Mirnader Ghazali

Real-Time Water Quality Monitoring: Assessment of Multisensor Data Using Bayesian Belief Networks

Real-time sensing in water distribution systems provides a potentially powerful analytical tool for providing water security. Through monitoring surrogate parameters (e.g., pH, turbidity, and residual chlorine) over time, the natural variations of a distribution system’s parameters are established, allowing rapid detection of changes in water quality. However, the level of performance that water quality event detection algorithms have exhibited to date is insufficient for real-world utilization. Bayesian belief networks (BBNs) offer a formalized method of reasoning under uncertainty and are well suited to the analysis of multiple sources of information. The application of a BBN to water quality event detection is described. Surrogate parameters (pH, conductivity, and turbidity) were monitored during an experimental E. coli contamination. Difference filtration using a 60-s moving window of observations identified rapid rates of change present in the surrogate parameter signals, demonstrated as responsive t...

Current Technologies For On-Line Monitoring of Drinking Water Distribution Systems

Increased risks of drinking water contamination are incentives for implementation of improved monitoring approaches for pathogens in drinking water distributio…

Simplex optimization of acoustic assay for plasminogen activators

This article discusses the optimization of a newly developed method for measuring the activity of plasminogen activators using a thickness-shear-mode acoustic sensor. A variable-size simplex algorithm was used for optimization. Preliminary tests were performed to design the first simplex. A desirability function was defined to translate each performance value to a membership value of 0 to 1. If there was more than one performance variable, their membership values were translated to an aggregated membership value using another function that considers their individual influence on sensor performance. Two rounds of optimization were carried out for streptokinase followed by a single optimization for tissue-type plasminogen activator. In the last optimization, ratios of control variables were used in order to reduce the number of parameters and to formulate easily adjustable assay conditions. The results showed the usefulness of the simplex method for optimizing this type of assay, and the importance of preliminary tests and prior knowledge in providing rapid convergence using fewer experiments. The optimized plasminogen activator assay can be considered a reference method for measurement of all members of this drug class.

Acoustic determination of performance and equivalence of plasminogen activators

A reliable method for the measurement of different plasminogen activators is of great interest for both manufacturing and clinical medicine. A one-step assay based on a thickness shear mode acoustic sensor has been developed for this purpose. Two separate mixtures of substrates (fibrinogen and plasminogen) and enzymes (thrombin and the plasminogen activator) were mixed, and placed on the acoustic sensor surface. During the assay, the resonant frequency of a quartz crystal oscillating in the thickness shear mode was measured and used to find a characteristic clot dissolution time, from the sample addition to the time at the maximum dissolution rate. Calibrations of the acoustic assay were done for tissue-type plasminogen activator (t-PA) as well as for the other plasminogen activators: urokinase (u-PA); streptokinase (SK) and staphylokinase (SAK). All gave relative standard deviations of about 12%. Since the same method was used for all of the activators, their activities were compared, resolving the differences between their unit definitions. Linear relationships were found between urokinase and streptokinase which activate plasminogen directly and between t-PA and staphylokinase which require fibrin as a cofactor. The relationship between the groups was found to curve, indicating the difference between the two mechanisms. The acoustic method, therefore, may be used as a rapid and cost-effective reference method for the standardization and comparison of different plasminogen activators.