16,849 research outputs found
Anisotropic superconducting properties of aligned MgB2 crystallites
Samples of aligned MgB2 crystallites have been prepared, allowing for the
first time the direct identification of an upper critical field anisotropy
Hc2^{ab}/Hc2^{c}= xi_{ab}/xi_{c} ~ 1.73; with xi_{o,ab} ~ 70 A, xi_{o,c} ~ 40
A, and a mass anisotropy ratio m_{ab}/m_{c} ~ 0.3. A ferromagnetic background
signal was identified, possibly related to the raw materials purity.Comment: 4 pages, 4 figures; Revised version to appear in Phys. Rev. Let
Laboratory experiments on the generation of internal tidal beams over steep slopes
We designed a simple laboratory experiment to study internal tides
generation. We consider a steep continental shelf, for which the internal tide
is shown to be emitted from the critical point, which is clearly amphidromic.
We also discuss the dependence of the width of the emitted beam on the local
curvature of topography and on viscosity. Finally we derive the form of the
resulting internal tidal beam by drawing an analogy with an oscillating
cylinder in a static fluid
Van der Waals spin valves
We propose spin valves where a 2D non-magnetic conductor is intercalated
between two ferromagnetic insulating layers. In this setup, the relative
orientation of the magnetizations of the insulating layers can have a strong
impact on the in-plane conductivity of the 2D conductor. We first show this for
a graphene bilayer, described with a tight-binding model, placed between two
ferromagnetic insulators. In the anti-parallel configuration, a band gap opens
at the Dirac point, whereas in the parallel configuration, the graphene bilayer
remains conducting. We then compute the electronic structure of graphene
bilayer placed between two monolayers of the ferromagnetic insulator CrI,
using density functional theory. Consistent with the model, we find that a gap
opens at the Dirac point only in the antiparallel configuration.Comment: 5 pages, 4 figure
Extreme vortex pinning in the non-centrosymmetric superconductor CePtSi
We report on the vortex dynamics of a single crystal of the
non-centrosymmetric heavy-fermion superconductor CePtSi. Decays of the
remnant magnetization display a clean logarithmic time dependence with rates
that follow the temperature dependence expected from the Kim-Anderson theory.
The creep rates are lower than observed in any other centrosymmetric
superconductor and are not caused by high critical currents. On the contrary,
the critical current in CePtSi is considerably lower than in other
superconductors with strong vortex pinning indicating that an alternative
impediment on the flux line motion might be at work in this superconductor.Comment: 4 pages, 5 figure
Google Glass as a learning tool: sharing evaluation results for the role of optical head mounted displays in education
This paper provides an overview of the findings from an evaluation of the role of Google Glass in education over the past three years. The authors have experimented with Optical Head Mounted Displays as a support tool for various learning activities over the past few years. The study described in the paper commenced back in 2014 and continued despite the fact that the development of the Google Glass technology was paused and then shifted towards enterprise clientele. This was a result of our confidence that the future of learning interfaces is aligned to the proliferation of augmented reality and the fact that the Google Glass interface offers an ideal tool for learners due to its light structure and seamless wearing experience. The paper discusses how Google Glass has been used for a range of learning activities and describes the learners’ experiences from using the device. The main contribution of the paper is in the form of measuring the success of the specific interface by sharing the results of three years of evaluations. The evaluation results are further analysed taking under consideration a number of profiling techniques of the learners involved including their personality type and learning style
Small Kerr-anti-de Sitter black holes are unstable
Superradiance in black hole spacetimes can trigger instabilities. Here we
show that, due to superradiance, small Kerr-anti-de Sitter black holes are
unstable. Our demonstration uses a matching procedure, in a long wavelength
approximation.Comment: 7 pages, 1 figure, RevTeX
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