Showing papers in "Journal of Physics E: Scientific Instruments in 1988"
TL;DR: In this paper, the superposition of pulsed gradient spin-echo (PGSE) and NMR imaging experiments results in a spin density image which is phase and amplitude modulated according to the local self-correlation function for nuclear spin displacements over the time between the PGSE gradient pulses.
Abstract: The superposition of pulsed gradient spin-echo (PGSE) and NMR imaging experiments results in a spin density image which is phase and amplitude modulated according to the local self-correlation function for nuclear spin displacements over the time between the PGSE gradient pulses. It is shown that such an experiment can image both static and dynamic spin displacements, the reciprocal space for these image spaces being termed k-space and q-space respectively. Simultaneous imaging of diffusion and flow at microscopic resolution is demonstrated and the Poiseuille velocity distribution agrees well with the velocity map obtained for the motion of water in a 0.7 mm capillary tube.
253Â citations
TL;DR: In this article, the effects of stray capacitances on the measurement system must be minimized, in order to achieve high measurement sensitivity and good signal-to-noise ratio.
Abstract: Reviews existing instrumental techniques suitable for industrial measurement of capacitance in the range 0.1-10 pF, including resonance, oscillation, charge/discharge and AC bridge methods. It shows that in order to achieve high measurement sensitivity and good signal-to-noise ratio, the effects of stray capacitances on the measurement systems must be minimised. Several intrinsically stray-immune measuring circuits are described, including an audio-frequency transformer-ratio-arm bridge and a charge/discharge measuring circuit capable of operating at frequencies up to several MHz. The active guard method and suitable guard driving techniques for reducing the effects of strays on the measurement of grounded capacitances sensors are described. Techniques for reducing the baseline drift of the capacitance measuring circuits, such as auto-balancing and auto-calibration, etc., are also discussed.
191Â citations
TL;DR: In this paper, a target field method for designing coils to produce any desired field configuration is presented, which has the advantage of giving coils of the minimum inductance consistent with the field specification.
Abstract: A new target field method for designing coils to produce any desired field configuration is presented. This method has the advantage of giving coils of the minimum inductance consistent with the field specification, thus enabling the most rapid switching possible of gradient or main fields.
181Â citations
TL;DR: In this paper, a single-crystal diamond anvil cell is described which has been successfully cycled down to liquid helium temperatures in numerous experiments, and a recalibration of the superconducting critical temperature, Tc, of Pb as a function of pressure has been carried out.
Abstract: A single-crystal diamond anvil cell is described which has been successfully cycled down to liquid helium temperatures in numerous experiments Superconducting transitions are detected by a low frequency AC technique employing a radially compensated gradient coil and a commercial RF SQUID system The pressure is determined at room temperature by the ruby fluorescence technique with a focused laser beam Pressure changes between room temperature and low temperature are minimised A recalibration of the superconducting critical temperature, Tc, of Pb as a function of pressure has been carried out The so-called Pb manometer turns out to be a very suitable pressure gauge up to about 30 GPa At higher pressures the Tc of Pb is suppressed below 12 K and hence, for normal purposes, is inconveniently low At the present limit of resolution the Pb I-II phase transition at 13 GPa is not reflected in the smooth Tc-P dependence
147Â citations
TL;DR: In this article, the most remarkable characteristics of metallic glasses as well as their main technological applications are reviewed and the possibility of tailoring transition metal-metalloid amorphous alloys is analyzed and attention is also paid to the role and stability of properties such as a magnetostriction and magnetic anisotropy in connection with such applications.
Abstract: The most remarkable characteristics of metallic glasses as well as their main technological applications are reviewed. Particular interest is focused on stress transducers and magnetic field sensors. The possibility of tailoring transition-metal-metalloid amorphous alloys is analysed and attention is also paid to the role and stability of properties such as a magnetostriction and magnetic anisotropy in connection with such applications.
116Â citations
TL;DR: The physical properties that make silicon so useful for these applications and the technology specific to the fabrication of sensors are discussed in this paper, where the authors describe the application of silicon to sensors in which strain is detected.
Abstract: Describes the application of silicon to sensors in which strain is detected. The physical properties that make silicon so useful for these applications and the technology specific to the fabrication of sensors are discussed.
106Â citations
TL;DR: In this article, a fine wire probe is raster scanned over the surface of the sample under examination, and the modulated capacitance between the probe and the vibrated sample is used to maintain the probe just above the surface.
