Wikipedia:Reference desk/Archives/Science/2010 November 30

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November 30

Position of maximum depression on classical guitar top.

At present I am in the process of writing an article on the construction of the classical guitar, and am proposing a different method of reinforcing the top-plate. The method consists of a set of bars, radiating from a position in front of the bridge, which is where maximum deflection occurs, due to the action of the strings when plucked. Where that position is, can be calculated, I believe, with a formula to do with Modulus of Elasticity, when the following is known: The type of wood and thickness of the top-plate. The total tensile and torsional force applied to the bridge, from the strings. The edge pressure from the bridge. This little information is gained from the mechanical drafting certificate course I did more than 40 years ago, hence the sketchy description. —Preceding unsigned comment added by 58.175.87.33 (talk) 04:27, 30 November 2010 (UTC)

And your question is . . . ? 87.81.230.195 (talk) 14:25, 30 November 2010 (UTC)

We do have articles on Classical guitar and Classical guitar_making -- are they helpful? --- Medical geneticist (talk) 21:41, 30 November 2010 (UTC)

How accurate do you want the results? There is no shortage of finite element analysis applied to guitar body: Modal analysis of an acoustic guitar by finite element came up in a web search; and you can find even more scholarly, technical, and accurate modeling with a little effort. Obviously, the specific node point of maximum vibration amplitude is going to depend on the guitar body shape, materials, and how accurately your mathematical model matches physical reality. Nimur (talk) 21:49, 30 November 2010 (UTC)

Relativity questions

Expand long text

The Phenomenon of Far Event Dilation For a given event eA happened at time tA and location A, an observer at location O uses a camcorder with timer to record event eA, then the recorded event time ta will always behind tA, this is the phenomenon of Far Event Dilation. This is prepared for "Distance Relativity", please comment. 1. The Equation of Far Event Dilation The recorded event time ta can be calculated by ta=tA+(AO/c’) ---(1), c’ is the speed of light in the environment. 2. The Equation of Event Period If the event ends at location B and time tB, then the recorded time period can be calculated by (tb-ta)=(tB-tA)+((BO-AO)/c’) ---(2). 2-1. When BO=AO, that means, if A and B are located on the same sphere with center O, then, the recorded event period is always the same as the actual time period. 2-2. When BO>AO, that means, the event ends at a point farther away, then the recorded event period is larger than the actual event period. The event looks happening slower in the video. 2-3. When BO<AO, that means, the event ends at a point closer to O, then the recorded event period is smaller than the actual event period. The event looks happening quicker in the video.Jh17710 (talk) 06:27, 30 November 2010 (UTC) Distance Relativity Now, let us study the Far Event Dilation in one dimension space. We assume the event points A or B and the location O of the observer are always on the same line. We also focus on cases that either the event moves or the observer moves at constant velocity v. Then we will have two sets of time equations and one set of velocity equations. This is the main subject, please comment. 3. When observer moves, then |BO-AO|=v(tb-ta) 3-1. When BO>AO, (tb-ta)=(c’/(c’-v))(tB-tA) ---(3) 3-2. When BO<AO, (tb-ta)=(c’/(c’+v))(tB-tA) ---(4) 4. When event moves, then |BO-AO|=v(tB-tA) 4-1. When BO>AO, (tb-ta)=((c’+v)/c’)(tB-tA) ---(5) 4-2. When BO<AO, (tb-ta)=((c’-v)/c’)(tB-tA) ---(6) 5. Let the event be the motion of an object from A to B under the constant velocity of v and let the speed of that object be calculated as V by the observer, then: 5-1. When BO>AO, V=(c’/(c’+v))v ---(7), particularly when v=c’, we have V=c’/2. 5-2. When BO<AO, V=(c’/(c’-v))v ---(8), when v=c’, we find out V is infinitely fast. For example, if a base ball flies to me at the speed of c’ and when it passes the sign of 30 feet, that particular picture will take about 100 nanoseconds to reach my eyes, but, at around 99 nanoseconds, that base ball already hits my nose so that the speed of that base ball is unlimited fast to me. Actually, all photons run into our eyes at infinite fast speed.Jh17710 (talk) 06:27, 30 November 2010 (UTC) The Phenomenon of Far Ball Contraction We can calculate the distance of a ball by the equation based on the phenomenon of Far Ball Contraction, which is “A ball looks smaller when it is farther away.” This is just to show the fact that we cannot see the dimension representing far and near, we calculate that dimension. 6. Far Ball Contraction Formula If we hold a ruler 1 foot away from our eyes and measure a ball of radius r feet at distance of L feet away from our eyes to get radius of R feet, then, when the ball moves to another distance of L’ feet, the measured radius R’ feet will be R’=(RL)/L’ ---(9). We should keep both of L and L’ larger than (1+2r) feet to make the measuring job practical. 7. When the Ball is Replaced by a Brick If we replace the far ball by a Brick and look at the length and height side of that brick, then, we don’t know how wide that brick is. That means, we judge the distance of an object by the image of the length and height of the object that is perpendicular to our sight line, and normally, we have no way to tell how wide or how deep that object is.Jh17710 (talk) 06:27, 30 November 2010 (UTC)

