1,720,971 research outputs found
VO2 nanoparticles and their application in thermochromic coatings and films for smart windows: An in-depth study of the thermodynamics and kinetics of the structural phase transition
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Development and characterisation of nano-porous vanadium dioxide coatings for energy efficient windows
No full textGlass windows allow natural light to enter buildings, but the main disadvantage is that heat from the sun penetrates, increasing the inner temperature. Therefore, the aim of a smart window is to diminish the solar heat gain dynamically throughout the day without an external control system. Vanadium dioxide (VO2) is a thermochromic material with a transition temperature (Tc) which allows perspective for implementation into coatings. • When T of the coating Tc → blocking of IR light. VO2-based coatings display a low transmission in the visible (~40 %), which is too low for application on architectural glazing. Furthermore, dopants are required to lower the transition temperature from 68 °C to 20-30 °C. However, dopants reduce the switching temperature and solar modulation behaviour. The objective is to a develop nano-porous thermochromic VO2-coating, with a switching temperature between 20-30 °C, and increased transmission in the visible. A liquid citrato-oxalato-VO2+ solution is dried using a freeze dryer, this solid complex is annealed under nitrogen in a tube furnace. Many parameters need to be monitored, the main ones are; heating rate, final temperature and isothermal period at final temperature. Annealing allows the formation of the VO2 and removal of organic material. The quality of the produced monoclinic VO2 depends on the parameters, therefore the dependence on each is investigated. High temperatures remove more organic material and improve the quality. Further optimisation is required to form the desired phase of VO2, without oxidising the vanadium to other phases. Additionally, comparison with doped precursor with different metals will be carried out
VO2 nanoparticles and their application in thermochromic coatings and films for smart windows: An in-depth study of the thermodynamics and kinetics of the structural phase transition
No full textNot availabl
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
Organic modification of silica-based ionogels improves the electrolyte/electrode contact and influences their functional properties
No full textThe energy transition necessitates sustainable energy storage to address the mismatch between the production and consumption of renewable electricity. Sodium-ion batteries (SIBs) are a promising candidate for stationary energy storage as an alternative for lithium-ion batteries (LIBs). In spite of their lower energy density, SIBs have advantages over LIBs.1 Sodium is considerably more abundant than lithium (2.83% versus 0.01%) and, evenly distributed across the Earth, implying that SIBs may be less expensive and more sustainable than LIBs.1,2
Conventional LIBs contain flammable organic liquid electrolytes (e.g. alkyl carbonates) with limited thermal stability. Thermal runaway can therefore lead to cell ignition, causing a significant safety hazard. Non-flammable electrolytes can be based on ionic liquids, which are molten salts with flame retarding properties and negligible vapor pressures. However, the possibility of leakage and related environmental hazards remains a concern.3 This risk can be mitigated by the use of solid electrolytes. Apart from circumventing safety issues, solid electrolytes may allow a significant increase in energy density. After all, they take up less dead volume than liquid electrolytes and can allow the use of alkali metals as negative electrodes.
An attractive type of solid electrolyte is the class of silica-based ionogels, owing to their high ionic conductivity, thermal stability, and broad electrochemical window.4 They comprise an ionic liquid electrolyte (ILE, a salt dissolved in ionic liquid) confined in the pores of a solid silica matrix. The silica matrix is electrochemically inactive but influences the functional properties of the resulting solid material. Ionogels based on solely silica (SiO2) as matrix tend to crack easily when subjected to pressure as the rigid Si-O-Si bonds result in high Young’s modulus materials. Furthermore, materials with high Young’s moduli cannot adapt easily to electrode surfaces, resulting in higher charge-transfer resistances (Rct) between the solid electrolyte and electrode. One way to reduce the stiffness of silica-based ionogels is to modify the silica matrix with e.g. organic groups. Ormosils® are a class of materials completely consisting of organically modified silica and show mechanical properties from glassy to rubbery depending on the amount of organic modification.5
Here, the concepts of ionogels and Ormosils® are combined to produce sodium-ion conducting organically modified ionogels. Two different phenyl-bearing silanes (phenyltrimethoxysilane, PhTMS, or diphenyldimethoxysilane, DPhDMS) are for the first time used as organic modifiers in silica-based ionogels. A non-aqueous sol-gel route with formic acid (FA) is used to synthesize the monoliths. Incorporating phenyl groups allow to reduce the Young’s modulus from 29 MPa down to 6 MPa. The charge-transfer resistances (Rct) of Na|ionogel|Na2Ti3O7 half cells, determined with electrochemical impedance spectroscopy (EIS), followed the trend of the ionogels’ Young’s modulus. Through NMR spectroscopy, pi-stacking was observed between the matrix phenyl moieties and IL imidazolium cations. Furthermore, the organic modification diminished the formation of hydrogen bonds between IL anions and matrix silanol groups. This shows that the organic modification of the matrix can have a pronounced effect on the coordination of the ILE components, which ultimately determine the solid electrolyte’s functional properties. In summary, incorporating phenyl groups in the silica matrix of ionogels improves the mechanical properties and charge transfer resistances, but impairs ionic conductivity.
