937 resultados para Thin-walled structures Design and construction


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Nowadays, on a global level, the Higher Education System has a complex and broad horizon of curricular tools to use in the teaching and learning process. In addition to these new educational instruments, full of possibilities, we face specific socio-economic conditions that affect in a significantly way the Curriculum Development in certain knowledge areas (areas traditionally built on a methodology based on a physical presence of students in the classroom). Some areas such as Restoration, Rehabilitation or Construction Pathologies, and the construction sector in general, require very defined and particular knowledge that only a small number of experts claim as specialized training. All these aspects condition the teaching methodology performed in a physical classroom at a university campus (the only option used until recent years) and made us consider the integration of online teaching in these areas too. The present work shows the teaching methodology used for the development of two online courses, where we offer distance learning for "highly specialized" formation in the Edification area (an area where traditionally there was only classroom training). At the beginning, both courses were designed by classroom training, but got a really small number of applications due to the specialized topic proposed. Later, we proposed a "Curriculum Redesign" of the contents, offering an online modality, which implied a significant demand both within and outside the university area. A notable feature of this educational experience is the great spectrum opened for attendees of both courses in the online version. This situation improved significantly the "Curriculum Development" for the student and implied an interesting new proposal on the offered contents and materials (what would have been really difficult to get in a face to face classroom). In conclusion, the absence of certain types of specialized contents in the academic university curricula makes essential to raise new methodologies to save the gap in this area through additional training courses as those analyzed in this paper. Thus, our experience opens a debate on the appropriateness of implementing online training in relation to the face to face training in constructive content subjects and, especially, presents a new scheme, not without controversy, for the curriculum design.

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Mode of access: Internet.

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"Aeronautical Research Laboratory. Contract AF 33(616)-3885, Project no. 7(8-1367), Task no. 70524."

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Mode of access: Internet.

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Previously published under title: The half-timber house... New York, McBride, Nast & company, 1912.

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Experimental and theoretical methods have been used to study zeolite structures, properties and applications as membranes for separation purposes. Thin layers of silicalite-1 and Na-LTA zeolites have been synthesised onto carbon-graphite supports using a hydrothermal synthesis procedure. The separation behaviour of the composite membranes was characterized by gas permeation studies of pure, binary and ternary mixtures of methane, ethane and propane. The influence of temperature and feed gas mixture composition on the separation and selectivity performance of the membranes was also investigated. It was found that the silicalite-1 composite membranes synthesised onto the 4 hour oxidized carbon-graphite supports showed the most promising separation behaviour of all the composite membranes investigated. Molecular simulation methods were used to gain an understanding of how hydrocarbon molecules behave both within the pores and on the surfaces of silicalite-1, mordenite and LTA zeolites. Molecular dynamic simulations were used to investigate the influence of temperature and molecular loadings on the diffusional behaviour of hydrocarbons in zeolites. Both hydroxylated (surface termination with hydroxyl groups) and non-hydroxylated silicalite-1 and Na-mordenite surfaces were generated. For both zeolites the most stable surfaces correspond to the {010} surface. For the silicalite-1 {010} surface the adsorption of hydrocarbons and molecular water onto the hydroxylated surface showed a favourable exothermic adsorption process compared to adsorption on the non-hydroxylated surface. With the Na-mordenite {010} surface the adsorption of hydrocarbons onto both the hydroxylated and non-hydroxylated surfaces had a combination of favourable and non-favourable adsorption energies, while the adsorption of molecular water onto both types of surface was found to be a favourable adsorption process.

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The design and construction of a sputtering system for the deposition of barium titanate thin films is described. The growth and structure of barium titanate films deposited on a variety of substrates including amorphous carbon fi1ms, potassium bromide single crystals, and polycrystalline gold films has been studied. Films deposited on all substrates at room temperature were amorphous. Polycrystalline titanate films were formed on polycrystalline and amorphous substrates at temperatures above 450°C while films with a pronounced texture could be expitaxially deposited on single crystal potassium bromide above a temperature of only 200°C. Results of dielectric measurements made on the films are reported. Amorphous films were highly insulating (resistivities ~1014 ohm.cm with dielectric constants of between 10 and 20.