Response

Jh17710: People who patrol the reference desk aren't going to answer homework questions for you; also we generally need questions to answer. It looks above like you have copied large swaths of text from some physics text somewhere. Is there a question anywhere in all of this? --Jayron32 06:48, 30 November 2010 (UTC)

Thanks for allow this section to stay. Yes, some question is big like the idea of "infinite speed".Jh17710 (talk) 05:30, 1 December 2010 (UTC)

There is no infinite speed. Speed is always relative between frames of reference. The practical limit to speed is the speed of light, which is very finite. The problem comes not in objects moving relative to each other; but in accelerating an object from "rest" (as defined in its own reference frame) to the speed of light. To do so would require infinite energy, which is impossible. --Jayron32 05:48, 1 December 2010 (UTC)

Let us look at your comment one by one. I believe that there is no actual infinite speed in real world too. Yes, speed can be relative speed to a reference frame or even, visual speed like if a ball flies at speed of c/2, then, how a camcorder records that ball moving forward and backwards at distance marks of 300 feet, 600 feet, and 900 feet? We will find out the forward speed is c and the backward speed is c/3. The actual speed may not excess c, but, we are unable to prove it yet. The main reason that we are unable to accelerate an object to the speed c should be the limitation of the speed of force. If the speed of force is c, then, a force will not push or pull an object to a speed higher than c, that is reasonable. Isn't it? If a visual speed can excess c we can enjoy the feeling of the speed of light or ultralight when technology advances to certain level.Jh17710 (talk) 04:34, 2 December 2010 (UTC)

... (earlier reply) ... and the point that the text seems to be trying to make appears false to me. For both ball and brick, we infer both distance and depth from past experience, and if we have doubt about our guess, we use parallax to check. The idea of "infinite speed" is also wrong. Have you read our article on Special relativity? Dbfirs 07:41, 30 November 2010 (UTC)

I will read it again. However, what do you think about the recorded event time period may be smaller than the actual event time period when event started and moved closer to the observer? I can derive it in detail.Jh17710 (talk) 05:30, 1 December 2010 (UTC)

I should also note that you're getting close to where fair use may give way to copyright violation, unless you're actually going to discuss bits and pieces of all that stuff in detail. Wnt (talk) 10:44, 30 November 2010 (UTC)

This is my idea. I posted it once early 2008.Jh17710 (talk) 05:30, 1 December 2010 (UTC)

Yes, there is the well-known Doppler effect where both the recorded time period and the frequency are changed by relative motion (as in an approaching emergency vehicle), but the equations are not the same for light as they are for sound (see Relativistic Doppler effect). Dbfirs 08:35, 2 December 2010 (UTC)

