quite possible to see the aurora at 'noon' - since the sun is below the horizon. I myself saw it around lunchtime in Bodø one January about a decade back, when I was working there for a short while.

The further north you go the more days of no sun there is, logically that gives you a better chance of seeing it. WegianWarrior (talk) 17:13, 15 August 2013 (UTC)[reply]

Yes, but then given how extremely expensive Norway is, I'm not going to stay there for long (I paid 60 Euros for just a simple meal with potatoes vegetables and meat :( ). I was worrying about about the typical daylight aurora not being so bright as the evening one, combined with the fact that the Sun at Noon time not very far below the Horizon in Northern Norway, so you'll have some twilight that may drown out the aurora unless it is unusually bright. In Tromso the Sun will be only about 3 degrees below the Horizon around 21 December, while in Svalbard it will be 12 degrees below the Horizon.

But then I could go to Svalbard in Winter anyway to get to see a totally dark night sky for the first time in my life... Count Iblis (talk) 23:39, 15 August 2013 (UTC)[reply]

Electric rocket propulsion: propellants and ground based use

I read the Ion thruster & Electrically powered spacecraft propulsion articles, and I am not sure what prevents the use of air as a propellant. Why can’t one be used in a vehicle that runs on the ground? I know that chemical rockets & jets are not used in a medium sized ground vehicles like cars because of low efficiency and massive fuel consumption. But that shouldn't stop us from using an arcjet with air as a propellant, right? Diwakark86 (talk) 16:34, 15 August 2013 (UTC)[reply]

Those sorts of thrusters have a high propellant efficiency, but very low thrust. The majority of the examples listed in ion thruster have power outputs that don't compare favorably to a gasoline engine at all. Luckily, on the ground, we don't have to worry about propellant efficiency - instead of ejecting propellant to gain momentum we can just push off the ground with wheels. This is a very efficient way to transfer energy and it doesn't require propellant to be consumed. Also, the arcjet article mentions that the 100kW jet has a 10mile/sec exhaust - I don't think you want cars driving around with that coming out the back. The ion thruster article also explains that propellants are chosen for ionization properties and low erosion, you can't just replace xenon with air and have it work the same way. Jessica Ryan (talk) 16:53, 15 August 2013 (UTC)[reply]

For an example of an ion thruster that uses air as the propellant, see Ionocraft. --Carnildo (talk) 00:56, 16 August 2013 (UTC)[reply]

Chrysler Turbine Cars might be of interest here. While the exhaust wasn't nearly as fast as that from an ion thruster, it's heat was still problematic, as was the noise. That technology was used in the M1 Abrams main battle tank, though, where heat and noise are less problematic. StuRat (talk) 07:02, 16 August 2013 (UTC)[reply]

That Chrysler is a really interesting car - I never realized that any manufacturer developed a gas-turbine car all the way to being basically production-ready! Old helicopter turbines show up in boats every so often, and I think I read about Jay Leno driving a motorcycle that someone managed to fit one into... However, I read the question as using the rocket effect to accelerate - gaining forward momentum by putting an equal amount of momentum into the propellant, which is ejected. A gas turbine car still moves by pushing wheels against the ground. I suppose you could duct an ion thruster through a turbine and use that to get power to the ground, but I have a feeling it is a lot more efficient (and simpler/cheaper) to use the electricity to run an electric motor instead. Jessica Ryan (talk) 11:46, 16 August 2013 (UTC)[reply]

Thanks for the response. Looking back at the article there is one more thing I didn’t understand: why is the thrust for an electricity/ion based jet low? Is there a design constraint that prevents us from building a more powerful thruster, like material that handles high plasma temperatures or is it just that it is not as efficient as a magnet pushing a current carrying wire in a motor? Also is there any method available to compare the efficiency of pushing the ground for thrust as opposed to pushing air?Diwakark86 (talk) 17:13, 19 August 2013 (UTC)[reply]

August 16

Identification of bug

I found this bug on the wall next to my front door this afternoon. Any idea what it is? NealCruco (talk) 00:29, 16 August 2013 (UTC)[reply]

That's a nice katydid, note the long antennae. Generally a harmless and interesting insect. Getting any more specific than that ~~will~~ might require some location information, and perhaps a sample specimen and Identification key. SemanticMantis (talk) 01:20, 16 August 2013 (UTC)[reply]

Maybe a common true katydid: Pterophylla camellifolia? Vespine (talk) 02:11, 16 August 2013 (UTC)[reply]

Well, I live in the CST time zone of the US. Is that specific enough? NealCruco (talk) 20:02, 16 August 2013 (UTC)[reply]

Your latitude is probably at least as important as your longitude. Nyttend (talk) 02:06, 18 August 2013 (UTC)[reply]

Vacuum pump

Do foot operated manual vacuum pumps exist, which are able to attain partial pressures involved in Büchner filtration? Plasmic Physics (talk) 01:54, 16 August 2013 (UTC)[reply]

Could you state the level of vacuum needed, in case someone is more familiar with pumps than with the particular process? Lots of gas chemistry was done in the 19th century with manually operated equipment. ~~Hard vacuums were achieved with mercury operated pumps rather than mechanical pumps.~~ Edison (talk) 14:23, 16 August 2013 (UTC)[reply]

The article on the process says an aspirator will work.I would call it a "suction" rather than a vacuum process, so comments about high vacuum do not apply. Foot operated aspirators are available, though the supplier I found is a wholesaler. See Medical foot operated manual vacuum aspirator where the FOB price is stated as $30-$180, so shop around. If you are handy, it might be possible to alter a typical foot operated inflator pump so that it acts as a suction pump. Here is a different design of foot operated aspirator which produces 300 mm of suction. There are also venturi suction devices which use the flow of tap water through a device to create suction, and cost about $7. Edison (talk) 14:44, 16 August 2013 (UTC)[reply]

Water-tap aspirators are pretty commonly used for this application. I've had problems with these sorts of filtrations when the vacuum source is pulsed rather than a more constant pull, but it depends on the nature of the liquid, solid, and filter-medium being used.. DMacks (talk) 15:28, 16 August 2013 (UTC)[reply]

The idea is to save on utilities, I don't want to be running up my parents' bills. I'm visualizing something like a spinning wheel - a pump which converts reciprocal motion to rotational motion.

