1,720,958 research outputs found
Photovoltaic properties of PSi impregnated with eumelanin
No full textA bulk heterojunction of porous silicon and eumelanin, where the columnar pores of porous silicon are filled with eumelanin, is proposed as a new organic-inorganic hybrid material for photovoltaic applications. The addition of eumelanin, whose absorption in the near infrared region is significantly higher than porous silicon, should greatly enhance the light absorption capabilities of the empty porous silicon matrix, which are very low in the low energy side of the visible spectral range (from about 600 nm downwards). The experimental results show that indeed the photocarrier collection efficiency at longer wavelengths in eumelanin-impregnated samples is clearly higher with respect to empty porous silicon matrices
Nuove tecnologie web per e-learning. Primi risultati della serimentazione in un liceo scientifico
No full textNuove tecnologie web come i sistemi CMS rendono la realizzazione di piattaforme multimedialidi supporto all'insegnamento un obiettivo fattibile dal punto di vista tecnologico, pur senza grandi investimenti finanziari, di grande interesse dal punto di vista didattico. Si analizzano le caratteristiche generali dei sistemi CMS disponibnili e vengono presentati i primi risultati della sperimentazione di un sistema di e-learning basato su CMS nel biennio di un liceo scientifico
Porous silicon-based potentiometric triglycerides biosensor
No full textIn this paper we report on the fabrication and characterization of a potentiometric biosensor for the detection of triglycerides, based on lipase impregnated mesoporous silicon matrices. Prototypes, realized on 1x1 cm n+-type silicon wafers, show a very high enzymatic activity. Moreover the properties of these biosensors have been stable in a several months time interval, clearly showing their advantages with respect to traditional triglycerides detection systems
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
REALISATION ET ETUDE DE STRUCTURES A MODULATION D'INDICE OPTIQUE EN SILICIUM POREUX
No full textAbstract : This work concerns the study of the vertical and lateral modulation of the optical index in the porous silicon.To realise performing optical structures, we focused our efforts on the optical losses due to the p-type porous silicon samples interfaces. A study on the changes induced by the formation temperature on the interface roughness has been performed to reduce the losses. For a formation temperature of –35°C, and using the most critical formation currents, we obtained a striking improvement, reducing the interface roughness by a factor of 6.This roughness decrease allowed us to realise Bragg mirrors and microcavities of very high optical quality, with reflectivity coefficients as high as 99.5% and cavity mode widths of 5nm. The determination of such high reflection coefficients was realised using very precise measurements by “ring down” spectroscopy, with a precision of 0.01%. Thanks to the characterisation of these structures we were able to evidence a difference in the optical properties between simple layers and underlying layers. The modifications of the refractive index and of the formation velocity have been determined quantitatively by studying the photoluminescence and by simulating the reflection spectra. We also show that dye molecules can be used to efficiently fill the porous silicon cavities,independent on the low or high porosity degree. Moreover, the filling of the pores may be eased by oxidation of the porous silicon layer prior to the filling. Our results show that porous silicon can be a very good matrix for dye molecules, that stay enough dispersed to emit light. The use of dye-filled porous silicon microcavities allow for a sharpening and an amplification of the dye emission. To characterise the lateral refractive index modulation, obtained by photodissolution and photo-electro-formation of the porous silicon layer, we studied the influence of the presence of light on the porosity and on the optical properties of p- and n+-type porous silicon monolayers. Based on this study, we were able to determine the optimal formation parameters for gratings with lateral refractive index modulation. The light diffraction from these samples has also been studied. Keywords: Porous Silicon, optical index modulation, reflectivity, interface roughness, Bragg mirrors, laser dyeCe travail concernait l'étude des modulations verticales et latérales de l'indice optique dans le silicium poreux.Dans le but de réaliser des structures optiques performantes, nous nous sommes intéressés aux pertes dues à la rugosité des interfaces présentes dans les échantillons de silicium poreux de type p. Une étude sur l'influence de la température de formation du silicium poreux a été menée dans le but de réduire ces pertes. Pour la température de formation de -35°C pour les courants les plus critiques, nous avons obtenu une remarquable diminution de la rugosité, qui peut aller jusqu'à un facteur 6.Cette diminution de la rugosité nous a permis de réaliser des miroirs de Bragg et microcavités de très bonne qualité optique avec des coefficients de réflectivité de 99.5% et des largeurs de mode de la cavité de 5 nm. La détermination des grands coefficients de réflectivité est réalisé grâce à des mesures très précises de spectroscopie « ring down » avec une précision de 0.01%. La caractérisation de ces structures nous a permis de mettre en évidence une différence des propriétés optiques des couches simples et des couches enterrées, la variation de l'indice optique et de la vitesse de formation a été quantifiée par une étude de la luminescence et par la simulation des spectres de réflectivité. Nous avons montré que les molécules de colorant peuvent imprégner efficacement les couches de silicium poreux, qu'elles aient une faible ou une grande porosité, et que l'imprégnation peut être favorisée par l'oxydation préalable des couches poreuses. Ces résultats montrent que le silicium poreux peut être une très bonne matrice pour les molécules de colorant qui restent suffisamment dispersées pour pouvoir émettre de la lumière. L'utilisation de structures de type microcavité permet un rétrécissement et une amplification de l'émission du colorant. Pour caractériser la modulation latérale d'indice, obtenue par une photodissolution ou photoélectroformation de la couche de silicium poreux, nous avons étudié l'influence de la lumière sur la porosité et les propriétés optiques des monocouches de silicium poreux de type p et de type n+, ce qui a déterminé les conditions de formation des réseaux à modulation latérale d'indice optique. La diffraction de la lumière des échantillons ainsi obtenus a été étudiée. Mots clés : Silicium poreux, Modulation d'indice optique, Réflectivité, Rugosité d'interface, Miroir de Bragg, Microcavité, Colorant laser
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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