ABSTRACT The objective of this study is to establish the Forming Limit Diagram (FLD) of tubes. An experimental system of tube hydroforming, the electrical chemical etching method and the image process system are used to carry out the sheet metal forming test and the hydraulic bulge-forming test of annealed aluminum alloy tubes. Furthermore, Hill¡¦s new yield criterion is also used to predict the Forming Limit Curves of sheets. The predicted forming limit diagrams are compared with experimental data. The forming limit diagrams of tubes are coincident with those of sheets. Also, the predicted forming limit curves by Hill¡¦s new yield criterion agree quite well with those by experiments. Therefore, Hill¡¦s new yield criterion can be used to establish the forming limit curves of sheets or tubes.

In this study, the non-binary coding, elitist strategy, increasing mutation rate, extinction, and immigration strategy are used to improve the simple genetic algorithms. The improved search technique can reduce the possibility of falling into the local optimum due to the premature convergence in a large searching space, and increase the chance of finding out the near-optimal parameters. The hydraulic forming machine used in this thesis, includes a power source of a hydraulic motor and a actuator of two hydraulic cylinders. Both the internal pressure and axial force are controlled to hydroform the tubes into the shapes we want. The PID fuzzy logic controller is implemented to control the proportional direction valve and pressure reducing valve of this dual-cylinder electro-hydraulic system so that the loading path can follow the optimal forming curve of axial-feeding and pressure prescribed. From the experimental results, it is clear that the near-optimal PIDFLC controller designed via modified genetic algorithms can make the loading path follow the prescribed curve, and effective for reducing system uncertainty caused by the varying loads and system unstability resulting from the nonlinear characteristics of the hydraulic system.

Weight reduction is a hot topic in automotive industry. Both the applications of tube hydroforming technique and magnesium alloys offer a large potential for reducing the weight of automotive components. In this research, the relationship between forming pressure and bulge height, the maximum forming pressure and the forming limit during the tube hydraulic bulging process are first analysed. A self-designed warm hydraulic bulge forming equipment and the seamlessly extruted magnesium alloy AZ61 tubes, are used for carrying out a series of warm hydraulic bulge tests, and discussing the formalibility of the magnesium tubes at various temperatures. Furthermore, the flow stress curves are determined by the mathematical model in this paper with the bulge forming test results. Then the validity of the analytical model is verified by comparing the forming pressure and bulge height between analytical and experimental values.

Magnesium alloy tubes have good formability at elevated temperatures. In this study, a finite element code DEFORM 3D is used to simulate the result of T-shape hydroforming at working temperatures 150¢J and 250¢J with magnesium alloy AZ61 tubes and then conducts the hydroforming experiments. By modifying the loading paths, products with uniform thickness and branch height are obtained 49mm. The results of simulation are compared with the experimental results to verify the validity of this modeling. On the other hand, the effects of the die fillet radius on tube formability during y-shape hydroforming are discussed. With the right die fillet radius r1¡×10mm and the left die fillet radius r2¡×30mm, a better formability of the tube is obtained.

Organic acids are usually the reactants which proceed in chlorination reaction into products of disinfection by-products in water treatment plant. The purpose of this study is by using tests of kinetics and equilibrium adsorptions to investigate adsorption characteristics and kinetic model evaluations of selected organic acid in solution. We use commercial carbon nano-tube for the adsorbents. The major factors in adsorption tests include the concentration of fulvic acid (a typical organic acid in raw water), pH, ionic strength and temperature. Experiment results exhibited kinetic adsorption reached equilibrium about 120 minutes, the adsorption capacity increased with concentrations increasing of fulvic acid and decreased with ionic strengths. The best selection in kinetic models evaluation, fitting models such as Modified Freundlich equation, Pseudo-1st-order equation and Pesudo-2nd-oder equation is Modified Freundlch equation model. In addition, intraparticle diffusion equation model was fitted well and showed adsorption process was controlled with pore diffusion. The maximum adsorption capacity varied from 26.094 to 20.772 mg/g when temperature ranging from 4 to 45¢J. Isotherm adsorption results were fitted on Langmuir and Freundich models. The £GG¢X values ranged from -0.930 to -1.014 kcal/mol, £GH¢X:-1.561 kcal/mol and £GS¢X:-2.02 cal/mol. Thermodynamic parameters indicated that the adsorption is spontaneously and an exothermic reaction. Adsorption of fulvic acid by carbon nano-tube has a good performance when operation conditions of higher fulvic acid concentration, lower ionic strength, lower pH and lower temperature.

Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Numerous experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work /REM 1993/, /THF 1997/, /CHU 1999/. For pre- and post-test calculations of Lower Head Failure experiments like OLHF or FOREVER it is necessary to model creep and plasticity processes. Therefore a Fi-nite Element Model is developed at the FZR using a numerical approach which avoids the use of a single creep law employing constants derived from the data for a limited stress and temperature range. Instead of this a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. A main task for this approach is the generation and validation of the CDB. Additionally the implementation of all relevant temperature dependent material properties has been performed. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The validation of the numerical model is performed by the simulation of and com-parison with experiments. This is done in 3 levels: starting with the simulation of sin-gle uniaxial creep tests, which is considered as a 1D-problem. In the next level so called "tube-failure-experiments" are modeled: the RUPTHER-14 and the "MPA-Meppen"-experiment. These experiments are considered as 2D-problems. Finally the numerical model is applied to scaled 3D-experiments, where the lower head of a PWR is represented in its hemispherical shape, like in the FOREVER-experiments. This report deals with the 1D- and 2D-simulations. An interesting question to be solved in this frame is the comparability of the French 16MND5 and the German 20MnMoNi55 RPV-steels, which are chemically nearly identical. Since these 2 steels show a similar behavior, it should be allowed on a lim-ited scale to transfer experimental and numerical data from one to the other.

Hintergrund: Heiserkeit und Halsschmerzen sind häufige Intubationsfolgen. Ziel dieser Arbeit ist das Erfassen deren postoperativer Inzidenz und Intensität unter Betrachtung der gewählten Tubusart. Methodik: Das Votum der Ethikkommission der Universität Leipzig liegt vor. Es wurden in einem Zeitraum von einem halben Jahr im Fachbereich Kinderanästhesie insgesamt 103 Kinder im Alter von 3 – 12 Jahren zu elektiven kinderchirurgischen Eingriffen in Allgemeinanästhesie eingeschlossen. Die Randomisierung erfolgte per Losentscheid. Die Patienten wurden entweder Gruppe I (Tubus ohne Cuff) oder Gruppe II (Tubus mit Cuff) zugeordnet. Die Kinder wurden vom ersten bis zum dritten postoperativen Tag zu Halsbeschwerden befragt und diese als Heiserkeit oder Schluckbeschwerden erfasst. Bei Angabe von Halsschmerzen wurden diese durch die VAS (1 – 10) objektiviert. Ergebnisse: Halsbeschwerden nach Intubation wurden am ersten postoperativen Tag von 21,4 % der 103 Kinder angegeben. Dabei trat Heiserkeit mit 19,4 % häufiger als Schluckbeschwerden mit 5,8 % auf. Halsschmerzen gaben 5,8 % aller intubierten Patienten an. In der Gruppe I (n = 50) wurden am ersten postoperativen Tag keine Halsschmerzen angegeben. Jedoch gaben in der Gruppe II (n = 53) 12 % der Patienten Halsschmerzen (VAS > 3) an (p < 0.05). Am zweiten postoperativen Tag hatten noch 6,8 % aller Patienten Halsbeschwerden. Am dritten postoperativen Tag waren alle Kinder beschwerdefrei. Schlussfolgerungen: Kinder zeigten nach Intubation am ersten postoperativen Tag sehr häufig Halsbeschwerden, die bis zum dritten postoperativen Tag abklangen. Halsschmerzen wurden nur von den Kindern angegeben, bei denen ein Tubus mit Cuff verwendet wurde.

Thesis (M.S.)--Eastern Illinois University, 2004. / Includes bibliographical references (leaves 49-54).

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Neural Tube Defects (NTDs) are a group of common congenital malformations that result from incomplete neural tube closure leading to abnormalities of the brain and/or spinal cord. Unfortunately, their etiology remains unknown, probably due to complex multifactorial interactions. The protective effect of dietary folates in preventing NTDs is well known, but this beneficial effect is limited to the 60 to 70% of cases; leaving 30% of the population without any known option for improving pregnancy outcomes. The mechanism by which folates rescue NTD-affected embryos is poorly understood, but the ability of folate supplementation to overcome a significant percentage of NTDs and the critical role of 5-methyltetrahydrofolate in the remethylation of homocysteine (Hcy) to methionine in the placenta suggests that folate binding and/or transport might play a critical role during development. We hypothesized that maternal autoantibodies (AB) targeting placental folate receptor alpha (FRα) are blocking the receptor and limiting the ability of the FRα to bind folates, reducing intraembryonic folate levels. Furthermore, we hypothesized that AB binding to other relevant proteins required for trophoblastic growth and placentation can be involved in activating pathologic inflammatory pathways that can result in suboptimal uptake of nutrients and contribute to an abnormal closure of the neural tube. We developed a high throughput ELISA to evaluate whether mothers experiencing pregnancies complicated with NTDs are more likely to have placental AB to FRα than are mothers experiencing normal pregnancies. We optimized and simplified a protocol for AB elution from placental tissues and determined whether these antibodies were blocking the FRα from binding with available folates. Although anti-FRα IgG antibodies were not associated to the blocking activity in this study, we found that the blocking activity was higher in the placentas from NTD-affected pregnancies compared to controls, that FRα IgM antibodies are most likely the type of antibody produced during gestation that is most relevant to the blocking activity and that it is unlikely that autoimmunity against other developmental proteins associated with NTDs is generating the NTDs. / text