Laser Welding of Ultrahigh Strength Steels at Subzero Temperatures

AbstractUltrahigh strength steels like press hardened 22MnB5 and S1100QL make good construction materials, however when fusion welded they bring the disadvantage of softening in heat affected zones (HAZ). State of the art research of Laser welding ultrahigh strength steels shows that neither increasing the welding velocity, nor post weld heat treatment have an effect on the strength and hardness drop in the HAZ. The key to improving these material characteristics is to increase heat dissipation out of the workpiece. To do so, the cooling conditions while laser welding press hardened 22MnB5 and S1100QL were dramatically increased. Experiments were carried out at subzero temperatures down to -98°C by using a mixture of liquid and gaseous nitrogen. To further improve heat dissipation, the clamping jaws were entirely made of copper. Hardness measurements and tensile tests were conducted to compare joints welded at room temperature with those welded at -98°C. Whilst an improvement of the hardness values could be achieved for the press hardened 22MnB5 and the S1100, no change in the mechanical behavior regarding tensile tests could be observed. Thus, it can be noticed that there is no possibility to improve the strength levels of martensitic steels throughout varying process parameters (like welding velocity) or utilizing an active cooling, even if subzero temperatures down to -98°C are applied. A further improvement at lower temperatures is unlikely because heat dissipation in the work piece itself is the limiting factor

Education and the boarding school novel : examining the work of José Régio

This thesis is centred on the work of Portuguese writer José Régio (1901-1969). He was a teacher-writer and, arguably, the most philosophical of Portuguese school novel authors. In his novel ‘A Drop of Blood’ (1945), Régio shows interest in the formation of the artist as the special object of education – the ‘marked man’ –, whose sensitivity distances him irremediably from the crowd. He adopted the radical individualism of Nietzsche not in order to be ‘for’ or ‘against’ this or that schooling model but to exemplify the perpetual clash, inherent in mankind, between the individual and the group, the artist and the non-artistic person, the young and the adult, the son and the father and the self and the world. Published Proquest ebook version: http://ebookcentral.proquest.com/lib/canterbury/detail.action?docID=4799556 (UC Staff and Student use only

Lesions of the Dorsal Medial Hippocampus induce different forms of Repetitive Behaviour in the rat

The dorsal dentate gyrus (DDG) of the hippocampus plays a role in the expression of different forms of flexible behaviour mainly due to its ability to sustain neurogenesis throughout life. In the present thesis, we examined the role that the DDG and its adjacent areas, both collectively referred to as dorsal medial hippocampus (DMH), play in flexible, adaptive behaviour and cognitive processing. We used the neurotoxin, colchicine, to induce lesions of the DDG, which were found to affect neighbouring areas. Thus these lesions will be referred to as lesions of the DMH. In the first experiment, rats were tested for (1) perseverative behaviour before and after receiving chronic methamphetamine (METH) treatment, (2) METH-induced locomotor activity and stereotypy in an open field, and (3) working memory in a T-maze. The results showed that rats with lesions of the DMH exhibited perseveration and supersensitivity to the locomotor- and stereotypy-inducing effects of METH (0, 0.1, 0.3, 1 mg/kg i.p.) as well as increased long-term METH sensitization. Rats with DMH lesions also showed significant working memory deficits. Taken together, these results reveal specific forms of behavioural inflexibility in rats with lesions of the DMH that are mainly associated with perseveration, drug-related behaviours, including stimulant motor supersensitivity and drug sensitization, and impaired working memory functions

Mathurin

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