1,720,976 research outputs found
Optical and EPR spectroscopy in pure and blended films of a novel low band gap polymer
No full textEfficient charge transfer between a newly synthesized
low band gap (LBG) conjugated polymer and the C60 derivative
PCBM is demonstrated. Spectral and time-resolved photoluminescence
(PL) measurements show strong quenching and charge separation in
the picosecond time range. The charge transfer is further
confirmed by light-induced electron paramagnetic resonance (EPR)
measurements of both the positive polarons and the fullerene
radicals, which can be resolved in high-frequency EPR. The
potential for the LBG polymer to act as acceptor was examined in
blends with the para-phenylene-vinylene polymer MDMO-PPV. No
charge transfer, but instead energy transfer from MDMO-PPV to LBG
occurs in these blends, as shown by PL spectroscopy
Design of Low Band Gap Polymers: An Effort to Broaden the Optical Response of the Active Layer in Plastic Solar Cells
No full textSemiconducting polymers could perhaps have the greatest impact upon society through the development of polymer photovoltaic cells for power generation. The demand of energy has increased worldwide, mainly due to the development in areas like Asia and Africa. Currently this demand in energy is satisfied mainly by fossil fuels and nuclear power. However, these energy sources are limited and their use has a serious environmental impact. Therefore research toward renewable energy sources has increased in last decades. Among others, photovoltaics (PVs) offer great technological potential as a renewable, alternative source for electrical energy. Today Si-based solar cells are by far the most dominating type of PVs used and account for 99 % of all solar cells. However, to improve processability, lower manufacturing costs, and create flexibility, solar cells based on conjugated polymeric materials are extensively investigated during the last decade. The work described in this thesis focuses mainly on the design of low band gap polymers and their use in these plastic solar cells. A critical issue for this type of solar cells is the rather narrow absorption of the active layer. Since most of the available conjugated polymers were originally developed for visible-LEDs, they exhibit band gaps > 2 eV. Hence, there is a clear mismatch between the absorption spectrum of these materials and the terrestrial solar spectrum. The latter extends into the near infrared therefore, new low band gap materials with absorption extending to the 700-900 nm (Eg = 1.7 – 1.3 eV) region are needed for efficient photon harvesting.Misschien hebben halfgeleidende polymeren wel de grootste impact op onze maatschappij via de ontwikkeling van polymere zonnecellen. De vraag naar energie is immers wereldwijd gestegen, hoofdzakelijk vanwege de ontwikkeling van gebieden zoals Azië en Afrika. Momenteel wordt deze vraag naar energie hoofdzakelijk tegemoetgekomen door het gebruik van fossiele brandstoffen en kernenergie. Nochtans, zijn deze energiebronnen beperkt en hun gebruik heeft een ernstige invloed op het milieu. Als alternatief voor de fossiele brandstoffen bezit de zon de nodige vereisten om door te gaan als ideale energiebron. Ze is gratis, betrouwbaar en onuitputtelijk. Het gebruik van zonnecellen is niet nieuw en vandaag de dag zijn silicium gebaseerde zonnecellen veruit het meest gebruikte type en vertegenwoordigen ze een marktaandeel van 99 %. De productiekost van deze anorganische zonnecellen is echter te hoog voor het gebruik ervan op grote schaal. Een nieuwe klasse van zonnecellen dringt zich dus op. Deze nieuwe zonnecellen zijn gebaseerd op organische halfgeleiders, waaronder geconjugeerde polymeren. Ze zijn potentieel goedkoper, gemakkelijker te produceren en vertonen mechanische flexibiliteit. Een nadeel van de organische zonnecel is echter de eerder smalle absorptieband van de actieve laag. Aangezien de meeste beschikbare geconjugeerde polymeren oorspronkelijk voor LEDs werden ontwikkeld, hebben zij band gaps die groter zijn dan 2 eV. Hierdoor is er een duidelijke mismatch tussen het absorptiespectrum van deze materialen en het emissiespectrum van de zon. Daarom zijn nieuwe low band gap materialen nodig met een absorptieband tot 700-900 nm (Eg = 1.7 – 1.3 eV). Het werk dat in deze thesis wordt beschreven focust hoofdzakelijk op het ontwerpen van low band gap polymeren en hun gebruik in organische zonnecellen
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
Low band gap donor-acceptor conjugated polymers toward organic solar cells applications
No full textAbstract: Mixtures of conjugated polymers and fullerenes command considerable attention for application in organic solar cells. To increase their efficiency, the design of new materials that absorb at longer wavelengths is of substantial interest. We have prepared such low band gap polymers using the donor 12acceptor route, which is based on the concept that the interaction between alternating donors and acceptors results in a compressed band gap. Furthermore, for application in photovoltaic devices, sufficient polymer solubility is required. We have prepared four low band gap conjugated polymers, with a bis(1-cyano-2-thienylvinylene)phenylene base structure, and achieved an excellent solubility by the introduction of long alkoxy and alkyl side chains. The polymers were synthesized via an oxidative polymerization. Their electronic properties were determined from electrochemical and optical measurements, which confirm that they indeed have a low band gap. In the blend of such a low band gap polymer with PCBM, evidence for efficient charge transfer was obtained from PL and EPR measurements. However, bulk heterostructure solar cells made of such blends display only low efficiencies, which is attributed to low charge carrier mobilities
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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