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.

High Resolution Observations of the Submillimetre Stratospheric Emission Spectrum

Abstract: THIS letter reports the preliminary results of some recent measurements of the thermal emission spectrum of the stratosphere in the submillimetre region. This follows analysis of previous measurements from aircraft1–3 using Fourier spectroscopic techniques which snowed how, using a Michelson interferometer with a Golay cell detector, spectra may be obtained to a maximum resolution of about 0.2 cm−1. From such results, the mixing ratios of H2O and O3 may be determined relative to O2. Several emission lines due to H2O, O2 and O3 were also observed for the first time in the atmosphere, which raised the possibility that other much weaker lines due to minor atmospheric gases might be observed.

An Investigation of the Fretting Corrosion of Closely Fitting Surfaces

Abstract: The paper describes an experimental investigation of the mutual corrosion of metal surfaces in closely fitting contact when subject to vibration. It is shown that the corrosion is mechanical rather than chemical in character. Vibration or alternating surface stress alone will cause no corrosion and it is established that some surface slip, alternating in direction, is the necessary condition. Slip effectively causes corrosion even if reduced to the order of molecular dimensions, and this has been found to occur without exception, whatever the condition of the surfaces. Lubricants modify but do not prevent corrosion. Softer materials in general tend to seize and harder materials to produce corrosion debris. The amount of corrosion does not appear to depend on the intensity of normal pressure, but only on the occurrence of contact. Comparative tests of many pairs of materials show differences in the resistance offered to corrosion, but no pair of materials has been found to be free from the effect. A theore...

The Route to Atomic and Quantum Standards

Abstract: Over the past half-century, there has been a shift away from standards based on particular artifacts toward those based on physical effects, the most stable being based on quantum properties of systems. This change was proposed at the end of the 19th century but is still not complete at the start of the 21st. We discuss how this vision has been implemented through recent advances in science and metrology and how these may soon lead to an SI system finally free from artifact standards, with a consistency based on fundamental constants.

The Hydrodynamical Theory of Film Lubrication

Abstract: The equations of film lubrication are derived from the general equations of hydrodynamics assuming only that the motion is steady, and that it takes place between two surfaces, in relative motion, which are both close together and nearly parallel. Consideration of the relative magnitude of the various term sunder typical conditions as measured in a bearing shows that they are of very unequal orders of magnitude, and that in particular the inertia term s in the momentum and the dilatation and conductivity term s in the energy equation can be neglected. I t is shown that film lubrication is possible if, and only if, either the distance between the surfaces decreases in the direction of motion (the geometric wedge), or the density of the fluid decreases in the same direction (the thermal wedge). These types of film are approximately equal when compared on a basis of equal film thickness and equal decrease. With the geometric wedge a much greater decrease, and therefore load-carrying capacity, is possible, but the thermal wedge from its simpler mechanical construction should be able to equalize matters by running with a thinner film. The equations of film lubrication are derived from the general equations of hydrodynamics assuming only that the motion is steady, and that it takes place between two surfaces, in relative motion, which are both close together and nearly parallel. Consideration of the relative magnitude of the various terms under typical conditions as measured in a bearing shows that they are of very unequal orders of magnitude, and that in particular the inertia terms in the momentum and the dilatation and conductivity terms in the energy equation can be neglected. It is shown that film lubrication is possible if, and only if, either the distance between the surfaces decreases in the direction of motion (the geometric wedge), or the density of the fluid decreases in the same direction (the thermal wedge). These types of film are approximately equal when compared on a basis of equal film thickness and equal decrease. With the geometric wedge a much greater decrease, and therefore load-carrying capacity, is possible, but the thermal wedge from its simpler mechanical construction should be able to equalize matters by running with a thinner film. The equations are reduced to non-dimensional form and the equation of state discussed. For the general case the integration is probably a major computing operation and, in view of the uncertainties in the exact form of the equation of state, not worth while. For the infinite bearing, on the other hand, integration is comparatively simple and has been carried out in the Mathematics Division, N.P.L., for a series of representative cases. The results show that viscosity variation has a profound effect on the performance of the thermal wedge, and that the additional wedging action provided by change of density is likely to be small unless the lubricating surfaces are close together. On the other hand, for surfaces close together and a small variation of viscosity the thermal wedge altogether outclasses the geometric.

Polyaniline/polymeric acid composite, a novel conducting rubber

Abstract: Preparation du composite par addition de polyaniline a une solution aqueuse de poly (acide styrenesulfonique) puis sechage. La conductivite electrique du composite augmente lentement avec la proportion en polyaniline jusqu'au seuil de percolation (11,6%) puis augmente brusquement. La conductivite augmente egalement avec le taux d'etirage du composite. Discussion de la structure