1,721,453 research outputs found
Performance analysis of a reduced cost manufacturing process for composite aircraft secondary structure
No full textIn the current, environmentally-aware, climate aircraft designers are under increasing pressure toproduce fuel efficient vehicles. Weight reduction is an important method for increasing fuelefficiency. Fibre reinforced polymer (FRP) composites are known to offer weight savings overtraditional metallic components, due to their excellent stiffness and strength to weight ratios.However, the major limiting factor for the use of aerospace quality composites is themanufacturing cost. The costs incurred in the conventional process of prepreg cured in anautoclave are well documented. The research in this thesis is concerned with reducing the cost ofmanufacturing aircraft standard carbon fibre composite sandwich panels, whilst maintainingmechanical performance.The overall aim of the EngD is to provide a unified approach for assessing the performance ofcarbon fibre sandwich secondary structure that are manufactured using several differenttechniques. Cost and performance criteria are defined so that an optimal panel can be produced.The work has been motivated by the industrial sponsor, GE Aviation Systems. Five combinationsof raw material and processing techniques, manufacturing options (MOs) were considered inincremental steps from the baseline of unidirectional prepreg cured in an autoclave to the noncrimpfabric (NCF) infiltrated using resin film infusion (RFI) and cured in a conventional oven.For cost and performance analysis a generic panel has been designed that is representative ofsecondary wing structure on commercial passenger aircraft. The cost was estimated by monitoringthe manufacture of generic panels using each MO, whilst the performance was measured by bothmechanical characterisation tests and by full scale tests on a custom designed rig. The rig applies apressure load using a water cushion and allows optical access to the surface of the panel enablingthe use of optical techniques, i.e. thermoelastic stress analysis (TSA) and digital image correlation(DIC). Feasibility tests on TSA and DIC demonstrated their use on the materials considered inthis thesis, and were used to validate finite element (FE) models.The RFI out-of-autoclave process was found to reduce generic panel manufacture time by almost30%, and the material cost was reduced by almost 40%. The mechanical characterisation testssuggested the ‘new’ process could produce laminates with a similar fibre volume fraction to that ofthe original process and similar in and out-of-plane mechanical properties. The in-plane stiffnesswas slightly reduced by 7 %, but the strength showed an increase of 12%. Full scale tests on thegeneric panels using point out-of-plane deflection measurements and full field TSA demonstratedthe panel produced using the ‘new’ process has adequate performance. Moreover the full-fieldtests indicated an improvement in performance. Further work is required to optimise the design ofthe panel for weight, in particular the weight of the raw material, and investigating methods formodelling the NCF for certification
Probabilistic gradients for fast calibration of differential equation models
No full textCalibration of large-scale differential equation models to observational or experimental data is a widespread challenge throughout applied sciences and engineering. A crucial bottleneck in state-of-the art calibration methods is the calculation of local sensitivities, i.e. derivatives of the loss function with respect to the estimated parameters, which often necessitates several numerical solves of the underlying system of partial or ordinary differential equations. In this paper we present a new probabilistic approach to computing local sensitivities. The proposed method has several advantages over classical methods. Firstly, it operates within a constrained computational budget and provides a probabilistic quantification of uncertainty incurred in the sensitivities from this constraint. Secondly, information from previous sensitivity estimates can be recycled in subsequent computations, reducing the overall computational effort for iterative gradient-based calibration methods. The methodology presented is applied to two challenging test problems and compared against classical methods
Infrared spectroscopy of size selected anion complexes and clusters
Full text link© 2003 Dr. Duncan Andrew WildGas phase anion clusters, consisting of solvent molecules hydrogen bonded to halide anions, are characterised by vibrational predissociation spectroscopy using a combination of mass spectrometry and laser spectroscopy. Monitoring changes in the vibrational properties of neutral solvent molecules when they are attached to a halide anion allows one to infer cluster structures. In some cases, the spectra contain rotationally resolved features, so that quantitative structural parameters can be obtained. (For complete abstract open document
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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