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Showing papers by "National Physical Laboratory published in 1978"


Journal ArticleDOI
TL;DR: A new algorithm is described for indefinite quadratic programming which utilizes methods for updating positivedefinite factorizations only and can be used for the positive-definite case without loss of efficiency.
Abstract: Numerically stable algorithms for quadratic programming are discussed. A new algorithm is described for indefinite quadratic programming which utilizes methods for updating positivedefinite factorizations only. Consequently all the updating procedures required are common to algorithms for linearly-constrained optimization. The new algorithm can be used for the positive-definite case without loss of efficiency.

166 citations


Journal ArticleDOI
TL;DR: In this article, the vapour pressure of a liquid mixture is determined accurately by a static method and a new apparatus has been described, which is designed to work in the temperature range 298.15 to 423.15 K for pressures up to 1.5 MPa.

127 citations


Journal ArticleDOI
TL;DR: In this article, the solution obtained by Cox and Isham to correct coincidence counting data for the effects of dead time and accidental coincidences between events in the two detectors, where one non-extending dead time is an integer multiple of the other, is discussed in detail.

121 citations


Journal ArticleDOI
TL;DR: In this paper, a polarization interferometer employing free standing wire grid polarizer and beamsplitter and reflection dispersive Fourier transform spectrometry is used to determine the optical constants of water in the region 5-220cm −1.

95 citations


Journal ArticleDOI
TL;DR: A series of glasses of stoichiometric composition with varying proportions of TiO2 and/or ZrO2 as nucleating agent have been studied to examine the effect of nucleation addition on the sequence of crystallization and transformation to the stable phase, cordierite.
Abstract: A series of glasses of stoichiometric composition with varying proportions of TiO2 and/or ZrO2 as nucleating agent have been studied to examine the effect of nucleation addition on the sequence of crystallization and transformation to the stable phase, cordierite. It is shown that TiO2 is the most effective nucleating agent and that if large amounts of ZrO2 are substituted for TiO2 cristobalite forms as an intermediate phase and is associated with rapid volume changes and consequently with weak porous products. Substitution of ZrO2 for TiO2 also causes other changes in phase development, especially in the relative proportions of β-quartz solid solution and magnesian petalite produced during the early stages of crystallization. The use of a combination of experimental techniques (dilatometry, DTA, X-ray diffraction and electron microscopy) has proved most effective in studying phase development and the relationship between processing characteristics and composition.

89 citations


Book ChapterDOI
TL;DR: Although the aim of the research is to develop techniques useful to the engineer, developments are also being made in the use of speckle patterns for information processing, where the pattern is employed as an optical carrier.
Abstract: Publisher Summary This chapter discusses the nature of the speckle pattern and defines some of its basic characteristics. The speckle effect in optics is the generation of a random intensity pattern formed when coherent light is scattered by a rough surface or is diffused by a medium containing scattering centers. The chapter concentrates on the instrumental aspects of speckle interferometry and their applications rather than a detailed theoretical treatment. It is seen that a considerable degree of ingenuity has had to be employed to overcome the inherent difficulties that occur when interference takes place among randomly distributed phase fields rather than among smoothly varying ones. Although the aim of the research is to develop techniques useful to the engineer, developments are also being made in the use of speckle patterns for information processing, where the pattern is employed as an optical carrier.

60 citations


Journal ArticleDOI
TL;DR: In this article, a thin protective oxide formed on a Ni-197 Cr-24 Al alloy in air at 850°C was examined and it was shown that the oxide was duplex with an inner chromium-rich layer of NiCr2O4 + Cr2O3 with probably some NiAl2O 4 + Al2O 3 + NiO 3 and an outer nickel rich layer, principally NiO The oxide grew faster in the presence of NaCl and it differed significantly in microstructure and composition from a very early stage.
Abstract: A thin protective oxide formed on a Ni-197 Cr-24 Al alloy in air at 850°C Microstructural examination of stripped films showed that the oxide was duplex with an inner chromium-rich layer of NiCr2O4 + Cr2O3 with probably some NiAl2O4 + Al2O3, and an outer nickel-rich layer, principally NiO The oxide grew faster in the presence of NaCl and it differed significantly in microstructure and composition from a very early stage The thicker regions of the oxide assumed regular polyhedral shapes in air + NaCl, rather than the irregular nodular shape exhibited in clean air, as well as becoming richer in chromium The results suggest that chloride vapor increases cationic mobility in the oxide It is proposed that Cl− ions are incorporated in the oxygen close-packed lattice, thereby increasing ionic mobility in Cr2O3

