Multi-point aerodynamic optimisation of sailplane horizontal tailplanes

MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2016A new horizontal tailplane for a high performance sailplane was developed through multi-point aerodynamic optimisation. This was achieved through the use of logged flight data, from which the operating spectrum of the horizontal tailplane of a specific sailplane was obtained. With the operating spectrum, a modified lifting line model implementing Xfoil and the Generalised Reduced Gradient optimisation algorithm were used to optimise the aerodynamic performance of the JS1-C 21m horizontal tailplane. Verification of the planform calculations was conducted with the commercial CFD software package Star-CCM+. The k - w SST turbulence and y - Reθ transition models were used for aerodynamic analysis in the verification process. The design of new horizontal tailplane tip sections was also performed with the use of CFD. Firstly the elevator span to horizontal tailplane span ratio best suited to the operating spectrum of the horizontal tailplane was evaluated. Secondly a wingtip shape proposed by Hoerner (1965) was implemented. The flight data-based multipoint optimisation of the planform of the horizontal tailplane shows appreciable performance increases compared to a baseline tailplane. Calculations show a 14% drag reduction for the tailplane over a sample flight. The tip design also shows a drag decrease of 1.1% at 150km/h and 3.3% drag decrease at 250km/h compared to the baseline tip section shape.Master

Biomechanischer Stabilitätsvergleich am suprakondylären Femur: Analyse des Einflusses einer additiven Drahtcerclage bei der Versorgung einer extraartikulären, distalen Schrägfraktur mittels polyaxialer, winkelstabiler Plattenosteosynthese