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Cold roll forming of thin-walled sections is a very useful process in the sheet metal industry. However, the conventional method for the design and manufacture of form-rolls, the special tooling used in the cold roll forming process, is a very time consuming and skill demanding exercise. This thesis describes the establishment of a stand-alone minicomputer based CAD/CAM system for assisting the design and manufacture of form-rolls. The work was undertaken in collaboration with a leading manufacturer of thin-walled sections. A package of computer programs have been developed to provide computer aids for every aspect of work in form-roll design and manufacture. The programs have been successfully implemented, as an integrated CAD/CAM software system, on the ICL PERQ minicomputer with graphics facilities. Thus, the developed CAD/CAM system is a single-user workstation, with software facilities to help the user to perform the conventional roll design activities including the design of the finished section, the flower pattern, and the form-rolls. A roll editor program can then be used to modify, if required, the computer generated roll profiles. As far as manufacturing is concerned, a special-purpose roll machining program and postprocessor can be used in conjunction to generate the NC control part-programs for the production of form-rolls by NC turning. Graphics facilities have been incorporated into the CAD/CAM software programs to display drawings interactively on the computer screen throughout all stages of execution of the CAD/CAM software. It has been found that computerisation can shorten the lead time in all activities dealing with the design and manufacture of form-rolls, and small or medium size manufacturing companies can gain benefits from the CAD/CM! technology by developing, according to its own specification, a tailor-made CAD/CAM software system on a low cost minicomputer.

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The fossil arthropod Class Trilobita is characterised by the possession of a highly mineralised dorsal exoskeleton with an incurved marginal flange (doublure). This cuticle is usually the only part of the organism to be preserved. Despite the common occurrence of trilobites in Palaeozoic sediments, the original exoskeletal mineralogy has not been determined previously. Petrographic data involving over seventy trilobite species, ranging in age from Cambrian to Devonian, together with atomic absorption and stable isotope analyses, indicate a primary low-magnesian calcite composition. Trilobite cuticles exhibit a variety of preservational textures which are related to the different diagenetic realms through which they have passed. A greater knowledge of post-depositional processes and the specific features they produce, has enabled post-mortem artefacts to be distinguished from primary cuticular microstructures. Alterations of the cuticle can either enhance or destroy primary features, and their effects are best observed in thin-sections, both under transmitted light and cathodoluminescence. Well-preserved trilobites often retain primary microstructures such as laminations, canals, and tubercles. These have been examined in stained thin-sections and by scanning electron microscopy, from as wide a range of trilobites as possible. Construction of sensory field maps has shown that although the basic organisation of the exoskeleton is the same in all trilobites, the types of microstructures found, and their distribution is species-specific. The composition, microstructure, and architecture of the trilobite exoskeleton have also been studied from a biomechanical viewpoint. Total cuticle thickness, and the relative proportions of the different layers, together with the overall architecture all affected the mechanical properties of the exoskeleton.

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Presented in this report is an investigation of the use of "sand-lightweight" concrete in prestressed concrete structures. The sand-lightweight concrete consists of 100% sand substitution for fines, along with Idealite coarse and medium lightweight aggregate and Type I Portland Cement.

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The interaction of magnetic fields generated by large superconducting coils has multiple applications in space, including actuation of spacecraft or spacecraft components, wireless power transfer, and shielding of spacecraft from radiation and high energy particles. These applications require coils with major diameters as large as 20 meters and a thermal management system to maintain the superconducting material of the coil below its critical temperature. Since a rigid thermal management system, such as a heat pipe, is unsuitable for compact stowage inside a 5 meter payload fairing, a thin-walled thermal enclosure is proposed. A 1.85 meter diameter test article consisting of a bladder layer for containing chilled nitrogen vapor, a restraint layer, and multilayer insulation was tested in a custom toroidal vacuum chamber. The material properties found during laboratory testing are used to predict the performance of the test article in low Earth orbit. Deployment motion of the same test article was measured using a motion capture system and the results are used to predict the deployment in space. A 20 meter major diameter and coil current of 6.7 MA is selected as a point design case. This design point represents a single coil in a high energy particle shielding system. Sizing of the thermal and structural components of the enclosure is completed. The thermal and deployment performance is predicted.