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ulrichw.bsky.social

@ulrichw.bsky.social
829 followers 984 following 725 posts
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Reposted by @ulrichw.bsky.social
Postmedia delenda est @olenargy.bsky.social · 10/09/2026
Can’t replace a leader of the free world but if we try hard enough we might be able to reconstruct one in aggregate
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Reposted by @ulrichw.bsky.social
Ted Underwood @tedunderwood.com · 08/09/2026
so sick of AI / fluid dynamics discourse on this app; now to relax with a big swig of hot milky tea
GPT-5.6: This is actually a lovely everyday visualization of Navier–Stokes.

The coffee and cream are fluids with a velocity field \mathbf u(\mathbf x,t): at every point in the cup, the liquid has some direction and speed. Navier–Stokes describes how that field evolves,

\rho\left(\frac{\partial \mathbf u}{\partial t}+\mathbf u\cdot\nabla\mathbf u\right)
= -\nabla p+\mu\nabla^2\mathbf u+\mathbf f.

In the photograph you can almost assign each term a visible role:

* \mathbf u\cdot\nabla\mathbf u: advection/inertia. The curling cream filaments reveal parcels of liquid being swept around by the existing circulation. Their folds and tendrils are basically tracers of the hidden velocity field.
* -\nabla p: pressure forces. Pressure gradients help establish and redirect the circulating flow, especially after pouring or stirring.
* \mu\nabla^2\mathbf u: viscosity. This damps sharp differences in velocity. The whorls don’t keep getting faster and finer forever; their kinetic energy dissipates and the coffee eventually becomes still.
* \mathbf f: body forces, especially gravity/buoyancy. If the cream and coffee differ in density or temperature, buoyancy can generate some of the rising and sinking plumes.

There is one nice wrinkle: Navier–Stokes itself does not directly describe the changing cream color. The cream concentration c is approximately a passive scalar obeying an advection–diffusion equation

\frac{\partial c}{\partial t}+\mathbf u\cdot\nabla c
= D\nabla^2 c.

So the spectacular visible swirls are the cream making the invisible Navier–Stokes velocity field visible. Advection stretches the cream into long thin sheets; molecular diffusion then mixes efficiently across those increasingly narrow sheets.

The picture therefore captures a central fluid-dynamical idea very well: flow creates structure at large scales, stretching and folding pushes it toward smaller scales, and viscosity/diffusion ultimately erase it.This is actually a lovely everyday visualization of Navier–Stokes.

The coffee and cream are fluids with a velocity field \mathbf u(\mathbf x,t): at every point in the cup, the liquid has some direction and speed. Navier–Stokes describes how that field evolves,

\rho\left(\frac{\partial \mathbf u}{\partial t}+\mathbf u\cdot\nabla\mathbf u\right)
= -\nabla p+\mu\nabla^2\mathbf u+\mathbf f.

In the photograph you can almost assign each term a visible role:

* \mathbf u\cdot\nabla\mathbf u: advection/inertia. The curling cream filaments reveal parcels of liquid being swept around by the existing circulation. Their folds and tendrils are basically tracers of the hidden velocity field.
* -\nabla p: pressure forces. Pressure gradients help establish and redirect the circulating flow, especially after pouring or stirring.
* \mu\nabla^2\mathbf u: viscosity. This damps sharp differences in velocity. The whorls don’t keep getting faster and finer forever; their kinetic energy dissipates and the coffee eventually becomes still.
* \mathbf f: body forces, especially gravity/buoyancy. If the cream and coffee differ in density or temperature, buoyancy can generate some of the rising and sinking plumes.

There is one nice wrinkle: Navier–Stokes itself does not directly describe the changing cream color. The cream concentration c is approximately a passive scalar obeying an advection–diffusion equation

\frac{\partial c}{\partial t}+\mathbf u\cdot\nabla c
= D\nabla^2 c.