Meaning, I'm not going to waste perfectly good water. Plasmic Physics (talk) 05:01, 17 August 2013 (UTC)[reply]

The spinning wheel is supposed to function as a fly wheel, preventing a pulsed vacuum. Plasmic Physics (talk) 08:12, 17 August 2013 (UTC)[reply]

'Suction'/vacuum', 'tomato'/'potato'. Thanks, I'll have a look at those. Plasmic Physics (talk) 01:09, 17 August 2013 (UTC)[reply]

Gingko biloba cutting

I took a 12 in. cutting from a tree a few weeks ago and have kept the proximal end in water ever since. For about 2 weeks it was doing fine and all the leaves remained moist and green and everything nice. But then, without warning, it shriveled and now I had to throw it out. Anything I should have done differently? My plan was for it to sprout rootlings and then I could plant it in soil and get a tree eventually by transferring it into a backyard. DRosenbach ^{(Talk | Contribs)} 03:48, 16 August 2013 (UTC)[reply]

Maybe should have used Indole-3-butyric acid? See cutting (plant). Wnt (talk) 04:03, 16 August 2013 (UTC)[reply]

Using water alone to propagate woody plants is always going to be problematic. The time taken for roots to appear is almost always longer than the time that mould or fungus takes to infect the cutting. This page suggests (1/3 way down) 15 centimetre cuttings of semi-ripe wood in summer in a cutting compost, this is a standard procedure for woody subject. My intuition tells me that gingko biloba are not that easy to root but I can't point you at a citation. Good luck, they are very interesting trees. Richard Avery (talk) 06:27, 16 August 2013 (UTC)[reply]

I'm about to stick a few cuttings in the ground. Spring soon where I am. I shall let you know in three months time. HiLo48 (talk) 07:07, 16 August 2013 (UTC)[reply]

As per above, I'd use some rooting hormone, and a little fungicide (neither of which has to be noxious). Rooting woody plants in water-only is often a bad idea, but they also must not be allowed to dry out in the first several weeks. Finally, a fun trick: Salix spp. root very well in pure water, and that water can then be used to root other plants, since it will have dissolved hormones from the willow! SemanticMantis (talk) 13:26, 16 August 2013 (UTC)[reply]

Ginko is a very primitive type of plant and is very different from other more advanced broadleaved trees. Our article Ginkgo biloba says; "most intentionally planted ginkgos are male cultivars grafted onto plants propagated from seed, because the male trees will not produce the malodorous seeds." The fact that cultivated root-stocks are grown from seed suggests that it's probably not easy to propagate it from a cutting. Alansplodge (talk) 13:36, 16 August 2013 (UTC)[reply]

But apparently it can be done: "The Ginkgo can also be propagated by cuttings (best way to be sure of the sex). Take young or half-ripe wood about 15 cm long during May-July. Put these in a frame and keep moist. They usually start growing best in their second year. You may also take cuttings of mature wood of the current year's growth. Shoots about 15-30 cm long are taken in December and placed in a frame. They should root in the spring."[1] Alansplodge (talk) 13:39, 16 August 2013 (UTC)[reply]

Fireflies completely gone from Indianapolis suburbs! Why?

Thirty years ago the suburban Indianapolis farm where my uncle has lived for nearly a century was teaming with fireflies at at least three or four per square foot on August nights. Today there are NONE. I stood outside wandering around the three acre plot for four hours and did not see a single firefly. I do not believe the explanations in http://www.firefly.org/why-are-fireflies-disappearing.html because there is no light pollution here: the same lights are in the same place and the road traffic is the same volume as it was 30 years ago. What do the reliable peer reviewed sources say about this tragedy? 98.220.133.91 (talk) 05:09, 16 August 2013 (UTC)[reply]

Indy got hit hard by the 2012–13 North American drought--Digrpat (talk) 09:42, 16 August 2013 (UTC)[reply]

True, but we also did here in central IL, and we had a fine firefly season this year. Actually, it peaked almost a month ago, and there are very few left. So perhaps the OP might have found a few round last month? SemanticMantis (talk) 13:27, 16 August 2013 (UTC)[reply]

Our article does say that they prefer "marshes or in wet, wooded areas"...so I could imagine a drought hitting them hard. SteveBaker (talk) 15:44, 16 August 2013 (UTC)[reply]

If it is a working farm I would ask about recent pesticide usage. Wnt (talk) 19:16, 17 August 2013 (UTC)[reply]

Indianapolis isn't the only firefly-free part of Indiana. There are very few fireflies around my house (whether in the woods or in the fields), and I'm in a rural area near Lake Monroe, south of Bloomington. We've been hit at least as hard as Indianapolis has by the drought (although not as badly as the areas west of Evansville); friends of mine in town have a stream in front of their house, but both last summer and this summer have seen it completely dry when it's normally a foot or two deep. Nyttend (talk) 01:56, 18 August 2013 (UTC)[reply]

Update — immediately after leaving this note, I stepped outside to watch for fireflies; my house is in the woods. In approximately four minutes, I saw exactly six of them: that's fewer than I'd see in one minute as a child in rural western Ohio. If you've been down toward the Hoosier National Forest, you'll know that we have few marshes down here, so they have to depend on the existence of wet, wooded areas. Nyttend (talk) 02:02, 18 August 2013 (UTC)[reply]

identify a plant

Can anyone identify this plant, please? I found it growing in the gap between two concrete slabs in my walkway, in St. Louis, Missouri.—msh210℠ 07:07, 16 August 2013 (UTC)[reply]

Pokeweed Phytolacca americana --Digrpat (talk) 09:23, 16 August 2013 (UTC)[reply]

Many thanks.—msh210℠ 18:23, 16 August 2013 (UTC)[reply]

Bom

How powerful would a bomb have to be for a tremor to be felt at the top of mount everest if it detonated at the deepest part of the ocean? 163.202.48.125 (talk) 12:09, 16 August 2013 (UTC)[reply]

Using this program, modeling the effects of an explosion as similar as one due to an impact (except for the air blast):

Input: Distance from Impact: 5000.00 km ( = 3110.00 miles ) Projectile diameter: 15.00 km ( = 9.32 miles ) Projectile Density: 8000 kg/m3 Impact Velocity: 30.00 km per second ( = 18.60 miles per second ) Impact Angle: 50 degrees Target Density: 1000 kg/m3 Target Type: Liquid water of depth 10.0 km ( = 6.2 miles ), over crystalline rock.

Energy:

Energy before atmospheric entry: 6.36 x 10^24 Joules = 1.52 x 10^9 MegaTons TNT

Seismic effects:

The major seismic shaking will arrive approximately 16.7 minutes after impact. Richter Scale Magnitude: 10.7 (This is greater than any earthquake in recorded history) Mercalli Scale Intensity at a distance of 5000 km:

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.

V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.

Tsunami:

The impact-generated tsunami wave arrives approximately 4.5 hours after impact.

Tsunami wave amplitude is between: 255.0 meters ( = 837.0 feet) and 510.0 meters ( = 1670.0 feet).

