TL;DR; Mein Lieblingsthema Bedingte Wahrscheinlichkeiten, Bayes, und Sigmas

Ich habe jetzt mal meine Bedingte-Wahrscheinlichkeiten-Predigt gehalten, und am Beispiel Masernfälle in Disneyland durchgerechnet, weshalb 18% Geimpfte unter den Erkrankten nicht bedeutet, dass das Vakzin schlecht wirkt.

Es ist einfach immer spannend, wenn Mathe so unmittelbar Alltags/gesellschaftsrelevant wird und in so schön konkrete und quantitative ethische Überlegungen einfließt.

I've been involved in #hamradio #electronics for a while now. And I still think it is some form of high magic to be able to hook up a quartz crystal to some silicon crystals, cut a wire to the right length, and use that to excite one of the fundamental forces of the universe to send a message to the other side of the globe.

Somehow, day-to-day business always threatens to drown out the sense of wonder of how mind-boggling this is, and it takes some effort not to take it for granted.

For an idealized infinite DM mass (compared to the other energy scales), the velocity of the outgoing Xe nucleus is twice the DM velocity.

Its energy in natural units is 1/2 mXe v^2 = 2 mXe vDM^2

So: 250 keV = 2*131 GeV * vDM^2

If we approximate 250 ~ 262 this results in

v=0.001 (units of c)

so

v=300 km/s
as the candidate Dark Matter velocity for the scattering DM particle

Our velocity through the galaxy is about 230 km/s, so this is quite fast, but in a plausible range

#physics
#scicomm
#astronomy

The nuclear recoil energy of 248 keV is apparently relatively large compared to expectations. Not 100% sure, but this also seems to imply that for vanilla interactions one would expect more lower-energy events in the same experiment -
For this reason, the researchers seem to invoke a certain type of interaction in their modeling (though not terribly speculative, one of the possible interaction types), a momentum dependent interaction, to suppress events at lower energy.

That could be a slight strike against the observation being a real signal, but this is all me speculating.

The mass of xenon itself is about 130 GeV, so a 250 keV recoil would correspond to a heavy particle doing a strong collision at about a pretty fast for dark matter standards of 300 km/s.

#particlephysics #physics #astronomy #science #scicomm

Oh look, a direct detection dark matter search experiment, LUX Zeplin, has detected a remarkable deviation beyond the expected background - albeit one event!

[edit, thanks for the hint] The candidate mass is said to be at least 200 GeV
(for comparison, the heaviest known elementary particle, the top quark, is just above 170 GeV, so this dark matter candidate would also be the heaviest known elementary particle if it is one.)

#physics
#astronomy
#darkmatter

https://newscenter.lbl.gov/2026/09/01/lz-sees-surprising-result-in-search-for-dark-matter/

Ich habe das #noAfD "Regierungsprogramm" gelesen, damit ihr es nicht müsst. Nur eines der folgenden Ziele steht NICHT drin. Findet ihr heraus, welches? :)

Can we for concreteness discuss this DIY arrangement from
https://homebrewcorner.blogspot.com/p/pa-150-hf-linear-200w-amplifier.html

just as an example for the kind of design I am talking about.

This apparently uses such a push pull configuration with two separate core halves. The OM says they get appropriate power levels out of this and there is no reason to doubt the measurements shown.

But how? Is this due to high quiescent current settings making the "off" transistor still do some work on the other half wave, or do the parallel caps work some magic here?
#hamradio
#electronics

Hello #hamradio #electronics folks, maybe you can help me - I have a serious problem in my understanding of RF power transformers.

Often you see designs that have two ferrite sleeves, and there is a copper or brass tube on each side forming the primary windings connected to the transistors, along the lines of the attached picture.

Now, in push pull designs I've often seen proposals which use the left brass tube as the primary winding for Transistor 1, and the right brass tube as the primary winding for Transistor 2. The secondary windings go through both holes.

Now, my problem with this construction is the following: if I have one transistor on for each half wave and one transistor off, one of the brass tubes ideally is always an open circuit. This means that the secondary windings going through that side basically form a high impedance ferrite choke with no induction from a primary. The result being that the output impedance is gigantic and no powerful current can form.

So in my mind, this design does not work, or if it does, only by coincidence when mosfet drain output impedances are low even in the off state because of output capacitance.

What am I missing?

We did this fun thing in class today, anyone recognize what it is?

And OF COURSE just turning it on as-is, it oscillates :)

So next time we'll look at careful choices of bias and drain to gate negative feedback
(we actually saw these instabilities in LTSpice for some parameter choices)

#electronics

My students designed, simulated and built this #hamradio PA, isn't it pretty?

