Table of contents

Yarn velocities in the false twist texturing process are a function of time and position within the process. The ability to measure the yarn velocity at discrete positions along the process would be a major step forward for those investigating the process characteristics. Synthetic textile yarns, such as nylon and polyester, have inherent static electric charge associated with them due to their method of manufacture. These charges are detected by two simple noncontacting electrodes connected to charge-to-voltage converters of relatively wide frequency bandwidth. The resulting voltages are cross correlated using a dedicated hardware correlator to give the thread line velocity. A measuring system is used on an experimental computer-controlled machine. Results are presented relating measured velocities to controlled roller velocities.

Speckle interferometric techniques can be used for measurement of displacement. An improvement in accuracy can be obtained by using multiple exposures, and this method is particularly useful in measuring the uniform speed of an object. The main feature is its simplicity and low cost.

The design and performance of a miniature 250 Hz, TEA CO₂ laser using H₂ buffered mixtures is described. 6 W average power has been obtained from a 10³ mm³ discharge volume.

It is demonstrated that, in case of transverse excitation, amplified spontaneous emission is the best source of pure continuum background for high-resolution pulsed laser spectroscopy.

A low-temperature cell for polarised Raman spectroscopy is described which facilitates the growing of single crystals from the liquid, and the determination of the orientation of the samples with the aid of X-ray diffraction.

A transformer-coupled LC-tuned detection method in AES has improved the signal-to-noise ratio of Auger spectra over the conventional CR-coupled detection method. The superior common mode rejection capability makes it possible to use a high-voltage power supply with ripple voltages as high as 30 V peak-to-peak at 50 and 100 Hz for an electron multiplier, without detectable difference in Auger spectra.

An easy to build low cost interface between a Biomation 805 waveform recorder and a Princeton Applied Research 4202 Signal Averager is described. This allows averaging of faster signals than is possible with the PAR 4202. A circuit modification of the PAR 4202 Signal Averager permits remote control of the front panel functions CLEAR/START/STOP and ERASE MEM. The function of this apparatus is demonstrated in the recovery of a decay curve from a weak fluorescent signal.

Describes a technique for the numerical modelling of stress wave propagation in pressure bars, using the theoretical dispersion relations. The method is applied to remove the effects of dispersion from experimental records, and pulses which show a moderate amount of dispersive distortion can be processed successfully. The technique is simple and comparatively rapid, and can be applied on a routine basis to correct the results from split Hopkinson bar tests and similar high strain rate and impact stress measurements.

A straining and heating stage has been built for a H700H Hitachi microscope. It provides a tilt angle of +or-45 degrees , a maximum specimen elongation of 3 mm which is achieved through a pneumatic device. Two examples are shown of dislocation sub-boundary interaction during creep of aluminium at an intermediate temperature and of copper-silica deformation of 1000K.

A method for the direct measurement of electron diffraction patterns in a Philips EM400T transmission electron microscope is described. Use is made of the diffraction lens shift-tilt coils to bring any desired diffraction spot to the centre of the screen. By monitoring the voltage applied to the coils, the position of any diffraction spot can be determined. After calibration d values and angles between the diffraction spots can be calculated without the need of a photographic recording. Advantages of the method are high speed, combined with accuracy. The conversion of the microscope and the calibration procedure are described and illustrated with some experimental results.

A spectrometer for the energy analysis of soft X-ray fluorescence spectra is described. The instrument is based on the photoelectric conversion technique, in which fluorescent photons from a sample irradiated with X-rays are allowed to ionise a converter gas with a sharp ionisation line and the resultant photoelectrons energy analysed with an electron energy analyser equipped with a multichannel detector. The photon energy range of the instrument was approximately 50 eV<h nu < approximately 5 keV with a resolution of less than 1 eV. High resolution spectra of the lines of O K (from Li₃PO₄, 526 eV), and Mo L₃M_4,5 (2293 eV) are presented.

An experimental determination has been made of the rates at which SnO₂-Pd and SnO₂-Pt catalysts recombine CO and O₂ at low concentrations in a basic gas mixture of CO₂, N₂ and He at a total pressure of one atmosphere. Significant rates were measured over the whole temperature range of the investigation (-27 degrees C to 44 degrees C). This information has enabled these catalysts to be used, unheated, in sealed CO₂ TEA lasers operating with mixtures of these gases containing high concentrations of CO₂. Their use has overcome the most important factor previously limiting the life of such lasers (especially at high pulse repetition frequencies), i.e. the generation of O₂ and CO by the dissociation of CO₂ during operation.

Details are presented of a double-collector static mass spectrometer that can determine precise stable carbon isotope ratios for samples of the order of 10^-8 g carbon as CD₄. Measurements are performed by analysis of the ion-beam intensities at m/z=20 (¹²CD₄⁺)and 21 (¹³CD₄⁺). The instrument is capable of long-term reproducibility (the 20/21 ratio of 23 consecutive aliquots of standard gas analysed over the course of a day varies by only +or-0.16 per mille); its ability to provide comparative isotopic measurements ( delta values) has been assessed by a zero-enrichment check which affords a value of -0.012+or-0.25 per mille.

Precise carbon isotope analysis at the nanogram level, using the static mass spectrometer, requires that sample carbon be in the form of deuteromethane. The authors describe the apparatus and technique for a low blank and quantitative deuteration reaction using a nickel catalyst for the conversion of carbon dioxide to deuteromethane. A regular relationship exists between the ¹²C/¹³C ratio for carbon dioxide measured conventionally at the microgram level and the m/z 20/21 ratio of CD₄ produced from 7-24*10^-9 g carbon aliquots of four samples of carbon dioxide whose carbon isotope compositions span most of the known natural abundance range.

