Showing papers in "British Journal of Applied Physics in 1961"
TL;DR: In this article, the authors extended the calculations of Stimson and Jeffery of the force on two spheres moving coaxially through a viscous liquid to the case when the spheres move at different rates.
Abstract: The calculations of Stimson and Jeffery of the force on two spheres moving coaxially through a very viscous liquid are extended to the case when the spheres move at different rates. This result is used to calculate the effect of the bottom of the vessel in a falling sphere viscometer and that of the upper surface of the liquid. Approximate solutions are also found in a form suitable for practical use.
194 citations
TL;DR: In this article, experimental data of the drag exerted by the walls of a cylindrical vessel on a sphere falling axially down it through a liquid are given for Reynolds numbers, based on the diameter of the sphere, between 0.05 and 20 000.
Abstract: Experimental data of the drag exerted by the walls of a cylindrical vessel on a sphere falling axially down it through a liquid are given for Reynolds numbers, based on the diameter of the sphere, between 0.05 and 20 000. Existing wall-correction formulae are examined in the light of the new data, the conclusion being that the Francis (1933) and Munroe (1888) equations are the most reliable in the laminar- and turbulent-flow regions respectively. Graphs show the correction to be applied in the intermediate-flow region.
147 citations
TL;DR: In this paper, two different lengths of wire, of the same diameter, were electrically heated in vacuo, and the wire emissivity was measured from the readings of wire resistance and current.
Abstract: The method of measurement of the emissivities is described. Two different lengths of wire, of the same diameter, were electrically heated in vacuo. By this procedure the end cooling correction could be eliminated experimentally. From the readings of wire resistance and current the net rate of radiant energy loss from the wire to the surroundings, and hence the wire emissivity, could be found. The values of emissivity are compared with those for platinum wires and also with values calculated from wire resistivity on the basis of electromagnetic theory.
95 citations
TL;DR: In this article, it is suggested that the reaction leading to significant increases in temperature at relatively low ambient temperatures is not that responsible for ignition; ignition appears to be mainly the result of other reactions which become appreciable only at higher temperatures.
Abstract: The self-heating and self-ignition of fibre insulating board and similar materials are discussed in the light of the well-known theory of thermal explosion. It is pointed out that the simple theory for a single reaction neglecting reactant loss during the induction period is inadequate for the interpretation of all the data published by Mitchell (1951). In the case of wood fibre insulating board it is suggested that the reaction leading to significant increases in temperature at relatively low ambient temperatures is not that responsible for ignition; ignition appears to be mainly the result of other reactions which become appreciable only at higher temperatures. Some experimental results in support of this contention are given, and it is estimated that the total heat of reaction is 80 cal g-1. The induction times reported by Mitchell for three materials show one of them (cotton linters) to be different in its behaviour from the other two.
84 citations
TL;DR: In this paper, an experimental technique has been developed for the measurement of the temperature distribution in the deformation zone and in the chip and tool during orthogonal cutting, where the cutting edge of the tool is perpendicular to the direction of relative motion of the workpiece and tool.
Abstract: An experimental technique has been developed for the measurement of the temperature distribution in the deformation zone and in the chip and tool during orthogonal cutting. The term orthogonal cutting is used for the special case where the cutting edge of the tool is perpendicular to the direction of relative motion of the workpiece and tool. The method involves photographing the chip, tool and workpiece in a plane perpendicular to the cutting edge, using an infra-red sensitive photographic plate. The optical density of the plate is determined over the relevant field by means of a microdensitometer. A heated tapered strip, on which the temperature distribution is measured by means of a series of thermocouples, is photographed simultaneously with the tool and workpiece. This enables the optical density of the plate to be calibrated in terms of temperature, and the temperature distribution over the chip, tool and workpiece can hence be determined. The effect of surface emissivity and of other factors on the accuracy of the technique are considered, and the results of an experiment using the photographic technique are presented and discussed in relation to previous theoretical and experimental work.
83 citations
TL;DR: In this article, the temperature of a thin metal foil illuminated by the high intensity electron beam of the modern microscope may at the centre of illumination reach a temperature above that of the melting point of iron.
Abstract: The temperature of a thin metal foil illuminated by the high intensity electron beam of the modern microscope may at the centre of illumination reach a temperature above that of the melting point of iron. An attempt has been made to measure and calculate the temperature distribution for any given metal under various illumination conditions and to determine also the stress fields produced in the foil by such temperature distribution.
