1,720,979 research outputs found
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
Characterisation of integrated WAAM and machining processes
Full text linkThis research describes the process of manufacturing and machining of wire and arc additive manufactured (WAAM) thin wall structures on integrated and non¬integrated WAAM systems. The overall aim of this thesis is to obtain a better understanding of deposition and machining of WAAM wall parts through an integrated system. This research includes the study of the comparison of deposition of WAAM wall structures on different WAAM platforms, namely an Integrated SAM Edgetek grinding machine, an ABB robot and a Friction Stir Welding (FSW) machine. The result shows that WAAM is a robustly transferable technique that can be implemented across a variety of different platforms typically available in industry.
For WAAM deposition, a rise in output repeatedly involves high welding travel speed that usually leads to an undesired humping effect. As part of the objectives of this thesis was to study the travel speed limit for humping. The findings from this research show that the travel speed limit falls within a certain region at which humping starts to occur.
One of the objectives of this thesis was to study the effect of lubricants during sequential and non-sequential machining/deposition of the WAAM parts. Conventional fluid lubricants and solid lubricants were used. In addition, the effect of cleaning of deposited wall samples with acetone was also studied. A systematic study shows that a significant amount of solid lubricant contamination can be found in the deposited material. Furthermore, the results indicate that even cleaning of the wire and arc additive manufactured surfaces with acetone prior to the weld deposition can affect the microstructure of the deposited material
Alignment measurements uncertainties for large assemblies using probabilistic analysis techniques
Full text linkBig science and ambitious industrial projects continually push forward with technical requirements beyond the grasp of conventional engineering techniques. Example of those are ultra-high precision requirements in the field of celestial telescopes, particle accelerators and aerospace industry. Such extreme requirements are limited largely by the capability of the metrology used, namely, it’s uncertainty in relation to the alignment tolerance required. The current work was initiated as part of Maria Curie European research project held at CERN, Geneva aiming to answer those challenges as related to future accelerators requiring alignment of 2 m large assemblies to tolerances in the 10 µm range. The thesis has found several gaps in current knowledge limiting such capability. Among those was the lack of application of state of the art uncertainty propagation methods in alignment measurements metrology. Another major limiting factor found was the lack of uncertainty statements in the thermal errors compensations applied to assembly’s alignment metrology. A novel methodology was developed by which mixture of probabilistic modelling and high precision traceable reference measurements were used to quantify both measurement and thermal models compensation uncertainty accurately. Results have shown that the suggested methodology can accurately predict CMM specific measurement uncertainty as well as thermal drift compensation made by empirical, FEM and FEM metamodels. The CMM task specific measurement uncertainties made at metrology laboratory were validated to be of maximum 7.96 µm (1σ) for the largest 2 m assemblies. The analysis of the results further showed how using this method a ‘virtual twins’ of the engineering structures can be calibrated with known uncertainty of thermal drift prediction behaviour in the micrometric range. Namely the Empirical, FEM and FEM Metamodels uncertainties of predictions were validated to be of maximum: 8.7 µm (1σ), 11.28 µm (1σ) and 12.24 µm (1σ)
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
Robotic polishing of large optical components
Full text linkLightweight space mirrors have been widely used in earth observation and astronomy applications. Many organizations and companies, such as NASA in America, ESA in Europe, SSTL in UK as well as CASC in China, have spent a lot of money and effort on researching new materials for larger size space mirrors to meet both the payload weight constraints of launch and the increased advanced manufacturing process demanded for higher observations quality.
This project is aimed at robot neutral polishing of lapped, ground and polished optical substrates using an industrial FANUC robot system. The project focused on three main fields which were: robot polishing with polyurethane tool and cerium oxide, pitch polishing with pitch tool and cerium oxide, as well as polishing of a 400mm ULE component. The polishing process targets were to achieve: 1) a surface roughness (Ra) of 10 nm and a surface profile (Pt) of 6 µm and 2µm on lapped and ground substrates respectively with polyurethane based tools and 2) a surface roughness (Ra) of 2nm with a surface profile (Pt) unchanged on robot neutral polished substrates using pitch based tools.