References:
1 A. Eftekhari & D.-W. Kim, J. Power Sources, 395 (2018) 336-348
2 P.K. Nayak et al., Angew. Chem. Int. Edit., 57 (2018) 102-120
3 S. Brutti et al., J. Power Sources, 479 (2020) 228791
4 M.-A. Néouze et al., Chem. Mater., 18 (2006) 3931-3936
5 J.D. Mackenzie et al., J. Solgel Sci. Technol., 4 (1995), 141-15
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
Organic modification of silica-based ionogels improves the electrolyte/electrode contact and influences their functional properties
No full textThe energy transition necessitates sustainable energy storage to address the mismatch between the production and consumption of renewable electricity. Sodium-ion batteries (SIBs) are a promising candidate for stationary energy storage as an alternative for lithium-ion batteries (LIBs). In spite of their lower energy density, SIBs have advantages over LIBs.1 Sodium is considerably more abundant than lithium (2.83% versus 0.01%) and, evenly distributed across the Earth, implying that SIBs may be less expensive and more sustainable than LIBs.1,2
Conventional LIBs contain flammable organic liquid electrolytes (e.g. alkyl carbonates) with limited thermal stability. Thermal runaway can therefore lead to cell ignition, causing a significant safety hazard. Non-flammable electrolytes can be based on ionic liquids, which are molten salts with flame retarding properties and negligible vapor pressures. However, the possibility of leakage and related environmental hazards remains a concern.3 This risk can be mitigated by the use of solid electrolytes. Apart from circumventing safety issues, solid electrolytes may allow a significant increase in energy density. After all, they take up less dead volume than liquid electrolytes and can allow the use of alkali metals as negative electrodes.
An attractive type of solid electrolyte is the class of silica-based ionogels, owing to their high ionic conductivity, thermal stability, and broad electrochemical window.4 They comprise an ionic liquid electrolyte (ILE, a salt dissolved in ionic liquid) confined in the pores of a solid silica matrix. The silica matrix is electrochemically inactive but influences the functional properties of the resulting solid material. Ionogels based on solely silica (SiO2) as matrix tend to crack easily when subjected to pressure as the rigid Si-O-Si bonds result in high Young’s modulus materials. Furthermore, materials with high Young’s moduli cannot adapt easily to electrode surfaces, resulting in higher charge-transfer resistances (Rct) between the solid electrolyte and electrode. One way to reduce the stiffness of silica-based ionogels is to modify the silica matrix with e.g. organic groups. Ormosils® are a class of materials completely consisting of organically modified silica and show mechanical properties from glassy to rubbery depending on the amount of organic modification.5
Here, the concepts of ionogels and Ormosils® are combined to produce sodium-ion conducting organically modified ionogels. Two different phenyl-bearing silanes (phenyltrimethoxysilane, PhTMS, or diphenyldimethoxysilane, DPhDMS) are for the first time used as organic modifiers in silica-based ionogels. A non-aqueous sol-gel route with formic acid (FA) is used to synthesize the monoliths. Incorporating phenyl groups allow to reduce the Young’s modulus from 29 MPa down to 6 MPa. The charge-transfer resistances (Rct) of Na|ionogel|Na2Ti3O7 half cells, determined with electrochemical impedance spectroscopy (EIS), followed the trend of the ionogels’ Young’s modulus. Through NMR spectroscopy, pi-stacking was observed between the matrix phenyl moieties and IL imidazolium cations. Furthermore, the organic modification diminished the formation of hydrogen bonds between IL anions and matrix silanol groups. This shows that the organic modification of the matrix can have a pronounced effect on the coordination of the ILE components, which ultimately determine the solid electrolyte’s functional properties. In summary, incorporating phenyl groups in the silica matrix of ionogels improves the mechanical properties and charge transfer resistances, but impairs ionic conductivity.
References:
1 A. Eftekhari & D.-W. Kim, J. Power Sources, 395 (2018) 336-348
2 P.K. Nayak et al., Angew. Chem. Int. Edit., 57 (2018) 102-120
3 S. Brutti et al., J. Power Sources, 479 (2020) 228791
4 M.-A. Néouze et al., Chem. Mater., 18 (2006) 3931-3936
5 J.D. Mackenzie et al., J. Solgel Sci. Technol., 4 (1995), 141-15
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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