Die operative Versorgung suprakondylärer Frakturen des Femurs ist herausfordernd. Eine Cerclage kann bei Frakturen als Hilfsmittel und in Kombination mit einer Osteosynthese als Implantat verwendet werden. Die vorliegende Arbeit untersucht erstmalig den Einfluss einer zusätzlichen Cerclage auf die Stabilität und Belastbarkeit der mit einer NCB-DF Platte versorgten suprakondylären Femurfraktur (AO-Typs 32-A2.3). Hierfür wurden acht Paar mit Formalin fixierte, humane Kadaverknochen von Köperspendern untersucht (Durchschnittsalter 74 Jahre, Alterspanne 57 bis 95 Jahre). Mittels radiologischer Kontrollen und Knochendichtemessungen konnten Osteolysen, Frakturen sowie das Vorliegen einer Osteoporose ausgeschlossen werden. Es folgte die zufällige Aufteilung der Paare in zwei Gruppen. Alle 16 Knochen wurden nach Einführung einer Schrägfraktur des AO-Typs 32-A2.3 mit einer winkelstabilen Plattenosteosynthese versorgt. In Gruppe 2 erfolgte die zusätzliche Versorgung der Bruchstelle mit einer doppelläufigen Drahtcerclage. Die Knochen wurden anschließend retrograd, der physiologischen Kraftachse gerecht, in eine Instron 5566 Belastungsmaschine eingespannt. Einem standardisierten Prüfungsprotokoll folgend wurden die Knochen nach einer Vorlast von 100 N zyklisch mit steigender Kraft belastet. Beginnend bei 800 N und 500 Wiederholungen wurde die Belastung nach Abschluss jedes Prüfungsprotokolls um 200 N erhöht, bis die Osteosynthese versagte. Als Versagensgrenzen galten eine plastische Deformierung größer 20 mm und/ oder ein plötzlicher Kraftabfall größer 30 %. Alle Knochenpaare konnten mindestens einer Belastung von 1200 N standhalten. Die mittlere Druckkraft bei Osteosyntheseversagen lag in Gruppe 1 bei 2450 N (95 % KI: 1996-2904 N). Im Vergleich erreichte die Gruppe 2 mit zusätzlicher Cerclage eine mittlere Belastungsgrenze von 3100 N (95 % KI: 26623538 N). Mit Ausnahme des Probenpaares 3 (je 3200 N) waren die Belastungsgrenzen der Gruppe 2, mit einer zusätzlichen Cerclage, stets höher. Der Unterschied der Belastungsgrenzen zwischen den Gruppen 1 und 2 war statistisch signifikant (p = 0,018). In beiden Gruppen war der häufigste Versagensgrund mit 87,5 % eine Verformung des distalen Fragmentes > 20 mm. Nur bei einem Paar kam es zu einem plötzlichen Kraftabfall größer 30 %. Hinsichtlich der Versagensart konnten drei Mechanismen unterschieden werden. In beiden Gruppen war die Lockerung der distalen Schrauben mit folgendem Abscheren des distalen Fragmentes entlang des Frakturspaltes am häufigsten (Gruppe 1: 62,5 %; Gruppe 2: 75 %). Hervorzuheben ist aber ein neu entstandener Frakturkeil entlang der Cerclage in Gruppe 2 sowie das Reißen der Cerclage selbst. Die irreversible Verformung der Platte unter der Belastung trat in Gruppe 2 mit Cerclage zweimal auf, in Gruppe 1 einmalig. In beiden Gruppen versagte der Schaft je einmal multifragmentär. Für die Berechnung der Steifigkeit und der plastischen Verformung wurde die höchste erreichte Belastungsstufe aller Knochen von 1200 N herangezogen. Die Steifigkeit beider Gruppen war vergleichbar mit einer mittleren Steifigkeit von 2,00 N/ m in Gruppe 1 (95 % KI: 1,11-2,90 N/ m) und von 1,49 N/ m in Gruppe 2 (95 % KI: 1,04-1,94 N/ m) (p = 0,208). Die Analyse der plastischen Verformung zeigte für die Belastung von 1200 N einen signifikanten Unterschied zwischen den beiden Gruppen (p = 0,035). Die mittlere plastische Verformung in der Gruppe mit der zusätzlichen Cerclage (Gruppe 2) betrug 0,37 mm (95 % CI 0,22-0,51 mm). Im Vergleich dazu betrug die mittlere plastische Verformung der Gruppe 1 0,6 mm (95 % CI: 0,38-0,81 mm) und zeigte somit eine höhere Variabilität für die plastische Verformung. Die Arbeit konnte höhere Belastungsgrenzen für eine Schrägfraktur des distalen Femurschaftes zeigen, wenn diese mit einer kombinierten Osteosynthese aus winkelstabiler Platte und Cerclage versorgt wurde. Deshalb ist bei der Versorgung einer Schrägfraktur des distalen Femurschaftes aus biomechanischer Hinsicht eine zusätzliche