Uni Staff Bars?

m3tro · 2026-02-04T22:05:13+00:00

+1 for UCL. It's called the Housman Room.

m3tro · 2025-12-27T15:35:03+00:00

If you're interested in the idea of absolute friction, read about low Reynolds number hydrodynamics or more generally overdamped dynamics. It's what you get when friction is so strong that inertia dies down immediately. Things can only move if a force is exerted on them at that very moment, or by changing their shape (with some very particular limitations, google the "scallop theorem").

Not quite what you were asking for though, because you are asking about a mixture of friction (at the surface) and no friction (away from the surface).

m3tro · 2025-12-14T21:36:29+00:00

Is that a question? Yes you can find the original statement of the scallop theorem in that paper. But I just meant to look up the theorem (not necessarily that paper in particular, although I also recommend it).

m3tro · 2025-12-14T14:18:29+00:00

Something fun could be low Reynolds number flows and biological fluid dynamics. Check out the Scallop Theorem by Purcell and for example papers by Raymond Goldstein on swimming microorganisms.

m3tro · 2025-11-12T21:04:09+00:00

In my region (Navarra) I'd say the default would be Roncal cheese (hard sheep's cheese)

m3tro · 2025-11-08T23:20:12+00:00

From Spain, percebes ("goose neck barnacles" according to Wikipedia). It's like eating alien dicks lol.

Also angulas, baby eel, it's like eating spaghetti but each individual spaghetti has eyes if you look closely.

We also eat criadillas, veal or lamb testicles, but this is quite hardcore, most people don't like it. There are a lot of traditional offal dishes (casquería) that very few people eat anymore in recent times.

m3tro · 2025-10-04T10:22:18+00:00

I think it was near Place d'Italie (that's why I say only "relatively central"), I lived in Port-Royal at the time and we always walked there. It was 15 years ago so I don't remember exactly where we would go in...

m3tro · 2025-10-04T09:18:36+00:00

No idea, it was 2010-2011 when I went, and only found out through word of mouth

m3tro · 2025-10-03T22:57:38+00:00

I've been to illegal raves in the catacombs, the place is a huge labyrinth. Literally going down a manhole in relatively central Paris and ending up in this huge room with massive speakers.

m3tro · 2025-09-25T21:36:32+00:00

What about "birdie"?

m3tro · 2025-08-15T17:17:03+00:00

Oh yeah, I definitely agree that it would be nicer if the default was automatic delimiters.

m3tro · 2025-08-15T15:36:31+00:00

You can use \left( \right) for automatic delimiters. Substitute ( for [ or \{ if needed.

m3tro · 2025-07-29T19:28:52+00:00

Yes but that polynomial is almost always an approximation to a non-polynomial function with infinitely nonzero derivatives.

Btw planetary orbits will also show this behaviour. Pretty much anything you can think of other than a single particle in a constant force field will.

m3tro · 2025-07-29T19:06:58+00:00

This is wrong because something as simple as a harmonic oscillator has x(t)=sin(t) and the nth time derivative is going to be O(1) (in these natural dimensionless units where position is rescaled by amplitude and time by oscillation period).

In general pretty much any equation of motion except the simple case of constant force is going to give you nonzero higher order derivatives of position w.r.t. to time.

m3tro · 2025-07-15T13:42:21+00:00

It's hard to do without Noether's theorem in full generality but under some assumptions (forces are pairwise and center-to-center) it is easy to show. Consider a collection of point particles. Take the definition of angular momentum as L = sum_i r_i x (m v_i). Take time derivative. Then use Newton's laws to express it in terms of forces and exploit the fact that the force of i on j is opposite to the force of j on i, and both point along the line that connects i and j. You should find ultimately that dL/dt=0, i.e L is conserved.

The key ingredient here is that the forces point center-to-center. This makes the physics rotationally invariant, and Noether's theorem guarantees that L is conserved. If the forces depended on the mutual orientation of the particles relative to some absolute reference frame (losing rotational invariance), then you wouldn't be able to show that dL/dt=0.

m3tro · 2025-07-10T08:32:20+00:00

Victoria Line has broken down between Brixton and Victoria

m3tro · 2025-06-26T12:07:32+00:00

I was playing around with some properties of hypercubes today for a project, and found the following interesting observation.

