Showing papers in "British Journal of Applied Physics in 1956"
TL;DR: In this article, a new determination of the equal-loudness relations for pure tones in free-field conditions has been carried out at the National Physical Laboratory as a result of requests from organizations interested in various aspects of the acoustics of hearing.
Abstract: The paper describes a new determination of the equal-loudness relations for pure tones in free-field conditions which has been carried out at the National Physical Laboratory as a result of requests from organizations interested in various aspects of the acoustics of hearing. The equal-loudness contours are of considerable importance in this field, being fundamental to a proper understanding of aural judgments of the loudness of sounds of all kinds. They are also concerned in numerous practical applications in the study of noise. The first set of contours for free-field conditions was given by Fletcher and Munson in 1933, and a second determination was carried out by Churcher and King in 1937, but these two investigations showed considerable discrepancies over parts of the auditory diagram. The present work has been carried out on a more extensive scale, using a large team of otologically normal persons, and new techniques have been introduced enabling reliable measurements to be made over a wider range of intensity than has hitherto been possible. The new results cover a range of frequency of from 25 to 15 000 c/s and of sound pressure level up to about 130 dB relative to 0.000 2 dyn/cm2. The data show a greater degree of regularity than the former results, and allow the equivalent loudness of a pure tone of any frequency to be expressed by formulae quadratic in the sound pressure level, the coefficients varying smoothly with frequency. The results include a new determination of the normal threshold of hearing in free field, which is highly consistent with the equal-loudness contours. At frequencies above 1000 c/s account needs to be taken of variations due to the age of the observers, which become of particular importance at the upper end of the frequency range. The new results have indicated the causes of some of the discordant features in the earlier determinations and it is hoped that the work will facilitate agreement on a standard set of equal-loudness contours. On account of its relevance to noise measurement, some extension to equal-loudness relations for bands of noise is being undertaken.
457 citations
TL;DR: In this article, it was shown that the indentation hardness is essentially a measure of the plastic yield stress of the metal and not the brittle properties of the solid. But this was not the case with spherical indenters, since the hardness increases with the size of indentation.
Abstract: A study of the plastic deformation of metals by hard indenters shows that the indentation hardness is essentially a measure of the plastic yield stress of the metal. With pyramidal (and conical) indenters the hardness, because of geometric similarity, is independent of the size of the indentation. With spherical indenters this is not so, the hardness increasing with size of indentation. From the increase in hardness with load, a semi-quantitative estimate may be made of the work-hardening characteristics of the metal. In the scratching and indentation of brittle solids such as minerals it is shown that the high hydrostatic pressures developed around the deformed region are often sufficient to inhibit brittle fracture. Under these conditions the deformation is primarily plastic. For this reason there is fairly good correlation between indentation and scratch hardness since both are essentially a measure of the plastic and not the brittle properties of the solid. From this approach it is possible to provide a physical basis for Mohs' scratch-hardness scale and to show that, excluding diamond, there is a reasonable equality of intervals between each number on the scale.
277 citations
TL;DR: In this article, the wall effect was found to be caused by a redistribution of a portion of the suspension particles on entering the tube of the viscometer, leading to a reduction in both the concentration and viscosity near to the walls of the tube.
Abstract: When the viscosity of a suspension of spherical particles uniformly distributed in a simple liquid is measured in a capillary tube viscometer, a wall effect, which is not found with coaxial rotating cylinder viscometers, is observed. The paper suggests that it may be caused by a redistribution of a portion of the suspension particles on entering the tube of the viscometer, leading to a reduction in both the concentration and viscosity of the suspension near to the walls of the tube. The diminution in concentration is measured experimentally and found to yield a value for the wall effect which is in agreement with that obtained from viscosity measurements. The reason for the redistribution of the particles at the tube inlet is discussed.
67 citations
TL;DR: In this article, two methods have been developed for the removal of carbon replica films directly evaporated on to etched metal surfaces, which involve either electropolishing or chemically etching after deposition of the carbon.
