A new engineering approach to predict the hydrostatic strength of uPVC\ud pipes

Extruded unplasticised Poly(Vinyl Chloride) (uPVC) pipes are certified using pressurised pipe tests.\ud During these tests the pipes are subjected to a certain temperature and internal pressure, while the\ud time-to-failure, the time at which the internal pressure drops due to rupture or fracture, is measured.\ud These tests are time consuming and are therefore costly. To circumvent these costs a model-based\ud approach is proposed where the time-to-failure is predicted. The input parameters for this approach\ud can be determined using short term measurements. The approach uses the observation that the timeto-\ud failure kinetics of uPVC pipes subjected to an internal pressure is independent of the type of failure\ud mode (ductile, semi-ductile or brittle). This supports our statement that the underlying mechanism\ud that initiates failure is similar for these types of failure. Local deformation of the material up to a\ud critical value of the anelastic strain is believed to determine the start of failure of the material. This\ud critical strain appears to be constant for the testing conditions used during this study. A pressure\ud modified Eyring expression is employed to calculate the strain rate resulting from the applied stress\ud at a certain temperature. The time-to-failure follows from the calculated strain rate and the critical\ud strain of the material. This approach has been verified against literature data and shown to hold\ud quantitatively. Furthermore, the model seems to hold for different processing conditions

A new engineering approach to predict the long-term hydrostatic strength of unplasticized poly(vinyl chloride) pipes

Extruded polymer pipes are qualified using pressurized pipe tests. With these tests the long-term hydrostatic strength is determined by subjecting the pipes to an internal pressure, while measuring the time-to-failure. Although these tests can be accelerated (at higher temperatures), they remain time consuming and require a spacious experimental setup. To circumvent this costly method a model based approach is proposed by which the long-term hydrostatic strength is predicted. Using short term measurements, the input parameters for this approach can be determined. In this engineering approach the effects of physical aging are included. The approach is capable to quantitatively predict the (long-term) failure time of pipe sections under internal pressure

Hysterectomy in the rural tropics

A clinical study on hysterectomy in the rural tropics of Ghana and the challenges faced by rural health care providers to render effective and meaningful medical assistance to rural patients due to the scarcity of medical equipment and medical drugs in such neglected outlying areas..A retrospective study of hysterectomy at a rural hospital in Ghana revealed a high incidence of emergency cases. Uterine fibroids were the commonest indication for elective hysterectomy, followed by surgery for suspected cervical carcinoma. Most emergency hysterectomies were performed because of uterine rupture. The difficulties of managing these problems against the background of the diagnostic and therapeutic facilities available are discussed

Ontwikkeling hoezo?

De vraag of er ontwikkeling is, kan altijd en overal positief worden beantwoord. Maar de betekenis ervan verschilt voor een visser in Indonesië of een handelaar in Honduras. De Sociologie van Ontwikkeling staat voor een niet-normatieve benadering van ontwikkeling en tracht de meervoudigheid ervan in de praktijk van het alledaagse leven te begrijpen. Een kritische toetsing van regels en modellen vraagt de noodzakelijke aandacht voor de diversiteit en creativiteit van mensen die ontwikkeling in eigen hand willen houden in de marges van de globale wereld

Genetic and environmental factors affecting the coumarin anticoagulant level

This introductory chapter has illustrated that various factors, such as genetic factors, drugs, diet and intercurrent diseases may affect anticoagulation levels. Most of the clinical and pharmacological data related to coumarin anticoagulants have so far been obtained from studying warfarin. Because of the different pharmacokinetic properties of each individual drug, the results of these studies can probably not be directly extrapolated to the other coumarin anticoagulants. Therefore, the aim of this thesis was to study the various genetic and environmental factors affecting the anticoagulation levels of acenocoumarol or phenprocoumon among outpatients of an anticoagulation clinic. In chapter 2 genetic factors influencing the coumarin anticoagulant level are examined. Chapter 2.1 describes how the coumarin anticoagulant dose is affected by polymorphisms of the cytochrome P450 enzyme 2C9 allele. In chapter 2.2 we describe the influence of these polymorphisms on the occurrence of bleeding complications. CYP2C9 variant alleles seem to have several biological consequences. For instance, it has been associated with an increased risk of myocardial infarction in women [57]. Therefore, in chapter 2.3 the risk of myocardial infarction was studied in patients with a CYP2C9 variant allele compared to patients with the wild type genotype. Chapter 2.4 concerns the influence of apolipoprotein E genotype on the coumarin anticoagulant level. In chapter 3, several drugs are identified with a high risk of overanticoagulation during coumarin use. Chapters 3.1 and 3.2 focus on antibacterial drugs and antifungal agents, chapters 3.3 on laxatives, and 3.4 on nonsteroidal anti-inflammatory drugs as risk factors for overanticoagulation. The study described in chapter 4 aims at investigating the influence of heart failure on the anticoagulant level. The role of dietary intake of vitamin K as a risk factor for overanticoagulation is evaluated in chapter 5. Finally, in chapter 6 the strengths and limitations of this thesis are discussed, together with the implications for coumarin anticoagulant therapy, and suggestions for future research are given

Condition monitoring of uPVC gas pipes

No abstract

Scenarios for Resilient Shrimp Aquaculture in Tropical Coastal Areas

We contend there are currently two competing scenarios for the sustainable development of shrimp aquaculture in coastal areas of Southeast Asia. First, a landscape approach, where farming techniques for small-scale producers are integrated into intertidal areas in a way that the ecological functions of mangroves are maintained and shrimp farming diseases are controlled. Second, a closed system approach, where problems of disease and effluent are eliminated in closed recirculation ponds behind the intertidal zone controlled by industrial-scale producers. We use these scenarios as two ends of a spectrum of possible interactions at a range of scales between the ecological, social, and political dynamics that underlie the threat to the resilience of mangrove forested coastal ecosystems. We discuss how the analytical concepts of resilience, uncertainty, risk, and the organizing heuristic of scale can assist us to understand decision making over shrimp production, and in doing so, explore their use in the empirical research areas of coastal ecology, shrimp health management and epidemiology, livelihoods, and governance in response to the two scenarios. Our conclusion focuses on a series of questions that map out a new interdisciplinary research agenda for sustainable shrimp aquaculture in coastal area