1,720,998 research outputs found
La rugosità: i parametri, le misure e l’influenza nella progettazione
No full textNegli ultimi anni lo studio dei parametri che caratterizzano la superficie di un componente meccanico ha subito un notevole impulso che si è tradotto sia nello sviluppo di nuove tecnologie di misura che nella creazione e standardizzazione di nuovi parametri descrittivi della rugosità. Parallelamente le lavorazioni meccaniche hanno consentito di raggiungere finiture superficiali impensabili solo fino a qualche decennio fa. Le motivazioni dell’attenzione a tale settore trovano molteplici giustificazioni; la principale è che lo stato superficiale condiziona fortemente il comportamento meccanico e strutturale degli oggetti. La rugosità, infatti, è direttamente correlata alla resistenza a fatica di un componente ed a tutti gli aspetti tribologici, quali il contatto, l’attrito le lubrificazione ecc., quindi ne influenza notevolmente le performance sotto diversi punti di vista. Si pensi che il 90% delle rotture in campo meccanico partono dalla superficie di un pezzo a causa di fenomeni di fatica, cricche, corrosione, usura superficiale, fenomeni di adesione e saldature di superfici ecc..
La rugosità è direttamente legata al processo produttivo ed alle tecnologie impiegate, quindi è possibile tarare le lavorazioni in funzione delle prestazioni desiderate oppure prevedere il comportamento di un componente dalla valutazione dei parametri che caratterizzano la sua superficie, ovvero dall’analisi della sua texture. In prima approssimazione si potrebbe dire che “meno rugoso è un componente, meglio è”, ma questo non sempre è vero; nella lubrificazione ad esempio è auspicabile una rugosità con determinate caratteristiche, per fornire alla superficie la capacità di trattenere il lubrificante. Anche i costi giocano un ruolo importante; ottenere superfici molto lisce richiede un costo che aumenta con legge esponenziale rispetto alla diminuzione della rugosità, e talvolta le creste della superficie, qualora ci siano dei componenti a contatto in moto relativo, sono asportate nella fase di rodaggio. Inoltre la rugosità finale, oltre che dal tipo di lavorazione, è fortemente influenzata da altri fattori connessi alcuni dei quali non facilmente prevedibili e controllabili, quali stato dell’utensile, velocità di lavorazione, profondità di lavorazione, eventuali vibrazioni ecc..
Come si può intuire il problema è complesso e coinvolge diverse discipline scientifiche. Nei seguenti paragrafi cercheremo di valutare tutti gli aspetti connessi, comprese le tecniche di misurazione ed analisi oggi disponibili
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
Shape optimization and tolerance analysis of dental implants by means of virtual models
Full text linkOsseointegrated implants are commonly used to support the partial or full structure for dental
replacement. Many practical techniques use a dental impression to extract information about the
positioning of implants in order to improve the precision of fitting. Due to different expertise,
geometrical misalignments and interference defects, some permanent deformations and misfits may
occur during components mounting and dismounting activities. These errors cannot be completely
avoided, but an accurate choice of the geometrical parameters, materials and procedures may reduce
the risk of system failure, local damages or harmful behaviour for the patient. For this purpose
computer aided design modelling and finite element analysis can be valid instruments to build virtual
simulation, have objective assessment of mechanical behaviour, perform tolerance allocation and
optimize shapes. In this paper some case studies integrating CAD and FEM for implant
biomechanical evaluation and shape optimization are discussed and innovative solutions have been
presented
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
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
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