1,721,069 research outputs found
Alcune osservazioni sul Paris. Gr. 1182
No full textSpadaro Maria Dora. Alcune osservazioni sul Paris. Gr. 1182. In: Scriptorium, Tome 34 n°2, 1980. pp. 253-261
Nanoparticelle metalliche/di ossido: dalla sintesi e fine analisi strutturale alle proprietà magnetiche, catalitiche e plasmoniche
No full textLo sviluppo delle tecniche di crescita di nanoparticelle con forma e dimensione controllabili rappresenta uno dei principali aspetti della ricerca scientifica nel campo delle nanotecnologie.
Nell’ambito dei metodi di sintesi fisica delle nanoparticelle, la tecnica del ‘magnetron sputtering’ inserito in una sorgente di aggregazione a gas si è dimostrata essere molto promettente in termini di controllabilità di forma e dimensione delle nanoparticelle.
Nanoparticelle con una specifica forma e dimensione presentano particolari proprietà che possono essere sfruttate in diversi campi, quali ad esempio il magnetismo, la catalisi e la plasmonica. Al fine di poter controllare e studiare in dettaglio le proprietà delle nanoparticelle prodotte, è fondamentale caratterizzare questi sistemi, utilizzando tecniche con un alto grado di risoluzione; fra tutte la microscopia elettronica a trasmissione risulta essere la più adatta grazie alla possibilità di ottenere informazioni sulle nanoparticelle con un elevato grado di risoluzione spaziale.
Nel presente lavoro di tesi sono stati studiati tre diversi sistemi, così da dimostrare la versatilità della tecnica di crescita utilizzata.
Nanoparticelle di nickel, materiale ferromagnetico, circondate da un materiale antiferromagnetico, ossido di nickel o ossido di cobalto, sono state sintetizzate in modo da verificare la capacità di stabilizzare la magnetizzazione delle nanoparticelle di nickel, anche di piccola dimensione, sfruttando l’effetto di exchange bias che si realizza all’interfaccia tra il metallo e l’ossido. In particolare, a parità di diametro delle nanoparticelle di nickel, è stata investigata la dipendenza dell’exchange bias dallo spessore del guscio esterno di ossido e dall’anisotropia dello stesso. Dalle misure di microscopia elettronica a trasmissione ad alta risoluzione è stato possibile approfondire le caratteristiche dell’interfaccia metallo-ossido.
E’ stato effettuato uno studio dettagliato su nanoparticelle di diossido di cerio, un sistema che trova applicazione nei processi di catalisi grazie alla sua capacità di immagazzinare o rilasciare ossigeno in determinate condizioni ambientali. A tale scopo è importante definire come le sue proprietà siano legate al processo di sintesi, alla dimensione e alle superfici cristallografiche esposte. Nel presente lavoro è stata studiata l’influenza di questi parametri, osservando in particolare che la procedura di crescita e di ossidazione influenza significativamente la densità e la distribuzione dei siti di Ce3+ e dei difetti strutturali, che a loro volta influenzano la mobilità degli ioni di ossigeno.
Infine, sono state indagate le proprietà plasmoniche di nanoparticelle di argento e di nanoparticelle di argento ricoperte da un guscio di ossido di magnesio. L’aggregazione tra le diverse nanoparticelle e le interazioni con il substrato di silicio adoperato influenzano le proprietà plasmoniche del sistema. In particolare, nel caso delle nanoparticelle protette da uno strato di ossido di magnesio, si rileva che le proprietà plasmoniche del sistema si conservano nel tempo.The development of nanoparticles growth techniques with desired nanoparticle shape and size is an aspect of major interest in the scientific research on nanotechnology.
Among the nanoparticles physical synthesis techniques, the magnetron sputtering technique implemented in a gas aggregation source proves to be very promising in terms of tunability of shape and size of nanoparticles.
Nanoparticles with a specific shape and size show particular properties that can be exploited in several fields, such as magnetism, catalysis and plasmonics. In order to control and study in detail the properties of the produced nanoparticles, it is important to characterize these systems, using techniques with a high resolution degree; the transmission electron microscopy is an optimal technique thanks to the possibility to obtain information on nanoparticles with a high spatial resolution degree.
