Showing papers in "Journal of Physics E: Scientific Instruments in 1969"
TL;DR: An analysis of the spatial resolution of the Kovasznay vorticity meter and arrays for measuring velocity derivatives in isotropic turbulence is presented in this article, where Pao's three-dimensional spectrum is used, allowing calculations of the measured values of the one-dimensional VOR spectrum and mean-square velocity derivatives to be compared with their predicted values.
Abstract: Analyses of the spatial resolution of the Kovasznay vorticity meter and of arrays for measuring velocity derivatives in isotropic turbulence are presented. Pao's three-dimensional spectrum is used, allowing calculations of the measured values of the one-dimensional vorticity spectrum and mean-square velocity derivatives to be compared with their predicted values. It is found that for accurate measurement the array size should be of the order of the Kolmogorov microscale of the turbulence field.
165 citations
TL;DR: In this paper, an alternative model is proposed which interprets the output frequency in terms of a particle crossing a set of fringes, real or virtual, and a simplified optical system is then described which can be used with both a gas laser and a pulsed laser.
Abstract: The operation of a laser Dopplermeter has been generally described in terms of the Doppler effect. An alternative model is proposed which gives a more complete description of the performance of the system. This model interprets the output frequency in terms of a particle crossing a set of fringes, real or virtual. A simplified optical system is then described which can be used with both a gas laser and a pulsed laser, which is not practical with previous systems. It also shows that a laser is not essential, but only convenient.
152 citations
TL;DR: In this paper, the need for depth sounding in glaciers, ice sheets, and ice shelves is discussed and a v.h.f. radar, designed specifically to produce continuous profiles of ice depth is described.
Abstract: The glaciological need for depth-sounding in glaciers, ice sheets, and ice shelves is discussed. A v.h.f. radar, designed specifically to produce continuous profiles of ice depth is described. Some practical problems of field operation are mentioned and there is reference to the results so far obtained.
79 citations
IBM1
TL;DR: In this paper, a detailed description of the cathode structure is given and the effects of poor vacua on cathode performance are discussed, together with estimated lifetimes for several operating brightnesses.
Abstract: Measured lifetimes, heating powers and brightnesses are presented for the lanthanum hexaboride rod cathode electron gun together with estimated lifetimes for several operating brightnesses. A detailed description of the cathode structure is given and the effects of poor vacua on the cathode performance are discussed.
70 citations
TL;DR: A new type of image intensifier, a channel plate, has been used to increase the image brightness in the field-ion microscope as mentioned in this paper, which yielded images without significant loss of contrast or resolution at brightness gain of more than 103.
Abstract: A new type of image intensifier, a channel plate, has been used to increase the image brightness in the field-ion microscope Both electromagnetic and proximity focusing of the secondary electrons have yielded images without significant loss of contrast or resolution at a brightness gain of more than 103 The channel plate operates satisfactorily in the presence of the imaging gases normally used in field-ion microscopy
66 citations
TL;DR: The results of the theoretical analysis of the relationships between the four-point probe factors are presented in this article. But they do not consider the relationship between the potential and current parameters of the probe factors.
Abstract: The results of the theoretical analysis of the relationships between the four-point probe factors are presented. For any configuration of the four electrodes on the thin film specimen there are at the most three different correction factors, in respect to the absolute value, if the potential and current electrodes are arbitrarily chosen. There are certain groups of electrode configurations for which the three factors are related by exponential relationships. If the electrodes are placed along the thin film boundary, one of the equations gives Van der Pauw's equation. Two practical applications of the theoretical results are shown, namely an experimental method of calibrating some four-point arrays, and the four-point method utilizing the balanced distribution of the four deposited electrodes, in order to increase the precision of the sheet resistivity measurement.
58 citations
TL;DR: In this article, the formation of hologram vibration interference fringes under the assumption that an object may vibrate in any linear combination of its permissible modes, even while executing forced vibration at a single frequency.
Abstract: In this paper the authors offer an explanation for the holographic observation of vibration patterns that do not agree with the classical mode theory of vibrating objects. The equations are derived for the formation of hologram vibration interference fringes under the assumption that an object may vibrate in any linear combination of its permissible modes, even while executing forced vibration at a single frequency. The modes appear to combine by phasor addition in these equations to give fringe loci that depend strongly on the relative phase of the combining modes. A set of experiments are reported which demonstrate this behaviour and allow quantitative comparison to the theory. Finally, the equations are derived for combinations of modes vibrating with independent frequencies, and again a set of experiments is reported which demonstrates this behaviour and permits quantitative comparison. Here the resultant fringes appear as the product of the fringe patterns of the component modes.
