1,720,957 research outputs found
Static, dynamic and impact properties of a high-performance flax-fiber composite
No full textAs environmental issues become increasingly relevant nowadays, the need to develop new materials entirely or partially based on renewable resources is one fundamental step to reduce the consumption of fossil fuels and CO2 emissions. In that sense, natural fiber composites might represent an environmentally sustainable alternative to conventional solutions such as glass and carbon fiber composites, standard today for many lightweight structural applications; however, solutions are several and diverse in terms of technological process, base materials, mechanical properties, and analysis of their behaviour, necessary for safe industrial use, is still lacking for most resin-fiber combinations. Consequently, this work presents a comprehensive material characterization of a flax-fiber reinforced composite material, analyzing both the static and dynamic mechanical performances, targeting future crashworthiness applications. In particular static tensile, compressive, flexural and shear properties were investigated, while low-speed indentation, high strain-rate tensile and ballistic tests were carried out to probe the dynamic and impact features
DISPOSITIVO DI POMPAGGIO E COMMUTAZIONE ED UN APPARATO DI SELEZIONE E SMISTAMENTO DI FLUIDI
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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
The glucosinolates and their health effects
No full textreservedI glucosinolati sono composti chimici che appartengono ad una famiglia di oltre 120 metaboliti secondari. Si trovano principalmente nelle Brassicaceae, ovvero una famiglia di piante commestibili di cui fanno parte i broccoli (Brassica oleracea var. italica), il cavolo (B. oleracea var. capitata f. alba), il cavolfiore (B. oleacera var. botrytis), la colza (B. napus), la senape (B. nigra) e il rafano orientale (Armoracia rusticana).
La composizione quantitativa e qualitativa dei glucosinolati varia a seconda della specie vegetale (es.: nella colza è predominante la sinigrina). Quando queste piante vengono consumate senza cottura, l’enzima mirosinasi presente nei tessuti idrolizza i glucosinolati in vari metaboliti secondari come gli isotiocianati ed i nitrili.
D’altra parte, quando le crucifere vengono consumate dopo cottura, la mirosinasi viene denaturata e i glucosinolati vengono in parte assorbiti a livello intestinale.
Questi composti conferiscono agli alimenti un gusto amaro e pungente; inoltre, queste sostanze hanno effetti antiossidanti e anticancerogeni. Di conseguenza, grazie alle loro caratteristiche sono stati condotti numerosi studi per conoscerne a pieno le potenzialità.
Questa Tesi ha lo scopo di illustrare le caratteristiche dei glucosinolati, i loro effetti sulla salute e gli aspetti più importanti legati alla lavorazione, alla conservazione e ai trattamenti termici.
Nella prima parte della Tesi viene illustrata la loro struttura chimica, la classificazione, in quali alimenti sono presenti e il loro metabolismo all’interno della pianta.
Successivamente viene trattato il complesso enzimatico mirosinasi in merito alla sua composizione, la sua funzione e il suo coinvolgimento nell’idrolisi dei glucosinolati.
In seguito, vengono descritti i composti che derivano dai glucosinolati, la loro importanza e la loro biodisponibilità. Viene posta una particolare attenzione al sulforafano, ovvero l’isotiocianato che deriva dalla glucorafanina, essendo il più studiato e tra i più importanti.
Inoltre, vengono trattati i fattori che influenzano la concentrazione e la degradazione dei glucosinolati all’interno degli alimenti.
Negli ultimi capitoli vengono esaminati i metodi analitici per la rilevazione di questi composti e le applicazioni di queste sostanze nell’industria alimentare.The glucosinolates are chemicals compounds that belong to a family of over 120 secondary metabolites. They are found in Brassicaceae, that is a family of edible plants of which they are a part broccoli (Brassica oleracea var. italica), cabbage (B. oleracea var. capitata f. alba), cauliflower (B. oleacera var. botrytis), rapeseed (B. napus), mustard (B. nigra) and eastern horseradish (Armoracia rusticana).