Count Iblis (talk) 13:31, 16 August 2013 (UTC)[reply]

Bom 2

How powerful would a bomb have to be for a tremor to be felt at the deepest part of the ocean if it detonated at the top of mount everset? 163.202.48.125 (talk) 12:09, 16 August 2013 (UTC)[reply]

About as big as Bom 1 Caesar's Daddy (talk) 13:06, 16 August 2013 (UTC)[reply]

Much bigger, because you only get a big air blast; the seismic effects are then much less for the same explosion yield. Count Iblis (talk) 13:37, 16 August 2013 (UTC)[reply]

One problem is that Everest is a long way from the nearest ocean...and just about the opposite side of the planet from the Marianas trench (which is the deepest part of the ocean). That's a much bigger issue than whether you're at the top of a mountain or not. Another problem here is that you say "...for a tremor to be felt..." - you mean felt by a person? I guess their feet can't be touching the ground at the bottom of the deepest part of the ocean...so it's a bit hard to know how much seismic motion there needs to be under those circumstances. Is the person in a submarine? Either way, it's a heck of a lot more than if you were standing on the ground.

This document (which is talking about long distance seismic waves) says that "...larger power sources tend to produce lower frequencies." Unfortunately, humans are less good at detecting low frequency waves through our feet - a wave that moves the surface through (say) a millimeter over a time period of several minutes is detectable by instruments pretty easily - but not by humans. So we wouldn't "feel" the highest power sources. A very high frequency vibration of a tiny fraction of a millimeter is easy to feel...but that's not what you'll get here.

Underwater, you might feel a resulting tsunami - but not that far from land - and certainly not so deep.

The 1883 eruption of Krakatoa caused an explosion was estimated to be about 200 Megatons - four times larger than Tsar Bomba - the largest nuclear weapon ever made. Krakatoa is by far the largest explosion to have happened on earth in recorded history. It makes a great example of what could perhaps be achieved here.

That explosion was heard up to 3,000 miles away(!) - nowhere near far enough for your thought-experiment - so a guy sitting in a rowboat above the Marianas trench wouldn't hear it. Seismic instruments everywhere in the world measured the seismic waves - which looped around the world at least seven times before they faded too much to be measured. But those instruments are vastly more sensitive than people can feel themselves. Air pressure sensors also measured the change all around the world - but those effects wouldn't be noticable at the bottom of the ocean.

Smaller water waves were detected in fairly crude tidal gauges in the English channel - which is about as far from Krakatoa as you can get - so our guy in his rowboat might be able to detect it - but again, you wouldn't feel those at the bottom of the ocean - only in the surface layers of the water.

There don't seem to be any reports of people FEELING the explosion at ranges out at 3,000 miles where they could only just barely HEAR it...so people didn't feel the explosion on the other side of the world. It's pretty clear that 200 Megatons is nowhere near enough to do what you're looking for.

So the nearest I can get to a conclusion is that you need much MUCH more than 200 Megatons - which is already four times that of the biggest nuclear weapon ever manufactured.

The Valdivia Earthquake in Chile in 1960 (the largest earthquake in recorded history) produced seismic waves with 12 times more energy than Krakatoa - with an energy of around 2.7 gigatons - and even that was not felt by humans around the world - although it wasn't technically an explosion, so perhaps it doesn't count.

I doubt it can be done with any reasonable technology.

SteveBaker (talk) 15:31, 16 August 2013 (UTC)[reply]

One nitpicky detail: Everest is not really all that far from the Mariana Trench. Antipodes shows that the opposite side of the world from Everest is some distance off the west coast of Chile. The Trench is south of Japan and east of the Phillipines, and its antipode is somewhere around the coast of Brazil. As to setting off a bomb atop Everest, I would think Everest itself would absorb (and possibly be damage by) such a blast. Supposedly the crust under mountain ranges is much thicker than in the flatter areas of the continents, so the bomb would have to have the energy of a major earthquake - and that would take a huge amount of TNT. What humans can do pales by comparison with what Mother Nature can do. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:35, 17 August 2013 (UTC)[reply]

As a point of comparison, the Tunguska event in Siberia in 1908 knocked down an estimated 80 million trees over an area covering 2,150 square kilometres (830 sq mi), and it was only about 40% the power of Tsar Bomba. Krakatoa was 10 times as powerful as Tunguska, and Valdivia was 12 times as powerful as Krakatoa (or 120 times as powerful as Tunguska - roughly equivalent to the destruction of 10 billion trees). -- Jack of Oz ^{[pleasantries]} 20:09, 18 August 2013 (UTC)[reply]

Neutron gamma gamma

The article Neutron gamma gamma was created on August 14, 2013 and says things like"When two gamma photons are in contact, and unlike charge state (+ -), [3], are engaged by the ultra-high electric hook." "The two photons gamma (gamma pair) move at the speed of light, but the ultra-electric hook bend their trajectories rotating them on a imaginary center mass " and "Stability of gamma pair becomes unbalanced at about 10.3 minutes (statistical), but not broken. [26]" Is it the gibberish it sounds like? Are there little "gamma gammas" spinning around which resemble the Yin Yang images?Individually there are a number of verifiable facts in the article, but is it overall an accurate depiction of a notable topic in physics, or is it original research? Edison (talk) 15:26, 16 August 2013 (UTC)[reply]

The article obviously needs either deleting or serious and ruthless editing, but I'm not sure which. We need a particle physicist. There is a process called Neutron-gamma (η,γ) otherwise known as Neutron capture, but we already have an article on this. Is User:MARCOS BUIRA PARDO trying to explain this, or some other process? Dbfirs 16:30, 16 August 2013 (UTC)[reply]

The phrase "neutron gamma gamma" - which I have never heard before - is never explained, or even used - and does not appear in any of the "references" listed at the bottom; so at the very least, we can say the article is improperly titled. The references themselves are mostly reasonable and reputable websites, but they do not validate the material in the article or mention the title. In other words, Template:Irrelevant_citation and Template:Failed_verification applies.

