Table of contents

The main areas where the measurement of gaseous oxygen is required are briefly reviewed. The basic principles of the methods and techniques which underlie the design of current oxygen sensors are outlined, and examples given of sensor designs used in commercial instruments. A brief look at future developments is presented.

A method is demonstrated for investigating the shape of the curved surface of a hollow conducting tube by using it as a microwave cavity and applying a perturbation method to the observed resonant frequencies.

An automatic and absolute system for the position measurement of specimen edges has been developed. The system is composed of a laser source for illuminating specimen edges, an image following system with a servomechanisms driven by a microcomputer, two edge image detectors with optical-fibre bundle sensors, and an absolute length measurement system with a Michelson interferometer. No reduction in accuracy was observed for various shapes of specimen edges such as flat sharp edges dull edges, tilted edges, cylindrical edges and transparent sharp edges. The accuracy of the position determination of the edge image was confirmed to be within 0.1 mu m.

A method for dynamically calibrating a static Askania gravimeter by the step excitation method is presented. The problem of applying a true force step to such a spring system by means of the micrometer is specially addressed and the rheological properties are modelled. The nonlinear least-squares technique is used for obtaining the transfer function in analytical form. Accuracies of 0.1% and 0.1 degrees for the amplitude and phase response respectively are obtained in the tidal wavebands by stacking 21 step responses.

The use of computers in the control, monitoring and analysis of results in investigations into plastic collapse loads of model cylindrical pressure vessels with saddle supports.

Temperature measurement inside high pressure cells is most conveniently made with a thermocouple, since unless there is a large temperature difference between the thermocouple junction and the region of the pressure seal where the pressure gradient occurs, the ambient pressure-temperature calibration can be used. The authors have used a thermocouple pair of rhodium +0.5 at.% iron-chromel. This pair provides usable sensitivity down to liquid-helium temperatures (lowest sensitivity approximately 4 mu V K^-1 at 15K) together with sufficient mechanical strength to withstand the handling necessary to pass the pair into the pressure cell. This has been incorporated in a beryllium-copper cell for use up to 1.5 GPa over the temperature range 4-400K.

A humidity control unit was developed for the growth of single crystals by the slow evaporation of water. The system uses a capacitive humidity sensor to adjust the air flow through an easily replaced silica gel unit, so that low relative humidities can be maintained to +or-0.3%.

A hot-wire for use in laboratory clouds is presented. The instrument is light, robust and easy to construct. Tests were performed in a cloud and when the probe is operated at a wire temperature of 76 degrees C has an accuracy of 4% for a liquid water content of 1.0 g m^-3.

Clinical NMR motion picture (movie) images can be produced routinely in real-time by ultra-high-speed echo-planar imaging (EPI). The single-short image quality depends on both pixel resolution and signal-to-noise ratio (S/N), both factors being intertradeable. If image S/N is sacrificed rather than resolution, it is shown that S/N may be greatly enhanced subsequently without vitiating spatial resolution or foregoing real motional effects when the object motion is periodic. This is achieved by a Fourier filtering process. Experimental results are presented which demonstrate the technique for a normal functioning heart.

A computerised set-up using laser beams is described for the simultaneous measurement of the growth rates of the (001) and (110) faces of the B and C polymorphs of stearic acid. The stearic acid is grown in a flow system form organic solvents such as decane. The growth rates of the lateral (110) face is measured directly by means of an optical microscope, while an interference technique is necessary for the (001) face.

A computational analysis of single-reflection time-domain reflectometry using synthetic waveforms is used to study the effects of incorrect time alignment, waveform truncation and added noise, as a function of frequency, upon calculated permittivity values. Large errors in both the real ( epsilon ') and imaginary ( epsilon ") parts of the permittivity resulted from time misalignments of only 2 ps, from truncating waveforms to less than three relaxation times, and with signal-to-noise ratios of less than 20 dB. The calculated value of relaxation frequency was particularly sensitive to waveform truncation. An automatic alignment algorithm, presented as an appendix, was accurate to within one sample period (1 ps) in the few cases tested. The commonly used technique of determining permittivity from sample length and delay time is examined. Significant errors occur when the returned _TDR pulse has strong spectral components near the material relaxation frequency.

