1,720,958 research outputs found
Design of a metamaterial-based hand held vibration probe
No full textLe misure vibrazionali sono un punto di riferimento nella dinamica strutturale. Lo stesso vale anche per la diagnostica dei guasti e la valutazione della qualità del prodotto in vari campi dell'industria, dalle linee di produzione dei componenti ai prodotti finiti. Queste misure sono solitamente eseguite utilizzando accelerometri piezoelettrici collegati alla struttura in esame. Il collegamento è solitamente realizzato tramite adesivi o cera d'api, magneti o perni filettati. Tuttavia, il processo di installazione di questi sensori può richiedere molto tempo e, in alcuni casi, può essere irreversibile o addirittura non consentito. Le sonde vibrazionali di tipo hand-held sono state ampiamente utilizzate in passato, anche se le loro prestazioni (ad es. gamma di frequenze di lavoro e accuratezza complessiva) risultano inferiori rispetto alle installazioni fisse. Tuttavia, la diffusione dei robot nell'ambito dell'industria 4.0, caratterizzata dall'obiettivo di produzione a zero difetti, ha motivato un nuovo interesse per questo tipo di soluzione.
Le sonde di misura vibrazionali tipo hand-held sono costituite da componenti che devono garantirne la linearità entro un determinato intervallo di frequenza e il contatto costante con la struttura in prova. Inoltre, le vibrazioni spurie, dovute alla manipolazione da parte di un operatore umano o di un robot, devono essere evitate introducendo un elemento di disaccoppiamento. Normalmente, vengono impiegati materiali convenzionali come la gomma e il silicone, per via del loro comportamento viscoelastico. Tuttavia, questi materiali possono subire modifiche al loro comportamento dinamico quando soggetti a condizioni ambientali diverse. Lo scopo di questa tesi è dimostrare il vantaggio nell'adottare metastrutture come elementi di disaccoppiamento nelle sonde vibrazionali di tipo hand-held. La metastruttura sviluppata si basa su una ripetizione periodica di celle unitarie caratterizzate da una forte separazione modale. Ne consegue, quindi, un ampio intervallo di frequenze di funzionamento.Vibrational measurements are a landmark in structural dynamics. This is true also for fault diagnosis and product quality assessment in various fields of industry, from production lines of components to finite products. These measurements are usually performed using piezoelectric accelerometers attached to the structure under investigation. The connection is usually made using adhesive or bees-wax, magnets or threaded pins. However, the process of installing these sensors can be time-consuming and, in some cases, irreversible or even not allowed. Hand-held vibration probes were widely used in the past, even though their performances (i.e. working frequency range and overall accuracy) were lower compared to fixed installations. However, the spread of robots in the framework of industry 4.0, characterized by the zero defect manufacturing target, caused a new interest in this solution.
Hand-held vibration measurements probes are made of components that must guarantee linearity within certain frequency range as well as constant contact with the structure being tested. Furthermore, spurious vibrations, due to the handling by a human operator or a robot, need to be avoided introducing a decoupling element. Normally, conventional materials, like rubber and silicon, are exploited, taking advantage of their viscoelastic behavior. However, these materials may undergo changing on their dynamic behavior when subject to different environmental conditions. The aim of this thesis is to demonstrate de advantage of adopting metastructures as decoupling elements in hand-held probes. The design of the metastructure developed is based on a periodic repetition of unit cells characterized by a strong mode separation and, thus, a wide frequency bandgap
Static and Dynamic Characterization of a Vibration Decoupling Element Based on a Metamaterial Structure
No full textTime stability of the dynamic behaviour of a 3D-printed airless wheel by stereolithography
Get PDFn this paper, the dynamic behavior of an airless wheel made by additive manufacturing is investigated. A lattice geometry is chosen as the cyclic pattern from which the wheel is built. Initially, a linear numerical model is used to preliminarily assess resonance frequency and mode shapes of the wheel. Afterwards, specimens were tested twice, in August 2020 and after six months, highlighting a relevant frequency and damping shift in the vibrational response. To better understand the reason behind the change over time in the wheel dynamic behavior, dedicated structural dynamics tests at varying temperature and humidity set points were performed in an environmental chamber, consisting in measuring the wheel vibrational response when subjected to temperature and humidity variation
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
Validation of an energy-based material selection algorithm for fruit bruising and impact damage reduction in olive trunk shaker harvesting
Get PDFThis study validates an algorithm that evaluates the performance of four different materials for use in mechanical harvesting of table olives, which are particularly susceptible to damage. Through a series of olive drop tests, the energies involved during the impact are analysed, and the results are compared with visual damage assessments conducted by agronomists. The best performing material demonstrates the highest cushioning material and the lowest bounce heigh
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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