54 citations
TL;DR: In this paper, a stereographic technique has been developed for the accurate determination of the dimensions of features on scanning electron micrographs, which is necessary largely because of the wide range of operating angles available in the scanning electron microscope.
Abstract: A stereographic technique has been developed for the accurate determination of the dimensions of features on scanning electron micrographs. More general methods than those used previously are shown to be necessary largely because of the wide range of operating angles available in the scanning electron microscope. An experimental verification of the method is described which shows that results accurate to ±5% can be obtained, without precision measuring equipment.
54 citations
TL;DR: In this article, a ratio transformer bridge for comparison of capacitances in a differential capacitance transducer gives a seven figure bridge reading which is linear in displacement or tilt.
Abstract: Use of a ratio transformer bridge for comparison of capacitances in a differential capacitance transducer gives a seven figure bridge reading which is linear in displacement or tilt. Principal application is to a portable tiltmeter reading to 10−9 rad with a range of 10−2 rad.
51 citations
TL;DR: In this article, a concentric guarded probe assembly suitable for measurements of the distribution of static electric charge density on dielectric surfaces is described, and the procedure for calibrating the probe is given.
Abstract: A concentric, guarded probe assembly suitable for measurements of the distribution of static electric charge density on dielectric surfaces is described. The procedure for calibrating the probe is given. Application of the device is illustrated by studies of the density of electric charge on a perspex surface.
45 citations
TL;DR: In this article, a least squares collocation method was used to calculate the potential distributions of electrostatic einzel lenses consisting of three thin apertures, and the focal lengths, principal plane positions and spherical aberration coefficients were obtained by numerical integration of the ray equations.
Abstract: A least-squares collocation method has been used to calculate the potential distributions of electrostatic einzel lenses consisting of three thin apertures. The focal lengths, principal plane positions and spherical aberration coefficients have been obtained by numerical integration of the ray equations.
TL;DR: In this article, a computer-linked micro-densitometer was constructed by fitting a stage with cross-slides driven by impulse motors to a commercial projection microscope, and its accuracy and speed were compared with those of a cathode-ray-tube micro-DENITometer.
Abstract: A computer-linked microdensitometer has been constructed by fitting a stage with cross-slides driven by impulse motors to a commercial projection microscope. Its accuracy and speed are compared with those of a cathode-ray-tube microdensitometer. The procedure and requirements for analysing x-ray photographs from biological fibres are described.
TL;DR: A method is described whereby contrast resulting from potential variations on the specimen appears in the final display, whereas contrast arising from other mechanisms is almost completely cancelled.
Abstract: Contrast in a scanning electron microscope can arise from potential variations on the surface of the specimen or from a number of other causes such as the topography of the surface. A method is described whereby contrast resulting from potential variations on the specimen appears in the final display, whereas contrast arising from other mechanisms is almost completely cancelled.
TL;DR: In this article, a combined gas chromatograph-mass spectrometer was used to obtain data from an IBM 1800 computer and also on an off-line digital magnetic tape recorder for later processing of the data by the computer.
Abstract: Data from a combined gas chromatograph-mass spectrometer have been obtained and recorded on-line to an IBM 1800 computer, and also on an off-line digital magnetic tape recorder for later processing of the data by the computer. Incremental and continuous modes of recording were used and in all cases a fast electronic mass marker established the mass scale. Several hundreds of mass spectra were consecutively recorded. Computer programs have been developed to evaluate the mass spectrometric data.
TL;DR: In this paper, a modification of the method of expansion in terms of Bessel functions has been developed for the accurate calculation of the potential distributions of cylindrically symmetric electrostatic lenses.
Abstract: A new and simple modification of the method of expansion in terms of Bessel functions has been developed for the accurate calculation of the potential distributions of cylindrically symmetric electrostatic lenses. The method has been used to give the potential distributions of some double-aperture immersion lenses, and the positions of the cardinal points and the spherical aberration coefficients of these lenses have been calculated by numerical integration of the ray equations. The calculated values are accurate to better than 1%, and differ significantly from previous experimental values.