Abstract: Two methods have been developed for the removal of carbon replica films directly evaporated on to etched metal surfaces. These involve either electropolishing or chemically etching after deposition of the carbon. The film removed by electropolishing gives a replica of high resolution, whilst with the etching technique extraction replicas may be prepared from multiphase alloys and the extracted phases identified by electron diffraction. Some examples of the application of the techniques to carbon and alloy steels are given.
54 citations
TL;DR: In this paper, a method for the measurement of the tensile strength of coal by bending thin strips has been described, which has been shown to decrease with the increasing size of the sample.
Abstract: Apparatus is described which has been developed for the measurement of the tensile strength of coal by bending thin strips. Measurements on four coals show that the strength depends on the type of coal and on the direction of loading relative to the bedding planes. One coal has been studied in some detail and the tensile strength is shown to decrease with increasing size of specimen. The effect is attributed to the increased probability of finding in larger specimens a weakness which imparts a low strength. It is estimated that for a given size of specimen the tensile strength is of the order of one-tenth of the compressive strength. Further, it has been found possible to rejoin broken strips of this coal so that up to ten successive tensile tests can be performed on a single strip, thus enabling the distribution of the weaknesses to be studied. In general, there is an increment of strength between successive breakages, and after ten breaks the tensile strength is roughly double the value obtained at the first break. This method of studying distribution of strength does not appear to have been used previously, although it is likely to have applications to many other brittle materials.
53 citations
TL;DR: In this paper, the authors discuss the effects of transient stress wave propagation in elastic and visco-elastic solids, as well as in solids stressed beyond the elastic limit.
Abstract: The aim of this paper is to discuss, in fairly elementary fashion, the topic of the transmission of transient stress pulses of short duration in solids, together with the associated problem of the measurement of pressures subject to very rapid changes. The pressure bar method, devised by Betram Hopkinson, forms one of the basic experiments in the field and it is described in some detail. An analysis of the limitations of the method leads to a discussion of the change of form of stress wave pulses as they recede from the origin, and the main features of the distortion are discussed when the pulses are propagated in (a) elastic solids, (b) visco-elastic solids, and (c) solids stressed beyond the elastic limit.
53 citations
49 citations
TL;DR: In this article, it was shown that a particle entering a tube non-axially would be expected to move with a component of translation normal to the streamlines and directed towards the axis.
Abstract: It was shown theoretically in a previous paper that during the laminar flow of a suspension through a tube, and for least action, a suspended particle would follow a path adjacent to the tube axis. In general, therefore, a particle entering a tube non-axially would be expected to move with a component of translation normal to the streamlines and directed towards the axis. In the present paper this theory is developed and leads to the conclusion that for a particle at any given point in the tube this component increases with particle size. Experiments are described in which streams of coloured particles of mixed sizes suspended in water were admitted at a given point on the horizontal diameter of a tube placed horizontally, through which a steady flow of water was maintained. These coloured streams diverged on entry to the water and formed filaments in a horizontal plane. A study of the lateral movement of these filaments relative to one another, as the point of their admission to the tube and the rate of flow of water in the tube are varied, leads to the conclusion that lateral forces act on the suspended particles. Such forces, the magnitudes of which increase with particle size and with mean shear gradient, result from the motion of the particles in non-uniform velocity gradients. The motions observed lead directly to a simple flow mechanism, independent of particle configuration and orientation, which is shown to be qualitatively consistent with a number of well-established phenomena.
37 citations
TL;DR: In this paper, the authors showed that for fluids with a viscosity in the range 0.01 to 400 P, the cavitation threshold pressure Pc is given by the empirical relation Pc = κη0.2.
Abstract: Under similar conditions of transient loading the cavitation thresholds of syrup and olive oil are 130 × 106 dyne/cm2 and 29 × 106 dyne/cm2 respectively. For fluids with a viscosity (η) in the range 0.01 to 400 P the cavitation threshold pressure Pc is given by the empirical relation Pc = κη0.2. This result can be interpreted on the basis of the growth of cavitation nuclei in viscous liquids subjected to transient stresses.
