John Cuthber

If we are looking at PhDs then we need to try to work out which schools will be appropriate in about 6 years time. In a field like robotics, that could easily change between when he's 12 and when he's old enough to be doing a doctorate.

"" Given that, why not simply point out, during the meltdown, that the stuff that didn't hurt anything would be diluted to harmlessness, so there was no reason to be concerned about ecological damage in the first place? That's your argument now. Why not make it then? " " OK, the answer to that silly question is Because there's a difference between short term and long term and also because people live in the vicinity of reactors, rather than the middle of the ocean. "So? You keep repeating that like it means something. It sounds as if you are estimating the cesium radiation risk from the current open water concentrations of cesium, and finding it to be low. " Yes and no. It was measured and found to be low- you may remember that there was a picture of the distribution It's about a hundred times less radioactive than the natural background and the ecosystem copes with the background so it will cope with this small increase. The assumption I'm making is that a cell cannot tell if a beta particle has come from a potassium nucleus or from a caesium nucleus. If you don't agree with that then please let us know what particular re-writing of the laws of physics you are using. "Beta particles from ambient water concentrations of cesium are not what most concerns anyone worried about ecosystem damage from Fukushima cesium exposure." OK, what is? You may wish to consider two factors. If it's more mobile than Cs (like Xe for example) then it's even more dilute. If it's immobile then it won't have got far from the reactor and is trapped in a small area that is unfortunately, a write-off as far as normal life is concerned. It's not clear what you mean by "assume the hundredfold enrichment exposure never happened during the Fukushima meltdown emissions, " OK, where the meltdown happened was inside a building. That's a fundamentally artificial system, and the only bit of the ecosystem there I'm bothered about is people. Now there's no evidence that people selectively enrich caesium rather than potassium a hundredfold from their diet. Or are you talking about the fact that at some point in time the concentration was a hundred times higher? I already mentioned the fact that there will have been damage to the system near the site but , since the area affected is small and the raised levels temporary, the long term effect will be small. And thanks for quoting what I said. Now see if you can understand why it differs from what you claimed. Here are some hints. what you said was "We avert our eyes from the one that argued ecological harmlessness from cesium because it was in the same periodic element group as the potassium so much more abundant in the Ocean, and biological organisms treat elements in a given periodic group the same." On theother hand, here's what I said. "What I said was "Both will bioaccumulate to a similar extent ) because they have fairly similar chemistries." "What we are talking about are two materials that are chemically fairly similar, tend to get mistaken for one another by biological systems..." Now the point is that as long as they dissimilarities are not a hundred fold, I'm right. Now you did spot that there's a difference between those- you called it weasel wording- though it's not, it's just an indication that the exact sizes of the effects aren't known. So, why are you now saying that they are the same? And finally, apart from "RADIATION!" do you have any evidence yet

Then you will have no problem quoting where I did so. Actually, it's based mainly on the fact that there'as a lot more radioactivity in the water due to potassium, than due to caesium. If there's a hundred times more beta particles from potassium then form caesium, then, unless the relative enrichment of caesium over potassium is a hundredfold then most of the radiation dose will still be from the natural background. They don't need to be "identical" or anything close to it. Pointing it out five times doesn't affect it, but it indicates that you don't understand it.

So, still no actual evidence of damage then? Nice set of strawmen there. For example "We avert our eyes from the one that argued ecological harmlessness from cesium because it was in the same periodic element group as the potassium so much more abundant in the Ocean, and biological organisms treat elements in a given periodic group the same." Nobody actually said that did they? What was said was that the two metals tend to behave in a similar way (which is boringly true) and the the radiation dose from the small amount of Cs is much less than that from K, (which is also boringly true). "We likewise, out of courtesy, pass in silence over the argument that accumulations of cesium in organisms are ecologically harmless because they dissolve back into the water when the organism dies." or possibly we just pointed out that bio-accumulation is unlikely for something very soluble and not very biologically useful, which isn't the same thing. And so on.

