1,720,961 research outputs found
FTIR and WAXS analysis of periodate oxycellulose: Evidence for a cluster mechanism of oxidation
No full textCellulose paper (Whatman no.1, chromatographic grade) was oxidised with 0.1 M sodium metaperiodate at different oxidation levels (0–11
days at room temperature), and analysed with FTIR before and after chemical treatments (reduction, further oxidation, alkaline hydrolysis). The
deconvolution of infrared data allowed us to verify that periodate oxidises cellulose in isolated domains, leading to the decrease of crystallinity, in
agreement with the results of wide angle X-ray scattering (WAXS). In particular, the alkaline hydrolysis (b-alkoxy fragmentation) followed by
mild acid treatment removed the oxidised groups and recovered most of the crystallinity of cellulose, as determined by the FTIR crystallinity index
Caratterizzazione chimico fisica di legni bagnati e confronto con legni archeologici
No full textQuesto lavoro presenta una metodica per la diagnostica e la caratterizzazione di legni
bagnati basata sull’uso di alcune tecniche di indagine chimico fisica: diffrazione dei
raggi X (XRD), analisi termica differenziale (DTA) e termogravimetrica (TG), calorimetria
a scansione differenziale (DSC), misure di colore, spettroscopia infrarossa in
trasformata di Fourier (FTIR), fluorescenza dei raggi X (XRF). Castagno (hardwood) e abete
(softwood) sono stati i tipi di legno presi in esame per verificare tale metodica. I campioni di
castagno e abete, tal quali e dopo l’inserimento di chiodi metallici, sono stati immersi in acqua
deionizzata e acqua di mare sintetica a temperatura ambiente e a 40°C per effettuare una impregnazione
preliminare.
Il periodo di immersione è durato per tempi variabili ed al minimo per otto settimane. I chiodi
usati sono stati di ferro e rame, metalli molto diffusi in antichità. La penetrazione degli ioni
metallici è stata controllata tramite misure di fluorescenza dei raggi X.
Ogni settimana sono state eseguite misure di colore e di peso sui campioni e si è provveduto
alla sostituzione dell’acqua con altra fresca.
Dopo l’immersione, tramite operazioni di segatura e macinatura sono stati ottenuti campioni
polverizzati. La macinatura provoca, come noto, una diminuzione del grado di cristallinità della
cellulosa nei legni, ma non vi è alcun dato quantitativo circa tale effetto, che ci proponiamo
di valutare tramite un proseguimento della nostra ricerca. Lamacinatura è, comunque, necessaria
per ottenere campioni omogenei e misure riproducibili.
Le analisi diffrattometriche, termiche e calorimetriche hanno permesso di mettere in evidenza
l’effetto di degrado provocato sulle due specie lignee da parte dell’acqua di mare e dei metalli.
Per studiare il deterioramento del legno si è proceduto alla misura del grado di cristallinità dei
campioni tramite XRD tenendo in considerazione il picco principale della cellulosa (002) che
cade a circa 22,4° di 2θ. Sui legni archeologici è stata ripetuta la stessa serie di indagini e i risultati
sono stati confrontati con quelli ottenuti per i legni campione. Inoltre la spettroscopia infrarossa
in trasformata di Fourier (FTIR) è stata utilizzata quale ulteriore convalida dei confronti effettuati.
Infine, la sequenza delle reazioni di decomposizione termica è stata valutata tramite una serie
di prove condotte eseguendo combustioni parziali di campioni di abete a temperature via via
crescenti, comprese tra 225° e 350°C, in ambiente ossidante. I prodotti sono stati caratterizzati
mediante misure di perdita in peso e di cristallinità, che hanno permesso di individuare le principali
frazioni, amorfe o cristalline, coinvolte nei processi ossidativi
Caratterizzazione di legni antichi provenienti da Tantura (Israele) e Pisa e paragone con essenze di legno moderno
No full text
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
Degradation Products from Naturally Aged Paper Leaves of a 16th-Century-Printed Book: A Spectrochemical Study
No full textIn this work, we present a wide-range spectrochemical analysis of the degradation products from naturally aged paper. The samples obtained from wash waters used during the de-acidification treatment of leaves from a 16th-century-printed book were analysed through NMR, IR, Raman UV/Vis, EPR and X-ray fluorescence (XRF) spectroscopy and HPLC-MS and inductively coupled plasma (ICP) analysis. By these methods we also studied some of the previous samples treated by acidification (sample AP) and catalytic hydrogenation (sample HP). Crossing all the data, we obtained precise indications about the main functional groups occurring on the degraded, water-soluble cellulose oligomers. These results point out that the chromophores responsible for browning are conjugated carbonyl and carboxyl compounds. As a whole, we show that the analysis of wash waters, used in the usual conservation treatments of paper de-acidification, gives much valuable information about both the conservation state of the book and the degradation reactions occurring on the leaves, due to the huge amount of cellulose by-products contained in the samples. We propose therefore this procedure as a new very convenient general method to obtain precious and normally unavailable information on the cellulose degradation by-products from naturally aged paper. Shining light on paper browning: Cellulose degradation products have been extracted from leaves of a 16th-Century-printed book. Broad spectrochemical characterisation led to the identification of the main chromophoric groups (see figure)
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