The composition quantitative and qualitative of glucosinolates varies according to the vegetable specie (ex: sinigrin is predominant in rapeseed). When these plants are consumed without cooking, myrosinase enzyme present in the tissues hydrolyzed glucosinolates in various secondary metabolites like isothiocyanates and nitriles. On the other hand, when cruciferous are consumed after cooking, myrosinase is denatured and glucosinolates are partially absorbed in the intestine.
These compounds give foods a bitter and pungent taste; moreover, these substances have antioxidant and anticarcinogenic effects. Consequently, thanks to their characteristics, numerous studies have been conducted to fully understand their potential.
This Thesis aims to illustrate the characteristics of glucosinolates, their effects on health and the most important aspects relate to their processing, storage, and heats treatments.
Subsequently the enzyme complex myrosinase is treated, about its composition, its function, on which movement in the hydrolysis of glucosinolates.
Afterwards, the compounds deriving from glucosinolates are described, their importance and their bioavailability. Particular attention is paid to sulforaphane, or the isothiocyanate that derives from glucoraphanin, being the most studied and among the most important.
Furthermore, the factors are treated so that their influence, their concentration, and their breakdown of glucosinolates inside foods.
In the later chapters the analytical methods are examined to quantify these compounds and the application of these substances in the food industry
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
Material characterization of a flax fiber reinforced composite for crashworthiness applications
Full text linkLAUREA MAGISTRALEI materiali compositi costituiti da fibra di origine naturale possono rappresentare una alternativa ecosostenibile rispetto alle soluzioni attualmente offerte dal mercato, come compositi in fibra di vetro e fibra di carbonio. Lo scopo di questa tesi è quello di eseguire una campagna di test su un materiale in fibra di lino, al fine di analizzarne le sue caratteristiche meccaniche, sia a livello statico che dinamico, valutando possibili utilizzi in campo crashworthiness.
I provini in composito utilizzati durante le prove sperimentali sono costituiti da fibre di lino ampliTex 300 twill 2/2 e resina epossidica IMP 503ZHT BC. Sebbene il materiale testato sia un tessuto, sono state eseguite prove indagando sia le prestazioni lungo la direzione 0° (ordito) che quelle lungo la direzione 90° (trama). Più in dettaglio, le proprietà di trazione, compressione, flessione e taglio sono state ottenute durante le prove statiche, mentre le proprietà dinamiche di indentazione, trazione e la risposta dinamica ad impatti ad alta velocità sono state analizzate al fine di approfondire le caratteristiche di resistenza agli urti.
Un modello numerico del materiale è stato realizzato mediante l'utilizzo del software LS-DYNA, allo scopo di effettuare una indagine preliminare valutando le scelte di modellazione più idonee. In particolare, la scelta del tipo di elementi numerici, insieme alla scelta della scheda del materiale, sono state eseguite in modo da approssimare al meglio sia le prestazioni meccaniche che il comportamento del materiale durante i fenomeni di deformazione.
I risultati sono stati discussi ampiamente, riportando anche i possibili miglioramenti attuabili al fine di migliorare le procedure di test. Infine, i possibili sviluppi futuri relativi ai materiali bio-compositi sono stati riportati.Natural fiber composites might represent an environmentally sustainable alternative to conventional solutions such as fiberglass and carbon fiber composites. The aim of this work is to perform a material characterization of flax-fiber reinforced composite material, so as to investigate both the static and dynamic mechanical performances for possible future crashworthiness applications.
The specimens employed during experimental tests are composed by ampliTex 300 twill 2/2 fibers and IMP 503ZHT BC epoxy resin. Although a fabric material was considered, static tests were performed in order to examine the properties in both warp direction at 0° and weft direction at 90°. In detail, tensile, compressive, flexural and shear properties were achieved from static tests, while indentation, ballistic impact and tensile dynamic responses were analyzed to probe the crashworthiness features.
In order to produce a representative numerical model of flax composite material, numerical activity was performed through the use of LS-DYNA software. The choice of suitable numerical elements and material card was accomplished so as to approximate both the mechanical performances and behaviour of the material.
Eventually, a wide discussion about the results, further improvements and the future development of bio-composites was performed
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