Computer control of chemical process plants with special reference to distillation

A sieve plate distillation column has been constructed and interfaced to a minicomputer with the necessary instrumentation for dynamic, estimation and control studies with special bearing on low-cost and noise-free instrumentation. A dynamic simulation of the column with a binary liquid system has been compiled using deterministic models that include fluid dynamics via Brambilla's equation for tray liquid holdup calculations. The simulation predictions have been tested experimentally under steady-state and transient conditions. The simulator's predictions of the tray temperatures have shown reasonably close agreement with the measured values under steady-state conditions and in the face of a step change in the feed rate. A method of extending linear filtering theory to highly nonlinear systems with very nonlinear measurement functional relationships has been proposed and tested by simulation on binary distillation. The simulation results have proved that the proposed methodology can overcome the typical instability problems associated with the Kalman filters. Three extended Kalman filters have been formulated and tested by simulation. The filters have been used to refine a much simplified model sequentially and to estimate parameters such as the unmeasured feed composition using information from the column simulation. It is first assumed that corrupted tray composition measurements are made available to the filter and then corrupted tray temperature measurements are accessed instead. The simulation results have demonstrated the powerful capability of the Kalman filters to overcome the typical hardware problems associated with the operation of on-line analyzers in relation to distillation dynamics and control by, in effect, replacirig them. A method of implementing estimator-aided feedforward (EAFF) control schemes has been proposed and tested by simulation on binary distillation. The results have shown that the EAFF scheme provides much better control and energy conservation than the conventional feedback temperature control in the face of a sustained step change in the feed rate or multiple changes in the feed rate, composition and temperature. Further extensions of this work are recommended as regards simulation, estimation and EAFF control.

A study of the effects of orally administered female hormones on the volume and composition of lacrimal fluid related to the toleration of corneal contact lenses

This study was designed to evaluate the effects of certain orally active contraceptive steroids on the eye, related to the tolerance of a corneal contact lens. An oestrogen, ethinyloestradiol BP. 0.05 mg, a progestogen, norethisterone acetate BP. 2.50 mg and a control tablet (vitamin C, 50 mg) were utilised. The effect of these preparations on corneal curvature, lacrimal fluid volume and protein composition and directly on corneal lens tolerance was monitored in a group of 23 volunteer patients. The progestogen was found to produce a significant (P≥ 0.05) decrease in tear volume as measured by a 3 minute Schirmer test. A smaller volume reduction was observed with ethinyloestradiol. A normal cornea appears unaffected, within the measurement limits available, by the use of either hormone. However, in the presence of a corneal lens, oestrogen was found to induce substantial corneal steepening, indicative of tissue oedema, during the initial 2-3 weeks of medication. Progestogen occasionally produced a similar effect, which could recur with either hormone shortly after the end of the treatment period. A new method of acrylamide gel electrophoresis was developed for examination of the protein concentration and composition of lacrimal fluid. This allowed much greater resolution of microquantities of unconcentrated fluid than anything previously reported. Quantitation by densitometry has permitted the recording of medication and lens-induced changes in the protein pattern. Tear albumin has been shown to differ from serum albumin and to consist of up to 3 subfractions, 7 further protein fractions may also be resolved. The concentration and probable origin of these proteins have been established and the overall effects of hormone administration described. Individual idiosyncratic responses are also discussed. The study has established tbenature of some effects of contraceptive steroids on the anterior eye, and the probable reasons for resultant corneal lens intolerance.

Fish farm effluent control and the development of an expert system

In recent years, freshwater fish farmers have come under increasing pressure from the Water Authorities to control the quality of their farm effluents. This project aimed to investigate methods of treating aquacultural effluent in an efficient and cost-effective manner, and to incorporate the knowledge gained into an Expert System which could then be used in an advice service to farmers. From the results of this research it was established that sedimentation and the use of low pollution diets are the only cost effective methods of controlling the quality of fish farm effluents. Settlement has been extensively investigated and it was found that the removal of suspended solids in a settlement pond is only likely to be effective if the inlet solids concentration is in excess of 8 mg/litre. The probability of good settlement can be enhanced by keeping the ratio of length/retention time (a form of mean fluid velocity) below 4.0 metres/minute. The removal of BOD requires inlet solids concentrations in excess of 20 mg/litre to be effective, and this is seldom attained on commercial fish farms. Settlement, generally, does not remove appreciable quantities of ammonia from effluents, but algae can absorb ammonia by nutrient uptake under certain conditions. The use of low pollution, high performance diets gives pollutant yields which are low when compared with published figures obtained by many previous workers. Two Expert Systems were constructed, both of which diagnose possible causes of poor effluent quality on fish farms and suggest solutions. The first system uses knowledge gained from a literature review and the second employs the knowledge obtained from this project's experimental work. Consent details for over 100 fish farms were obtained from the public registers kept by the Water Authorities. Large variations in policy from one Authority to the next were found. These data have been compiled in a computer file for ease of comparison.

