John R. Pugh

Clinical evaluation of patient tolerance to autorefractor prescriptions.

Background: In clinical optometric practice, autorefractors are used as an objective measure of refractive error prior to subjective refraction. We evaluate the clinical efficacy of autorefractor measurements by determining whether spectacles can be prescribed from autorefractor results.

Bend Pressure Drop Predictions Using the Euler-Euler Model in Dense Phase Pneumatic Conveying

Pneumatic conveying of powdered and granular materials is a very common transport technology across a broad range of industries, for example, chemicals, cosmetics, pharmaceuticals, and power generation. As the demands of these industries for greater efficiency increases and to comply with environmental regulations there is a need for a more fundamental understanding of the behavior of materials in pneumatic conveying systems. The approach presented in this article is to develop a model of a section of pneumatic conveying line, a horizontal or vertical 90° bend, in the commercial CFD software package FLUENT and to describe the multiphase flow behavior by the mixture or Eulerian method. Models of this type have been used in the past to show qualitative and quantitative agreement between model and experiment. The model results presented were compared with experimental data gathered from an industrial-scale pneumatic conveying test system. Broad qualitative agreement in trends and flow patterns were found. Quantitative comparisons were less uniform, with predictions from around 10% to 90% different from experimental results, depending on conveying conditions and bend orientation.

Twin channel infrared optometer for recording binocular accommodation.

A twin channel infrared (IR) optometer for recording accommodation from each eye is described. Some modifications to a conventional single channel optometer design are necessary to facilitate binocular recording. The optometer incorporates an on-line microcomputer for data acquisition and processing. Processing includes power spectrum and correlation analysis, and a facility for performing cursor controlled measurement of time delays. Accommodation responses recorded are shown to be independent of horizontal eye movements, and little affected by the drug used for mydriasis.

The use of coherence functions in the study of ocular mechanisms

The study of ocular mechanisms is often concerned with the possible interaction of two systems. Spectral analysis has been used previously by many investigators as a tool to investigate the interrelationships in the behaviour of two or more systems. This note demonstrates the value of computing coherence functions following spectral analysis to obtain a more rigorous tool for the investigation of synergy between two systems.

An experimental technique for the analysis of slug flows in pneumatic pipelines using pressure measurements

An experimental technique has been developed to measure the flow characteristics of slugs in dense phase pneumatic conveying using pressure measurements. This method is based on the unique characteristics of slug flows in pipes, i.e., an axial pressure fluctuation along the pipeline and a pressure difference in the radial direction at the back of a slug. Standard differential pressure transducers were used in this study and the influence of the finite response time of these transducers was considered. Experiments were conducted over a range of gas-solids flow conditions and experimental data were analyzed to describe the behavior of solids slugs through pipes. The calculated slug velocity and length using axial pressure measurements were confirmed by video recordings, and the synthesis between axial and radial pressure signals showed reasonable agreement in flow pattern analysis. This relatively simple measuring technique has been found effective in detecting solids slugs traveling through horizontal pipes and will distinguish various flow regimes. It provides a useful and easily applied tool for system optimizing and benchmarking in industrial applications.

CLINICAL EVALUATION OF INFRARED AUTOREFRACTORS FOR USE IN CONTACT LENS OVER-REFRACTION

We examined the ability of autorefractors to provide an accurate means of contact lens over-refraction measurement. Over-refraction measures, performed using six commercially available automated infrared autorefractors and retinoscopy, were compared with subjective refraction. A total of 40 contact lens wearers (20 soft lens wearers and 20 rigid gas permeable (RGP) lens wearers) participated in the study. All six autorefractors were able to provide over-refraction measures in all subjects. Data analysis revealed differences in autorefractor performance between the two types of contact lens wearer with greater accuracy and lower variability being found in the soft lens wearing subjects compared with the RGP group. The level of agreement between retinoscopy and subjective over-refraction results was lower in soft lens wear and higher in RGP wear than the levels found between the autorefractor and subjective over-refraction measures. We conclude that autorefractors provide a useful means of measuring contact lens over-refraction in soft lens wearers. Over-refraction results should be treated more cautiously in RGP wearers.

The Measurement of Small Eye Movements Using an Infra-Red Limbus Reflection Technique

Infrared eye-movement detection systems have not in general been used to measure small eye movements. A system based on the limbus reflection technique has been developed which employs chopped infrared sources with synchronous demodulation. The results of theoretical and experimental investigations of the system performance are presented. Measurements of the electronic noise inherent in the system have been used to determine the limits on the measurement of small eye movements. The measurements show that the system is capable of the measurement of small eye movements. Initial results on use of the system to investigate the synchronicity of small eye movements between the two eyes are presented.

Analysis and Measurements from a Prototype In-Line Thermal Solids Mass Flowmeter in an Industrial Scale Dilute Phase Pneumatic Conveying System

The in-line measurement of solids mass flow rate in a prototype industrial scale pneumatic conveying pipeline by a thermal method has been investigated over a range of dilute conveying conditions. A thermal method of determining solids mass flow rate should, in principle, be capable of achieving a reliable measurement regardless of; inhomogeneities in solids’ distribution, irregularities in velocity profile and variations in particle size or shape. The instrument described in this article operates by the injection of heat energy into the pipeline by way of a heated section and measuring the resultant change in solids’ temperature using infrared sensors. Initial results from the thermal instrument are compared with measurements from a gain in weight system showing good correlation. The importance of sensor window condition and temperature on measurement is discussed.

Axial and Radial Pressure Drops of Dense Phase Plugs

ABSTRACT An experimental technique to measure various characteristics of plug flow in dense phase pneumatic conveying systems based on the unique characteristics of plug flow, i.e., the fluctuation of axial pressure drop along a pipeline and pressure difference in the radial direction at the back of a plug, was developed by Li et al. (2002). Based on this work, a further experimental study combined with numerical modeling was carried out to describe the structure of plugs through the analysis of the measurements of pressure difference in both axial and radial directions. A theoretical explanation of these pressure differences was proposed and agrees very well with the recorded signals of pressure difference from differential transducers. This explanation will prove useful in understanding plug structures in industrial applications.

Evaluation of the International Standards Organisation/Draft International Standard model eye for use with automated infra-red optometers

A recent Draft International Standard describes a method for establishing the accuracy of automated infra-red optometers, using model eyes. In the present study we evaluate the performance of a series of automated infra-red optometers using model eyes constructed to the specifications of the Draft International Standard. The results demonstrate systematic differences between the values predicted by calculation from the standard and those found by measurement. These differences were reduced but not eliminated when the effects of non-paraxial refraction through the limiting aperture of the model eyes was taken into account. We conclude that the formula used to predict values of refractive power from the Draft International Standard is inappropriate because it fails to account for higher order aberrations.