Thanks for the response. I will look into the Doppler effect for sound. Could you tell me which step of the follwoing is wrong? 1. The Equation of Far Event Dilation, event happens at point A and time tA, a camcorder at point O recorded event time ta, then ta can be calculated by ta=tA+(AO/c’) ---(1), c’ is the speed of light in the environment. 2. The Equation of Event Period, if the event ends at location B and time tB, then the recorded time period can be calculated by (tb-ta)=(tB-tA)+((BO-AO)/c’) ---(2). 3. Now, let us study the Far Event Dilation in one dimensional space. We assume the event points A or B and the location O of the observer are always on the same line. We also focus on cases that event moves at constant velocity v, then |BO-AO|=v(tB-tA). When BO<AO, (tb-ta)=((c’-v)/c’)(tB-tA) ---(6), that is when event started at far end and finished at near end. 4. When v=c'/2, then (tb-ta)=(tB-tA)/2, for a base ball flies from A to B, the recorded time period is just half of the actual time period. 5. That means, the recorded speed of that base ball is twice as fast as the actual speed, from A to B. All above steps just show that the visual speed of an object can be very fast, even faster than the speed of light.Jh17710 (talk) 03:01, 3 December 2010 (UTC)

Yes, the apparent speed of approach is given by ${cv} \over {c-v}$ without relativistic adjustment (could an expert please check the adjustment needed here?) so it appears to easily exceed c (the speed of light) from a Newtonian viewpoint. This does not mean that anything is actually travelling at a speed greater than c. An observer sitting on the baseball would see things differently. A similar effect can be seen when shining a rotating beam of light on a distant panorama. The reflection can appear to be travelling faster than light, but this is just an effect. No object, not even a single photon, is exceeding c. Dbfirs 15:02, 3 December 2010 (UTC)

I told you that speed is a visual speed, not actual speed. That equation itself is the relativistic adjustment to the actual speed. I do like to understand your similar effect in more detail. Does a rotating beam of light on a distance panorama like on a big cylinder screen at far away? Does the reflection mean the refected light from the screen that the person at the center point sees? That will make a very good sample for "something" runs faster than the speed of light, but, that something is not one object. that circle of light appears at far distance are created by different photons being emitted to different directions. Do you think photons run into our eyes at unlimited fast speed?Jh17710 (talk) 06:56, 4 December 2010 (UTC)

Photons always travel at the speed of light when they are travelling. They can be absorbed and re-emitted by transparent materials, and this explains why they appear to travel at a speed less than c in a medium with high refractive index. You might be interested in the article on phase velocity which can exceed c (and I think can approach infinity in recent experiments where photons are "stopped") Dbfirs 16:03, 4 December 2010 (UTC)

Yes, I think we all understand this. I should ask my question differently; do you think our brain will calculate the speed of photons run into our eyes at unlimited fast of speed? I think that is the reason why every instant view in front of our eyes is so clear, no matter how fast we turn our focus points to different location. And the whole view appears right at the moment we open our eyes. Our brains do have a limit speed of images processing, however, the infinitely fast visual speed of incoming photons does help us to have very stable views. Thank God.Jh17710 (talk) 22:05, 5 December 2010 (UTC)

is it possible to blow up a planet like in Star Wars?

Lets say there were a really big gun or energy beam aimed at a planet the size of Earth? Could it actually cause the Earth to blow up, or would it just cause earthquakes and cause the rock to melt and things like this? I am not talking about an impact event, this is like something worse than that, like the Death Star, pretty much. But would the laws of phsics allow a planet to EXPLODE? is it even posible? —Preceding unsigned comment added by The Fat Man Who Never Came Back (talk • contribs) 03:42, November 30, 2010

Sure, it's possible in some sense, but not like in Star Wars. All in all, you should realize this planet is basically a lump of metal several thousand miles in diameter, stuff that likes to congregate (gravity) and will not easily be scattered into a gazillion pieces. The energy required to actually blow it up as you describe would be an immense amount.--Rallette (talk) 09:00, 30 November 2010 (UTC)

Someone worked out details on what you'll need to do it here. Have fun! --Sean 14:22, 30 November 2010 (UTC)

Also, the Earth is largely magma already, but supplying enough energy to destroy it would surely melt the rest of it, so it would look more like blowing a raindrop apart than a solid object. Sci-fi shows never seem to get this right. StuRat (talk) 23:50, 30 November 2010 (UTC)

Incidentally, the amount of energy required to vaporize a mass of iron the size of earth is around 3.7x10^31 Joules. That is equal to 9,232 trillion 1 megaton nuclear warheads, or 85 billion years of current human energy consumption. Googlemeister (talk) 16:51, 2 December 2010 (UTC)

What would happen if scientists blew up the moon?