So the spectacular visible swirls are the cream making the invisible Navier–Stokes velocity field visible. Advection stretches the cream into long thin sheets; molecular diffusion then mixes efficiently across those increasingly narrow sheets.

The picture therefore captures a central fluid-dynamical idea very well: flow creates structure at large scales, stretching and folding pushes it toward smaller scales, and viscosity/diffusion ultimately erase it.
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Reposted by @ulrichw.bsky.social
Asawin Suebsaeng @swin24.bsky.social · 13/08/2026
I am not the first to make this point but imagine a woman president obsessing constantly over her “ballroom” as the economy imploded and her war spun out of control
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Rafe Meager (they/them) @economeager.bsky.social · 11/08/2026
we have got to put that into a causal inference lecture
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Rav BOO!dram 🎃👻 @rvbdrm.com · 22/07/2026
Quick thinking having a tablecloth handy. I didn’t even notice the twitching from that dead robot.
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Ariella Elm @ariellaelm.com · 22/07/2026
There is no such thing as the perfect candidate. The only candidate that is perfect to you, the only candidate that could ever say everything you want to hear and nothing you don’t, is literally you. 1/
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Elizabeth V @geolizzy.bsky.social · 17/07/2026
The fact this “gold” coin won’t have any actual gold is quite the metaphor www.mining.com/trumps-us-go...
mining.com
Trump’s US ‘gold dollar’ coin has no precious metal
The Mint's gold Trump $1 coin for America's 250th anniversary stirs debate on its gold content, legality, and symbolism.
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Sen. Pumpkin Gogurt @ugarles.bsky.social · 18/07/2026
the future is here and it is picking images for news alerts
HEADLINE: Taylor Farms pulls iceberg lettuce linked to cyclosporiasis outbreak (CBS News)

IMAGE: Taylor Swift and Travis Kelce
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Catherine Rampell @crampell.bsky.social · 14/07/2026
We’ve opened the strait that was never closed, ceasing a ceasefire for a war that was never a war, stopping Iran from charging tolls because tolls are illegal, all so Trump can charge his *own* tolls because *his* tolls are legal. This will hurt affordability which is a hoax anyway
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Norm Eisen @normeisen.bsky.social · 13/07/2026
BREAKING: huge victory for our 35 judges in the slush fund case *Knocks out any legal basis for the $1.8B *Also undermines the accompanying settlements *And opens the way to ethics & financial SANCTIONS H/t to cocounsel @democracydefendersaction.org, Platkin LLP & Susman Godfrey
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Ed Markey @edmarkey.bsky.social · 10/07/2026
ICE shot and killed a man in Houston with no criminal record who was not even their target. They pushed him off the road. And now he is gone forever. ICE is a domestic terrorist organization. We need to abolish ICE now and stop Trump’s murderous thugs.
The New York Times: Man Killed by Federal Agent in Houston Was Not the Target of ICE Search
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Matthew Gertz @mattgertz.bsky.social · 10/07/2026
A definitely real job is when a billionaire takes a flier on your future political career by staking you as a venture capitalist.
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Such a Kevin @kevinkohler.bsky.social · 30/06/2026
JD Vance puts the Christ in "Christ, what an asshole."
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Mrs. Betty Bowers @mrsbettybowers.bsky.social · 28/06/2026
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Pete Buttigieg @petebuttigieg.bsky.social · 26/06/2026
This week someone targeted my family for harm with a false report. We’re physically OK, but that doesn’t mean we weren’t harmed. I am beyond furious. Whatever your politics, this is awful, wrong, and can never become normal.
substack.com
A Terrible Thing Happened to My Family
Even in today's climate, there should be one fundamental principle everyone respects: whatever you think about someone in politics, you leave their kids alone.
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Gef the Toking Mongoose @geftokingmongoose.bsky.social · 07/06/2026
ok water calm down
A diagram of two hydrogen and one oxygen molecule that looks like a but in revealing black bottoms
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Jeff Tischauser @jtischauser.bsky.social · 29/05/2026
Greg Bovino will speak at a white nationalist conference in Portugal tomorrow. He will share the stage with no fewer than five people who idolize Hitler, including one who joined a group created by two Nazi SS members. Another guy is a self-described racist who refers to women as "cockroaches."🧵
a bunch of white supremacists looking like dogs
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Katie Mack @astrokatie.com · 29/05/2026
It’s truly astonishing to see how comprehensively the US government is tearing down every part of the system that has made it up until now a world-leading power in science, research, and technological development. The entire world will suffer from this wanton destruction.
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Will Stancil @whstancil.bsky.social · 11/05/2026
Hey @pearlmania500.bsky.social if you had a hint of integrity you would: 1. Delete this episode 2. Make a post explaining what went wrong (i.e. you didn't do any research, despite that being the premise of your show, and just repeated something you saw on your TikTok feed) 3. Publicly apologize
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Thorne 🌸 - Play Cozysters! @ens0.me · 08/05/2026
Quacks love ivermectin and are now recommending it for hantavirus. Obviously, it doesn't work. But why ivermectin? Why this drug in particular? I wrote a bit about why. smol.news/p/why-the-iv...
smol.news
Why the Obsession with Ivermectin?
The quacks sure seem to love ivermectin. But why the fixation on this specific drug in the first place.
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Alt_Rogue @altrogue.bsky.social · 09/05/2026
"The Titanic had a ballroom and yet it still sank."