In the present thesis work three different systems have been studied, demonstrating in this way the high versatility of the used growth technique.
Nickel nanoparticles, a ferromagnetic material, surrounded by an antiferromagnetic material, nickel oxide or cobalt oxide, have been synthetized in order to verify the possibility of stabilizing the nickel nanoparticles magnetization, even at low dimension, exploiting the exchange bias effect that arises at the metal-oxide interface. In particular, at constant nickel nanoparticle size, the exchange bias dependence on the oxide shell thickness and anisotropy has been investigated. From the high resolution transmission electron microscopy measurements it has been possible to study the metal-oxide interface characteristics.
A detailed study on cerium dioxide nanoparticles was also carried out, because CeOx is a material that finds its application in catalysis processes thanks to its ability to store and release oxygen depending on the ambient conditions. For this aim it is important to understand how its properties are related to the growth process, to the size and to the exposed crystallographic planes. In the present thesis work it has been investigated the influence of these parameters, observing in particular that the synthesis procedure has a strong influence on the density and distribution of Ce3+ sites and of structural defects, which in turn determinate the mobility of the oxygen ions.
Finally, the plasmonic properties of silver nanoparticles and silver nanoparticles embedded in magnesium oxide have been investigated. The nanoparticles aggregation and their interaction with the substrate influence the system plasmonic properties. Furthermore, in case of silver nanoparticles embedded in magnesium oxide, it has been demonstrated that the plasmonic properties of the system are preserved in time
Low pressure bottom-up synthesis of metal@oxide and oxide nanoparticles: control of structure and functional properties
Full text linkExperimental activity on core@shell, metal@oxide, and oxide nanoparticles (NPs) grown with physical synthesis, and more specifically by low pressure gas aggregation sources (LPGAS) is reviewed, through a selection of examples encompassing some potential applications in nanotechnology. After an introduction to the applications of NPs, a brief description of the main characteristics of the growth process of clusters and NPs in LPGAS is given. Thereafter, some relevant case studies are reported:
Formation of native oxide shells around the metal cores in core@shell NPs.
Experimental efforts to obtain magnetic stabilization in magnetic core@shell NPs by controlling their structure and morphology.
Recent advancements in NP source design and new techniques of co-deposition, with relevant results in the realization of NPs with a greater variety of functionalities.
Recent results on reducible oxide NPs, with potentialities in nanocatalysis, energy storage, and other applications.
Although this list is far from being exhaustive, the aim of the authors is to provide the reader a descriptive glimpse into the physics behind the growth and studies of low pressure gas-phase synthesized NPs, with their ever-growing potentialities for the rational design of new functional materials
A literature review on Knowledge Management in SMEs
No full textPurpose - The aim of this paper is to provide a comprehensive research review on knowledge management in small and medium enterprises in order to identify gaps in the body of literature. By connecting these gaps to business future trends we identify several future research avenues for each research area.
Design/methodology/approach - The main objective of this literature review is to analyse the state-of-the-art of knowledge management in small and medium sized firms from the management perspective in order to identify relevant research gaps. The review has been carried out using Scopus and Web of Science Academic databases, and it has been conducted using the keyword "knowledge management" in combination with "SMEs" or "small firms" or "small business". Seventy papers in total were selected and studied in detail; they are all relevant scientific papers covering the topic of KM in SMEs from 2003 to 2013.
Originality/value - This methodology puts in evidence the current situation in knowledge management in SMEs' research field.
Practical implications - The outcomes of the application provide a valuable understanding of both knowledge management's best researched topic, which concerns the factors affecting knowledge management in SMEs and the knowledge management topics which are poorly investigated which concern KMSs adoption in SMEs, the barriers hindering their dissemination and the impact of KM on firm performance. From a practical perspective, the review concludes that the barriers connecting to KMSs implementation seem to belong more to cultural area rather than technological one and need to be exploited more in depth
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
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