Abstract: A novel mechanically scanned and non-contacting surface profiling instrument has been developed in which a fine wire probe is raster scanned over the surface of the sample under examination. Measurement of the modulated capacitance between the probe and the vibrated sample is used to maintain the probe just above the surface. In the prototype instrument described, an in-plane resolution better than 2 mu m is achieved by the use of an etched tungsten wire probe, while the perpendicular resolution is 6 nm. Both insulating and conducting samples may be scanned and the technique makes it possible to measure electrical properties of the surface under the probe as well as the surface microtopography.
105Â citations
TL;DR: In this article, two methods are described which allow precise measurements of the ultrasonic absorption coefficient of liquids between about 5 and 400 MHz and 1 and 50 MHz, respectively, where RF substitution techniques are applied to determine the attenuation of pulsed signals transmitted through the sample cell.
Abstract: Two methods are described which allow precise measurements of the ultrasonic absorption coefficient of liquids between about 5 and 400 MHz and 1 and 50 MHz, respectively. In both cases RF substitution techniques are applied to determine the attenuation of pulsed signals transmitted through the sample cell. In the former method a cell with variable spacing of the piezoelectric transmitter and receiver crystal is used and the measurements are automatically driven by a process control computer. The latter method is based on a cell of fixed pathlength, using a simple electronic set-up and a manual mode of operation. The construction of the cells is given in detail and the relative merits and limitations of the two methods are briefly discussed. Examples of acoustic absorption spectra are presented to demonstrate the accuracy of measurements.
72Â citations
TL;DR: In this paper, the authors describe a mass spectrometer, gas inlet and operating protocol which have been developed for the purpose of making stable isotope measurements of subnanomole quantities of nitrogen gas.
Abstract: Describes a mass spectrometer, gas inlet and operating protocol which have been developed for the purpose of making stable isotope measurements of subnanomole quantities of nitrogen gas. The mass spectrometer achieves high levels of sensitivity by operating in the static vacuum mode; the levels of precision attainable have been assessed in a number of ways. The instrument is capable of obtaining comparative nitrogen isotopic compositions ( delta 15N values) to a precision of +or-0.240/00 from samples of 0.4 nmol, as determined from a zero-enrichment test performed throughout a single day on 40 consecutive samples. The absolute accuracy of the method, as derived from measurements on samples of known isotopic compositions, is about +or-0.50/00. The instrument was designed to work routinely with samples of between 0.07 and 0.4 nmol of nitrogen but is demonstrated that the equipment can handle 20 pmol quantities of gas. The performance is difficult to quantify at these low levels since the inlet system does not have the facility to reproducibly introduce such small gas samples.
70Â citations
TL;DR: In this paper, the accuracy and suitability of hot-wire velocity calibration relations for implementation on a micro/minicomputer were investigated. But the main part of the investigation was related to a typical moderate velocity range of 3-30 m s-1, with complementary data being presented for a large velocity range, 4-90 m s − 1, and at low velocities, 1-6 m s− 1.
Abstract: Describes a study of the accuracy and suitability of hot-wire velocity calibration relations for implementation on a micro/minicomputer. The investigation has covered simple and extended power laws, polynomial fits of three types and spline fits. The main part of the investigation was related to a typical moderate velocity range of 3-30 m s-1, with complementary data being presented for a large velocity range, 4-90 m s-1, and at low velocities, 1-6 m s-1. By careful attention to measurement errors, the suitability or limitations of the various calibration relationships have been identified. Optimisation for both accuracy and computational convenience identified no simple method as being the best, but three methods: simple power law or a fourth-order polynomial in E or a third-order polynomial in E2, were shown to give similar results.
65Â citations
TL;DR: In this article, it was shown that a correction to the water vapour term in Edlen's equation is required to achieve the highest accuracy, which can be obtained either by calculation using Edlen equation or by direct measurement using a gas refractometer.
Abstract: When optical techniques are applied to high-accuracy length measurement in the free atmosphere it is essential to apply a correction for the refractive index of the air. This can be obtained either by calculation using Edlen's equation or by direct measurement using a gas refractometer. An investigation of the accuracy achievable using Edlen's equation has been made using a high-precision interference gas refractometer developed at the NPL. The results have shown that a correction to the water vapour term in Edlen's equation is required to achieve the highest accuracy.
TL;DR: In this article, a technique for the extraction and purification of sub-nanomole quantities of nitrogen for stable isotopic analysis is described, which is intended for use with a high-sensitivity static vacuum mass spectrometer such as that described by Wright et al. (1988).
