A. van Zyl

Sensorless current control for active rectifiers

A novel model-based sensorless input current controller for three phase active rectifiers is presented. The proposed algorithm is based upon a load conductance rectifier controller, which was previously implemented using current sensors. The paper presents analytical studies, simulation results and discusses a simple implementation using a low-cost integrated microcontroller. Experimental verification utilizes a 50 kVA active input/output IGBT converter. Simulation and experimental results for the proposed controller are compared to that of the sensor based version to validate the efficacy of this novel algorithm.

A new unified approach to power quality management

A new control algorithm for a power converter-based device that is capable of alleviating the problems of harmonic interference and voltage regulation on radial distribution lines is introduced. It comprises a relocatable converter in series with a passive filter and is known as the Power Quality Manager. Simulation results based on an existing 88-kV line are presented. Experimental results are presented, based on a three-phase 200-VA scaled model of the existing 88-kV system. It is a cost-effective and flexible solution to improving power quality.

Antiretroviral treatment in the Northern Cape.

To the Editor: We would like to report on our experience with the first 100 paediatric patients started on antiretroviral treatment in the Northern Cape. All of these patients were on treatment for at least 6 months. Patients were started on treatment between August 2003 and September 2004, with ages ranging between 3 months and 13 years (mean 66 months). They were all World Health Organization (WHO) paediatric stages 2 and 3 (stages 1-3). Eighty-six patients were from Kimberley, 13 were from other towns in the Northern Cape and 1 was from a neighbouring province. Two patients had received nevirapine at birth in an attempt to prevent transmission of the virus from mother to child. Ninety-six patients had CD4 counts below 15%; in 28 of these cases CD4 counts were below 5%. Only 1 patient with bronchiectasis had a CD4 count above 20%. Eighty-two of our patients had viral loads above 100 000 copies/ml. Stavudine and lamivudine formed the backbone of treatment in 98 of the patients. The choice of the third drug depended on patient weight, previous exposure to nevirapine, treatment for tuberculosis and viral load. Patients with viral loads greater than 750 000 copies/ml were put on lopinavir/ritonavir. Forty-eight patients were started on efavirenz, 38 on lopinavir/ritonavir and 14 on nevirapine. Extra ritonavir was added in the case of 1 patient on lopinavir/ritonavir because the patient was also on treatment for tuberculosis. Outcome after at least 6 months on treatment is shown in Table I. One patient was resistant to treatment and was changed to abacavir, ddI, lamivudine and lopinavir/ritonavir. This patient had previously been exposed to monotherapy and dual therapy in the private sector. He is currently improving on this regimen. We are working on adherence in the other 11 patients with viral loads above 100 000 copies/ml and a final decision on resistance still has to be taken. All 72 patients with loads below 10 000 copies/ml are doing well. Three patients on nevirapine were changed to efavirenz. One patient on lopinavir/ritonavir was changed to efavirenz, and 1 patient on nevirapine to lopinavir/ritonavir. No changes were made to the nucleoside reverse transcriptase inhibitors. One of the 9 deaths was probably caused by AZT bone marrow suppression. This patient was placed on AZT because of a severe HIV encephalopathy. Three of the deaths occurred in the first month after treatment was commenced, and 2 deaths 6 months …

Episodic replacement of clotting factor concentrates does not prevent bleeding or musculoskeletal damage – the MUSFIH study

A longitudinal study was carried out in 255 children from 10 centres in nine developing countries over 5 years to assess the musculoskeletal outcome of children on episodic factor replacement. Outcome was documented by assessment of the annual joint bleeding rate (AJBR), WFH clinical and Pettersson radiological joint scores as well as the FISH score for activities. Of the 203 patients for whom data was available at the end of 5 years, 164 who had received only episodic treatment are included in this report.

Inhibition of peroxidase activity by some non-steroidal anti-inflammatory drugs

Abstract The non-steroidal anti-inflammatory drugs, indomethacin, flufenamic acid and naproxen inhibited thyroid peroxidase-catalyzed iodination of BSA in vitro . Inhibition by all three drugs was affected more effectively in a hydrogen peroxide generating system than in an incubation system in which hydrogen peroxide was added. Naproxen differed from the other two drugs in so far as it inhibited mainly hydrogen peroxide generation while its comparatively low inhibitory influence (>20%) on TPO was not dose-dependent. The inhibitory influence of these anti-inflammatory drugs was also observed when other peroxidases, such as lactoperoxidase, chloroperoxidase and horseradish peroxidase were used for catalyzing BSA iodination in a hydrogen peroxide generating system. No iodination of BSA was obtained with horseradish peroxidase when hydrogen peroxide was added instead of generated so that the inhibitory nature of these drugs could not distinguish between their direct effect on horseradish peroxidase or on hydrogen peroxide generation. However, in lactoperoxidase and chloroperoxidase-catalyzed BSA iodinations in non-H 2 O 2 -generating systems naproxen had no appreciable inhibitory influence below a 1 millimolar concentration. On another thyroid peroxidase activity, namely its catalyzing influence on the exchange reaction between inorganic iodide and organic iodine in diiodotyrosine, indomethacin and naproxen showed unappreciable effects lower than 1 mM concentrations. Similarly, on thyroid peroxidase and lactoperoxidasecatalyzed deiodination of thyroxine they were ineffective inhibitors. The data suggest that these antiinflammatory drugs are effective inhibitors of iodination reactions but ineffective inhibitors of deiodination reactions.

