Showing papers by "National Physical Laboratory published in 1979"
TL;DR: In this paper, a compilation of all published measurements of electron inelastic mean free path lengths in solids for energies in the range 0-10 000 eV above the Fermi level is presented.
Abstract: A compilation is presented of all published measurements of electron inelastic mean free path lengths in solids for energies in the range 0–10 000 eV above the Fermi level. For analysis, the materials are grouped under one of the headings: element, inorganic compound, organic compound and adsorbed gas, with the path lengths each time expressed in nanometers, monolayers and milligrams per square metre. The path lengths are vary high at low energies, fall to 0.1–0.8 nm for energies in the range 30–100 eV and then rise again as the energy increases further. For elements and inorganic compounds the scatter about a ‘universal curve’ is least when the path lengths are expressed in monolayers, λm. Analysis of the inter-element and inter-compound effects shows that λm is related to atom size and the most accuratae relations are λm = 538E−2+0.41(aE)1/2 for elements and λm=2170E−2+0.72(aE)1/2 for inorganic compounds, where a is the monolayer thickness (nm) and E is the electron energy above the Fermi level in eV. For organic compounds λd=49E−2+0.11E1/2 mgm−2. Published general theoretical predictions for λ, valid above 150 eV, do not show as good correlations with the experimental data as the above relations.
4,486 citations
TL;DR: The complete distribution of hearing levels for each audiometric frequency in the range 0.125-12 kHz and at any age can be estimated with the aid of tabulated coefficients and some simple rules.
Abstract: Numerical data from the literature on presbyacusis, in the form of pure-tone hearing threshold levels as a function of age, are subjected to critical evaluation and analysis. A formula is derived for predicting the age effect for otologically screened groups of males and females. Further, the complete distribution of hearing levels for each audiometric frequency in the range 0.125-12 kHz and at any age can be estimated with the aid of tabulated coefficients and some simple rules. The study was undertaken in connection with the work of ISO on standardization of normative audiometric data.
143 citations
TL;DR: In this paper, an assessment of the 32 available equilibrium measurements for surface segregation in substitutional pure binary alloy systems has been made in relation to the various terms proposed for the free energy of segregation.
129 citations
TL;DR: In the QZ algorithm, the eigenvalues of Ax = Ax = λ$Bx are computed via a reduction to the form λ-Bx, where λ is upper triangular as mentioned in this paper.
82 citations
TL;DR: In this paper, it is shown how the probability of failure of an inhomogeneously stressed structure can be estimated from a knowledge of the expected defect population and the local fracture criterion relating the local stress for failure to the defect size.
Abstract: For brittle materials it is shown how the probability of failure of an inhomogeneously stressed structure can be estimated from a knowledge of the expected defect population and the local fracture criterion relating the local stress for failure to the defect size. Account is taken of the possibility that a sample of material contains no defects so that failure is then caused by another mechanism. It is shown that the theory presented is very closely related to the classical theory of Weibull. Furthermore it is demonstrated how account may be taken of loading uncertainties which are experienced in practice. As an example of an inhomogeneous stress state, the pure bending of a beam has been considered in detail. Such an analysis offers a convenient experimental method of determining the defect characteristics of a material. It is shown that a consistency check is possible by estimating experimentally the distribution of failure-initiating flaws and comparing it with a theoretical prediction.
67 citations
TL;DR: In this article, Quinn et al. used a transducer used to excite their acoustic interferometer, which led to low pressure curvature in their acoustic isotherm.
