Gail Shaw wrote:

> And it is possible for particles to travel faster than the 'speed of light'
> in a particular material. (Though, of course not faster than c)
> This is most commonly seen around submerged nuclear reactors and is called
> Cherenkov radiation. If you've ever seen a picture of a submerged reactor,
> it's that eery blue glow.

Gail... You're a DBA. Why do you know about Chernkov radiation?

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"Orchid XP v7" <voi### [at] devnull> wrote in message
news:4734c9d3$1@news.povray.org...
> Gail Shaw wrote:
>
> > And it is possible for particles to travel faster than the 'speed of
light'
> > in a particular material. (Though, of course not faster than c)
> > This is most commonly seen around submerged nuclear reactors and is
called
> > Cherenkov radiation. If you've ever seen a picture of a submerged
reactor,
> > it's that eery blue glow.
>
> Gail... You're a DBA. Why do you know about Chernkov radiation?

That's an odd question. Why would my experience with databases preclude
knowledge of science? I could as well say you're a system admin, why do you
know about Fourier Transformations?

I have a B.Sc in Physics. Wanted to go into physics as a career, but there's
no jobs other than teaching in this country.
I still read articles on astrophysics, quantum physics and relativity for
fun (when I can get the time)

I actually saw Cherenkov radiation once. Was during a trip to a nuclear
research institute, as part of a prize for coming in the top 50 in the
country's science olympiad.
It's eery to see.

btw, it's also possible to see Cherenkov radiation in the upper atmosphere
(though diffuclt to see from earth) when high velocity cosmic
particles/solar wind particles impact the atmosphere at speeds very close to
c.

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Darren New nous apporta ses lumieres en ce 2007/11/08 19:28:
> Alain wrote:
>> A wave guide have ior <1 for radio waves. You can't find the 
>> equivalent for IR and visible light.
> 
> Huh. Why not?  Just because of the size of the atoms you'd have to build 
> it from or something?
> 
A wave guide ior tend to go higher as the wave length go shorter. There is a 
wave length rhere it's ior is = 1, and at shorter wave length, it goes > 1.
If you reduce the openings, the critical wave length diminish, but only by a 
diminishing fraction of the change.

-- 
Alain
-------------------------------------------------
It is the passion that is in a kiss that gives to it its sweetness; it is the 
affection in a kiss that sanctifies it.
~Christian Nevell Bovee

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Orchid XP v7 nous apporta ses lumieres en ce 2007/11/07 16:50:
> Warp wrote:
>> Invisible <voi### [at] devnull> wrote:
>>> Mmm, I wonder if POV-Ray can do this?
>>
>>   Probably not. AFAIK povray has a very specific refraction formula, 
>> which
>> it converts to total internal reflection when needed. I'm all but certain
>> that this formula does not support the concept of negative IOR.
> 
> That was more or less my diagnosis, yes. ;-)
> 
> It's not something any typical implementation would support unless the 
> designer purposely had this in mind, I would think.
> 
> Now negative light sources........ ;-)
And negative colours, and negative diffuse, ambient, filter,  transmit, specular 
and phong.
Why not! Perfectly possible, try it!
Negative light on a negative pigment returns a positive colour.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you think 80s movies have the 
funniest special effects.
Aaron Gage a.k.a Slartibartfast

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Invisible nous apporta ses lumieres en ce 2007/11/08 07:30:
> scott wrote:
>>> I find it rather bizare that electronic properties should actually 
>>> affect optical ones, but there we are.)
>>
>> Well yeh, what's light?
> 
> It's a phenomenon that has something to do with electricity, magnetism, 
> waves and particles, but nobody really understands what exactly. ;-)
> 
> Specifically, light is an electromagnetic wave (or is it a subatomic 
> particle?) in a particular frequency range (or is that particle energy?) 
> that registers in our eyes due to the chemical transformations it 
> induces in certain protein groups.
Light is BOTH a wave AND a particle. Some times, it act more like a particle, 
other, more like a wave. So does electrons and protons.
> 
> However, it's really damn unusual for a material's electrical or 
> magnetic properties to have any bearing at all on its optical properties.
Unusual, yes. DAMN unusual, no.
> 
> * Impure water is an excellent conductor, while pure water is a very 
> good insulator. Yet both substances have almost identical optical 
> properties.
ABSOLUTELY pure water is a prety good insulator, but just the tyniest impurety 
will change it into a conductor.
> 
> * Iron is highly magnetic, while aluminium isn't. Good luck telling the 
> two metals apart by their appearence!
Prety easy just looking. Alu is much "whiter".
Telling cobalt apart from iron from platinum by apearance is much harder.
> 
> * Electricity does not, under any remotely "normal" conditions, produce 
> light or affect it in any way. (E.g., you can't bend light using 
> electricity.) The same goes for magnetism.
Since when electricity don't produce light under "normal" conditions?
> 
> Sure, theoretically they're related. But it's not something you see in 
> the real world very often. ;-)
> 
> (I still can't figure out why you can use an oscilator to make radio 
> waves, but not light rays...)
Wait till we manage to create an oscilator that can ossilate fast enough... That 
would require the construction of a nano-scaled magnetron plunged in a magnetic 
field of a few K teslas.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you think 80s movies have the 
funniest special effects.
Aaron Gage a.k.a Slartibartfast

