We run a regular programme of seminars for staff and students.
Driving a nanomechanical resonator with phonon wind in superfluid 4He
Microelectromechanical (MEMS) and nanoelectromechanical systems (NEMS) are ideal candidates for exploring quantum fluids, since they can be manufactured reproducibly, cover the frequency range from hundreds of kilohertz up to gigahertz and usually have very low power dissipation.
Their small size offers the possibility of probing the condensate on scales comparable to, and below, the coherence length. That said, there have been hitherto no successful measurements of NEMS res- onators in the liquid phases of helium.
Here we report the operation of doubly-clamped aluminum nanocantilevers in superfluid 4He at temperatures spanning the superfluid transition. The devices are shown to be very sensitive detectors of the superfluid density and the normal fluid damping. We use nanomechanical resonators with extremely high quality factor to probe superfluid 4He at millikelvin temperatures, as well.
The high sensitivity of these devices to thermal excitations in the environment makes it possible to drive them using the momentum transfer from phonons generated by a nearby heater. This so-called phonon wind is a reverse thermomechanical effect that until now has never been demonstrated.
Wednesday 10 October 2018
Representational learning with interactive simulations
Analysing, constructing, and translating between graphical, pictorial, and mathematical representations of physics ideas and reasoning flexibly through them (representational competence) is a key characteristic of expertise. It is challenging for learners to develop, but little instruction is explicitly designed with this purpose in mind.
This talk will focus on the role of interactive computer simulations with appropriate scaffolding in supporting representational learning. We have been developing combined simulation-tutorials for the learning of quantum mechanics, whereby students first work on problems independently, constructing representations they will later see in the simulation, followed by further problems with simulation support.
This talk will describe the structure and sequencing of the simulation-tutorials and present results from pre-, mid- and post-tests to assess student learning.
Wednesday 3 October 2018