Zero voltage switching used for a reversible DC-DC converter

Abstract A novel bi-directional dc-dc converter with Zero Voltage Switching (ZVS) and interleaving for dual voltage systems in automobiles is presented. A variable frequency extended band hysteretic current control method is proposed. In comparison with classical fixed frequency current control PWM, the reverse polarity peak current needed for ZVS operation is kept constant. Inductor current ripple decreases with load reduction. Automatic changes in operation between buck and boost modes are accomplished without transient currents. Converter simulations are carried out using Matlab/Simulink platform

LV and MV distribution networks reconfiguration for minimum losses

Abstract: The reconfiguration of the distribution network feeders can be defined as the restructuring of the feeders through the changing of the open/close states of the sectionalizing and tie switches. This creation of a new distribution network topology is normally required to improve the performance of the network, and thus sometimes the efficiency of the electricity supply. For optimum loss reduction, feeder reconfiguration is often considered as an option. This, however, requires the implementation of an appropriate switching control strategy. It would be desirable for the switching to be automatic, that is to follow the connected load situation of the feeder. The proposed optimal reconfiguration of the phase balancing using the heuristic method proves to be robust compared to neural network method, to turn ON and OFF the different switches, allowing the three phases supply of the transformer to the end-users to be balanced. This paper presents the application examples of the proposed method using the real data

Forecasting model for energy consumption in South Africa correlated with the income

Abstract This paper presents a mathematical model that forecasts the energy consumption in South Africa. The model is correlated to the income of the consumers. The study made use of the real energy consumption audit in South Africa. The mathematical model in this work is developed around the variables identified from the survey. The model can be applied to other utilities worldwide with some modifications in the influencing parameter values. The model developed was used to study the effect of certain indices; such as society, personality, and fixed contribution index on the electricity consumption. Different results obtained and presented in this work clearly show that the income is a major determinant of energy consumption

Performance evaluation of a three-phase induction machine with auxilliary winding fed by a leading reactive current

Abstract In this paper the performance of three-phase induction machine equipped with a three-phase auxiliary winding which is only magnetically coupled to the stator main winding is evaluated. A capacitive load is connected in parallel to each phase of the auxiliary winding and serves to inject a leading reactive current into the machine. Steady state and dynamic performance of the machine are evaluated under various loading and compensative conditions. The experimental results show that it possible to obtain a comparatively good power factor with a fixed capacitive load for various loadings of the asynchronous machine

Strategy for power quality improvement and maximum demand smoothing

Abstract: In this paper, a distributed strategy for improving the power quality and maximum demand smoothing is presented. Many authors have presented the power quality improvement as a centralized issue, which implies high power capability of compensators. Based on multi-functionality of specific switching-mode converters, a decentralised model is presented. A discussion of simultaneity of different functions is presented in details. The results of this paper are intended to be a guideline for application designer

Bioconversion of Aspergillus niger KM treated Rice and Wheat Bran for Experimental Rat Feed Formulation

This study investigated the nutritional value of pre-treated rice and wheat bran wastes as feed formulation in experimental rats. Aspergillus niger KM isolated from decomposing organic matter was tested for cellulase assay. The lignocellulosic agricultural residues (wheat bran and rice bran) were pretreated with ammonia and diluted sulfuric acid after which solid substrate fermentation with Aspergillus niger KM was carried out. Determination of reducing sugar was carried out and the fermented residues were included as components in feed formulation and were fed to different groups of rats for four weeks. The proximate analysis of the feed formulation showed that the NH3 pretreated feeds gave higher protein content of 21.94%, relative to the control or other groups. Growth performances of animals fed with NH3 pretreated wheat bran significantly increased from 158.25 to 201.66 g throughout the feeding periods. Evaluation of the various feeds’ effect on tissue marker enzymes revealed inconsistent alterations relative to the control. Bioconverted wheat or rice bran has nutritive value to support animal growth and could be explored in animal feed preparation

The ASOS Surgical Risk Calculator: development and validation of a tool for identifying African surgical patients at risk of severe postoperative complications

Background: The African Surgical Outcomes Study (ASOS) showed that surgical patients in Africa have a mortality twice the global average. Existing risk assessment tools are not valid for use in this population because the pattern of risk for poor outcomes differs from high-income countries. The objective of this study was to derive and validate a simple, preoperative risk stratification tool to identify African surgical patients at risk for in-hospital postoperative mortality and severe complications. Methods: ASOS was a 7-day prospective cohort study of adult patients undergoing surgery in Africa. The ASOS Surgical Risk Calculator was constructed with a multivariable logistic regression model for the outcome of in-hospital mortality and severe postoperative complications. The following preoperative risk factors were entered into the model; age, sex, smoking status, ASA physical status, preoperative chronic comorbid conditions, indication for surgery, urgency, severity, and type of surgery. Results: The model was derived from 8799 patients from 168 African hospitals. The composite outcome of severe postoperative complications and death occurred in 423/8799 (4.8%) patients. The ASOS Surgical Risk Calculator includes the following risk factors: age, ASA physical status, indication for surgery, urgency, severity, and type of surgery. The model showed good discrimination with an area under the receiver operating characteristic curve of 0.805 and good calibration with c-statistic corrected for optimism of 0.784. Conclusions: This simple preoperative risk calculator could be used to identify high-risk surgical patients in African hospitals and facilitate increased postoperative surveillance. © 2018 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.Medical Research Council of South Africa gran

Maternal and neonatal outcomes after caesarean delivery in the African Surgical Outcomes Study: a 7-day prospective observational cohort study.