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Invisible nous apporta ses lumieres en ce 2007/11/08 08:08:
> M_a_r_c wrote:
> 
>>> (I still can't figure out why you can use an oscilator to make radio 
>>> waves, but not light rays...)
>>
>> Is not a laser an excitated resonant optical cavity eg a oscillator?
> 
> Actually, I thought it was a tube full of extremely hot gas with some 
> mirrors at the ends? (I don't know a huge amount about lasers.)
There are laser diodes, no gas at all and barely any heat. How about crystal 
lasers, the ruby ones been the archetype of all lasers: the famous RED laser 
beam! Gas lasers use cool, and idealy COLD low presure gas, and may NOT have ANY 
mirror at all, and often only one if they have any.
Usualy, heat is the enemy of lasers: they need to stay cool to stay 
monochromatic and keep a parallel beam.
You can build a nitrogen UV laser in your kitchen! You need a large 2 faces 
project board, some coper fold, some palstic, a screw, a bunch of capacitors and 
diodes, an ossilator, a nitrogen source, a cheap water jet vacuum pump, a 
welding iron and welding strip. ANYBODY can gather all components.
I have the plans if you want. They where published in the Scientific America 
magazine, with all needed instructions, as well as the working principles.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you've ever "lost" a Julia fractal 
because you're not quite sure how to align things in four dimensions.
Dylan Beattie

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Invisible nous apporta ses lumieres en ce 2007/11/09 04:47:
> Darren New wrote:
>> Invisible wrote:
>>> However, it's really damn unusual for a material's electrical or 
>>> magnetic properties to have any bearing at all on its optical 
>>> properties.
>>
>> That's why mirrors made out of wood work so well, after all. :-)
> 
> Well, you know, there are conductive materials that are reflective, and 
> ones that aren't. There are insulators that are reflective, and ones 
> that aren't. There seems to be little correlation here.
> 
>>> * Iron is highly magnetic, while aluminium isn't. Good luck telling 
>>> the two metals apart by their appearence!
>>
>> Magnetism is a field of photons at a frequency you just can't see.
> 
> What an interesting concept...
> 
>>> * Electricity does not, under any remotely "normal" conditions, 
>>> produce light or affect it in any way. (E.g., you can't bend light 
>>> using electricity.) The same goes for magnetism.
>>
>> Except for photoelectric effects, LEDs, solar cells, florescent light 
>> bulbs, all that sort of thing.
> 
> Solar cells work by using strange chemistry rather than directly turning 
> light into electricity. (Presumably that's why they're so inefficient.)
There is NOTHING chemical about solar cells, it's all a purely physical effect.
> 
> Florescent light bulbs work by stimulating atoms to release photons, not 
> by directly turning electric oscilations into light.
> 
> I have no clue why LEDs work. But apparently they do. ;-)
They convert electrical energy directly into light without heat.
> 
>> Don't you use a computer? What do you think you're looking at?
> 
> Electricity can be used to excite atoms in such a way that they release 
> photons. So can heat energy, chemical energy, and all kinds of other 
> energy. It's hardly unique to electricity. Basically if you get atoms 
> excited enough, they glow.
> 
>>> (I still can't figure out why you can use an oscilator to make radio 
>>> waves, but not light rays...)
>>
>> You can. It just has to osscilate a lot faster.
> 
> I think I've found an answer for this one.
> 
>   frequency = velocity / wavelength
> 
> For light, the velocity varies a little, but it's roughly 300,000 km/s. 
> That means that even if each wave is 1 km long (pretty damn long wave!), 
> it's going to have a frequency of 300 kHz. If you make that wave 1 m 
> long, that becomes 300 MHz, and by the time you get down to an utterly 
> *microscopic* wavelength, you're well above the THz range.
> 
> AFAIK, nobody has ever made an oscilator that goes that fast... (Indeed, 
> maybe there's even a quantum-mechanical reason why you *can't* do this? 
> Don't electrons have a "frequency" after all?)
> 
> So it seems that unless you can find a material with an index of 
> refraction of several thousand, you aren't going to make light with an 
> electric oscilator.


