Integration of inverter constraints in geometrical quantification of the optimal solution to an MPC controller

Published Conference ProceedingsThis paper considers a model predictive controller with reference tracking that manipulates the integer switch positions of a power converter. It can be shown that the optimal switch position can be computed without solving an optimization problem. Specifically, in a new coordinate system, the optimization problem can be solved offline, leading to a polyhedral partition of the solution space. The optimal switch position can then be found using a binary search tree. This concept is exemplified for a three-level single-phase converter with an RL load

Fitness and body composition profiling of elite junior South African rugby players

Objective. The aim of this study was to describe the body composition, strength and speed characteristics of elite junior South African rugby players. Design. Cross-sectional. Setting. Field study. Subjects. Rugby players (16 and 18 years old, N = 174) selected for the South African Rugby Union National Green Squad. Outcome measures. Body composition, 10 m and 40 m speed, agility, 1RM bench press, underhand pull-ups, push-ups, multistage shuttle run. Results. The under-16 players were on average shorter (175.6 ± 5.7 v. 179.2 ± 6.7 cm), weighed less (76.5 ± 8.2 v. 84.8 ± 8.3 kg) had less upper body absolute strength (77.1 ± 11.8 kg v. 95.3 ± 16.7 kg) and muscular endurance (41 ± 12 v. 52 ± 15 push-ups) and aerobic fitness (87.1 ± 19.4 v. 93.5 ± 15.3 shuttles) than the under-18 players. There were no differences in body fat, sprinting speed (10 m and 40 m) or agility between the two age groups. There were differences between playing positions, with the props having the most body fat, strongest upper bodies, slowest sprinting speed, least agility and lowest aerobic capacity compared with players in the other positions. Conclusion. This study provides data for elite junior rugby players and can be used to monitor the progression of players after intervention while also assisting with talent identification for the different playing positions. South African Journal of Sports Medicine Vol. 18 (2) 2006: pp. 38-4

Fitness and body composition profiling of elite junior South African rugby players

Objective. The aim of this study was to describe the body composition, strength and speed characteristics of elite junior South African rugby players. Design. Cross-sectional. Setting. Field study. Subjects. Rugby players (16 and 18 years old, N = 174) selected for the South African Rugby Union National Green Squad. Outcome measures. Body composition, 10 m and 40 m speed, agility, 1RM bench press, underhand pull-ups, push-ups, multistage shuttle run. Results. The under-16 players were on average shorter (175.6 ± 5.7 v. 179.2 ± 6.7 cm), weighed less (76.5 ± 8.2 v. 84.8 ± 8.3 kg) had less upper body absolute strength (77.1 ± 11.8 kg v. 95.3 ± 16.7 kg) and muscular endurance (41 ± 12 v. 52 ± 15 push-ups) and aerobic fitness (87.1 ± 19.4 v. 93.5 ± 15.3 shuttles) than the under-18 players. There were no differences in body fat, sprinting speed (10 m and 40 m) or agility between the two age groups. There were differences between playing positions, with the props having the most body fat, strongest upper bodies, slowest sprinting speed, least agility and lowest aerobic capacity compared with players in the other positions. Conclusion. This study provides data for elite junior rugby players and can be used to monitor the progression of players after intervention while also assisting with talent identification for the different playing positions

Playing time between senior rugby players of different ethnic groups across all levels of South African rugby, 2007- 2011

Background. The South African Rugby Union (SARU) has had a continual challenge to make the game representative of players of all ethnic groups at all levels of play. In response to this challenge SARU has implemented several programmes designed to accelerate the development of players from previously disadvantaged areas with the goal of making the game more representative. However, the success of these programmes to transform the player profile at different levels of rugby cannot be evaluated because the players representing different ethnic groups have not been quantified in a systematic way.Objectives. To quantify the number and playing time of South African professional players (Vodacom, Currie Cup, Super Rugby and Springboks) from different ethnic groups from 2007 to 2011 to determine whether there are any changes in the profile of the players over this period.Methods. Playing time was recorded for all players in sanctioned matches. Players were divided into the ethnic classifications used by SARU (i.e. white, coloured and black).Results. At all levels of competition there were proportionally more white players, followed by coloured players and then black players. This pattern did not change from 2007 to 2011. Based on the ratio of number of players v. playing time, the white players played more time than expected at the Springbok level, whereas the black players played less than expected for the number of players from 2007 to 2011. At the Vodacom level the white players played more than expected in 2007 and 2008 and played less than expected in 2010 and 2011, whereas the black players played more than expected in 2010 and the coloured players played more than expected at the 2011 tournament. The Super Rugby tournamenthad the most consistency between players and expected playing time for the different ethnic groups.Conclusions. Despite the effort to support players from disadvantaged backgrounds since 1998 with facilitative programmes and selection targets, the professional game is still dominated by white players at all levels

