Showing papers in "British Journal of Applied Physics in 1952"
TL;DR: In this paper, an analysis of the effect of orientation of the fibres on the stiffness and strength of paper and other fibrous materials is made, and the results of the analysis are applied to certain samples of resin bonded fibrous filled materials and moderately good agreement with experimental results is found.
Abstract: An analysis is made of the effect of orientation of the fibres on the stiffness and strength of paper and other fibrous materials. It is shown that these effects may be represented completely by the first few coefficients of the distribution function for the fibres in respect of orientation, the first three Fourier coefficients for a planar matrix and the first fifteen spherical harmonics for a solid medium. For the planar case it is shown that all possible types of elastic behaviour may be represented by composition of four sets of parallel fibres in appropriate ratios. The means of transfer of load from fibre to fibre are considered and it is concluded that the effect of short fibres may be represented merely by use of a reduced value for their modulus of elasticity. The results of the analysis are applied to certain samples of resin bonded fibrous filled materials and moderately good agreement with experimental results is found.
3,284 citations
TL;DR: In this paper, the dependence of the relative viscosity on the size distribution of the suspended spheres was explained, and it was shown theoretically that if the spheres are of very diverse sizes, the relative viscousity is (1 - c)-2.5 for all values of the volume concentration c.
Abstract: An explanation is given of the dependence of the relative viscosity on the size distribution of the suspended spheres, an effect recently observed by Ward and Whitmore.(1) It is shown theoretically that if the spheres are of very diverse sizes, the relative viscosity is (1 - c)-2.5 for all values of the volume concentration c. For spheres of equal size, the validity of the Einstein expression for the relative viscosity (1 + 2.5c) is restricted to concentrations well below c = 0.05; while for medium and high concentrations the relative viscosity is given by the theoretical expression (1 - 1.35c)-2.5. The use of the latter formula in interpreting measurements on the viscosity of solutions is briefly indicated.
997 citations
TL;DR: In this paper, a solution of the heat conduction problem in which a sphere generating heat at a constant rate is embedded in an infinite medium of different thermal properties is given. But the solution is of use in a consideration of the disinfestation and sterilization of biological materials by differential heating due to the application of h.f. fields.
Abstract: A solution is given of the heat conduction problem in which a sphere generating heat at a constant rate is embedded in an infinite medium of different thermal properties. The solution is of use in a consideration of the disinfestation and sterilization of biological materials by differential heating due to the application of h.f. fields. Typical curves are given showing the transient temperature at the centre of the sphere for various ratios of the physical constants involved.
150 citations
TL;DR: In this article, the minimum intensities of irradiation required to ignite wood, with and without the presence of a pilot flame, have been determined, and found to be approximately constant for nearly all species.
Abstract: The minimum intensities of irradiation required to ignite wood, with and without the presence of a pilot flame, have been determined, and found to be approximately constant for nearly all species. Empirical expressions have been obtained which relate the time taken to ignite with the intensity of irradiation and the density of the wood for these two types of ignition.
115 citations
TL;DR: In this paper, the form of the saturation curve is investigated theoretically and experimentally in a parallel plate ionization chamber and it is shown that very high ionization intensities can be measured in such a chamber, provided the spacing of the plates is small.
Abstract: In this paper the form of the saturation curve is investigated theoretically and experimentally. It is shown that saturation curves taken under different conditions on a parallel plate ionization chamber are transformed into a single general curve when plotted in terms of a dimensionless product of the several variables. The experimental work utilized an ionization chamber with thin foil electrodes. A coin-shaped region between the foils was ionized by a beam of fast electrons. Dose rates up to 100 000 e.s.u./cm3 × sec could be attained. It is shown that very high ionization intensities can be measured in a parallel plate chamber, provided the spacing of the plates is small.
113 citations
TL;DR: Experiments have been carried out on hot cathode, highvoltage three-electrode electron guns and the brightness has been measured and found under optimum operating conditions to approach closely the value expected from the theoretical considerations developed by Langmuir.
Abstract: Experiments have been carried out on hot cathode, high-voltage three-electrode electron guns. The brightness has been measured and found under optimum operating conditions to approach closely the value expected from the theoretical considerations developed by Langmuir. The effect of varying geometry over a fairly wide range is shown to be of secondary importance, except in as far as it influences the bias conditions and current efficiency. The mechanism of electron beam formation is discussed briefly.