80 citations
TL;DR: In this article, it was shown that within a critical range of deposition conditions, sufficient energy may be imparted to spherical particles to activate a process of ordered packing, initiated at a wall.
Abstract: Measurements of the packing of spherical particles poured into a cylindrical container show that the intensity of deposition, the height of drop and the elasticity of the particle material influence the packing equally. Minor departures from perfect sphericity tend to mask the influence of elasticity. Optimum packing of poured spherical particles occurs when the energy increment imparted to the bed by each impacting particle exceeds a critical value, the rate of renewed application of increments is above a critical value and the intensity of deposition is below a critical level. Within a critical range of deposition conditions, sufficient energy may be imparted to spherical particles to activate a process of ordered packing, initiated at a wall. These conditions are fulfilled when 0.125 in. diameter spheres fill a 3 in. diameter glass cylinder at 1400 particles per second with impact velocities greater than 120/{½(1 + em)}12 in/s, em being the resilience of the particle material. Determinations of wall effect show that these conclusions and the derived mechanism of packing are valid for the packing of an infinitely extensive bed.
74 citations
TL;DR: In this article, a rotary multiple electrode containing eight pairs of electrodes was incorporated in a simple and efficient fractionation-filtration unit to limit the duration of breakdown current, and the results showed the formation of a region of very low refractive index at the cathode.
Abstract: The work is a contribution to the understanding of the mechanism of electric breakdown in liquid dielectrics. The liquid dielectric chosen throughout the experiments was n-hexane, because an extensive literature exists on the breakdown of this material. The applied voltage was a rectangular pulse of different durations supplied from a 125 kv, five-stage Marx-Goodlet impulse generator. A novel rotary multiple electrode containing eight pairs of electrodes was incorporated in a simple and efficient fractionation-filtration unit. A protection circuit, incorporating an inverter and a trigatron, limited the duration of breakdown current. A series of photographs of the state of n-hexane under the applied electric field was taken by Schlieren technique, using a spark light-source and a still camera. A statistical survey of the results shows the formation of a region of very low refractive index at the cathode. It is suggested that this is due to streamers with a very large number of branches, which propagate towards the earthed electrode. The rate of growth increases with voltage and above a certain voltage, if enough time is allowed, the stepped streamers bridge the electrode gap and breakdown of the liquid results.
62 citations
TL;DR: In this article, a treatment of the permeability of a heterogeneous medium consisting of a regular lattice of rectangular parallelepipeds in a continuum has been given, and the treatment is also valid for the thermal or electrical conductivity, permittivity, or magnetic permeability.
Abstract: A treatment has been given of the permeability of a heterogeneous medium consisting of a regular lattice of rectangular parallelepipeds in a continuum. Effects on the permeability due to surface resistances on the upstream and downstream faces of the parallelepipeds have been considered, and also aspects of the role of particle shape and orientation. The treatment provides an approach to the permeability of and fractionation by foam plastic membranes. When the disperse phase has molecular sieve properties, high continuous fractionation factors for appropriate composite membranes and mixtures of diffusants are found to be possible. The treatment is also valid for the thermal or electrical conductivity, permittivity, or magnetic permeability of such a lattice.
61 citations
TL;DR: In this paper, the effect of string rigidity on the capstan equation is considered, and two cases which cover the most likely situations are distinguished -contact of the string with the peg at a point, and contact over an arc.
Abstract: The effect of string rigidity on the capstan equation is considered. Two cases which cover the most likely situations are distinguished - contact of the string with the peg at a point, and contact over an arc. The analysis of these situations is facilitated by an approximation derived for the curvature for the leads of string on either side of the peg. If the friction is governed by Amontons' law the correction of the capstan equation for string rigidity will usually be small, but in the case of arc contact and load-dependent coefficient of friction, the correction could be important.
44 citations
TL;DR: In this paper, general formulae are presented for square and linear probe arrays on circular specimens which permit the calculation of sheet resistivity from voltage and current measurements made with the probes in any position.
Abstract: General formulae are presented for square and linear probe arrays on circular specimens which permit the calculation of sheet resistivity from voltage and current measurements made with the probes in any position. From these formulae it is deduced that the square probe array is preferable on small specimens on the grounds of accuracy, as well as from spatial considerations.