What would be the consequences here on Earth if we blew up the moon? I imagine there would be all sorts of environmental disasters, but would there be any benefits?--The Fat Man Who Never Came Back (talk) 08:44, 30 November 2010 (UTC)

Some of this was discussed at Wikipedia:Reference_desk/Archives/Science/2006_November 7#Blowing up the moon and Wikipedia:Reference_desk/Archives/Science/2007 May 6#Earth's Spin. Wnt (talk) 10:47, 30 November 2010 (UTC)

This is one advantage. Paul (Stansifer) 14:41, 30 November 2010 (UTC)

This is another. ;) --Link ^(t•c•m) 19:47, 30 November 2010 (UTC)

You attribute some pretty impressive powers to these 'scientists'. In any event, the answer depends on what you mean by 'blew up'. If you just fracture it without giving any of the chunks lunar escape velocity, then they'll pretty much settle back into a new Moon. (The surface features won't be the same, obviously, but if the whole system stays gravitationally bound then you'll eventually get a Moon-sized approximately-spherical lump back.) If you manage to compress enough of it into a wee tiny black hole (bigger than CERN LHC-sized, so it won't evaporate immediately) it will eventually all collapse into a stable Moon-massed black hole (see Roger MacBride Allen's The Ring of Charon). In either case, not a whole lot happens on Earth. The former case generates an impressive light show, and the latter case makes it a bit darker at night, but tides won't be appreciably affected and the Earth will carry on essentially unchanged.

If you redistribute the mass of the Moon (as by pulverizing it into a ring in lunar orbit), or remove the Moon and all its mass entirely by some yet to be discovered magical phenomenon (or by virtue of it actually being a camouflaged alien spaceship, see David Weber's Mutineers' Moon) then you have serious effects on Earth. Getting rid of tides (well, most tides — there will still be miniscule tides from the Sun's attraction) will screw over a lot of coastal life. Depending on how quickly you remove or re-adjust the Moon's position, you might also get some serious earthquakes going on, as rapidly removing the Moon's pull on Earth may have the effect of 'twanging' crust.

If you use some unimaginably violent explosion to 'blow up' the Moon in what might be the most conventional picture of such an event, you're very likely to have some Texas-size chunks hit the Earth. When that happens, we have a massive winter, and most life on Earth dies. What benefits did you have in mind? TenOfAllTrades(talk) 14:45, 30 November 2010 (UTC)

Here's a fun article on the subject : The Straight Dope:I plan to destroy the moon. What effect would this have on the earth?

APL (talk) 15:37, 30 November 2010 (UTC)

Related question: does humanity at present time have the capacity to blow the Moon to smithereens? Bus stop (talk) 15:45, 30 November 2010 (UTC)

Certainly not. --Sean 18:51, 30 November 2010 (UTC)

All this and yet nobody mentions the late Alexander Abian. --Anonymous, 23:24 UTC, November 30, 2010.

Can we blow up comets?

A few years ago, we tried and failed to blow up a comet. We shot a missile at it, and it caused an explosion and released a dust cloud, but unfortunately the comet was not destroyed. In the future, if we shoot more powerful projectiles at comets, is it possible to destroy them altogether? What would happen to the galaxy if we eliminated all comets and meteors and asteroids?--The Fat Man Who Never Came Back (talk) 08:48, 30 November 2010 (UTC)

I think you've read the article wrong if you think the Deep Impact space mission was an attempt to destroy a comet. Nil Einne (talk) 10:53, 30 November 2010 (UTC)

If you blow it up, you just seperate a mass into smaller bits of mass. Each of the bits are still comets, just smaller. So nothing would "happen to the galaxy", except it would have smaller comets. --Lgriot (talk) 12:15, 30 November 2010 (UTC)

As has been hinted at above you should read the galaxy article to adjust your mental image of the scale of things.