After trying to read two or three paragraphs, I am inclined to declare the page "patent nonsense," and at the risk of escalating accusations about my grouchiness, I recommend deleting the article. It satisfies several criteria for deletion, and I do not believe even generous editorial help can save the article. Nimur (talk) 17:23, 16 August 2013 (UTC)[reply]

It looks like nonsense, but not quite patent. I'd take it to AfD rather than {{db-nonsense}}. --Trovatore (talk) 21:12, 16 August 2013 (UTC)[reply]

So nominated per WP:DUCK. Clarityfiend (talk) 00:53, 17 August 2013 (UTC)[reply]

I expect little subatomic particles, however small would spin madly about their "imaginary center of mass," even if they were somehow oppositely charged but massless, and the article may contain numerous true and referenced statements and facts, but may not have a subject that satisfies WP:V and WP:N. The article creator's lack of fluency in English might be part of the problem. Edison (talk) 04:42, 17 August 2013 (UTC)[reply]

When a neutron star explodes (by nuclear reaction), what expelling? quarks or gamma photons. MARCOS BUIRA PARDO (talk) 14:07, 17 August 2013 (UTC)[reply]

Marcos, could you tell us what you read to get the information for this article? Are you describing Neutron capture? Dbfirs 07:33, 17 August 2013 (UTC)[reply]

Sorry for the confusion, I'm Spanish, I'm using Google translator. Neutron gamma gamma, is a neutron model not based on 3 quarks. But it has a precise mathematical support for size,energy and mass. Thank you very much.MARCOS BUIRA PARDO (talk) 14:07, 17 August 2013 (UTC)[reply]

Google translate is not really suitable for writing Wikipedia articles (though it is useful for translating articles into your own language). Perhaps you should write the article in Spanish and try it on the Spanish Wikipedia, but you will need to provide references. I wonder if the best place for alternative theories on neutron structure might be the article on Neutron. Dbfirs 16:22, 17 August 2013 (UTC)[reply]

... later ... I don't read Spanish, but I'm told that the article doesn't make much sense in Spanish either. What references are you using? If this is just your own theory, then Wikipedia is definitely not the place to publish it because we don't allow original research. Dbfirs 07:26, 18 August 2013 (UTC)[reply]

How to compute the RGB values from the raw data of the camera?

As I understand it, a digital camera only has 3 sensors for each pixel with different spectral sensitivities. These don't correspond to the spectral sensitivities of the cells in our eyes, a linear transformation (the color matrix) is used to compute the RGB values and then some nonlinear transforms are used. However, I don't see how you could ever get the RGB values right if you only have 3 independent measurements that do not correspond to RGB.

So, the problem is that the "color space" of each pixel is infinite dimensional, because you have specify the amplitude of each frequency. Then what we perceive is always is the projection onto a 3 dimensional subspace, that subspace being defined by the spectral sensitivities of the cells that can detect red, green and blue light. But the camera has 3 different sensors, it project each pixel in a different 3 dimensional subspace. Count Iblis (talk) 18:07, 16 August 2013 (UTC)[reply]

SCIEN recently had an excellent presentation on this topic: essentially, a digital camera's electronics and computer is numerically inverting for several optical and physical processes, not least of which is the color filter array. Count Iblis correctly notes that the problem is underconstrained (in the pure mathematical sense of that word); this means that each implementer has to use a lot of heuristic tricks, leaving much room for error. I will see if the presentation video or slides are available to the public. Nimur (talk) 18:22, 16 August 2013 (UTC)[reply]

Thanks, it would be interesting to read more about this. I had not read into this issue before. It was only after I bought my Sony camera and the software for processing the raw files didn't work on my computer that I started to read about this. Alternative software is available but my camera isn't supported so I needed to find out about the way the colors are computed from the camera sensors. Count Iblis (talk) 19:22, 16 August 2013 (UTC)[reply]

Unfortunately the presentation I linked is available but non-free. In the interrim, we have a modest article on the generic color image pipeline; you can implement such a processing flow in software. The naive implementations for each stage are generally self-evident; the hard part is making algorithmic improvements that work without loss of generality. But if you're only processing a few images, this need not be an urgent concern. I'm not aware of any good free software implementations, but if you're willing to do a lot of manual work to tune up the results, dcraw can be used in GIMP; or if you prefer commercial software, you can download a Sony raw data plugin for Adobe Photoshop. Aperture (software) also works with Sony cameras, out of the box. Nimur (talk) 17:53, 17 August 2013 (UTC)[reply]

You may be overlooking that any three independent linear combinations of the cone response curves are as good as the actual cone response curves—they span the same (co-)subspace. Also, real-world spectra are pretty simple, otherwise a small change in illumination or a slightly tinted filter would totally change the apparent color of everything. Camera sensor response curves that aren't quite right won't distort the colors of real scenes too badly. -- BenRG (talk) 12:27, 20 August 2013 (UTC)[reply]

About running--------

If a person having weight 50 K.g.is running everyday in the morning about an hour with walking of 4 kilometers.He consumes less food than he want to eat.So what should be the effective change in the body? — Preceding unsigned comment added by Titunsam (talk • contribs) 18:17, 16 August 2013 (UTC)[reply]

There are many online sites showing how many calories you consume with exercise ([2] for example).

Basically, the calories from running for an hour will vary between about 470 to over 1000 depending on how fast you run. To get much over 600, you'll have to be running faster than most people can sustain for an hour - so 500 calories is probably a good number to go with. Walking 4km (2.5 miles) at a normal pace (around 2.5 mph) means that you're doing an hour of general walking - which consumes maybe another 180 calories. So you're consuming 680 from exercise. If you'd sat and watched TV for those two hours, you'd only have consumed around 220 calories - so you'd about 460 ahead of the game - which is about as much as one slice of pizza. (This is why exercise doesn't really excite me! I'd rather not bother with the exercise and eat one less slice of Pizza...but that's just me!)

It takes 3700 calories to make one pound of body fat - so you have to eat 3700 calories less than you burn in order to lose one pound.

So if you're only eating the barest minimum to keep your weight stable without exercise - then your exercise program should help you lose nearly a pound every week...which is a pretty good, sensible weight loss rate.

However, one extra slice of pizza per day - or a bag of potato chips every two days - completely wipes out the weight loss effect of all that exercise.

The problem is with "He consumes less food than he wants to eat". That's not a useful measure of what's good for you. If I eat whatever I want to - I'll go 500 calories over my ideal calorie intake every day. It only takes half a bag of chips to do that! And then I'll pack on a pound a week - and within a year I'll be seriously overweight.

To do this properly, you need to count and weigh EVERYTHING that passes your lips. Do this for a week - and by then you'll have a pretty good idea of what you're really consuming - in terms of calories.

For "numbers geeks" like me - I strongly recommend "The Hacker's Diet" - it's a great book that explains all of this clearly. Follow what it says to the letter and you'll lose a pound a week. Don't try to lose any faster than that though or you risk putting your metabolism into "starvation mode" - at which point losing weight becomes a major problem.

