Ben Krasnow Identifying Chemicals by Nuclear Quadrupole Resonance


At 29:29 there's an interesting macro-micro-scale interaction going on between thermal fluctuations and nuclear spin.

Here's his video on the Zeeman Effect:

.. and a follow-up video:

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Here's a video by w2aew on superhet radio receivers:

I can barely follow this at all (WTF is a mixer, really?). I remember once seeing that many of these ideas made perfect sense when I knew how the Fourier series combined, but that was a long time ago. I guess it was linear combinations and the pair of properties Shift in time / Modulation in frequency and Shift in frequency / Modulation in time. I was teaching a maths course and so I was always trying to find  practical applications of the mathematical theorems to provide some physical intuition for understanding the maths.

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Here's a review of The Art of Electronics by Horowitz and Hill (and others) ... 

It's not too hard to find a PDF of the second edition. See page 885 (831 of the PDF) for an intelligible-looking account of mixers.

My favorite part of this book is this section:

15.17 Time-to-amplitude converters

In nuclear physics it is often important to know the distribution of decay times of some short-lived particle. This turns out to be easy to measure, by simply hooking a time-to-amplitude converter (TAC) in front of a pulse-height analyzer. The TAC starts a ramp when it receives a pulse at one input and stops it when it receives a pulse at a second input, discharging the ramp and generating an output pulse proportional to the time interval between pulses. It is possible to build these things with resolution down in the picoseconds. Figure 15.42 shows a measurement of the muon lifetime made by a student by timing the delay between the capture of a cosmic-ray muon in a scintillator and its subsequent decay. Each event creates a flash of light, and a TAC is used to convert the intervals into pulses. A cosmic-ray muon decayed in this student's apparatus once a minute on the average, so he accumulated data for 18 days to determine a lifetime of 2.198 ± 0.02μs (accepted value is 2.197134 ± 0.00008μs). ...

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