Wikipedia:Reference desk archive/Science/2006 October 8

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[edit] The effects of a smoker and non-smoker in the cold

Does a smoker feel the effects of the cold sooner than a non-smoker?12.145.200.157 00:29, 8 October 2006 (UTC)Jerry McShane—

Define "feel the effects of the cold". Are you asking if a smoker feels cold sonner when walking into air conditioning? Are you askign if a smoker catches a cold sooner? Are you asking if a smoker gets frostbite sooner? As it is, your question is too general to provide a discrete answer. --Kainaw (talk) 00:56, 8 October 2006 (UTC)
If the non-smoker is wearing gloves and is busy keeping his body warm, while the smoker is waving his naked hand around in the air and busy taking puffs on his cigarette, then yes of course the smoker would feel the cold. This really has nothing to do with smoking though.  freshofftheufoΓΛĿЌ  03:29, 8 October 2006 (UTC)
If the circulation has been resricted by aretheroma, then yes probably.--Light current 09:02, 8 October 2006 (UTC)

I often wonder whether the heat from a cigarette itself keeps people warm (presumably the smoke inhaled is warmer than say the cold air). Having never tried the stuff I have no idea if what i've just written is just crazy-talk or actually accurate!! ny156uk 16:47, 8 October 2006 (UTC)

By far, the greatest effect is that smokers stand outside in the cold getting their nicotine fix, where smoking indoors is prohibited. I'm sure they suffer more from the cold, as a result. StuRat 20:49, 8 October 2006 (UTC)

I work with smokers and in the winter with all things being the same the smoker seems to be effected by the cold much easier than the non-smoker. This is made me wonder why the smoker needs the heat turned up so much higher than the non-smoker. One thing that is made eveident is the fact that the smoker will burn you out with heat. could this be do to the capularies being restricted with blood flow.

If the circulation has been restricted by aretheroma, then yes probably.--Light current 21:00, 9 October 2006 (UTC)

[edit] Cold and fat

Does a person with higher body fat percentage feel the effects of cold sooner than someone with a lower body fat percentage? (The above question reminded me to ask.) Hyenaste (tell) 00:51, 8 October 2006 (UTC)

No, just the opposite, fat is an excellent thermal insulator. That's why you won't see any thin Inuits. StuRat 03:35, 8 October 2006 (UTC)
Some fat and short people I've seen are quite afraid of cold. Some may not be mentally adapted to the cold. -- Toytoy 03:52, 8 October 2006 (UTC)
I agree that fat is a good insulator, but it can also have to do with the reason people are fat. If it's because of hypothyroidism, then they'll probably feel the cold because overweight and cold sensitivity are two common symptoms. Anchoress 04:13, 8 October 2006 (UTC)

[edit] Germs

I recently read that you should wash handkerchiefs in hot water because they will survive a cold water wash. a) is this true, and b) even if they did survive, would they survive direct sunlight for an average day (i.e., on a clothesline)? BenC7 04:47, 8 October 2006 (UTC)

Was that "germs" or "vampires" you were asking about? B00P 04:59, 8 October 2006 (UTC)
Not really, leaving them exposed to the Sun won't do a job as good as boiling the handkerchief in hot water (much like in pasteurization). The ideal is, of course, put the handkerchief in boiling water for a few minuts and letting it dry on the Sun later. It should be pretty much sterile as far as I can tell. ☢ Ҡi∊ff⌇↯ 07:21, 8 October 2006 (UTC)
How do you get your 'kerchief ON the sun? And wouldnt that plasmarise it?8-)--Light current 09:05, 8 October 2006 (UTC)

Bleach is also useful for disinfection. StuRat 20:42, 8 October 2006 (UTC)

Bleach tends to rot your clothes.--Light current 22:36, 8 October 2006 (UTC)

Bacteria are killed by UV light, so the efficacy of disinfection by sunlight would be dependent on the UV intensity of the sunlight eg. see [1]. So if you live in a place where the UV intensity is high then this effect will be more significant. The problem with threating handkerchiefs in this way in that bacteria on the skin (and in the nose) are often pigmented, ie. they produce coloured compounds. These compounds serve to absorb certain frequencies of light and thus enable them to survive better in sunlight. We used to do an experiment at university where we took a petri dish and left it out in the air for a few minutes then put it in the incubator. The bacteria that grow up are mostly pigmented, the reason being that it is them that can survive longer exposure to the sun. Personally, I use high temperature washing for handkerchiefs - and bath towels for that matter. Azaroonus 07:28, 15 October 2006 (UTC)

