Table of contents

Marine research is becoming increasingly important. Weighing of substances is, of course, one of the most common needs for experimental scientific work. Balances of normal design for the use on the mainland depend on the constancy of the acceleration due to gravity, but the movements of a ship will generally produce varying accelerations. In the approach presented here two balances are used: one carries a fixed load and measures the momentary acting accelerations, the other has the unknown mass that is to be determined. The experimental set-up, the computer program and possible error sources are described. The total accuracy of the experimental set-up, as tested with cruises on a ship, was found to be similar to the accuracy of the balance on the mainland.

A better knowledge of the electric breaking-arc can be obtained through electrical, optical and magnetic diagnoses. Therefore, a system called 'magnetic camera' has been devised and developed. It consists of a V-shaped matrix, with some 70 probes, each of which gives the shape of magnetic induction versus time in the gap between two electrodes. The various shapes assumed by the arc can be determined by means of data-acquisition and processing software within a few minutes. This type of camera is characterized by a maximum speed of exposure which is five times faster than that of an ultra-high-speed optical camera. Moreover, the diagnosis obtained is closer to the basically electric nature of the arc.

The temperature distribution over the molten surface of niobium has been measured. The temperature differences are assessed by comparing the light fluxes radiated from different points of the hot surface. The light measurements were performed using a CCD sensor. The vapour flux distribution over the metal surface was found to be quite constant due to the small temperature variation of about 150 K.

A study of the transient and frequency response of a heat flux probe is reported. The probe consists of a metallic film sensor deposited onto a substrate and covered by a thin protective coating. This study considers the case of constant sensor temperature operation with the probe mounted in an isothermal wall and one probe surface exposed to a convecting environment. A two-dimensional numerical analysis of the probe subjected to both step change and periodic boundary conditions is presented. The effect of probe design on temporal and frequency response and probe sensitivity is demonstrated.

Analytical and numerical solutions for the radial distribution of the current density in coils with constant stress throughout the layers are developed to discuss the design of pulsed magnets approaching the 100 T level. The results focus on the pulse duration which is shown to depend critically on the peaks in the current distribution at the inner and outer surfaces. The trade-off between cutting off these peaks and the peak field, wire strength, coil size and energy are determined. For large coils, the axial stresses result in a substantial increase in the total stress. This effect is included in the calculation of the current density distribution. Design principles and limitations are illustrated with a practical example.

In the measurement system under investigation two light beams of different colour and small difference angles ( delta beta approximately=0.1") are focused within a telescope onto two displaced spots, which are then chopped by a piezoelectric transducer and directed to red- and blue-sensitive detector elements. The distance of the focal points is proportional to the angle between the two light beams, which can be calculated with the phase difference of the photodiode signals and the speed function of the chopper. The accuracy and sensitivity of this principle are demonstrated by various experiments under reproducible conditions.

An instrument for measurement of sequences of fluorescence decay curves in terms of their dependence on emission wavelength, time from the start of the experiment and excitation intensity is described. It consists of a commercially available signal analyser MFA-105-C (Centre of Scientific Instruments, Berlin) with an additional step motor driver card, a nitrogen laser-dye laser system for sample excitation and a step-motor-driven monochromator for emission wavelength selection. The instrument is applied to the measurement of the fluorescence of 4-methylumbelliferon (4-MUF) in ethanol-water solvent systems.

A fluoro-immunosensor has been developed using evanescent wave technology. The system uses a disposable device consisting of the waveguide and the flow cell. The effect of an excitation wavelength on the sensitivity of an evanescent wave immunoassay system has been studied experimentally. Background fluorescence from the polymethylmethacrylate waveguide is reduced by shifting to a longer excitation wavelength. The system using an excitation wavelength of 650 nm is found to possess sensitivity an order of magnitude higher than that obtained in conventional systems.

A system is described which makes possible the automated acquisition of resonance Raman spectra of a material as a function of excitation wavelength. The issues of wavelength accuracy, stabilization of the laser power, and control of the laser beam direction are discussed. Resonance Raman profiles of Raman spectra of Cd_1-xMn_xTe double quantum well heterostructures are presented to illustrate the wealth of detailed data that can be obtained in a routine fashion.