TL;DR: In this article, it was shown that with simple equipment for measuring mutual inductance over a range of frequencies, the method can be used to measure resistivities from 2 × 10-9 ohm cm upwards, and the necessary functions are tabulated.
Abstract: The resistivity of a sample can be deduced from the change in mutual inductance between two coils when the sample is inserted. It is shown that with simple equipment for measuring mutual inductance over a range of frequencies, the method can be used to measure resistivities from 2 × 10-9 ohm cm upwards, and the necessary functions are tabulated.
TL;DR: In this article, the mechanical forces in electrically stressed dielectrics have been derived on the basis of the principle of minimum potential energy, and a brief discussion is given with particular reference to their effects on the dielectric breakdown.
Abstract: On the basis of the principle of minimum potential energy, mechanical forces in electrically stressed dielectrics have been derived. These forces are appreciable in strong electric fields. A brief discussion is given with particular reference to their effects on the dielectric breakdown.
TL;DR: A 36 kc/s underwater acoustic echo-ranger, fitted to R.R.S. ''Discovery II'' for work on fish detection problems, has also proved to be a valuable tool for marine geological investigations as discussed by the authors.
Abstract: A 36 kc/s underwater acoustic echo-ranger, fitted to R.R.S. `Discovery II' for work on fish detection problems, has also proved to be a valuable tool for marine geological investigations. The axis of the acoustic beam is perpendicular to the fore and aft line of the ship and may be rotated from the horizontal to the downward vertical. Stabilization is provided against the roll of the ship. Beam width and side lobe patterns are adjustable with minimum widths, between 3 dB points, of 1.3° in plan and 12° in elevation (beam axis horizontal). The recorder provides a range of 800 yards and scanning is achieved by steaming the ship past the features to be investigated.
TL;DR: In this article, X-ray diffraction of foils produced sharp patterns of spots which indicated a principal orientation of crystallites in direct alignment with the substrate crystal, together with twins whose presence was confirmed by metallography.
Abstract: Foils up to 2.5 × 10-3 cm in thickness, of Cu, Ag, Pd and Au, have been evaporated on to LiF and mica crystals, epitaxial growth was observed within fixed temperature ranges for each substrate-metal combination. X-ray diffraction of the foils produced sharp patterns of spots which indicated a principal orientation of crystallites in direct alignment with the substrate crystal, together with twins whose presence was confirmed by metallography. The observations are discussed in terms of a nucleation and growth model.
TL;DR: In this paper, the action of two etchants on magnesium oxide has been studied and the etch pits, pyramids and hillocks may be produced and both etch agents dissolve away the crystal surface.
Abstract: The action of two etchants on magnesium oxide has been studied. Etch pits, pyramids and hillocks may be produced and both etchants dissolve away the crystal surface. Activation energies for dissolution are estimated and the etching processes discussed with particular reference to dislocations and impurities.
TL;DR: In this paper, the rate of deposition of sputtered molybdenum films in the abnormal glow discharge in inert gases over the pressure range 3-21 mm Hg, as a function of the gas pressure p and the current i through the discharge tube, was found to be proportional to (i/p)2.5 in both neon and the Penning mixture 99% neon-1% argon.
Abstract: Measurements have been made of the rate of deposition of sputtered molybdenum films in the abnormal glow discharge in inert gases over the pressure range 3-21 mm Hg, as a function of the gas pressure p and the current i through the discharge tube. The rate of sputtering was found to be proportional to (i/p)2.5 in both neon and the Penning mixture 99% neon-1% argon. In helium sputtering was negligible, but the addition of only a trace of neon caused appreciable sputtering to occur.
TL;DR: In this paper, it was shown that the experimental results confirm a previously reported model of the sorption process, where gas ions enter a heterogeneous collection of capture sites of various energies of binding in the glass walls.
Abstract: The ion pumping of five noble gases by Bayard-Alpert ionization gauges has been studied extensively, employing an ultra-high-vacuum system which could be operated statically or dynamically. The dependence of the important pumping parameters, initial pumping speed and maximum quantity of gas pumpable, upon gas composition, electrode potentials and gauge temperature have been investigated. The relationship between instantaneous pumping speed and the quantity of gas pumped has been deduced, and observations upon the recovery of gas, following sorption, at ambient and elevated temperatures has also been made. It is shown that the experimental results confirm a previously reported model of the sorption process, where gas ions enter a heterogeneous collection of capture sites of various energies of binding in the glass walls. The observed form of a static pump-down is interpreted in terms of the kinetic processes which can occur at these sites.