Just microwave your damp handkerchief until it steams. You can treat kitchen sponges the same way. -THB 09:44, 16 October 2006 (UTC)

[edit] Disease

Please tell me which disease shows the following symptoms: 1. Body pain 2. Unability to remember anything new 3. Unability to concentrate 4. Loss of Reading speed 5. Headache(sometimes)

P.S. These symptoms are of a 15 year old

There is no amount of warning I can give you that would justify a non-professional answer to this question. The symptoms you describe are VERY SERIOUS and if you or someone you know are suffering of these symptoms, go to a qualified doctor IMMEDIATELY.  freshofftheufoΓΛĿЌ  07:00, 8 October 2006 (UTC)
Sure, but that wasn't the question. Are you assuming the questioner is a moron? DirkvdM 11:00, 8 October 2006 (UTC)
Well, the symptons match for it (just kidding). - Dammit 11:04, 8 October 2006 (UTC)
Did I respond innapropriately to this? Should we answer this kind of question? I honestly can't think of a reason why this question should be asked in a place like this, or a reason why it should be answered. What am I missing?  freshofftheufoΓΛĿЌ  16:47, 8 October 2006 (UTC)
Like I said, you didn't answer the question. The purpose of the ref desk is to answer questions. Some will give bad answers and therefore anything said here shouldn't be taken at face value, but that is so obvious that it hardly worth mentioning. Imagine a bar with a warning sign that medical issues may not be discussed there. :) DirkvdM 08:48, 9 October 2006 (UTC)
You know I'll be the last person to say that medical questions shouldn't be answered on the science desk. I just can't see the sense in asking such a question, unless it's some sort of homework, in which case they should have mentioned that in the first place.  freshofftheufoΓΛĿЌ  09:14, 9 October 2006 (UTC)
The bad news: it is harder to imagine a vaguer and less specific list of symptoms. Every single symptom affects someone sometime. There are a thousand diseases and conditions that can cause these, ranging from depression or sleep deprivation to encephalitis or hypothyroidism. We are not going to be able to give you a diagnosis. alteripse 13:28, 8 October 2006 (UTC)
Sounds like has a crush on someone. ♥ ♥ ♥ Tell him to ask her out! Hyenaste (tell) 17:28, 8 October 2006 (UTC)
Well this could be medical homework and not sufferred by the questioner!--Light current 17:32, 8 October 2006 (UTC)
I once suffered a few of the symptoms (concentration, reading, memory) in the short term after going all day not eating or more importantly drinking anything. I had trouble putting sentences together until i had a good drink of water. Any change you're not getting enough water throughout the day? Benbread 17:55, 8 October 2006 (UTC)

Severe tiredness, coupled with irritability caused by the tiredness. Philc TECI 21:13, 8 October 2006 (UTC)

Falling down while drunk. -THB 09:45, 16 October 2006 (UTC)

[edit] sensitivity to sound

True or false: If a person is hypersensitive to sound, he/she cannot be hyposensitive to sound?

  • True, Hyper-, and Hypo- are opposite prefixes, so noone can be hyper, and hypo anything --Englishnerd 11:58, 8 October 2006 (UTC)

But could they be hypersensitive to some sounds and hyposensitive to others?

Yes! See deafness. Hyper sensistivity to some sounds can occur after hearing damage.--Light current 17:34, 8 October 2006 (UTC)
I can attest to that. As a child I had a case of Cholesteatoma in one ear, which damaged my middle ear bones. I had surgery several times to treat the condition, but only very little could be done to restore my hearing in that ear. However, some sounds in the highest range of human hearing still pass through. Unfortunately this also leaves me very sensitive to these frequencies, because the inner ear is usually understimulated. --Pekaje 20:25, 8 October 2006 (UTC)

False, because sounds can occur at different frequencies. One could be hypersensitive to high-pitched sounds and hyposensitive to low-pitched sounds, for instance.

There is a company that markets a device to emit loud noises at frequencies that teenagers can hear but older adults cannot. It is used to keep the teenagers from hanging out at the convenience store parking lot. -THB 09:48, 16 October 2006 (UTC)

[edit] cochlea

True or false: 70%-80% of the cochlea is devoted to low frequencies?