A high-sensitivity far infrared magneto-optical spectrophotometer, capable of measuring the dependences of the transmission and reflection of samples over a wavelength range of 40 to 1200 mu m on the temperature and the magnetic field, is described. The modular design enables measurements in both partly or fully polarized light, as well as obtaining dependences on the orientation of the light polarization plane with respect to the sample axes. Examples of the temperature and magnetic field dependent transmission spectra of a YbIG sample are demonstrated.

A high repetition rate (4.46 kHz) picosecond laser system for time-resolved resonance Raman spectroscopy has been developed with a time resolution of 10 ps. Probe beam pulses are tunable from 550 nm to 655 nm and the pump beam is generated by frequency doubling of the probe beam. Stabilized pulse energies at the sample are >1 mu J/pulse (probe) and >0.2 mu J/pulse (pump). Further tuning is possible using stimulated Stokes-Raman generation in dimethyl sulphoxide (2923 cm^-1) which gives up to 35% energy conversion in the first and up to 7% energy conversion in the second Stokes-Raman line.

This paper describes an approach for determining the individual analyte concentrations in a mixture of analytes using sensor fusion. Sensor fusion here is considered to be a process of gathering information from many different sources and combining these data to acquire pertinent information. The research reported in this paper uses sensor fusion and simulated, partially selective sensors. Through the use of simulated sensors, this research has investigated the advantages and limitation of sensor fusion and artificial neural networks. A three-layer back-propagation network was trained on a subset of component space and it was tested for its ability to generalize, where component space is defined as all possible combinations of input analyte concentration. A learning rate of 0.1 was used and no momentum terms were used. This research has shown that sensor fusion with an artificial neural network can accurately map sensor outputs to the actual input analyte concentrations. This research has also shown that increasing the number of sensors used improves the neural network performance. The neural network approach was found to be, under most circumstances, as good as or better than a mathematical technique using a curve fitting method of addressing the problem. The neural network technique was also found to be significantly faster than the mathematical technique and to possess good noise rejection attributes.

An objective method has been developed for measuring the minimum resolvable temperature difference (MRTD) of infrared imaging systems employing focal plane detector arrays. The resulting MRTD is uniquely determined by applying discrete Fourier analysis, thus avoiding the previous multi-valued problem associated with the non-isoplanatic property of discrete devices. The derivation is based on sinusoidal wave input targets but a practical measuring procedure has been developed using conventional bar patterns, alternatively the MRTD may be calculated by measuring the MTF using the line spread function.

A computer-adjustable laser diode temperature control system yielding +or-2 mK temperature stability is described. An integrated circuit temperature sensor and a Peltier heater/cooler are used as the basis of this arrangement. Rather than a conventional bridge, a 16-bit A/D converter is incorporated to determine the temperature to high accuracy. The system is designed primarily to generate rapid temperature scans but is also capable of maintaining a set point temperature for long periods.

Single mode tuning of a cw colour-centre laser (F_A (II)-centres) over a wavelength range 2.5-3.0 mu m has been demonstrated by using a simple backlash-free tilting device for a solid state CaF₂ etalon. The etalon and its mechanically and thermally stable tilting device are described. A quasi-simultaneous tuning of the etalon and a Littrow-grating as a rough tuning element are performed by computer controlled positioning with stepping motors. It is shown experimentally that a resolution of about 0.01 cm^-1 can be reached. Transitions to rotational levels of molecular vibrations of H₂O vapour at room temperature are resolved with a linewidth of about 0.02 cm^-1, in agreement with literature values.

Acoustic emission has previously been shown to be a useful technique in monitoring the state of wear in machine tools. The piezoelectric transducers conventionally used for acoustic emission detection are contacting devices with a limited bandwidth. Operationally, a non-contacting transducer of broader bandwidth would be preferred. The authors have accordingly developed a technique based on optical interferometry, using fibre optics, to produce a miniature and robust probe for detecting acoustic emission by measuring the small amplitude ( approximately 0.1 nm), high frequency (0.1-1 MHz) surface vibrations that it produces. They demonstrate the technique in measurements made probing both the workpiece and the rotating tool holder during face milling of mild steel.

