1,721,203 research outputs found
All-optical switching and filtering based on liquid crystals and photosensitive composite organic materials
No full textIntegrated optic devices using low driving power are crucial to develop new photonic systems
both for optical communications and for sensing. The large electro-optic effect and nonlinear
optical properties of liquid crystals (LC) and doped LC novel materials allow the realization of low
cost optoelectronic devices. We present our recent experimental and theoretical results on optical
channel waveguides based on LC made on both glass and silicon substrates. Devices made of
waveguides using a LC core can operate both in linear [1] and nonlinear optical regime at 1550 nm
wavelength spectral region [2]. As linear waveguides they can behave both as variable optical
attenuators and as optical switches by exploiting the electrooptic effect in a nematic LC (NLC). An
applied voltage lower than just 5 V was required to drive an electro-optic switch with an on-off
contrast of more than 40 dB. Optical Freedericks transition was also experimentally observed when
an input optical power of just 25 mW was fiber coupled to the same NLC waveguide. Modelling of
the waveguide was obtained by minimizing the LC total free energy, including the dielectric energy
at optical frequencies by using finite elements. Preliminary simulations of waveguides using azodye
doped LC indicate that a further reduction of driving power is possible. All-optical tunable
filters can also be obtained by using photosensitive composite materials.
Recent experimental findings will be presented on an integrated optic filter, which combines the
simple and low cost ion-exchange waveguide technology with a composite LC methyl red (MR)
azo-dye photosensitive compound to obtain full optical tuneability. The structure of the integrated
optical filter recalls a previous POLICRYPS based electro-optic tuneable filter [3]. The prototype
showed a pass-band with more than 20 dB signal suppression at the Bragg wavelength with a
bandwidth of the transmitted notch of about 3 nm. A tuning range of 6.6 nm was observed by
applying a pump signal of 45 mW [4]. Full consistency between experiment and simulation results
was found. The measured shift is nearly double from previous results achieved in electro-optically
tunable POLICRYPS based filters, because of the nematic liquid crystals methyl red properties.
These devices can trigger the development of a new generation of low power, compact and low cost
all-optical components for next generation fiber optic telecom and sensor systems.
References
[1] D. Donisi, B. Bellini, R. Beccherelli, R. Asquini, G. Gilardi, M. Trotta, and A. d’Alessandro, “A switchable liquidcrystal
optical channel waveguide on silicon”, IEEE J. Quantum Electron. 46, 762–768 (2010).
[2] A. d’Alessandro, R. Asquini, M. Trotta, G. Gilardi, R. Beccherelli and I. C. Khoo, “All optical intensity modulation
of near infrared light in a liquid crystal channel waveguide”, Appl. Phys. Lett. 97, 093302 (2010).
[3] A. d’Alessandro, D. Donisi, L. De Sio, R. Beccherelli, R. Asquini, R. Caputo, and C. Umeton, “Tunable integrated
optical filter made of a glass ion-exchanged waveguide and an electro-optic composite holographic grating”, Opt.
Express 16, 9254–9260 (2008), Patent US 7925124 B2 (2011).
[4] G. Gilardi, L. De Sio, R. Beccherelli, R. Asquini, A. d’Alessandro, and C. Umeton, “Observation of tunable optical
filtering in photosensitive composite structures containing liquid crystals”, Opt. Lett. 36, 4755–4757 (2011)
La performance italiana per alcuni prodotti orticoli sul mercato della Germania Federale confrontata con quella dei paesi maggiori concorrenti.
No full textAnalisi della performance italiana sul mercato della Germania federale quale esportatore di prodotti orticoli comparata con quella dei maggiori competitori
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
STABILITY CONSTANTS OF METHOTREXATE-CYCLODEXTRIN COMPLEXES DETERMINED USING THE MEMBRANE PERMEATION TECHNIQUE
No full textInvestigation on the detergent role in the function of secondary quinone in bacterial Reaction Centers
No full textAppropriate 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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