"Cheers".

Picture of the Titanic sinking.
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Anders Östlund @andersostlund.bsky.social · 09/05/2026
The U.S. had to step in and pressure Ukraine so that little Ruasia can hold its pathetic parade. Great power Russia cannot secure even the absolute center of its fascist empire. How embarrassing. How weak.
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Alastair Campbell @alastaircampbell2.bsky.social · 05/05/2026
Banksy. Genius.
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Liberal Currents @liberalcurrents.com · 04/05/2026
There isn't "some set of single-seat districts that will create 435 compact, competitive, and representative districts. The way people and their partisan preferences are distributed across space makes this utterly impossible. Expanding the size of the House would help, but not enough."
liberalcurrents.com
Lessons from the Redistricting Wars
Gerrymandering is just tweaking a bad system at the margins.
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Dark Laughter @darklaughtertdb.bsky.social · 02/05/2026
Yeah, and with that moron you might get a whole rogues' gallery of idiotic flatterers in his cabinet. Truly a vivid and frightening scenario. Good thing we have Congress and the Supreme Court to check them in the unlikely event that happens, right?
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emptywheel @emptywheel.bsky.social · 28/04/2026
Statue of limitations has not expired on this tweet.
A Jack Posobiec tweet reading just:

86 46
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Oliver Willis @owillis.bsky.social · 27/04/2026
fyi this is the kimmel comedy routine MELANIA DOES NOT WANT YOU TO SEE. definitely do not like and share it or else the MOST UNPOPULAR FIRST LADY IN HISTORY will be mad. youtu.be/GRjKhsJc95o
youtu.be
Jimmy Kimmel Roasts Trump & His MAGA Minions at Our Alternative White House Correspondents’ Dinner
YouTube video by Jimmy Kimmel Live
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Brendan Nyhan @brendannyhan.bsky.social · 25/04/2026
Exactly why we should be moving to a multi-party system per @leedrutman.bsky.social and many others. The binary choice our system requires locks too many people in place who can see what's wrong but won't vote to put the other side in power.
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Evan Bernick, a finite mode with a smol hooman and a lorg floof @evanbernick.bsky.social · 23/04/2026
"Constitutional scholar Evan Bernick has argued that the attack on birthright citizenship is anti-constitutional, “reconfigur[ing] the Reconstruction Constitution into a means of perpetrating the very evils that abolitionists and Republicans sought to eradicate.” jacobin.com/2026/04/trum...
jacobin.com
Trump Won’t Stop at Attacking Birthright Citizenship
Central to Donald Trump’s assault on birthright citizenship, enshrined in the Fourteenth Amendment and a key feature of American jurisprudence, is the creation of an underclass of hyperexploited labor...
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Hoodlum 🇺🇸 @nothoodlum.bsky.social · 09/04/2026
This is so well done. 👌
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Paulley Ticks @tomadelsbach.bsky.social · 03/04/2026
BREAKING: Donald Trump meets privately with Kash Patel and Pete Hegseth to assure them their jobs are secure, amidst swirling rumors that they may be the next cabinet members to be fired. #KashPatel #PeteHegseth
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William B. Fuckley @opinionhaver.bsky.social · 03/04/2026
Having a PhD doesn’t mean you’re always right, but it does mean that you unlock new and more powerful ways to be wrong.
