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Website: https://www.francois-rincon.org
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Learning shit: since 1978

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2026-07-04T05:15:09Z

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Last Notes

2025-12-15 07:25:35 GMT

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Right, I'll try to resume and finish this solar dynamo thread. tl;dr: we've been at it for a 100+ years to figure out how the Sun got it's magnetic field and activity cycle but:
- mathematical theory is largely impotent because it's a 3D, highly-multiscale nonlinear problem
- laboratory experiments are largely impotent because you can't reproduce the Sun with liquid sodium
- numerical experiments are largely impotent because they can't get to the right electrical conductivity and turbulence regimes of the Sun.
Here's for instance the status of numerical simulations just a few years ago (from Paul Charbonneau's 2020 review). As you can see the periods of simulated cycles, when the simulations produce some, are all over the place.
https://social.sciences.re/system/media_attachments/files/115/722/386/175/970/818/original/7047730c4ed818a7.png

2025-12-11 17:38:11 GMT

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And so, that's where we are on the numerical front. And now that the stage is set, I will make a pause and continue later after dinner is made and clothes have been taken out of my own (non-leaking, non liquid-sodium but cubic) washing machine. See you later.

2025-12-11 17:36:47 GMT

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This simulation, and many others, are super-nice. But this one, the biggest one of all, for instance, has a problem. If you read on page 3 of their paper "in this study, the dynamo has not constructed the large-scale magnetic field (Supplementary Fig. 2), probably due to
lack of calculation time for the large-scale dynamo or insufficient suppression of the convection velocity. It is possible that the longer-time calculation changes the amplitude of the magnetic field. This is still out of our reach."
In other words. It doesn't produce a large-scale dynamo of the kind the Sun produces. Despite 500 effing millions of CPU hours spent and going all in on realism. Why ? Well, because electrical resistance, viscosity and resolution. You can't do miracles, because of the intrinsic computation complexity of multidimensional turbulent (magneto-) fluid dynamics. And their simulations has a (non-dimensional) electrical resistivity still a thousand times larger than that of the Sun, and a viscosity 10 millions times larger. Imagine stirring with a wooden spoon a Sun made of honey, a Sun in which electrons have a hard time flowing. That's not the Sun. It's not a cubic cow anymore, but it ain't an elephant with a nice trunk and hard hair on a hard skin either.

2025-12-11 17:31:03 GMT

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And they went all in on making the most realistic possible numerical model of the Sun, in a sphere, with realistic rotation, luminosity, radial structure, capuccino-latte-vanilla flavoured convection, you name it, the whole shebang. But numerics is a hard mistress and, well, in the end they had finite resolution too, and so it was. Their simulations produced a dynamo effect (sometimes), and cycles (not always), but they were all over the place, and not two groups agreed together on what was going on. There is also a lot of dubious numerical cooking recipes involved to simulate the implicit effects of all the swirls that you can not explicitly resolve, and everyone has their own cooking recipe (that's still the case).
This industry is still going on and flourishing, and this is the kind of things it delivers these days. Not bad, eh ? This is a japanese-american thing this time, which run on a BBBBIIIIG supercomputer. 500 millions CPU hours were spent on this one simulation, I was told (not a typo, 5 with 8 zeros after).
https://www.nature.com/articles/s41550-021-01459-0
https://social.sciences.re/system/media_attachments/files/115/702/113/348/928/435/original/625a44e3c29f7d98.png

2025-12-11 17:25:20 GMT

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Still, many people, especially in the US, were like "yeah we are american, the land of opportunity and hope, we'll do it soon. Anyways we are the only ones who can do it, you should spend your time on something else". I'm not exaggerating, Juri Toomre, who was running the biggest operation of this kind in Boulder, told me exactly this back in 2003 when I was a PhD student.

2025-12-11 17:23:40 GMT

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But even these experiments where like giant resistors. When the liquid sodium washing machine was running it was heating like crazy from resistive (Ohmic) dissipation, and they had to let it cool for many hours after each run. So, again, not like the Sun.
On the numerical front, there was a problem. If you want to make things more turbulent and less resistive, you need to increase the resolution. But this is not a very nice system. To just double your turbulence or divide your resistivity by two, you need to roughly spend ~16 times more computing time. And (in adequate nondimensional formulation) if the resistivity of the Sun was 1, the resistivity of the lab experiments was something like 100000, and that in numerical simulations with their resolution 10000. I'll let you do the maths, but essentially, you can't replicate the Sun in a computer.