57 citations


Journal ArticleDOI
TL;DR: In this article, a number of beam-splitter designs utilizing thin metal films are discussed, and it is shown that, using conventional techniques, the required phase difference can be readily achieved using, for example, combinations of gold, chromium and aluminium films.
Abstract: The measurement of displacement using a Michelson-type interferometer requires a beam-splitter coating that ideally produces two signals in phase quadrature. In this paper a number of beam-splitter designs utilizing thin metal films are discussed. Problems associated with film deposition and monitoring are considered, and it is shown that, using conventional techniques, the required phase difference can be readily achieved using, for example, combinations of gold, chromium and aluminium films.

54 citations


Journal ArticleDOI
TL;DR: A servocontrolled 1-m plane-parallel Fabry-Perot interferometer has been developed at NPL for the precise intercomparison of laser wavelengths and has been used to measure the wavelength ratio of a 679-nm radiation and that from a 633-nm iodine-stabilized He-Ne laser.
Abstract: A servocontrolled 1-m plane-parallel Fabry-Perot interferometer has been developed at NPL for the precise intercomparison of laser wavelengths. This instrument has been used to measure the wavelength ratio of a 679-nm radiation and that from a 633-nm iodine-stabilized He–Ne laser, achieving an accuracy of 2.9 parts in 1011. The 679-nm light was derived from a stabilized CO2 laser radiation by upconversion, and the wavelength of this 9.3-μm laser radiation can be calculated from the visible wavelength result. Frequency measurements on the same CO2 laser radiation have already been made in this laboratory, so that the experiment reported here leads to a precise value for the speed of light in vacuum and to the value of 473, 612, 380.5 ± 0.3 MHz for the absolute frequency of the visible radiation from a He–Ne laser stabilized to component d of127I2.

44 citations


Journal ArticleDOI
TL;DR: In this article, the accuracy of interpolation by means of the equation with the fewest coefficients was investigated with a view to its use for estimating the vapour pressures of compounds for which the data are incomplete.

43 citations


Journal ArticleDOI
TL;DR: In this paper, the enthalpy of combustion of 1,1, 1,2,2-tetrachloroethane at 29815 K was determined by rotating-bomb calorimetry.

Journal ArticleDOI
01 Jun 1978-Polymer
TL;DR: In this article, the thermodynamic state of densified glasses is discussed and the authors make use of differential scanning calorimetry (d.s.c.) and specific volume measurements on polystyrene glasses formed by cooling from the melt under pressure.

Journal ArticleDOI
TL;DR: In this paper, the shrinkage of polyacrylonitrile (PAN) fibres is reported to occur from 200°C to 1000°C, the extent of which has been found to depend on the time of preoxidation, the type of oxidizing gas and the carbonization conditions.
Abstract: A systematic study of the shrinkage taking place during the carbonization of polyacrylonitrile (PAN) fibres is reported Shrinkage occurs from 200°C to 1000°C, the extent of which has been found to depend on (a) the time of preoxidation, (b) the type of oxidizing gas and (c) the carbonization conditions The carbonization shrinkage is found to be independent of length changes during the preoxidation but can decrease from the usual 23% to about 2% by applying tension during the carbonization A reaction is proposed to explain the shrinkage between 600°C and 800°C The strength as well as Young's modulus of carbon fibres of under-oxidized fibres can be improved by applying tension during the carbonization It is further predicted that the mechanical properties of carbon fibres preoxidized to the optimal level would decrease if carbonized under excessive tension Das Schrumpfen von PAN-Fasern wahrend der Carbonisierung wurde untersucht Das Schrumpfen erfolgt bei Temperaturen zwischen 200 und 1000°C, wobei das Ausamas von der Voroxidationszeit, der oxidierenden Atmosphare und den Carbonisierungsbedingungen abhangt Die Schrumpfung erwies sich als unabhangig von den Langenanderungen wahrend der Voroxidation, jedoch von 23%auf2% verringert werden, wenn wahrend der Carbonisierung ein Zug ausgeubt wird Es wird eine Reaktion vorgeschlagen, die die Schrumpfung zwischen 600 und 800°C erklart Mechanische Eigenschaften der Fasern konnen durch Ausubung von Zug wahrend der Carbonisierung verbessert werden

Journal ArticleDOI
TL;DR: In this article, the real refractive index of water vapour between 10 and 50 cm −1 using the Gross line shape has been compared with measurements made using dispersive Fourier transform spectrometry.

