1,721,019 research outputs found
Numerical investigation of efficiency loss mechanisms in light emitting diodes and determination of radiative and non-radiative lifetimes for infrared optoelectronics
Full text linkThe year 2015 was defined the international year of light and light-based technologies. This title did not come unexpected, the research activity in solid-state lighting intensified during the last decade striving to improve solid-state light sources in terms of power consumption and fabrication costs. Emerging technologies are going to improve and amplify the scope of applicability of current solid-state lighting technology. This work would like to give a contribution to scientific research in solid-state lighting on two fronts. First, by contributing to the determination of the optical properties of germanium and germanium-tin alloy and second, by searching for remedies to the temperature dependent efficiency loss in GaN/InGaN based blue light emitting diodes. On these premises, this work has been splitted in two parts. In part one, the Auger recombination properties of germanium and radiative and Auger recombination properties for germanium-tin alloy have been calculated. In case of germanium, the application of a minimum biaxial tensile strain turns the material to a direct gap semiconductor, suitable for active and passive optoelectronic applications. On the other hand, the germanium-tin alloy is even more interesting due to its tunable band-gap energy and the capability to turn into a direct gap material above a certain molar fraction. On top of that, both materials may represent cheaper alternatives to materials currently used for the fabrication of high performance photodetectors and active optoelectronic devices. For both materials, the Auger and radiative recombination properties have been determined through a novel numerical approach that applies a Green's function based model to the full band structure of the material. In part two, the temperature dependent efficiency loss, experimentally detected in a reference GaN/InGaN based single quantum well light emitting diode, has been numerically studied by measn of a commercial simulation software Crosslight APSYS © . The charge transport mechanism in the device has been modeled through an improved drift-diffusion scheme and compared to the real device current-voltage characteristics. Once an agreement between real and simulated current-voltage characteristics was achieved, the impact of Shockley-Read-Hall recombination mechanism on the device internal quantum efficiency function of temperature has been throughfully studied
Numerical study on the optical and carrier recombination processes in GeSn alloy for E-SWIR and MWIR optoelectronic applications
Full text linkThe contribution of the De Filippi expedition (1913-1914) to the geological knowledge of the Aksai Chin region (western Himalaya)
No full textBetween the years 1913 to 1914 the De Filippi Expedition, led by the Italian explorer and
mountaineer Filippo De Filippi (1869–1938), traversed the Himalayan Range from Kashmir
to Baltistan and Xinjiang. Exploring mostly unknown territories, traveling more than 2000
kilometers, and equipped with advanced instruments for geodetic and meteorological
measurements, the expedition members surveyed, mapped and collected rocks and fossils
including from the remote Aksai Chin region. After almost two years, the expedition
returned to Italy, however, publication of the findings was delayed due to the outbreak of
the First World War. The fossil material and syntheses of the geology and stratigraphy of
the area represented unique documents on this sector of Western Tibet, with the Cretaceous
Period being documented by the expedition for the first time in the whole Trans-Himalayan
Range. The Aksai Chin region remains poorly explored even today, and the De Filippi
collection which is housed in the Natural History Museum of the University of Florence now
represents one of the few records available for reconstructing the stratigraphy of the area. It
constitutes a valuable resource regarding the history of the scientific exploration and
understanding of the geology and paleontology of the region, providing a unique window
into a very remote and fascinating part of the world
Revisione di macroforaminiferi eocenici della collezione Dainelli conservati presso il Museo di Storia Naturale dell’Università degli Studi di Firenze
No full textLa collezione di macroforaminiferi dell’Eocene friulano, raccolta negli anni 1900-1901, descritta in una monumentale monografia da Giotto Dainelli (Dainelli, 1915) e oggi conservata presso il Museo di Storia Naturale dell’Università degli Studi di Firenze (Dominici & Monechi, 2011) è stata oggetto di un riordino finalizzato alla revisione tassonomica del materiale.
Secondo i cartellini originali le specie prese in esame sono 46, di cui quattro attribuite ad Alveolina, sei ad Assilina, nove a Discocyclina, 23 a Nummulites, tre ad Operculina e una ad Orthofragmina. Si è intrapresa la revisione iniziando dalle specie dei generi Alveolina e Nummulites, di maggior interesse biostratigrafico e rappresentanti da soli oltre la metà dei taxa.
Dopo circa un secolo le preparazioni di Dainelli risultano non conservate in modo ottimale a causa della cristallizzazione e dell’ingiallimento del balsamo del Canada. In particolare, le superfici esterne dei nummuliti sono a volte parzialmente occultate dallo strato di balsamo che le ricopre, mentre le sezioni equatoriali di nummuliti e quelle assiali di alveoline sono di solito ben visibili.
La fauna proviene da una successione carbonatica affiorante nei pressi della collina di Rosazzo, in provincia di Udine, in massima parte da «un potente banco coralligeno e conchigliare» in località Noax e da successioni stratigraficamente sovrastanti, affioranti attorno alla località di Monte Plauris. In base alla composizione faunistica complessiva, comprendente anche molluschi e coralli (Dominici & Monechi, 2011), e alle sue somiglianze con la fauna veneta di San Giovanni Ilarione, Dainelli attribuì l’intera successione del Friuli orientale al Luteziano (Eocene medio, 48-40 Ma; Dainelli, 1915)
Dato il grande valore biostratigrafico dei macroforaminiferi del Friuli, si è ritenuto opportuno iniziare un lavoro di revisione ed aggiornamento delle specie presenti in collezione. La nuova determinazione dei taxa ci permette di datare i giacimenti friulani, incluse alcune località oggi non più accessibili, e di conseguenza di aggiornare le età delle faune a molluschi e coralli associate ai macroforaminiferi.
Bibliografia:
Dainelli G. (1915). L’Eocene Friulano – Monografia geologica e paleontologica. 721 pp. Ed. “ Le Memorie
Geografiche”, Firenze.
Dominici S. & Monechi S. (2011). Invertebrati paleogenici. In Monechi S. & Rook L. (ed.), Il Museo di Storia
Naturale dell'Università degli Studi di Firenze. Le collezioni geologiche e paleontologiche. Firenze University Press, Firenze, 117-123
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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