2025-12-11 17:18:21 GMT

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Since then, a long time has passed. I'll spare you the incremental, struggling story of dynamo theory in the 1980s and 1990s. the people interested in the Earth magnetic field also got at it. In 1995 notably, a PhD student of gilman, Gary Glatzmeier made the cover of Nature with a massive 3D simulation of the geodynamo. It was also not in the right regime, but much more convincing than the original 1980s stuff, and it was a big success story at the time. in 2001, the Karlsruhe dynamo experiment (machine illustrated earlier) was successful with producing a convincing large-scale field from small-scale constrained helical flow of liquid metal through an alpha effect. In 2007, it was the turn of the French to do this in Cadarache with a much more convincing turbulent flow of liquid sodium. A liquid metal washing machine called VKS.
It's a fun story. It was a very big team with three main labs involved, but Romain Monchaux, a PhD student at the time, is the first author of the french paper in PRL, by pure chance, because they had a team policy to have the name of the authors rotate.
https://social.sciences.re/system/media_attachments/files/115/702/065/154/535/282/original/a6d144af1bc33526.png

2025-12-11 17:11:36 GMT

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But there were a few problems even with that. Here too the resolution/grid was very low, and a lot of simplifying assumptions applied. Also when your resolution is very low, that means you can't really describe the very intricate multiscale turbulent motions, and so all these simulations had pretty simple flows, far from what we believe (and see at the surface) solar convection looks like. It also means you can't really simulate fluids, like the solar plasma, which have high electrical conductivity. Gilman and Meneguzzi's numerical fluids where essentially big fluid resistors, with just enough conductivity to let the magnetic field grow a bit. So, fluidly, we knew something was not like the Sun already there. 1983, that was.

2025-12-11 17:08:48 GMT

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Well, there was a trick of course. This was all done in a 3D box with periodic boundary conditions. It is to the Sun what a cubic cow sliced in 32^3 little cubes is to a real elephant. John von Neumann is famous for saying that you can model an elephant with 4 parameters, and have his trunk wiggle using a 5th parameter. He was kind of right.
That left us with unsatisfactory theory, very dubious experiments, and over-simplified numerical simulations. Right after that, Peter Gilman, an american, came up with the first fully-explicit *spherical* numerical models of dynamos driven by rotating convection. They are american, they are powerful, they have the biggest (computer) in the room, everything is possible in this land of hope and opportunity. And so it was. It was very important. He found dynamo cycles too.

2025-12-11 17:04:10 GMT

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Then, it meant we had to wait for the big CRAY supercomputers in the early 80s to try numerical simulations of the dynamo effect. And the first one was done by...French people 🐓 🇫🇷 : Meneguzzi, Frisch and Pouquet, in 1981 (known as MFP81). The grid resolution was very limited (32^3 and 64^3), but just doing this kind of stuff at the time could heat a whole university for a year -- I'm barely exaggerating. Anyways, Maurice Meneguzzi and co showed that the alpha effect was not just a phenomenological fantasy of Parker, or a calculational mistake of the soviet and easter german physicists who had to use very crude perturbative math techniques to get to a result (and there was no guarantee this worked). And that meant, for the first time: signal, beautiful dataviz, quantitative analysis ! Judge for yourself.
https://social.sciences.re/system/media_attachments/files/115/702/010/258/671/010/original/23f908d4f8091fbe.png

2025-12-11 16:57:45 GMT

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So, there was theory, and there were experiments. And, at the same time, thanks to the insights of people like american mathematician John von Neumann, there were computers. Numerical simulation of fluid flow started in the 1960s too, and it started to be applied to magnetohydrodynamics and the dynamo in the early 1980, later than in climate science (you should read @npub1eak…ha4p book on how the climate computations started, it makes for a super interesting read). Why ? well, you can already do basic things to model the fluid motions of the Earth atmosphere using 1D simulations. You can't for dynamo. Because of f* Thomas Cowling and his ilk, who told us dynamos only work in 3D (Zel'dovich and many others found many variants on the original Cowling antidynamo theorems, so many theorems that it became a national sport in the UK applied maths community to have one named after you -- my former postdoc supervisor, Michael Proctor, was one of them).

2025-12-11 16:50:52 GMT

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And guess what ? This started a german and soviet industry to build dynamo experiments with crazy machines using liquid metals. These were notably the Ponomarenko experiment and later the Riga experiments. At the same time, the science of flows interacting with electromagnetic fields, called magnetohydrodynamics, was taking off because liquid sodium was used to cool off nuclear power plants by injecting it in pipes, and the flow of that was in itself complicated. Soviet stuff, I tell you. The germans became quite good at it, too, below is an image of the design of the Karlsruhe dynamo. Not really the Sun, eh ?
https://social.sciences.re/system/media_attachments/files/115/701/974/427/714/897/original/22aad66b9ab1e8c6.png

2025-12-11 16:47:39 GMT

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It wasn't a rigorous derivation, just a phenomenological argument. And there was another 10 years of paucity of results on the subject (remember we didn't have computers that could do any of this back then). In the late 60s and 70s, then, Eastern German theoreticians, Steenbeck, Krause & Radler, russian theoreticians, people like Ya B. Zel'dovich, of fame in so many areas of astrophysics, and Viktor Kazantsev, another irishman, Robert Kraichnan (who was also the last postdoc of Einstein), and a scottish mathematician, Keith Moffatt, came up with the first analytical derivations of the alpha effect derived from the fluid and Maxwell equations. This was a big breakthrough ! Initially the Germans, who where the first on this but were isolated in their country, published in German and it is another british man, Paul Roberts, who later discovered their work and had it translated in English in 1971 thanks to the help of Michael Stix, another german solar physicist. Their original paper has gothic letters in the equations, see for yourself.
https://social.sciences.re/system/media_attachments/files/115/701/948/223/448/052/original/05e6805a2bfc723e.png