Converter based solution to power quality problems on radial distribution lines

In this paper it is shown that the power converter-based power quality manager is a viable solution to power quality problems on radial lines. It is capable of harmonic isolation, improving voltage regulation and flicker compensation simultaneously. These functions can also be implemented independently. The power quality manager is a hybrid device comprising passive components and a power converter. The converter power rating is lower than that required by an equivalent active filter or converter based static VAr compensator.

Histological and immunohistochemical evaluation of sentinel lymph nodes in breast cancer at a tertiary hospital in the Western Cape, South Africa

BACKGROUND Breast carcinoma remains the most prevalent cancer among women, with over 300 000 deaths annually worldwide. Axillary lymph node status is essential for the clinical staging of breast carcinoma and remains the single most important predictor of disease-free survival in breast carcinoma. OBJECTIVE To determine effective histological examination of sentinel lymph node (SLN) sections for the detection of metastatic breast carcinoma. METHODS A prospective hospital-based study was done, including 20 patients with confirmed infiltrating breast carcinoma who underwent tumour excision or simple mastectomy as well as SLN biopsies. All the lymph nodes harvested were sectioned and embedded. Three sets of 15 consecutive serial sections were prepared from each case at one sitting, each measuring 3 - 5 μm in thickness and mounted on separate slides. Each set of 15 consecutive sections was grouped into three levels, each comprising 5 serial sections. The first 4 sections were stained with haematoxylin and eosin (H&E). The fifth section was stained for pancytokeratins, using MNF116. RESULTS Twenty patients who met the inclusion criteria of this study underwent SLN biopsies and simple mastectomies or tumour excisions. Twelve SLNs of 11 patients contained metastatic carcinoma, all detected at level I, with one case requiring MNF116 immunohistochemistry staining, revealing metastatic carcinoma, measuring 0.08 × 0.08 mm (micrometastases). The size of metastatic carcinoma ranged between 0.08 × 0.08 mm (micrometastases) and 25 × 15 mm. Nine cases showed macrometastases, varying in size between 2 × 3.5 mm and 25 × 15 mm. Tumour sections of three patients with infiltrating carcinoma, of no specific type (NST), revealed lymphovascular invasion. The breast tumour sizes of these cases measured 40 × 25 mm (1/1 node involved), 30 × 20 mm (1/3 nodes involved) and 15 × 12 mm (1/1 node involved), respectively. Nine patients (19 nodes in total, mean 2.1, range 1 - 5) did not have demonstrable metastatic disease in the 45 sections of levels I - IX, including MNF116 on every fifth section. Patients with negative SLNs varied in age between 29 and 68 years and had breast tumour sizes ranging between 10 × 10 mm and 30 × 30 mm, respectively. CONCLUSION This study supports a conservative and cost-effective approach that comprises embedding of the entire SLN and the histopathological examination of four H&E-stained sections, which will usually demonstrate metastatic carcinoma. In the event of absence of metastatic carcinoma, immunohistochemical staining for pancytokeratin will detect tumour cells in a small percentage of cases. Examination of additional H&E- or pancytokeratin-stained sections is not cost effective. This finding can guide decisions pertaining to protocols for the histopathological assessment of SLN in breast carcinoma especially in resource-limited settings.

Letter to the editor: Letter to the Editor

To the Editor: We thank Dr. Slone and colleagues for their response to our article and addressing our omission of Botswana, as a country that offers cancer treatment to children [1]. The aim of our article was to present an overview of the present situation in Africa regarding available childhood cancer services, based on the analysis of previous published articles and two surveys conducted. Figure 1 of our article includes only countries with responses to the limited surveys and some of the GFAOP members and is not intended to be a comprehensive list. There are indeed other pediatric oncology units offering cancer treatment in Africa such as Angola, Mauritania, Gabon, Mauritius, and new countries or units, which joined the GFAOP more recently. It is notable that Botswana has a fully nationalized health service and therefore cancer care is provided free of charge [2]. As suggested in our article Slone et al. document the successful partnering of childhood cancer health care services with established HIV/AIDS pediatric health care services. The Baylor-Botswana example provides an excellent model for other African countries and their HIV/AIDS partners in developed countries, to extend the pediatric HIV health care offered, to health care for children with cancer in the region. Of note is the important article in 2013 that documents the possibility of clinical remission in children with HIV/AIDS and concomitant Kaposi sarcoma in resource limited settings, including data from Botswana [3]. The planned Baylor-Botswana hematology-oncology training fellowship program will assist in local capacity building and is of particular importance in Africa, where there is a lack of skilled pediatric oncologists. Pediatric oncology units in South Africa already offer fellowship training opportunities to other African pediatricians, assisting in South-to-South capacity building programs in an environment, simulating the scenario of the home country, and in recent years countries such as Ghana, Uganda, Sudan, and Rwanda have greatly benefited [4,5].