Upon what do you bass that assertion ? :-) StuRat 20:07, 8 October 2006 (UTC)
Sounds like you're causing treble again? 8-)--Light current 22:32, 8 October 2006 (UTC)
We make such comments with far too high of a frequency. :-) StuRat 03:20, 9 October 2006 (UTC)
I cant top that!--Light current 03:59, 9 October 2006 (UTC)

Spiralling back to the original question, I'd note that the cochlea operates by sorting sounds by wavelength, so by definition, the first octave's worth of sensor must occupy 50% of the length of the cochlea, the second octave's worth of sensors must occupy the next 25% of the length, and so on...

So if by "low frequencies" you mean the first two octaves of frequencies to which the cochlea is sensitive, then I'd say that must be just about right.

Atlant 17:08, 9 October 2006 (UTC)

Hey thats clever reasoning!! Like a string instrument: it takes half the string for the first octave , then a quarter for the next, etc 8-)--Light current 21:02, 9 October 2006 (UTC)

[edit] Electromagnetic radiation.

What radiation will be emitted from an electrical substation on a housing estate, and how can I shield my house?

I think we had this one not so long ago.--Light current 22:33, 8 October 2006 (UTC)
I shouldnt worry. The transformer is surrounded by a metal casing connected to earth and acts as a Faraday cage. I would worry about it blowing up though, especially if it is old! 8-)--Light current 02:00, 9 October 2006 (UTC).
There is more to it than the transformer. Unless the substation uses shielded underground cables and gas insulated buswork and switchgear, there is likely to be an electromagnetic field propagated (60 Hz in the US, 50 Hz most other places) from the power lines and buswork. See "Power Over People" by Louise B. Young, Paperback: 272 pages,Publisher: Oxford University Press, USA; Rev&Updtd edition (September 3, 1992) Language: English ISBN: 0195075781. It has a good if dated treatment of some issues regarding electromagnetic radiation. The distribution lines near homes also generate electromagnetic radiation. Also see "Health concerns" in the article Electric power transmission. Electric blankets, other appliances and wiring inside your home will doubtless produce a higher electromagnetic fiels than a substation a considerable distance away. Studies on health effects of powerline frequency electromagnetic radiation have shown mixed results. There does not appear to be a Wikipedia article on the possible harmful effects of power line radiation. Given the contentiousness of the issue, I wonder if there was one which got deleted. Edison 18:31, 9 October 2006 (UTC)
Sorry, you are ill informed. All switchgear busbars and UG cables (LV and HV) are surrounded by earthed metal sheaths right up to your dostribution panel in your house! Switch gear does not have to be GIS to be sheilded. THere is absolutely no EMF on the outside of switchgear abart from tiny pulses cuased by partial discharge activity.
Overhead lines are another matter altogether.--Light current 21:09, 9 October 2006 (UTC)
I have spent many years working in substations near (but not too near)open air high voltage buswork which was not surrounded by grounded metal as you claim it all is.See the image, from Electrical substation. the conductors are up in the air, widely separated.
A 115 kV to 41.6/12.47 kV 5000 kVA 60 Hz substation with circuit switcher, regulators, reclosers and control building
A 115 kV to 41.6/12.47 kV 5000 kVA 60 Hz substation with circuit switcher, regulators, reclosers and control building
Many substations, those without gas insulated buswork and switchgear, have high voltage buswork at 69kv, 138kv, 345kv or 765 kv which is tubular aluminum or which is stranded cable and which is in the air above the high voltage circuit breakers and disconnects. It is insulated from the metal or wooden support structure by porcelein insulators, but is otherwise air insulated. Because the conductors are necessarily many feet apart to prevent flashover, the electromagnetic fielsd do not cancel with respect to some point near the substation fence., Therefore there willl be an electromagnetic field. Overhead transmission lines and many distribution lines are also not surrounded by grounded metal.Edison 04:44, 16 October 2006 (UTC)

You cannot shield your house but you can protect your children: AFDB. -THB 09:51, 16 October 2006 (UTC)

[edit] Euphoria caused by Victory?