Abstract: The recent value of the gas constant, determined acoustically by Quinn et al. (1976), suffered from a hitherto unsuspected systematic error which was attributable to a slight nonlinearity in the transducer used to excite their acoustic interferometer. This effect, which led to low pressure curvature in their acoustic isotherm, has now been corrected for. When allowance is also made for high pressure curvature due to the third acoustic virial coefficient as determined by new measurements at higher pressures, a linear isotherm results. It exhibits the slope recently predicted by Rowlinson & Tildesley (1977) on the basis of pressure-volume-temperature measurements and of new work on the intermolecular potential of argon. The nonlinearity corrections having been made, the original work is entirely compatible with the new high pressure results and the two sets of data have been combined to form a new isotherm. A value of the gas constant $(R=8314.48$ $\text{J K}^{-1}\text{kmol}^{-1})$ has been derived from the intercept of this isotherm, which has an overall uncertainty of only 0.21 J K$^{-1}$ kmol$^{-1}$ or, fractionally, $25/10^{6}$. This value of $R$ $\text{is}$ $8/10^{6}$ above the conventionally determined, accepted value of Batuecas, $37/10^{6}$ above the new, conventionally determined value of Pereira Cordido and $1/10^{6}$ below that recently obtained by Colclough (1979a) from the comparison of gas and acoustic thermometry in the range 4.2-20 K. All these values agree with the present one to within their respective random uncertainties.
66 citations
TL;DR: The difficulties in providing accurate estimates are considered and what tests can be made in order to check the validity of the estimates obtained and it is shown that some algorithms are particularly sensitive to errors in the estimates.
Abstract: Almost all efficient algorithms for constrained optimization require the repeated computation of Lagrange-multiplier estimates. In this paper we consider the difficulties in providing accurate estimates and what tests can be made in order to check the validity of the estimates obtained. A variety of formulae for the estimation of Lagrange multipliers are derived and their respective merits discussed. Finally the role of Lagrange multipliers within optimization algorithms is discussed and in addition to other results, it is shown that some algorithms are particularly sensitive to errors in the estimates.
59 citations
TL;DR: In this paper, an experimental investigation has been made of the irreproducibility of the International Practical Temperature Scale of 1968 below 273.15 K. The results show that differences between calibrations at the fixed points are the major cause of irreproachability in IPTS-68 and progress towards a more reproducible scale will come most readily through a reassessment of the choice of defining fixed points and the manner of their realization.
Abstract: An experimental investigation has been made of the irreproducibility of the International Practical Temperature Scale of 1968 below 273.15 K. Ten national standards laboratories submitted a total of 23 capsule-type platinum resistance thermometers to NPL where, together with a further 14 NPL thermometers, they were intercompared at 50 temperatures between 4.2 and 373.15 K. Most of the thermometers submitted had been calibrated on IPTS-68 as realized in the laboratory of their origin and our measurements thus allow us not only to compare fixed point realizations and the resulting differing versions of T68, but also to separate the component of irreproducibility that results from fixed point differences from that which reflects intrinsic thermometer variation. As a result of these measurements it is clear that differences between calibrations at the fixed points are the major cause of irreproducibility in IPTS-68 and that progress towards a more reproducible scale will come most readily through a reassessment of the choice of defining fixed points and the manner of their realization.
57 citations
56 citations
01 Apr 1979-Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology
TL;DR: In this article, a bi-directional fringe-counting Michelson interferometer is described that is used in conjunction with a frequency-stabilised laser for precise length measurement.
Abstract: A bi-directional fringe-counting Michelson interferometer is described that is used in conjunction with a frequency-stabilised laser for precise length measurement. The two counting signals, in phase quadrature and sinusoidally related to path difference, are produced by a novel system that does not employ any form of modulation. Under optimum conditions, the instrument is capable of measuring displacement to a precision of 0.1 μm and the correct fringe-count is maintained even with a signal attenuation corresponding to a 99% loss of intensity in one arm of the interferometer. This performance can be further improved by the application of an automatic gain control system. The interferometer is simple in concept, cheap to produce and easy to set up and align.
55 citations
TL;DR: A detailed study of the effect of tension during low temperature stabilisation on the mechanical properties of carbon fibres (HTT 1000°C) has been carried out in this paper, where the best properties are attained even where the fibre has an ultimate shrinkage of about 7 percent, a result in contrast with the previous belief of obtaining maximum mechanical properties only with ultimate elongation during early stabilisation.
TL;DR: In this paper, the cumulative failure probability of an inhomogeneously stressed structure may be estimated when the material contains N different types of defect, each having its own fracture criterion.
