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No description available.

Future railway trends require travelling at high speeds without deterioration in the ride quality, but further improvement of the ride quality by optimisation of the passive suspension components has reached its limits. This suggests that active suspensions should be used. Rigorous studies over the past four decades have shown that this technique is able to overcome the passive suspension limitation in terms of improving the overall ride performance of the railway vehicle with the incorporation of additional active elements i.e. actuators, sensors and processors. The work in this thesis investigates a novel method for controlling the actuators within the suspension system, something which has been neglected in previous studies. It is a particular problem because at higher frequencies, when the suspension is providing isolation of the car body from the track irregularities, the actuator must accommodate the suspension movements whilst producing very small forces, otherwise the ride quality substantially deteriorates. Instead of considering more complex active suspension control strategies, which tend to be complex and may be impractical, the performance of the actuator across the secondary suspension is investigated. This research looks into improving actuator technologies for railway secondary suspensions in order to achieve the full benefits of active control. This thesis explores novel methods to improve the ride quality of the railway vehicle through secondary suspension actuator and controller design, with the ultimate aim of integrating this technology into a fully active railway vehicle. The focus of this active suspension research is therefore upon incorporating real actuator technology, instead of the usual assumption of ideal actuators. For meaningful and reliable research a simple, well established active control strategy is used for assessment to highlight the degradation in the suspension performance compared with the ideal actuators. Preliminary investigation demonstrates significant degradation of the ride quality caused by real actuators in the secondary suspension, and this research looks at methods to reduce this effect. Including actuators within a secondary suspension system is a difficult actuator problem compared to the normal application of actuators such as position control. This is because the actuator controller design process requires the consideration of the interaction of the vehicle suspension. The actuators that have been identified as suitable for the application are the electromechanical and servo-hydraulic types, and these are incorporated across the secondary suspension. The effects of the actuator dynamics have been analysed. Practical classical controllers are used to provide force-feedback control of both types of actuator in the secondary suspension. A variety of actuator control techniques are considered including: optimisation of the actuator controller parameters to solve the multi-objective and multivariable problem, the introduction of feed forward techniques and the use of optimal control approaches.

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The sub-population of quasars reddened by intrinsic or intervening clouds of dust are known to be underrepresented in optical quasar surveys. By defining a complete parent sample of the brightest and spatially unresolved quasars in the COSMOS field, we quantify to which extent this sub-population is fundamental to our understanding of the true population of quasars. By using the available multiwavelength data of various surveys in the COSMOS field, we built a parent sample of 33 quasars brighter than J = 20 mag, identified by reliable X-ray to radio wavelength selection techniques. Spectroscopic follow-up with the NOT/ALFOSC was carried out for four candidate quasars that had not been targeted previously to obtain a 100% redshift completeness of the sample. The population of high AV quasars (HAQs), a specific sub-population of quasars selected from optical/near-infrared photometry, some of which were shown to be missed in large optical surveys such as SDSS, is found to contribute 21%(+9)(-5) of the parent sample. The full population of bright spatially unresolved quasars represented by our parent sample consists of 39%(+9)(-8) reddened quasars defined by having A(V) > 0.1, and 21%(+9)(-5) of the sample having E(B-V) > 0.1 assuming the extinction curve of the Small Magellanic Cloud. We show that the HAQ selection works well for selecting reddened quasars, but some are missed because their optical spectra are too blue to pass the g - r color cut in the HAQ selection. This is either due to a low degree of dust reddening or anomalous spectra. We find that the fraction of quasars with contributing light from the host galaxy, causing observed extended spatial morphology, is most dominant at z less than or similar to 1. At higher redshifts the population of spatially unresolved quasars selected by our parent sample is found to be representative of the full population of bright active galactic nuclei at J < 20 mag. This work quantifies the bias against reddened quasars in studies that are based solely on optical surveys.