-- 
Alain
-------------------------------------------------
Agnostic: Shit might have happened; then again, maybe not.

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Nicolas Alvarez nous apporta ses lumieres en ce 2007/11/09 10:19:
> Gail Shaw escribió:
>> "Invisible" <voi### [at] devnull> wrote in message
>> news:47342cbb$1@news.povray.org...
>>> For light, the velocity varies a little, but it's roughly 300,000 km/s.
>>
>> Ur, no. The speed of light in a vacuum doesn't vary at all. It's a 
>> universal
>> constant.
>>
>> 299 792 458 m.s^-1
> 
> ...
> 
> How the HECK did they measure that o_O
A stationary mirror and a spinning rotor holding 8 others. Shine a light on the 
spining mirror so it encounter the stationary one. With the spining mirror 
stoped, mark where the return beam goes. Start the rotor and look as the return 
beam move.
At stop, the light hit rotor mirror #1, reatch the stationary one, return on 
rotor mirror #3. When the rotor is spining, it have moved before the light that 
hit the frist surface can return, so, it's reflected in a slightly different 
direction.
I've redone the experiment in colege. The aparatus is not that large, nor 
costly, and you only have to look in the eye piece to clearly see the movement.
You could do it yourself. You need: some mirrors, 2 razor blades, a drill, an 
eye piece, a light source, a plank of wood and some nails or screws, a dark room 
or the night. Some flat black paint is recomended.

-- 
Alain
-------------------------------------------------
Commercialism: Let's package this shit.

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Invisible nous apporta ses lumieres en ce 2007/11/09 10:21:
> Gail Shaw wrote:
>> "Invisible" <voi### [at] devnull> wrote in message
>> news:47342cbb$1@news.povray.org...
>>> For light, the velocity varies a little, but it's roughly 300,000 km/s.
>>
>> Ur, no. The speed of light in a vacuum doesn't vary at all. It's a 
>> universal
>> constant.
>>
>> 299 792 458 m.s^-1
> 
> Yes, the speed of light *in a vacuum* doesn't vary.
> 
> The speed of light in other mediums varies though. ;-)
Yes. the formula is simply: c = C / ior. "c" been the speed in that medium.

-- 
Alain
-------------------------------------------------
Wars are not paid for in wartime, the bill comes later.
Benjamin Franklin

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Invisible nous apporta ses lumieres en ce 2007/11/09 04:49:
> Darren New wrote:
>> Invisible wrote:
>>> bizare that electronic properties should actually affect optical 
>>> ones, but there we are.)
>>
>> Actually, the only interactions that take place outside the nucleus 
>> are between electrons (and antielectrons, I guess) and photons, so it 
>> seems pretty *necessary* more than *bizarre*. :-)
> 
> Well, sure, at quantum scales perhaps. At macroscopic scales? Well, 
> let's put it this way: there's no simple, easily observable correlation 
> between these variables in everyday life. I'm not denying that whoever 
> wrote this thing knew what they were talking about...
There are real substances that become transparent or opaque or reflective when 
exposed to some electrical field, and some that do the same if a beam of light 
hit them in a sertain way. The later are colour specific: a white beam pass 
trough, a red control beam will cause it to reflect red of the exact same wave 
length as that of the control beam. There are ongoing researches done to create 
a working computer from those. They do have some working prototypes that have 4 
states "bits" for 30 or so independent colours...

-- 
Alain
-------------------------------------------------
   It's tough to stay married. My wife kisses the dog on the lips, Yet she won't 
drink from my glass!
	Rodney Dangerfield

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