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.

Analytical techniques for trace element analysis: an overview

Abstract: Techniques for the analysis of trace elements have developed rapidly in response to the increasing need for accurate measurements at extremely low amount of contents in diverse matrices. We review potentiometric, voltammetric, atomic spectrometric, X-ray and nuclear techniques and discuss the extent to which they have been shown to give comparable results in typical applications.

Luminous Efficiency of Rays entering the Eye Pupil at Different Points

Abstract: WE have shown1 that the impression of brightness produced by a light ray which forms an image on a fixed area of the retina depends in high degree on the position of entry of the ray in the eye pupil. For the ratio of the apparent brightness for peripheral entry to the apparent brightness for central entry, values as low as 0.2 were found for white light and foveal vision. The following new features of the phenomenon have been revealed by later work:

The effect of wind-tunnel screens on nominally two-dimensional boundary layers

Abstract: Spanwise variations of surface shear stress, amounting to 10% or more, may be produced in nominally two-dimensional boundary layers by a spatial instability of the flow through the wind-tunnel damping screens: boundary layers are shown theoretically to be very sensitive to variations of free-stream direction. Screens with open-area ratios more than about 0·57 do not produce appreciable spanwise variations in the boundary layer, and it is recommended that tunnels for boundary-layer measurements should be fitted with such screens. The critical open-area ratio does not seem to depend noticeably on Reynolds number in the usual range encountered in wind tunnels, but the figure of 0·57 should not be taken as general until measurements have been made in representative selection of wind tunnels in other laboratories.

Automatic fringe analysis with a computer image-processing system

Abstract: The application of a general-purpose image-processing computer system to automatic fringe analysis is presented. Three areas of application have been examined where the use of a system based on a random access frame store has enabled a processing algorithm to be developed to suit a specific problem. Furthermore, it has enabled automatic analysis to be performed with complex and noisy data. The applications considered are strain measurement by speckle interferometry, position location in three axes, and fault detection in holographic nondestructive testing. A brief description of each problem is presented, followed by a description of the processing algorithm, results, and timings.