202 reputation
18
bio website whereofonecannotspeak.wordpre…
location Brighton, United Kingdom
age
visits member for 3 years, 9 months
seen Jul 21 at 23:27

Jun
30
awarded  Curious
Jun
29
comment Rules of thumb for estimating visual angles
Luckily, it's dark ;)
Jun
29
comment Rules of thumb for estimating visual angles
That's a creative suggestion. Not sure I can execute it (and then move my arms to the right position) even remotely accurately. One can rule out the 46 degree halo with only one halving, or see if the diameter is 92 without any halving at all.
Jun
29
asked Rules of thumb for estimating visual angles
Jun
21
awarded  Yearling
Jun
21
comment Calculating the resistance of a 3D shape between two points
My model above has about 10,000 nodes. It took about 100,000 iterations to converge. I hope I've done it right, some reverse engineering implies what I've been doing is solving Laplace's equation $\nabla^2 \phi = 0$ with boundary conditions $(\hat{n} \cdot \nabla) \phi = 0$ for non-contacts and $\phi = const$ for the contacts. This seems very plausible to me now. You've been very helpful, thanks.
Jun
21
comment Calculating the resistance of a 3D shape between two points
OK, I'm convinced, and I have a much better understanding now, thanks. See question for some plots.
Jun
21
revised Calculating the resistance of a 3D shape between two points
added some simulations based on an answer below
Jun
21
comment Calculating the resistance of a 3D shape between two points
I've just about coded a basic relaxation procedure in 2D. I'll put some results in the OP when I've got some.
Jun
20
comment Calculating the resistance of a 3D shape between two points
I'm not 100% convinced, but you've persuaded me to code something up and see. Assuming this is correct though, doesn't it suggest an equation expressed in terms of the minimisation of some function?
Jun
20
comment Calculating the resistance of a 3D shape between two points
I'd decided this approach was incorrect, though perhaps you could persuade me otherwise. The reason I had decided this was this: Lets say we use a rectangular grid. Now consider a relatively thin straight object. If the object, of length $l$ is aligned with the grid, it would contain $n$ resistors and have a resistance $R$, if it lies diagonally to the grid, then it would contain $~\sqrt{2}n$ resitors and have a resistance of $\sqrt{2}R$. Perhaps you are suggesting modifying the resistances as part of the relaxation, though I'm not sure how one would go about that.
Jun
20
revised Equation derivation for skipping rocks
fixed links
Jun
20
suggested approved edit on Equation derivation for skipping rocks
Jun
20
asked Calculating the resistance of a 3D shape between two points
Sep
24
awarded  Popular Question
Jun
23
comment Virtual photons, what makes them virtual?
@Qmechanic Thanks. The end of Arnold Neumaiers answer addresses my question directly, though his opinion seems to be rather controversial.
Jun
23
asked Virtual photons, what makes them virtual?
Jun
17
comment Is it possible to increase refractive index at lower densities?
My intention was to ask about the change in density for one material, but I do like the reference.
Jun
17
comment Is it possible to increase refractive index at lower densities?
Ha! I can't get the paper right now, but I'm guessing the collection of points (first figure) are made with different materials, or at least different phases, right?
May
23
comment Quantum mechanics and everyday nature
Also, this is basically why colour vision doesn't work at night.