Abstract: It is shown how the cumulative failure probability of an inhomogeneously stressed structure may be estimated when the material contains N different types of defect, each having its own fracture criterion. The theory is applied to:
It is also shown how to account for defects which grow in size because of fatigue and/or creep mechanisms. As an example the fatigue crack growth of defects, in a material having an inhomogeneous distribution of fracture toughness, is discussed. A method of accounting for defect nucleation during service is described.
TL;DR: In this paper, an energy balance fracture criterion and a constant crack opening displacement criterion are discussed and rationalized in connection with the prediction of crack growth rates in linear viscoelastic materials.
Abstract: An energy balance fracture criterion and a constant crack opening displacement criterion are extensively discussed and rationalized in connection with the prediction of crack growth rates in linear viscoelastic materials. It is shown that both approaches lead to the same crack growth law when small scale yielding conditions prevail and when the applied stress is constant during propagation. Based upon an approach already appearing in the literature an analysis is presented deriving crack growth laws which are valid for quite general creep functions. The standard linear solid and generalized power law materials are discussed. Growth laws, valid for both small and large scale yielding, are derived for Maxwell solids using the above two fracture criteria.
TL;DR: In this paper, it is suggested that the microstructure produced by pretreatment strengthened the alloy so that it resisted the deformation normally produced by growth stresses, leading to a permanent reduction of stress.
TL;DR: The temperature variation of refractive indices (ne, ne), birefringence (δn), density (ρ) and order parameter (S) of two liquid crystals, namely, N-(p-hexyloxybenzylidene)-p-toluidine (HBT) and N-(...
Abstract: The temperature variation of refractive indices (ne, ne), birefringence (δn), density (ρ) and order parameter (S) of two liquid crystals, namely, N-(p-hexyloxybenzylidene)-p-toluidine (HBT) and N-(...
TL;DR: In this paper, the impact of surface science in metallurgy is outlined, in particular in those entailed segregation or adsorption to the three interfaces: grain boundaries, free surfaces and interphase surfaces.
TL;DR: In this paper, the amplitude and phase transmission spectra of free-standing grids wound from 5 μm diameter tungsten wire with 100, 50 and 25 μm wire spacing are presented for the frequency range 40-300 cm−1 The case of normal incidence with the electric vector either parallel or perpendicular to the wires is examined.
TL;DR: In this paper, an improved technique for producing free-standing grids from 5 μm tungsten wire with 12.5 μm periodicity is described, along with typical spectra obtained using one as a beam divider in a polarizing Michelson interferometer.
TL;DR: In this paper, DSC shows a variety of potentially confusing curves that result from a coupling of instrumental-and sample-based rate effects, which can be used to give true glass temperatures that characterise the method of glass formation.
Abstract: The heat capacity of an amorphous polymer is insensitive to molecular and processing variables except in the glass transition region. Here DSC shows a variety of potentially confusing curves that result from a coupling of instrumental- and sample-based rate effects. The curves can be simply analysed to give true glass temperatures that characterise the method of glass formation.
TL;DR: In this paper, the vertical structure of the equatorial electrojet, the relation between strength of the jet and the magnetic field variation at the ground and the causes of large day-to-day variability of the amplitude of H variation were investigated.
Abstract: Several rocket borne magnetometer experiments have been conducted from Thumba to measure the equatorial electrojet currents under different solar and geophysical conditions. The data from these experiments have been used to study the vertical structure of the electrojet, the relation between strength of the jet and the magnetic field variation at the ground and the causes of large day-to-day variability of the amplitude of H variation. The results show that the experimentally measured current density peaks at a significantly different altitude compared to the altitude of the peak of Cowling conductivity calculated using model values of ionospheric parameters. The analysis indicates that given the magnetogram from a station under the electrojet, it is possible to predict the vertical distribution of current density in the electrojet on a quiet day. The mechanism of stabilisation of two stream instability suggested by the theoretical workers ro explain the back scatter radar echoes from type I irregularities on high jet days does not become operative atleast upto jet strengths equivalent to ΔH≤140nT.