36 citations
TL;DR: The working rule that the resolution obtainable in the electron image of a biological specimen is of the order of one-tenth of its thickness is quantitatively explained in terms of the energy loss of electrons scattered in the specimen and of the chromatic aberration of the objective lens.
Abstract: The working rule that the resolution obtainable in the electron image of a biological specimen is of the order of one-tenth its thickness is quantitatively explained in terms of the energy loss of electrons scattered in the specimen and of the chromatic aberration of the objective lens. This limitation holds true down to the thinnest sections (100-200 A) that can be cut at present. That they normally do not show a resolution approaching 20 A is ascribed to lack of contrast. The use of a filter lens, rejecting all electrons that lose more than 10 V, would improve both contrast and resolution. Its use is even more important for rendering visible carbonaceous structures of size comparable with the instrumental resolving power. A lower accelerating voltage than currently used for electron microscopy is desirable for specimens of poor contrast.
35 citations
TL;DR: In this paper, the static electric strength of a number of pure hydrocarbon gases over a range of pressure and spark-gap spacings, including the Paschen minimum, is reported.
Abstract: Careful measurements of the static electric strengths of a number of pure hydrocarbon gases over a range of pressure and spark-gap spacings, including the Paschen minimum are reported. A relationship between strength and molecular structure is found which, if unsaturated compounds such as ethylene, acetylene and butadiene are included, is not so simple as hitherto reported. The possible correlation of electric strength with the ultra-violet spectra and Ramsauer cross-sections of these gases is discussed briefly. Pulse discharges which occur readily in these gases at fields below the breakdown value are attributed to the exceedingly small secondary ionization coefficients (γ).
TL;DR: The magnetostrictive properties of binary nickel-cobalt alloys in the range 0-23% cobalt are discussed, with particular reference to the use of these materials for transducers Measurements, at various polarizing fields, of the electromechanical coupling coefficient, reversible permeability and Young's modulus are described as discussed by the authors.
Abstract: The magnetostrictive properties of binary nickel-cobalt alloys in the range 0-23% cobalt are discussed, with particular reference to the use of these materials for transducers Measurements, at various polarizing fields, of the electromechanical coupling coefficient, reversible permeability and Young's modulus are described Various criteria which govern the choice of magnetic materials for ultrasonic transducers are discussed and it is shown that two alloys, containing respectively about 44 and 184% cobalt, give good performance as transducer materials
TL;DR: In this paper, a small spherical or cubic specimen is placed in a cavity resonating in the H011 mode, and the reduction in Q due to eddy-current loss in the specimen is measured.
Abstract: A method is described for measuring the resistivity of semi-conductors at centimetre wavelengths. A small spherical or cubic specimen is placed in a cavity resonating in the H011 mode, and the reduction in Q due to eddy-current loss in the specimen is measured. The theory given enables the resistivity of the material to be calculated. It is shown that resistivities in the range 0.005 to 10 cm can be determined.
TL;DR: In this paper, the inner surfaces of both pipes near their juncture, as caused by internal pressure, were determined by the frozen stress photoelastic technique, and an approximate method of calculation was developed and a measure of agreement between the calculated and measured stresses was found.
Abstract: The stress distribution on the inner surfaces of both pipes near their juncture, as caused by internal pressure, was determined by the frozen stress photoelastic technique. An approximate method of calculation (based on the theoretical solution for a hole in an infinite plate under uniform tension) was developed and a measure of agreement between the calculated and measured stresses was found.
TL;DR: In this paper, a review of structural changes such as crystal lattice transformations or melting that produce increases of entropy and thus can favour thermodynamic transitions in solids is presented, with particular attention directed towards the structural elucidation of the following anomalies.