TL;DR: In this paper, the problem of dielectric particles becoming embedded in the multilayers of a laser mirror was discussed and an apparatus was described which was successfully used to reduce this effect to a very low level on one inch diameter, 23 layer mirrors.
Abstract: Some of the problems involving the production of high efficiency laser mirror coatings are discussed. Gross scattering losses caused by dielectric particles becoming embedded in the multilayers present a major problem. An apparatus is described which was successfully used to reduce this effect to a very low level on one inch diameter, 23-layer mirrors.
TL;DR: In this article, a semi-automatic pipette-puller was used to produce glass micropipette electrodes with extremely fine tips and high mechanical rigidity, which are then inserted into living cells.
Abstract: Glass micropipette electrodes with extremely fine tips and high mechanical rigidity have been fabricated with a semi-automatic pipette-puller. The fabrication involves a two stage pull of a heated glass capillary held horizontally by a pair of non-slip clamps. Air is automatically blown from symmetrically located nozzles on to the softened portion of the capillary at the onset of the second pull. With this technique micropipettes with a relatively short taper and large cone angle at the very tip are produced, which not only possess high mechanical rigidity, but also a fineness at the tip (500 A or less). A special advantage of the large cone angle at the tip is that such an electrode has a much lower electrical impedance than a conventional micropipette electrode with a comparable tip diameter. The size and shape of the micropipette can be easily altered to meet the specific need. The principle of differential vapour pressure has been utilized to fill the micropipettes with the desired electrolytes. A vibration technique for inserting a microelectrode into living cells is also described.
TL;DR: In this paper, it is shown that, to minimize errors in double-spiked isotopic analyses, spike mass numbers should alternate with normal. But the model is based on an idealized model, and the error multipliers are obtained by combining a coefficient of variation eP due to fluctuations in ion emission with (ii) a resistor noise index eR and (iii) a shot noise index ES: the noise indices are the ratios [error due to noise]/[error (i) due to emission fluctuation] for the largest ion beam in the spectrum.
Abstract: Using an idealized model it is shown that, to minimize errors in double-spiked isotopic analyses, spike mass numbers should alternate with normal. The comprehensive error analysis which follows assumes that the individual ion currents are the independent varietes for statistical purposes: errors in these are obtained by combining (i) a coefficient of variation eP due to fluctuations in ion emission with (ii) a resistor noise index eR and (iii) a shot noise index eS: the noise indices are the ratios [error due to noise]/[error (i) due to emission fluctuation] for the largest ion beam in the spectrum. Methods of computing error multipliers (operating on eP) from eR, eS and the isotopic abundances, are developed. For a particular element each error multiplier can be regarded as a function of two variables, the ratio of the two spikes selected and the spike/normal ratio, which can then be optimized by numerical methods. Optimum values of spike composition and spike/normal ratio are given for observations of isotopic fractionation of lead, molybdenum and iron using various pairs of spike mass numbers. If both noise indices are taken to be zero the minimum error multipliers are not very much increased by deviations from the ideal model. When eR is given values corresponding to experience with a typical electrometer, it is shown that satisfactory results would be obtained on Pb and Mo with quite low ion currents, but that for iron, because of its difficult isotopic composition, the maximum ion current should be as large as possible. Some possible deviations from first-order fractionation theory are considered. A general algebraic analysis for the determination of radiogenic isotopes is given, and different approaches to fractionation computations are discussed.
TL;DR: In this paper, the oscillatory laminar flow of a Newtonian fluid in a circular tube has been investigated when the fluid is subjected to a periodic pressure gradient and a technique has been developed which allows the velocity amplitude to be determined as a function of radius.
Abstract: The oscillatory laminar flow of a Newtonian fluid in a circular tube has been investigated when the fluid is subjected to a periodic pressure gradient. A technique has been developed which allows the velocity amplitude to be determined as a function of radius and the results agree closely with theoretical predictions. The work is being continued with a view to employing the technique for the determination of the rheological properties of viscoelastic fluids.
TL;DR: In this paper, a cheap, accurate and extremely flexible dynamometer is described which has been used for measuring mixing torques from 5×10−3 to 2 N m. The main advance over other dynamometers is the use of a combined thrust and journal air bearing which supports the mixing vessel and is almost frictionless.