BACKGROUND: Maternal and neonatal mortality is high in Africa, but few large, prospective studies have been done to investigate the risk factors associated with these poor maternal and neonatal outcomes. METHODS: A 7-day, international, prospective, observational cohort study was done in patients having caesarean delivery in 183 hospitals across 22 countries in Africa. The inclusion criteria were all consecutive patients (aged ≥18 years) admitted to participating centres having elective and non-elective caesarean delivery during the 7-day study cohort period. To ensure a representative sample, each hospital had to provide data for 90% of the eligible patients during the recruitment week. The primary outcome was in-hospital maternal mortality and complications, which were assessed by local investigators. The study was registered on the South African National Health Research Database, number KZ_2015RP7_22, and on ClinicalTrials.gov, number NCT03044899. FINDINGS: Between February, 2016, and May, 2016, 3792 patients were recruited from hospitals across Africa. 3685 were included in the postoperative complications analysis (107 missing data) and 3684 were included in the maternal mortality analysis (108 missing data). These hospitals had a combined number of specialist surgeons, obstetricians, and anaesthetists totalling 0·7 per 100 000 population (IQR 0·2-2·0). Maternal mortality was 20 (0·5%) of 3684 patients (95% CI 0·3-0·8). Complications occurred in 633 (17·4%) of 3636 mothers (16·2-18·6), which were predominantly severe intraoperative and postoperative bleeding (136 [3·8%] of 3612 mothers). Maternal mortality was independently associated with a preoperative presentation of placenta praevia, placental abruption, ruptured uterus, antepartum haemorrhage (odds ratio 4·47 [95% CI 1·46-13·65]), and perioperative severe obstetric haemorrhage (5·87 [1·99-17·34]) or anaesthesia complications (11·47 (1·20-109·20]). Neonatal mortality was 153 (4·4%) of 3506 infants (95% CI 3·7-5·0). INTERPRETATION: Maternal mortality after caesarean delivery in Africa is 50 times higher than that of high-income countries and is driven by peripartum haemorrhage and anaesthesia complications. Neonatal mortality is double the global average. Early identification and appropriate management of mothers at risk of peripartum haemorrhage might improve maternal and neonatal outcomes in Africa. FUNDING: Medical Research Council of South Africa.Medical Research Council of South Africa

Adaptation of the Wound Healing Questionnaire universal-reporter outcome measure for use in global surgery trials (TALON-1 study): mixed-methods study and Rasch analysis

BackgroundThe Bluebelle Wound Healing Questionnaire (WHQ) is a universal-reporter outcome measure developed in the UK for remote detection of surgical-site infection after abdominal surgery. This study aimed to explore cross-cultural equivalence, acceptability, and content validity of the WHQ for use across low- and middle-income countries, and to make recommendations for its adaptation.MethodsThis was a mixed-methods study within a trial (SWAT) embedded in an international randomized trial, conducted according to best practice guidelines, and co-produced with community and patient partners (TALON-1). Structured interviews and focus groups were used to gather data regarding cross-cultural, cross-contextual equivalence of the individual items and scale, and conduct a translatability assessment. Translation was completed into five languages in accordance with Mapi recommendations. Next, data from a prospective cohort (SWAT) were interpreted using Rasch analysis to explore scaling and measurement properties of the WHQ. Finally, qualitative and quantitative data were triangulated using a modified, exploratory, instrumental design model.ResultsIn the qualitative phase, 10 structured interviews and six focus groups took place with a total of 47 investigators across six countries. Themes related to comprehension, response mapping, retrieval, and judgement were identified with rich cross-cultural insights. In the quantitative phase, an exploratory Rasch model was fitted to data from 537 patients (369 excluding extremes). Owing to the number of extreme (floor) values, the overall level of power was low. The single WHQ scale satisfied tests of unidimensionality, indicating validity of the ordinal total WHQ score. There was significant overall model misfit of five items (5, 9, 14, 15, 16) and local dependency in 11 item pairs. The person separation index was estimated as 0.48 suggesting weak discrimination between classes, whereas Cronbach's α was high at 0.86. Triangulation of qualitative data with the Rasch analysis supported recommendations for cross-cultural adaptation of the WHQ items 1 (redness), 3 (clear fluid), 7 (deep wound opening), 10 (pain), 11 (fever), 15 (antibiotics), 16 (debridement), 18 (drainage), and 19 (reoperation). Changes to three item response categories (1, not at all; 2, a little; 3, a lot) were adopted for symptom items 1 to 10, and two categories (0, no; 1, yes) for item 11 (fever).ConclusionThis study made recommendations for cross-cultural adaptation of the WHQ for use in global surgical research and practice, using co-produced mixed-methods data from three continents. Translations are now available for implementation into remote wound assessment pathways