Recent content by jeffbarrington

Ah thanks, I began to suspect I might have been learning about GaAs specifically. I've done a year of undergraduate condensed matter physics plus almost another year, and this heavy/light hole stuff came up when we started photonics.

Does that mean to say there is a lifting of degeneracy though? I know the effective mass of an electron is different to an actual electron mass, but is there an analogy in the conduction band to the degeneracy lifting in the valence band? I suppose there is an infinity of bands at ever higher...

So some materials have sub-bands of the valence band, known as heavy and light holes (they have different curvature so different effective masses, this I understand). Sources seem to give different reasons for this, either because of anistropy in the crystal or some sort of coupling effect, but...

Of course, but the pairing term of the SEMF is to be thought of as being to do with pp and nn pairs in the nucleus. Is this an effect of the shell model? Like how in atoms it's lower energy (high binding energy) for the spins to be aligned if the electrons are all in different orbitals?

I am curious as to why proton-proton, neutron-neutron bonds are preferable in the nucleus; the pairing term in the semi empirical mass formula for the nucleus comes from the fact that pp and nn bonds are more stable in the nucleus (higher binding energy or more negative potential energy, however...

I have marked this as high school level, although I am studying an undergraduate general relativity course, and just want to get some basics right. Whenever I look for a 'cheap and dirty' method of calculation for the age of the universe, with a Hubble constant not changing with time, I am met...

Ah, so they do. I hadn't realized the delta^++ was considered as such, thanks. re the box diagram - it's fine that it's suppressed, that's what the question is getting at (it's easy to draw scattering for Z^0 and a photon, the latter of which has highest amplitude as you say).

Thanks, so yeah I was thinking how unlikely this would be too. But then again, you would be left with three up quarks which can't form a hadron, something else would have to happen, and I'm not sure what.

Hello, I'm wondering how you would go about drawing a Feynman diagram for a weak charged current scattering interaction of a positron and a proton. I have attached a diagram of what I have tried but it doesn't conserve lepton number (I think this is a problem, from what I gather...

So this is sort of what I'm getting at - I understand that it is not either/or. What I mean to say is, the total rate of some process involves summing up an infinite number of contributions from Feynman diagrams, higher order being much less significant (except with the strong force). Some of...

Just a basic question which I will ask through an example: An electron and positron can scatter by annihilating to form either a virtual Z or virtual photon, either of which can then pair produce to give an electron/positron pair (amongst an infinity of other processes whose contributions need...

Thank you very much for your reply; I can certainly see what you mean, and to be honest the most capable people I know would frown upon spelling or grammatical errors, so it is certainly a good indicator (especially for someone applying for a programming role as you point out).

I'm not getting at you, but I really want to get into the mind of an employer, and this is interesting - you would put ability to spellcheck above competence at the job? It's true that employers behave like this? Obviously spellcheck is incredibly easy to do, and you've got to sort the wheat...

Hi, I am a bit confused about rotational and irrotational flows, in this way: When I do exam questions/problems, there is often a bit at the start of a question on flows about why you can treat the velocity as the gradient of a potential. The only information it gives you is that it is...

Really? I don't understand how that's the case, they're both the particle's energy. edit - I actually get something viable by considering dE/dt = grad(E) dot dr/dt, since r is a function of time and I forgot to chain rule it.