Showing papers by "National Physical Laboratory published in 1985"
TL;DR: In this article, a new electrical-substitution absolute radiometer operating at 5 K, based on a standard commercial helium cryostat, which has been developed at NPL for optical radiant power measurements, is described.
Abstract: The adoption in 1979 of a new definition of the candela, which permitted a detector-based approach to the realization of the unit, has emphasized the importance of high-accuracy absolute radiation detectors. This paper describes a new electrical-substitution absolute radiometer operating at 5 K, based on a standard commercial helium cryostat, which has been developed at NPL for optical radiant-power measurements. The principal advantages of operating the radiometer at liquid helium temperatures are that the detector can be a large, highly absorbing cavity (absorptivity 99.998%) and that exact equivalence of electrical and radiant heating can be clearly demonstrated. It will be the primary absolute detector for a new realization of the candela at NPL and will provide the basis for the development of a wider range of radiometric and spectroradiometric standards. The use of the radiometer to measure the radiant power of an intensity-stabilized laser source at the milliwatt level with an uncertainty of 4 parts in 105 is also described, together with its application in the determination of the responsivity of transfer-standard detectors, such as silicon photodiodes.
248 citations
TL;DR: The total radiant exitance of a black body at the temperature of the triple point of water, T$\text{tp}}$ (273.16 K), and at a series of other temperatures in the range from about 233 K (-40 degrees C) to 373 K (100 degrees C), has been measured by using a cryogenic radiometer as discussed by the authors.
Abstract: The total radiant exitance of a black body at the temperature of the triple point of water, T$\_{\text{tp}}$ (273.16 K), and at a series of other temperatures in the range from about 233 K (-40 degrees C) to 373 K (100 degrees C), has been measured by using a cryogenic radiometer. From the measurements at T$\_{\text{tp}}$ a value for the Stefan-Boltzmann constant $\sigma $ has been calculated: $\sigma $ = (5.669 67 $\pm $ 0.000 76) $\times $ 10$^{-8}$ W m$^{-2}$ K$^{-4}$. This is the first radiometric determination of $\sigma $ having an uncertainty comparable with that calculated directly from fundamental physical constants. This measured value differs from the calculated one by 13 parts in 10$^{5}$, which is less than the combined standard deviations of the measured and calculated values. From the measurements of exitance at the other temperatures, values of the corresponding thermodynamic temperature T have been calculated by using Stefan's fourth-power law. Since the temperature of the radiating black body was also measured by platinum resistance thermometers calibrated on IPTS-68, values of (T-T$\_{68}$) were obtained. These range from about -(5 $\pm $ 1.6) mK at 20 degrees C to -(28 $\pm $ 2.5) mK at 100 degrees C and +(5 $\pm $ 1.5) mK at -40 degrees C. The results confirm to within a few millikelvins the departure of T$\_{68}$ from T above 0 degrees C already discovered by gas thermometry and show that similar departures, but of opposite sign, exist down to the lowest temperature measured, -40 degrees C. The uncertainties associated with these new values of T and (T-T$_{68}$) are similar to those of the best gas thermometry.
135 citations
TL;DR: In this paper, a cooperative climb over groups of particles leads to a resistance to deformation, rather than a threshold stress that is insensitive to the particle size but which depends strongly on applied stress.
124 citations
TL;DR: The absorption coefficient of p + -, p - -and n - -doped Ga 0.47 In 0.53 As layers, grown lattice-matched to InP, has been calculated over the wavelength range 1.0-1.7 μm from transmission and reflection measurements.
Abstract: The absorption coefficient of p + -, p - -and n - -doped Ga 0.47 In 0.53 As layers, grown lattice-matched to InP, has been calculated over the wavelength range 1.0-1.7 μm from transmission and reflection measurements.
115 citations
TL;DR: In this paper, various models of creep deformation of composite materials are reviewed and their predictions compared with available experimental data, and the value of analysing transient creep following stress changes to elucidate the creep mechanisms is discussed.
90 citations
01 Oct 1985-Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology
TL;DR: In this paper, the design of a common-path polarimetric interferometer system, developed primarily for measuring the profiles of super-smooth surfaces, is described and measured comparisons with a mechanical stylus technique are discussed.
Abstract: The design of a common-path polarimetric interferometer system, developed primarily for measuring the profiles of ‘super-smooth’ surfaces, is described and measured comparisons with a mechanical stylus technique are discussed. The instrument has a sensitivity to changes in surface height of better than 0.1 nm and is capable of a lateral resolution of 1 μm with a helium-neon laser light source.
