Biomedical subjects

I B Lee

Publications and source records attributed to I B Lee.

7 recordsLinked to original sources

PubMed2006

Sensor fault diagnosis in a wastewater treatment process.

There are many sensors in a wastewater treatment process (WWTP) plant for monitoring process performance and condition. Sensor validation is essential to the success of process monitoring. In this paper, various sensor faults which can occur in WWTP are identified for taking proper remedial action at an early time. A proposed sensor fault isolation method is based on the variable reconstruction using principal component analysis (PCA). Even though several methods have been developed to identify sensor faults, they are only applicable to a static process. In other words, they cannot be successfully used to monitor severe dynamic processes such as WWTPs. We have removed this limitation by developing reconstruction methods based on a dynamic version of PCA. Artificial scenarios of sensor faults generated from the simulation benchmark have been used to validate the proposed sensor identifying methodology. Also, it is compared to a previous method to show its relative superiority in sensor fault validation in the WWTP.

Automation↗

PubMed2006

Sensor validation and reconciliation for a partial nitrification process.

Wastewater treatment plants (WWTP) are notorious for poor data quality and sensor reliability due to the hostile environment in which the measurement equipment has to function. In this paper, a structured residual approach with maximum sensitivity (SRAMS) based on the redundancy of the measurements is used to detect, identify and reconstruct single and multiple sensor faults in a single reactor for high activity ammonia removal over nitrite (SHARON) process. SRAMS is based on inferences, which are insensitive to the faults in the sensor of interest and sensitive to faults in the other sensors. It is used for four types of sensor failure detection: bias, drift, complete failure and precision degradation. The application of sensor validation shows that single and multiple sensor faults can be detected and that the fault magnitude and fault type can be estimated by the reconstruction scheme. This sensor validation method is not limited by the type or application of the considered sensors. The methodology can thus easily be applied for sensor surveillance of other continuously measuring sensors and analysers.

Bioreactors↗

PubMed2005

A new method to measure the polymerization shrinkage kinetics of light cured composites.

This study was undertaken to develop a new measurement method to determine the initial dynamic volumetric shrinkage of composite resins during polymerization, and to investigate the effect of curing light intensity on the polymerization shrinkage kinetics. The instrument was basically an electromagnetic balance that was constructed with a force transducer using a position sensitive photo detector (PSPD) and a negative feedback servo amplifier. The volumetric change of composites during polymerization was detected continuously as a buoyancy change in distilled water by means of the Archimedes' principle. Using this new instrument, the dynamic patterns of the polymerization shrinkage of seven commercial composite resins were measured. The polymerization shrinkage of the composites was 1.92 approximately 4.05 volume %. The shrinkage of a packable composite was the lowest, and that of a flowable composite was the highest. The maximum rate of polymerization shrinkage increased with increasing light intensity but the peak shrinkage rate time decreased with increasing light intensity. A strong positive relationship was observed between the square root of the light intensity and the maximum shrinkage rate. The shrinkage rate per unit time, dVol%/dt, showed that the instrument can be a valuable research method for investigating the polymerization reaction kinetics. This new shrinkage-measuring instrument has some advantages that it was insensitive to temperature changes and could measure the dynamic volumetric shrinkage in real time without complicated processes. Therefore, it can be used to characterize the shrinkage kinetics in a wide range of commercial and experimental visible-light-cure materials in relation to their composition and chemistry.

Bisphenol A-Glycidyl Methacrylate↗

PubMed2004

Dynamic monitoring system for full-scale wastewater treatment plants.

This paper proposes a new process monitoring method using dynamic independent component analysis (ICA), ICA is a recently developed technique to extract the hidden factors that underlie sets of measurements, whereas principal component analysis (PCA) is a dimensionality reduction technique in terms of capturing the variance of the data. Its goal is to find a linear representation of non-Gaussian data so that the components are statistically independent. PCA aims at finding PCs that are uncorrelated and are linear combinations of the observed variables, while ICA is designed to separate the ICs that are independent and constitute the observed variables. The dynamic ICA monitoring method is applying ICA to the augmenting matrix with time-lagged variables. The dynamic monitoring method was applied to detect and monitor disturbances in a full-scale biological wastewater treatment (WWTP), which is characterized by a variety of dynamic and non-Gaussian characteristics. The dynamic ICA method showed more powerful monitoring performance on a WWTP application than the dynamic PCA method since it can extract source signals which are independent of time and cross-correlation of variables.

Algorithms↗

PubMed2003

New monitoring technique with an ICA algorithm in the wastewater treatment process.

A new monitoring method using independent component analysis (ICA) is suggested for the wastewater treatment process (WWTP). ICA is an extension of PCA (Principal Component Analysis). While PCA can only impose independence up to the second order (mean and variance) with constraint on the direction vectors to be orthogonal, ICA imposes statistical independence up to more than second order on the individual component and has no orthogonal condition. When the variables have the Gaussian distribution, PCA itself provides a satisfactory result in monitoring performance. However, the measured variables are not often normally distributed. In this case, ICA can provide better monitoring results than PCA since ICA is based on the assumption that the latent variables are not normally distributed. In this paper, the ICA monitoring algorithm with kernel density estimation was applied to fault detection and diagnosis of the wastewater simulation benchmark. ICA with kernel density estimation gives better results than PCA in disturbance detection in spite of severe periodic features of the wastewater plant.

Algorithms↗

PubMed2002

Cascade control strategy for external carbon dosage in predenitrifying process.

We propose a cascade control strategy composed of two Proportional-Integral (PI) controllers to regulate the nitrate concentration in the predenitrifying process by manipulating the external carbon dosage. It controls the nitrate concentrations in the effluent as well as in the final anoxic reactor simultaneously to strictly satisfy the quality of the effluent as well as to remove the effects of disturbances more quickly. The design of two PI controllers in the cascade control loop can be completed with the Ziegler-Nichols (Z-N) tuning rule together with a simple relay feedback identification method. Results from the Benchmark simulation confirm that both good set point tracking and satisfactory disturbance rejection can be guaranteed due to the structural advantages of the proposed cascade control strategy. Also, compared with a previous work, the fluctuation of the nitrate concentration in the effluent has been decreased significantly.

Algorithms↗

PubMed2001

Thermal analysis on the cure speed of dual cured resin cements under porcelain inlays.

The reaction kinetics of five commercial dual cured resin cements (Bistite, Dual, Scotchbond, Duolink and Duo) were investigated when cured under varying thicknesses of porcelain inlays by chemical or light activation. The effect of the porcelain disc on the rate of polymerization of dual cured resin cement during light exposure was evaluated using thermal analysis, thermogravimetric analysis and differential scanning calorimetry. Inorganic filler weight %, the heat of cure (Delta H), the maximum rate of heat output and the peak heat flow time were measured when the polymerization reaction occurred by chemical cure only or by light exposure through 1, 2 and 4-mm thick porcelain discs. In 4-mm thick porcelain discs, the exposure time was varied from 40 to 60 s to investigate the effect of the exposure time on polymerization reaction. Cure speed by light exposure was 5--20 times faster than by chemical cure. The dual cured resin cements differed markedly in their sensitivity to light and chemical activation. The peak heat flow time increased by 1.51, 1.87 and 3.24 times as light cure was carried out through 1, 2 and 4-mm thick porcelain discs, respectively. Exposure times recommended by the manufacturers were insufficient to compensate for the attenuation of light by the 4-mm thick porcelain disc.

Algorithms↗