Institutional contradiction and management control innovation:a field study of total quality management practices in a privatised telecommunications company

The purpose of this paper is to theorise the changes surrounding the introduction of a management control innovation, total quality management (TQM) techniques, within Telecom Fiji Limited. Using institutional theory and drawing on empirical evidence from multiple sources including interviews, discussions and documents, the paper explicates the institutionalization of these TQM practices. The focus of the paper is the micro-processes and practice changes around TQM implementation, rather than the influence of the macro-level structures that are often linked with institutional theory. The change agents used Quality Action Teams and the National Quality Council to introduce new TQM routines. The present study extends the scope of institutional analysis by explaining how institutional contradictions impact to create and make space for institutional entrepreneurs, who in turn, modify existing routines or introduce new routines in fluid organizational environments which also exhibit evidence of resistance.

An enhanced scalable probe-based multicast admission control scheme

To guarantee QoS for multicast transmission, admission control for multicast sessions is expected. Probe-based multicast admission control (PBMAC) scheme is a scalable and simple approach. However, PBMAC suffers from the subsequent request problem which can significantly reduce the maximum number of multicast sessions that a network can admit. In this letter, we describe the subsequent request problem and propose an enhanced PBMAC scheme to solve this problem. The enhanced scheme makes use of complementary probing and remarking which require only minor modification to the original scheme. By using a fluid-based analytical model, we are able to prove that the enhanced scheme can always admit a higher number of multicast sessions. Furthermore, we present validation of the analytical model using packet based simulation. Copyright © 2005 The Institute of Electronics, Information and Communication Engineers.

Phytoestrogens modulate breast cancer resistance protein expression and function at the blood-cerebrospinal fluid barrier

PURPOSE: Breast cancer resistance protein (BCRP/ABCG2) is a drug efflux transporter expressed at the blood cerebrospinal fluid barrier (BCSFB), and influences distribution of drugs into the central nervous systems (CNS). Current inhibitors have failed clinically due to neurotoxicity. Novel approaches are needed to identify new modulators to enhance CNS delivery. This study examines 18 compounds (mainly phytoestrogens) as modulators of the expression/function of BCRP in an in vitro rat choroid plexus BCSFB model. METHODS: Modulators were initially subject to cytotoxicity (MTT) assessment to determine optimal non-toxic concentrations. Reverse-transcriptase PCR and confocal microscopy were used to identify the presence of BCRP in Z310 cells. Thereafter modulation of the intracellular accumulation of the fluorescent BCRP probe substrate Hoechst 33342 (H33342), changes in protein expression of BCRP (western blotting) and the functional activity of BCRP (membrane insert model) were assessed under modulator exposure. RESULTS: A 24 hour cytotoxicity assay (0.001 µM-1000 µM) demonstrated the majority of modulators possessed a cellular viability IC50 > 148 µM. Intracellular accumulation of H33342 was significantly increased in the presence of the known BCRP inhibitor Ko143 and, following a 24 hour pre-incubation, all modulators demonstrated statistically significant increases in H33342 accumulation (P < 0.001), when compared to control and Ko143. After a 24 hour pre-incubation with modulators alone, a 0.16-2.5-fold change in BCRP expression was observed for test compounds. The functional consequences of this were confirmed in a permeable insert model of the BCSFB which demonstrated that 17-β-estradiol, naringin and silymarin (down-regulators) and baicalin (up-regulator) can modulate BCRP-mediated transport function at the BCSFB. CONCLUSION: We have successfully confirmed the gene and protein expression of BCRP in Z310 cells and demonstrated the potential for phytoestrogen modulators to influence the functionality of BCRP at the BCSFB and thereby potentially allowing manipulation of CNS drug disposition.