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.

Recent advances in traceable nanoscale dimension and force metrology in the UK

Abstract: It is now fully appreciated that metrology will play an integral role in the successful development and commercialization of micro- and nanotechnology. To this end, the UK Government, through the National Measurement System, funded several groundbreaking projects in its 2002–2005 Programme for Length. This paper will briefly describe the background of the research, concentrating on the technical details of the projects. The Programme for Length normally only funds work into dimensional metrology but this funding cycle also funded work into low force metrology as this area is crucial to most mechanical probing techniques. The projects described include a traceable areal contacting instrument designed to calibrate areal transfer artefacts and hence offer traceability for industrial areal instruments, the production of the areal transfer artefacts, the development of Internet-based softgauges for profile parameters, a primary low force balance with a force resolution of 50 pN and the development of methods for measuring complex micro-scale structures. Amongst others, the projects involved collaboration with PTB, TNO, Taylor Hobson, AWE, Rubert & Co. and the Universities of Warwick, Huddersfield and Eindhoven.

Absolute frequency measurement of the 674-nm 88 Sr + clock transition using a femtosecond optical frequency comb

Abstract: The frequency of the $5s{}^{2}{S}_{1/2}$--$4d{}^{2}{D}_{5/2}$ electric quadrupole transition at 674 nm in a single, trapped, laser-cooled ${}^{88}{\mathrm{Sr}}^{+}$ ion has been measured with respect to the Syst\`eme International (SI) second using a femtosecond laser optical frequency comb. The measured frequency of 444 779 044 095.52 kHz, with an estimated standard uncertainty of 0.10 kHz, is more accurate than, and in agreement with, the value previously measured using a conventional frequency chain.

The Tensile Properties of Single Crystals of High-Purity Iron at Temperatures from 100 to -253 degrees C

Abstract: An account is given of the deformation and fracture characteristics of single crystals of high-purity iron of various orientations when tested in tension at temperatures from 100 to -253 degrees C. At temperatures down to -124 degrees C, the crystals were fully ductile, giving chisel-edge fractures and 100% reduction in area. At -196 degrees C, depending on the orientation of the stress axis, the behaviour covered the whole range from fully ductile with 100% reduction in area to completely brittle with cleavage fractures and no apparent deformation. Between these limits, mixtures of slip, twinning and cleavage were obtained. At -253 degrees C, the crystals gave cleavage fractures, and, over most of the orientation range studied, this occurred without prior deformation. It is shown that the resolved shear stresses required to produce slip or twinning at -196 degrees C vary with the orientation; in particular, the values are higher for orientations within 20 to 25 degrees of the [001] than elsewhere in the unit triangle, and these values are not reached in this region before failure occurs by cleavage. A mechanism is put forward to explain this in terms of 'locking' of dislocations. The cleavage strength resolved normal to the cleavage plane is not constant with change in temperature, as is commonly supposed, but is substantially higher at -253 degrees C than at -196 degrees C.

Physically based damage models for laminated composites

Abstract: The computing power that is available for engineering calculation continues to grow at a dramatic pace. Engineers in industry want to have seamless models that can be used to design across ...