1,720,962 research outputs found
Universal Design Rules for Flory–Huggins Polymer Photonic Vapor Sensors
No full textMultilayered photonic sensors that rely on polymer-solvent Flory-Huggins interactions are drawing increasing interest owing to their broad-band selectivity, even among mixtures, without the need for chemical targeting. Moreover, these sensors provide simple colorimetric responses, and easy, quick fabrication both on laboratory and industrial scales. However, complex optical responses and slow response times are limiting their development. In this work, the behavior of different photonic sensor architectures is analyzed to speed up response time and define a strategy to simplify their spectral behavior. To this end, the effect of interfaces, materials order, and thickness on the diffusion kinetics of a single reference analyte in the multilayered sensors is studied to design the optimal structure
Polymer photonic aegises as near-infrared reflectors
Full text linkYear by year, thermal shielding has seen an increase in importance for reduction of energetic consumption in vehicles and buildings as a passive method of cooling opposed to traditional antiecologic air conditioning. In this work, we report on the design and fabrication of flexible, multilayer polymer photonic crystals films, namely aegises. Exploiting their peculiar optical properties, aegises are designed to act as selective reflectors for the near-infrared radiation, principal cause of radiative heating by sunlight, while keeping a relative transparency in the visible range. Different polymers are used as alternating building blocks, and the efficiency of the fabricated structures is assessed via thermal experiments, achieving efficiencies greater than 25% in heating reduction
Control of near-infrared dye fluorescence lifetime in all-polymer microcavities
No full textThe control of radiative decay rate is a crucial issue both for fundamental studies in quantum electrodynamics and for the development of efficient lasers, light emitting devices and photovoltaic cells. In this paper we investigate the integration of a near-infrared molecular fluorophore in an all-polymer planar microcavity. Subsequently, we report the modulation of the fluorescence decay and radiative rate of the dye used and, in addition, of its fluorescence spectral line-shape and intensity. These effects have been possible through engineering the dielectric contrast of the polymers used to grow the flexible dielectric mirrors, thus blazing a trail to innovative opportunities for invisible near-infrared-light communications and wireless technologies
Aquivion–Poly(N-vinylcarbazole) Holistic Flory–Huggins Photonic Vapor Sensors
No full textA holistic detection system, in principle sensitive to any molecular species in the vapor phase is proposed. The sensor consists of a polymeric multilayered distributed Bragg reflector made of a perfluorinated polar polymer, Aquivion, and a nonpolar polymer, poly(N-vinylcarbazole). Alternated layers of the two polymers provide a characteristic optical response that depends on the chemical species intercalating within the structure. Such differences arise from Flory–Huggins polymer–solvent interactions. Then, the presence of polar, nonpolar, and perfluorinated moieties in the structures, potentially, allows sensitivity to any molecular species, providing a detection system with no need for any additional chemical receptors. As a proof of concept, the study demonstrates the sensitivity of the sensor to very diverse classes of molecules in the vapor phase including perfluorinated, nonpolar hydrophobic, and hydrophilic species and the capability to distinguish them, even in binary mixtures. Additionally, a connection between the dynamic temporal response of the sensors and the chemical–physical properties of the analytes, their concentration, and effective diffusion coefficient within the polymer structure is revealed
Strategies for dielectric contrast enhancement in 1D planar polymeric photonic crystals
No full textHistorically, photonic crystals have been made of inorganic high refractive index materials coupled to air voids to maximize the dielectric contrast and in turn the light confinement. However, these systems are complex, costly, and time-demanding, and the fabrication processes are difficult to scale. Polymer structures promise to tackle this issue thanks to their easy solution and melt processing. Unfortunately, their low dielectric contrast limits their performance. In this work, we propose a concise but exhaustive review of the common polymers employed in the fabrication of planar 1D photonic crystals and new approaches to the enhancement of their dielectric contrast. Transfer matrix method modeling will be employed to quantify the effect of this parameter in standardized structures and to propose a new polymer structure for applications dealing with light management
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
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