TL;DR: In this article, the authors described experiments in which ion beams of the order of five micro-amperes with a low energy spread have been used to bombard a tungsten surface.
Abstract: Experiments are described in which ion beams of the order of five micro-amperes with a low energy spread have been used to bombard a tungsten surface. Sorption values for the surface are given for neon, argon and krypton and show that a maximum sorption exists at any particular bombarding ion energy. Using several simplifications a value for the depth of penetration of the ions is derived from the results and this is shown to be in reasonable agreement with values quoted by other workers. Results from a second series of experiments where ions of a second gas release the sorbed ions of the first gas are also presented.
TL;DR: In this article, a brief review of low temperature properties of silicon and germanium diodes is given, which are relevant to the performance of p-n junctions at liquid helium temperatures.
Abstract: This paper gives a brief review of those low temperature properties of silicon and germanium which are relevant to the performance of p-n junctions at liquid helium temperatures. Experimental results are presented for germanium and silicon diodes and their interpretation is attempted. It is found that germanium devices behave in a manner similar to room temperature behaviour provided the ohmic contacts are adequate. Silicon diodes exhibit anomalies owing to insufficient doping of the end regions or to trapping in the base.
TL;DR: The mathematical expressions for the field intensities external to spheroids or an ellipsoid with uniform magnetization are given in this article, which are useful in predicting fields external to open-structure magnetic devices such as metallic or ferrite films, twistors or splinters.
Abstract: The mathematical expressions for the field intensities external to spheroids or an ellipsoid with uniform magnetization are given. They are useful in predicting fields external to (a) open-structure magnetic devices such as metallic or ferrite films, twistors or splinters, and (b) spheroidal and ellipsoidal samples which are often used in magnetic measurements. Curves are plotted to indicate the spatial variation of field intensity with the dimensional ratio of a spheroid as a parameter. In the region near the spheroid, field intensity is normalized against field intensity at the boundary. In the region far from the spheroid, field intensity is normalized against that of a dipole of the same dipole strength as the spheroid.
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TL;DR: A hundred years ago better navigational instruments, improved charts and the compilation of wind and current atlases brought much improvement to navigation as mentioned in this paper, and the advances made by modern instruments and theoretical methods are second-order steps, but they are just as exciting and with the increased pressure of to-day's civilization and industry, probably more important.
Abstract: A hundred years ago better navigational instruments, improved charts and the compilation of wind and current atlases brought much improvement to navigation. In comparison the advances made by modern instruments and theoretical methods are second-order steps, but they are just as exciting, and with the increased pressure of to-day's civilization and industry, probably more important. In particular we are beginning to get a better understanding of waves, currents and the general circulation in the oceans, which will allow us to make better use of the oceans, and to contend with them on more equal terms when necessary.
TL;DR: In this article, the spectral emissivity varied strongly with surface roughness and oxidation, but only slightly with temperature, and the significance of these variations to radiation pyrometry is briefly discussed.
Abstract: Results are given for surfaces of roughness 3 μ in., 115 μ in. and anodized aluminium within the wavelength range 1 to 14 μ. The spectral emissivity varied strongly with surface roughness and oxidation, but only slightly with temperature. Typical values at wavelengths 2 and 8 μ respectively were 0.09 and 0.04 for polished, 0.30 and 0.24 for roughened, 0.30 and 0.20 for anodized aluminium. Natural oxidation slightly increased the spectral emissivity at all wavelengths below 9 μ and had a marked effect between 10 and 12 μ. An anodic oxide film increased the spectral emissivity beyond 10 μ to greater than 0.70. The significance of these variations to radiation pyrometry is briefly discussed.
TL;DR: In this article, the effect of cutting stresses on the formation of sections is discussed and the parameters of microtome sectioning are defined, and the use of the diamond knife ultra-microtome for metallurgical studies is described.