92 citations
TL;DR: Comparison of the results for blood with those for water leads to approximate estimates of the erythrocyte intracellular ionic conductivity and haemoglobin hydration and the possibility that the dispersion in water is characterized by a narrow spectrum of relaxation times is briefly discussed.
Abstract: Methods used to measure the complex dielectric constant of water and blood at frequencies from 1.7 × 109 to 2.4 × 1010 c/s are described. The results obtained for water at temperatures between 0 and 60° C are given and analysed with relation to the Debye and the Cole-Cole dispersion equations. The possibility that the dispersion in water is characterized by a narrow spectrum of relaxation times is briefly discussed. The complex dielectric constant of whole human blood has been measured at temperatures between 15 and 35° C. The dispersion observed is attributed entirely to water relaxation. It is shown to fit the Debye dispersion equations if the effects of a frequency-independent ionic conductivity are allowed for. Comparison of the results for blood with those for water leads to approximate estimates of the erythrocyte intracellular ionic conductivity and haemoglobin hydration.
86 citations
TL;DR: In this paper, a Geiger-counter spectrometer was used to measure the proportion of elements of atomic numbers higher than 20 in steels by X-ray fluorescence.
Abstract: The measurement of the proportion of elements of atomic numbers higher than 20 in steels by X-ray fluorescence using a Geiger-counter spectrometer has been investigated, primarily with a view to determining the suitability of the method as a rapid means of analysis during the steel-making process, particularly for high alloy steels. A monitoring system to compensate for fluctuations in X-ray tube output is described and shown to increase the accuracy, though gives higher variances than theoretical once obtained by assuming a Poissonian distribution of counting events, and shows "drift" over long periods. From measurements on some iron/chromium/nickel steels it appears that unless a very powerful X-ray tube is used the method gives quick results of high accuracy only when more than about 10% of the alloying element is present. It is also shown that in some cases standard diagrams would have to be drawn up to allow for "mutual fluorescence." Certain possible improvements are noted. An Appendix gives the theory of this X-ray fluorescence analysis.
83 citations
TL;DR: In this article, a method is described to determine the onset of cracking in specimens of concrete subjected to tension or compression in mechanical testing machines, where measurements were made at intervals of the velocities of ultrasonic pulses passing through the test piece in the axial and/or transverse directions.
Abstract: A method is described to determine the onset of cracking in specimens of concrete subjected to tension or compression in mechanical testing machines. While the loads were being applied, measurements were made at intervals of the velocities of ultrasonic pulses passing through the test-piece in the axial and/or transverse directions. In compression, the velocity of the ultrasonic pulses in the direction of loading remained constant while the load was increased to failure, but in the transverse direction a fall in the velocity started at only a fraction of the ultimate load, and the velocity then decreased with increase of load. This indicated that cracking occurred internally parallel to the direction of loading. The load at which it started depended on the strength of the concrete and the uniformity of the stress distribution. In tension, fracture was preceded by only a very small, and often insignificant, amount of cracking which occurred at right angles to the direction of loading.
65 citations
TL;DR: The relationship of the elastic properties of solids to their frictional properties is discussed in this article, where it is shown that while the asperities on metallic surfaces are deformed plastically even at the smallest loads, this is not necessarily true of materials having lower elastic modulus.
Abstract: The relationship of the elastic properties of solids to their frictional properties is discussed. By applying Hertz's equation for deformation of solids in contact, it is shown that while the asperities on metallic surfaces are deformed plastically even at the smallest loads, this is not necessarily true of materials having lower elastic modulus. This is confirmed by measurement of the area of contact between a nylon hemisphere and a glass surface, and by frictional measurements on various nylon specimens. It is shown further that the observed decrease in friction of some high polymers on rough surfaces may be explained in terms of elastic deformation of the asperities.
63 citations
TL;DR: In this paper, the electrical resistance between the meshing teeth of rotating gears has been measured using a cathode-ray oscillograph, indicating values of resistance ranging from infinity to zero.
Abstract: In pursuit of information concerning the nature of lubrication in gears, measurements of the electrical resistance between the meshing teeth of rotating gears have been made using a cathode-ray oscillograph. Photographs of the trace on the screen of the cathode-ray oscillograph are shown indicating values of resistance ranging from infinity to zero. The variation of resistance depends on the load, though the resistance is always lowest where the sliding speed is highest and has its maximum value in the neighbourhood of the pitch-line where there is no sliding motion. Absolute values of film-thickness could not be determined.
TL;DR: In this article, the drop-size distribution in flat sprays produced by agricultural nozzles is discussed and an equation has been derived by dimensional analysis relating a mean drop diameter to operating conditions at the nozzle.