2025-12-11 16:39:03 GMT

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What Parker said was the following: ha, the convective fluid motions are influenced by rotation, they are screwed ! (in the first sense of screwed). Like a corkscrew, if you like. And then he did some geometric-driven back of the envelope calculations , and showed that this can generate magnetic field, which requires this kind of symmetry breaking. But in a particular way: it's a statistical emergent phenomenon. You need many little cyclonic swirls acting together cumulatively to generate a field on a much larger scale than the swirl itself (that of the Sun itself). and when you do some simple math with that, you can show that this, combined with the fact that the sun does not rotate uniformly, can create magnetic cycle. We call this a large-scale fluid dynamo effect, and that particular mechanism based on 3D cyclonic swirls is, in theoretician jargon, called the alpha effect.

2025-12-11 16:34:34 GMT

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In 1955, an american physicist, Eugene Parker (who recently died and gave his name to the Parker Solar Probe you may have heard of), nevertheless came up with a handwavy explanation for what may be going on: the outer third of the Sun is like a saucepan, the fluid in there is heated from below by the nuclear reactions in the core of the Sun, and it convects: in other words, it sets the fluid in motion, which then carries the heat to the surface. These motions are extremely turbulent in the Sun. For those who know, the Reynolds number of this flow, which characterises turbulence, is 10^10. Also, the Sun is rotating ~ once / month on itself. And at relatively large scale, of the order of ~50000km or more (the solar radius is 700000km), these turbulent convective motions they start to get influenced by the coriolis force, the same force that affect the rotation and pressure of our weather systems on Earth.

2025-12-11 16:30:36 GMT

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It's a problem. Because in the 1930s (and still today), making mathematical calculations on partial differential equations with several dimensions, including 3D of space (like the Navier-Stokes and Maxwell equations) is well, very hard. Like, very very hard. So the field was essentially stuck. Also, you don't find a fluid conducting of electricity everywhere, in a laboratory there are very few that do the job: liquid gallium and sodium essentially, and they have very bad properties otherwise. So, doing experiments was very hard too.

2025-12-11 16:28:40 GMT

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Solar sunspots were known to chinese astronomers and there are very ancien records. We also know from radioactive dating in trees and ice that the solar cycle has been there for many millions of years.
In 1919, an Irishman, Joseph Larmor, proposed that these spots were magnetic in origin, and that the magnetic field of the Sun was itself generated by the internal fluid movements in the Sun. Just like moving electrons in a wire generate a magnetic fields, moving plasma or fluids conducting of electricity (like the liquid iron bit of the Earth core, which also makes its own magnetic field) generate magnetic field through what we call electromotive forces.
He was right. However, in the early 1930s, an English astronomer, Thomas Cowling, first showed, using some symmetry principles applied to the equations of fluid motions and Maxwell's equations, that simple fluid motions with too much symmetry (like, flows not depending on longitude) or too low-dimensional (like, flows in a meridional plane) could not generate magnetic fields. For geometric reasons, the problem is, in essence, fully three-dimensional.

2025-12-11 16:23:26 GMT

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So, I'll try to give a flavour of what's going on. You've probably heard about the solar activity cycle. The Sun is an active star, it has transient spots at it's surface (we informally call the study of these spots solar dermatology) and a large-scale magnetic field notably responsible for spitting out particles occasionally towards us, and also reheating the atmosphere of the Sun (the corona) at millions of degrees, while the surface itself that we see in visible light is at less than 6000 degrees (hence it's yellowish appearance).
Both the number of spots and the magnetic field oscillate with a period of 11 years (but it's not truly periodic, it's chaotic, and not all cycles have the same amplitude). The spots also follow a relatively regular pattern in their appearance, called the butterfly diagram. As the cycle evolve, they appear closer and closer to the equator, in both hemispheres.
The illustrations below are satellite images and data records appearing in a review I published in 2019.
https://arxiv.org/abs/1903.07829v2
https://social.sciences.re/system/media_attachments/files/115/701/841/984/739/728/original/ab81e4ccf89ccf99.png

2025-12-11 08:01:08 GMT

It is far from the complete picture, but i think I have put my numerical finger on the asymptotic fundamental turbulent magnetohydrodynamic mechanism driving the solar dynamo activity cycle, and can reasonably explain why big "realistic" solar models get it wrong and why their results are scattered all over the place. It's a long physics and numerics story built on a lot of previous research from many groups, in particular that of my colleague Axel Brandenburg, whose insights and long-term efforts on this problem have been profound and essential.
#Astrophysics
Ultimate large-Rm regime of the solar dynamo
https://arxiv.org/abs/2512.09536
https://social.sciences.re/system/media_attachments/files/115/699/823/538/084/549/original/77a28c7efc6954d4.jpg

2025-12-08 18:19:19 GMT

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It's my favorite gotcha when I end up with a sign error in a plasma theory derivation involving lots of changes of variables.