SteveBaker (talk) 19:04, 16 August 2013 (UTC)[reply]

That's what works for you, Steve. This is very individual. Some people eat less when they exercise, because exercise fills the void that they used to fill with the potato chips. (Or, in my case, there was I time I was controlling my weight by swimming, and I think part of the effect was that it made me just a tiny bit sick to my stomach and I didn't want as much lunch afterwards.) There was a period of a good number of years where I was able to control my weight with exercise alone, eating pretty much whatever I wanted. That's not true anymore, but it got me through at least five years consecutively, which is not to be dismissed lightly. --Trovatore (talk) 19:14, 16 August 2013 (UTC)[reply]

Yes, I agree. The hackers diet book does go into the science of this in some detail - and there is more to this than meets the eye. Personally, I find that exercise makes me incredibly hungry - so afterwards I'll want two more slices of pizza - and that doesn't just reverse the effects of exercise - it makes matters worse. Buy yeah - everyone is an individual. The best answers we can give are broad-brush. SteveBaker (talk) 19:30, 16 August 2013 (UTC)[reply]

Yes, and my own experience would point to the calory intake not being relevant for your weight (within a reasonable bandwidth) provided you exercise vigorougly almost every day. It doesn't make sense to me that an animal that has to survive in the wild would starve to death if due to changes in the environment it had to spend a bit more energy to get its food and if the amount it would find were a bit less. Obviously, it would just adjust its metabolic rate to keep its weight constant, warm blooded animals must have such a mechanism to avoid starving to death for such trivial reasons (note that 100 Kcal/day deficit = 46 kg weight loss in ten year time, but I'm sure I won't starve to death in ten years if I were to eat a sandwich a day less and increase the time I exercise a bit).

I measure everything I eat, I know that I eat close to 4000 Kcal per day now. I have increased my calory intake a lot it used to be just over 3000 Kcal/day a few years ago, and yet I have lost some weight, I used to weigh about 61 kg and I'm now at 58 kg. This is consistent with my idea that the body is designed to regulate itself, and eating until you are full is part of a normal healthy routine but then so is running for at least 30 minutes per day (I run for 50 minutes, 5 times per week). Why on earth would the signal for feeling hungry be wrong so that listening to it would undermine your health? To me that doesn't make sense at all. And if this is actually the case for some people, then these people have some health problem to begin with, which in most cases I believe is that they are couch potatoes. Count Iblis (talk) 19:44, 16 August 2013 (UTC)[reply]

Thermic effect of food

I read over here that digesting food requires calories. I was wondering if there's any food that requires more calories to digest than they contain. ScienceApe (talk) 21:08, 16 August 2013 (UTC)[reply]

See our Negative calorie food article. DMacks (talk) 21:13, 16 August 2013 (UTC)[reply]

August 17

Early gum disease

The Reference Desk does not give medical advice. Please ask your dentist for advice on your gum disease.

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

Hello, I went to have a cleaning at my dentists and she said I "technically have gum disease (gingivitis)" on one or two of my teeth. They are the last teeth at the back of my mouth on the top and bottom, and they are a bit tender. She said to make sure I brush and floss twice a day, along with using a mouthwash, and I plan on doing so religiously. My dentist didn't say, and I have looked on the internet for an answer, but I can't seem to find a concrete one: how long does it usually take for the gums to stop being inflamed, and the general symptoms of gingivitis to go away? Thanks. 64.229.155.218 (talk) 04:21, 17 August 2013 (UTC)[reply]

using FASTA format

What's the meaning of the numbers in the 1st line of a particular sequence, like in the following example ?

>gi|5524211|gb|AAD44166.1| cytochrome b [Elephas maximus maximus] LCLYTHIGRNIYYGSYLYSETWNTGIMLLLITMATAFMGYVLPWGQMSFWGATVITNLFSAIPYIGTNLV EWIWGGFSVDKATLNRFFAFHFILPFTMVALAGVHLTFLHETGSNNPLGLTSDSDKIPFHPYYTIKDFLG LLILILLLLLLALLSPDMLGDPDNHMPADPLNTPLHIKPEWYFLFAYAILRSVPNKLGGVLALFLSIVIL GLMPFLHTSKHRSMMLRPLSQALFWTLTMDLLTLTWIGSQPVEYPYTIIGQMASILYFSIILAFLPIAGX IENY

Thanks, BentzyCo (talk) 16:05, 17 August 2013 (UTC)[reply]

~~These are accession numbers.~~ The first one is an unique identifier for this sequence (GI number). The second one (after gb|) is an accession number. See [3] for details. 31.11.184.50 (talk)

Engine braking II

I recently (August 12, 2013) posted a question on engine braking and got satisfactory answers, thanks to all who responded. Well I soon realized it provoked a new question: why is it needed at all? The negative aspects are obvious: a lot of noise, no additional energy is returned to the battery (a parasitic effect as someone, perhaps SteveBaker, said), why not to use simple mechanical brakes we all have in our cars?

Thanks, - Alex174.52.14.15 (talk) 16:58, 17 August 2013 (UTC)[reply]

Because, as our article Engine braking says (confusingly in the Legal Implications section) it "can help save wear on friction brakes." Using conventional brakes alone will result in their wearing out more quickly (and as a driver I can attest that replacing brake pads is not cheap, whereas I've never had to replace an engine before changing the car for a newer one).

In a car the additional use of engine braking is never likely to be strictly necessary as opposed to merely aiding economy, but on a heavily loaded truck going down an incline, mechanical brakes in less-than-good condition alone might prove insufficient and/or fail entirely. {The poster formerly known as 87.81.230.195} 90.213.246.168 (talk) 17:28, 17 August 2013 (UTC)[reply]

The use of engine braking versus friction braking comes down to one thing:

Which is cheaper - clutch or brakes?

On a large truck, the answer turns out to be "clutch"...engine braking takes a toll on the clutch - but in a big truck, it's cheaper to replace than all of those wheels.

In your car, the clutch is much more expensive than a set of brake pads - so you should probably rely mostly on friction brakes.

That said - there is a problem with friction brakes - they dissipate the kinetic energy of the vehicle into heat in the brakes and brake pads. If they get too hot, the brake fluid will boil - then there are bubbles of steam in your brake lines and since steam is easy to compress (and brake oil isn't) - when you stomp on the brakes, nothing happens! This is called "brake fade" and it's dangerous and scarey as all hell! Hence you should ALWAYS use engine braking when coming down a long hill to avoid overheating your brakes. Race car drivers also use engine braking for the same reason - but they can use both and brake much harder than they otherwise could. (They likely replace the brakes and clutch after every race anyway).

SteveBaker (talk) 22:15, 17 August 2013 (UTC)[reply]

How can I use engine braking in my small Honda sedan?