Wikipedia need work on the victory and euphoria articles, which offer nothing beyond a tiny, basic definition and disambiguation options. My question is, as you might guess from the subject, 'does victory cause euphoria?' A lot of cultures seem to describe victory (as a noun, I guess) as being a distinct emotion resulting from winning/success. I've never experienced anything I would describe as euphoria from victory, but I've heard it described by others as such. I realize this might be a very relative question, but I'd really like more information on the brain chemistry involved; there's certainly an evolutionary pressure for individuals to desire success for reasons beyond whatever they're succeeding in. I wish there was a better victory page. :( --Demonesque 10:52, 8 October 2006 (UTC)

Endorphins? --jpgordon∇∆∇∆ 05:02, 9 October 2006 (UTC)
Urrr, if you care that much about wining it might, i dunno. Philc TECI 17:30, 9 October 2006 (UTC)

[edit] Time Dialation Confirmation

I got into an argument yesterday about Time Dialation and if it is or is not necessarily proven. I've seen the experiments listed in the Time Dialation article we have, but I am not convinced that time is a physical dimension that can be effected by gravity and speed -- if it were, then "time travel" would be possible, which logic proves it isn't (unless "alternate universes" are created to deal with causality -- and that's just absurd).

Anyway, someone cited an experiment in which two atomic clocks were synced up, and one was taken on a high-speed plane and then they found out that they were out of sync afterwards. However, I never got a source for this. Could someone provide me with it, please?

Further, if time dialation is proven and concrete, how do those of us who define time as being a concept used to sequence events rather than a physical dimension justify that belief? --Demonesque 11:00, 8 October 2006 (UTC)

First of all, time dilation does not give rise to the classic time-travel paradoxes that disrupts causality. For that to happen you need to travel back in time (to reverse causality) so time can very much still be used, as you say, to sequence events. Infact, this is pretty much the definition of time (by the second law of thermodynamics). Not exactly, but pretty much anyway. Just because time goes at different speeds depending on gravity and velocity does not mean that it can suddenly travel backwards. Time dilation introduces ALOT of other paradoxes, but it does not introduce causality issues Oskar 12:07, 8 October 2006 (UTC)
As for experimental confirmation, see Hafele-Keating experiment, and related ones at Time dilation#Experimental confirmation Oskar 12:11, 8 October 2006 (UTC)


Yes, I know that Time Dialation doesn't introduce causality issues, but my question is -- if time can be affected by speed and gravity then it is a physical dimension which then, theoretically, enables backwards travel through time. Time Dialation (to me) means that it is a physical dimension. --Demonesque 13:35, 8 October 2006 (UTC)

Here's how I think about it.
  • The effects of speed and gravity on time doesn't make it a dimension, which I would say is just mathematical model of reality (though perhaps a very natural one).
  • If time is regarded a dimension, it's not obvious that you can travel in it. Atleast not the way you want to.
—Bromskloss 13:58, 8 October 2006 (UTC)
Look this is a very complicated matter, the exact nature of time, and it cannot be explained in a short answer on the reference desk. You are making some fundamental misunderstandings about time. It is not a dimension like x,y,z is a dimension, it is fundamentally different. We use it as a dimension in spacetime because then physics makes sense, but we never claim that it is an "equal" to the other three dimensions. And I still don't understand how you can make the logical jump from "in different reference-frames time can move in slightly different speeds" too "time can travel backwards!". It doesn't make any sense. Bring a concrete example of what you mean, and perhaps I can explain it too you. If you really are serious about learning about this stuff, buy A brief history of Time by Stephen Hawking. It explains all of these concepts in a simple straightforward way. Oskar 14:23, 8 October 2006 (UTC)
"...if time can be affected by speed and gravity then it is a physical dimension..." How did you reach this conclusion? Time is a dimension, just not a physical one. Clarityfiend 19:06, 8 October 2006 (UTC)
Well Oskar, thats strange! Einstein says in his book 'Relativity' that Minkowskis four dimensional space is real and 'time is robbed of its independence'. p57. To obtain this 4 dimensional space, merely requires the 4th dimension to be represented by i.ct, where i = sqrt(-1). THe only thing the i operator does IMO, is to place the new dimension orthogonal to the other 3.
Einstein also says:
We can regard Minkowski's 'world' in a formal manner as a four dimensional Euclidean space (with imaginary time cooordinate): the Loretz transformation then (merely) corresponds to a 'rotation'of the coordinate system in the four dimensional world
--Light current 02:15, 9 October 2006 (UTC)
So, its not time thats the fourth dimension, its the speed of light multiplied by time another direction altogether!!!
Speed x time = distance. Distance is not a dimension. JackofOz 02:30, 9 October 2006 (UTC)
Correct! ct is a distance in the 4 th dimension. THe direction of the fourth dimension is orthogonnl to the other 3.--Light current 02:46, 9 October 2006 (UTC)