Although surfactant selective electrodes have been employed for several decades, those electrodes "of the second kind" and those incorporating a liquid membrane suffered severe limitations. A large improvement in the reliability of such electrodes was achieved by Cutler (Ph.D. Thesis, University of Aberdeen, 1975) using a liquid plasticized PVC membrane in which the surfactant was directly complexed to the PVC. However, such electrodes still had several drawbacks including the solubilisation of the liquid plasticiser from the membrane and the influx of water through the membrane after only a few hours in solution. It was the purpose of this study to reproduce and perhaps improve upon the electrodes developed by Cutler and to use them to investigate the thermodynamics of colloidal ionic surfactant solutions. Initially, the electrodes developed for both cationic and anionic surfactants by Cutler were reproduced and during the course of the study were improved upon by replacing the liquid plasticizer content of the membranes by a high molecular weight PVC-compatible terpolymer. This polymeric blended membrane is much tougher than the liquid plasticized one and has a much higher resistance to the uptake of water. Thus, the useful lifetime of a membrane was extended from a period of hours to a period of weeks. In addition the polymer blended membrane has no liquid components and hence the solubilisation of membrane component in micellar solution is no longer a problem. The surfactant selective electrodes was used in conjunction with electrodes reversible to other common species in solution (Na+, Cl-, Br-, etc.) to construct cells without liquid junction for potential measurements. In addition to getting rid of the unavoidable error associated with potential measurements using cells with liquid junction, this experiment allowed for a direct determination of the surfactant monomer concentration above the CMC. This is, to the authors knowledge, the first time that such a measurement has been experimentally possible. Initially a well documented system was chosen for investigation: the micellisation of sodium dodecyl-sulphate in aqueous salt (NaBr) solutions. The well known depression of the CMC with increasing salt concentration was observed and from this the degree of dissociation of counterions from the micelles was calculated. This corresponded closely to other values reported in the literature. Recently a thermodynamic theory of the micellisation of ionic surfactants has been reported by Hall (1981) and using data obtained by the electrode measurements, three tests of the theory were possible. In each case the theory was found to correspond with the experimental measurements. Additionally using the electrode measurements it was possible to estimate the interaction or 'Harned' coefficient between the dodecylsulphate and sodium ions in aqueous salt solutions below the CMC. The use of the electrodes was extended to other 'non detergent' amphiphilic molecules and the aggregation of BDPH, a cationic drug, was investigated. These molecules were found to form pre-micelles before the onset of true micellisation and an iterative simulation procedure indicated that these pre-micelles were probably dimers. The effect of salt upon the CMC was also determined and hence, α, the degree of dissociation of counterions from the micelles was calculated. This value agreed well with other literature reports. The electrodes were also used to investigate the aggregation of ionic surfactants in mixed solvent media e.g. ethylene glycol + water and ethanol + water mixtures. The variation of a with solvent composition was observed and additionally it was demonstrated that the electrode measurements could be used to determine conveniently the solubility product of ionic surfactants in aqueous or mixed solvent systems. Mixed micellar systems were also studied. These included anionic-cationic, ionic-nonionic and ionic-zwitterionic systems and the composition of the mixed micelles in many cases was found to follow a very simple model based upon the regular mixing of the micellar components. The phase behaviour of these systems was also observed since many of them were found to form stable micelles only at certain compositions. Phase separation including precipitation, coacervation or liquid crystalline phase formation was found in many systems over certain solution compositions. The electrodes were used to calculate the α value of a mixed micellar system as a function of micelle composition. In the final chapter the binding of ionic surfactants to synthetic macromolecules is discussed and the results of electrode measurements are reported. The measurement of the adsorption isotherm of the surfactant into the polymer was found to be very quick and convenient and the systems investigated included both anionic and cationic surfactants binding onto either neutral polymers or highly charged polyelectrolytes. The effect of the solution composition variables (i.e. salt, surfactant and polymer concentrations) and the molecular weight of the polymer upon the binding process was determined for one system, sodium dodecylsulphate binding to polyvinylpyrollidene. A recent theory by Hall to account for the binding of ionic surfactant to neutral polymers is discussed and experiments were carried out to test this theory.