It sounds like you may have meant solar system instead of 'galaxy'. If so, have a read of the Oort cloud article to get an idea of what sized job ridding the solar system of all comets would be. Blakk and ekka 12:33, 30 November 2010 (UTC)

All the comets in the Solar System make up the mass of about 5 Earths, and less than 1% of the mass of the Solar System as a whole. There's nothing you can do to a comet to have much effect on the Solar System, much less the galaxy. --Sean 14:25, 30 November 2010 (UTC)

First, Deep Impact was not attempting to blow up a comet any more then someone who crashes their car into the side of a mountain is trying to blow up the mountain. Second, the results of destroying a comet would have only the very smallest of effects on the solar system (and even then, only if you used something like antimatter to remove the mass entirely). It is unlikely that such changes would be detectable. On a local scale, if you exploded a comet that transected the earth's orbit, you might have some nice meteor showers in the future, but impacts to the planetary orbits would be essentially unaffected. Googlemeister (talk) 16:41, 2 December 2010 (UTC)

Which organelles contain DNA?

I always thought it was just the nucleus & either mitochondria (in animals) or chloroplasts (in plants). However, I found a passage in Lewis Thomas's "The Lives of a Cell" where he intimates that this property is shared by other organelles too:

Mitochondria are stable and responsible lodgers, and I choose to trust them. But what of the other little animals, similarly established in my cells, sorting and balancing me, clustering me together? My centrioles, basal bodies, and probably a good many other more obscure tiny beings at work inside my cells, each with its own special genome, are as foreign, and as essential, as aphids in anthills.

Is this an inaccuracy? The book was written in 1974. Thanks. AGradman / how the subject page looked at 12:19, 30 November 2010 (UTC)

None of these sub-cellular bodies have their own genome. It sounds like Thomas may be putting forward a variation of Endosymbiotic theory. Blakk and ekka 12:49, 30 November 2010 (UTC)

I'm not sure if it was just a poor choice of words or genuine confusion but do note nearly all eukaryotes have mitochondrion, including plants. Nil Einne (talk) 13:53, 30 November 2010 (UTC)

In the case of centrioles, it may have been based on outdated research. From centrosome:

Research in 2006 indicated that centrosomes from Surf clam eggs contain RNA sequences. The sequences identified were found in "few to no" other places in the cell, and do not appear in existing genome databases. One identified RNA sequence contains a putative RNA polymerase, leading to the hypothesis of an RNA based genome within the centrosome. However, subsequent research has shown that centrosome do not contain their own DNA-based genomes. While it was confirmed that RNA molecules associate with centrosomes, the sequences have still been found within the nucleus. Furthermore, centrosomes can form de novo after having been removed (e.g. by laser irradiation) from normal cells.

--Sean 14:29, 30 November 2010 (UTC)

velocity of sound

why does the velocity of sound in water decrease after reaching a maximum velocity at a certain temperature —Preceding unsigned comment added by 41.221.209.6 (talk) 13:46, 30 November 2010 (UTC)

The effect I'm familiar with is that as a function of depth, the sound speed increases after reaching a minimum at a certain depth (which turns out to be temperature-related). Our Speed of sound article shows the effect but doesn't explain it well and explains it briefly. There's a better fuller discussion at DOSITS. In a nutshell: the speed of sound in seawater is proportional to temperature, to pressure, and to depth. Temperature decreases as depth increases, which is why the sound speed initially decreases as you descend below the surface. But then, of course, pressure begins to increase, and so the sound speed goes back up as you go really deep. —Steve Summit (talk) 14:12, 30 November 2010 (UTC), tweaked 14:48, 30 November 2010 (UTC), again 23:58, 30 November 2010 (UTC)

Speed of sound is related to density. Water is densest at 34F, so sound will travel through water fastest at that temperature. Pressure has a minor impact on the speed of sound in seawater, but it is a smaller impact then temperature. Googlemeister (talk) 16:36, 2 December 2010 (UTC)

3.98°C is about 39°F not 34°F Dbfirs 16:11, 4 December 2010 (UTC)