It's time dilation, not "dialation". StuRat 20:04, 8 October 2006 (UTC)

Stretch it any way you want!--Light current 02:15, 9 October 2006 (UTC)
Yes, I suppose you could put that spin on "dialation". :-) StuRat 03:17, 9 October 2006 (UTC)
Only if you have a very old phone! 8-)--Light current 03:23, 9 October 2006 (UTC)

[edit] Does snoring affect the snorer's hearing?

How does snoring affect the snorer's hearing? I would assume there is some sort of detrimental affect. Does anyone know of any studies on this? Thanks

I don't see why you should assume any detrimental effect on hearing. Most snoring is fairly quiet anyway.--Shantavira 17:20, 8 October 2006 (UTC)
I don't know of any studies, but it seems to be a truism to me that the cilia inside your ear would be affected by any external stimuli, whether you're awake to notice it or not. Would the average person's soft snoring be of any concern? I doubt it. Would it potentially be detrimental over a number of years if your snoring was unusually loud? Yes. --Aaron 17:32, 8 October 2006 (UTC)
I wouldt say most snoring is quiet!. I woke my self up at least once with my own snoring!--Light current 17:38, 8 October 2006 (UTC)
What? What's that you say?Edison 18:51, 9 October 2006 (UTC)

[edit] bizarre

Science says protons are positively charged and tightly clustered in the nucleus, but like-charges would strongly repel in such close proximity. Why doesn’t the nucleus fly apart?

kylie

The strong (or weak - can't remember which, sorry) nuclear forces hold them together. —Daniel (‽) 13:57, 8 October 2006 (UTC)
It's the strong force Oskar 14:26, 8 October 2006 (UTC)
It's the quantum chemistry that does it, they don't orbit, they delocalize--71.249.23.233 14:55, 8 October 2006 (UTC)
Quantum chemistry talks about the electrons not the nucleons. Strong force is the right answer. Protons not only have positive electric charge, but also so-called colour charge which subjects them to the strong attractive effect of the stron force. See there for details. Simon A. 18:56, 8 October 2006 (UTC)
Since protons do not carry color charge, nuclear force is a slightly better answer. Melchoir 22:23, 8 October 2006 (UTC)

A slightly easier-to-understand explanation than is found in the article can be found here. (Use the arrows in the top-right of the screen to go backwards and forwards.) If you don't understand it the first time, don't worry. I had to read it a couple of times before I properly 'got' it, too. BenC7 05:16, 9 October 2006 (UTC)

[edit] difference between AC DC current

can anyone please tell me the difference between AC and DC current

See alternating current and direct current for explanations of those terms. TenOfAllTrades(talk) 14:57, 8 October 2006 (UTC)

[edit] Heart Rate

During a strenuous mountain race which I completed in 6 hours, I notice from my heart rate monitor that for the first three hours my heart rate averaged about 160 bpm which is consistent with my training experience, whilst for the second half the average was about 140 bpm which is substantially lower than expected. The terrain was equally difficult at all stages of the race. The question then, does heart rate decline as an endurance athlete grows progressively more tired - especially if he has passed the 'exhaustion limit' built up by training ? I personally 'hit the wall' at about 4 hours.--Dr snoobab 17:10, 8 October 2006 (UTC)

Was it possible you were suffering palpitations, or escaped beats?--Light current 17:45, 8 October 2006 (UTC)

Valid point about the palpitations - noting reference made in the article to overexertion, faintness, dizziness - all of which I experienced.--Dr snoobab 16:02, 9 October 2006 (UTC)

[edit] technology in manufacturing surgical instrument

I am interested in knowing the latest technology being employed in the manufacturing of surgical instruments. are there CNC machines available for making dies which could be then used for manufacturing of instruments on large scale?