Abstract: Describes a technique for the extraction and purification of sub-nanomole quantities of nitrogen for stable isotopic analysis. The procedures described are intended for use with a high-sensitivity static vacuum mass spectrometer such as that describes by Wright et al. (1988). It is essential that low nitrogen blanks are obtained during the sample treatment; it can be demonstrated that contributions of nitrogen from the extraction and subsequent gas handling procedures can be limited to as little as 0.021 nmol. Experiments are described to verify that species such as CO2, CO and CH4, which would otherwise interfere with the nitrogen isotopic measurements, can all be removed during the purification operations. A study of the difficulties which might be encountered if some nitrogen were converted to nitrogen oxides has also been undertaken. It is concluded that N2O would be totally decomposed to the elements during purification but nitrogen in the form of NO and NO2 is only partially recovered. A method for investigating whether nitrogen oxide production is a real problem during the analysis of geological samples has been devised. Some examples using the technique are presented.
TL;DR: In this paper, the effects of component conductivity on capacitance measurements of two-component fluids using the charge transfer method are analyzed theoretically and tested experimentally using a capacitance transducer based on the charge-transfer method, which can be reduced by using semiconductor switches with low ON resistance and fast commutation time to control the charge and discharge of the sensor.
Abstract: Describes an investigation into the effects of component conductivity on capacitance measurements of two-component fluids using the charge transfer method. Various capacitance sensor systems are represented using three typical equivalent circuit models according to their electrode configurations and the type of mixture between the electrodes. The effects of conductive elements on the measurement of these models are analysed theoretically and tested experimentally using a capacitance transducer based on the charge transfer method. It is shown that the conductance effects can be reduced by using semiconductor switches with low ON resistance and fast commutation time to control the charge and discharge of the sensor. Measurements of glass bead concentration in water-based conductive slurries from an industrial wet peening process and water contentin oil/water mixtures are described as practical applications.
TL;DR: In this paper, the authors examined the basis of NMR imaging in terms of water and mobile proton content in biological and other systems, and discussed the generalised principles of NMRI imaging using the reciprocal space approach.
Abstract: The basis of NMR imaging is examined in terms of water and mobile proton content in biological and other systems. Relaxation time effects are also discussed and their importance as additional spin parameters examined. The generalised principles of NMR imaging are discussed using the reciprocal space approach. The timing details of the common imaging methods, together with a number of image examples are presented. A discussion of image quality and imaging time is given. Other matters of practical importance in obtaining good quality images are also considered. Some general comments concerning present day imaging and future perspectives are presented.
TL;DR: In this paper, a current sensor based on a stabilised fibre-optic Sagnac interferometer has been constructed and preliminary tests have been carried out Measurements made with this system are independent of variations in the following parameters: laser intensity, light intensity injected into the optical fibre and birefringence within the fibre.
Abstract: A current sensor based on a stabilised fibre-optic Sagnac interferometer has been constructed and preliminary tests have been carried out Measurements made with this system are independent of variations in the following parameters: laser intensity, light intensity injected into the optical fibre and birefringence within the fibre The stabilised output is obtained by electronically combining the output signal from the interferometer with samples of the signal which have traversed the optical fibre in opposite directions The mathematical basis for the stabilisation technique and construction details for the instrument are given
TL;DR: Major improvements in the resolution of the photochromic dye method for measuring the instantaneous velocity profile for pulsatile flow are described, and a split-beam measurement method whereby the velocity profiles at three different positions along a flow vessel can be measured simultaneously is developed.
Abstract: Major improvements in the resolution of the photochromic dye method for measuring the instantaneous velocity profile for pulsatile flow are described. Specifically, improvements in the optical design have reduced the trace width from approximately 1.2 to 0.2 mm. Detailed studies were conducted using a 2.9 Hz sinusoidal flow superimposed on a steady flow through a straight rigid tube of 4.85 mm inside diameter. Velocity profiles were measured throughout the flow cycle and these, together with the wall shear stresses, were compared with those predicted from the Womersley rigid-tube flow equations. The excellent agreement between the experimental and predicted values illustrates the accuracy of the experimental technique. The authors have also developed a split-beam measurement method whereby the velocity profiles at three different positions along a flow vessel can be measured simultaneously. This technique provides an instantaneous description of the spatial relationship of the flow field, and is illustrated for pulsatile flow through a constricted tube.
TL;DR: In this article, a review summarises the body of principles employed in this type of sensor and discusses the implementation of these principles in the design of such sensors and in the associated instrumentation.
Abstract: The development of optical fibre sensors for chemical species has attracted much interest. This review summarises the body of principles employed in this type of sensor and discusses the implementation of these principles in the design of such sensors and in the associated instrumentation. The use of this type of sensor in various fields of application is illustrated through a description of some representative examples. The trends that are observed, as well as the problems that are encountered, in the development of this type of sensor are also presented.