Daytime flash dreams

Sometimes I tend to experience ultra-short (for about 0,5 sec) unconscious flash dreams while not sleeping, just resting. They look like normal night dreams, but appear even when my eyes are open. Most recently for example I saw a nice red motorcycle with bald biker. Is there a name for such phenomenon? —Preceding unsigned comment added by 89.77.158.172 (talk) 17:01, 30 November 2010 (UTC)

Well, this is not really a medical question and is quite common, so see daytime parahypnagogia--Aspro (talk) 17:09, 30 November 2010 (UTC)

Margarine and oils without saturated fat

Are there any brands or kinds of margarines and oils with little saturated fat? Even the "Light" margarine I have in front of me is over 9% saturated fat. Thanks 92.28.247.40 (talk) 17:26, 30 November 2010 (UTC)

Shortenings like margarine and crisco are just vegetable oil that's been "partially hydrogenated". Saturation is one of the main reasons these things are solid at room temperature. The unsaturated fat is lowers the melting temperature to make vegetable oil a liquid). The lowest saturated-fat content I see on that article's table is canola oil at 7%, and all the solid ones are somewhat higher. DMacks (talk) 17:34, 30 November 2010 (UTC)

In general the more saturated the oil the lower the melting point. So unsaturated oils are liquid at room temperature. However the length of the molecule (called the chain length) also plays a role, the shorter the chain the lower the melting point. As far as health goes just looking at saturated vs unsaturated is not enough, there is plenty of evidence that certain chain lengths are much unhealthier. In general longer chains are less healthy. So you can have an unsaturated, long chain oil that is less healthy that a short chain, but saturated oil. This is the main reason people switched to saturated palm oils, they might be saturated, but their oil has few bad health effects, and some believe actually improve health! In general it's best to eat oils that are commonly found in food. The reason is that the health effects of the oil are directly related to how well the body can "burn" the oil (lipid) for fuel. To burn the lipid requires enzymes, and the body has more enzymes for some types than for others. Another thing, Essential fatty acids (EFA) are the best type of lipid to eat, but they are all liquid and polyunsaturated. A manufacturer has a choice - they can make the margarine with some saturated fat, and a little unsaturated, or they can make it with polyunsaturated and more saturated (the high and low melting points cancel each other out). Which is better? You are getting more saturated fat, but also more EFAs, or less saturated fat, but no EFAs. My feeling is that the version with saturated, but also polyunsaturated is better, but the exact answer on the proper balance requires lots of studies that as far as I know have not been done. A final point is that I think it's better to eat a margarine with a variety of fat types in it, vs. one that is just one kind of lipid - even if you have to eat some saturated fat in the process. Whew, this post was longer than I expected, I hope it helps you. Ariel. (talk) 19:17, 30 November 2010 (UTC)

I cannot see the answer to my question in there, but thanks for trying. 92.28.247.40 (talk) 20:07, 30 November 2010 (UTC)

Basically what he's? saying is 1) It's rather unlikely there are any margarines without saturated oils. 2) If your concerned about health, just avoiding all saturated fats likely isn't the way to go (technically you didn't ask about this but given your question I don't think it was an unresonable response). Note that considering no 2 even if someone could make an oil without saturated fats, it's not likely they would. According to [1] one of the lowest saturated fat oils is enova brand but um [2]... In any case it sounds like weird stuff [3] P.S. It's also possible Ariel missed your point about oils at first since you referred to the saturated fat content in margarine rather then oils. I did. Nil Einne (talk) 20:30, 30 November 2010 (UTC)

One point is that the people who first made margarine wanted it to resemble butter, but it was a white liquid, not a yellow solid, so they added coloring and saturated fats (or the even worse trans-fats). Now that we know how unhealthy it is to solidify the margarine (which pretty much also will solidify in your veins), perhaps we should re-evaluate our need for it to be solid. You can get a squirt bottle of liquid margarine, and that sounds fine to me. You can probably butter your toast even quicker that way. StuRat (talk) 00:20, 1 December 2010 (UTC)

I think it's important to bear in mind two things. First is that triglycerides and other lipids are a heterogeneous collection of compounds, with many individual variations of molecular structure, any and all of which may be significant. Each lipid chain of the triglyceride has a varying length and a variable pattern of double bonds. Things like omega-3 fatty acids, omega-6 fatty acids, conjugated linoleic acid, arachidonic acid, eicosapentanoic acid and so on all have their own special purposes and effects. They are not merely "fuel", but form the cell membrane, modify proteins, and are used to make potent signalling molecules like prostaglandins, ceramide, sphingolipids .... it's a whole branch of biochemistry.

