Analysis and design optimisation of grid-connected wound-rotor synchronous and induction motors

Thesis (DEng)--Stellenbosch University, 2019.ENGLISH ABSTRACT: The dissertation presents new approaches in the analysis, design and optimisation of three-phase cylindrical wound-rotor synchronous (WRSM) and induction (WRIM) motor types. The new approaches are based on the analysis of the steady-state finite element method (FEM) in which the parameters and performances of the motor types are predicted. Absolute optimum designed WRSM and WRIM motor types can at best be obtained by the use of improved parameters and performance calculation methods in the design optimisation process. This dissertation proposes simple, fast and accurate parameter and performance calculation modern approaches for grid-connected WRSM and WRIM motor types using two-axes electromagnetic models. The modern approaches are based on non-classical models in which iterative processes are utilised using static FEM in conjunction with the motor types phasor diagrams. During the iterative processes, the electric circuit and magnetic field equations are coupled to access important parameters of the motor types. The access of parameters using iterative processes solves the excitation currents at different operating points of the motor. The parameters are accurately calculated using a FEM based method of freezing the motor core permeance. The dissertation investigates and expands the use of these parameters as an effective and powerful tool for explaining the motor behaviour under different operating points. A great deal of attention is also given to the design optimisation of the motor types during which a relatively efficient optimisation procedure is shown. In this study, the proposed model approaches are verified by employing a commercial FEM ANSYS-Maxwell and experimental tests in the laboratory. The study also gives the model approach and the design optimisation procedure of a 6 MW slip-ring motor used for milling purposes. In the analysis of this, the skin effects are perfectly fitted in the proposed model approaches The study presents a successful application of the proposed model approaches to the parameters and performance prediction and the design optimisation of the grid-connected WRSM and WRIM motor types. The proposed model approaches demonstrate accuracy, simplicity and fastness which are some of the key aspects in the electrical machine design.AFRIKAANSE OPSOMMING: Die verhandeling stel nuwe benaderings vir die analise, ontwerp en optimering van drie-fase bewikkelderotor sinchroonmotor (WRSM) en induksiemotor (WRIM) tipes voor. Die nuwe benaderings is gebaseer op die analise van die bestendige toestand eindige element metodes (EEM) waarmee die vermo¨e van die motor tipes voorspel word. Die optimum ontwerpte WRSM en WRIM motors kan verkry word deur die gebruik van verbeterde parameter en vermo¨e berekeningmetodes in die ontwerp optimeringsproses. Hierdie verhandeling stel ‘n eenvoudige, vinnige en akkurate parameter en vermo¨e berekening vir netwerk-gekoppelde WRSM en WRIM voor deur gebruik te maak van twee-as elektromagnetiese modelle. Die moderne benaderings is gebaseer op nie-klassieke modelle waarin iteratiewe EEM in samewerking met die motor fasor diagramme gebruik word. Tydens die iteratiewe proses, word die elektriese stroombaan en magnetiese veld vergelykings gekoppel om belangrike motor parameters te kry. Die magnetiese veld vergelykings los die opweksstrome op by verskillende werkspunte van die motor. Die parameters word akkuraat bereken deur die gebruik van EEM gebaseer op die metode van die vries van die motor kern permeansies. Hierdie parameters word as ‘n effektiewe hulpmiddel gebruik om die motorgedrag by verskillende werkspunte te verduidelik. Aandag word gegee aan die motorontwerp optimering, waartydens ‘n effektiewe optimeringsproses gewys word. In die studie word die voorgestelde benaderingsmodelle deur ‘n kommersi¨ ele EEM pakket (ANSYS-Maxwell) en toetse in die laboratorium geverifieer. ‘n Benaderingsmodel en die ontwerp optimering van ‘n 6 MW sleep-ring motor vir wals toepassings word ook gegee, waar die benaderingsmodel aangepas word om huid effekte in ag te neem. Die studie wys ‘n suksesvolle toepassing van die voorgestelde benaderingsmodel vir parameter en vermo¨e voorspelling en ontwerp optimering van netwerk-gekoppelde WRSM en WRIM motor tipes. Die voorgestelde benaderingsmodel is akkuraat, vinnig en eenvoudig, wat van die sleutelaspekte in elektriese masjien ontwerp is.Doctora

Investigating the effect of sex hormones on the immune response to TB and HIV.