63 citations
TL;DR: In this article, the Helmholtz Reciprocity Principle is used to determine reflection properties of materials or components, and their validity depends on their validity on the principle of reciprocity.
Abstract: Many measurements of reflection properties of materials or components depend for their validity on the Helmholtz Reciprocity Principle. Yet this principle is widely misunderstood, and is stated in ...
63 citations
TL;DR: In this article, a diffuse reflectometer/transmissometer was designed to determine a complete set of absolute spectral radiometric quantities for any kind of sample, whether or not it has a regular component of reflectance or transmittance.
59 citations
TL;DR: In this paper, a new method of precursor modification was proposed which not only reduced the activation energy of cyclization but also improved the properties of the resulting carbon fibres, showing an improvement in tensile strength and Young's modulus.
58 citations
TL;DR: The radiolytic reduction of dichromate ion in acidic aqueous solution has been investigated as a potential dosimetry system for the 10 −40 kGy range of absorbed dose as mentioned in this paper.
36 citations
TL;DR: A Monostatic acoustic sounder has been operating at the National Physical Laboratory, New Delhi (India) for several years as discussed by the authors for the period from May 1977 to April 1982, and a systematic classification of the observed structure has also been proposed to give information on the prevailing Pasquill stability category which determines pollution dispersion.
TL;DR: Doppler-free spectra of 130 Te 2 have been investigated in the region of 486 nm, close to the Balmer-β transitions atomic hydrogen and deuterium as discussed by the authors.
TL;DR: In this paper, a heteropoly blue method with ascorbic acid and antimony as reducing agents was used to determine silica in water, which is comparatively fast and sensitive.
TL;DR: In this article, the effect of sulphide inclusions on the corrosion fatigue of mild steel in 0.6 M NaCl solutions was studied and it was shown that a sulphur-enriched band of ferrite exists around the inclusions and that corrosion occurs in this contaminated band, both in the presence and absence of applied stress.
TL;DR: Digitization of signatures is described and features are developed to allow comparisons, and it has been possible to achieve rejection of 97% of examples of name writing which were not genuine signatures, at thresholds which accepted 90% of authentic signatures.
Abstract: Digitization of signatures is described and features are developed to allow comparisons. Using data reduction techniques, a list of between 2 and 7 values can be obtained to give a coded description of a signature, which can subsequently be used in authentications. Between one and six specimens can give an adequate database. Thus it has been possible to achieve rejection of 97% of examples of name writing which were not genuine signatures, at thresholds which accepted 90% of authentic signatures. The system may provide some support to document examiners in cases of skilled forgery, and is of limited value in author identification.
TL;DR: In this paper, a hot box type solar cooker having a double glass cover and a plane mirror reflector has been tested for its thermal performance in different months in Delhi and the data suggest that modifications are needed in the cooker design if it is to be used satisfactorily throughout the year in Delhi.
TL;DR: It is shown that the Gadd Severity Index and the Head Injury Criterion are plausible and fundamentally correct forms of criteria, in contrast to criticisms which have appeared in the literature.
TL;DR: In this article, it has been shown that it is necessary to restrict the applied bias voltage to the very minimum necessary to produce photocurrent saturation, otherwise non-reversible degradation of quantum efficiency may occur.
Abstract: Oxide-bias measurement techniques to determine front-surface recombination losses in the silicon photodiode self-calibration technique have been investigated. With the water-drop method it has been shown necessary to restrict the applied bias voltage to the very minimum necessary to produce photocurrent saturation, otherwise non-reversible degradation of quantum efficiency may occur. The corona technique has been found to give satisfactory results only on initial application, as a drastic increase in front-region recombination loss is produced.
TL;DR: In this article, the depth resolution of evaporated silver layers on polished polycrystalline copper substrates was studied at various temperatures during argon ion sputtemg with AES, and a detailed analysis of the profile shape at the interface revealed the nature of contributions to the terms governing interface resolution.
TL;DR: In this article, a method of extracting displacement components from a double exposure holographic interferogram is described, which involves the determination of fringe order at different positions on the reconstruction, from a number of viewing directions.
Abstract: The quantitative evaluation of holographic interferometer fringes for the determination of components of three-dimensional deformation requires the accurate measurement of many fringe patterns. The use of computer image analysis techniques plays an important part in achieving rapid quantitative interferogram interpretation. One method of extracting displacement components from a double exposure holographic interferogram is described. This involves the determination of fringe order at different positions on the reconstruction, from a number of viewing directions. The techniques of fringe analysis used to give vector displacements are presented.