Cerclage zu empfehlen. Das gilt besonders in der Gruppe älterer Patienten, für welche eine frühzeitige postoperative Übungsstabilität von großer Bedeutung ist.The surgical treatment of supracondylar fractures of the femur is challenging. A cerclage can be used as an adjuvant in fractures and as an implant in combination with osteosynthesis. The present study is the first to investigate the influence of an additional cerclage on the stability and load-bearing capacity of a supracondylar femur fracture (AO type 32A2.3) treated with an NCB-DF plate. Therefore eight pairs of formalin-fixed human cadaveric bones from cadaveric donors (average age 74 years, age range 57 to 95 years) were examined. Osteolysis, fractures and the presence of osteoporosis were excluded by means of radiological controls and bone density measurements. The pairs were then randomly divided into two groups. All 16 bones were treated with an angular-stable plate osteosynthesis after creation of an oblique fracture of AO type 32-A2.3. In group 2, the fracture site was additionally treated with a double-looped wire cerclage. The bones were then retrogradely positioned in an Instron 5566 loading machine according to the physiological force axis. Following a standardized test protocol, the bones were loaded cyclically with increasing force after a preload of 100 N. Starting at 800 N and doing 500 repetitions, the load was increased by 200 N after completing each test protocol until osteosynthesis failed. The failure thresholds were a plastic deformation greater than 20 mm and/ or a sudden drop in force greater than 30 %. All bone pairs withstood at least a load of 1200 N. The mean compressive force for osteosynthesis failure in group 1 was 2450 N (95 % CI: 1996-2904 N). In comparison, group 2, with additional cerclage, reached a mean load limit of 3100 N (95 % CI: 2662 3538 N). With the exception of sample pair 3 (3200 N each) the load limits of group 2 were always higher. The difference in load to failure between group 1 and group 2 was statistically significant (p = 0.018). In both groups, the most frequent reason for failure was a deformation of the distal fracture fragment > 20 mm (87.5%). In one pair was there a sudden loss of resistance greater than 30%. With regard to the type of failure, three mechanisms could be distinguished. The most common in both groups was the loosening of the distal screws with subsequent shearing of the distal fragment along the fracture gap (group 1: 62.5%; group 2: 75%). However, a newly developed fracture wedge along the cerclage in group 2 as well as the tearing of the cerclage itself should be emphasized. Irreversible deformation of the plate under load occurred twice in group 2 with cerclage and once in group 1. The femoral shaft broke multifragmentarily once in both groups. For the calculation of stiffness and plastic deformation the highest load level achieved on all bones (1200 N) was used. The stiffness of both groups was comparable. With a mean stiffness of 2.00 N/ m in group 1 (95 % CI: 1.11-2.90 N/ m) and of 1.49 N/ m in group 2 (95 % CI: 1.04-1.94 N/ m) (p = 0.208). The plastic deformation analysis showed a significant difference between the two groups at a load of 1200 N (p = 0.035). The mean plastic deformation in the group with the additional cerclage (group 2) was 0.37 mm (95 % CI 0.22-0.51 mm). In comparison, the mean plastic deformation of group 1 was 0.6 mm (95 % CI: 0.38-0.81 mm), showing a higher variability for plastic deformation. This study demonstrated the higher load to failure for an oblique fracture of the distal femoral shaft when it was treated with a combined osteosynthesis consisting of an angle-stable plate and a cerclage. Therefore, when treating an oblique fracture of the distal femoral shaft, an additional cerclage is recommended from a biomechanical point of view. This especially applies for the group of older patients for whom early postoperative full weight bearing is of major importance

