robryk @robryk@qoto.org

Delta is a Polish #math/#physics/#compsci monthly magazine, mainly aimed at high school students, but read by people of all ages (as evidenced by participation in their send-in monthly problem league). For some unknown to me reason, its April 2025 issue has an English translation: https://deltami.edu.pl/media/issues/2025/04/delta-2025-04-EN.pdf

Enjoy :)

My fridge's duty cycle, courtesy of ewz.

Mein Stromzähler wurde diese Woche mit einem "Smart Meter" ersetzt. Bezüglich Datenschutz gibt ewz an:

> Die Datenübertragung ist zwar eine wichtige Funktion, die der intelligente Stromzähler mit sich bringt. Gesendet wird aber nur einmal täglich und zwar in verschlüsselter pseudonymisierter Form. Das heisst: Übermittelt werden lediglich die Nummer Ihres intelligenten Zählers und die aktuellen Verbrauchswerte. (...) So kann aufgrund der Verbrauchsdaten nicht darauf geschlossen werden, welche Tätigkeiten die Bewohner*innen ausüben.
-- https://www.ewz.ch/de/private/strom/anschluesse/smart-meter.html#faq

Das ist schon ein bisschen überverspechend: tagliche Stromverbrauchwerte lassen jemand feststellen, ob ich weg (im Urlaub) sind, oder ob ich an diesem Tag gekocht habe (und vielleicht ob für mehrere Personen gekocht wurde).

Danach habe ich aus Neugiere auf mein ewz geguckt und hat da Stromverbrauch separat für jede 15 Minuten gefunden. Das ist sicherlich genug um viel mehr über meine Tätigkeiten festzustellen: wenn ich komme nach Hause, wenn ich Tee am Morgen mache, vlt. wenn ich koche, usw.

Ich bin ein bisschen enttäuscht mit dem Kleinmachen und irreführenden Erklärungen (wie beim Datenschutz vom Swisspass, der "nur" ein Kennnummer ablesen lässt). Ich bin auch neugierig, ob Angriffversuche auf den System von den Einbrechern finanziert werden.

https://atomic-spectra.net/ shows emission spectra of various atoms _with intensities_ and with pictures acquired experimentally.

TIL that in oceans (assuming lack of salinity gradients) it's actually the coldest water that sinks:

> The temperature of maximum density and the freezing point of water decrease as salt is added to water, and the temperature of maximum density decreases more rapidly than the freezing point. At salinities less than 24.7 psu the density maximum is reached before the ice point, while at the higher salinities more typical of the open oceans the maximum density is never achieved naturally.
-- https://www.britannica.com/science/seawater/Thermal-properties

How does metallic gallium damage eyes? I see lots of SDSs for gallium claiming that it's corrosive (well, that's kinda true) and that it causes heavy eye damage in contact with eyes.

Let the Polish air force lethargy and delaying and pretend actions befall the people whose decisions cause it twice over.

TIL that fraction of deuterium in hydrogen in e.g. water depends on location and source of water (lake, ocean, precipitation): https://en.m.wikipedia.org/wiki/Hydrogen_isotope_biogeochemistry

@whitequark would your headmate perhaps be willing and able to give a pointer to a reasonable point to start reading about this?

Like, why does transferrin exist? Why isn't all iron transport done with ferritin? (There's probably some extremely obvious reason, but I'm not a biochemist sadly.)

It feels really weird that we have proteins that transport something small (like oxygen or iron, below 100 daltons heavy) that can transport something like four of the things in question at a time and weigh _tens of kilodaltons_. And they're still more efficient than direct dissolution.

In other news, it's likely that we know the proximal reason for my recent poor sleep.

Amusing differences in prescriptions: apparently >30mg of Fe2+ per dose requires prescription in Poland. According to pharmawiki something with 100mg/dose is in category D in Switzerland.

@_thegeoff who specifically might find it interesting

Consider a pot with a convex bottom (i.e. it will stand on its midpoint) with sufficiently large radius of curvature to make it stable when filled to any level. When you put such a pot on an electric hotplate and get it boiling, it starts rocking: https://www.youtube.com/watch?v=vB_szsLa3zk

I have a hypothesis on what's going on (the pot rocks away from the area where the boiling is more intense due to density difference, contact with hotplate increases rate of heating, so there's more heating on the side that's currently lower and thus any rocking gets amplified). Sadly, I don't have the pot anymore and didn't thing at that time of any experiments that could falsify this hypothesis.

We have a practical case of #Unicode encoding of country flags causing problems.

To recap, flags are encoded as sequences of codepoints corresponding to letters in the country's ISO code (so, Polish flag is <flag-p> <flag-l>). There is no heed paid to their mutability over time.

The Syrian flag will at some point start being rendered differently. Then, all the previous statements about Assad's government that used the flag will start rendering as if they were about the rebels.

I'm sad at Unicode's failures to fully and immutably encode the meaning of whoever wrote the text (see Han unification for counterexample to "fully").

@_thegeoff btw I've realized that heterodynic(sp?) interferometry is a thing, but haven't managed to dig up how it works exactly (in particular, what's the nonlinear mixer that can accept light and can emit RF, or how does it work without that).