John Cuthber

Can white light be coherent? (OK,a short enough pulse might have enough uncertainty to have a wide enough bandwidth to count as white.)

I still keep a slide rule on my desk at work, but it's only to frighten the uninitiated. On the other hand (no pun intended) I have been known to count on my fingers. Is this the first "digital" computer? (OK, that pun was intentional)

Did you have a look at those 2 papers? Here are a couple of quotes- one from each. "Abstract. Stable lasing has been obtained on and color centers in additively colored OH:NaCl crystals. " "This thesis reviews the development of an APM laser based on the NaCl:OH(-) color center laser. " The thing about materials with colour centres in them is that they 1 are not white and 2 are not strictly NaCl. It's like calling a ruby laser an Al2O3 laser. Al2O3 is the matrix that holds the Cr(III)ions , they do the lasing.

I'd imagine that it's probably easier with sperm cells than most others.

Salt is white. It doesn't absorb visible light. That makes it unlikely to emit visible light (I realise red hot salt will glow red, but I don't think that there are any specific transitions involved). Salt is also use for "optics" in infra red work becaue it doesn't absorb IR much. I think it's pretty transparent in the UV too. I wouldn't say it was impossible to make a salt laser but it's going to be very difficult. Why did you ask?

I once built a (really crap) robot using relays for all the control logic.

This thread looks like it's going to turn into the Dilbert cartoon that finishes up with someone saying "Ones AND zeros? We had to make do with just zeros".

No. BTW, I think all telescopes focus.

Rereading the question I see that no solvent is specified. Could be in horse urine for all we know. If it is a dilute solution in water then you can assume that the quaternium salt is a strong base then you only need to know the acidity constants for the phosphoric acid/ phosphate system

Last time I checked the sun was a star. Anyway, most of these absorbtions don't have a lot to do with the hydrogen lines.

You are going to need pKa data measured in that ionic liquid too. Good luck finding any.

http://www3.interscience.wiley.com/journal/119959841/abstract?CRETRY=1&SRETRY=0

So, what was the paperclip comment about?

Relays with AC coils are perfectly common and they work just fine. http://www.maplin.co.uk/Module.aspx?ModuleNo=2567 When the current flows one way the coil becomes a magnet and atracts the armature. When the current reverses exactly the same thing happens. The reason you can't generally stick a paperclip to a magnet is that most of the flux flows round a closed loop.

Just a relay might work. You might need one with a coil voltage rather less than 9V because the impedance will be higher for an AC drive and you would need a relatively big relay so the switch is too big and heavy to react in the 1/100 sec or so between cycles.

I think each doubling of the f number quadruples the time so 1/125 @f/8 1/31.25 @f/16 1/7.8@f/32 1/1.95@f/64 i.e 0.512 sec @f/64 2.05@f/128 8 sec @ f/256 32.768 @ f/512 131.072@ f/1024 I think you need to check your arithmetic, but I'm not sure. I have a cold and my head's not working properly.

That's interesting because it means that it still moves at that "magic" velocity when the sound has dies away and it's actually stationary. (I'm ignoring the quantum effects for simplicity). Somehow I doubt that. The speed that a wave runs up and down the string depends on the properties you mention, but the speed of the string is dependent on the amplitude of vibration. When you pluck the string you stretch it and that stores potential energy in the string. When you let it go that potential energy is converted to kinetic energy. Since relatively little energy is lost as sound (during any one vibration of the string) the square of the string's peak velocity is roughly proportional to the initial displacement. Of course, there are potential problems as the speed of the string reaches the speed of sound- not least the assumption that the rate of energy loss is small is no longer true.

Distillation would work. Steam distillation might work better. Add some water to the aldehyde and distill the "mixture" (they don't mix well) The steam will carry any HCN with it. It will also carry some of the aldehyde over. The solution of HCN in water is less hazardous to work with. HCN does boil at a low temperature, but the amount of it in the benzaldehyde is small so you probably wouldn't get a proper low boiling fraction rich in HCN then a high boiling one rich in aldehyde. If you plan to do this make sure you add some boiling chips or something to the flask you distill from. Also you might want to try adding about 5 or 10% salt to the water so it forms the bottom layer in the flask - that way the bubbles of steam are forced to go through the benzaldehyde (which would normally sit at the bottom of the flask because it's denser than water).

A hydrogen filled gas discharge lamp has several species in it like H2 and H3+ as well as H and all of these have nmany excited states which can emit light. Once you have more than 1 atom you also have vibrational and rotational states that add to the number of possible lines. BTW I rather doubt that you normally see absorbtion lines as Severian says.

Wonderful and, so far as I can tell, pointless so I guess it's art.

Ebay or a scrap metal dealer look like good options. What do you want it for?

You need to know about reciprocity failure too. http://en.wikipedia.org/wiki/Reciprocity_(photography)

I will stick to C13 cake thanks. I might not live as long, but I won't glow in the dark. But you are right, without a lot of long term study this is almost pure speculation.

I didn't.

Long ago and far away a researcher at a well known University was told to do some lecturing and to set an exam. He didn't want to- it got in the way of his research- and he said so. They told him to do it anyway. He taught the course- badly. Then he set the exam- an absolute bastard by all accounts but, strictly within the rules. They never asked him to teach again. The University quietly "adjusted" people's marks.