Journal ArticleDOI
TL;DR: In this article, a method for computing the coefficients of a vapour-pressure equation applicable over a long range from observed values in a limited range is described, and the equation used is one proposed by Wagner.

Journal ArticleDOI
TL;DR: Four steplength algorithms are presented for minimizing a class of nondifferentiable functions which includes functions arising froml1 andl∞ approximation problems and penalty functions arisingfrom constrained optimization problems.
Abstract: Four steplength algorithms are presented for minimizing a class of nondifferentiable functions which includes functions arising from $\ell_1$ and $\ell_\infty$ approximation problems and penalty functions arising from constrained optimization problems Two algorithms are given for the case when derivatives are available wherever they exist and two for the case when they are not available We take the view that although a simple steplength algorithm may be all that is required to meet convergence criteria for the overall algorithm, from the point of view of efficiency it is important that the step achieve as large a reduction in the function value as possible, given a certain limit on the effort to be expended The algorithms include the facility for varying this limit, producing anything from an algorithm requiring a single function evaluation to one doing an exact linear search They are based on univariate minimization algorithms which we present first These are normally at least quadratically convergent when derivatives are used and superlinearly convergent otherwise, regardless of whether or not the function is differentiable at the minimum

Journal ArticleDOI
TL;DR: An extension of a theory of linear viscoelastic fracture is derived in this paper, which removes a former restriction that Poisson's ratio is a constant and includes both material property characteristics, i.e. the bulk (dilatation) and shear (distortion) linear viscocelastic compliances.
Abstract: An extension of a theory of linear viscoelastic fracture is derived which removes a former restriction that Poisson's ratio is a constant. The new formulation thus includes both material property characteristics, i.e. the bulk (dilatation) and shear (distortion) linear viscoelastic compliances. Characteristic crack growth laws, assuming a Dugdale region ahead of the crack, are developed for creep laws which depend linearly upon time but are thought to be representative of more general materials. Examples include a single crack, a linear array of cracks, and a specialized cyclic load application.

Journal ArticleDOI
01 May 1978-Pramana
TL;DR: In this paper, the effect of heat treatment in oxygen atmosphere, rate of deposition and the extent of Al doping on the resistivity, photo-response spectral characteristics, rise and decay time of photo-current, etc.
Abstract: Photoelectric properties of pure and Al doped vacuum deposited CdS films have been studied to explore the possibility of their application in photoactivated liquid crystal light valves. The effect of heat treatment in oxygen atmosphere, rate of deposition and the extent of Al doping, etc. on the resistivity, photo-response spectral characteristics, rise and decay time of photo-current, etc. have been investigated. It has been found that in contrast to pure CdS films, the properties of Al-doped films significantly depend on both the rate of deposition and the extent of Al doping. The dark resistivity in all cases was found to increase with heat treatment in oxygen. Unlike pure CdS films, Al doped films show photo-conductivity which is enhanced by heat treatment. Al doped films deposited at higher rates show better photo response even at lower light levels. At various light levels the rise and decay time of Al-doped films were found to be fairly constant and lower than that for pure CdS films. All these properties have been explained in terms of the presence of trapping levels due to doping. These trapping levels are also indicated by TSC, optical absorption and EPR studies.


Journal ArticleDOI
01 Jul 1978-Nature
TL;DR: The authors reported independent determinations of the [HNO3]/[NO2] ratio which apparently support the measured values2 at levels above 25 km, but which are nearer the calculated values below this level.
Abstract: A RECENT NASA report1 discussed the relative amounts of nitric acid and nitrogen dioxide present in the stratosphere, and pointed out that the values of the ratio [HNO3]/[NO2] measured by Evans et al.2 are, in fact, considerably lower than the values predicted theoretically using the latest values for rate constants and photodissociation coefficients for the appropriate reactions. This letter reports independent determinations of the [HNO3]/[NO2] ratio which apparently support the measured values2 at levels above 25 km, but which are nearer the calculated values below this level.

