1,720,958 research outputs found
Demonstration of the optical limiting effect for an hemiporphyrazine
No full textThe hemiporphyrazine complex 9,22-bis(dibutoxy)hemiporphyrazinato
chloroindium(III) (1) is one of the few examples
for this class of compounds, which displays the nonlinear
optical effect of reverse saturable absorption for nanosecond
laser pulses in the visible spectrum. The high linear transmission
combined with the fast switching into a strongly absorbing
excited state in the same spectral range (400–650 nm), renders
the studied hemiporphyrazine an ideal material for the passive
shuttering of pulsed radiations
Large two-photon absorption cross sections of hemiporphyrazines in the excited state: The multiphoton absorption process of hemiporphyrazines with different central metals
No full textA series of five hemiporphyrazines (Hps) with different coordinating central atoms (H2, GeCl2, InCl, Pt, Pb), and the acyclic derivative 1,3-bis-(6′-amino-4′-butoxy-2′-pyridylimino)-1,3-dihydroisoindoline have been synthesized and their multiphoton absorption properties examined at the second harmonic frequency of the Nd:YAG laser in the nanosecond time regime. Metal-free and platinum Hps display saturation of optical transmittance within incident fluence values of 6 J cm−2. Comparison with other similar molecular structures like phthalocyanines and related molecules shows that Hps are strong nonlinear absorbers. The experimental curves of nonlinear transmission at 532 nm have been fitted by means of a three-level model with the occurrence of simultaneous two-photon absorption from an excited state. In the sole case of the InCl complex we found that a five-level model is needed because of the participation of triplet states. Contrary to phthalocyanines, naphthalocyanines, and porphyrins, a heavy central atom does not improve the nonlinear absorption properties since a different excited states dynamic is involved. The large nonlinear absorption of Hps combined with the very small absorption in the visible spectral range makes these molecules a very interesting class of molecules for nonlinear optical applications
Synthesis and high ranked NLT properties of new sulfonamide-substituted indium phthalocyanines
No full textThe synthesis and characterization of three new indium phthalocyanines bearing eight N-alkyl- or N-arylsulfonamide
groups is described. The new compounds are {2,3,9,10,16,17,23,24-octakis[4-(4-methoxyphenylaminosulfonyl]
phenoxy]phthalocyaninato}indium(III) chloride (7), {2,3,9,10,16,17,23,24-
octakis[4-diethylaminosulfonyl)phenoxy]phthalocyaninato}indium(III) chloride (8) and {2,3,9,10,16,17,
23,24-octakis[4-didodecylaminosulfonyl)phenoxy]phthalocyaninato}indium(III) chloride (9), and were
obtained in 23–49% yields. The precursors of phthalocyanines 7–9 are sulfonamide-substituted phthalonitriles
that can be prepared by reacting 4,5-bis(4-chlorosulfonylphenoxy)phthalonitrile (3) with amines.
The nonlinear transmission (NLT) of complexes 7–9 was determined at 532 nm using ns pulses. All three
phthalocyanines behave as reverse saturable absorbers with increasing efficiency of optical limiting in
the order 7 < 8 < 9. A comparative analysis of the NLT results is attempted in terms of the structural
differences in 7–9
Tetrabrominated Lead Naphthalocyanine for Optical Power Limiting
No full textThe complex 2,(3)-tetrabromo-3,(2)-tetra[(3,5-di-tert-butyl)phenyloxy]-naphthalocyaninato lead [Br4(tBu2C6H3O)4NcPb, 1] has been prepared and its optical limiting properties for ns light pulses have been measured. Complex 1 behaves as a reverse saturable absorber within the spectral range 440–720 nm with a limiting threshold of 0.1 J cm−2 at 532 nm. The lifetime of the absorbing triplet excited state has been evaluated as 3.8×10−7 s and the quantum yield of triplet formation has been measured as 0.07 in toluene. The nonlinear optical transmission properties of complex 1 have also been determined in Plexiglas [naphthalocyanine content: 5.0×10−4 M (0.1 % by weight)]. A reversible nonlinear absorption was again observed for a fluence above 0.4 J cm−2, but through different excited-state dynamics. This may be rationalized in terms of aggregation of the molecule in the polymer matrix
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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