TL;DR: In this article, the authors describe the development of a probe method of measuring thermal conductivity k, to enable one to obtain k at times t before the linear domain of probe temperature against ln t is properly established.
Abstract: The author describes the development of a probe method of measuring thermal conductivity k, to enable one to obtain k at times t before the linear domain of probe temperature against ln t is properly established. A variety of probe structures can be accommodated. A probe was constructed and the experimental procedure plus the associated analysis (using a simulation model PROBE) was verified by making measurements on materials of known properties. The technique was applied to an unconsolidated coarse granular medium, a pebble bed consisting of graded river pebbles with equivalent spherical particle diameters 24+or-7 mm, and a bed porosity of 0.396.
TL;DR: In this paper, a technique and apparatus is described which has permitted the production of fibre-reinforced NiAl/Al2O3 and Ni3Al/al 2O3 composites.
Abstract: Liquid metal infiltration techniques for producing metal-matrix composites offer economic advantages. To date metal-matrix composites produced by casting have been limited to low-temperature metals such as Al, Mg and Pb because of the serious problems inherent in high-temperature casting. A technique and apparatus is described which has permitted the production of fibre-reinforced NiAl/Al2O3 and Ni3Al/Al2O3 composites. The technique involves liquid metal infiltration of Al2O3 fibres under gas pressure.
TL;DR: In this paper, the design of a small DC planar magnetron source and its use in a research-scale UHV getter sputter deposition system was described, which was used for depositing a range of refractory materials as well as some metal multilayer structures (single crystal, polycrystalline and amorphous).
Abstract: Details are presented of the design of a small DC planar magnetron source and its use in a research-scale UHV getter sputter deposition system. The system has been used for depositing a range of refractory materials as well as some metal multilayer structures (single crystal, polycrystalline and amorphous). For some of these structures a relatively high sputtering pressure is required and a study has been made of the deposition rate as a function of pressure for a range of different elements. This illustrates the effect of the momentum and energy transfer of the sputtered atoms as they travel from the target to the substrate.
TL;DR: A review of flame failure detection in fossil-fuel-fired boilers can be found in this paper, where the authors show how advances in combustion systems have necessitated the continuing development of improved methods of fire failure detection to maintain acceptable performance characteristics.
Abstract: The safe operation of fossil-fuel-fired boilers is dependent to a large extent on the stability of the combustion process. Flame instability can be both inefficient and pollutant forming. but in extreme cases flame extinction can occur. Unless immediate action is taken in such circumstances, large quantities of unburnt fuel can be admitted to the combustion chamber and subsequently re-ignite explosively with serious consequences to both personnel and equipment. To eliminate such potentially dangerous situations. a need has been identified for reliable monitors capable of rapidly detecting the loss of flame. This review shows how advances in combustion systems have necessitated the continuing development of improved methods of flame failure detection to maintain acceptable performance characteristics.
TL;DR: In this paper, the concept of zoomed real-time echo-planar imaging (ZEPI) was introduced, where the image zone is defined by two selective RF pulses and the receiver bandwidth.
Abstract: To overcome the problems of gradient strength, large receiver bandwidth and computing time in nuclear magnetic resonance real-time echo-planar imaging (EPI) with large pixel arrays, the concept of zonal image magnification or zoomed EPI (ZEPI) is introduced. The image zone is defined by two selective RF pulses and the receiver bandwidth. For a fixed image array size it is shown that zooming requires less gradient strength to achieve a given spatial resolution than in an equivalent unzoomed image. Two different zoom techniques are described, ZEPI-1 and ZEPI-2, which employ a single and a double pulse sequence respectively. Experimental results obtained with these sequences on a phantom and a live piglet are presented.
TL;DR: In this paper, a computer-based system for plotting the DC magnetisation loops of amorphous magnetic ribbons is described, which overcomes the problems associated with very low coercivity materials by using a nonlinear H-field function that can be adjusted for a particular loop.
Abstract: A computer-based system for plotting the DC magnetisation loops of amorphous magnetic ribbons is described. The system overcomes the problems associated with very low coercivity materials by using a nonlinear H-field function that can be adjusted for a particular loop. The problem of drift is overcome by the use of a hybrid analogue/digital integrator and software correction. Commonly used magnetic parameters are calculated from the digitised data. In particular, coercivities of less than 1 A m-1 can be reliably measured. Typical results are presented to illustrate the performance.
