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.

Focusing of high-intensity ultrasound through the rib cage using a therapeutic random phased array.

Abstract: A method for focusing high-intensity ultrasound (HIFU) through a rib cage that aims to minimize heating of the ribs while maintaining high intensities at the focus (or foci) was proposed and tested theoretically and experimentally Two approaches, one based on geometric acoustics and the other accounting for diffraction effects associated with propagation through the rib cage, were investigated theoretically for idealized source conditions It is shown that for an idealized radiator, the diffraction approach provides a 23% gain in peak intensity and results in significantly less power losses on the ribs (1% vs 75% of the irradiated power) compared with the geometric one A 2-D 1-MHz phased array with 254 randomly distributed elements, tissue-mimicking phantoms and samples of porcine rib cages are used in experiments; the geometric approach is used to configure how the array is driven Intensity distributions are measured in the plane of the ribs and in the focal plane using an infrared camera Theoretical and experimental results show that it is possible to provide adequate focusing through the ribs without overheating them for a single focus and several foci, including steering at ± 10–15 mm off and ± 20 mm along the array axis Focus splitting caused by the periodic spatial structure of ribs is demonstrated both in simulations and experiments; the parameters of splitting are quantified The ability to produce thermal lesions with a split focal pattern in ex vivo porcine tissue placed beyond the rib phantom is also demonstrated The results suggest that the method is potentially useful for clinical applications of HIFU, for which the rib cage lies between the transducer(s) and the targeted tissue (E-mail: vera@aplwashingtonedu)

Altitude profiles of aerosol BC, derived from aircraft measurements over an inland urban location in India

Abstract: [1] Altitude profiles of aerosol black carbon (BC) in the atmospheric boundary layer and above it were measured for the first time in India, over the urban location Hyderabad, onboard an aircraft during two consecutive days of February 2004. The profiles on both the days were consistent, and showed a rapid decrease in BC concentration within the boundary up to ∼550 m AGL (where convective activity prevailed). Sodar measurements from the nearby location revealed the mean boundary layer height to be ∼600 m during the flight period. The decrease in BC above the boundary layer was quite weak up to ∼2.2 km AGL.

Dielectric dispersion in pure polar liquids at very high radio-frequencies I. Measurements on water, methyl and ethyl alcohols

Abstract: The results are given of some measurements of the absorption coefficient and refractive index of water, methyl and ethyl alcohols at wave-lengths of 6·2 mm, 1·24 cm and 3·21 cm over the temperature range —10 to 50°C, including some observations on water in the supercooled state. The method used is based upon the fact that the rate of attenuation of radio-frequency energy along a wave-guide filled with the liquid is dependent upon both the absorption coefficient and the refractive index when the guide is operated near to the cut-off condition. The electrical characteristics of water vary in a continuous manner through the normal freezing-point of 0°C down to at least —8°C. The measurements indicate that both alcohols, like water, have relatively high atomic polarizations.

Towards geometrical calibration of x-ray computed tomography systems—a review

Abstract: Industrial x-ray computed tomography (XCT) is seen as a potentially effective tool for the industrial inspection of complex parts. In particular, XCT is an attractive solution for the measurement of internal geometries, which are inaccessible by conventional coordinate measuring systems. While the technology is available and the benefits are recognized, methods to establish the measurement assurance of XCT systems are lacking. More specifically, the assessment of measurement uncertainty and the subsequent establishment of measurement traceability is a largely unknown process. This paper is a review of research that contributes to the development of a geometrical calibration procedure for XCT systems. A brief introduction to the geometry of cone-beam tomography systems is given, after which the geometrical influence factors are outlined. Mathematical measurement models play a significant role in understanding how geometrical offsets and misalignments contribute to error in measurements; therefore, the application of mathematical models in simulating geometrical errors is discussed and the corresponding literature is presented. Then, the various methods that have been developed to measure certain geometrical errors are reviewed. The findings from this review are discussed and suggestions are provided for future work towards the development of a comprehensive and practical geometrical calibration procedure.