"sometimes" doesn't enter into it. I'm talking about a specific pair of signals. One is created by FM, the other by AM, but the output is the same. Either decoder would give an ouput, but the outputs would be different. Which one is right?

It would seem strange tome that you can't find washing soda for sale. Another option to look for would be baking soda (sodium bicarbonate) However, if you want, you can convert the percarbonate to the carbonate by heating it.

Fundamentally, the operation of amplitude modulation is a multiplication of the two signals. The square wave has an infinite series of harmonics and those are carried through the multiplication process. you can generate the spectra of the two components (the sinusoidal carrier and the square signal) by calculating the Forier transform of them. Then, using this http://en.wikipedia.org/wiki/Convolution_theorem you can show that the spectrum of the AM signal is the convolution of those two spectra. the convolution doesn't remove the harmonics- they are still there even if you choose the frequencies and phase so that the transitions of the square wave correspond to zero crossings in the sine wave. I'm waiting for studiot to accept that, but I'm not sure he understand the problem. Now the point I made earlier is that the spectrum of a sine wave amplitude modulated by a sine wave is the same as the spectrum of a sine wave frequency modulated by a square wave. There's no way to tell those signals apart so they would obviously interfere with each other.

"Hello! If I add Potassium Carbonate And Sodium Nitrate mixed together in water i will get Sodium Carbonate and potassium nitrate, " Why?

The problem there is the analogy fails. Tigers are not rendered essentially harmless by dilution. Nor is there a background level of "tiger threat" with which we can compare the addition of some finite number of tigers. So, yet again, any actual evidence of damage?

Well, the British government are in bed with the American government. I'm not sure that the people agree. Also,l (unsurprisingly) we do a lot more trade with Europe than with the US.

In order to understand why that's wrong you need to look at Fourier analysis and, in particular, at apodization.

"Why did the UK opt out of the Schengen agreement?" We didn't. This guy did http://en.wikipedia.org/wiki/John_Major but there's no evidence that he asked the rest of us. Of course it may be that it would have made it difficult to police this http://en.wikipedia.org/wiki/The_Troubles

Are people who make judgements wrong?

Except that, nobody saw the tiger. You haven't produced any evidence of a threat. So what we have is a man who claims he saw a tiger- but nobody else has ever seen it. There was a brief look for the tiger- no evidence was found. Yet the man keeps on saying "you are ignoring the risk of the tiger". And whenever someone asks for evidence of the tiger's existence, he fails to produce any. So, where's the tiger; where's the evidence? ( A slightly better analogy might be to use a poisonous tropical spider. We never saw the spider and, even if it was there 4 years ago the Winters will have killed it.)

By a happy coincidence he is in Canada. (according to his profile) So we can imagine that in 6 years or so he will go for an interview at UVIC and they will say " we have a queue of ten thousand applicants- why should we choose you?" And, unless he has grown up in the mean time, he will tell them that they can leave. So, as a backup, perhaps someone should also let him know what the second-best school is.

Thanks for that. Let's just consider the Morse code for a start. To make it easy we can look at a set of consecutive dots, separated by gaps equal to the lengths of the dots (I'm not sure if that meets the standards for good keying, but it's not an unreasonable model) In effect we have a square wave with a period of half a second, so the frequency of that square wave is about 2 Hz. So, lets see what the spectrum of that looks like (before we use it to modulate anything) The spectrum of a square wave is a well documented exercise in maths the results are here http://en.wikipedia.org/wiki/Square_wave and the spectrum is an infinite series of increasing frequencies (with the amplitudes slowly dropping away as the frequency rises). The frequencies are all the odd multiples of the square wave frequencies so that's 2 Hz, 6 Hz 10Hz and so on- without any theoretical limit So, before you use it to modulate the 550MHz signal, there are (in principle) components with higher frequencies than that already present. There's nothing explicit in the modulation that removes those frequencies. So the spectrum of the transmitted Morse signal includes frequencies that are higher than the carrier. Which rather kills this assertion " With ideal equipment, there would be no harmonics, but we don't have ideal equipment." Ideal equipment ( a perfect Morse key) would give you a signal with infinite bandwidth. Perhaps you would like to comment on my observation that it's possible to have an FM signal and an AM signal that are exactly the same; in particular, how would you stop two signals like those interfering with each other?.