- Alex — Preceding unsigned comment added by 174.52.14.15 (talk) 23:10, 17 August 2013 (UTC)[reply]

Downshift to a lower gear to slow the car down. RudolfRed (talk) 00:29, 18 August 2013 (UTC)[reply]

...and take your foot off the gas. It can seem alarming because the engine revs so high - but that's OK because without much gas in the cylinders, there is little stress. SteveBaker (talk) 01:44, 19 August 2013 (UTC)[reply]

Dragonfly behaviour

I was up at a cottage (in Central Ontario) for the last week and, while there, I spent some time watching the dragonflies. At one point I saw some odd behaviour. Two fairly large dragonflies (I'm guessing common hawkers, but I'm no expert) were performing what I assumed was a mating flight, riding piggyback intermittently along the edge of a small lake (however, this indicates it's not nearly so straightforward as I thought). Afterwards, one of them began dipping itself into the water, but it was not dipping the tip of the abdomen, where any eggs would come out, but rather the thorax/legs area. It touched the water surface like so, then flew on a few inches and repeated, again and again for at least a few minutes. The abdomen was kept fairly stiff and definitely up out of the water. It was not hurt or having trouble flying (and there was a lot of vegetation it could have landed on if it was having trouble) and it performed at least a few dozen of these dip maneuvers before it flew off. It seemed to be aiming for open areas of water rather than tight against the water lilies. What was going on here? Dragonflies are (AFAIK) purely flight-based predators as adults, so it was not likely hunting anything. Given the fish population it was quite risky behaviour to engage in, so I'm assuming there's some reason behind it? Matt Deres (talk) 21:19, 17 August 2013 (UTC)[reply]

August 18

what substance is this

hello, we all know these electronic devices, mostly for computers, with a fancy casing that feels rubber-like or velvety to the touch. I have a DVB-T adapter like this. The thing is, its casing got sticky and somewhat gooey over time, I think because of this coating, whatever it is. What is it and is it dangerous (notorious plasticizers evaporating and whatnot?) Уга-уга12 (talk) 01:25, 18 August 2013 (UTC)[reply]
If I'm worried, is there a way to get checked for this stuff (absent concrete medical complaints)? Will one's GP do it? (I think not), and if not, who will? Thank you everyone Уга-уга12 (talk) 01:37, 18 August 2013 (UTC)[reply]

We won't be able to give you medical advice, but without even knowing the make and model of the device, it's unlikely that anybody will be able to give you any information at all. Looie496 (talk) 20:03, 18 August 2013 (UTC)[reply]

How accurate is long-range DNA analysis?

Consider this scenario:

There are two men, who are non-identical brothers, and I know that one of them is my father, but not which one. Today, DNA analysis can tell me with certainty which one is my dad.

Suppose now that I am not the son of one of those men, but the great great grandson of one of them, and that we have their DNA profiles on record. Is it just as easy to say which one of them was my great great grandfather? And if not, for how many generations is the verdict’s certainty beyond doubt, and for how many before it has no value at all?

And is the scenario different if the siblings are two women, or one women and one man? Myles325a (talk) 01:58, 18 August 2013 (UTC)[reply]

Straight line male ancestors generally are identifiable a long way back. Red Y-chromosomal Adam for some info on this. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:15, 18 August 2013 (UTC)[reply]

Wouldn't Y-Chromosome testing be almost useless in determining which of two siblings is the father? If Y-Chromosome is useful in identifying patriarcal lineage because it changes very little, it also means two male siblings would have almost the same Y-Chromosome as their own father. The test can be useful over several generations to determine if you are patrilineally related to a person, but I'm not sure it would be useful in determining which of two brothers is the father (assuming the brothers have the same father) Effovex (talk) 18:18, 18 August 2013 (UTC)[reply]

Ah, I think you're right that the Y-Chromosome wouldn't be enough to fit your scenario. It should be enough to prove that the great-great-great-grandfather was (or was not) in your line. But not enough to prove which of his sons was your great-great-grandfather. Additional information would be needed. As with the blood test, it can be a lot easier to disprove paternity than to prove it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:58, 18 August 2013 (UTC)[reply]

The most powerful method is whole-genome sequencing. Given that the body of Richard III, who died in 1485, was recently identified by comparison with the DNA of a known modern descendant, it's clear that the approach can go back a long away. Not indefinitely, because each extra generation cuts the signal in half, but quite a long way. Looie496 (talk) 19:59, 18 August 2013 (UTC)[reply]
- Richard III was identified by matrilineal descent -- mitochondrial DNA passed down almost unchanged from Richard's mother down a line of females to the mothers of two test subjects today, which all matched.
For the scenario raised, you need to be looking at autosomal DNA -- ie DNA from chomosomes other than X and Y. The simplest example of that is the CODIS test used in forensics. But the amount of autosomal DNA inherited from a particular ancestor halves with each generation you go back -- so whereas 13 CODIS markers is very likely to be enough to determine paternity, it may or may not be enough even at the level of grandparentage. (You would need to be very sure of all three other grandparents' CODIS markers, and hope that the two to four markers inherited from the ambiguous fourth grandparent, (i) are different between the two candidates, and (ii) are different from what might have come from any of the other three grandparents).

You can get round that to some extent by going to more markers, eg an Affymetrix 500,000 SNP marker chip as used by eg 23andMe, though those are SNP markers, which have less variation (both intrinsically, and in the population) than the STR markers used for forensic DNA, so you need a lot more SNP markers even to be as informative as the CODIS STR markers.

But there certainly is some current interest from people really into genealogical DNA in trying to see whether they can find blocks of DNA that remote cousins may each have inherited from a common ancestor. But it's hit-and-miss, because different cousins will for the most part have inherited quite different blocks of DNA from their common ancestor, and the size of blocks also can be fairly random, so there's a real possibility that there may turn out to be no DNA that the distant cousins may in fact have inherited in common.

You would also need to establish that the brother ancestor contender had different DNA in that block (on both chromosomes), so you would need to find yet more cousins that happened to pinpoint (both copies of) his DNA for that exact same block. No doubt somebody here can give more of an estimate for the exact numbers, but I suspect at even the level of only a few generations back, you would need to be finding a lot of different cousins to try to establish the brother's likely DNA marker values; and there's also a very good the relevant sections of the brother's DNA might not have successfully been passed down to anybody -- see Galton-Watson process for how really quite likely it is that a particular DNA section (originally somebody's Y-chromosome, but a similar analysis actually applies to any distinctive section of DNA) may end up not being represented in the population at all.
So probably you may by chance find particular blocks of DNA that can be traced back to particular ancestors. But probably it quite rapidly becomes really quite unlikely for you to be able to expect to be able to find a block of DNA that can be used to identify any particular given individual ancestor. Jheald (talk) 20:56, 18 August 2013 (UTC)[reply]
- Here's some information from ISOGG about 23andMe's "Relative Finder" feature, which attempts to do this; though it looks like the page was created in 2010, and may not have been updated that much since. Jheald (talk) 21:16, 18 August 2013 (UTC)[reply]

Basics of blisters

After doing a bunch of insufficiently-gloved shovelling today, I read the blister article and was left wondering on a few things:

"Causes" says that blisters cushion tissues under damaged skin, "protecting it from further damage and allowing it to heal". Does this mean that friction-caused blisters only form when all layers of the skin have been damaged?
Why do blistered areas feel "hot"? Does the serum exert some weird kind of pressure on the underlying tissues, or is this an effect of the damage that provokes the formation of the blister?
"Treatment" says that the fluid comes from the damaged cells, while the intro says that it's Serum (blood). Is one wrong, or is blood serum somehow inside the damaged cells? If so, how does it get in the cells, while if not, how does it leave blood vessels (without visible bleeding happening) to collect and form a blister?

