OT Stellar noise measures star's gravity

This was a kinda fun.

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Reply to
George Herold
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Sort of similar to the old Intensity Interferometer of Hanbury Brown done in the 1950s and 60s for measuring star diameters. Different value being measured, but similar idea in looking at 'speckle' to see what you can get out of it.

Reply to
Adrian Jansen

Yeah similar in that noise is under lying it. (and I must admit I posted it thinking of Phil H, who likes HB&T...) But this noise is excess due to random-ish oscillations at 10 -1000 uH (uH = 10^-6 Hz) and HB&T were up at (?) 100's of MHz. and had to do with correlations due to the relative size of the sun and not it's fluctuations in brightness.

Excess noise can be interesting...

George H.

Reply to
George Herold

On a sunny day (Thu, 14 Jan 2016 10:43:56 -0800 (PST)) it happened George Herold wrote in :

When I was reading that i was immediately thinking audio. And they mentioned FFT of an FFT, was thinking hearing the speed at which somebody changes the bass and treble controls of a [near] white noise signal is possible. Finding the frequency change speed of the frequency curve. Interesting, our ears do in fact an FFT (hairs in inner ear), and the brain then does the second.

No surprises really. ?

But halfway through I skipped a few lines... once I thought I got the concept. Bubbles rising from a boiling pot of fluid (say water versus what have we now LEAD ..) the sound at the surface. Quite universal actually, I am sure subconsciously we already use that in every day life. Sound from car tires... Noisy roads, I remember driving in Germany once.. well sidetracks, thanks for the links.

Reply to
Jan Panteltje

FFT(FFT(X)) == X

Some processing inbetween might be a handier function though.

Tim

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Reply to
Tim Williams

FT(FT(x(t))) = x(-t)

That's the signals & systems way of showing that the real image formed by a single lens is inverted.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

On a sunny day (Fri, 15 Jan 2016 05:57:19 -0800 (PST)) it happened Phil Hobbs wrote in :

Yes, the world is interesting,

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in my early days I made hot sausages with a piece of wood and 2 nails with the sausages in between at 220V AC 50 Hz,

Reply to
Jan Panteltje

And FT(f(-t)) = FT(f(t))(-s),

And IFT(f(t)) = F(f(-t))

All those "duality" properties...:(

One of my favorite applications of the FT is in the solution of the PDE wave equation (using Green's functions) in three dimensions for the EM field generated by AC current flowing down a long wire.

Apparently there is an ambiguity in the contour integral used to evaluate the transform (taking the contour above or below a singularity) which causes an ambiguity in time, i.e. there should be waves travelling backwards in time...

From the same book I learned that a reason we may live in a universe with three spatial dimensions is that it's the lowest number of dimensions in which Hyugen's principle applies (i.e. a delta function over there in space, like a lighthouse flash, lets us see a delta function over here.)

I guess the next one up is seven, but then the cross product is weird...

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Reply to
bitrex

That is what we called Ohm sausages in the Helsinki University of Technology campus about 50 years ago, before microwave ovens.

To protect the fuses, a pressing iron in series with the thing helped a lot.

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Reply to
Tauno Voipio

The causality and stability conditions are actually the same, a very pretty result first proved by Titchmarsh, I think. I go gently through the math in Section 13.8.4 of the second edition.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Second edition of what now?

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Reply to
bitrex

My book.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Noice, I don't really work with optics that much but it seems like it has some good tidbits so I'll put it on the list.

As it seems you're still working a "regular" job designing, I'd guess you're not making "f*ck you" money via book sales, but does selling through Amazon.com at least earn you decent beer scratch?

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Reply to
bitrex

May you read it in good health.

You don't get rich writing technical books, at least not optics ones. (I im agine Win and Paul have each got a place in Aruba by now.) ;)

Wiley has sold probably 6000-7000 copies since 2000, and I get roughly $10 per copy. In optics circles that counts as a runaway bestseller (which, inc identally, accounts for the generally high price of optics books).

I started writing it in 1994, and spent most of 1998 finishing the first ed ition. Fortunately IBM Research was fairly tolerant of people goofing off t o write books at that stage.

I spenr a year going back and forth with Wiley about the length--at one poi nt they were going to make it 2 volumes, so I reorganized it that way, and then they complained that the second volume didn't have conceptual unity.

I pointed out that that was because vol 1 was "optics that work" and vol 2 was "everything you need to know to build electrooptical instruments, excep t optics."

We wound up pushing the thermal control chapter and the problems onto a web site, and publishing the rest as one volume.

The second edition grew another 100 pages, but they srank the type and the margins so it fit in nearly the same space.

The draft third edition is down to about 150 FIXMEs, but some of them are s ort of open-ended, e.g. relating the Schawlow-Townes laser linewidth formul a to the Leeson model of oscillator noise, so it may not be out for a year or two. I haven't really stopped writing it since 1994.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

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