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Chatter detection in linear time periodic systems with stiffness variation
No full textLAUREA MAGISTRALEIl chatter rigenerativo è una vibrazione autoeccitata causata dall'interazione utensile-pezzo durante la lavorazione. Può causare condizioni di taglio instabili con effetti dannosi che causano perdita di produttività e qualità, costi aggiuntivi, problemi di sicurezza, ecc. Per far fronte al chatter, in letteratura sono stati impiegati approcci di variazione di rigidità (SV) con diversi meccanismi di attuazione per la soppressione attiva del chatter nelle operazioni di tornitura, alesatura e fresatura. Durante la SV, la modulazione continua della rigidità altera la dinamica della macchina utensile introducendo caratteristiche lineari tempo-periodiche (LTP). Tuttavia, la maggior parte degli studi sul chatter in letteratura si basa su un'ipotesi di sistema lineare tempo-invariante (LTI) semplificata. Pertanto, è necessario un algoritmo generalizzato che copra sia le caratteristiche del sistema LTI che LTP per un ambiente industriale in continua evoluzione per una determinazione affidabile dello stato di taglio e il rilevamento del chatter all'inizio. In questo lavoro, un approccio di filtro adattivo già collaudato viene esteso alla dinamica LTP in termini di formazione di bande laterali attorno a frequenze periodiche e l'algoritmo di rilevamento del chatter basato sul filtro adattivo viene ampliato includendo l'estensione LTP e SV. I parametri del filtro vengono studiati per il segnale di accelerazione raccolto da un'operazione di fresatura di un pezzo ingombrante e confrontati con lo studio di riferimento, in cui viene proposto l'algoritmo del filtro adattivo. Dopo la separazione, il rapporto di varianza (VR) tra il segnale non periodico filtrato e il segnale originale viene calcolato come indicatore di chatter e le sue prestazioni vengono studiate per tre stati di taglio (stabile, chatter, soppressione del chatter con SV) a diversi casi di velocità del mandrino. Infine, le informazioni sulla frequenza vengono ottenute con i metodi del dominio tempo-frequenza (TF) per trovare la frequenza di chatter dominante. Il segnale non periodico filtrato viene scomposto con i metodi di decomposizione della modalità empirica (EMD), ensemble-EMD (EEMD) e decomposizione della modalità variazionale (VMD). Dopo la loro valutazione, le prestazioni di decomposizione di VMD in termini di localizzazione TF per le modalità sensibili con informazioni ricche di chatter risultano superiori alle altre. Grazie al filtro adattivo esteso, le informazioni provenienti da un'operazione di taglio possono essere elaborate per ogni lunghezza di dati di 0,5 secondi calcolata per l'indice di chatter ogni 0,3 secondi. Ciò consente di localizzare sia le informazioni di tempo che di frequenza in modo robusto per una determinazione tempestiva dello stato di taglio con e senza SV.Regenerative chatter is a self-excited vibration caused by tool-workpiece interaction in machining. It can result in unstable cutting conditions with detrimental effects causing loss of productivity and quality, additional costs, safety concerns, etc. To cope with chatter, stiffness variation (SV) approaches with different actuation mechanisms have been employed in the literature for active suppression of chatter in turning, boring, and milling operations. During SV, the continuous modulation in stiffness alters the machine tool dynamics by introducing linear time-periodic (LTP) characteristics. Nevertheless, most of the chatter studies in the literature are based on a simplified linear time-invariant (LTI) system assumption. Therefore, a generalized algorithm covering both LTI and LTP system features for an ever-changing industrial environment is needed for reliable cutting state determination and chatter detection on the onset. In this work, an already proven adaptive filter approach is extended to LTP dynamics in terms of sideband formation around periodic frequencies, and the chatter detection algorithm based on the adaptive filter is enlarged by including LTP extension and SV. The filter parameters are investigated for the collected acceleration signal from a milling operation of a bulky workpiece and compared with the reference study, where the adaptive filter algorithm is proposed. After the separation, the variance ratio (VR) between the filtered non-periodic signal and the original signal is computed as a chatter indicator, and its performance is investigated for three cutting states (stable, chatter, chatter suppression with SV) at different spindle speed cases. Lastly, frequency information is obtained with the time-frequency (TF) domain methods to find the dominant chatter frequency. The filtered non-periodic signal is decomposed with empirical mode decomposition (EMD), ensemble-EMD (EEMD), and variational mode decomposition (VMD) methods. After their evaluation, the decomposition performance of VMD in terms of TF localization for the sensitive modes with chatter-rich information is found to be superior to the others. Thanks to the extended adaptive filter, the information coming from a cutting operation can be processed for each 0.5-second length of data computed for the chatter index at every 0.3 seconds. This makes it possible to localize both time and frequency information in a robust way for timely determination of the cutting state with and without SV
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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