This paper presents a novel broad band short-pulse ultrasonic system for the simultaneous measurement of compression and shear acoustic wave velocities in thin solid slabs. Using a goniometer stage a test sample is immersed in a water cell between two axially aligned thick ultrasonic transducers. Compression and shear wave reverberations are generated in the test material and the resulting compression waves in the water on the receiver side are received and digitized. Each wave reverberation can be separately time resolved and time-of-flight (TOF) measurements can be made. A time domain model of the wave system in the solid is presented with comparisons with existing frequency domain models. The measured arrival times of the successive reverberations are input to a computer algorithm derived from the time domain model which, using a parameter fitting routine, calculates the acoustic wave velocity for both the compression and shear reverberations in the sample. The problem of interference between successive reverberations in the time domain is greatly reduced due to the wide bandwidth/short pulse operating mode possible with acoustically thick transducers.

The sensitivity of an electrostatic transducer determines the range of pulse-echo detection. Maximum sensitivity can be achieved by increasing the bias voltage within certain limits and by using a light membrane. The tension of the membrane was not found to affect the transducer's sensitivity. By using a uniformly grooved backplate the acoustic properties of the transducer can be optimized. The different sensitivity factors of the electrostatic ultrasonic transducer were confirmed with experimental results. High sensitivity can be achieved by using well manufactured backplates with shallow grooves and a small ridge angle.

The spatial profiles of molecular beams formed by both single and multicapillary sources have been investigated for He, Ne, Ar, Kr, H₂ and N₂. The profile measurements were undertaken at distances from the source exit and driving pressures which are typical of those used in atomic collision experiments (1-5 mm and 0.02-10 Torr respectively). The experimental results indicate the clear superiority of a capillary array source over a single tube source, of similar overall dimensions, in producing a well collimated molecular beam over a wide range of driving pressures and distances from the capillary exit. They also indicate that there is a measurable dependence of the beam profile on gas species, particularly at the higher pressures studied. The significance of this result for the relative flow, cross section normalization technique is discussed.

A quantitative laser schlieren technique has been developed to measure the changes in neutral gas density inside a spark gap switch after breakdown. The measurement system incorporates an array of narrow laser beams which are used to probe the inter-electrode gas volume at discrete distances from the spark axis. Changes in the refractive index gradient within the switch, caused by variations in neutral gas density, result in beam deflection, which is measured using a neutral density wedge/photodiode combination. The resulting schlieren profiles yield both spatially and temporally resolved refractive index data, which enable calculation of the gas density. The use of four averaged trials to obtain the final neutral gas density profiles minimizes errors caused by the turbulent nature of the cooling gas. A typical set of results is presented for SF₆ at a pressure of 0.5 bar.

The authors report on the measurement, over the frequency range 10 Hz to 3 GHz, of the complex susceptibility, chi ( omega )= chi '( omega )-i chi "( omega ), of a magnetic fluid with manganese ferrite particles of median diameter 9.4 nm in a hydrocarbon carrier. This upper frequency was realized by use of a HP Network Analyser which operates over the frequency range 300 kHz to 3 GHz and has enabled a more complete susceptibility-frequency profile to be determined. The presence of a loss-peak at 30 MHz in the chi "( omega ) component is a demonstration of the phenomenon of superparamagnetism in small ferromagnetic particles whilst the transition of chi '( omega ) to a negative value at 65 MHz is indicative of ferroresonance.

A microprocessor-based tethered balloon sounding system has been developed at the University of Athens. It can provide accurate measurements of relative pressure, dry and wet bulb temperature, wind speed and wind direction. Certain features arise from the implementation, like easy data handling, cheap and easy construction and maintenance, increased reliability and, above all, system adaptability to different experimental needs, as well as flexibility and expandability. Advantages and disadvantages of the method are discussed, as well as the implementation of the whole sounding system.

This paper presents a novel technique for rotary or linear direction sensing by means of external delays applied to the signals involved. It is applicable to any transducer which generates a pair of waveforms 90 degrees out of phase. The very simple working principle of the circuit makes it reliable and easy to test.

The authors have described a pressure-resisting glass cell with which high-resolution ESR measurement of liquid samples under pressures up to 900 bar can be carried out on an ordinary high-resolution spectrometer. Recent investigations at high pressures have been presented.

We show, using a Jones matrix analysis, that rotating the two orthogonal linearly polarized inputs of a heterodyne interferometer relative to the polarizing beam splitter axes, produces second harmonic errors in an otherwise ideal interferometer. The error undergoes two cycles as the optical pathlength difference changes from 0 to 2pi. This behaviour is distinct from previously reported periodic errors resulting from polarization leakage and frequency mixing. It is found that as the angular misalignment increases, the amplitude of the periodic errors also increases, and may reach substantial values.