Theoretical expressions and charts for obtaining the maximum cyclic shear strains due to the passage of P and S waves in an elastic isotropic half space are presented. Plane, cylindrical and spherical P waves, and plane and cylindrical S waves are considered. The results are presented in terms of two main parameters which can be measured, i.e. peak particle velocity and P or S wave velocity in the medium. The expressions and charts are of practical value in methods of analysis that require direct use of the shear strains induced by ground vibrations, e.g. in the ‘threshold strain’ approach.

The critical shear stress approach is an alternative approach in storm sewer design. Analysis is conducted on this approach as a criterion in sediment transport in storm sewer and subsequently compared to the velocity approach. Comparison made showed that the critical shear stress method gives higher velocity than the velocity approach. The difference in assessing the shear stress is the main reason for this approach to produce high velocity.

Water absorption into concrete was measured by ISAT method. Concrete samples with different aggregate size, duration of moist-curing and water-cement ratio were tested. The results showed that by decreasing the duration of moist-curing and water-cement ratio, the water absorption decreases, but the increase of the aggregate size will decrease the rate of absorption.

The effects of aggregate-cement and water-cement ratios on the relationship between ultrasonic pulse velocities and the cube compressive strength of concrete under continues wet curing and wet curing for specific periods were studied. The relationship of the velocity with the compressive strength almost unaffected by the aggregate-cement ratios between 4.8 and 6.8, but the variation of water-cement ratio between 0.45 and 0.67 has some effect. The differences become more pronounced in the wet cured samples which have been exposed to the laboratory conditions. The ultrasonic velocities of similar samples and cured in similar manner but were tested at different ages follow the same velocity-strength relationship.

This paper describes an investigation into the scale effect of model sizes on the particle retention efficiency of the stilling pond type storm sewage overflows. The scaling criteria for model-prototype similarity were examined. Data from previous studies on scale effect were reviewed and analysed and their shortcomings discussed. A qualitative comparison of the present model results with the prototype data obtained by Saul (1977) were presented and confirmed the findings that an increase in model size resulted in a decrease in the efficiency of a chamber.

The production of the enzyme cytochrome P-450 by Saccharomyces cerevisiae N.C.Y.C. 754 in batch fermentations using a coconut water based medium was scaled-up from shake flask to a 2-liter stirred – tank fermenter scale using the method of constant volumetric transfer coefficient (k_La) of oxygen. k_La values were derived by fitting the mass transfer equation to the data of dissolved oxygen tension (DOT) versus time on computer using the Simplex Method with two unknowns, namely k_La and the electrode mass transfer coefficient (ka_p) of oxygen. The stirrer speed (RPM) and the air flowrate, (A) in the 2-liter fermenter that produced the value of k_La found in the optimised conditions in shake flask was approximated by trial and error. A fermentation run in the 2-liter fermenter using these values of RPM and A gave an enzyme yield comparable to that achieved in shake-flasks.

Experiments on using acclimated culture were carried out to determine if compounds other than glucose could be effective as cosubstrate in biodecolourisation of an azo dye. The role of cosubstrate was found to be not structure dependent hence cometabolism was not likely to be involved in biodecolourisation. This finding also offers opportunities for use of carbon sources other than glucose and for mixing of wastewaters to facilitate biodecolourisation.

A study on the effects of aeration on biodecolourisation of an azo dye was carried out using acclimated culture. Oxidation reduction potential was used as a measure of degree of aeration. The results showed biodecolourisation to be dependent on degree of aeration with negative or very low oxidation reduction potential being favourable for decolourisation. This finding was in line with the postulation that biodecolourisation occurred via azo bond cleavage.

In this paper we describe the fabrication and evaluation of on-chip silicon-based gas pressure sensors. The sensor is fabricated using standard Integrated Circuit (IC) fabrication technology except the final etching to delineate cantilever beams. The beam which is the key element in the sensor system is driven to its resonant frequency by the difference in thermal expansion between silicon and oxide. The output detection is done by utilising the piezoresistive effect in a polysilicon resistor defined on top of the oxide layer. It is found that the resonant frequency (fR)) varies linearly with the gas pressure from 100 mmHg to about 500 mmHg, thus it is possible for system to be used as a gas pressure sensor.

Switched-capacitor techniques are applied to the design of a bandpass filter circuit satisfying the specification for filters used in acoustical measurement. Dependence of the switched-capacitor filter characteristics on its clock frequency allows the achievement of the whole range of preferred midband frequencies from 10 Hz to 20 kHz by a single circuit. The design produces a circuit which is insensitive to parasitic capacitances and element-value variations. This offers the possibility for the filter and all its accessories to be fully integrated using MOS technology.