1,720,962 research outputs found
Synthesis and characterization of Pd nanoparticles for plastic plasmonic sensing applications
No full textIt is well known that hydrogen mixed with air forms a highly flammable mixture. There is an urgent need for selective and accurate sensors, since hydrogen very often serves as a fuel or energy storage medium. Given the fact that even the smallest leak can lead to an explosion, it is very important for sensors to be reliable and safe, i.e. not ignite the gas themselves. Sensors with an optical read-out are under current interest, hence nanoparticles are examined towards this goal.As a response to the above, this thesis discusses the synthesis of palladium nanoparticles with a standard surfactant as a stabilizer together with their characterization. Nanoforms of palladium are a perfect platform for hydrogen sensing, forming a hydride when exposed to hydrogen, making them very selective. However, there are compounds which strongly influence hydrogen sensing and often obscure the activity of palladium nanoparticles. Four common capping agents utilized in palladium nanoparticles synthesis were investigated to address this issue: hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), tetraoctylammonium bromide (TOAB), polyvinylpyrrolidone (PVP).Palladium nanoparticles were applied towards hydrogen sensing giving promising results. In order to achieve the goal to create a hydrogen sensor, nanoparticles were successfully incorporated into a poly(methyl methacrylate) (PMMA) polymer matrix. The created nanocomposite serves as a platform for two hydrogen sensing devices with plasmonic optical read-outs. On top of that it was found that among all four tested capping agents for palladium nanoparticles, PVP enhances hydrogen absorption kinetics whereas CTAB, CTAC and TOAB decrease absorption kinetics
Synthesis and characterization of Pd nanoparticles for plastic plasmonic sensing applications
No full textIt is well known that hydrogen mixed with air forms a highly flammable mixture. There is an urgent need for selective and accurate sensors, since hydrogen very often serves as a fuel or energy storage medium. Given the fact that even the smallest leak can lead to an explosion, it is very important for sensors to be reliable and safe, i.e. not ignite the gas themselves. Sensors with an optical read-out are under current interest, hence nanoparticles are examined towards this goal. As a response to the above, this thesis discusses the synthesis of palladium nanoparticles with a standard surfactant as a stabilizer together with their characterization. Nanoforms of palladium are a perfect platform for hydrogen sensing, forming a hydride when exposed to hydrogen, making them very selective. However, there are compounds which strongly influence hydrogen sensing and often obscure the activity of palladium nanoparticles. Four common capping agents utilized in palladium nanoparticles synthesis were investigated to address this issue: hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), tetraoctylammonium bromide (TOAB), polyvinylpyrrolidone (PVP). Palladium nanoparticles were applied towards hydrogen sensing giving promising results. In order to achieve the goal to create a hydrogen sensor, nanoparticles were successfully incorporated into a poly(methyl methacrylate) (PMMA) polymer matrix. The created nanocomposite serves as a platform for two hydrogen sensing devices with plasmonic optical read-outs. On top of that it was found that among all four tested capping agents for palladium nanoparticles, PVP enhances hydrogen absorption kinetics whereas CTAB, CTAC and TOAB decrease absorption kinetics
Synthesis of Nanoparticles and Organometallic Complexes for Gas Sensing
No full textCurrently metal nanoparticles (NPs) are a subject of interest regarding many applications, in particular chemical gas sensing, as the associated environmental issues are of substantial importance. Metal NPs are attractive due to their fascinating optical properties and primarily, localized surface plasmon resonance (LSPR) which strongly depends on size and shape of NPs. Desired size and shape of NPs can be achieved by colloidal synthesis that allows for flexibility in the reaction conditions, although it demands high precision and understanding of how different factors affect NP formation, which can influence the quality of synthesized NPs. Regarding chemical sensing, phthalocyanines possess strong activity towards some gases, and they carry interesting optical properties, therefore their application is also interesting. This thesis focuses extensively on the synthesis and characterization of Pd NPs for hydrogen sensing. The Pd NPs synthesis was optimized with regard to the concentration needed for efficient response from the sensor. The Pd NPs were incorporated into a polymer matrix to be protected from poisoning, which also led the diffusion path between hydrogen and Pd NPs to be extended. Different stabilizing agents for Pd NPs were examined in order to explore how common stabilizing compounds and their interactions with Pd NPs may influence the sensing process. The work was focused on the use of homogeneous surfactant and polymer coatings on Pd nanofabricated surfaces, which were examined and analyzed in hydrogen sensing. Additionally, to address hydrogen sensing problems i.e. hysteresis, PdAu alloys with various Pd:Au ratios were colloidally synthesized and thoroughly characterized. PdAu alloys exhibited excellent results of hysteresis removal at specific Pd:Au ratios. Moreover, phthalocyanine based complexes; Zn, Co, Cu, Fe, were synthesized for application in NOx monitoring
Synthesis of Nanoparticles and Organometallic Complexes for Gas Sensing
No full textCurrently metal nanoparticles (NPs) are a subject of interest regarding many applications, in particular chemical gas sensing, as the associated environmental issues are of substantial importance. Metal NPs are attractive due to their fascinating optical properties and primarily, localized surface plasmon resonance (LSPR) which strongly depends on size and shape of NPs. Desired size and shape of NPs can be achieved by colloidal synthesis that allows for flexibility in the reaction conditions, although it demands high precision and understanding of how different factors affect NP formation, which can influence the quality of synthesized NPs. Regarding chemical sensing, phthalocyanines possess strong activity towards some gases, and they carry interesting optical properties, therefore their application is also interesting. This thesis focuses extensively on the synthesis and characterization of Pd NPs for hydrogen sensing. The Pd NPs synthesis was optimized with regard to the concentration needed for efficient response from the sensor. The Pd NPs were incorporated into a polymer matrix to be protected from poisoning, which also led the diffusion path between hydrogen and Pd NPs to be extended. Different stabilizing agents for Pd NPs were examined in order to explore how common stabilizing compounds and their interactions with Pd NPs may influence the sensing process. The work was focused on the use of homogeneous surfactant and polymer coatings on Pd nanofabricated surfaces, which were examined and analyzed in hydrogen sensing. Additionally, to address hydrogen sensing problems i.e. hysteresis, PdAu alloys with various Pd:Au ratios were colloidally synthesized and thoroughly characterized. PdAu alloys exhibited excellent results of hysteresis removal at specific Pd:Au ratios. Moreover, phthalocyanine based complexes; Zn, Co, Cu, Fe, were synthesized for application in NOx monitoring
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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