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.

CVI. A molecular theory of friction

Abstract: (1929). CVI. A molecular theory of friction. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 7, Supplement, pp. 905-939.

The Luminous Efficiency of Rays Entering the Eye Pupil at Different Points

Abstract: The effect to be described in this paper was discovered in attempting to develop an apparatus for measuring the area of the eye pupil, using a photometric principle. The idea involved is made clear by the diagram fig. 1. The subject applies his eye to the eye-ring E and fixes his eye on the aperture in the diaphragm D. He then sees a photometric field divided into two parts. The lower half is illuminated by light diffused from the opal O, which itself receives light from the lamp S. The rays from this half of the field form a diverging beam which completely fills the pupil of the subject’s eye. The upper half of the field is illuminated by the method of Maxwellian view. An image of the small aperture P is focussed by the lens L on to the middle point of the eye-ring E. This image is only about 1.5 mm. in diameter and all the light is collected by the subject’s eye, provided the pupil of the latter is concentric with the eye-ring and has a diameter exceeding 1.5 mm. A variable graduated neutral wedge W is inserted at the aperture P and this enables the two halves of the photometric field to be adjusted to equality of brightness by the subject.

The Optical Properties of 'Moth Eye' Antireflection Surfaces

Abstract: A ‘moth eye’ antireflection surface is a very fine array of protuberances which behaves as a gradation of refractive index, and which substantially reduces the reflectance. The reflection and transmission properties of such surfaces are described, and are shown to be equal to those of the best multilayer antireflection coatings.

Mobility particle size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions

Abstract: Mobility particle size spectrometers often referred to as DMPS (Differential Mobility Particle Sizers) or SMPS (Scanning Mobility Particle Sizers) have found a wide range of applications in atmospheric aerosol research. However, comparability of measurements conducted world-wide is hampered by lack of generally accepted technical standards and guidelines with respect to the instrumental set-up, measurement mode, data evaluation as well as quality control. Technical standards were developed for a minimum requirement of mobility size spectrometry to perform long-term atmospheric aerosol measurements. Technical recommendations include continuous monitoring of flow rates, temperature, pressure, and relative humidity for the sheath and sample air in the differential mobility analyzer. We compared commercial and custom-made inversion routines to calculate the particle number size distributions from the measured electrical mobility distribution. All inversion routines are comparable within few per cent uncertainty for a given set of raw data. Furthermore, this work summarizes the results from several instrument intercomparison workshops conducted within the European infrastructure project EUSAAR (European Supersites for Atmospheric Aerosol Research) and ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) to determine present uncertainties especially of custom-built mobility particle size spectrometers. Under controlled laboratory conditions, the particle number size distributions from 20 to 200 nm determined by mobility particle size spectrometers of different design are within an uncertainty range of around ±10% after correcting internal particle losses, while below and above this size range the discrepancies increased. For particles larger than 200 nm, the uncertainty range increased to 30%, which could not be explained. The network reference mobility spectrometers with identical design agreed within ±4% in the peak particle number concentration when all settings were done carefully. The consistency of these reference instruments to the total particle number concentration was demonstrated to be less than 5%. Additionally, a new data structure for particle number size distributions was introduced to store and disseminate the data at EMEP (European Monitoring and Evaluation Program). This structure contains three levels: raw data, processed data, and final particle size distributions. Importantly, we recommend reporting raw measurements including all relevant instrument parameters as well as a complete documentation on all data transformation and correction steps. These technical and data structure standards aim to enhance the quality of long-term size distribution measurements, their comparability between different networks and sites, and their transparency and traceability back to raw data. © Author(s) 2012.

Theory, developments and applications of optical coherence tomography

Abstract: In this paper, we review the developments in optical coherence tomography (OCT) for three-dimensional non-invasive imaging. A number of different OCT techniques are discussed in some detail including time-domain, frequency-domain, full-field, quantum and Doppler OCT. A theoretical treatment is given and some relevant comparisons made between various implementations. The current and potential applications of OCT are discussed, with close attention paid to biomedical imaging and its metrological issues.