1,720,989 research outputs found
Statistical Process Control for Geometric Specifications: On the Monitoring of Roundness
No full textQuality of mechanical components is critically related to both dimensional and geometric specifications. Traditionally, approaches for statistical process control (SPC) focused on the first type of specification only. When the quality of a manufactured product is related to geometric specifications (e.g., profile and form tolerances as straightness, roundness, cylindricity, flatness, etc.), the process should be considered in control if the relationship used to represent that profile or surface in the space is stable over time. This paper presents a novel method for monitoring bidimensional profiles. The proposed method is based on combining a spatial autoregressive regression (SARX) model (i.e., a regression model with spatial autoregressive errors) with control charting. To show the effectiveness of the proposed method, the approach is applied to real process data in which the roundness of items obtained by turning has to be monitored. A simulation study indicates that the proposed approach outperforms competing methods (based on monitoring the out-of-roundness value for each profile) in terms of the average number of samples required to detect out-of-control conditions arising in phase II and due to spindle-motion errors
Optimization of processing parameters of a ball mill refiner for chocolate
No full textThe aim of this work was to optimise the ball mill based refining process of chocolate, in terms of refining time and energy consumption. Experiments were planned following a central composite design (CCD), considering refining time (rt) and agitator shaft speed (as) as factors. The experimental variables measured were chosen from the main characteristics that describe unmoulded chocolate. A complete second order model was fitted to the experimental data. The most significant coefficients were that of energy consumption, iron content and particle size. Optimisation consists in a bound minimization of refining time using the desirability function. The optimum conditions calculated were as follows: 58 rpm for as and 38.5 min for rt. A control experiment carried out in the optimised conditions to corroborate the results obtained, confirmed calculated expectations of response variables. In conclusion, the study enabled to identify new working conditions for the ball mill considered, rising output from 109 kg/h to 156 kg/h, with a 43% increase in productivity
Modelling of back tempering in laser hardening
No full textBack tempering is one of the most critical problems in laser hardening of extended surfaces. In this type of treatment, several laser tracks are slightly overlapped to obtain a uniform hardened surface. Due to the overlapping, tempered zones are generated on the treated surface with the consequent lack of uniformity in the surface hardness. In this work, a regression model was developed to estimate the loss of hardness due to the tempering effect as a function of the thermal cycle. A specific test, named laser surface treatment test, was designed and executed to reproduce the hardness reduction due to the tempering effect. An analytical thermal model was developed to evaluate the thermal cycle undergone by the material during this test. By the results of the laser surface treatment test combined with the analytical model, a prediction model was estimated. Good agreement was found between predicted and measured hardness decrease, and the identified model could be integrated in a numerical code to evaluate the optimal process parameters
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Configuration of AMSs: Stochastic models for performance evaluation of automated manufacturing systems
No full textThis chapter proposes an integrated approach for supporting firms in the phase of detailed dimensioning of Advanced Manufacturing Systems. The problem is closely related to the performance evaluation of the system since discriminating indicators are necessary to rank different alternatives. Approximate stochastic models are proposed to estimate the performance of Advanced Manufacturing Systems. The accuracy of the proposed models is shown by applying them to several test and real cases. © 2005 Springer
Quality control of geometric features: monitoring roundness profiles obtained by turning
No full textManufacturing processes leave on the machined surface a specific “fingerprint” of the process used, which can be usefully adopted to improve the quality control strategy (i.e., to reduce the time required to detect out-of-control conditions). Approaches proposed up to now in the literature are mainly devoted to monitoring simple signatures, where data measured on the profile are not autocorrelated. Unfortunately, most of the times data collected on a machined profile are autocorrelated because they are obtained in similar condition of the machining process and because they are related to local properties of the material machined. This paper presents a novel method for monitoring bi-dimensional profiles when the autocorrelation structure is modeled as a part of the manufacturing signature. The proposed method is based on combining a regression model with autocorrelated errors to a multivariate Hotelling T2 control chart and it is applied to real process data in which the roundness of items obtained by turning has to be monitored. A simulation study indicates that the proposed approach outperforms competing method (based on monitoring the out-of-roundness value for each profile) in terms of the average number of samples required to detect out-of-control conditions.
http://www.amstat-online.org/sections/qp/qprc/2006/JRC%20Presentations/Presentation_JRC_QPRC2006_Colosimo.pd
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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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