sci — scientific instruments, taken apart

The rule. Every mechanism claim on a page traces to a primary source, and the source is on the page. Every number is computed from constants and closed-form physics in front of you, not quoted — and the solver that computes it is checked against an analytic solution on every build.

Instruments

MRI rust → wasm 4 parts + console

The most celebrated instrument in applied physics detects its signal with a coil of wire — and almost everything strange about it follows from that one fact. Four parts, each built on a solver you drive, and a console that runs all four at once.

the sensor — Faraday induction in the near field, reciprocity turning a hard reception problem into a Biot–Savart integral, and a coil that goes deaf when you point it down the bore.
k-space — if the sensor has no spatial resolution, where do the pixels come from? Run an acquisition on a phantom whose k-space is evaluated in closed form, and watch an EPI image slide by exactly the predicted number of pixels.
contrast — an MRI does not measure tissue; it measures a tissue's response to a schedule. Measured T₁/T₂, sequence equations checked against a Bloch simulation, and the curve where two tissues become invisible.
why it screams — ninety kilograms of Lorentz force per metre of winding, and an acoustic comb locked to the pulse sequence's own clock. Synthesised in the browser; drag the timing and hear the pitch move.
▶ the console — all four at once. Every knob belongs to one part, one image comes out, and the SNR law shows which knob paid for it.

the next instrument unchosen

The MRI breakdown is complete, so the wing needs a second subject. The criterion is the same one that made this one work: an instrument whose usual explanation is wrong in a way the literature can settle.

Why

Most instrument explainers stop at the block diagram. The interesting part is always one level below it — the place where a physical constraint forces the design to be the shape it is. An MRI scanner is enormous and cold and expensive because of a factor of B₀ that belongs to the detector rather than to the physics, which is why ultra-low-field machines that detect differently can be neither. You cannot see that from a block diagram, and you can see it immediately from a graph you are allowed to drag.

engines: rust → wasm, no dependencies, known-answer tested · mino.mobi