Abstract: The drop-size distribution in flat sprays produced by agricultural nozzles is discussed and an equation has been derived by dimensional analysis relating a mean drop diameter to operating conditions at the nozzle. The equation has been applied to experimental data for agricultural nozzles with satisfactory results. The development of the spray sheet with pressure increase is shown by high-speed photographs
TL;DR: In this paper, a method has been described for the rapid determination of the total emissivity of metals and oxides in the temperature range 300-800° C. The effect of particle size of the oxides and the variation of emissivities with angle of emission have been studied.
Abstract: A method has been described for the rapid determination of the total emissivity of metals and oxides in the temperature range 300-800° C. Values have been obtained for lampblack and polished platinum and also for Nimonic 75, pure nickel, and stainless steel, with various surface conditions. The total emissivities of the pure oxides ceria, zirconia, thoria, magnesia, alumina and fused silica have also been determined. The effect of particle size of the oxides and the variation of emissivity with angle of emission have been studied.
TL;DR: In this article, it was shown that the adhesion between indium and metal surfaces depends only on the area of contact and on the time of breaking of the indium surface.
Abstract: Experiments are described showing that (in the absence of surface contamination) the adhesion between indium and metal surfaces depends only on the area of contact and on the time of breaking. The detailed behaviour may be correlated with the creep properties of indium. With non-metals such as diamond, glass, thick metal oxides and certain plastics very strong adhesions to indium are observed whilst with polytetrafluorethylene, which has a very low coefficient of friction, the adhesion is negligibly small. These results suggest that in the sliding of non-metals, adhesion at the interface plays a part in the frictional mechanism analogous to the cold-welding process in the friction of metals.
TL;DR: In this paper, a treatment of the aberrations caused by the extension of the X-ray source, specimen and receiving slit normal to the plane of the camera or spectrometer is given.
Abstract: A treatment is given of the aberrations caused by the extension of the X-ray source, specimen and receiving slit normal to the plane of the camera or spectrometer. A detailed examination is made of the aberrations which occur: (a) when the height of the specimen is the sole cause, and (b) when the vertical divergence of the X-ray beam is limited by Soller slits, the displacement and profile of the line being determined in each case. It is shown that vertical mis-alinement of a spectrometer can cause an additional broadening of the lines, especially in the back-reflexion region.
TL;DR: In this paper, the elastic constants of the piezoelectric crystals Rochelle salt, potassium dihydrogen phosphate, ammonium dihydric phosphate, quartz, sodium chlorate and sodium bromate are assembled and the variability of the results discussed.
Abstract: The values available in the literature for the elastic constants of the piezoelectric crystals Rochelle salt, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, quartz, sodium chlorate and sodium bromate are assembled. The averages and standard deviations of the estimates are calculated, and the variability of the results discussed. The direct extension and lateral contraction stiffnesses of Rochelle salt show great variability which, however, is much reduced when the elastic constants are expressed as compliances. Little, if any, evidence is found of similar behaviour in the other materials. For comparison with the results on piezoelectric crystals, the available determinations on the non-piezoelectric crystals sodium chloride, lithium fluoride and pyrites are also summarized. It is concluded that elastic constants of crystals are seldom known to better than 1%, and in many cases the uncertainty is considerably larger. This variability is probably due to inherent variability in the materials rather than to experimental error or to differences caused by the use of different experimental methods.
TL;DR: In this paper, the theory of deflexion of anisotropic plates under bending and twisting loads is summarized and experimental methods for investigating the theory are described and tested on metal plates.
Abstract: The theory of the deflexion of anisotropic plates under bending and twisting loads is summarized; experimental methods for investigating the theory are described and tested on metal plates. The results of experiments on plywood cut at various angles to the grain are given and found to conform with the theory.
TL;DR: In this paper, the experimental skin temperature rise in the initial stages of a microwave exposure is consistent with a thermal conductivity for tissues of 0.005 cal cm-1 sec-1?C-1.
Abstract: Experimental investigations of temperature rises produced in parts of the human body during exposure to microwaves of 10 and 9.4 cm wavelength are described. Application of linear heat flow theory shows that the experimental skin temperature rise in the initial stages of a microwave exposure is consistent with a thermal conductivity for tissues of 0.005 cal cm-1 sec-1 ?C-1. With occlusion of the blood supply to the irradiated region the conductivity remains at this value until the pain threshold is reached. With no occlusion, increase in blood supply due to heating causes the effective conductivity to rise during exposure, but the theory becomes inapplicable as soon as heat flow is non-linear. Comparison is made of theoretical and experimental subcutaneous and muscle temperatures after microwave exposure and the differences explained. The influence of wavelength variation and air-cooling of the skin are discussed.