The role of prenatal alcohol exposure in abruptio placentae

Objective. To investigate the association between preconception and prenatal alcohol use and abruptio placentae. Methods. A case-control study of women with the clinical diagnosis of abruptio placentae, 65 cases.and 66 controls, at Tygerberg Academic Hospital, Western Cape, South Africa. Women in whom a retroplacental blood clot, covering at least 15% of the placental surface, was found at delivery at 24 weeks’ gestation or later were asked to complete a timeline follow-back questionnaire to determine their alcohol intake 12 and 3 months before and during pregnancy. The same questionnaire was administered to a control group of high-risk women who had no antepartum haemorrhage. Outcome. Women who drank alcohol 12 months before conception were more than 4 times more likely to develop abruptio placentae than the control group (odds ratio (OR) 4.49, p=0.00009). Women who drank alcohol 3 months prior to conception were 3 times more likely to develop abruptio placentae than the control group (OR 3.06, p=0.003). Drinking alcoholic beverages during pregnancy carried a more than 3 times greater risk of developing abruptio placentae (OR 3.52, p=0.0006). In the study group, women consumed a mean of 13.6, 12.0 and 11.2 standard drinks in a typical week at 12 and 3 months before and during pregnancy, respectively. The study group demonstrated a binge-drinking pattern, with two to four sessions per month. Conclusion. An association was found between preconception and prenatal consumption of alcohol and abruptio placentae

Rapid Synthesis of [Au₂₅(Cys)₁₈] Nanoclusters via Carbon Monoxide in Microfluidic Liquid-Liquid Segmented Flow System and their Antimicrobial Performance

Atomically precise thiolate-gold nanoclusters with well-defined structures attract attention for use in various applications. However, most of the recently reported synthetic methods rely on prolonged synthesis times (a few hours to days) in order to produce high purity materials with a single cluster size. Such extended synthesis times make these processes ill-suited for adaptation to industrial scale production with continuous flow. In this work, an improved method for the synthesis of thiolated Au25 nanoclusters is presented utilising a microfluidic system and CO-mediated reduction. The optimized system, based on a coiled flow inverter with inner diameter of 1 mm operating at 80 °C and 500 kPa took only 3 min for the synthesis of atomically precise cysteine-capped [Au25(Cys)18] nanoclusters, as characterized by ultraviolet–visible spectroscopy and electrospray ionization mass spectrometry. The productivity of the system was increased by using higher reactant concentrations which led to a throughput of 0.9 gAu per day, without changing the reaction time or affecting the product purity. The Au nanoclusters were used as photobactericidal enhancement materials. In antimicrobial testing against S. aureus, encapsulation of the Au nanoclusters into crystal violet impregnated silicone showed high photobactericidal activity (~1.7 log reduction in viable bacteria) upon 6 h illumination of white light at ~312 lx, while crystal violet did not show significant photobactericidal activity on its own

Comparing visual skills in sedentary and active work environments

A comparative study was conducted between training recruits (n = 138) and undergraduate university (n = 169) students to assess whether physical activity enhances visual skills. The results indicated that recruits, who lead an active lifestyle, possess superior skills in eye-hand coordination and reaction time. However, students possess superior skills in tracking and sequencing.This paper was initially delivered at the Annual Congress of the Biological Sciences Division of the South African Academy for Science and Art, ARC-Plant Protection Research Institute, Roodeplaat, Pretoria, South Africa on 01 October 2010.http://www.satnt.ac.zaam2014ay201

Comprehensive survey of the distribution of colour and phenolics of different red grape wine vineyard blocks from the Robertson area in South Africa

CITATION: Van der Merwe, H., Nieuwoudt, H. H., De Beer, D. & Du Toit, W. J. 2012. Comprehensive survey of the distribution of colour and phenolics of different red grape wine vineyard blocks from the Robertson area in South Africa. South African Journal of Enology and Viticulture, 33(1):58-71, doi:10.21548/33-1-1307.The original publication is available at http://www.journals.ac.za/index.php/sajevColour and phenolic content of red grapes are two of the most important constituents required to produce a quality red wine. In the Robertson grape growing area, difficulty is sometimes experienced with colour development of grapes. This is especially linked to location and most probably greatly influenced by season. Forty four vineyard blocks of the cultivars Pinotage, Merlot, Cabernet Sauvignon and Shiraz, were studied over 3 seasons primarily to focus on colour and phenolic content, but secondly on total soluble solids, titratable acidity and pH of the grapes. High performance liquid chromatography and spectrophotometric methods were used to determine various colour and phenolic parameters present at harvest. This data was used to indicate how colour and phenolic constitution of a part of the Robertson grape growing area was distributed in relation to various factors, such as cultivar and season. GPS points were used to map data for the blocks visually. Results showed variable colour and phenolic content for these grapes based on blocks and phenolic compounds investigated. Shiraz displayed a wider distribution of certain phenolic compounds over the three seasons than the other 3 cultivars. Seasonality had a great influence on these results, with outlying blocks being identified.http://www.journals.ac.za/index.php/sajev/article/view/1307Publisher's versio

Analysis of Granular Flow in a Pebble-Bed Nuclear Reactor

Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a major impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6cm-diameter spheres draining in a cylindrical vessel of diameter 3.5m and height 10m with bottom funnels angled at 30 degrees or 60 degrees. We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.Comment: 18 pages, 21 figure