Abstract: A cheap, accurate and extremely flexible dynamometer is described which has been used for measuring mixing torques from 5×10−3 to 2 N m. The main advance over other dynamometers is the use of a combined thrust and journal air bearing which supports the mixing vessel and is almost frictionless.
TL;DR: In this paper, a flashlamp-pumped dye laser has been developed to measure minor constituents of the upper atmosphere by resonance scattering, and the construction of the laser and the procedures for tuning are described in detail.
Abstract: A flashlamp-pumped dye laser has been developed to measure minor constituents of the upper atmosphere by resonance scattering. The construction of the laser and the procedures for tuning are described in detail. The spectrum has been narrowed to 5 pm, tuned to one of the sodium D lines, and measurements of atmospheric sodium have been made. The possibility of measuring other atmospheric constituents by the same method is briefly considered.
TL;DR: In this paper, the optimum conditions for generating channelling patterns (i.e., orientation dependent lines and bands of contrast) in the scanning electron microscope were discussed, and it was shown that the highest angular resolution may be obtained by establishing a compromise between a small divergence in a collimated beam and a high beam current at the specimen surface.
Abstract: The optimum conditions are discussed for generating channelling patterns (i.e. orientation dependent lines and bands of contrast) in the scanning electron microscope. From considerations of the electron optics it is shown that patterns of highest angular resolution may be obtained by establishing a compromise between a small divergence in a collimated beam and a high beam current at the specimen surface. It is also shown that surface detail finer than 50 μm may be resolved and superimposed on channelling patterns with only small loss in pattern resolution. Finally, a technique is presented for obtaining selected area channelling patterns from areas smaller than 100 μm across.
TL;DR: In this paper, a simple continuous transfer liquid helium cryostat for an ultra-high vacuum field ion microscope has been constructed, where liquid helium is continuously transferred from a conventional 30 or 50 1 storage vessel, employing a standard transfer line, to a small reservoir which is in direct contact with the field ion microscopy specimen holder.
Abstract: A simple continuous transfer liquid helium cryostat for an ultra-high vacuum field ion microscope has been constructed. In this cryostat the liquid helium is continuously transferred from a conventional 30 or 50 1 storage vessel, employing a standard transfer line, to a small reservoir which is in direct contact with the field ion microscope specimen holder. The enthalpy of the outgoing cold helium gas is used to cool a copper radiation shield which surrounds both the specimen holder and the reservoir section of the cryostat. The economical operating temperature range of this cryostat is 8"~ to room temperature with a temperature stability of better than k 0.1 degK over most of this temperature range. Details of construction and the operational characteristics are presented.
TL;DR: In this article, the focal properties of a three-element lens can be determined in terms of the properties of two-element lenses, and a graph is presented which can be used to design a lens of unit magnification which will work over a specified extreme voltage ratio in the range 6·25:1 to 170:1.
Abstract: A procedure is described by which the focal properties of a three-element lens can be determined in terms of the properties of two-element lenses. Examples are given in some detail of the design of lenses to meet specific requirements and a graph is presented which can be used to design a lens of unit magnification which will work over a specified extreme voltage ratio in the range 6·25:1 to 170:1. The range of applicability of the method is discussed and a comparison made with measurements by Imhof and Read where only a limited agreement is expected. This comparison supports both the method and its limitations.
TL;DR: In this paper, two frequencies are simultaneously applied to a vibrating capacitor for making contact potential difference measurements, where the potential difference across the capacitor is usually a nonlinear function of the electrode spacing and the resultant signal consists of one frequency modulated in amplitude by the other.
Abstract: Two frequencies are simultaneously applied to a vibrating capacitor for making contact potential difference measurements. Since the potential difference across the capacitor is usually a nonlinear function of the electrode spacing the resultant signal consists of one frequency modulated in amplitude by the other. By detecting only this amplitude modulation it is possible to observe contact potential differences while one of the surfaces, forming the capacitor, is emitting electrons or ions. Also the reproducibility of contact potential difference measurements is increased by a factor of ten over the more usual single frequency method. The system uses integral feedback to provide a self-balancing facility. The temperature coefficient of the minimum work function for a caesiated surface was found to be − 1·2±0·2×10−3 eV degK−1 over the temperature range 300 to 850°K. The work functions of tungsten (100) and (110) surfaces were measured to be 4·645±0·005 eV and 5·141±0·007 eV respectively, assuming that of the polycrystalline reference surface to be 4·550 eV.