Master of Medical Science in Microbiology. University of KwaZulu-Natal, Medical School 2015.Background: Global incidence rates for tuberculosis (TB) indicate a gender-bias to the disease, with almost twice as many men actively infected than women (male/female ratio of 1.9). Sex hormones are known to regulate immune function and their role in tuberculosis has been suggested experimentally in animal models. However the role of sex hormones in human TB infection and whether there is any synergistic effect in HIV and TB co-infection is unknown. In addition, there is data to suggest that manipulation of sex hormones with progestin-based injectable contraceptives, particularly DMPA, increases susceptibility to both HIV and TB. Quantitation of sex hormones has relied on antibody based immunoassays, such as ELISA, which suffer both from a lack of specificity and sensitivity. Aims: Consequently, the purpose of this study was to develop a method for quantitation of sex hormones and their contraceptive analogues utilizing a targeted LC-MS/MS approach that has been demonstrated to increase the accuracy of hormone quantitation and to determine the effect of sex hormones and hormonal contraceptives on the immune response to TB and HIV. Method: Sex hormone levels were measured in plasma samples from three separate cohorts, using MRM run in positive ESI mode, on a ABSciEx Q-TRAP 5500 mass spectrometer. The method was validated and DMPA levels were measured in the FRESH cohort (n= 62) and CAPRISA CAP004 study (n= 38) to determine effects on DMPA on increased risk in HIV acquisition. Testosterone, progesterone and DMPA levels were measured in the HIV chronic patients from the Cryptococcal cohort (n = 271) and sex hormone associated changes in phenotypic expression and immunological responses using intracellular cytokine staining were determined by flow cytometry analysis. Results: We validated our assays and were able to identify and quantitate levels of DMPA in two blinded studies. In the FRESH cohort, we were able to correctly identify and quantitate DMPA levels in Depo-Provera users and injectable progestin-based (IPC) contraceptive use was associated with high risk of HIV acquisition (p = 0.0142). IPC users were found to have significant increase in CCR5+CD4+ T cells in the cervix as well as increased CCR5 expression. Preliminary data in the CAP004 study, showed differential expression of mucosal proteins in the cervicovaginal lavage associated with DMPA use. In the Cryptococcal study, we found, as expected, significant differences in testosterone and progesterone levels between male and female patients, p <0.0001 and p=0.0001 respectively. Given that only 3 female patients reported to be using the contraceptive DMPA, we identified 42 of the total number of 172 females to have significant levels of DMPA (greater than LOQ = 0.064ng/ml) and these females had significantly lower progesterone levels than females not using DMPA (p <0.0001). This large under-reporting of contraceptive use indicates the value in direct measurement as opposed to self-reporting. As expected negative correlation was observed between progesterone and DMPA levels (p = 0.0016, r = -0.2445). However, individual response profiles are highly variable and decay rates of DMPA in longitudinal samples vary greatly between individuals. We hypothesis this will impact the immunomodulatory effect of DMPA, again suggesting the need for direct measurement. In this small sample we find no significant differences in activation and exhaustion of CD4 and CD8 T cells (determined using HLA-DR, CD38 and PD1 expression), as well as T regulatory cells (FoxP3 expression) when comparing female patients with high progesterone, low progesterone, and injectable contraceptive DMPA users, as well as males with high testosterone and low testosterone levels. However, females with high progesterone levels generally had higher CD38 expression, though non-significant. Also, we observe no significant differences in cytokine expression (TNFα, IFNγ, and IL-2) as well as markers, CD107a and Mip-1β, upon stimulation with SEB, PPD, pp65 CMV and HIV peptides. Conclusion: We successfully optimized and validated a method for quantitation of sex hormones using LC-MS/MS and were able to detect and quantify levels of testosterone, progesterone and DMPA. This method has the potential in clinical studies, to eliminate the need to rely on self-reported information, as exogenous hormones or contraceptive analogues can be detected with high sensitivity and specificity. Changes in the female genital tract which may be associated with increased risk of HIV were found in injectable progestinbased contraceptive users, particularly DMPA. However, no significant immunological effects of hormone levels on immune response and phenotype expression were found in blood

Cross-coupling inductance parameter estimation for more accurate performance evaluation of wound-field flux modulation machines

CITATION: Mabhula, M., Akuru, U. B. & Kamper, M. J. 2020. Cross-coupling inductance parameter estimation for more accurate performance evaluation of wound-field flux modulation machines. Electronics, 9(11):1748, doi:10.3390/electronics9111748.The original publication is available at https://www.mdpi.comPublication of this article was funded by the Stellenbosch University Open Access FundENGLISH ABSTRACT: In this paper, a proposed numerical frozen permeability modeling procedure is fully derived to accurately estimate the parameters of two variants of wound-field flux modulation machines (WF-FMMs) namely: wound-field flux switching machine (WF-FSM) and DC-excited vernier reluctance machine (DC-VRM). During the procedure, the contribution of saturation to the variation of the machine parameters is investigated. The parameter variation effects on the machine performance is also investigated. It is shown that analysis of WF-FMMs is better understood by using the proposed procedure which computes accurately the machine parameters.https://www.mdpi.com/2079-9292/9/11/1748Publisher's versio