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A research report submitted to the Faculty of Medicine, University of the Witwatersrand, in partial fulfillment of the requirements for the Degree of Master of Medicine in the division of Plastic and Reconstructive Surgery. Johannesburg 2014 / With 67% of the world’s human immunodeficiency virus (HIV) infected population existing in Sub-Saharan Africa and recent access to highly active antiretroviral therapy (HAART); demand for plastic surgical intervention in addressing HIV-associated lipodystrophy has expanded dramatically. This study assessed the prevalence of lipodystrophy in a random clinic cohort, the demand for surgical correction, and risk of treatment non-compliance A questionnaire and database cross-sectional review of 554 patients was performed over a three-month period at the Themba Lethu Clinic, Johannesburg, South Africa. A total of 479 patients completed the questionnaire, 83% were female. Nearly 90% of patients were currently being treated, or had been treated with stavudine (d4T). The prevalence of lipodystrophy was 11.7%. Nearly 5.9% of patients had considered stopping treatment due to changes in body morphology following the onset of HAART, 47% of patients interviewed would consider surgery to correct unwanted physical changes following treatment with HAART. Male patients were satisfied by physical changes in their body habitus following treatment (pre-treatment satisfaction 38% vs. post-treatment satisfaction of 94%). Female patients had 6.5 times more breast hypertrophy related symptoms than in their pretreatment state. This study identified a prevalence of 11.7% of patients with HIV-associated lipodystrophy. A total of 3.8% of all patients would consider non-compliance on the basis of this side effect alone. The demand for surgical correction is significant, extends beyond patients diagnosed with HIV-associated lipodystrophy, and needs to be addressed.

M.Sc. (Epidemiology), Faculty of Health Sciences, University of the Witwatersrand, 2011 / Background and Objectives The advent of Highly Active Antiretroviral Therapy (HAART) has resulted in a significant reduction in HIV/AIDS related morbidity and mortality in sub-Saharan Africa. However, toxicities due to HAART continue to pose challenges to the success of different regimens. Severe hepatotoxicity is one of the significant adverse events occurring in patients on HAART. Information on the incidence and risk factors for severe hepatotoxicity in cohorts from resource poor settings is limited. It is against this background that we undertook the study to determine the incidence and explore factors associated with severe hepatotoxicity following HAART initiation in a South African cohort. Materials and Methods Secondary data analysis of a prospective cohort 9764 HIV-infected adult patients initiated on HAART at the Themba Lethu clinic antiretroviral rollout facility in Johannesburg, South Africa between 1st April 2004 and 30th June 2009 was conducted. Severe hepatotoxicity cases were identified within the first 12 months of initiating HAART as grade 3 or 4 elevation in baseline ALT levels. The incidence rate of severe hepatotoxicity was calculated and potential socio-demographic and clinical predictors were explored using Cox proportional hazard regression modelling. Results At baseline, 91.8% of patients were commenced on an efavirenz-based regimen while only 8.2% were on a nevirapine-based regimen. The median CD4 count at v initiation of HAART for this cohort was 80 cells/ mm3, a figure lower than the Department of Health (DoH) CD4 cut off for initiating HAART of 200 cells/ mm3. The overall incidence rate of severe hepatotoxicity was 10.7 (95% CI: 8.7 – 13.1) cases per 1000 p-yrs of follow-up. The period with the highest risk of severe hepatotoxicity was within 2 months of initiating HAART. Incidence of severe hepatotoxicity was 21.1(95% CI: 12.7 – 34.9) cases per 1000 p-yrs among patients on a nevirapine-based regimen and 9.7 (95% CI: 7.8 – 12.1) cases per 1000 p-yrs in those on an efavirenz-based one. The hazard for severe hepatotoxicity within the first year of initiating HAART was 2.17 times higher in individuals on a nevirapine-based regimen compared to those on an efavirenz-based regimen after adjusting for baseline ALT, baseline CD4, age and gender (HR = 2.17; 95%CI = 1.18 – 3.97; p = 0.013). Though imprecise, the estimate for baseline ALT category suggested an increased risk for severe hepatotoxicity in individuals with a baseline ALT more than 40 I.U/L compared to those with a baseline ALT of less than 40 I.U/L (HR = 1.63; 95%CI = 1.00 – 2.67; p = 0.050). Conclusion The results of the study suggest that severe hepatotoxicity following initiation of HAART in this cohort is low compared to other previously studied cohorts. The high incidence rate of severe hepatotoxicity in the first two months of initiating HAART necessitates the need for more frequent and careful monitoring of ALT levels early during therapy. Patients on a nevirapine-based regimen have a higher risk of developing severe hepatotoxicity when compared to their counterparts on an efavirenz-based regimen, a result consistent with findings from previous studies.