Journal ArticleDOI
TL;DR: In this article, the use of platinum as secondary emitter is anticipated to result in 100 000 hours of life of crossed-field devices and this device provides the flexibility of sophisticated wave shape pattern generation.
Abstract: Crossed-Field Devices are high-power devices and are associated with high efficiency, small weight, adequate bandwidth and good performance as regards various parameters such as phase coherence, jitter, fast frequency sweep and phase versus frequency. Distributed-emission type devices using cold secondary emitter cathode have the advantage of no heater requirement and thereby stand-by requirements are eliminated. Use of platinum as secondary emitter is anticipated to result in 100 000 hours of life of crossed-field devices. In linear format costly modulator is not required and this device provides the flexibility of sophisticated wave shape pattern generation. A number of tubes can be operated in parallel resulting in high output power and at the same time providing redundancy to prevent a total system failure if one tube fails. Same tube type with power dividers can be used as a driver as well as the PA, thereby simplifying the logistics. Life of microwave tubes can be significantly increased and mainten...

Journal ArticleDOI
TL;DR: In this article, an absolute method for the determination of complex reflectivity has been applied to a specimen of high purity silicon between 5 and 120 cm −1 at 290 K, establishing its amplitude reflectivity with a precision of 10 −4.

Journal ArticleDOI
TL;DR: In this article, a modular interferometer is described that has been used for dispersive Fourier transform determinations of the complex Fresnel reflectivities of absorbing solids from 5 to 450 cm −1 at ambient temperature.

Journal ArticleDOI
01 Mar 1978-Vacuum
TL;DR: In this article, a description of an apparatus used at the National Physical Laboratory for the calibration of vacuum gauges in the range 10−4-10 Pa by the orifice flow method is given.

Journal ArticleDOI
TL;DR: In this paper, the frequencies of four lasing transitions in CH 3 OD have been measured to accuracies of a few parts in 10 7 by comparison with a microwave oscillator near 20 GHz via a Josephson harmonic mixer.

Proceedings ArticleDOI
18 Apr 1978
TL;DR: In this paper, a direct experimental comparison of speckle photography with photoelasticity and with finite element analysis on a notched tensile test specimen showed that serious errors could occur due to local surface tilting and to aberrations of the imaging lens.
Abstract: Speckle photography is a simple technique for measuring displacement in the plane of a surface, so allowing the strain field to be evaluated in two dimensions. A direct experimental comparison of speckle photography with photoelasticity and with finite element analysis on a notched tensile test specimen showed that serious errors could, however, occur due to local surface tilting and to aberrations of the imaging lens. Methods of minimising these effects and those of the speckle decorrelation that can also take place, are discussed.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Journal ArticleDOI
TL;DR: In this article, a 30:1 scale model technique has been developed for investigating the propagation of noise from traffic on major roads and motorways and validation studies have been carried out for a range of different road/housing configurations by comparing relative noise levels obtained using the model with field data obtained specifically for the purpose.


Journal ArticleDOI
TL;DR: In this paper, samples of n type GaAs implanted with 1015Zn+/cm2 at room temperature were irradiated with a ruby laser of pulse length 0.8 ms.
Abstract: Samples of n type GaAs implanted with 1015Zn+/cm2 at room temperature were irradiated with a ruby laser of pulse length 0.8 ms. For samples coated with Si3N4 a laser energy of 1.5?2.5 J/cm2 produced electrical activity of 40?50% of the implanted dose. Peak hole concentrations up to about 7 × 1019 cm?3 were measured. Uncoated samples irradiated with similar laser energies were not electrically active.

Journal ArticleDOI
TL;DR: The refractive index of a germanium prism was measured by two different laboratories for wavelengths in the 8-14-microm range and agreed to within 0.0003 in agreement with the uncertainty analysis presented.
Abstract: The refractive index of a germanium prism was measured by two different laboratories for wavelengths in the 8–14-μm range. The sample was a single crystal of known purity and growth history. Index results from the two experiments agreed to within 0.0003 in agreement with the uncertainty analysis presented.