1,720,955 research outputs found
New Polymer and Composite Structures for Photonic Applications
No full textThe focus of this thesis is the development of materials and architectures for all-polymer functional structures for photonic applications. The first part concerns the improvement and optimization of colorimetric and fluorescent sensing structures for the detection of various analytes in the vapor phase. Optical-readout sensors are portable and can provide an easy interpretation that needs no specialized training and can be visible to the naked eye. This makes them promising for applications in environmental control, health monitoring and food safety. The objective of the work was to investigate analyte diffusion processes into multilayered structures of polymer submicrometric films, and then optimizing the structure design and expanding the materials used in the field. First, sensors based on vapor diffusion in multilayered polymer dielectric mirrors with structural coloring were developed. Given their clear color change, this typology of sensors has been shown to be promising in the literature. However, as their response is limited by the diffusion speed of molecular species, they can suffer from slow detection of vapor-phase analytes. Next, I examine the use of fluorescent polymer films sensitive to microviscosity changes caused by exposure to volatile organic compounds and observing the changes in fluorescence during said exposure. The effect on the overall diffusion of capping layers deposited on top of the fluorescent polymer was investigated to quantify the effect of the barrier polymer on the selectivity of the sensor. Finally, I employed the solution processing protocols developed for novel low refractive index polymer suspensions that were initially utilized for the sensors to engineer structures for fluorescence control.
When two highly reflecting structures encapsulate a luminescent material in a submicrometric space, this changes the photoluminescence properties in structures called optical microcavities. While the highly reflecting structures can be metallic mirrors, these have limited reflectance intensity, high absorbance losses, as well as a lack of tunability. Instead, the use of dielectric mirrors enables very high reflectance at desired wavelengths. In addition, the use of compliant polymer materials allows the future use of these structures to construct more efficient flexible devices. I was able to develop highly reflecting microcavities for emitters in the visible range as well as in the near infrared. Besides achieving high amplification of fluorescence intensity, I was also able to report for the first time a change in the radiative rate of the fluorescence for polymer structures. As these effects were so far only observed in planar structures of inorganic nature or more complex polymer three-dimensional systems, this presents a breakthrough in the field.
In this introduction I will give a wide but deep overview of the optics of multilayered polymer films, their diffusion peculiarities, and use for sensing. Furthermore, I will address the topic of solid-state organic fluorophores and controlling their photoluminescence through engineering the dielectric environment. This will be followed by a chapter-by-chapter exploration of the results obtained during the doctoral training as adapted from already published or drafted work. Finally, the outlook and possible future implications and developments of this research will be examined
Mild Sol-Gel Conditions and High Dielectric Contrast: A Facile Processing toward Large-Scale Hybrid Photonic Crystals for Sensing and Photocatalysis
No full textSolution processing of highly performing photonic crystals has been a towering ambition for making them technologically relevant in applications requiring mass and large-area production. It would indeed represent a paradigm changer for the fabrication of sensors and for light management nanostructures meant for photonics and advanced photocatalytic systems. On the other hand, solution-processed structures often suffer from low dielectric contrast and poor optical quality or require complex deposition procedures due to the intrinsic properties of components treatable from solution. This work reports on a low-temperature sol–gel route between the alkoxides of Si and Ti and poly(acrylic acid), leading to stable polymer–inorganic hybrid materials with tunable refractive index and, in the case of titania hybrid, photoactive properties. Alternating thin films of the two hybrids allows planar photonic crystals with high optical quality and dielectric contrast as large as 0.64. Moreover, low-temperature treatments also allow coupling the titania hybrids with several temperature-sensitive materials including dielectric and semiconducting polymers to fabricate photonic structures. These findings open new perspectives in several fields; preliminary results demonstrate that the hybrid structures are suitable for sensing and the enhancement of the catalytic activity of photoactive media and light emission control
All-Polymer Microcavities for the Fluorescence Radiative Rate Modification of a Diketopyrrolopyrrole Derivative
Full text link[Image: see text] Controlling the radiative rate of emitters with macromolecular photonic structures promises flexible devices with enhanced performances that are easy to scale up. For instance, radiative rate enhancement empowers low-threshold lasers, while rate suppression affects recombination in photovoltaic and photochemical processes. However, claims of the Purcell effect with polymer structures are controversial, as the low dielectric contrast typical of suitable polymers is commonly not enough to provide the necessary confinement. Here we show all-polymer planar microcavities with photonic band gaps tuned to the photoluminescence of a diketopyrrolopyrrole derivative, which allows a change in the fluorescence lifetime. Radiative and nonradiative rates were disentangled systematically by measuring the external quantum efficiencies and comparing the planar microcavities with a series of references designed to exclude any extrinsic effects. For the first time, this analysis shows unambiguously the dye radiative emission rate variations obtained with macromolecular dielectric mirrors. When different waveguides, chemical environments, and effective refractive index effects in the structure were accounted for, the change in the radiative lifetime was assigned to the Purcell effect. This was possible through the exploitation of photonic structures made of polyvinylcarbazole as a high-index material and the perfluorinated Aquivion as a low-index one, which produced the largest dielectric contrast ever obtained in planar polymer cavities. This characteristic induces the high confinement of the radiation electric field within the cavity layer, causing a record intensity enhancement and steering the radiative rate. Current limits and requirements to achieve the full control of radiative rates with polymer planar microcavities are also addressed
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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