TL;DR: The characteristics of wear debris found in the lubricant flow of a machine are reviewed along with their relationships to specific wear processes in this article, with reference to systems at the research and development stage.
Abstract: The characteristics of wear debris found in the lubricant flow of a machine are reviewed along with their relationships to specific wear processes. Current wear-debris detection and analysis techniques are described with reference to systems at the research and development stage. The features of these systems are compared with those of an ideal system and an outline of a novel technique is given.
TL;DR: In this article, an all-solid-state pulser for the excitation of repetitively pulsed gas lasers is described, which uses thyristor switching followed by a ferrite core pulse transformer and a four-stage pulse compression system using DC biased ferrite magnetic switches.
Abstract: An all-solid-state pulser for the excitation of repetitively pulsed gas lasers is described which uses thyristor switching followed by a ferrite core pulse transformer and a four-stage pulse compression system using DC biased ferrite magnetic switches. An analysis of energy losses in the complex high voltage circuit is made, and an energy conversion efficiency of 73% overall is shown to be obtained, using commercially available ferrite materials. Interfacing of the circuit to the TEA CO2 laser is discussed.
TL;DR: In this paper, a double-pass double-monochromator spectrometer (DMDP2000) was designed for low-frequency light-scattering studies, which achieved high resolving power with a free spectral range of 2000 cm-1 and high luminosity, contrast and stability.
Abstract: The characteristics of a new double-pass double-monochromator spectrometer (DMDP2000) especially designed for low-frequency light-scattering studies are reported. Preliminary spectra are presented to show the high resolving power achieved with a free spectral range of 2000 cm-1, as well as the high luminosity, contrast and stability. Spectra obtained with a single-pass Fabry-Perot interferometer are also shown for comparison.
TL;DR: In this article, the performance of integrated thermopile vacuum sensors as a vacuum gauge is discussed and the zero repeatability is shown to be approximately 10 mPa in the optimum pressure range of 1-100 Pa, while the upper pressure limit of the sensors is of the order of 5-50 kPa.
Abstract: A quantitative insight is given into the performance of integrated thermopile vacuum sensors as a vacuum gauge. After a short resume of their operation principle three pressure ranges are discussed. The zero repeatability is shown to be approximately 10 mPa. In the optimum pressure range of 1-100 Pa the error of prediction of the sensors is 2-3% while the upper pressure limit of the sensors is of the order of 5-50 kPa. Finally, a comparison with conventional Pirani gauges is made.
TL;DR: In this article, a method was developed to measure the absolute hypersonic absorption of liquids in the frequency range from 0.3 to 3 GHz with 1% accuracy using a pulse transmission technique.
Abstract: A method has been developed to measure the absolute hypersonic absorption of liquids in the frequency range from 0.3 to 3 GHz with 1% accuracy using a pulse transmission technique. Excitation of surface vibrations on small rod-shaped piezoelectric LiNbO3 crystals at variable transducer spacing is combined with a direct parallel RF substitution technique in which a below-cut-off piston attenuator is used as reference. Sensitive superheterodyne detection followed by signal averaging and multiple data recording allow for a low input power level so that heating of the small sample volume (<1 ml) is avoided. The measurements are automatically driven by a process control control.
TL;DR: In this article, the double peak cross-correlation function caused by the saddle velocity distribution encountered in oil/gas risers is measured and a theoretical model for the measurement of bubble velocity is developed and supported by experimental results.
Abstract: The pulsed ultrasonic cross-correlation system is attractive for measuring the dynamic flow characteristics of two component liquid/gas mixtures because the sensors are invasive but do not extend into the pipe and, in contrast to previous continuous wave systems, have a uniform spatial sensitivity due to the absence of standing waves. The potential for measuring the flow characteristics in industrial processes including oil/gas risers is demonstrated by the measurement of the double peak cross-correlation function caused by the 'saddle' velocity distribution encountered in these risers. A theoretical model for the measurement of bubble velocity is developed and supported by experimental results.
TL;DR: In this article, a technique for measuring magnetisation in very high magnetic fields (up to 90 T) produced by single-turn coils was developed for measurements of magnetic substances in a wide temperature range from room temperature down to 4.2 K.
Abstract: A technique has been developed for measuring magnetisation in very high magnetic fields (up to 90 T) produced by single-turn coils. The system is applied for measurements of high-field magnetisation of magnetic substances in a wide temperature range from room temperature down to 4.2 K. In a simple magnetic system, the one-dimensional Ising antiferromagnet CsCoCl3, the magnetisation curve was successfully obtained up to 90 T including a stepwise change around 40T at 4.2 K.