The other thing to bear in mind is that partially hydrogenated vegetable oil is not a natural fat, but a crude chemical mock-up of an animal fat in which the precise chemical components have been randomized. It's well known that trans fats have little place in normal biology, but there could be other random alterations.

What I would draw from this is that one should be very conservative regarding lipid sources, choosing sources with a long history of use like olive oil over those which someone has just started pressing out of a new plant, or worse, which have been created chemically. Wnt (talk) 11:04, 1 December 2010 (UTC)

It comes from a plant in either case, whether a biologic plant or a chemical plant. :-) StuRat (talk) 23:21, 1 December 2010 (UTC)

Bioluminescence

hi, Today I saw (in a video) a creature which made a Bioluminescence. It looked like fireworks. the liquid which he spitted (it was a marine animmal) had glown for 3 seconds,and then turn-off. and then, like a lightning it glew powerfully. does anyone know what that sea animmal's name? 84.228.119.63 (talk) —Preceding undated comment added 17:51, 30 November 2010 (UTC).

Well. There is this one, and as ever, Wikipedia has an article on it:Heterocarpus--Aspro (talk) 19:41, 30 November 2010 (UTC)

We also have Bioluminescence of course which lists a bunch of animals Nil Einne (talk) 21:32, 30 November 2010 (UTC)

The article on Heterocarpus however, features a shrimp which spits streams of blue luminous secretions and thus directly address the OP's question, which Bioluminescence does not. Otherwise, I would have provided that link. Which I did not, because it didn't. Yet, Heterocarpus links to any way -if you had read it!--Aspro (talk) 23:31, 30 November 2010 (UTC)

Apologies I misread the OPs question as being about which when splited grew for 3 seconds which I thought could easily apply to many animals showing bioluminescence. However I still believe the link was helpful as it teaches the OP that we also have an article on general concepts such as this, which list animals which show the concept so they may be more aware they can look themselves in the future (although unfortunately in this case the bioluminescence article doesn't seem to list Heterocarpus either directly or indirectly). While it's true (and expected) the article links to the concept, it may not occur to the OP to click on it.

Also, while it seems most likely your answer is what the OP is referring to, and this is not a field I know much about, I wonder if it's really the only possible correct answer as your second response seems to imply. As I understand the Vampyroteuthis infernalis article (which is linked from bioluminescence) they release a 'bioluminescent mucus containing innumerable orbs of blue light' (our article actually refers to fireworks although that may be a common description for bioluminescence). This may not be really liquid, although it's not clear how precise that term was meant (did the OP actually see the liquid, did they just see it in water and it looked like liquid?). (There may also be debate about whether spit is accurate for what the vampire squid does although again it seems possible the OP is using the term loosely.) Even less likely but perhaps still worth mentioning, our article says Antarctic krill spits out biolumiscent phytoplankton. If it is possible the OP is referring to something else, it seems to me there's even more merit to the general link

Nil Einne (talk)

P.S. [4] claims there's also planktonic protozoans that spit bioluminescent 'stuff' but unfortunately I've been unable to find what they're referring to from quite a few searches. Planktonic protozoans sounds unlikely to be thought of as marine animals, but who knows I guess. Nil Einne (talk) 12:55, 1 December 2010 (UTC)

P.P.S. From what I can tell, we don't have any real videos of Vampyroteuthis infernalis releasing their bioluminescent liquid (some simulations are all I could find), perhaps not surprising given the depth they live in, so it seems unlikely this is what the OP saw. (Planet Earth did have video of it using its photophores.) Nil Einne (talk) 12:55, 1 December 2010 (UTC)