A stamped or die-pressed surgical instrument would be of poor quality. That might make a reasonable starting point for machining a tool with sharp edges, such as a scalpel, however. StuRat 19:57, 8 October 2006 (UTC)


[edit] how to make this

in the following website there is a pic of a plant cell .I plan to make it for my bio project .i think i will use gypsum to make the structure of the organelles . is it a good idea . what should i do about the cytoplasm and valcuole (they are supposed to be transperant ,are'nt they).any suggestions or comments to make it better[ http://sps.k12.ar.us/massengale/cell_model_instructions.htm]Mi2n15 18:10, 8 October 2006 (UTC)any idea how to construct the endoplasmic retticulum ,the golgi apparatus and the mitochondria.Mi2n15 18:14, 8 October 2006 (UTC)

Maybe you could use dense clear gelatin for the cytoplasm. I don't know if that would cause your gypsum organelles to fall apart though. For the vacuole, you could place an inflated balloon in there while the gelatin sets and then remove it once it has solidified. I remember when I did this project, I used plastic wrap for cytoplasm and a clear balloon for the vacuole. I totally wanted to use gelatin though. Hyenaste (tell) 18:19, 8 October 2006 (UTC)

i think gelatin would be messy , any idea how to carge the cell wall and other organelles out of gypsum, do you get coloured gypsum??Mi2n15 17:37, 9 October 2006 (UTC)

[edit] Popping pimples

What is the clear fluid that emerges when you squeeze a pimple for too long? And the semi-solid stuff that comes out when I pop a lump with a small black dot in the center? Scienceman123 talk 19:09, 8 October 2006 (UTC)

Have you read our article on pimple? Or did you seriously not expect us to have one? Of course, we have, because Wikipedia knows everything. Now, the kind of pimple with black dot is simple. The black dot is dirt that obstructs the exit of a sebaceous gland, such that the sebum fills up the gland, letting it swell. Over time, the sebum becomes hard and "semi-solid" as you call it. For the clear fluid I am unsure. Maybe it is sebum, maybe it is pus. Anybody else in the know? Simon A. 19:25, 8 October 2006 (UTC)

The white stuff is pus, which is a mixture of bacteria and white blood cells, which are fighting the bacteria. The clear stuff is sebum, mostly oil, produced by sebaceous glands and sent up via pores to the skin. The pimple develops in the pore and blocks the flow of oil to the skin. The exposed portion of the pus can dry to form a whitehead and that can then absorb dirt to become a blackhead. I've found that consumption of trans-fats thickens the sebum and further aggravates acne. If you limit your fat consumption to vegetable oils, they will stay liquid and flow out of the pores without causing acne. StuRat 19:20, 8 October 2006 (UTC)

Actually the black stuff is not dirt, it's oxidised sebum. And the clear stuff can be sebum, but in a pimple it's plasma (blood without the red corpuscles), drawn to the pimple by inflammatory agents. Anchoress 19:48, 8 October 2006 (UTC)

So are the things that hurt when you pick them and try to pull them out, and when you finally do, you see that it is actually something like consolidated oil, modified sebum? — X [Mac Davis] (SUPERDESK|Help me improve)15:13, 9 October 2006 (UTC)

I agree with Anchoress. The clear stuff in question is probably blood plasma, which is usually runny and less viscous than oil or sebum. - Cybergoth 16:01, 9 October 2006 (UTC)


Some of the clear stuff may also be cytosol, and if the pimple is red and the fluid is whitish, there may be some pus mixed in. You shouldn't be squeezing that hard, or using your fingernails, and you should take a hot shower first. Try some 10% benzoyl peroxide creme at night and you won't have to. -THB 10:01, 16 October 2006 (UTC)

[edit] ABOUT PHARMACY?!!!

HI I'm attending the faculity of pharmacy in Syria,Middle East. And I just wanna know about the majors in pharmacy?!! thank you alot

Wouldn't your faculty be a better place to ask that question? -Obli (Talk)? 22:37, 8 October 2006 (UTC)

[edit] Quercus × rosacea

How does one pronounce the x in Quercus × rosacea? --Auximines 20:40, 8 October 2006 (UTC)