Abstract: The parameters of microtome sectioning are defined, and the use of the diamond knife ultra microtome for metallurgical studies is described. The effect of cutting stresses on the formation of sections is discussed. It is reasoned that vibration of parts of the cutting system would only be excited by the first impact of the specimen or the knife and not by the forces acting on them throughout cutting. Vibration is shown to produce smooth variations in section thickness, the thickness being constant all along any normal to the direction of cutting, and varying along the direction of cutting. Knife marks are shown to be due to variations in cutting stress associated with knife edge defects; these produce variations in the thickness and structure of the section, even when the mechanism proposed by Farrant cannot apply. Some folds and wrinkles are explained as being due to variation in cutting stress due to variations in knife edge quality. All the above defects can be avoided by a proper choice of experimental conditions, but it is shown that there is a shear stress imposed on the section during cutting which in the majority of cases permanently deforms it, producing a surface structure characteristic of the material being cut.
TL;DR: In this article, the intergranular cohesion of granular masses is investigated with an apparatus which in principle is a Couette viscometer, with the difference that the plastic yield point S0 of a granular mass is a function of the pressure p which acts normally on the yielding plane.
Abstract: The intergranular cohesion of granular masses is investigated with an apparatus which in principle is a Couette viscometer. Rheologically, the granular mass behaves as a plastic solid, with the difference that the plastic yield point S0 of a granular mass is a function of the pressure p which acts normally on the yielding plane. In an (S0, p) diagram, a cohesionless mass will be represented by a straight line passing through the origin and having a limiting slope of 0.193, while a granular mass with cohesion will show a lesser slope, the departure from the limiting value being a convenient measure of the cohesion. Powders which are not free-flowing will be represented in the (S0, p) diagram by lines, which are not necessarily straight, with an intercept on the S0 axis. The cohesion of a few samples of sand of different granularity and that of a few other granular masses has been measured.
TL;DR: In this paper, it was confirmed that the use of gas and vapour mixtures stored in cylinders under pressure is a suitable method for calibration and that such mixtures are stable with time.
Abstract: With the increasing use of physical methods of gas and vapour analysis, there is a need for a convenient means of calibration. It is confirmed that the use of gas and vapour mixtures stored in cylinders under pressure is a suitable method. Such mixtures are stable with time. The analysis of gas and vapour mixtures has been found to agree to within 1% of the calculated value.
TL;DR: In this paper, the authors made a study of the frictional properties of lignum vitae, an extremely hard wood which finds an important application in underwater bearings. And experiments showed that this is due to the lubricating action of woodwaxes expressed from the wood during sliding.
Abstract: A study has been made of the frictional properties of lignum vitae, an extremely hard wood which finds an important application in underwater bearings. In the dry state, the friction of this material is comparable with that of P.T.F.E. and experiments show that this is due to the lubricating action of woodwaxes expressed from the wood during sliding. The rolling friction due to hysteresis losses is very small. The sliding friction can be explained satisfactorily in terms of an adhesion mechanism.
TL;DR: In this article, the authors used a combination of mechanical polishing and chemical etching to obtain a film about 1000 A thick, suitable for observing dislocations by transmission electron microscopy.
Abstract: Films about 1000 A thick, suitable for observing dislocations by transmission electron microscopy, have been prepared from the brittle semiconductors germanium and silicon by a combination of mechanical polishing and chemical etching.
TL;DR: Spark planing, a new spark erosion method for the production of flat smooth metal surfaces, is described and its application to single metal crystals and to metallographic preparation is illustrated as mentioned in this paper.
Abstract: Spark planing, a new spark erosion method for the production of flat smooth metal surfaces, is described and its application to single metal crystals and to metallographic preparation is illustrated. The use of conventional spark erosion methods for crystal cutting and forming is also described. The spark planing technique is far more rapid and accurate than chemical or electrochemical machining and it causes very much less damage to the surface than the most careful grinding operation. Spark planed surfaces have been examined by x-ray diffraction, reflection electron microscopy and a Talysurf tracer: these results are presented and the nature and extent of surface damage to various metals is discussed.
TL;DR: In this paper, the relationship between transfer and circuit inductance at very low values of the inductance has been determined for platinum and palladium contacts operating at potential differences of the order of one volt.
Abstract: The use of radioactive isotopes in the measurement of the transfer of metal from one electrode of an electrical contact to the other is described and details of the experimental procedure are given. The relation between matter transfer and circuit inductance at very low values of the inductance has been determined for platinum and palladium contacts operating at potential differences of the order of one volt. It is shown that for these metals there is no range of inductance down to 10-8 H over which the transfer is independent of inductance. The amount of transfer in relation to the volume of the molten metal bridge between the electrodes is considered, and the significance of the results in the light of theories of the phenomenon of transfer is discussed.