An apparatus for the measurement of the rotational viscosity coefficient gamma ₁ of nematic liquid crystals is described. The commonly used method with a rotating magnetic field is improved by using a rotating sample and a fixed magnetic field, which allows larger field strengths and sample diameters. This technique and a precise determination of the torque on the sample lead to relative errors of measurement of the order of 0.3%. Wall effects, which can cause serious errors, are discussed. Their influence on the gamma ₁ values obtained is small if magnetic fields of sufficient strength are used. Kinematic and dynamic rotational viscosity coefficients for the nematic liquid crystals MBBA and 4-n-octyloxyphenyl 4-n-pentyloxybenzoate are presented.

A method for measuring the spontaneous polarisation and the dielectric constant as a function of the temperature of ferroelectric materials is presented. It is based on the extrapolation of the saturated (linear) part of the hysteresis loop. This extrapolation can be easily and accurately carried out by means of simple electronic circuits. Results of measurements at triglycine sulphate are given, as well as a detailed description of the electronic circuits. The systematic error in the spontaneous polarisation caused by the measurement at nonzero electric field is discussed and a suitable correction procedure is given.

An electroreflectance spectrum of the front surface of an UV enhanced silicon photodiode has been recorded in the spectral range from 300 to 500 nm. From this spectrum, the correction on the calculation of the diode absolute spectral response, due to the change in its reflectance during the 'oxide bias experiment', has been found to be no greater than 0.2%.

Conventional photon drag detectors for CO₂ lasers with two ring electrodes at the ends of the active cylinder typically have up to 40% change of sensitivity across the active area. It is shown that this arises from the current patterns in the device. A modified system has been developed with four rings in which the signal is developed across the central pair while the outer pair is loaded to reduce the sensitivity at the edges. With the appropriate outer load resistance the new arrangement can give a sensitivity within 5% of the central value over the whole active area whereas the conventional system typically gives this over only 30% of the diameter. Possible further improvements by changing other parameters are discussed.

The construction and performance of multigap plane multiwire proportional chambers (MWPCS) 108*108 cm² are described. Relevant details on the construction procedure and the results of operating tests are reported. These chambers are operating in the NAl experiment at SPS, CERN.

The theory of optimal filtering and smoothing of noisy data is presented. Implementation of this theory is made on the AS/7000 computer at Daresbury Laboratory. The Fortran code and examples of application on 'typical' spectroscopic data are given. The routine size is 35 kbytes and the CPU time 0.11 s for 1024 points.

Digital control theory is applied to the control of evaporation rate from a thermal source. The system is designed to have rapid response to transients in the evaporation rate without compromising stability. Evaporation rate is monitored by a quartz crystal microbalance. A triac is used to control power to the source and a novel method for determining the conduction angle is presented. Results are given for experiments carried out to verify the theory and demonstrate the effectiveness of the controller.

A constant-temperature hot-wire anemometer circuit using a new, low noise and large frequency bandwidth operational amplifier is described. Dynamic tests showed that the circuit response was as fast as a commercial unit. Further measurements in various classical turbulent flows with hot wires and hot films, in air and water, proved the new circuit to have identical spectral behaviour and comparable noise levels with much simpler design and lower cost. In addition, the design of the circuit includes convenient features such as internal square-wave test, digital resistance dial for a wide range of overheat settings, and compensation for two cable lengths. The circuit has been built in a Tektronix module.

A triple hot-wire method is proposed for measuring the instantaneous velocity vector of turbulent flows. The evaluation method is based on the concept of an effective cooling velocity. The instantaneous velocity components are calculated iteratively from the measured cooling velocities of the three sensors by a modified Newton algorithm. The three wires are orientated such that the probe has superior qualifications for analysing the Reynolds stress tensor. The probe has been manufactured locally from three commercially available subminiature hot-wire probes in such a way that the sensors have an effective sample of only 1.8 mm diameter. Qualification tests in highly turbulent flows have shown that serious inaccuracy occurs if the mean flow direction and the probe axis are misaligned by more than 15 degrees .

The measurement of transverse velocity fluctuations and Reynolds stresses with heated cylindrical sensors is studied at low mean velocities, 0.5 m s^-1<U<10 m s^-1, using a dynamic technique. It is concluded that the yaw sensitivity has a significant dependence upon the mean velocity within this range. The results indicate that there may be considerable difficulty in obtaining accurate turbulence measurements in large meteorological wind tunnels run at the low velocities.

Calibration experiments of conical hot-film probes moving along a tank filled with thermally regulated mercury are described. It is shown that heat transfer from the sensor, due to natural convection, dramatically decreases with velocity in the range 0-10 mm s^-1. It then becomes virtually negligible as velocity is further increased.

Velocity probes consisting of heated thin films mounted on the front of 0.90 mm diameter cylinders have been calibrated in the centre-line position of a pipe using theoretical predictions of the steady-flow velocity profile. The theoretical model interpolates between the laminar and fully turbulent regimes and accounts for the effects of entry length. The response of the probes in unsteady flows was found to be quasi-steady to within 5% for frequencies up to 5 Hz. These results were obtained in sinusoidal towing-tank flows and in oscillatory pipe flows of large pulsatile Reynolds number. For the pipe flows studied, the gauges could be located in the centre-line position at both 230 mm and 1.6 m from the pipe entrance, that is within the inlet and filled regions of the steady-flow entry length.