Regulation, Cross Border Migrants and the Choice of Remittance Channels in South Africa

Remittances have become an increasingly important factor in developing economies. Among others, compliance with onerous regulation requirements discourages the use of formal methods of remittances. The paper discusses results from a survey of the influence of regulation on the choice of migrants’ remittance channels in South Africa. It aims to highlight how regulation affects the choice between formal and informal channels of remitting funds. A questionnaire was administered to collect primary data from migrants seeking documentations from the Department of Home Affairs, those remitting funds at taxi ranks or bus terminals, and those remitting through commercial banks and money transfer operators. 275 responses were analysed using a Likert rating scale format of 1 (highest) to 5 (lowest). Regulatory requirements of documentary evidence are an important factor influencing the choice of the remittance channel used. Documentation requirement in the formal market causes migrants to be ineligible for the formal channels of remittances and is a factor that influences the choice of remittance channel. Restrictive visa requirements could easily push migrants to become illegal aliens which further deny them access to formal remittance channels. The paper adds to the academic literature on the determinants of remittance channels in Africa. Understanding the relevant issues could assist regulatory authorities to restructure the remittance market with a view to encouraging migrant workers to enter the formal financial system

Diatom diversity and response to water quality within the Makuleke Wetlands and Lake Sibaya

MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2017All forms of life are dependent on water for survival. South Africa is a water scare country, due to seasonal rainfall and high temperatures, thus it is important to manage water resources in such a way that it benefits the needs of humans and maintains the integrity of aquatic ecosystems. Agriculture activities, industrial activities and poor sanitation are some of the threats to water resources. Biomonitoring is one of several methods used to evaluate changes within aquatic ecosystems and makes use of the organisms found within the ecosystem to monitor the ecological integrity of that ecosystem — terrestrial or aquatic. As the aquatic organisms are continuously exposed to the environmental conditions within the ecosystem they are constantly exposed to the effects of pollution in the ecosystem which in turn modifies community structure. Biomonitoring could potentially be applied to all aquatic ecosystems including rivers, lakes, oceans, estuaries and wetlands. Wetlands are important ecosystems as they are areas with a large variety of biota and provide numerous resources and ecological services for humans. However, wetlands are susceptible to nutrient enrichment and pollution as materials are brought into the ecosystem by water, wind and humans in the catchment area. As wetlands acts as ‘sinks’ sediment and pollutants, including nutrients, accumulate in wetland ecosystems. These pollutants enter the ecosystem through runoff, seepage, direct application or are wind driven. As humans make use wetlands as a source of food and water and wetlands support an abundance of biota it is important to monitor the health of these aquatic ecosystems. Monitoring of wetland biota can be problematic at times as the variability in depth and inundation time does not allow some systems to support fish and/or macroinvertebrates. For this reason, diatoms are useful as biological indicators to monitor wetlands as they are microorganisms. Furthermore, diatom communities are species rich, respond rapidly to changes in the environment, are easy to collect, abundant and are the most diverse algae group. There is a paucity of aquatic biodiversity information on South Africa’s Ramsar wetlands and specifically the diatom communities. The present study focused on two Ramsar wetlands in South Africa namely Lake Sibaya and the Makuleke Wetlands. The aims of the study were to determine the distribution and occurrence of diatoms in the Makuleke Wetlands and Lake Sibaya in relations to water quality and secondly, to determine if European diatom-based indices for indicating wetland water quality conditions. Water and diatom samples were collected from the Makuleke Wetlands during a wet (April 2015) and dry season (September 2015). Lake Sibaya was sampled during a winter (July 2015) and two summer seasons (November 2015 and February 2016). The nutrient concentrations present in the water column were measured. Diatom taxa from both wetlands were identified and indicator species were used to determine the trophic level and ecosystem quality of these wetlands. Measured phosphate and inorganic nitrogen concentrations indicated both Lake Sibaya and the Makuleke Wetlands as nutrient enriched. The diatom community and indices (Specific Pollution sensitivity Index (SPI) and Generic Diatom Index (GDI)) correlated with the measured water quality and indicated both sites as nutrient enriched. The measured water quality variables indicated the wetlands to be either mesotrophic, eutrophic or hypertrophic. Diatom indices indicated that the study sites were in a bad/poor quality state with dominant diatom species occurring in polluted and nutrient enriched ecosystems. Thus, both wetlands are undoubtedly enriched with nutrients, however, it is unsure if these levels can be considered natural for these systems as nutrient accumulation is a key feature of wetlands. Diatom taxa identified in the Makuleke Wetlands ranged from 12 – 20 species between the pans with a total of 70 species identified in the wetland as a whole. A total of 59 species were identified in Lake Sibaya with a ranging from 20 – 35 species identified at the sampling sites. Dominant diatom species in the Makuleke Wetlands included Aulacoseira granulata, Gomphonema parvulum, Navicula sp. and Nitzschia sp. Dominant species at Lake Sibaya included Cocconeis placentula, Epithemia adnata and Gomphonema sp. Dominant species for both wetlands were indicators of nutrient enriched ecosystems and tolerant of generally polluted conditions. The diatom community (dominant species and diatom indices) and water quality indicated increased nutrients in the studies wetlands, suggesting a declining ecosystem quality. It is concluded that methods for diatom community analysis and water quality analysis were successfully applied and indicated both wetland ecosystems as nutrient enriched, however there are doubts as to whether this can in turn be viewed as indicating poor ecosystem health in general. Thus it is recommended that further in-depth studies be completed on diatom community structure and water quality of wetland ecosystems to determine how to define natural conditions. This will enable better understanding of the nutrient levels within wetlands as well as the use of diatoms as bio-indicators for wetland ecosystemsMaster

« Captations d’héritages » : les enjeux juridiques et judiciaires d’un combat anticlérical (France, 1880-1905)

Pendant l’âge d’or de la « République anticléricale » (1880-1905), le clergé français est régulièrement accusé de captation d’héritage, un motif qui n’a pas été étudié par l’historiographie de l’anticléricalisme, pourtant foisonnante. Ce terme désigne les manœuvres déployées par les clercs pour faire main basse sur la fortune de certains catholiques, tout particulièrement les malades et les vieillards. Il constitue le moyen d’une attaque en règle contre la générosité pieuse. Bien qu’utilisées dans la presse pour désigner des procès intentés par des héritiers, à des membres du clergé ayant reçu un don ou legs, de la part de leur parent défunt, les captations d’héritages ne correspondent pas vraiment à une catégorie juridique. Elles n’ont dans le Code civil qu’une acception restreinte, tandis que de nombreuses dispositions dérogatoires encadrent et limitent la générosité pieuse. Trois affaires passées devant les tribunaux civils entre 1880 et 1905 montrent que si les héritiers s’estimant lésés s’efforcent de prouver qu’il y a bien eu captation d’héritage, les juges écartent ce motif. Ils décident d’annuler les donations litigieuses en appliquant le régime d’exception juridique qui encadre les dons et legs au clergé. Cela n’empêche la presse de désigner ces affaires comme des captations d’héritages, en leur appliquant une grille de lecture anticléricale et fictionnalisante. Ce motif imprègne ainsi l’imaginaire social, au point d’influencer le comportement des héritiers qui attaquent en justice certains membres du clergé, et, dans un cas, celui des magistrats chargés de rédiger le jugement, alors pétri par l’imaginaire anticlérical