TL;DR: In this article, a prototype free precession magnetometer is described which uses a SQUID to detect the precessing nuclear magnetisation of a sample of 3He and the expected sensitivity is compared with that of a simple SQUID.
Abstract: A prototype free precession magnetometer is described which uses a SQUID to detect the precessing nuclear magnetisation of a sample of3He. The expected sensitivity is compared with that of a simple SQUID . Other advantages to be gained from this low noise absolute magnetometer are also discussed.
TL;DR: Differences of up to 40% in the spatial-average temporal-average and spatial-peak pulse-average intensities are shown to be a result of the different definitions of beam area and pulse duration.
Abstract: Comparison is made between the values obtained for the acoustic output from different types of medical ultrasonic equipment when determined according to the definitions given in different documents. In particular, the American Institute of Ultrasound in Medicine with the National Electrical Manufacturers Association Safety Standard for Diagnostic Ultrasound Equipment, the U.S. Food and Drug Administration Diagnostic Ultrasound Reporting Guide (1980) and the proposed International Electrotechnical Commission standard are compared for pulse-echo and Doppler equipment. Differences of up to 40% in the spatial-average temporal-average and spatial-peak pulse-average intensities are shown to be a result of the different definitions of beam area and pulse duration.
TL;DR: In this article, the NPL realization of the SI ohm using a calculable capacitor was described and the present determination gives?NPL -?SI = (-0.97 ± 0.09)?? on August 15, 1983.
Abstract: Further developments in the NPL realization of the SI ohm using a calculable capacitor are described. The present determination gives ?NPL - ?SI = (-0.97 ± 0.09) ?? on August 15, 1983.
TL;DR: In this article, new vapor pressure equations were derived for 4He and 3He in terms of the Provisional 05 to 30 K temperature Scale (EPT-76) for 3He and 4He.
Abstract: Attention is drawn to new vapor pressure equations which have been derived for4He and3He in terms of the Provisional 05 to 30 K temperature Scale (EPT-76) These equations should now be used in place of the T58 table for4He and the T62 equation for3He Although the EPT-76 extends only to 05 K, the new3He equation is valid down to 02 K
TL;DR: In this article, it was shown that inhomogeneities in glasses may give rise to apparent height changes of 1 nm or more, significantly greater than the claimed sensitivities of interferometers now coming into use for the measurement of surface roughness, and experimental verification is called for.
Abstract: Interferometry provides a measure of optical and not of geometrical path difference. In interferometric measurements of topography, optical inhomogeneities may therefore be misinterpreted as changes in micro-topography. An estimate of the magnitude of this effect shows that inhomogeneities in glasses may give rise to apparent height changes of 1 nm or more. This is significantly greater than the claimed sensitivities of interferometers now coming into use for the measurement of surface roughness, and experimental verification is called for.
01 Jan 1985
TL;DR: A major intercomparison of balloon-borne stratospheric sensors took place in fall 1982 and spring 1983 as discussed by the authors, where 4 gondolas were launched close together from Palestine, Texas.
Abstract: Major intercomparisons of balloon-borne stratospheric sensors took place in fall 1982 and spring 1983. In each campaign, 4 gondolas were launched close together from Palestine, Texas. Profiles of many constituents were determined by a variety of instruments, both radiometric and spectrometric, some observing the sun and some sensing atmospheric emission. Column amounts of some constituents were determined by supporting spectroscopic measurements from the ground and from aircraft.
TL;DR: In this article, the difference between the International Practical Temperature Scale (IPTS-68) and thermodynamic temperature in the range 457 °C-630 °C using the NPL photon-counting pyrometer was measured.
Abstract: This paper describes the measurement of the difference between the International Practical Temperature Scale (IPTS-68) and thermodynamic temperature in the range 457 °C-630 °C using the NPL photon-counting pyrometer. This instrument operates at sufficiently low radiance temperatures to allow the gas thermometry results of Guildner and Edsinger, which cover the range from 0 °C to 457 °C, to be extended upwards. The results agree well with the recent measurements of Jung (1984). Their implications with respect to the differences at still higher temperatures are discussed briefly.
TL;DR: In this paper, the relativistic predictions for the nonlinear calibration of a spherical sector electron spectrometer, operated with retardation in the constant δ E / E mode, are verified to an accuracy of ± 0.05 eV over the energy range 0-2500 eV.
TL;DR: In this article, upper bounds on the intensity of any discrete structure that may be superimposed on the generally accepted form of the broad far-infrared absorption profile of liquid acetonitrile are presented.