1,720,989 research outputs found
Misure meccaniche e termiche. Grandezze tempo-varianti
No full textIl nuovo ordinamento, le nuove offerte, la nuova e variegata organizzazione didattica (corsi trimestrali, semestrali ed annuali) hanno portato ad una riformulazione dei percorsi formativi, dei programmi e dei contenuti delle varie discipline. In particolare, nel settore delle Misure Meccaniche e Termiche, area trasversale ed appartenente a corsi di laurea diversi, si sono dovute aggiornare le metodologie didattiche e revisionare i programmi per fornire risposte rapide, chiare e significative.
I contenuti didattici tradizionali della materia, essenzialmente rivolti alle applicazioni sperimentali, comprendono una prima parte teorica, di carattere generale ed una seconda operativa rivolta all’analisi dei sistemi di misura delle grandezze meccaniche e termiche. Il tutto gestito in forma unitaria, consolidatasi nel tempo e, storicamente, strutturata in un ciclo didattico annuale.
L’esperienza, maturata in questi ultimi anni, ha guidato gli autori a considerare una nuova suddivisione del contenuto della materia con l’intento di fornire due prodotti didattici autonomi, si spera efficaci e, per quanto possibile, esaurienti, come richiesto dai corsi di studio.
Contrariamente a quanto avviene normalmente, questa prima editazione dell’opera interessa il modulo più a valle; tale scelta è stata voluta e condotta a conferma, sia dell’autonomia delle due proposte, sia dell’importanza che esse possono rivestire individualmente. Lo spunto è nato revisionando una prima bozza degli appunti delle lezioni svolte nelle rispettive sedi dagli autori, con l’obiettivo di unificazione dei programmi.
Il risultato di tale lavoro ha portato alla stesura di un testo a livello universitario che non ambisce ad essere dotto ed omnicomprensivo ma che manifesta la peculiarità di essere concepito soprattutto per finalità didattiche.
A tale proposito si sono volute, non solo evidenziare le ipotesi che sono sovente alla base dei modelli presentati, ma è stato anche compiuto uno sforzo suppletivo per cercare di dimostrare ogni affermazione fatta. Il numero delle espressioni matematiche e dei passaggi si è dilatato, ma a beneficio di una maggiore completezza degli argomenti.
Si è dato ampio spazio ai diagrammi, agli esempi ed alle dimostrazioni di laboratorio per fornire concretezza ai concetti esposti, la cui chiarezza e comprensione, nell’intento degli autori, è stata ricercata costantemente in tutta l’opera.
Ai fini di facilitare l’interfacciamento dei lettori con il testo si è implementato il volume con numerose figure, molte delle quali a colori.
E’convinzione dei sottoscritti che la comprensione dei fenomeni, soprattutto se complessi, possa essere facilitata dalla chiarezza di esposizione dei concetti ma che un approccio positivo alla disciplina possa solo scaturire dalle motivazioni, dalla trama didattica e dalla finalizzazione operativa degli argomenti trattati. Se anche un piccolo passo è stato compiuto in questa direzione, a vantaggio degli allievi e della società, la fatica ed il tempo impiegati per realizzare questa prima opera non sarà stata inutile
Experimental investigation on buoyancy-induced convection in aluminum metal foams|Étude expérimentale sur la convection provoquée par poussée hydrostatique dans les mousses métalliques en aluminium
No full textIn this work, we studied the thermal performance of aluminum metal foams in buoyancy-induced convection. We investigated the effect of heat transfer performance on metal foam fins heated from below due to the use of different aspect-ratio. The samples used in the trial were characterized by a square base of 50 mm length and seven different heights, which ranged from 10 mm to 150 mm. The samples were made of aluminum metal foam characterized by 5 PPI and a porosity of 0.95. The analysis showed that the heat dissipation increased asymptotically with the height of the sample. The results also showed that the Darcy characteristic length should be not correlated to the sample height. A novel empirical correlation is proposed for the computation of Nusselt number as a function of Rayleigh and Darcy numbers, and a shape function η
Three‐dimensional assessment of upper limb proprioception via a wearable exoskeleton