TL;DR: A capacitive proximity gauge is described, which has a novel configuration of electrodes and makes use of the fringing capacitance between them, and has certain advantages, particularly in the linearity of its output and the down-grading permissible in the performance of connecting leads.
Abstract: A capacitive proximity gauge is described, which has a novel configuration of electrodes and makes use of the fringing capacitance between them. The device is shown to have certain advantages, particularly in the linearity of its output and the down-grading permissible in the performance of connecting leads. The variation of characteristics with geometrical details has been established experimentally, allowing optimum designs to be made to meet any chosen performance specification.
TL;DR: In this paper, the authors used a directional sensitive detector to reveal the appearance of'shading' of surface detail, revealing more clearly the nature of shallow undulations, with a three-dimensional effect similar to that obtainable by optical microscopy with side illumination.
Abstract: Directionally sensitive detectors have been used in the scanning electron microscope to reveal additional detail due to deflection or non-uniformity of the spatial emission distribution of the secondaries which form the electron picture of the surface under examination. Deflection may occur as a result of electric or magnetic fields above the surface; also the emission characteristic may be anisotropic, or modified in shape and direction by local surface structure. These effects all occur in addition to the principal source of contrast in the scanning electron microscope, i.e. changes of secondary emission coefficient. The directional content of contrast is normally small, but the system discussed causes considerable enhancement of these effects. Results have the appearance of `shading' of surface detail, revealing more clearly the nature of shallow undulations, with a three-dimensional effect similar to that obtainable by optical microscopy with side illumination. Comparative results are presented which indicate the advantages to be gained for examination of small surface detail. By appropriate adjustment of electrostatic bias on electrodes, the detector system can provide magnetic contrast, potential contrast due to changes in surface electric potential, electric contrast from horizontal electric fields and improved sensitivity to surface topography. To a considerable extent these can be separately identified by observation under several different detector field configurations.
TL;DR: In this paper, a number of experiments are described which verify the suggestion that the changes occurring in the pulse-height distribution of proportional counters after 108-1010 counts can be explained by assuming the accumulation of a deposit on the anode wire.
Abstract: A number of experiments are described which verify the suggestion that the changes occurring in the pulse-height distribution of proportional counters after 108-1010 counts can be explained by assuming the accumulation of a deposit on the anode wire. The counters were irradiated with monochromatic radiation of 2·1, 5·4 and 8·34 A. Ar-10% CH4 and Ar-20% CO2 were used as counter gases; the changes were less pronounced with CO2 than with CH4. An X-ray fluorescence analysis of the deposit on the wires of some of the CH4 counters showed the presence of carbon. Some possible sources for the deposit material are discussed.
TL;DR: In this article, a cryostat was used for sample temperature control in a pulsed n.m.r. spectrometer in the range 78°K to room temperature.
Abstract: A cryostat is described which has been used for sample temperature control in a pulsed n.m.r. spectrometer in the range 78°K to room temperature. The temperature controller may be preset to the sample temperature required and the sample subsequently maintained at this temperature to better than 0·5 degK for long periods of time. The advantages of this method of temperature control over the more conventional gas-flow and controlled heat-leak methods are discussed.
TL;DR: In this paper, a vibrating gold wire probe senses an area of about 04 mm2 as compared to the more usual few square centimetres employed in surface potential measurement, and a d.c. backing-off potential enables a null measurement to be made on a cathode-ray oscilloscope after frequency-selective amplification.
Abstract: There is considerable current interest in the detection and measurement of surface potential difference and charge density on metal oxide layers and on dielectrics. The Kelvin vibrating capacitor method has been developed so as to give a high degree of localization in the measurement of surface potential. This apparatus was designed and used to measure the potential distribution left on a cathode or anode surface by the track of a 1000 A electric arc. A vibrating gold wire probe senses an area of about 04 mm2 as against the more usual few square centimetres employed in surface potential measurement. A MOST is the detector, and a d.c. backing-off potential enables a null measurement to be made on a cathode-ray oscilloscope after frequency-selective amplification. A sensitivity in measurement of about 001 v on the surface under examination is obtained.