TL;DR: The phase diagram for the Co-Cr-Zr system has been calculated from thermodynamic data for the binary systems involved as mentioned in this paper, indicating eutectic behaviour between fcc Co-based solutions and the (Co,Cr)2Zr Laves phase.
Abstract: The phase diagram for the Co-Cr-Zr system has been calculated from thermodynamic data for the binary systems involved. Ten isothermal sections for temperatures between 1900 and 1300 K are given. Portions of the diagram, indicating eutectic behaviour between fcc Co-based solutions and the (Co,Cr)2Zr Laves phase, are in excellent agreement with experimental studies made subsequent to the calculations. A set of thermodynamic data for the Co-Zr system which is consistent with the experimental phase diagram has been derived.
TL;DR: In this paper, the electric quadrupole moment (QN2) of the nitrogen molecules was determined from the results using two different analytical methods, at each of these temperatures, yielding an average value of (1.3 ± 0.2) × 10−26 esu cm2.
Abstract: Measurements of the absorption in compressed nitrogen gas in the spectral region 20–200 cm−1 have been made at temperatures of 200, 293, 320, and 353 K. Values of the electric quadrupole moment QN2 of the nitrogen molecules are determined from the results using two different analytical methods, at each of these temperatures, yielding an average value of (1.3 ± 0.2) × 10−26 esu cm2. The data are then applied in a study of the far-infrared transmission of the upper atmosphere at a mean temperature of 220 K, where it is shown that up to 8% absorption can occur in a vertical path above 12 km, while over a near-horizontal path from this level the absorption can be 40% or greater. Such results are of importance to atmospheric and astronomical measurements in the 100 cm−1 region.
TL;DR: The design principles and structure of an existing Fortran program library whose primary application is to solve optimization problems are discussed, as well as specific instances of the results of decisions to include particular desirable features.
Abstract: : This paper discusses in substantial detail the design principles and structure of an existing Fortran program library whose primary application is to solve optimization problems. Such a discussion not only helps to clarify the scope of application for potential users of the library, but also is useful for workers on other software projects. The fundamental objectives of the present library have been to produce sound, careful implementations of reliable methods that represent the state of the art in numerical optimization. The general implications of these overall design aims are presented, as well as specific instances of the results of decisions to include particular desirable features. (Author)
TL;DR: In this paper, the effects of V2O5 addition on the densification and the magnetic properties of the Ni-Zn ferrites have been studied, and the maximum density was observed at a V 2O5 content of 0.2 mo1% and 0.5 mo 1% in iron excess and deficient ferrites respectively.
TL;DR: In this paper, the electron paramagnetic resonance method (EPR) has been used to detect the presence of ultraviolet sensitive EPR signals in polycrystalline CaS samples with g values 1.9998 and 2.0018.
TL;DR: In this paper, Batuecas's value of the gas constant (R = 8.31441 J mol -1 K -1 ) was compared to the results of Quinn, Colclough & Chandler (Q. C.).
Abstract: Six acoustic isotherms have been plotted in the range 4.2–20 K. When thermodynamic temperatures are calculated from their intercepts on the basis of Batuecas’s value of the gas constant ( R = 8.31441 J mol -1 K -1 ), no significant systematic departure from the results of Berry’s gas thermometry is discernible. If one assumes Berry’s work to be thermodynamically correct and the present work to be thermodynamically linear, a value of the gas constant is implied only (7 ± 27 (lσ)) R / 10 6 higher than that of Batuecas, but 152 R / 10 6 lower than that of Quinn, Colclough & Chandler (Q. C. C.). Such a value is close to that expected from a forthcoming revision of the work of Q. C. C. and is in line with recent criticisms of Rowlinson et al . of their value. If this expectation is borne out gas and acoustic thermometry will be in good agreement in this range. Final results are quoted on the basis of Batuecas’s value of the gas constant and in terms of R to facilitate their recalculation as new information on the value of the gas constant becomes available.
TL;DR: In this paper, well-characterized fractions of linear poly(vinylacetate) have been used to establish the validity of universal calibration for that polymer in gel permeation chromatography.