Describes a simple technique for producing a high-energy electron beam and sweeping it across a narrow slit in a very short time so as to obtain a pulsed electron beam. X and Y plates similar to those employed in a cathode-ray oscilloscope are incorporated here to deflect the beam. Transistors working in the avalanche mode produce fast rising pulses to be impressed on the deflection plates. A 4 keV DC beam of current 0.9 mA when swept across a 1 mm wide slit produces a charge pulse of 1.5 pC with a duration of 1.7 ns.

The design parameters of an electron probe-forming lens with a zero-bore flat-face single pole piece have been considered under nonsaturation conditions. From the measured axial flux density distribution of an experimental single-pole-piece lens, the maximum flux density, the spherical and chromatic aberration coefficients, the focal length and the object position have been investigated in terms of the diameter of the pole's flat face, which is the effective geometrical parameter. Empirical equations relating the geometrical electron-optical parameters have been put forward and compared with those of a different experimental lens reported in the literature. The focal properties of the probe-forming lens have also been investigated in the telescopic mode of operation. The results should be useful for preliminary design considerations of an unconventional electron probe-forming lens with zero-bore flat-face single pole piece for various types of electron-optical instruments according to the operational requirements.

A metastable molecule detector having an adjustable detection threshold is described. The metastable molecules are detected through an Auger de-excitation process on a metal surface and the ejected electrons are analysed in an electrostatic retarding field. The maximum kinetic energy of the electrons depends on the excitation energy of the metastable state and this fact in conjunction with the energy analysis is used to achieve the possibility of changing the threshold detection energy. The performance of the detector is illustrated for the case of metastable excitation functions obtained in nitrogen.

A pseudo-spark switch triggered by a pulsed low-current gas discharge has been developed. It switches medium voltages and currents of typically less than 20 kV and 10 kA, respectively. The switch works at high repetition rates of up to 100 kHz and fast rates of current rise of up to 5*10¹¹ A s^-1. At positive charging voltage, the jitter may be much smaller than 1 ns. This pseudo-spark switch has been successfully tested by running a discharge-heated longitudinal copper vapour laser and a transverse Blumlein N₂ laser, replacing a hydrogen thyratron and a high-pressure spark gap switch, respectively.

The design and performance of a compact cross-field 337 nm N₂ laser are described. The laser produces pulses of 2 MW peak power and 600 ps FWHM at an optimum pressure of 75 Torr and a repetition rate of 1 pulse/s, variable up to 12 pulse/s. The improvement in laser performance is a result of total impedance value reduction as well as careful adjustment of the electrical circuit parameters.

A new optical technique for the measurement of flow velocities with a laser interferometric technique was reported by Menn et al. (1981). Since then the technique has been improved and the authors describe the technique as well as a digital signal processing procedure which has been developed to computer the velocity components from the signal acquired. The method was used to measure velocity fluctuations and Reynolds stresses in an axisymmetric circular air jet. Experimental results are presented and compared with measurements of previous researchers.

High pressure equipment designed for low temperature magneto-optical experiments is described. The piston and cylinder type of pressure vessel was adapted to allow photocurrent experiments to be carried out at low temperatures and high magnetic fields. With a sapphire window the cell can be used in the far infrared region (3 mm-25 mu m wavelength) and in the near infrared at wavelengths shorter than 5.5 mu m. Hydrostatic pressures up to 1.8 GPa can be achieved at 4.2K. A suitable choice of window material allows the cell to be used in all spectral regions from far infrared to ultraviolet and over a temperature range from liquid helium to 500K. The use of a carbon bolometer allows transmission experiments to be performed.

The authors describe a method of in situ calibration for the quantitative analysis of alloy surfaces using Auger electron spectroscopy. They have used the technique to characterise the (111) surfaces of two Cu-Pd alloys containing 6.8% and 30.3% Pd. It was found that Ar⁺ bombardment produces Pd-enriched surfaces but subsequent annealing at temperatures above 400 degrees C results in top-layer compositions similar to those of the bulk.