2025-11-10 20:04:19 GMT

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roughly 3 people here understand and like this message 😅

2025-11-10 17:15:44 GMT

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This is not Nice (pun intended)

2025-11-05 16:51:26 GMT

"- Look, we are heading straight to +3° C
- We are so fucking doomed ."
#memecredi #climatecrisis #biodiversitycrisis #WASFD
https://social.sciences.re/system/media_attachments/files/115/498/107/680/978/806/original/a46aede5f0e528f9.png

2025-10-27 15:38:34 GMT

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crawfish ?

2025-10-08 13:57:13 GMT

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I wrote *for* zilch. So yes, for no good reason.

2025-10-08 13:03:20 GMT

Why ? is the only question that came to my mind when I read the abstract. And after reading the paper the answer is exactly what I had intuited it would be: for zilch. zero. naught. 0. This is literally a pissing contest. #fluids #physics
"To study the physics of small-scale properties of homogeneous isotropic turbulence at increasingly high Reynolds numbers, direct numerical simulation results have been obtained for forced isotropic turbulence at Taylor-scale Reynolds number Rλ=2500 on a 32768^3 three-dimensional periodic domain using a GPU pseudo-spectral code on a 1.1 exaflop GPU supercomputer (Frontier)"
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/smallscale-properties-from-exascale-computations-of-turbulence-on-a-mathbf327683-periodic-cube/ACBB7FFE296106B0F2E9CA1B50A1A456?WT.mc_id=New%20Cambridge%20Alert%20-%20Volumes

2025-10-03 05:53:48 GMT

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This is why physicists and many academics more broadly have no tolerance for crackpots, people "who did their own research", and people who are quick to claim some big problems have easy fixes. There's no short-circuit. You need to learn your shit and academic research field the deep, hard way before making any bold claim or even suggestion.

2025-10-03 05:46:51 GMT

#Physics is such an old field it's a real bitch.
1. Have a nice promising idea all by yourself
2. Find out a well-known guy had it 30 years ago
3. Refine the question so as to go further than the 1st dude.
4. Find out another even better-known guy who looked at this particular question 50 years ago.
5. Look at references in the paper.
6. Find out that Eddington first had a look at this in the early 1930s.
7. Give up and go back to your usual infinitesimally incremental shit or persevere by reading the 200 papers that you discovered along the trail of references, at the risk of facing an even more depressing surprise.
So, after thinking I had an original thought on Monday, here's me studying papers from a century ago to figure out if idea can be salvaged somehow.
#InfiniteLoop #ResearchIsHard #VisMaVieDeScientifique

2025-09-29 17:34:57 GMT

I just found I spent the day reinventing (without previous knowledge), in all its glory and speculativeness, a speculative 30yo theory by a well-known theoretical physicist 😬 How was yours ?

2025-09-24 07:03:21 GMT

Mastodon Wednesday vibe never disappoints. Have a nice day.
https://social.sciences.re/system/media_attachments/files/115/257/982/651/037/790/original/540252cbf49a0bd4.jpg

2025-09-22 15:23:19 GMT

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i'll tell you what happens when you have too much time on your hands for idle speculations (because my job is like this): not much, at least for me 😅 i don't really discard them, i don't develop them very far either. The more i go into that, the more come. Call it ADHD or whatnot, but it's very frustrating in the end to have all this time and thoughts zipping through the brain all the time and pretty much nothing coming out of it.

2025-09-03 12:15:12 GMT

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Thank you, I guess it means I'm a considerate person in posting stuff that is not going to be a waste of people's time 😉

2025-09-03 10:05:33 GMT

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who said mastodon was not as interesting as xwitter/bsky for scientists ?

2025-09-02 10:53:47 GMT

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there's some nice stuff in [@ct_bergstrom](https://fediscience.org/@ct_bergstrom ) Evolution textbook too.

2025-09-02 10:30:05 GMT

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in any case it makes for a fun story for an audience

2025-09-02 10:28:58 GMT

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well at least some of them are related to the volcanic eruptions

2025-09-02 10:12:25 GMT

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https://mastodon.social/@markmccaughrean/115053980866839361
https://climatejustice.social/@anlomedad/114790169599013595

2025-08-30 10:20:33 GMT

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as a russian colleague remarked publicly after my 1st big conference talk 20 years ago, "in the end you are asking morrre qvestchions than you arrre ansverrring ! *I* answerrr qvestchions !"

2025-08-30 08:59:45 GMT

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stay in your lane !