Perhaps the answers to #1 and #2 are in "Treatment", but I wasn't able to understand it well. Clarification of that section would be appreciated. Nyttend (talk) 02:19, 18 August 2013 (UTC)[reply]

The fluid in blisters comes from interstitial fluid, which in turn comes from serum. Fluid in suction blisters is even described by some sources as being interstitial fluid, or at least it is used as a stand-in for it for biomarker studies of the interstitial fluid.^[4][5][6] That said, blister fluid is not truly the same as interstitial fluid because of course the act of blistering itself involves things secreted to prevent infection or promote healing, such as lysozyme and thymosin beta 4.^[7] (As the latter factor can assist in scar-free healing of cardiac tissue,^[8] I think that a careful and systematic scientific reevaluation of cupping therapy as practiced by ancient Greek physicians and their intellectual heirs (e.g. hijama) may be advisable...) Wnt (talk) 21:35, 18 August 2013 (UTC)[reply]

audio recording

when one records audio from speakers with a microphone, why is the resulting sound different from the original? and how does one make it more similar? (i know the basics of acoustics, digital audio, how speakers and mics work, ect...) thank you, 70.114.248.114 (talk) 03:04, 18 August 2013 (UTC)[reply]

You're picking up sound through your ears in a somewhat different way than a microphone does. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:20, 18 August 2013 (UTC)[reply]

True, but I don't think that's quite what the OP is talking about. Let's say you're listening to music through a speaker, while holding a mic. If you play the sound recorded from that mic through the speaker it won't sound the same as it did the first time. There are any number of reasons for this, including the introduction of background noise (also known as "air"), and the reduction of stereophonic sound to mono because the mic cannot capture a binaural recording. The mic you're using is also unlikely to be as high quality as the one the original artist used. You can compare what's happening with path loss as some of the concepts are similar. There's also information at high fidelity. As for increasing the fidelity, the easiest way is always to get the best possible initial recording rather than to try to fix it afterwards (for example, dubbing rather than using a mic). A sound engineer (even an amateur one) is the kind of person you'd need to talk to for advice, but I suspect that a lot of it comes down to drudge work, as is the case with most restoration projects. Matt Deres (talk) 14:44, 18 August 2013 (UTC)[reply]

Thanks for the detailed info. He's basically asking the same question as below, only for audio. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:20, 19 August 2013 (UTC)[reply]

recording video

i'm not asking cause i want to record copyrighted stuff, but is it possible to get nearly perfect quality by placing a video camera in front of a screen playing a video file? and if so, how? thanks, 70.114.248.114 (talk) 03:38, 18 August 2013 (UTC)[reply]

At the very least, I expect the camera would need to be totally in sync with the TV, e.g. by having the same megapixel dimensions and exactly synching with the scanning process. Check out Kinescope and see how they did it in the old days. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:53, 18 August 2013 (UTC)[reply]

At the very least, the recording camera would have to have twice the linear resolution (ie four times the number of megapixels) of the original picture because unless the alignment between camera and TV is 100% perfect, you're resampling the image and the Nyquist limit kicks in. But realistically - no, you'll never get a perfect quality image - there is sure to be some degradation no matter what. SteveBaker (talk) 23:45, 18 August 2013 (UTC)[reply]

Concur with others comment here. The quality of video from a camera pointed at a TV is going to be much less than the original, unless specialised equipment is used. Even still pictures of TV turn out rather poorly (wp:OR). See also Scan conversion. The ref I just added to that page maybe of interest "Digital scan converter" which also mentions the use of vacuum tube converter technology for applications such as converting radar & sonar displays. This indicates the lengths needed to got to to get good results say when converting film to video. --220 of ^Borg 12:02, 19 August 2013 (UTC)[reply]

Contradicting specification on the density of Sulfur hexafluoride ?

In the body text of the article "Sulfur hexafluoride". The density is said to be 6.12 g/L at sea level conditions. But the right side property column says 6.17 g/L. And a yahoo answer says 6.52 g/L using (density = 146.06 g / 22.4 L = 6.52 g/L). So which is it? Electron9 (talk) 15:51, 18 August 2013 (UTC)[reply]

Which reliable source is connected to which numbers? Find the original reference work, and you can find out. It should be noted that based on differences in measuring techniques, different reliable sources may have different reported values. Gases, being compressible and highly dependent on temperature, have very variable density, and depending on which set of "standard" conditions (be it STP, or Standard state, or Room temperature, any of a number of other conditions) will greatly affect the value. So, 1) Check the original sources and 2) careful observe what conditions those sources used to obtain their results. That's how you're going to get your values. --Jayron32 19:48, 18 August 2013 (UTC)[reply]

Where to find a reliable (online) source for physical data on gases? Electron9 (talk) 21:06, 18 August 2013 (UTC)[reply]

Stephen Hawking and The "Multiverse" - Does he really believe it?

I was watching Into the Universe with Stephen Hawking - The Story of Everything. I couldn't really tell if the narrator was supposed to pretend that he was Stephen Hawking or a different voice, but the narrator gave his alternative explanation of a perfectly well-tuned universe - the hypothesis of a multiverse. So, I did a Google search on the topic of the multiverse, and as usual, Wikipedia appeared at the top of the search results. I went straight to the criticisms, which seemed to be fairly plausible. Does Stephen Hawking really believe in the multiverse speculation, or is that the opinion of the documentary's narrator? If it were me, then I'd probably say that our universe is just a very special place, carefully constructed and assembled by mother nature. Sneazy (talk) 20:24, 18 August 2013 (UTC)[reply]

One question to consider is whether you believe this is the only possible way the universe could have turned out. For example, a couple of estimates for the entropy of the entire observable universe are 2^305 bits (Seth Lloyd, 2002) or 2^350 bits (Charles Egan, 2010). Naively, that suggests that the present state of our universe is one out of 2^(2^305) or 2^(2^350) possibilities.