It is a Class-E nonlinear design and is supposed to output >100 W at 7 MHz.

***
On July 8 between 6-11pm CEST
***
depending on.how.fast we are setting up everything,
we will go on the air @DL0WH with a transmitter entirely made by students without fixed schematics, entirely from scratch

primarily on CW, and we want to see how far we can go.

If any of you would like to listen in and send a report, or respond, we would love to send you special QSL Cards.

Reports to:

qsl@facw.org

#electronics
#physicsedu

A bit of technical detail for the quantum mechanics savvy: the Delta in the free time evolution should actually be the full energy difference between the two hyperfine level states, but we make a basis change to absorb that into the definition of the states, and so what remains after the frame change is the frequency de-tuning between microwaves and atoms, Delta

So these are the rotation matrices inside the cavity (U1) and for free flight (U2), and the total action of the clock is then the triple matrix product U1.U2.U1. I plot the magnitude squared of the off-diagonal element which stands for the transition from lower to higher state which we want to count. In the first picture I chose a shorter gap time, in the second picture I chose a longer gap time.

As you can see, the function oscillates much quicker and these so-called fringes become narrower for a longer gap time. Now your clock oscillator sits on the central one, tunes a bit to the left and a bit to the right, and makes sure that it sits on the spot where the change is symmetric. Thanks to these narrow fringes, this is super sensitive to small changes in the frequency.

(the x axis shows the de-tuning, with the zero in the center meaning we are exactly on the cesium hyperfine frequency)

Anyway, I thought that was neat.

#physics #electronics #hamradio #scienceedu

So it turns out that one could just make it one big cavity. In this case, the closer I am to the famous 9 GHz transition which now is the official definition of the Second, the closer I get the more atoms get kicked into the higher energy state, and I count them in the end and adjust the frequency to maximize that.

Now, Ramsey had they genius idea to let nature do some more work in between. You see, in quantum mechanics, the phase of any quantum wave rotates with a frequency that is given by the energy, and the two cesium states have slightly different energy.

So what happens is the following: In the first cavity we apply the microwaves just strongly enough to turn the cesium into a quantum superposition of excited and unexcited state, then let them rotate according to their own frequency for a bit, letting them collect a bigger phase difference, and then finish the rotation into the wanted excited state.

The longer you make the flight time in-between, the more sensitive the final state will become to slight de-tunings of your frequency: the addiitonal phase that is collected during flight enhances the cancellation effects you get when the frequency is detuned.
This looks like this when you plot the probability over the microwave frequency (in arbitrary units): 2/3

#physics #electronics #hamradio #scienceedu

Tl;dr: I recreated a key bit of the quantum mechanics in cesium clocks in Mathematica, and it is rather pretty because it's just three matrices multiplied. It explains why cesium clocks have two microwave cavities with a long gap in-between, as the gap makes it more sensitive to tuning errors

So I just understood a cool aspect of Cesium beam clocks that I hadn't known before (you know, being a theorist and all...), namely Ramsey spectroscopy.

So I looked at the schematic here, and was wondering why the microwave cavity in the Cesium standard is apparently divided into two cavities with a gap in between. That didn't seem to make sense and I first thought I maybe misunderstood it, but no: One actually subjects the cesium to the microwaves, then lets it fly a bit all unperturbed, and then subjects it to the microwaves once more.

So why the gap? 1/3

#physics #quantumphysics #hamradio # electronics #scienceedu #scicomm

tl;dr rant about nuances and stuff

Don't know about you, but I'm really torn about "AI".

I find genAI Art and Pictures mostly disgusting and never want to read anything produced by an LLM that I didn't prompt myself for a specific purpose, and I will never publish any serious writing (fic or nonfic) that I haven't formulated myself. If there never was a single genAI picture, film or music ever again, we'd all be better for it.

On the other hand, I use LLMs+bells and whistles extremely productively to gain fast insights into technical things and do things I otherwise wouldn't bw able to do in finite time, and

I find Transformer architectures very fascinating on an intellectual level and think they might play.an important role in the future even if the brute force llm training done now will look primitive in hindsight.

So neither the hell yeah AI bros nor the "all AI is bullshit" crowds speak to me at all.
#ai

Guys look what I found in the claude source code

#claude

Dann das Universum bei 180 GeV knusprig braten

Willkommen bei meinem TED Talk ;-)

#physik #astronomie

https://www.starkenburg-sternwarte.de/event/2026-03-24/