247 research outputs found
Modelling of vorticity, sound and their interaction in two-dimensional superfluids
Vorticity in two-dimensional superfluids is subject to intense research
efforts due to its role in quantum turbulence, dissipation and the BKT phase
transition. Interaction of sound and vortices is of broad importance in
Bose-Einstein condensates and superfluid helium [1-4]. However, both the
modelling of the vortex flow field and of its interaction with sound are
complicated hydrodynamic problems, with analytic solutions only available in
special cases. In this work, we develop methods to compute both the vortex and
sound flow fields in an arbitrary two-dimensional domain. Further, we analyse
the dispersive interaction of vortices with sound modes in a two-dimensional
superfluid and develop a model that quantifies this interaction for any vortex
distribution on any two-dimensional bounded domain, possibly non-simply
connected, exploiting analogies with fluid dynamics of an ideal gas and
electrostatics. As an example application we use this technique to propose an
experiment that should be able to unambiguously detect single circulation
quanta in a helium thin film.Comment: 23 pages, 8 figure
Modelling of cavity optomechanical magnetometers
Cavity optomechanical magnetic field sensors, constructed by coupling a
magnetostrictive material to a micro-toroidal optical cavity, act as
ultra-sensitive room temperature magnetometers with tens of micrometre size and
broad bandwidth, combined with a simple operating scheme. Here, we develop a
general recipe for predicting the field sensitivity of these devices. Several
geometries are analysed, with a highest predicted sensitivity of
180~p at 28~m resolution limited by thermal
noise in good agreement with previous experimental observations. Furthermore,
by adjusting the composition of the magnetostrictive material and its annealing
process, a sensitivity as good as 20~p may be
possible at the same resolution. This method paves a way for future design of
magnetostrictive material based optomechanical magnetometers, possibly allowing
both scalar and vectorial magnetometers.Comment: 13 pages, 7 figures; manuscript contributed to the Special Issue
Sensors Based on Quantum Phenomen
Fracture properties of CrN hard coatings: Influence of the microstructure, alloying elements, and coating architecture
Transition metal nitrides are well known and applied as protective coating materials based on their unique refractory characteristics, such as high hardness or Young’s modulus. However, for long-term applications, the fracture toughness KIC is an essential factor as the integrity of the coating-substrate interface is impaired by cracking and subsequent environmental attacks.
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Precision ultrasound sensing on a chip
Ultrasound sensors have wide applications across science and technology. However, improved sensitivity is required for both miniaturisation and increased spatial resolution. Here, we introduce cavity optomechanical ultrasound sensing, where dual optical and mechanical resonances enhance the ultrasound signal. We achieve noise equivalent pressures of 8-300 micro Pascal per root Hertz at kilohertz to megahertz frequencies in a microscale silicon-chip-based sensor with >120 dB dynamic range. The sensitivity far exceeds similar sensors that use an optical resonance alone and, normalised to the sensing area, surpasses previous air-coupled ultrasound sensors by several orders of magnitude. The noise floor is dominated by collisions from molecules in the gas within which the acoustic wave propagates. This approach to acoustic sensing could find applications ranging from biomedical diagnostics, to autonomous navigation, trace gas sensing, and scientific exploration of the metabolism-induced-vibrations of single cells
Personalized web learning by joining OER
We argue that quality issues and didactical concerns of MOOCs may be overcome by relying on small Open Educational Resources, joining them into concise courses by gluing them together along predefined learning pathways with proper semantic annotations. This new approach to adaptive learning does not attempt to model the learner, but rather concentrates on the learning process and established models thereof. Such a new approach does not only require conceptual work and corresponding support tools, but also a new meta data format and an engine which may interpret the semantic annotations as well as measure a learner’s response to these. The EU FP7 project INTUITEL is introduced, which employs these technologies in a novel learning environment
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