This thesis comprises four main sections: a literature review, an experimental implementation, metrology and analysis, and the final conclusions. The experiment results measured with the metrology equipment selected were analysed. Conclusions of the relationship between the polishing performance of a specific sample and the selected polishing tool, polishing slurry, tool pressure, polishing time and other parameters were drawn.
Results obtained from robot neutral polishing were surface roughness (Ra) of 8-10nm and surface profile (Pt) of 6µm for 100mm square lapped and ground parts. The process scalability was demonstrated from robot neutral polishing in 45hours, a 400mm square ground component from a surface roughness (Ra) of 200nm to 10nm.
There is additional work to be implemented in the future, such as the development of robot pitch polishing of robot neutral polished parts to achieve 2nm Ra.MSc by Research Material
A laser-based multilateration system for measurement of metre-scale low-slope freeform non-specular surfaces.
Full text linkThe manufacture of metre–scale mirror segments for telescopes requires measurement
with low uncertainty to enable accurate form correction. The uncertainty of this measurement
has a direct effect upon the time to manufacture these segments; it is therefore
critical, to the viability of large optic manufacture, that a method for low uncertainty
measurement of these surfaces is developed and evaluated. The state-of-the-art system
for measurement of metre–scale surfaces has a length measurement uncertainty
of 1.2 µm over 1 m. Multilateration is a method for determining Cartesian coordinates
of measured positions utilising range displacement measuring stations. A four laser
tracker multilateration system has been proposed and tested with the aim to determine
whether a system can measure the specified surfaces with measurement uncertainties
below 1 µm. Influence factors that affect the multilateration input parameters have been
identified and utilised in Monte Carlo simulation of the multilateration system to estimate
the uncertainty associated with the coordinate measurement. A small flat optic
(0.2 m 0.2 m) was measured with the multilateration measurement setup to have z-coordinates
with a standard deviation, σz = 0.25 µm, and a large flat optic (0.4 m 0.4 m)
was measured with the multilateration measurement setup to have z-coordinates with
a standard deviation, σ∆ z = 0.73 µm. The 10 x 10 point multilateration measurement
of the large optic was repeated 10 times; the 100 points on the surface have a square
root mean variance, σz = 0.46 µm. Monte Carlo simulations indicate the independence
of measurement area and measurement noise for the experimental setup tested. It is
concluded that a laser–based multilateration system can measure a metre–scale optic with
z-coordinate measurement uncertainty below 1 µm. A 15.5 h measurement of the larger
flat was carried out to determine the effect of time dependent parameters on measurement
uncertainty. The measurement solution had a standard deviation of 1.88 µm: a factor of
approximately 2.4 times the equivalent short–term multilateration measurement solution.
Simulations have shown how this measurement drift is strongly related to temperature
change in the local environment of the measurement setup. This has been confirmed by
long–term measurements of laser tracker stationary SMR.PhD in Manufacturin
Selected area hot machining with a multi-tipped diamond tooling system.
Full text linkAn investigation of a novel ultra-precision tool is presented, the hot-milling multi-turret diamond tool. The tool implements micro-Laser Assisted Machining (μ-LAM) upon a multiple diamond fly cutter. Details of its design, both mechanical and optical, are presented- along with proposed modifications to Cranfield University’s Tetraform C machine to allow for its implementation. Relevant experimentation is presented- the modal analysis of the Tetraform C machine and the testing of laser heating on a silicon substrate. FE analyses are carried out and calculations presented to justify design choices. Analytical investigations predicted increased depths of cut by using laser, and indicated that at lower wavelengths of laser light and with lower feed rates that the depth of cut may be significantly increased. A novel method of selecting laser
wavelength based upon change in material absorptivity with temperature is investigated which may offer substantial increases in μ-LAM performanceMSc in Manufacturin
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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