National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

Graphene, universality of the quantum Hall effect and redefinition of the SI system

Abstract: The Systeme Internationale d'unites (SI) is about to undergo its biggest change in half a century by redefining the units for mass and current in terms of the fundamental constants h and e, respectively. This change crucially relies on the exactness of the relationships that link these constants to measurable quantities. Here we report the first direct comparison of the integer quantum Hall effect (QHE) in epitaxial graphene with that in GaAs/AlGaAs heterostructures. We find no difference in the quantized resistance value within the relative standard uncertainty of our measurement of 8.6◊10 11 , this being the most stringent test of the universality of the QHE in terms of material independence. The new quantum Systeme Internationale d'unites (SI) units for mass and current will be based on the fundamental constants of nature: Planck's constant, h, and the electron charge, e. Confidence in the new definition relies mainly on the ability to confirm experimentally the exactness of the relationships that link these constants to measurable quantities. The quantum Hall effect (QHE) defines one such relationship through the theoretical argument that the Hall resistance is quantized in units of h/Ne 2 , where N is an integer. The QHE 6 Author to whom any correspondence should be addressed.

Analysis of texture evolution in pure magnesium and the magnesium alloy AM30 during rod and tube extrusion

Abstract: The evolution of microstructure and texture during extrusion of pure magnesium and its single phase alloy AM30 has been studied experimentally as well as by crystal plasticity simulation. Microstructure and micro-texture were characterized by electron back scattered diffraction (EBSD), bulk-texture was measured using X-ray diffraction and deformation texture simulations were carried out using visco-plastic self consistent (VPSC) model. In spite of clear indications of the occurrence of dynamic recrystallization (DRX), simulations were able to reproduce the experimental textures successfully. This was attributed to the fact that the textures were c-type fibers with their axis of rotation parallel to the c-axis and DRX leads to simply rotate the texture around the c-axis.