2025-08-17 17:07:24 GMT

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L'aigrette garzette @npub1juv…xv5g prend un bain moussant dans #LeTarnCestMoche #Birding #Birdphotography
https://social.sciences.re/system/media_attachments/files/115/045/197/225/296/723/original/970410549c015182.jpeg

2025-08-15 12:02:42 GMT

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Bon je renonce, fétrocho. Comme d'hab le seul truc que j'ai pécho c'est l'oiseau facile, @npub1juv…xv5g l'aigrette garzette #birding

2025-08-15 11:53:18 GMT

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Allez repassez en plus y a du poiscaille qui fait des ronds dans l'eau à 10m de moi bazar ! #birding

2025-08-15 11:48:36 GMT

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Apparemment c'est la pause réglementaire chez les martins 😑#Birding #LesNormesReglementairesQuiEtouffentLesFrançaisCaSuffit

2025-08-15 11:16:14 GMT

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Update: ils sont DEUX ! #birding

2025-08-15 11:14:18 GMT

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Pourtant y a la branche parfaite pour se poser juste devant moi et j'ai mis le tshirt qui va bien #JeComprendsPasJaiToutBienFait #birding
https://social.sciences.re/system/media_attachments/files/115/032/480/718/277/563/original/2d3979d2306f6f38.jpg
https://social.sciences.re/system/media_attachments/files/115/032/480/844/572/429/original/6f02df4f079c9f96.jpg

2025-08-15 10:53:44 GMT

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12è passage de la bête en 3h et je suis toujours pas sur d'avoir un cliché net (et encore moins de près) #zen #birding

2025-08-15 07:23:31 GMT

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ALERTE MARTIN-PÊCHEUR 🚨 #birding

2025-08-15 07:05:44 GMT

#LeTarnCestMoche
https://social.sciences.re/system/media_attachments/files/115/031/502/624/835/739/original/1ed15869e0f6e4f3.jpg
https://social.sciences.re/system/media_attachments/files/115/031/502/976/797/913/original/a63ef7c8a78fcd72.jpg

2025-07-28 13:42:20 GMT

In France, we don't say "fuck you", we say "La porte-parole du gouvernement, Sophie Primas, recrute son futur dircab' a la FNSEA", and I think it's not really beautiful but hey that's what a corrupt state looks like.

2025-07-23 15:01:01 GMT

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Après cette très belle et longue descente dans la rocaille au milieu des pins, puis dans la forêt, on se retrouve au pied d'une montée de la route forestière déserte de la Coche, c'est parti pour 200D+ au Soleil vers 13h 🥵 , plusieurs kilomètres en lacets sur du goudron un peu défoncé, au milieu des arbres, de la prairie, des fleurs sauvages. Autour de nous, des papillona Apollon volètent dans tous les sens, je n'en ai jamais vu une telle densité. Les pauses me permettent de ressortir l'artillerie photographique lourde pour les capturer virtuellement. #Butterfly #wildlifephotography #LeVercorsCestMoche #BikeTooting #MountainBiking
https://social.sciences.re/system/media_attachments/files/114/903/138/424/242/269/original/c78da39162a30b15.jpeg
https://social.sciences.re/system/media_attachments/files/114/903/138/502/796/442/original/7bb81942bd21b33a.jpeg

2025-07-23 14:51:27 GMT

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Pause spoiler: on n'a pas vu ni Tetras-Lyre, ni bouquetins, ni chamois, ni beaucoup d'autre faune sauvage 😢 . On a prévu de faire une demande de réclamation à l'office du tourimse en donnant aussi l'adresse de @npub1juv…xv5g si jamais ils souhaitent porter plainte pour préjudice #Remboursay #OnAFaitMarcherLeCommerceLocalOnEnVeutPourNotreArgent

2025-07-23 14:47:40 GMT

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Un groupe de chocards se moque de moi alors que je rampe dans la prairie pour m'approcher des marmottes. On s'enfonce ensuite vers le nord, dans le seul chemin autorisé aux VTTs de la grande traversée du Vercors, entre la réserve d'hivernage des tetras-lyre à l'ouest et la réserve naturelle elle-même à droite. C'est parti pour presque 10km de descente douce dans des chemins caillouteux entre les pins à crochets qui embaument dans le Soleil de midi, et la bande-son des sauterelles #BikeTooting #MountainBiking #LeVercorsCestMoche
https://social.sciences.re/system/media_attachments/files/114/903/089/205/042/865/original/185033c916b30369.jpeg

2025-07-23 14:42:04 GMT

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C'est l'occasion de justifier d'avoir embarqué le téléobjectif en plomb #marmoton #wildlifephotography #LeVercorsCestMoche #BikeTooting #MountainBiking
https://social.sciences.re/system/media_attachments/files/114/903/066/224/676/553/original/14aa9b22ef963c23.jpeg
https://social.sciences.re/system/media_attachments/files/114/903/067/953/911/872/original/3374357b9ac8d181.jpeg
https://social.sciences.re/system/media_attachments/files/114/903/067/964/316/223/original/9ebe777f6aead344.jpeg

