Showing papers by "National Physical Laboratory published in 1970"
TL;DR: In this article, the authors investigated the acoustical properties of a range of fibrous absorbent materials and showed that the characteristic impedance and propagation coefficient of these materials normalize as a function of frequency divided by flow-resistance.
1,652 citations
01 Jun 1970
TL;DR: The reliability of these design wind loads depends to a very large extent on the accurate prediction of the most severe wind conditions to be experienced for many years into the future, and on the accuracy of the wind force and pressure coefficients applicable to the structure as discussed by the authors.
Abstract: After several spectacular collapses caused by wind, there has been increased interest in the accurate prediction of the wind loading to which buildings and structures are subjected. The reliability of these design wind loads depends to a very large extent on the accurate prediction of the most severe wind conditions to be experienced for many years into the future, and on the accuracy of the wind force and pressure coefficients applicable to the structure. Many factors influence these coefficients and hitherto many of these factors have not been reproduced in measurements on models in wind tunnels, so much of the existing data is of uncertain reliability.For many structures it is sufficient to regard the wind as causing static loadings and for this purpose to use time-averaged wind forces. However, the advent of modern design and fabrication of structures has rendered them more prone to respond to the dynamic action of wind. Increasing attention is therefore being given to the time-dependency of the wind ...
426 citations
TL;DR: In this article, the double-layer interaction free energy of two charged spheres with centers at distance R apart in electrolyte solution was investigated and a simple general form of the interaction energy at large separations suitable for all radii and potentials was obtained.
340 citations
TL;DR: In this article, the authors measured local displacements in the plane of an object surface illuminated by coherent light by recording double-exposure photographs of it and using the optical transform of the negative image.
Abstract: Local displacements in the plane of an object surface illuminated by coherent light may be measured by recording double-exposure photographs of it. When the surface is illuminated symmetrically by two oblique beams, ‘speckle correlation fringes’ appear in the doubly exposed negative, due to the non-linear nature of the photographic recording. Factors affecting the visibility of these fringes and the range of displacement which can be measured are discussed. The fringe visibility falls to zero for displacements larger than a speckle width, but measurements can then be performed upon the optical transform of the negative image. With uni-directional object illumination, the in-plane displacement can be measured on a point-by-point basis in magnitude and in direction from Young's fringes observed. With two symmetrical oblique illuminating beams the effect of a small surface strain is displayed, even if large lateral displacement has occurred, by using spatial filtering when viewing the photographic image.
302 citations
TL;DR: In this paper, the authors discussed the two mechanisms of energy dissipation which have been suggested to occur in a fiber composite of brittle fibres in a brittle matrix, namely pull out and debonding, and experiments to measure the latter were described.
Abstract: The stresses near the tip of a crack which lies normal to a set of alined fibres is discussed when the elastic properties of the composite are appropriate to those of a carbon reinforced epoxy resin. Splitting parallel to the fibres is expected to occur before fibre fracture only if an interface parallel to the fibres of one fiftieth the strength of the composite parallel to the fibres is present. The two mechanisms of energy dissipation which have been suggested to occur in a fibre composite of brittle fibres in a brittle matrix, namely pull out and debonding, are discussed. Experiments to measure the latter are described. The work of debonding ( 4 J m -1 ) is usually less than the work of pull out. The theory of pull out is described and experiments to support it noted. An important result is that the work of pull out increases linearly with fibre diameter, and is likely to be inconveniently small for fibres of diameter ≾ 10 μ m. The relative advantages and disadvantages of fibres of various diameters are discussed. Fibres of diameter ≿ 25 μ m lead to large works of pull out and are stable and easily handled. Thinner fibres ( μ m diameter) give rise to constraint effects which are important in metallic matrices.
292 citations
TL;DR: In this article, the vapour pressure of methanol, ethanol, pentan-1-ol, octan- 1-ol and octadecan-1 -ol have been measured.
267 citations
249 citations
TL;DR: In this article, the results of new measurements of the infrared spectra (3650-50 cm −1 ) together with the Raman shifts, wavenumbers for all the fundamental frequencies, and complete interpretations of the observed spectra are presented for the fifteen compounds p -XC 6 H 4 Y; X, Y = CH 3, F, Cl, Br or I.
111 citations
TL;DR: An enquiry into why “rod colour” should be blue, together with an examination of the similarities and dissimilarities of rods and “blue cones”, leads to the further suggestion that rods and "blue cones" exist separately but share a neural pathway.
