Seat assignment at Portland airport

I am currently waiting at Portland airport for the first of my flights back to Britain, after the APS DFD conference (which may be the subject of a future post).

One strange aspect of this airport is the way that seats will be assigned. At all other instances of flying, I have always been able to select a seat while checking in, before waiting at the gate. Here (and perhaps it’s specific to the airline Delta), people have not had their seats assigned to them yet; the gate staff is calling people up to the desk, one by one, to give us our seats.

This system is slow and inefficient. Moreover, calling people up by publicly announcing the names on our passports has questionable privacy implications: In particular, for transgender people who do not necessarily go by the names on their passports. (This provides another counterexample to the ‘nothing to hide’ argument.)

A spectral solver for Schrödinger’s equation

Here is a MATLAB program for solving the 1D time-dependent Schrödinger equation:
http://jftsang.com/code/schrodinger_spectral.m

You can specify a potential function and an initial condition, and the solver calculates the wavefunction at future times. Hopefully this will be useful for getting some intuition as to how solutions to Schrödinger’s equation behave.

Details

The solver uses a spectral method which performs the time-integration exactly. Errors come from the spatial discretisation. The calculation is done in a periodic domain, so edge effects may affect your solution, especially in scattering problems.

Postprocessing

Fourier-transforming the solution in space tells you about the relative strengths of different wavenumber components of the solution, and therefore about the momentum distribution at each time.

Fourier-transforming in time tells you about the different frequency components in the solution, which you can use to identify energy eigenstates. Note that you might have to calculate the solution for a long time before you have enough periods for the Fourier transform to be precise enough.

Not-so-continuum mechanics: A talk for the LMS

I will be speaking at the London Mathematical Society’s Graduate Students’ Meeting tomorrow morning, on Not-so-continuum mechanics: Mathematical modelling of granular flows. It’s meant to be a gentle introduction to granular phenomena, and I will introduce a basic version of the μ(I) rheology, a fairly (but not universally!) successful description of granular flow. Here’s a practice version of the talk.

The talks are meant to be aimed at `a general mathematical audience’. My talk assumes no mathematical knowledge beyond A-level Mechanics. I’m having some trouble understanding some abstracts for the other talks, and I’m not sure if my talk is just better-aimed at a general audience, or if theirs are, and there are just huge gaps in my mathematical training (which there are: I’ve never done any algebra beyond basic group theory, or any number theory or combinatorics).

Voter turnout for student elections and referenda

After the summer’s referendum on the EU which had the whole nation in discussion (even if the level of discourse was rather poor), the recent CUSU referendum has been much more low-profile and somewhat of a climbdown. The topic in question was the class lists, Cambridge’s traditional (and unique) practice of publishing lists of all students’ examination results, both physically outside the Senate House and in print and online, in the Reporter. The question put forward was: ‘Should CUSU campaign to keep the Class Lists with an easier opt- out process?’. Proponents argued that publishing results is useful for combating impostor syndrome, and that class lists are a Cambridge tradition that should not be allowed to die, while an unconditional opt-out procedure would make participation voluntary. Opponents argued that having one’s results published causes stress and that an opt-out system would still allow the best to boast about themselves, and that the most stressed students could find it hard to request an opt-out, even if the procedure was unconditional.

I found about about the referendum only four hours before voting closed, thanks to an email from the Trinity Maths Society’s president. The referendum was not advertised by CUSU, except being mentioned in passing in two newsletters. I therefore suspected that the turnout would be rather low, and that the legitimacy of the referendum would be questionable. I was quite surprised by the turnout: 4,758 votes cast, out of an electorate of 23,615, or 20%. (The proponents won by a margin of around 500 votes.)

For comparison, the referendum to disaffiliate from the NUS, back in May 2016, had a turnout of 6,178 out of 21,479, or 29%. Queens’ JCR’s referenda in Michaelmas 2011, one motion being ‘Queens’ College JCR should oppose the current government changes to higher education’, had a turnout of 34%.

It would be interesting to study voter turnouts at different colleges’ JCR and MCR elections. In which colleges are students most keen to take part in the way their college is run?