Nd:YAG Laser Welding of 5083 Aluminium Alloy using Filler Wire

High reflectivity and high thermal conductivity, high vapour pressure of alloyingelements as well as low liquid surface tension and low ionisation potential, make laser welding of aluminium and its alloys a demanding task.Problems that occur during welding are mainly process instabilities of the keyhole and the melt pool, increased plasma formation above the melt pool and loss of alloying elements. These problems lead to unwanted metallurgical defects like hot cracks and porosity in the weld bead andother problems concerning the shape and appearance of the weld bead. In order to minimise the defects and improve the weld quality, the process and beam parameters need to be carefully adjusted along with a consideration concerning the use of filler wire for the welding process. In this work the welding of 3,0 mm thick grade 5083 aluminium alloy plates using a 3,0 kW Nd:YAG laser with grade 5183 filler wire addition is investigated. The plates were welded as butt joints with air gap sizes 0,5 mm, 0,7mm and 1,0 mm. The analysis of the weld beads obtained from the weldedsamples showed that the least imperfections were produced with 0,7 mm air gaps at moderate welding speeds. The analysis also covered the calculation of the melting efficiency and the study of the shape of the weld bead. The melting efficiency was on average around 20 % for the melting process of the welded plates. The weld beads showed the characteristic V-shape of a laser weld and retained this shape during the whole series of experiments.

Effect of Shielding Gases in Laser Welding of Aluminium Alloys

High reflectivity to laser light, alloying element evaporation during high power laser welding makes aluminium alloys highly susceptibility to weld defects such as porosity, cracking and undercutting. The dynamic behaviour of the keyhole, due to fluctuating plasma above the keyhole and the vaporization ofthe alloying elements with in the keyhole, is the key problem to be solved for the improvement of the weld quality and stabilization of the keyhole dynamics isperhaps the single most important development that can broaden the application of laser welding of aluminium alloys. In laser welding, the shielding gas is commonly used to stabilize the welding process, to improve the welded joint features and to protect the welded seam from oxidation. The chemicalcomposition of the shielding gas is a key factor in achieving the final qualityof the welded joints. Wide range of shielding gases varying from the pure gasesto complex mixtures based on helium, argon, nitrogen and carbon dioxide are commercially available. These gas mixtures should be considered in terms of their suitability during laser welding of aluminium alloys to produce quality welds. The main objective of the present work is to study the effect of the shielding gascomposition during laser welding of aluminium alloys. Aluminium alloy A15754 was welded using 3kW Nd-YAG laser (continuous wave mode). The alloy samples were butt welded with different shielding gases (pure and mixture of gases) so that high quality welds with high joint efficiencies could be produced. It was observed that the chemical composition of the gases influenced the final weld quality and properties. In general, the mixture gases, in correct proportions, enabled better utilisation of the properties of the mixing gases, stabilized the welding process and produced better weld quality compared to the pure shielding gases.

Safety of intramuscular influenza vaccine in patients receiving oral anticoagulation therapy: a single blinded multi-centre randomized controlled clinical trial

Influenza vaccines are recommended for administration by the intramuscular route. However, many physicians use the subcutaneous route for patients receiving an oral anticoagulant because this route is thought to induce fewer hemorrhagic side effects. Our aim is to assess the safety of intramuscular administration of influenza vaccine in patients on oral anticoagulation therapy. Methods: Design: Randomised, controlled, single blinded, multi-centre clinical trial. Setting: 4 primary care practices in Barcelona, Spain. Participants: 229 patients on oral anticoagulation therapy eligible for influenza vaccine during the 20032004 season. Interventions: intramuscular administration of influença vaccine in the experimental group (129 patients) compared to subcutaneous administration in the control group (100 patients). Primary outcome: change in the circumference of the arm at the site of injection at 24 hours. Secondary outcomes: appearance of local reactions and pain at 24 hours and at 10 days; change in INR (International Normalized Ratio) at 24 hours and at 10 days. Analysis was by intention to treat using the 95% confidence intervals of the proportions or mean differences. Results: Baseline variables in the two groups were similar. No major side effects or major haemorrhage during the follow-up period were reported. No significant differences were observed in the primary outcome between the two groups. The appearance of local adverse reactions was more frequent in the subcutaneous administration group (37,4% vs. 17,4%, 95% confidence interval of the difference 8,2% to 31,8%). Conclusion: This study shows that the intramuscular administration route of influenza vaccine in patients on anticoagulant therapy does not have more side effects than the subcutaneous administration route

Centre d’estudiants de la UdG

Creació d’un nou equipament dins del campus de Montilivi de la Universitat de Girona que millori els serveis i ordeni l’entorn. Aquest nou edifici substituiria els mòduls prefabricats que hi ha actualment . Per a l’elaboració del projecte es fa un estudi del tres campus de la UdG, de la seva situació dins de la ciutat de Girona i de la seva evolució històrica

Centre d’estudiants de la UdG

Creació d’un nou equipament dins del campus de Montilivi de la Universitat de Girona que millori els serveis i ordeni l’entorn. Aquest nou edifici substituiria els mòduls prefabricats que hi ha actualment . Per a l’elaboració del projecte es fa un estudi del tres campus de la UdG, de la seva situació dins de la ciutat de Girona i de la seva evolució històrica

El Centre d'Estudis Històrics de Llagostera (1966-1973)

Aquest treball pretén, en primer lloc, analitzar la història del Centre d’Estudis de Llagostera. Durant les dècades dels quaranta, cinquanta i seixanta a les comarques gironines es creen un seguit de centres d’estudis amb la missió de fer recerca del passat a través de l’arqueologia. En segon lloc, pretén saber quina consideració tenia l’arqueologia després dels primers anys del règim franquista. En tercer lloc, es pretén estudiar com va renéixer l’arqueologia al municipi de la mà d’uns pocs membres cultes de la societat civil, la qual cosa ens permet esbossar com neixen les inquietuds pel descobriment dels orígens de la vila. En quart lloc, es pretén, recuperar la memòria oral mitjançant entrevistes a aquells membres cultes van que encara viuen al poble. El contacte amb aquestes persones que van estar immerses en el desenvolupament del Centre d’Estudis ha permès compilar alguns documents gràfics que posseïen alguns d’ells a les seves biblioteques particulars

Estudi de la implantació de sistemes vegetats en l'envolupant del Centre d'Interpretació del Montsec

Analitzar la repercussió que té en el comportament tèrmic d'un edifici en estudi la integració de sistemes constructius que incorporin vegetació en l'envolupant d'aquest (façana i coberta).