TL;DR: In this paper, the authors considered the problem of the absorption of a single drop from the point of view of geometric optics, from which approximate expressions were derived for the absorption index for any given wavelength and for the angular distribution of radiation transmitted by the single drop.
Abstract: An investigation of the efficiency of water sprays in the protection of buildings and fire-fighting personnel from heat radiation has resulted in a general theoretical study of the transmission of radiation through a layer of water spray of large drops. The treatment is based upon the work of Theissing(1) and takes account of multiple refractive scattering in dense sprays and extends the method to absorbing sprays. The problem of the single drop is approached from the point of view of geometric optics, from which approximate expressions are derived for the absorption of a drop in terms of the absorption index for any given wavelength and for the angular distribution of radiation transmitted by a single drop. Since the absorption of thermal radiation depends markedly on the drop size it is found that the transmission of such radiation departs from the simple exponential extinction law when the drops and the quantities of water in the sprays are small. When the drops are less than about 0.005 cm in diameter, back reflexion by the spray may become significant.
TL;DR: An examination of two sets of examples shows that the external field arising from the gap in a magnetic digit recording head is very insensitive to the pole-piece shape, so that head design should be decided by facility of manufacture rather than by theoretical perfection.
Abstract: An examination of two sets of examples shows that the external field arising from the gap in a magnetic digit recording head is very insensitive to the pole-piece shape. It follows that head design should be decided by facility of manufacture rather than by theoretical perfection.
TL;DR: In this article, an attempt has been made to list the errors, apart from those due to the use of imperfect material, which may occur in the determination of free boundary stresses from direct relative retardation observations on slices cut from "frozen stress" photoelastic models.
Abstract: An attempt has been made to list the errors, apart from those due to the use of imperfect material, which may occur in the determination of free boundary stresses from direct relative retardation observations on slices cut from "frozen stress" photoelastic models and, where possible, to estimate their magnitudes. Particular regard is paid to the important case of a stress concentration, where small radii will introduce errors which would be negligible at other points on the boundary.
TL;DR: In this article, the absorption of microwave radiation in the frequency range 109c/s to 3 × 1010 c/s is reviewed, with particular reference to materials of biological interest.
Abstract: Recent work on the absorption of microwave radiation in the frequency range 109 c/s to 3 × 1010 c/s is reviewed, with particular reference to materials of biological interest. The relative importance of ionic conduction, dipolar relaxation, particularly of water molecules, and resonance is discussed briefly. Conventional methods for dielectric constant and loss measurements at microwave frequencies can be adapted for use with biological materials and a number of such modifications is described. The results of investigations into the dielectric properties of water, the most abundant biological material, proteins and a variety of body tissues are outlined and discussed in terms of established dielectric theory. High power microwave generators have been used to study tissue heating, the heating pattern comparing favourably with predictions from the radiation propagation constants and the thermal properties of the materials. A few experiments on the effects of microwaves on animal tumours and on viruses are described.
TL;DR: A Conference of the X-ray Analysis Group of The Institute of Physics was held in London on 2-3 November, 1951 as discussed by the authors, where the first day's discussion related to the structures of calcium silicates and the second day's to layer lattice silicates.
Abstract: A Conference of the X-ray Analysis Group of The Institute of Physics was held in London on 2-3 November, 1951. The first day's discussion related to the structures of calcium silicates and the second day's to layer lattice silicates. An evening lecture was delivered on the felspars.
TL;DR: In this article, a rapid method for measuring the curvature distortion in the tracks of cosmic-ray particles in photographic emulsions is described, applied to the determination of curvature distortions contours on a 400 μ thick G5 nuclear research plate.
Abstract: A rapid method for measuring the curvature distortion in the tracks of cosmic-ray particles in photographic emulsions is described. The method is applied to the determination of curvature distortion contours on a 400 μ thick G5 nuclear research plate.
TL;DR: In this paper, simple numerical techniques which are used in finite difference mathematics to estimate the infinitesimal result from finite difference solutions taken with various network sizes are discussed, and the importance of selecting an extrapolation form consistent with the accuracy of the individual characteristic value determinations is emphasized.