2025-07-23 14:36:12 GMT

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Peu après, on croise des employé.e.s saisonnièr.e.s pas farouches probablement rémunéré.e.s par le parc régional #wildlifephotography #LeVercorsCestMoche #BikeTooting #MountainBiking #marmoton
https://social.sciences.re/system/media_attachments/files/114/903/042/713/528/173/original/a6c38da518dd5b17.jpeg

2025-07-23 14:29:08 GMT

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Un peu plus loin, on s'oriente vers le nord, et on commence à traverser des paysages qui ne sont pas sans rappeler les plateaux de #LesPyreneesCestMoche au niveau ambiance et végétation. #BikeTooting #MountainBiking #LeVercorsCestMoche #LandscapePhotography
https://social.sciences.re/system/media_attachments/files/114/903/016/639/796/876/original/f3df866be173c6b1.jpeg

2025-07-23 14:06:34 GMT

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La vue vers le sud et le Diois depuis le pas des Econdus, l'endroit idéal pour un premier pit-stop pâte de fruits. Toujours le bruit du vent, et c'est tout. #BikeTooting #MountainBiking #LeVercorsCestMoche #LandscapePhotography
https://social.sciences.re/system/media_attachments/files/114/902/928/995/931/874/original/b1be965887791080.jpeg

2025-07-23 14:01:18 GMT

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Une première descente suivie d'une première remontée, 1 bonne heure après le départ ça commence à se lever vers l'est, le mont Aiguille, le grand Veymont et les sommets du vercors sud qui vont nous accompagner toute la journée au fur et à mesure qu'on remonte vers Corrençon. Trois vautours fauve tournent en altitude, on entend juste le bruit du vent et un troupeau de brebis au loin. #BikeTooting #MountainBiking #LeVercorsCestMoche #LandscapePhotography
https://social.sciences.re/system/media_attachments/files/114/902/906/502/768/102/original/c072c7cee61f9e05.jpeg

2025-07-23 13:50:47 GMT

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Ca démarre vers l'est. On le savait mais ça commence par une montée très forte de 200D+ dans un chemin de caillasse inroulable par endroits, beaucoup de poussage assez inévitable. Après un bon coup de cul, nous voilà en haut d'un premier promontoire (c'est une station de ski), on aperçoit deux-trois randonneurs mais à part ça rien. Vue vers l'ouest #MountainBiking #BikeTooting #LeVercorsCestMoche #LandscapePhotography
https://social.sciences.re/system/media_attachments/files/114/902/862/371/466/405/original/a4fe2b5819771c92.jpeg

2025-07-23 13:47:19 GMT

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On part pour la journée avec Junior vers 10h30 depuis le sud du Vercors, le plateau de Beure au-dessus du col de Rousset, pour 45km et 1000D+ annoncés. Vent frais, le plafond nuageux est assez bas. 3L d'eau chacun et j'embarque aussi le matos photo dont le télé 300mm, les mules sont bien chargées sur le vélo #BikeTooting #MountainBiking

2025-07-23 13:38:12 GMT

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L'après-midi est pluvieux, les courbatures sont fortes, le canap' est confortable, et personne ne lit mastodon à cette heure-ci, c'est donc je crois le moment idéal pour poser ici un petit thread #VTT #BikeTooting #MountainBiking de la traversée des hauts-plateaux du #LeVercorsCestMoche par le tracé de la grande traversée du vercors. Le vélo de montagne (musculaire) au milieu de nulle part c'est mon kiff 🧵

2025-07-22 07:18:22 GMT

Bonjour, aujourd'hui c'est le jour tantadandu depuis 3 mois, safari photo-vtt avec junior sur les hauts plateaux 🤩 🥰 #levercorscestmoche

2025-07-18 19:56:07 GMT

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Sur le chemin... #Butterfly #naturephotography
https://social.sciences.re/system/media_attachments/files/114/875/990/841/504/635/original/18e496111faf8834.jpeg

2025-07-18 18:53:15 GMT

Aujourd'hui une toute autre ambiance avec la visite de Valchevrière. J'ai fait des belles photos, dignes du lieu j'espère, que je partagerai plus tard.

2025-07-14 16:53:26 GMT

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Grande Astrance 💚 #Bloomscrolling #FleurisTonFil
https://social.sciences.re/system/media_attachments/files/114/852/622/445/945/594/original/afd0f245e6a170e0.jpeg

2025-07-14 16:47:59 GMT

Mastoterelle #MacroPhotography #naturephotography
https://social.sciences.re/system/media_attachments/files/114/852/595/697/184/146/original/e61ced10d1168c28.jpeg

2025-07-10 10:35:26 GMT

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then ask people to do 4 pages proposals which can be recommended or not quickly (it takes 2 hours to do that), and make a random draw among those recommended. Tge science won't be much worse, and the time gained by everyone huge

2025-07-10 10:32:02 GMT

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you don't need 6 months to review 10 pages proposals, most of which are good anyways, only to largely arbitrarily select 10% of them in the end.