Abstract: Classical thermodynamics provides powerful methods for correlating various thermal parameters of a system. However, anomalies are found in the classical theory particularly for condensed phases, such as solids or liquids. A detailed study of the structure of such phases by what may be broadly termed crystallographic methods has thrown much light on the classical anomalies. The present review surveys various structural changes such as crystal lattice transformations or melting that produce increases of entropy and thus can favour thermodynamic transitions in solids. Particular attention is directed towards the structural elucidation of the following anomalies. Pre-transition and pre-melting phenomena. In many cases these can now be attributed to gradual structural changes within a crystal of the same kind as the discontinuous jump at a transition. The occurrence of smeared or continuous thermodynamic transitions, which are sometimes described as transitions of higher order. These can often now be attributed to the coexistence of regions of two slightly different structures or sub-units within a hybrid single crystal. Reference is made to some of the techniques of study that have been used to investigate such coexistence. The occurrence of hysteresis around a thermodynamic transition. This can arise from the same coexistence phenomena that lead to smeared thermodynamic transitions. Precision studies on single crystals of the kinds described seem likely to throw much light on thermodynamic transitions in solids.
TL;DR: In this paper, the results of a large number of measurements of total voltage, voltage gradient, current density and excitation temperature over a range of current, pressure, gap length and electrode condition for high-pressure steady-state discharges in hydrogen are given.
Abstract: The results of a large number of measurements of total voltage, voltage gradient, current density and excitation temperature over a range of current, pressure, gap length and electrode condition for high-pressure steady-state discharges in hydrogen are given. Tungsten and copper electrodes were used as these are typical refractory and non-refractory materials respectively. The results show that in the absence of metal vapour the cathode and column regions are quite independent, the state of one not affecting that of the other. With increasing current a change from the glow to an arc column occurs at a critical value of the gas temperature. At short gaps the column transition current is modified by heat transfer with the electrodes. With tungsten electrodes, increase in current causes a continuous transition between glow and arc at the cathode which is due to thermionic emission. With copper electrodes the cathode transition is discontinuous, erratic and independent of cathode temperature, being a function rather of the surface condition.
TL;DR: In this article, a hot tungsten filament emitting an abundance of electrons in a vacuum was employed as cathode, and the gap between the electrodes was therefore only partly occupied by the liquid.
Abstract: In order to analyse the pre-breakdown phenomena in insulating oil, a hot tungsten filament emitting an abundance of electrons in a vacuum was employed as cathode. The gap between the electrodes was therefore only partly occupied by the liquid. Currents measured with various voltages and depths of oil were explained on the basis of space-charge limitation in the oil, and the mobility of the negative ion in transformer oil formed by the attachment of electrons to oil molecules was found to be 1 × 10-4 cm/s per V/cm.
TL;DR: In this paper, a discussion of the determinations of the thermal expansion of mercury and fused silica has been conducted, and it is recommended that for the most accurate work, the expansion formula given by the latter authors should be used instead of that given by Sears.
Abstract: The determinations of the thermal expansion of mercury and fused silica have been reviewed. In principle the absolute hydrostatic balancing method is a more satisfactory way of measuring the expansion of mercury than deducing it from the expansion relative to a fused silica bulb, but a discussion of the determinations shows that despite the variability of the expansion of fused silica from specimen to specimen, systematic errors affecting the absolute determinations make them less reliable than the relative measurements of Harlow and Beattie and others. It is recommended that for the most accurate work, the expansion formula given by the latter authors should be used instead of that given by Sears. The present uncertainty of the change of volume with temperature is about one or two parts in a million of the volume at 0° C for temperatures from 0 to 300° C, and may be as much as one part in ten thousand at other temperatures.
TL;DR: In this paper, a method used to deposit carbon from hydrocarbons at high temperatures for the production of small tubular specimens was described, and measurements of thermal conductivity and electrical resistivity made over the range 20 to 200° C on commercial graphite and deposited carbons formed at temperatures of 1800, 1900, 2000 and 2100° C.