109 citations
TL;DR: In this article, the infrared and Raman spectra for fifteen compounds, o-, m- or p-XC6H4NO2; X = CH3, F, Cl, Br, or I are presented and interpreted in detail.
100 citations
TL;DR: In this paper, the authors used Landau-Lifshitz-Looyenga's formula for correlation of bulk and powder dielectric parameters at microwave and radio frequencies.
Abstract: Landau-Lifshitz-Looyenga's formula for correlation of bulk and powder dielectric parameters has been investigated at microwave and radio frequencies for a number of materials for wide enough experimental conditions of particle size, shape and packing fraction. It has been found that the formula gives good accuracy (about 3%) for dielectric constant determination for particle size not less than 50 μm. For fine powders (particle size less than 30 μm) the deduced dielectric constant is too low by about 3-8%. Dielectric loss determination from the formula is, however, less accurate, the deduced values being always too low by about 10-20%.
TL;DR: In this paper, the authors discussed the factors which determine the mean length of fiber pull-out during fracture in composites reinforced with continuous fibres having variously spaced points of weakness.
Abstract: Fibre fractures which occur near, but not at, the plane of matrix failure in a composite, lead to fibre pull-out during fracture. Energy absorbed in this process contributes directly to the work of fracture and hence to the toughness of the composite. Factors which determine the mean length of fibre pulled out during fracture are discussed for the case of composites reinforced with continuous fibres having variously spaced points of weakness. The presence of such weak points also affects the strength of the composite, but not all composites of the same strength have the same toughness. The greatest toughness for a given strength is always found in composites reinforced with discontinuous fibres.
TL;DR: The volume of work involved in a QR step is far less if the matrix is of Hessenberg form, and since there are several stable ways of reducing a general matrix to this form, the QR algorithm is invariably used after such a reduction.
Abstract: The QR algorithm of Francis [1] and Kublanovskaya [4] with shifts of origin is described by the relations
$$ \matrix{ {{Q_s}({A_s} - {k_s}I) = {R_s},} & {{A_{s + 1}} = {R_s}Q_s^T + {k_s}I,} & {giving} \cr } \matrix{ {{A_{s + 1}} = } \hfill \cr } {Q_s}{A_s}Q_s^T, $$
(1)
where Q s is orthogonal, R s is upper triangular and k s is the shift of origin. When the initial matrix A 1 is of upper Hessenberg form then it is easy to show that this is true of all A s . The volume of work involved in a QR step is far less if the matrix is of Hessenberg form, and since there are several stable ways of reducing a general matrix to this form [3,5, 8], the QR algorithm is invariably used after such a reduction.
TL;DR: In this article, complete assignments and full interpretations of the infrared (3650-50 cm−1) and Raman spectra for the fifteen compounds m-XC6H4Y were proposed.
TL;DR: In a recent paper [4] the triangularization of complex Hessenberg matrices using the LR algorithm was described and the final triangular matrix by T was described.
Abstract: In a recent paper [4] the triangularization of complex Hessenberg matrices using the LR algorithm was described. Denoting the Hessenberg matrix by H and the final triangular matrix by T we have
$${P^{ - 1}}HP = T$$
(1)
, where P is the product of all the transformation matrices used in the execution of the LR algorithm. In practice H will almost invariably have been derived from a general complex matrix A using the procedure comhes [3] and hence for some nonsingular S we have
$${P^{ - 1}}{S^{ - 1}}ASP = T$$
(2)
.
TL;DR: In this article, complete assignments and full interpretations of the infrared (3650−50 cm−1) and Raman spectra are proposed for the fifteen compounds o-C6H4Y; X, Y = CH3, F, Cl. Br or I.
TL;DR: Chebyshev polynomials have been used for the correlation of vapour pressure and temperature from the triple point to the critical point for two simple liquids (oxygen and methane) and also for some liquids containing more complex molecules (hydrocarbons and alcohols) as discussed by the authors.
TL;DR: In this paper, the effects of beam modulation in the recording of a hologram were discussed and a unified description of fringe loci and fringe localization that is valid for arbitrary object motions and arbitrary beam modulation was presented.
Abstract: A comprehensive formulation of hologram interferometry is modified to include the effects of beam modulation in the recording of a hologram. The result is a unified description of fringe loci and fringe localization that is valid for arbitrary object motions and arbitrary beam modulation. This result is used to discuss the effect of beam modulation on fringe loci and localization conditions for a wide variety of cases: where one time function is sufficient to describe the motion of all points on an object surface; where a combination of independent time functions is required; where a combination of dependent time functions is required; where phase modulation proportional to the time function of the object’s motion is introduced; and where an object may execute sinusoidal vibrations that must be added as phase vectors (phasor vibrations). Localization conditions are shown to have potentially useful properties, for example, to permit separate observation of independent object motions when they occur simultaneously.