Abstract: The note outlines briefly simple numerical techniques which are used in finite difference mathematics to estimate the infinitesimal result from finite difference solutions taken with various network sizes. By virtue of the direct analogy between first order difference operators and electrical network voltages, these techniques are directly applicable to extrapolation procedures on characteristic values obtained from networks. In using these procedures the importance of selecting an extrapolation form consistent with the accuracy of the individual characteristic value determinations is emphasized.
TL;DR: In this paper, the Shakespear katharometer was used to detect and measure the diffused gas in the case of iron and palladium, and the results agree well with those of other observers for large values of current density.
Abstract: Experiments have been made to test whether hydrogen produced electrolytically on one side of a metal plate will diffuse through the plate. The Shakespear katharometer was used to detect and measure the diffused gas. The metals examined were iron, nickel, cobalt, copper, zinc, silver, palladium, platinum, and lead. Only in the case of iron and palladium was any diffusion observed. Measurements were made with iron showing how the amount of diffused gas varied with time, and how the rate of steady diffusion varied with the thickness of the plate. The variation of the rate of diffusion with the electrolysing current density was observed for plates of iron and palladium. The results agree well with those of other observers for large values of the current density, but show that a threshold value of current density does not exist and that for low values of current density the rate of diffusion is approximately proportional to it. The diffused gas appears to be in the ordinary molecular state. A simple theory which explains the general character of the experimental results is given.
TL;DR: In this article, a study of liquid films ejected from the rims of rotating disks with liquid supplied at the centre is presented, with a distinction between films tending to ellipsoidal shape whose peripheral thicknesses vary within fairly wide limits, and substantially horizontal films whose dimensions are governed by the breaking thickness of the liquid concerned.
Abstract: A study is made of liquid films ejected from the rims of rotating disks with liquid supplied at the centre. The variation in film area with alteration in experimental conditions is best explained by the assumption of a limiting film thickness, the breaking thickness, for each liquid, below which the film can no longer exist unsupported in the air in the face of disruptive forces. This assumption is supported by experimental evidence including a study of the paths of liquid particles and liquid films before and after leaving the rotating disk, and a rough measurement of film thickness. A distinction is made between films tending to ellipsoidal shape whose peripheral thicknesses vary within fairly wide limits, and substantially horizontal films whose dimensions are governed by the breaking thickness of the liquid concerned. The mechanism of the formation and destruction of these liquid films is discussed and differences in the behaviour of water and glycol examined.
TL;DR: In this paper, the merits of different finite difference representations of the heat flow equation and a convection boundary condition equation are discussed in terms of the stability and accuracy of the solutions they yield.
Abstract: The merits of different finite difference representations of the heat flow equation and a convection boundary condition equation are discussed in terms of the stability and accuracy of the solutions they yield. A new method of deriving a condition for stability is given. This is applied to examples of heat conduction involving variable thermal diffusivity and heat transfer by convection at the surface. Some finite difference forms of this boundary condition impose stability criteria which are stricter than, or additional to, that required in the case of a prescribed surface temperature. A new finite difference representation of the surface heat flux equation is discussed. The accuracy of the various finite difference schemes is investigated by comparing both their analytical and numerical solutions with analytical solutions of the differential equation of heat flow.
TL;DR: In this paper, an attachment is described which fits over the objective lens of a bench metallurgical microscope, and enables replica supporting grids to be precisely positioned over a feature of interest in the microstructure.
Abstract: The difficulties involved in attempting to obtain optical and electron micrographs from the same area of a metal surface using the standard dry-stripping technique are outlined. An attachment is described which fits over the objective lens of a bench metallurgical microscope, and enables replica supporting grids to be precisely positioned over a feature of interest in the microstructure. By this method, optical and electron micrographs of the same area of the surface may be readily obtained. The mode of operation is described in detail and the applications of the method are indicated.
TL;DR: In this paper, a simple step-by-step method is given, using a procedure due to Fox and Goodwin for equations of the type d2y/dx2 = f(x)y.
Abstract: For the solution of the paraxial ray equation, a very simple step-by-step method is given, using a procedure due to Fox and Goodwin for equations of the type d2y/dx2 = f(x)y. The accuracy of the method can be increased to any desired extent without increasing the complexity. All sources of inaccuracy except those present in the given field data can thus be avoided, and the aberration integrals can be accurately evaluated. If required, an approximate solution may be obtained initially, which is easily modified later for better accuracy, without redundancy of the early work. Graded intervals are easily introduced. A worked example is given for a the early work. Graded intervals are easily introduced. A worked example is given for a strong electrostatic lens.