Rather than citing exam papers or other logical fallacies*, ( It's also irrelevant since my point is not that you can't modulate a signal any how you like, I'm saying that the two forms of modulation are not independent. You may recall me explaining that any FM signal that's fed to a real antenna will be amplitude modulated whether you like it or not.) you could answer my questions. How come I can generate two signals , both by modulating a 1MHz sine wave with a 1 KHz signal, that are identical even though one is AM and the other is FM? How would a receiver know which sort of signal it was? On a related note, perhaps you would like to tell us what sort of FM system transmission actually uses a signal like the one portrayed in post 41? In particular, since the frequency varies by a factor of about 3 or 4 to one, what frequency would you state on the application form if you applied for a licence for it? Citing something unrealistic like that then telling me to look at it doesn't help your case any. * it's an appeal to authority, which is a fallacy.

Why do you think it's a tardis?

First, stop being patronising and wrong. Second, it's not "end of" unless you answer the points I made Third, really, answer the questions I asked about spectra.

The evidence for the presence of a tiger in my bedroom is also unavailable. There's a reason for that. What you are labelling as "perfectly ordinary", is worrying about that tiger.

OK, so why do the put designs on the covers of books? And, on a related note, how else can you judge them?

Trust me, I know what FM is. Lets take a concrete example, a 1 MHz sine wave as a carrier and a 1 KHz square wave as the signal we want to transmit. (it looks like I'm back in the world of 1980s pop). I build a VCO with an output frequency of exactly 1MHz per volt. And I feed it with a signal that's a square wave centred on 1 volt and with a 1 mV amplitude. OK so, when the signal into the VCO is 0.999 volts the VCO produces 999 KHz and when it's 1.001 volts the output is 1,001 KHz. Since there's bound to be some switching delay on the square wave there will be times when the voltage is half way between the extremes and is 1 volt exactly so the VCO will also produce 1,000 MHz for some small part of the time. Now imagine that I look at the output of that through a spectrum analyser. What would I see? Well, the answer is simple, three spikes, one at each of those three frequencies. The middle spike's height will vary with the time take to switch. OK so far? Now let's look at another simple example. I amplitude modulate a 1 MHz sine wave with a 1KHz sine waver (it doesn't matter how- but let's say I use a 4 quadrant multiplier that's obligingly linear). Now imagine that I look at the output of that through a spectrum analyser. What would I see? I'd get the carrier and the sum and difference tones Well, the answer is simple, three spikes, one at each of those three frequencies. The middle spike's height will vary with the time take to switch modulation index. So, I can generate an FM signal that is exactly the same as an AM signal.* How do you propose to stop those interfering with each other? * yes, I know, I ignored the phase data in the spectral analysis. It doesn't trouble me much, I can pass the square wave through an all pass filter tailored to tweak the phase response

To whom was that addressed?

I already waited a few years, and there has been research. Anyway, it's a bizarre approach to take. 1st man "He's a bank robber!" Policeman "Got any evidence" 1st man- "Wait a few years" Policeman- "that's not evidence, it's slander".

"In an FM signal the carrier frequency is constantly varying. " No, the transmitted signal is constantly varying. The carrier isn't generally there (except, instantaneously, as the transmitted signal goes through zero). "In an FM signal all the modulation information is contained in the carier. Removal of the carrier will result in total loss of the information." No. If you were to get a very narrow notch filter and remove the nominal carrier you would still get a signal. "In an AM signal there is no modulation information in the carrier. In fact it is possible to remove the carrier entirely and some forms of AM do exactly this." Since, as you say, you can remove the original carrier frequency and yet keep the information, it's clear that the information is held by frequencies other than the carrier. The signal ended up on those frequencies because transmitted power was moved away from the carrier frequency. That's a change in frequency brought about by the modulation process. How is that modulation of the frequency not frequency modulation?