1,720,999 research outputs found
Elastomēra / nanografīta kompozītu sensorelementu sistēmu pjezorezistīvās īpašības
No full textPromocijas darba pētījums veltīts pjezorezistīvu poliizoprēna nanografīta kompozītu fizikālo īpašību izpētei un viscaur superelastīgu spiediena sensoru sistēmu izstrādei.
Darbā salīdzināta dažādu oglekļa alotropisko veidu un koncentrāciju ietekme uz kompozītu pjezorezistīvo jutību. Noteikta ultraskaņas apstrādes ietekme uz termiski eksfoliēta grafīta daļiņu ģeometriskajiem izmēriem un izgatavotiem kompozītu sastāviem noteikta pildvielas ģeometrisko izmēru ietekme uz pjezorezistīvo efektu.
Noteikti pjezorezistīvie efekti pie dažādām apkārtējās vides temperatūrām, kā arī noteikta elektriskās pretestības atkarība no temperatūras dažādu oglekļa alotropisko veidu poliizoprēna kompozītiem. Iegūtie rezultāti kvantitatīvi analizēti ar literatūrā pieejamiem matemātiskiem modeļiem, kā arī izstrādāts jauns matemātisks modelis, kas apraksta kompozītu elektriskās pretestības pieaugumu palielinoties temperatūrai, balstoties uz tuneļstrāvu samazināšanos un elektrovadošo kanālu trūkšanu matricas termiskās izplešanās rezultātā.
Izgatavotas dažādu ģeometrisko izmēru viscaur superelatīgu spiediena spiediena sensoru sistēmas, kuros kā izejmateriāls izmantots AS „Baltijas Gumijas Fabrika” izgatavotie poliizoprēna nanooglekļa kompozīti. Kompozīta sastāvam, kas izmantots spiedienu sensoru sistēmās kā jutīgais elements noteikta slogošanas frekvences ietekme uz pjezorezistīvo jutību
Improved Piezoresistive Sensitivity in Polyisoprene Nanostructured Carbon Allotrope Hybrid Composites
No full textIn previous studies we have reported that piezoresistive effect in polyisoprene electrically conductive filler composites is highly dependent on filler concentrations, dispersion efficiency and filler geometry. In this study polyisoprene nanostructured carbon allotrope hybrid composites have been elaborated using various ratios and concentrations of multiwall carbon nanotubes (outer diameter 50-80nm, length 0,5-2 μm, surface area 40 m2/g) and electrically extra conductive high structure carbon blacks (average particle diameter 30nmm, surface area 950 m2/g). The piezoresistive effects of the hybrid composites have been tested under 1 and 10 atmospheres of external pressure in cyclic loading/unloading regime using Zwick/Roell Z2.5 universal material testing machine, coupled and synchronized with Agilent A34970A digital multimeter/multiplexer. It has been observed, that composite with certain filler concentrations and ratios has a significantly higher piezoresistive sensitivity compared to polyisoprene carbon nanotube composites or polyisoprene carbon black composites. Based on these results the impact of the synenergy of
both carbon nanotubes and carbon black at different concentrations on the polyisoprene nanostructured carbon allotrope hybrid composites piezoresistive properties have been evaluated and improved piezoresistive sensitivity is discussed
Piezoresistivity and Electrical Resistance Relaxation of Polyisoprene Nanostructured Carbon Allotrope Hybrid Composites
No full textPolymer conductive filler composites are believed to be promising materials for flexible force
sensor manufacture. Polyisoprene various carbon allotrope hybrid composites were made and their
piezoresistive properties depending on the two filler concentrations and their ratio have been
determined. Electrical resistance relaxations of hybrid composites at constant pressure in room
temperature were determined as well. Experimental data of resistance relaxation was analyzed and
fitted similarly to stress relaxation of polymers at constant pressure
Piezoresistivity and Electrical Resistance Relaxation of Polyisoprene Nanostructured Carbon Allotrope Hybrid Composites
No full textPolymer conductive filler composites are believed to be promising materials for flexible force sensor manufacture. Polyisoprene/various carbon allotrope hybrid composites were made and their piezoresistive properties depending on the two type’s filler concentration and their ratio have been determined. Electrical resistance relaxations of hybrid composites at constant pressure in room temperature were determined as well. Experimental data of resistance relaxation was analysed and fitted similarly to stress relaxation of polymers at constant pressure
Polymer/Nanographite Composites for Mechanical Impact Sensing
No full textThe purpose of this chapter is to give a review of the polymer/nanographite composite (PNGC) materials specially developed for applications in mechanical strain and pressure sensors that can be used for design of flexible sensing systems. Our recent achievements in design, processing and investigation of physical prop-erties of elastomer and nanostructured carbon composites as prospective materials for mentioned sensors are also presented. In the beginning theoretical principles of tunneling percolation theory and piezoresistivity have been described. We discuss the most suitable polymer matrices and electrically conductive nanographite fillers for sensitive PNGC. Preparation methods of mechanically sensitive PNGC have been considered. Different particularly produced and tested polymer/nanographite composites are overhauled and possible advantages and disadvantages of PNGC in different possible applications are analyzed
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
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