1,721,052 research outputs found
Archeologia preistorica e analisi del DNA mitocondriale nella questione del popolamento delle Americhe
No full textNative Americans belong to one of the few extant human groups whose ancestors entered a vast uninhabited area and then apparently remained isolated from other human contacts for thousands of years. They are descendants of peoples, who, after their expansion to the Americas, underwent through a rapid process of tribal radiation and isolation, localised genetic and cultural differentiation, and adaptation to a variety of different environmental conditions. Although there is consensus that the provenance of the ancestral Native Americans was North-Eastern Asia, the diversity of opinions on the time of the earliest human entry into the Americas, and the number of migratory events has often been accompanied by an acrimonious debate. As a broad generalization, the discussants of the times of human colonization of the New World can be divided into two camps, one favoring an "early" entry [more than approximately 30.000 years before present (YBP)] , the other favoring a "late" arrival (less than approximately 13,000 YBP). As for the number of migratory events, the debate is between those who favor a single migration from Asia, followed by an "in situ" genetic and cultural differentiation, and those who favour multiple migration hypotheses. In this paper, we summarize the data concerning these issues that we have recently obtained through studies affering to two different and interrelated disciplines: molecular genetics and pre-historical archaeology. These data are strongly supportive of an "early" human colonization of the Americas, and indicate that the genetic and cultural heterogeneity of modern Native Americans is partially attributable to multiple migrations from Asia
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
Sintesi di nuovi polimeri semiconduttori a bassa gap per celle fotovoltaiche organiche
Full text linkIl gruppo di ricerca dell’Università di Modena e Reggio Emilia si è occupato della sintesi e della caratterizzazione di nuovi materiali polimerici da utilizzarsi come substrati attivi in prototipi di celle fotovoltaiche organiche al fine di valutarne l’efficienza. Sono stati sintetizzati tre nuovi polimeri, solubili in cloroformio, formati da unità tienotiofeniche o bitiofeniche alternate a unità benzobitiofeniche da assemblare in celle del tipo BHJ (Bulk HeteroJunction) con unità di [60] e [70]PCMB (rispettivamente l’estere metilico dell’acido [6,6]-phenyl-C61-butirrico e l’estere metilico dell’acido [6,6]-phenyl-C71-butirrico). Sono stati messi a punto i diversi step sintetici necessari all’ottenimento dei comonomeri. Successivamente i polimeri sono stati ottenuti tramite accoppiamento di Stille tra un dibromoderivato e un distannil derivato dei comonomeri sintetizzati.
La caratterizzazione, atta a valutare la struttura e la lunghezza delle catene polimeriche, è stata eseguita tramite tecniche di risonanza magnetica nucleare mono- e bi-dimensionali omo- ed etero-nucleari, tramite spettroscopia infrarossa a trasformata di Fourier e ultravioletta-visibile-vicino infrarosso e tramite cromatografia a permeazione di gel. Le caratteristiche di assorbimento nel visibile e nel vicino infrarosso indicano che l’approccio seguito per la pianificazione dei comonomeri e dei polimeri ha effettivamente portato il gruppo di ricerca dell’Università di Modena e Reggio Emilia a sintetizzare polimeri a basso gap HOMO-LUMO. Parallelamente l’ENEA si è occupata di testare i polimeri semiconduttori, sintetizzati dall’università durante la precedente annualità dell’accordo di programma MSE-ENEA, come materiali attivi in celle fotovoltaiche polimeriche aventi la struttura Substrato/ITO/PEDOT:PSS/Polimero:Fullerene/Ca/Al. Sono state condotte numerose prove al fine di ottimizzare il processo di realizzazione: infatti è noto dalla letteratura che ogni polimero necessità di ricette di deposizione personalizzate al fine di massimizzare le prestazioni del dispositivo finale. Le migliori efficienze raggiunte, ottenute utilizzando un copolimero delle unità benzoditiofene e bitiofene, sono state del 2.3%, valore interessante considerato il numero limitato di prove che si può fare su questi materiali che vengono sintetizzati su scala di laboratorio e quindi in quantità esigue
Anti-urokinase monoclonal antibody, matrix bearing it, test method, biochemical test kits which use it.
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