Now if those other states actually exist, then physics can leave it down to pure blind chance that we find ourselves in 1 out of the 2^(2^305) or 2^(2^350) possibilities. But if only this universe exists, then how did the information that selects it from 2^(2^350) other possibilities come about?

And beyond that, if the universe really could have turned out differently, then in some sense that in itself makes them "real" possible worlds -- if they are (or were) truly possible, then they are (or were) real alternatives.

If they are irretrievably separated, and can never ever interact, then arguably that makes it irrelevant whether they "really" exist in the present or not -- or only as alternatives that could have existed.

But positing that they do "really" exist is fun for physicists, because that opens the door that down the line maybe some form of interaction really is possible. It also saves physicists from having to explain how one possibility really turns out to happen (or to have happened), whereas all the others apparently didn't (or haven't). It probably helps sell books and tv documentaries too. 22:03, 18 August 2013 (UTC)

This is why Hawking believes in parallel universes. Count Iblis (talk) 22:43, 18 August 2013 (UTC)[reply]

I am not sure how one is going to test this. Maybe this is one of those unfalsifiable mysteries of the universe. Even if other universes exist, I cannot imagine how their existence would ever affect our universe, given the vast and accelerating expanse of our universe. So, I would agree with you that if they are irretrievably separated and can never interact, then that makes it irrelevant whether they really exist in the first place. It may be fun for a physicist, but practically speaking, I am not sure how you can test something without proposing any assumptions about it. If an alternative universe has a completely different set of physical laws, then everything else would be left to the imagination! For practical experimental purposes, maybe it's best to stay in this world, in this universe. When someone asks about the reason for why our universe is the way it is, we may simply answer, "Because that is just how our universe works, and we just happen to live in it. In any case, this is no longer a scientific question. Science can't answer everything; this is why you have the Humanities." Sneazy (talk) 23:20, 18 August 2013 (UTC)[reply]

It's not unfalsifiable, you can test if time evolution is unitary; to get rid of the "many worlds" of the Many Worlds interpretation of quantum mechanics requires a violation of unitary time evolution. Count Iblis (talk) 23:30, 18 August 2013 (UTC)[reply]

I don't think he "believes" in it in the sense that you beleive in God. I think like many rational people who have looked into this possibility, he thinks it is a very interesting hypothesis which deserves us attempting to test it, if we can. And if we can't, well it is still intellectually interesting, but he won't start making decisions about his own life based on a dogma that says that this must be true, or give 10% of his income to a church that says that this IS the truth. --Lgriot (talk) 11:10, 19 August 2013 (UTC)[reply]

August 19

Psychology of pricing and beach nourishment projects

Hi, I have learned that managed retreat (moving away from the shore) is an unpopular idea amongst the public, in part because of its high short term costs (both beach nourishment and maintaining coastal armoring structures such as jetties are more expensive over a long term period (eg. decades)). I was wondering, are there any psychological studies that show that consumers tend to be more afraid of making purchases that have high short term costs, than making purchases that have low short term costs but higher long term costs? Many people get in trouble with credit cards because they allow people to make quick convenient short term purchases, but often lead to higher long term costs (in the form of interest rates or late payment fees). Thanks. — Preceding unsigned comment added by 99.146.124.35 (talk) 00:06, 19 August 2013 (UTC)[reply]

There has been a lot of research about that topic. Our articles on temporal discounting and intertemporal choice describe some of it, although they are written at a pretty technical level. Looie496 (talk) 00:58, 19 August 2013 (UTC)[reply]

The world is rife with the consequences of that kind of thinking. When you buy an inkjet printer for your computer - it's amazingly cheap - under $100 in some cases. Then you go to buy a few grams of ink and you're paying $50. Computer game consoles like the PS-3 and Xbox 360 are sold for prices well below the manufacturing cost - and the companies that make games are forced to enter into costly licensing for the privilage to write games for them - the cost of games is therefore much higher than it would otherwise be in order that the sticker shock for the console hardware is lessened. Cellphones worth $300 to $400 are sold for $100 with a two year contract to buy cell phone service at significantly more than the going rate.

In every case, people are suckered into these expensive long-term costs by the short-term value. SteveBaker (talk) 01:38, 19 August 2013 (UTC)[reply]

Phone companies in the UK are starting to be clearer in their phone plans. The O2 refresh scheme gives a super clear explanation of exactly what you pay for your phone on different contracts. For example for the iPhone 5 you actually save £120 (20% of the cost of the phone) by fiddling with the contract you want - and a handy link to find the lowest price. For example. 110.3.247.175 (talk) 12:57, 19 August 2013 (UTC)[reply]

I've been reading that cancer cells communicate with each other...

and also that slime mold cells communicate with each other. How do the signalling methods compare? Thanks.76.218.104.120 (talk) 05:32, 19 August 2013 (UTC)[reply]

Most living cells communicate, to a greater or lesser degree. The subject that coveres this topic is Intercellular communication and it is very complex. Vespine (talk) 06:57, 19 August 2013 (UTC)[reply]

Upside down Mirror Image

why do some mirrors show images upside down. — Preceding unsigned comment added by 197.220.100.142 (talk) 11:43, 19 August 2013 (UTC)[reply]

See curved mirror. הסרפד (call me Hasirpad) 12:39, 19 August 2013 (UTC)[reply]

Antibiotics - Safe Amount To Take

My queastion is, how many courses of antibiotics (or how much) is safe to take per year ?
One reason for asking is I was prescibed antibiotics for a chest infection when I was little, but because I still had it a week or two after the course was finished (Not sure but I think it was a 28 day course) my parents took my back to the GP. This happened 3 or four times until my parents happen to mention that I've already had antibiotics when the GP suggested for me to have some more antibiotics . When he checked my records (he later claimed there was some sort of problem with their computers) he said I'd have to have something else because I'd taking more than the recommended amount for that year.
another reason is, years earlier a similar thing happened with my sister. She had a ear infection, & she was given so many courses of antibiotics (later explained to us by doctors in the hospital) that she went partialy deaf. When she was rushed to the hospital, where they took her off the antibiotics & gave her something else to take instead & they told my parents that her hearing might come back. Luckily it did. Scotius (talk) 12:38, 19 August 2013 (UTC)[reply]

Wikipedia does not respond to requests for medical advice. Ask a medically-qualified person. AndyTheGrump (talk) 12:41, 19 August 2013 (UTC)[reply]

I'm sorry - but the Wikipedia Reference Desk is not allowed to dispense medical advice. Besides that, the answer would be very complicated because it'll depend on body weight, gender, which antibiotics are being prescribed, other drug interactions and so forth. This is really a matter for a doctor to answer for each individual patient. SteveBaker (talk) 12:49, 19 August 2013 (UTC)[reply]