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Justin Wolfers @justinwolfers.bsky.social · 01/04/2026
Is the United States insolvent? Lemme youtubesplain: youtu.be/_Zhy-icOTjM?... I'm trying a few new things on my YouTube channel -- trying to make economics more accessible -- and so I'm also really interested in your feedback.
youtu.be
America's Debt Problem Is Real—But Not The Way You Think
Did the Treasury really declare the United States insolvent? No—and not even close. In this clip, Justin Wolfers breaks down a viral claim that America has effectively gone broke. The central…
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Jim Emmerling @jemmer.bsky.social · 01/04/2026
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Evan Bernick, a finite mode with a smol hooman and a lorg floof @evanbernick.bsky.social · 31/03/2026
"The support for Trump’s position ... developed only after he issued his executive order, says Evan Bernick... The 21st century law review articles Sauer cites in his brief are all from 2025. Bernick... called the recent research “entirely unconvincing.” www.bloomberg.com/news/article...
bloomberg.com
Trump Aims to Upend Long-Held Citizenship Rules at Supreme Court
When Donald Trump suggested he might end automatic birthright citizenship by executive order in 2018, the idea was unimaginable enough that then-House Speaker Paul Ryan dismissed it. The president, he...
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don-brown.bsky.social @don-brown.bsky.social · 29/03/2026
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Adam Parkhomenko @adamparkhomenko.bsky.social · 23/03/2026
HOWLING
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Cristian Farias @cristianfarias.com · 23/03/2026
The only reason the Supreme Court of the United States is now examining the legality of a mail ballot receipt law is that Donald Trump is an election denier who still can’t his loss, and Republican lawyers have decided to legitimize and sanewash that denialism as a matter of federal election law.
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Mrs. Betty Bowers @mrsbettybowers.bsky.social · 22/03/2026
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Denver is too damn high 🚲 @yodelinghippie.bsky.social · 22/03/2026
Meanwhile bike fuel prices have not changed at Costco.
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Ambassador Ken Fairfax (ret) @portlandken.bsky.social · 17/03/2026
Matson nails it.
Cartoon of Trump and the Ayatollah playing "Battleship" while Putin stands behind Trump with flash cards telling the Ayatollah where to attack.
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Jeffrey Vagle @jvagle.me · 06/03/2026
Or, more pithily:
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The New Yorker @newyorker.com · 04/03/2026
Today’s Daily Cartoon, by Brendan Loper. #NewYorkerCartoons
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Michael Stahlke @michaelstahlke.bsky.social · 26/02/2026
I think that if you are a United States Senator that wants to kill a bunch of people you should know at least as much about their country as Homer Simpson from an episode that aired thirty years ago.
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Mike Luckovich @mluckovich.bsky.social · 19/02/2026
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We Are Nothing Like the Gestapo. @why-gestapo-shaped.bsky.social · 11/02/2026
We Are Nothing Like the Gestapo.
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Arin Arcady @rnrkd.bsky.social · 07/02/2026
I'm sorry the guy changing the rules on the fly is named what
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