Abstract: Details are given of a method used to deposit carbon from hydrocarbons at high temperatures for the production of small tubular specimens. The density had been found to vary systematically with the temperature of deposition, and the present work relates to measurements of thermal conductivity and electrical resistivity made over the range 20 to 200° C on commercial graphite and deposited carbons formed at temperatures of 1800, 1900, 2000 and 2100° C. The thermal conductivities of the specimens deposited at 2000 and 2100° C were found to be exceptionally high. At 50° C the value for material deposited at 2000° C was approximately 20% greater than that of copper; for material deposited at 2100° C it was approximately 40% greater than that of copper. These measurements were made in a direction parallel to the axis of the tube for which direction the deposited carbon showed a pronounced layered structure. This, and an associated high electrical resistance normal to its plane, made it difficult to determine the electrical resistivity of the sample deposited at 2100° C. The high thermal conductivity appears to result from the high lattice conductivity of this material, the electronic component being only of the order of 1%.
TL;DR: In this paper, the flow of water is rendered visible by plastic tracers, of similar density to water, which are illuminated by continuous filament lamps, long-duration electronic flash lamps or vapour discharge lamps, according to the information required.
Abstract: The study of fluid flow in such gaseous systems as combustion chambers and furnaces is of value in the design and subsequent operation of the equipment. Useful information may be obtained from flow visualization in these systems under constant density conditions, even though in practice considerable density changes occur. Hydraulic models are then found to have distinct advantages over air models. Apparatus has been developed by means of which the flow of water may be studied in transparent models of the simulated air systems. The flow is rendered visible by plastic tracers, of similar density to water, which are illuminated by continuous filament lamps, long-duration electronic flash lamps or vapour discharge lamps, according to the information required. Selected parts of the flow field may be observed by means of a narrow, flat beam of light directed through the appropriate section of the model. Semi-quantitative records of flow components may be derived from photographs obtained with the flash illumination. Individual tracers may be observed by selective illumination involving an ultra-violet light source and fluorescent tracers. The subject is treated from a wholly practical point of view. Details of the apparatus and techniques are given, with examples of some of the types of information obtainable, and the elementary requirements for similarity with aerodynamic systems are stated.
TL;DR: In this article, theoretical and experimental values of the focal lengths of simple three-electrode electron lenses are compared and found to be in general agreement, in the form of graphs which show directly the dependence of focal length on lens geometry and voltage ratio.
Abstract: Published theoretical and experimental values of the focal lengths of simple three-electrode electron lenses are compared and found to be in general agreement. These are presented in the form of graphs which show directly the dependence of focal length on lens geometry and voltage ratio. Analogous graphs are derived for spherical and chromatic aberrations in the form of the ratios CS/S and CC/S (S being the separation of adjacent electrodes), and the general relation between the various curves is discussed.
TL;DR: In this article, an improved method was proposed to make use of electron diffraction of individual crystals in the electron microscope for determination of the unitcell dimension most nearly parallel to the electron beam.
Abstract: An improved method is detailed, making use of electron diffraction of individual crystals in the electron microscope, for determination of the unit-cell dimension most nearly parallel to the electron beam. A series of diffraction patterns is recorded from a crystal tilted through known angles by the device normally used for making stereomicrographs. One of these patterns serves as a datum, for location on each of the others of the centre of its almost circular Laue zones. A new method is described for calibration of the instrument without using additional apparatus; all the factors which vary with the electron-beam potential can then be derived from a single diffraction pattern of a standard substance. A graph has also been prepared to allow correction of errors in calculation due to large angles between the "third-row" axis and the electron beam. The improvement in accuracy due to the procedure is illustrated by results obtained using crystals of known unit-cells.
TL;DR: In this article, nuclear resonance absorption is induced in protons contained in mixtures of light and heavy water and the magnitude of the power absorption is used as a measure of the concentration of light water present and samples of known concentration are used to standardize the absorption.
