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.

The theory of carbon chemical shifts in N.M.R.

Abstract: An independent electron molecular orbital theory of diamagnetism is used to calculate carbon chemical shifts for some simple molecules characteristic of important organic groups. The molecules considered are ethane, ethylene, acetylene, allene, carbon disulphide, carbonate and formaldehyde. The theory predicts (1) a low field shift for molecules with low electronic excitation energies, (2) a high field shift if the carbon atom has high electron density, and (3) a multiple bond effect which may be estimated from molecular orbital bond orders between neighbouring atoms. It is shown that reasonable quantitative assumptions about these three effects in the molecules considered lead to calculated chemical shifts in satisfactory agreement with experimental data.

Surface texture measurement for additive manufacturing

Abstract: The surface texture of additively manufactured metallic surfaces made by powder bed methods is affected by a number of factors, including the powder's particle size distribution, the effect of the heat source, the thickness of the printed layers, the angle of the surface relative to the horizontal build bed and the effect of any post processing/finishing. The aim of the research reported here is to understand the way these surfaces should be measured in order to characterise them. In published research to date, the surface texture is generally reported as an Ra value, measured across the lay. The appropriateness of this method for such surfaces is investigated here. A preliminary investigation was carried out on two additive manufacturing processes—selective laser melting (SLM) and electron beam melting (EBM)—focusing on the effect of build angle and post processing. The surfaces were measured using both tactile and optical methods and a range of profile and areal parameters were reported. Test coupons were manufactured at four angles relative to the horizontal plane of the powder bed using both SLM and EBM. The effect of lay—caused by the layered nature of the manufacturing process—was investigated, as was the required sample area for optical measurements. The surfaces were also measured before and after grit blasting.

Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables

Abstract: Detecting ocean-floor seismic activity is crucial for our understanding of the interior structure and dynamic behavior of Earth. However, 70% of the planet’s surface is covered by water, and seismometer coverage is limited to a handful of permanent ocean bottom stations. We show that existing telecommunication optical fiber cables can detect seismic events when combined with state-of-the-art frequency metrology techniques by using the fiber itself as the sensing element. We detected earthquakes over terrestrial and submarine links with lengths ranging from 75 to 535 kilometers and a geographical distance from the earthquake’s epicenter ranging from 25 to 18,500 kilometers. Implementing a global seismic network for real-time detection of underwater earthquakes requires applying the proposed technique to the existing extensive submarine optical fiber network.

On convection velocities in turbulent shear flows

Abstract: The problem of defining an effective velocity of convection for turbulent fluctuations in a shear flow is considered, and the definitions adopted by various workers are discussed. An experiment in the shear layer of a circular jet has shown that the usual definitions, based on peaks of the space-time correlations of the fluctuations, yield convection velocities whose magnitudes depend on the value of space or time separation chosen. An alternative approach shows that, by considering the turbulent field as a superposition of harmonic travelling waves, a wave-number/velocity spectrum can be defined that lends itself to the definition of a wave-number-dependent convection velocity and an overall convection velocity, both of which have real physical significance. An experimental technique is described for obtaining the spectrum, and results are presented for one position in the shear layer of the jet.

Usability is Quality of Use

Abstract: Publisher Summary This chapter discusses the distinction between broad and narrow approaches to usability and identifies the broad approach to usability with the higher level quality objective of quality of use. It is suggested that quality of use should be the major design objective for an interactive product. This relates usability to business objectives and elevates usability from an optional extra to the prime design goal. The narrow approach is complementary and is concerned with the design of features of the product that are a pre-requisite for quality of use. The two different interpretations of usability lead to two approaches to the specification and evaluation of usability. The chapter describes that user-based evaluation can be used to validate achievement of these requirements. Usability attributes provide a contribution to achieving quality of use. The presence or absence of these attributes can be verified early in design. In addition, frequent user-based evaluation of early mock-ups and prototypes is required to give feedback on the quality of use of potential solutions.