Aggression, dementia, disinhibition

1) Some elderly people seem to be habitually hostile - are there any other things apart from dementia that cause this aggression in some elderly? 2) Does having dementia make people disinhibited? Thanks 92.28.247.40 (talk) 18:00, 30 November 2010 (UTC)

When any disease or injury effects the normal functioning of the pre-frontal cortex and especially when executive functions with in them are effected, it can result in more aggressive behaviour and/or dis-inhibition than would normally expected. Dementia does not always lead to more aggression but is more common than not. --Aspro (talk) 18:21, 30 November 2010 (UTC)

Ok, so aggression is a common result of dementia, but does being aggressive and elderly suggest dementia? Thanks. 92.28.247.40 (talk) 22:18, 30 November 2010 (UTC)

On its own - no. In combination with other things - maybe. Try the alzheimers-research.org.uk website for some more information. --Tagishsimon (talk) 22:22, 30 November 2010 (UTC)

Wouldn't hurt to check for it, but some old people can just be mean ol' bastards. HalfShadow 22:25, 30 November 2010 (UTC)

I seem to recall reading an article on social inhibitions, which claimed they were maximised in teenagers/young adults, and gradually decreased after that. This would suggest that elderly people in general are going to be less inhibited than other adults, regardless of whether they have dementia. Does anyone know more about this, or know where to find a referenced discussion? 86.161.108.241 (talk) 14:10, 1 December 2010 (UTC)

Being elderly and aggressive may suggest the effects of jading and nothing more. I wouldn't suggest that Grumpy Old Men have to have a medical reason for being that way when conditioning explains it quite well.
⋙–Berean–Hunter—► ((⊕)) 17:22, 2 December 2010 (UTC)

Why must some truffles be found and not grown?

This MSNBC article says that Piedmont white truffles cost around US$3,000 per pound because of low supply, and also claims "this is one food that can’t be formulated in a lab or grown in a greenhouse." Why? By now there must have been attempts to farm these truffles in order to try to cash in on this. What were the results? Comet Tuttle (talk) 19:02, 30 November 2010 (UTC)

That is a misleading statement. Truffle farms are, essentially, tree farms. It takes about 30 years to grow the trees (and the truffles). So, that statement could be true of any large tree. For example, you could claim that Christmas Trees are the one decoration that can't be formulated in a lab or grown in a greenhouse. What you actually mean is that the tree is big. You need a lot of room. So, for a lot of trees, you'd need an enormous greenhouse. Obviously, you'd use a field instead - which is what truffle farms use, large fields. -- kainaw™ 19:09, 30 November 2010 (UTC)

(after e/c)

Truffles grow on the roots of Oak trees. Perhaps they simply mean that truffles need vast orchards to cultivate, even though the truffles themselves are rather small? (Literally, adult oak trees are unlikely to grow in either a lab or all but the largest greenhouses.) APL (talk) 19:11, 30 November 2010 (UTC)

I see; thank you. I had jumped to the conclusion that finding truffles was a hunter/gatherer task and a crapshoot, rather than an organized and planned farming process. Comet Tuttle (talk) 19:26, 30 November 2010 (UTC)

Note that unsurprisingly our article has a section on cultivation Truffle (fungus)#Cultivation Nil Einne (talk) 20:34, 30 November 2010 (UTC)

The section is disappointingly sparse regarding information on which type of truffle is/has been cultivated. My understanding is that while black truffles are amenable to directed cultivation, white truffles are more recalcitrant. It isn't simply a matter of "plant tree->gather truffles". Not every tree of a host species will produce truffles, even if it's in a truffle producing area. We don't yet know exactly what the truffle is looking for in growing conditions. That's why it's said that (certain) truffles can't be cultivated. You can plant a bunch of host trees to increase the chance of getting truffles, but there's no guarantee that when they mature you'll be producing any significant amount of truffles from them. -- 140.142.20.229 (talk) 02:06, 1 December 2010 (UTC)

And it's not just getting them to grow on a tree's roots, but getting them to fruit and catching them when they do so. --Sean 16:02, 1 December 2010 (UTC)