M. Pharm., Faculty of Health Sciences, University of the Witwatersrand, 2011 / Background: According to the 2010 edition of the UNAIDS Report on the global AIDS epidemic, an estimated 320 000 (20%) fewer people died of AIDS-related causes in South Africa in 2009 than in 2004 due to the increase in availability of anti-retroviral medicines.(2) With this positive trend, the mindset should be shifted towards reducing adverse effects of ART. The need for permanent ART treatment and the significant increase in life expectancy have led to the observation of new, frequent, and sometimes severe drug-related adverse effects.(4) One of the most challenging and potentially dangerous side-effects is hyperlactataemia (Hlac) that may evolve to lactic acidosis (LA)(5) ART–associated Hlac may be asymptomatic, or symptomatic which in the extreme case can progress to life threatening acidosis. The latter, i.e. lactic acidosis is a fairly frequent and often misdiagnosed or under diagnosed and potentially fatal side effect of ARTs. (6) Objectives: To explore the relationship between Hlac/LA and gender, weight, dosage CD4 and regimen alterations in HIV patients on ARTs and to compare the earlier regimens to the revised regimens as independent risk factors for Hlac and LA. Sample size would be based on the hypothesis that newer regimens would reduce the incidence of Hlac and LA. Methods: A Retrospective study was conducted by reviewing 3 741 patient files from August 2004 to December 2007. This study was to assess the incidence and risk factors of Hlac/LA. Hlac was defined as a venous lactate measurement of ≥2.3mmol/L and LA was ≥5mmol/L. Immunological, virological, haemotological and biochemical results were recorded for all the patients. A second phase involved a Prospective study. Patients who were on treatment for >12 months were randomly selected from the queue at the clinic between the September 2008 and December 2009. Immunological, virological, haematological and biochemical information was recorded for all patients selected. Analysis involved descriptive statistics, comparison of means, frequency analysis and multivariate analysis. Results: Two-hundred and thirty two patients were identified with elevated lactate levels in the retrospective study. The incidence was 6.2% in this population, with gastro-intestinal symptoms, peripheral neuropathy, abdominal tenderness, rash and upper respiratory tract infection being the significant symptoms. The major risk factor was a low CD4 count. The prospective study included 292 patients with 24.3% with Hlac/LA with peripheral neuropathy (p 0.209), gastrointestinal symptoms (nausea, vomiting) (p 0.148) and abdominal tenderness (p 0.214) were the most significant symptoms. In terms of the hypothesis that newer regimens would lower the incidence of elevated lactate levels by 50%, the observed incidence of 24.3% is no different from previously reported rates. This therefore shows that although regimen changes have been implemented the overall incidence of Hlac appears to be unchanged but the LA rate was found to be significantly lower than before, 6.8 cases per 1000 patient years vs ±19 cases per 1000 person years.(16) Gastro-intestinal symptoms but not peripheral iv neuropathy; with low CD4 count, weight loss and low weight on entry were the significant risk factors, which is most likely representative of advanced disease. Conclusions: Although newer regimens have been introduced, Hlac/LA still exist. Healthworkers need to be on high alert for Hlac/LA particularly if a patient enters into the ART program with a low CD4 count and a low weight