1,720,978 research outputs found
Apparecchiatura e metodo per la stampa tridimensionale di materiali compositi a fibra continua
No full textL’invenzione è una stampante 3D per la realizzazione di oggetti tridimensionali in materiale composito a fibra continua. L’apparecchiatura è costituita da: - Un sistema di rulli che alimentano la fibra all’interno della stazione di impregnazione; - una testa di alimentazione, che comprende un dispositivo di polimerizzazione (per es. un LED a luce UV o laser o una fonte di emissione termica), posizionato in corrispondenza dell’ugello; - uno strumento di troncatura (per es. una coppia di lame mobili) del materiale composito configurato per interrompere l’alimentazione del materiale in uscita dall'ugello; - una macchina a controllo numerico su almeno 3 assi che ha il compito di movimentare la testa di alimentazione del materiale. La stazione di impregnazione consiste in uno o più bacini di contenimento della resina, all'interno della quale la fibra è annegata per un tempo di permanenza che dipende dalla viscosità della matrice e dalla struttura della fibra. Il bacino di contenimento può anche essere costituito da una tramoggia solidale alla testa di alimentazione. Può essere impiegata una qualsiasi tipologia di fibra (di vetro, di carbonio, kevlar, basalto ecc....) e matrice (resina allo stato liquido, in particolare una resina termoindurente, ad es. epossidica, acrilica, poliestere ecc....)
UV-assisted three-dimensional printing of polymer nanocomposites based on inorganic fillers
Full text linkIn this work, nanocomposites based on a UV-curable polymeric resin and different inorganic fillers were developed for use in UV-assisted three-dimensional (UV-3D) printing. This technology consists in the additive multilayer deposition of a UV-curable resin for the fabrication of 3D macro structures and microstructures of arbitrary shapes. A systematic investigation on the effect of filler concentration on the rheological properties of the polymer-based nanocomposites was performed. In particular, the rheological characterization of these nanocomposites allowed to identify the optimal printability parameters for these systems based on the shear rate of the materials at the extrusion nozzle. In addition, photocalorimetric measurements were used to assess the effect of the presence of the inorganic fillers on the thermodynamics and kinetics of the photocuring process of the resins. By direct deposition of homogeneous solvent-free nanocomposite dispersions of different fillers in a UV-curable polymeric resin, the effect of UV-3D printing direction, fill density, and fill pattern on the mechanical properties of UV-3D printed specimens was investigated by means of uniaxial tensile tests. Finally, examples of 3D macroarchitectures and microarchitectures, spanning features, and planar transparent structures directly formed upon UV-3D printing of such nanocomposite dispersions were reproducibly obtained and demonstrated, clearly highlighting the suitability of these nanocomposite formulations for advanced UV-3D printing applications. POLYM. COMPOS., 38:1662â1670, 2017. © 2015 Society of Plastics Engineers
Electroless plating of PLA and PETG for 3D printed flexible substrates
Full text linkThe NiP and Cu electroless metallization of 3D printed polymers is
presented. The plating process is tested on suitable samples, which
reproduce the printing morphologies used in the 3d printing of
objects. An alkaline etching is used for both the polymers in order
to modify the surface properties and enhance the adhesion and
uniformity of the metallic coating. For the activation of the surface
a tin free process involving an immersion in palladium and
subsequent reduction to form metallic nuclei is employed. The Cu
and NiP bath are selected to operate in temperature ranges
comparable to the glass transition temperatures of the polymers.
Adherent and uniform layers of NiP (3-4 % P wt.) and Cu can be
easily obtained for esthetic and functional applications
Electroless plating of NiP and Cu on polylactic acid and polyethylene terephthalate glycol-modified for 3D printed flexible substrates
Full text linkElectroless nickel and copper metallization of 3Dprinted polymers like polylactic acid and polyethylene terephthalate glycol modified is presented. The plating process is tested on suitable samples, which reproduce the characteristic morphologies used in 3D printing of objects. An alkaline etching is used for both polymers in order to modify the surface properties and to enhance the adhesion and uniformity of the metallic coating. In the case of polylactic acid, a plasma treatment is applied as well to further improve adhesion of the metallic coating. For the activation of the surface, a tin free process involving an immersion in a palladium solution and subsequent reduction to form metallic nuclei is employed. Electrolytes are formulated and selected to operate in temperature ranges comparable with the glass transition temperatures of the polymers. Adherent and uniform layers of NiP (3-4% P wt) and Cu can be easily obtained for esthetic and functional applications, also on flexible substrates
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
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
- …