Abstract: Nuclear resonance absorption is induced in protons contained in mixtures of light and heavy water. The magnitude of the power absorption is used as a measure of the concentration of light water present and samples of known concentration are used to standardize the absorption. Two techniques for inducing the absorption are described, one appropriate for H2O concentrations in the range 7-100% and the other for low concentrations. In both cases the signal output from the equipment rises almost linearly with H2O concentration. Using the first method, a signal-to-noise voltage ratio of twenty is obtained with a 7% concentration. A similar ratio is obtained from samples with 0.2% H2O by using the second technique. The effect of flowing low concentration samples through the apparatus has been studied. The signal output falls with flow rate and at 40 ml/s is half that obtained at zero flow. Suggestions are made for improving the stability of the equipment and for reaching a quantitative theoretical understanding of the absorption signal shapes observed.
TL;DR: In this article, the intensifying action of calcium tungstate screens in combination with X-ray film has been investigated over a wide range of Xray wavelengths equivalent to X-rays generated with energies of between 40-1200 kV.
Abstract: The intensifying action of calcium tungstate screens in combination with X-ray film has been investigated over a wide range of X-ray wavelengths equivalent to X-rays generated with energies of between 40-1200 kV. By means of the evaluation of the quantum- and energy-efficiencies of screen and film an understanding of their behaviour, i.e. their utilization of energy within this range of quantum energies, is obtained.
TL;DR: In this article, the conditions which lead to multiplicity in the mark left on the anode by a spark of short duration in air have been studied, and the results showed that multiplicity can be determined in the first few tenths of a microsecond of the life of the spark.
Abstract: The conditions which lead to multiplicity in the mark left on the anode by a spark of short duration in air have been studied. The anode surface condition is important in determining multiplicity and was controlled in this investigation by depositing various numbers of layers of barium stearate on clean palladium, aluminium and tin anodes. The nature of the mark is determined in the first few tenths of a microsecond of the life of the spark and depends chiefly on the number of contaminating layers on the anode, on the rate of rise of current in the spark and on the breakdown voltage of the spark gap.
TL;DR: In this article, the distribution of etch pits over various parts of a crystal has been studied and correlation has been obtained with the lifetime of minority carriers and with transistor action with respect to transistor action.
Abstract: Thermal stresses arising from differential shrinkage as the crystal cools down from the freezing point to room temperature are considered as a major source of structural defects. The distribution of etch pits over various parts of a crystal has been studied and correlation has been obtained with the lifetime of minority carriers and with transistor action.
TL;DR: An improved version of the Curie-type ionization chamber enables an accurate comparison to be made of the ionization currents produced by γ-rays as mentioned in this paper, and the linearity of response of this instrument has been investigated for radon sources up to 250 mc, with an argon gas filling.
Abstract: An improved version of the Curie-type ionization chamber enables an accurate comparison to be made of the ionization currents produced by γ-rays. The ionization current produced by 1 mc of radium can be measured with an accuracy of 0.02%. The linearity of response of this instrument has been investigated for radon sources up to 250 mc, with an argon gas filling. The half-life of radon measured in this way was found to be 3.8229 ± 0.00027 days.
TL;DR: In this article, the shadowing by metal evaporation in a vacuum has been adapted to the production of plane negative images of dust deposits on microscope slides at natural size by vacuum-evaporation of metal at right angles to the slide, and subsequent removal of the dust.
Abstract: The technique of shadowing by metal evaporation in a vacuum has been adapted to the production of plane negative images of dust deposits on microscope slides at natural size by vacuum evaporation of metal at right angles to the slide, and subsequent removal of the dust. The slide receives a precise impression of the geometric projections of the particles. The correspondence of image and object is exact. The thickness of the deposited film can be suited to the contrast requirements of an automatic particle counter; further, the film lies in one plane and is only a few hundred angstrom units thick. Many of the optical problems arising from the association of automatic counting techniques with high power light microscopy, namely, depth of focus and variable contrast between particles and background and between different parts of single particles, are avoided by substituting the shadow for the original specimen, as suggested by Whitaker.