Ferrocenyl and organic novobiocin derivatives: synthesis and their in vitro biological activity

publisher versionA focused series of novobiocin derivatives containing a ferrocene unit together with their corresponding organic novobiocin analogues have been synthesized in modest to good yields. These compounds were screened for biological activity against a chloroquine-sensitive strain of Plasmodium falciparum (3D7) and human breast cancer cell line (HCC38). With the exception of compounds 5c and 5d, the general trend observed is that incorporation of the ferrocene moiety into novobiocin scaffold resulted in compounds 6a–d/6f showing enhanced activity compared to organic analogues 5a–b and 5e–f

Ferrocenyl and organic novobiocin derivatives: synthesis and their in vitro biological activity

A focused series of novobiocin derivatives containing a ferrocene unit together with their corresponding organic novobiocin analogues have been synthesized in modest to good yields. These compounds were screened for biological activity against a chloroquine-sensitive strain of Plasmodium falciparum (3D7) and human breast cancer cell line (HCC38). With the exception of compounds 5c and 5d, the general trend observed is that incorporation of the ferrocene moiety into novobiocin scaffold resulted in compounds 6a–d/6f showing enhanced activity compared to organic analogues 5a–b and 5e–f

Association between injectable progestin-only contraceptives and HIV acquisition and HIV target cell frequency in the female genital tract in South African women: a prospective cohort study

BACKGROUND: The use of injectable progestin-only contraceptives has been associated with increased risk of HIV acquisition in observational studies, but the biological mechanisms of this risk remain poorly understood. We aimed to assess the effects of progestins on HIV acquisition risk and the immune environment in the female genital tract. METHODS: In this prospective cohort, we enrolled HIV-negative South African women aged 18–23 years who were not pregnant and were living in Umlazi, South Africa from the Females Rising through Education, Support, and Health (FRESH) study. We tested for HIV-1 twice per week to monitor incident infection. Every 3 months, we collected demographic and behavioural data in addition to blood and cervical samples. The study objective was to characterise host immune determinants of HIV acquisition risk, including those associated with injectable progestin-only contraceptive use. Hazard ratios (HRs) were estimated using Cox proportional hazards methods. FINDINGS: Between Nov 19, 2012, and May 31, 2015, we characterised 432 HIV-uninfected South African women from the FRESH study. In this cohort, 152 women used injectable progestin-only contraceptives, 43 used other forms of contraception, and 222 women used no method of long-term contraception. Women using injectable progestin-only contraceptives were at substantially higher risk of acquiring HIV (12·06 per 100 person-years, 95% CI 6·41–20·63) than women using no long-term contraception (3·71 per 100 person-years, 1·36–8·07; adjusted hazard ratio [aHR] 2·93, 95% CI 1·09–7·868, p=0·0326). HIV-negative injectable progestin-only contraceptive users had 3·92 times the frequency of cervical HIV target cells (CCR5+ CD4 T cells) compared with women using no long-term contraceptive (p=0·0241). Women using no long-term contraceptive in the luteal phase of the menstrual cycle also had a 3·25 times higher frequency of cervical target cells compared with those in the follicular phase (p=0·0488), suggesting that a naturally high progestin state had similar immunological effects to injectable progestin-only contraceptives. INTERPRETATION: Injectable progestin-only contraceptive use and high endogenous progesterone are both associated with increased frequency of activated HIV targets cells at the cervix, the site of initial HIV entry in most women, providing a possible biological mechanism underlying increased HIV acquisition in women with high progestin exposure. FUNDING: The Bill and Melinda Gates Foundation and the National Institute of Allergy and Infectious Diseases

Vaginal microbiome-hormonal contraceptive interactions associate with the mucosal proteome and HIV acquisition.

Alterations to the mucosal environment of the female genital tract, such as genital inflammation, have been associated with increased HIV acquisition in women. As the microbiome and hormonal contraceptives can affect vaginal mucosal immunity, we hypothesized these components may interact in the context of HIV susceptibility. Using previously published microbiome data from 685 women in the CAPRISA-004 trial, we compared relative risk of HIV acquisition in this cohort who were using injectable depot medroxyprogesterone acetate (DMPA), norethisterone enanthate (NET-EN), and combined oral contraceptives (COC). In women who were Lactobacillus-dominant, HIV acquisition was 3-fold higher in women using DMPA relative to women using NET-EN or COC (OR: 3.27; 95% CI: 1.24-11.24, P = 0.0305). This was not observed in non-Lactobacillus-dominant women (OR: 0.95, 95% CI: 0.44-2.15, P = 0.895) (interaction P = 0.0686). Higher serum MPA levels associated with increased molecular pathways of inflammation in the vaginal mucosal fluid of Lactobacillus-dominant women, but no differences were seen in non-Lactobacillus dominant women. This study provides data suggesting an interaction between the microbiome, hormonal contraceptives, and HIV susceptibility