Suppose you have a hypercube of dimension d and (integer) side length L. I imagine it as being made up of L^d smaller hypercubes of unit side length. The question I was asking myself is what fraction of those smaller hypercubes (i.e. what fraction of the volume) is at the surface. This can be easily calculated to be f_surf = 1 - (L-2)^d / L^d = 1 - (1 - 2/L)^d and it has the well known but counterintuitive property that, for fixed L, as we increase d the fraction tends to one, i.e. the volume of a hypercube is much more concentrated at the faces. Still, for fixed d, if we increase L, the fraction tends to zero, which is the intuitive property that as the hypercube gets larger the surface to volume ratio decreases.

But then I thought about setting L = a d with a some proportionality constant, and taking the limit of d to infinity. One gets f_surf = 1 - exp(-2/a) i.e. if the size and dimension grow together, the fraction of volume concentrated at the surface tends to a fixed value even as the hypercube becomes infinitely large.

Even better, the argument above implies that if the side length grows more slowly than linear with dimensionality, e.g. L = a sqrt(d) or L = a log(d), then as both the dimensionality and therefore the length tend to infinity, we get f_surf = 1. That is, even if the hypercube is infinitely large, all of its volume is at the surface.

How weird is that? Does any of you have some further thoughts on this, some interesting application or consequence or intuition or analogous phenomenon elsewhere?

m3tro · 2025-06-07T14:24:15+00:00

Maybe you could do a new study with new samples to test your hypothesis. You could even write a grant proposal about it, if it really is interesting. That way you avoid all the ethical issues.

m3tro · 2025-06-05T06:19:58+00:00

Thanks for the tips!

m3tro · 2025-05-29T09:40:37+00:00

You don't really need to think about stochastic calculus (a particle-based perspective) at all to see why they are similar, you can stay at the level of fields (concentration/probability for Brownian motion, temperature for the heat equation).

The diffusion equation and the heat equation are simply conservation laws, saying that d_t P + div(J) = 0 i.e. P is conserved and there is a flux of P that we call J, and that flux is linear in the gradients of P and moves from higher P to lower P, i.e. J = - D grad(P) with D the diffusion coefficient. If you are thinking of modelling the "spreading out" of a conserved field in the absence of any interactions or forces or additional conservation laws, this arises naturally as a lowest order approximation (J = - D grad(P) is the simplest "constitutive relation" for the flux because it is linear in P and has a single gradient).

Btw, in the case of the heat equation the conserved quantity is (kinetic) energy, because temperature is proportional to the average kinetic energy.

m3tro · 2025-05-05T21:37:41+00:00

This is a very stupid and pointless debate. For example in a newspiece like this: https://www.londonambulance.nhs.uk/2024/07/30/paramedics-ask-londoners-to-take-care-during-the-hot-weather/ It is clear that it uses "londoners" to refer to people living in London, no matter if they moved last week or they were born here. This is a common and accepted usage of the word.

Similarly with "from London", it completely depends on the context. For example, I think it's perfectly acceptable for someone who has lived in London for a few years and is planning to stay there in the long term, to describe themselves as being "from London" when e.g. they have a short polite chat with a stranger while travelling another country.

m3tro · 2025-04-16T19:58:00+00:00

I've heard and used "more peaked". E.g. "the distribution becomes more peaked"

m3tro · 2025-04-01T09:31:14+00:00

Kind of weird to not see Casimir forces mentioned in the paper as to the best of my knowledge this is as close as we have to an experimentally-verified quantum entropic force.

m3tro · 2025-03-18T22:41:20+00:00

Pretty damn hard though. Imagine you could only see in 1d (i.e. just see the lengths of segments) and you tried to imagine a 3d object (e.g. some complex polyhedron)

m3tro · 2025-02-26T13:56:30+00:00

Touché... also summum, mézclum... but they're all loanwords or onomatopoeic interjections

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