No full textProprioception—the sense of body segment’s position and movement—plays a crucial role in human motor control, integrating the sensory information necessary for the correct execution of daily life activities. Despite scientific evidence recognizes that several neurological diseases hamper proprioceptive encoding with consequent inability to correctly perform movements, proprioceptive assessment in clinical settings is still limited to standard scales. Literature on physiology of upper limb’s proprioception is mainly focused on experimental approaches involving planar setups, while the present work provides a novel paradigm for assessing proprioception during single—and multi‐joint matching tasks in a three‐dimensional workspace. To such extent, a six‐degrees of freedom exoskeleton, ALEx‐RS (Arm Light Exoskeleton Rehab Station), was used to evaluate 18 healthy subjects’ abilities in matching proprioceptive targets during combined single and multi‐joint arm’s movements: shoulder abduction/adduction, shoulder flexion/extension, and elbow flexion/extension. Results provided evidence that proprioceptive abilities depend on the number of joints simultaneously involved in the task and on their anatomical location, since muscle spindles work along their preferred direction, modulating the streaming of sensory information accordingly. These findings suggest solutions for clinical sensorimotor evaluation after neurological disease, where assessing proprioceptive deficits can improve the recovery path and complement the rehabilitation outcomes
Wavelet analysis ultra-thin metasurface for hypersonic flow control
No full textMetasurfaces are one of the new frontier of material science and engineering, finding widespread applications in a number of fields, including acoustics and aeroacoustics. In the present paper we propose a novel metasurface specifically fabricated for the hypersonic flow transition control, together with a new strategy for metasurface characterization in the ultrasonic regime. Instead of a conventional porous layer, the metasurface here presented consists in a flat plate with a set of regularly distributed sharp slots. We experimentally observed that such a geometry significantly reduces the wall reflection coefficient, which is known to play a fundamental role in the boundary layer transition phenomenon. Numerical simulations led us to interpret the incident wave scattering as the underlying mechanism related to the observed reflection coefficient reduction. The metasurface characterization has been carried out by comparing the conventional reflection coefficient in the Fourier domain with an innovative wavelet transform-based strategy. As an overall result, the surface geometry here proposed has been shown to offer a twofold advantage: i) it is more effective in ultrasonic incident wave control with respect to conventional porous layers, ii) it needs less manufacturing time, a primary requirement of this type of technology. More interesting, we have put in evidence how a multiresolution approach, like that here proposed, can be highly promising as characterization tool for further metasurfaces with a more complex and multi-scale geometry, being wavelets able to capture the multiscale behaviour of the reflected wave, overcoming the well-known limits of Fourier-based strategies of data analysis
A markerless system for gait analysis based on OpenPose library
No full textThe paper reports the performance of a low-cost markerless system for 3D human motion detection and tracking, consisting of the open-source library OpenPose, two webcams and a linear triangulation algorithm. OpenPose is able to identify anatomical landmarks with a commercial webcam, using Convolutional Neural Networks trained on data obtained from monocular images. When images from at least two different points of view are processed by OpenPose, 3D kinematic and spatiotemporal data of human gait can be also computed and assessed. Despite its potential, the accuracy of such a system in the estimation of kinematic parameters of human gait is currently unknown. With the aim to estimate OpenPose accuracy in 3D lower limb joint angle measurement during gait, two synchronized videos of a healthy subject were acquired, with two webcams, in a walking session on a treadmill at comfortable speed. 2-dimensional joint centers coordinates were assessed by OpenPose, and computed in 3D by triangulation algorithm. The resulting angular kinematics was, then, compared with inertial sensors outputs. Results showed that the system was generally able to track lower limbs motion, producing angular traces representative of normal gait similar to the ones computed by IMUs. However, OpenPose approach showed inaccuracy, mostly in the computation of maxima and minima joint angles, reaching error values up to 9.9°
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
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
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