2025-07-10 09:51:39 GMT

Could someone refresh my understanding of why, oh f* why, we need to wait between 6 and 12 months to learn whether our 10% success rate grant proposals are getting funded ? What is the f* bureaucracy doing with them all that time ? Why is it so hard to ask reviewers to send a review within a month and then have a committee that figures out the few outstanding proposals and then randomly draw a few among the remaining good ones, and that's it ?

2025-06-16 16:53:54 GMT

So, there was quite a lot of talk, in the workshop I just returned from, about the use of machine-learning for nonlinear physics (like astrophysics, atmospheric, or ocean turbulence).
In the end, my take on this problem has not changed much and can be summed up as follows.
- It can do some rather good things (like accelerating things or making things a bit more precise) on *interpolation* problems (i.e. to do inference on problems it was explicitly trained for, in physical regimes it was trained for based on full-physics simulations), and may even help to limit the use of full-scale HPC/numerical resoures in this context IF USED SMARTLY AND REASONABLY (a big if when I look at the way many astronomers are using it).
- It essentially remains untrustable and uncontrolled garbage for *extrapolation* problems, i.e. to provide new results in physical regimes well-beyond those it was trained on, and beyond those that we can explicitly simulate with physics codes. It notably remains utterly terrible when there is no proper separation of scale in the problem, that is for, well, most of the hard key problems we have to deal with in this field.
Most of the hype is about the latter, though. The progress with interpolation/fitting is real, but is much more incremental and much less flamboyant than the hypothetical conceptual breakthroughs promised by the proponents of AI. That ML performs well on interpolation problems is not particularly a surprise or controversial in itself either, as these things are essentially giant fitting factories.
All of this makes it very clear that it is critical to *define* what AI means, and the kind of things one wants to apply ML or other techniques on , before any useful and reasonable conversation on their merits can be had. #AI #physics #machinelearning

2025-06-03 20:39:45 GMT

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except for chinese-american professors, who i know a few who already have joint appointments, do you really think moving to totalitarian China is going to be an attractive mass alternative to your fellow US citizens ?

2025-06-03 19:21:56 GMT

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the number of permanent or temporary positions is clearly not going to be commensurate with the affected US research workforce. If you were to give just 150k$/person for 3 years (how much a phd grant at cnrs currently costs), with no support money, Europe by its current pledges would barely absorb 3000 people for that period.

2025-05-25 13:30:36 GMT

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Haven't felt in the zone for scientific work so much since i was a postdoc. Feels like i'm doing in a week the equivalent of what i was doing in a month or more until recently, and i thoroughly enjoy it. I know i'm probably overworking myself, but it feels really good to finally be in tune with your own aspirations and vocation again tbh. It took some time to settle but I think i made the right call with this ecology research transition. #academicchatter

2025-05-25 10:41:39 GMT

Paper-editing session POV #SilentSunday #Science #vismaviedescientifique
https://social.sciences.re/system/media_attachments/files/114/568/043/664/982/433/original/0a8d4b00cb16dcbe.jpg

2025-05-19 18:53:57 GMT

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If you want the latest in MHD on this, check out this paper by David Hosking. Best theory result in MHD of the last 30 years !
https://journals.aps.org/prx/abstract/10.1103/PhysRevX.11.041005

2025-05-11 14:26:00 GMT

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This is not a scientific experience you can run for real, it must remain at the stage of Gedankenexperiment or the parents will die of exhaustion of an over-tired crying kid who can't make it to school/kindergarten.

2025-05-11 10:36:37 GMT

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Pour @npub1w9u…5x06
#Bloomscrolling #FleurisTonFil #GardenPhotography
https://social.sciences.re/system/media_attachments/files/114/488/753/681/896/533/original/06bf09c4c06fd626.jpeg
https://social.sciences.re/system/media_attachments/files/114/488/753/693/051/976/original/f2ffaa10608050cb.jpeg

2025-05-11 10:33:10 GMT

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#grassmat Quand tu prends le petit dej au lit la tête dans l'oreiller
#siestodon #insectodon #FleurisTonFil #GardenPhotography #macrophotography
https://social.sciences.re/system/media_attachments/files/114/488/739/760/052/318/original/2174e5a92e139b19.jpeg

2025-05-11 10:28:07 GMT

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"Et n'oublie pas les petits gâteaux à la boulangerie en rentrant, Roger, c'est dimanche"
#GardenPhotography #macrophotography #Bloomscrolling #FleurisTonFil
https://social.sciences.re/system/media_attachments/files/114/488/718/813/959/364/original/df1ce56d772dd82d.jpeg

2025-05-11 10:24:49 GMT

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La petite mécanique de la vie
#GardenPhotography #macrophotography
https://social.sciences.re/system/media_attachments/files/114/488/708/583/892/863/original/27de8486f330dca6.jpeg

2025-05-11 10:21:45 GMT

La macro manuelle >> Emmanuel Macron
#insectodon #nature #GardenPhotography #macrophotography #FleurisTonFil #BloomScrolling
https://social.sciences.re/system/media_attachments/files/114/488/695/210/859/001/original/e4d92394378379d6.jpeg

2025-05-04 11:23:11 GMT

Just discovered an amazing search feature in #mastodon !
Use the field "in:library" to search only in the toots you have interacted with some day.
Using this, I just dug out a toot from an exchange I had in mid-2023 in 1 second, and which was lost among a gazillion of other bookmarks.
#Feditips #Mastotips

2025-04-09 21:34:09 GMT

Philippe Poutou qui devient libraire, beh je suis sincèrement content pour lui, il va surement pouvoir vivre une meilleure vie et c'est tant mieux comme ça.