TL;DR: In this article, the standard thermal neutron flux at the NPL has been used to measure a number of 2200 m/s activation cross-sections and resonance integrals relative to those of gold.
TL;DR: The enthalpies of formation in the gas-phase of eight straight-chain alkanones C n H 2 n O have been shown to vary linearly with n over the range n = 3 to 11 as discussed by the authors.
TL;DR: In this article, notched polycrystalline specimens of an Al 1 2% Mg alloy were fatigue-cracked at four different stress levels to a crack length of approximately 1 mm.
TL;DR: In this article, the effects of compositional changes on parameters used in the theory of superconductivity to describe the transition temperature have been investigated and it has been shown that changes in transition temperature with changes in composition cannot be explained simply on the basis of an alteration of the density of states except in the case of binary Nb-Ta alloys.
Abstract: The electronic specific heat coefficient, γ, the Debye temperature, θD, and the superconducting transition temperature, Tc, have been measured for binary b.c.c. alloys of V, Nb, and Ta. These results have been used to investigate the effects of compositional changes on parameters used in the theory of superconductivity to describe the transition temperature. It has been shown that changes in transition temperature with changes in composition cannot be explained simply on the basis of an alteration of the density of states except in the case of binary Nb-Ta alloys. It is concluded that, for V-Nb and V-Ta alloys, changes in the interaction responsible for superconductivity also govern changes in the transition temperature.
TL;DR: In this article, the authors used the Knudsen effusion method and radiochromium, 51 Cr to determine the Gibbs energies of chromium in ternary alloys.
TL;DR: In this paper, a new laser image called speckle interferometer, a device used for looking at vibrational modes on defusely reflecting surfaces, has been designed, making it possible to provide a reference field in the instrument that is substantially free from spurious pattern.
TL;DR: In many optical applications it is desirable to have extremely smooth surfaces to minimize diffusely scattered light and surface plasmon effects, but for measurements made in the uv and vacuum uv, the homogeneity of the surface of an optical flat is extremely important.
Abstract: In many optical applications it is desirable to have extremely smooth surfaces to minimize diffusely scattered light and surface plasmon effects. This is particularly important for measurements made in the uv and vacuum uv. In a previous paper one of us has shown that optical surfaces produced by the conventional fresh-feed polishing technique are rougher than those produced by the bowl-feed technique. On the other hand, for measurements made using polarized light, in particular for ellipsometric measurements, the homogeneity of the surface of an optical flat is extremely important. A residual modified layer at the surface left from the polishing process, or a thin dirt layer remaining after cleaning, can drastically affect the apparent thickness and optical
TL;DR: In this paper, electron density profiles were obtained from high power wave interaction measurements at The Pennsylvania State University during a solar flare which occurred on 21 October 1968, and the results indicated increases in electron density at all heights in the D -region, but especially above 70 km.
TL;DR: In this article, a new type of positive ion source based on an electrostatic charged particle oscillator was described, which is especially suitable for the controlled removal of material from solid surfaces or for the thinning of specimens for electron microscopy.
Abstract: A new type of positive ion source is described, based on an electrostatic charged particle oscillator described by McIlraith in 1966. The new source is especially suitable for the controlled removal of material from solid surfaces or for the thinning of specimens for electron microscopy. Ion current densities up to 300 μA cm−2 have been readily obtained. Large areas of sample can be bombarded and the working pressure of the device is low, normally below 10−3 torr. A specimen of OFHC copper exposed to a beam of argon ions at a density of 100 μA cm−2 was eroded at the rate of 1 μm per hour, corresponding to a removal rate about four atoms per incident ion.
TL;DR: In this article, the enthalpy of tris(hydroxymethyl)-aminomethane (Tris ) with excess dilute hydrochloric acid has been compared with the reaction of sulfuric acid with excess sodium hydroxide at low and high concentrations.
TL;DR: Changes in the outer surface of mammalian cells resulting from the malignant transformation have been observed in several types of cell and these include loss of contact inhibition, decreases in cell–cell adhesion and changes in electrical surface charge.
Abstract: CHANGES in the outer surface of mammalian cells resulting from the malignant transformation have been observed in several types of cell. These include loss of contact inhibition, decreases in cell–cell adhesion and changes in electrical surface charge1.