Try the Language Ref Desk (and what letter are you talking about, anyway ?) StuRat 21:19, 8 October 2006 (UTC)
It's not an x but a ×, which leads me to believe it is pronounced as the word "cross". Hyenaste (tell) 21:43, 8 October 2006 (UTC)
According to [2] it's simply an abbreviation indicating it's a hybrid, so I guess in your case it would be "Quercus hybridised with rosacea" -Obli (Talk)? 22:34, 8 October 2006 (UTC)
I think in this case, × rosacea is a named hybrid in which case I believe it should be pronounced "Quercus hybrid rosacea". For unnamed hybrids, the form would be (e.g.) Sarracenia alata × minor and this could be pronounced "Sarracenia alata crossed with minor" or "Sarracenia alata hyridised with minor". I think I've also heard "Sarracenia alata by minor" used, and this to me seems the most elegant, although I can't find a source to verify it so you may not be understood using that form. Hope that helps! --YFB ¿ 22:44, 8 October 2006 (UTC)
It strikes me as the sort of information that is obvious on the academic and professional level and is just passed on by word of mouth because it's too insignificant to put in a book. -Obli (Talk)? 23:13, 8 October 2006 (UTC)
The only reason I've encountered it is because I used to be very interested in carnivorous plants (still would be if I wasn't in Uni and had somewhere to put them), hence the Sarracenia example. It's the sort of thing I'd like to see included in hybrid name, if we can find some proper citations. --YFB ¿ 00:31, 9 October 2006 (UTC)

[edit] ACCELERATION of light

Is it safe to say that light does not accelerate, but always moves at c? If there was a chance it didn't, is it theoretically possible to measure such an acceleration? 81.93.102.3 20:52, 8 October 2006 (UTC)

To my knowledge, light does not accelerate. C is a constant, and therefore will not change at any time in a vacuum. However, if you change mediums, like going from water to air, you would have to use refraction indices and angles and plug into Snell's law to calculate the new velocity of light in the new medium. Hope I answered your question. --Nishkid64 21:02, 8 October 2006 (UTC)
A photon has 0 rest mass, so if it did accelerate, it would be instantaneous anyway, which is the same as no not having accelerated at all (i.e. always traveeling at c) i think. Philc TECI 21:10, 8 October 2006 (UTC)
First of all, acceleration doesn't necessarily mean "change in speed". An object moving in a circle is accelerating, but not changing speed, because only the direction of the velocity vector changes, not its magnitude. Second of all, light does not always move at c. Glass has an index of refraction of about 1.5, which means light moves at 2/3c through glass. So I guess you could say light "accelerates" at the surface of a piece of glass (and that's what causes refraction). Third of all, even in a perfect vacuum light doesn't move in straight lines, but geodesics of spacetime, which are affected by gravity according to general relativity. So I guess you could say light "accelerates" in a gravitational field too, which causes things like gravitational lensing. —Keenan Pepper 21:55, 8 October 2006 (UTC)
About the change of speed when moving from one medium to another. That is an acceleration, but only on average. As Philc said, I assume the change will be instantaneous. So even though, strictly speaking, there is an acceleration, that is a somewhat deceptive way of putting it. DirkvdM 08:55, 9 October 2006 (UTC)
It's not instantaneous for an index gradient. —Keenan Pepper 23:03, 9 October 2006 (UTC)
It's not really an acceleration either, because no one photon changes speeds. The photons always move at c, and in various materials they travel in a series of jumps (each at c) that average to a smaller speed. The patterns in the classical electric field or the quantum-mechanical photonic wave function may change speeds smoothly (on length scales large compared to the material components but small compared to the changes in refractive index), but there's no physical object that accelerates. This question doesn't really have a good answer because in order to speak properly about light such approximations as average values and smooth accelerations must often be abandoned. As far as general relativity goes, travelling along a geodesic is precisely the definition of not accelerating; locally, such paths are straight lines. --Tardis 16:39, 10 October 2006 (UTC)

[edit] What is the difference between a nuclear explosion and a nuclear reaction?

Does anyone know?

A nuclear explosion (see nuclear weapon) is just what happens when you have a really fast, uncontrolled nuclear reaction in a confined space. Nuclear reactions intended for electricity production or isotope production are controlled with things like graphite rods to slow down the reaction (see nuclear reactor). --Allen 23:40, 8 October 2006 (UTC)
Also see nuclear chain reaction... that's really what I'm talking about above; technically a nuclear reaction doesn't have to be exothermic or self-sustaining. --Allen 23:43, 8 October 2006 (UTC)
So, simply put, a nuclear explosion is a specific case of a nuclear reaction. DirkvdM 08:57, 9 October 2006 (UTC)