2025-03-23 20:04:21 GMT

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Singing in the rain #Birding #BirdPhotography
https://social.sciences.re/system/media_attachments/files/114/213/532/242/516/182/original/55981d237160d6f2.jpeg

2025-03-23 20:00:37 GMT

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#Birding #BirdPhotography x #Mosstodon x #LichenSubscribe
https://social.sciences.re/system/media_attachments/files/114/213/517/254/143/035/original/96b7205b028b55ec.jpeg

2025-03-23 19:56:57 GMT

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Ca y est j'ai graillé c'est parti #Birding #BirdPhotography
https://social.sciences.re/system/media_attachments/files/114/213/505/346/550/893/original/6b1c2049652a629f.jpeg

2025-03-23 18:45:45 GMT

🧵 #Zanimo après manger 😏 #Birding #BirdPhotography
https://social.sciences.re/system/media_attachments/files/114/213/242/881/715/946/original/98d11c86e15721e5.jpeg

2025-03-10 16:46:57 GMT

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What made you think in the first place there was even a chance it could be trusted ?

2025-02-27 17:31:42 GMT

Popotin d'orite 💚 #LAriegeCestMoche #Birding #BirdPhotography
https://social.sciences.re/system/media_attachments/files/114/077/037/694/706/551/original/0813e1d3d0b8f462.jpeg

2025-02-25 22:44:28 GMT

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Je l'ai utilisé à dessein au cas ou on me réponde en réutilisant le nom avec la bonne orthographe, sinon je n'aurais pas vu la réponse.

2025-02-25 22:09:13 GMT

C'est nul, avec mon filtre anti Musque, tous les pouets qui parlent de trucs au mois de mars sont maintenant masqués. C'est embêtant vu le calendrier.

2025-02-19 18:28:27 GMT

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A truly wonderful flower #macrophotography #Bloomscrolling #FleurisTonFil
https://social.sciences.re/system/media_attachments/files/114/031/962/751/607/016/original/94e1dfc25befcb9c.jpeg

2025-02-19 18:24:53 GMT

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#Bloomscrolling 💚 #FleurisTonFil #macrophotography
https://social.sciences.re/system/media_attachments/files/114/031/945/753/361/201/original/893438ddd9a435d0.jpeg

2025-02-19 18:14:54 GMT

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In the woods for love 💚 #BloomScrolling #Birding #BirdPhotography
https://social.sciences.re/system/media_attachments/files/114/031/902/921/282/462/original/d167aba91d279c68.jpeg

2025-02-19 18:06:58 GMT

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Looking up again #Birding #BirdPhotography
https://social.sciences.re/system/media_attachments/files/114/031/876/897/106/289/original/9ec660da56c8659f.jpeg

2025-02-19 18:05:12 GMT

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Can't get enough of this #mosstodon #macrophotography #LichenSubscribe
https://social.sciences.re/system/media_attachments/files/114/031/867/469/938/123/original/6685b62a13cdca95.jpeg

2025-02-19 18:00:40 GMT

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More #Mosstodon multiverse extravaganza #macrophotography
https://social.sciences.re/system/media_attachments/files/114/031/852/329/677/735/original/2829eecb0d6f1fa6.jpeg

2025-02-19 17:54:45 GMT

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Multiverse exists (zoom for details 🤩 ) #Mosstodon #macrophotography
https://social.sciences.re/system/media_attachments/files/114/031/827/004/310/208/original/3d0968c1c4c0aea3.jpeg

2025-02-19 17:48:46 GMT

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Les experts me corrigeront mais je crois qu'il s'agit d'un bruant fou, qui est reparti aussi vite qu'il était apparu #FirstTime #Birding #BirdPhotography
https://social.sciences.re/system/media_attachments/files/114/031/804/151/040/766/original/c08b9502f372ab1f.jpeg
https://social.sciences.re/system/media_attachments/files/114/031/804/186/368/843/original/1051f0cd93475ea0.jpeg

2025-02-19 17:14:07 GMT

◀️ a fait des photos de et dans #lariegecestmoche

2025-02-09 10:29:28 GMT

Bonjour les copain.e.s #Birding #BirdPhotography
https://social.sciences.re/system/media_attachments/files/113/973/455/913/511/317/original/2ed5a9cc6c6ba9c4.jpeg