1,720,957 research outputs found
Improvement on high rate performance of LiFePO4 cathodes using
No full textIn this work, the electrochemical properties of the LiFePO4 cathode using graphene as a conductive agent were revealed. Compared to the conventional LiFePO4 electrodes with carbon black as a conductive agent, the graphene sheets can establish a more effective conductive framework due to their layered structure and excellent electronic conductivity, leading to better electrochemical rate performance. Furthermore, the obverse of increasing graphene content is continued gains in high-rate performance of the LiFePO4 electrodes. The electrodes with 30 wt.% graphene show high capacities up to 103.1 mAh/g and 68 mAh/g during discharging with extremely high rates of 30 C and 50 C, respectively. Besides, good cycling performance at high rate is also achieved. The electrodes with 30 wt% graphene display a capacity retention higher than 80% after 1000 cycles at 30 C. These results not only indicate that the graphene could be a promising candidate as a conductive agent, but also provide a new insight for designing LiFePO4 electrodes with brilliant high-rate performance via a simple method
Study of Different Isocyanates on the Properties of Limonene and Geraniol Based Polyurethane Films
No full textPlant-and animal-derived materials are gaining attention as potential substitutes for petroleum-based polymers. Growing environmental consciousness and the demand for greener and more sustainable materials are some of the primary causes of this change. A way to support the green and safe use of polyurethane is the thiol-ene click reaction, which is used to create biobased polyols. Limonene and geraniol are both plant-derived chemicals that contain unsaturated C=C (carbon-carbon double) bonds. Mercaptoethanol was used as a thiol compound in the thiol-ene click reaction to prepare bio-based polyols. Polyurethane films were synthesized by reacting polyols with isophorone diisocyanate (IPDI) and cyclohexyl isocyanate (CHDI), followed by film casting. The resulting PU films were cured at 70C to ensure complete crosslinking. To understand the structural and morphological characteristics, Fourier Transform Infrared Spectroscopy (FTIR) will be used. Tensile and hardness tests are also conducted to determine the mechanical properties of the synthesized PU films. Thermogravimetric analysis (TGA) and differential calorimetry (DSC) were employed to investigate the thermal properties of the PU films. The gel fraction analysis further supported the crosslinking efficiency in the PU networks. In this work, when comparing IPDI and CHDI in terms of mechanical properties in PU films, IPDI provides better mechanical properties than CHDI. The Tg\u27s of LM+IPDI, LM+CHDI, GM+IPDI and GM+CHDI were 34.58, 56.49, 75 and 56.49 ℃, respectively. The GM+IPDI demonstrated better mechanical properties (Tensile Strength of 36.02 MPa) than the others due to the higher cross-linking density and complete network
Modified Limonene and Geraniol Via Thiolene Processes Under UV Curing to Obtain Polyurethane Films
Full text linkNatural product-derived materials have gained increasing attention as promising alternatives to petrochemically derived commodity polymers. This shift is driven by the growing awareness of environmental issues and the need for more sustainable and eco-friendly materials. The thiol−ene click reaction to prepare biobased polyols is a strategy to promote the green and environmental protection of polyurethane. Limonene is found in the essential oils of various citrus fruits, particularly in high concentrations in the peels of oranges, lemons, limes, and grapefruits. And geraniol is found in rose oil, citronella oil, and palmarosa oil. The excessive usage of thiol and low conversion of carbon−carbon double bonds (C=C) would severely limit the properties of polyurethane (PU). In this work, a set of limonene and geraniol-based polyols were prepared via the thiol−ene click reaction. I use mercaptoethanol and thioglycerol to produce thiols. Interestingly, the conversion of the C=C was nearly 100% at the limonene and various thiol compounds(-SH) in a stoichiometric ratio without excess of -SH. Then, the prepared polyols were reacted with Cyclohexyl isocyanate (CHDI) and Isophorone diisocyanate (IPDI), Followed by films was cured at 70°C. The structural morphology will be analyzed using Fourier Transform Infrared Spectroscopy (FTIR), while mechanical properties will be assessed through tensile and hardness tests. Thermal characteristics will be studied using thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). The Tg’s of LM+IPDI, LM+CHDI, GM+IPDI and GM+CHDI were 34.58, 56.49, 75 and 56.49 °C, respectively. The GM+SB+IPDI demonstrated better mechanical properties (Tensile Strength of 18 MPa) than the others due to the higher cross-linking density and complete network
Synthesis of Eugenol-Based Polyols via Thiol−Ene Click Reaction and High-Performance Thermosetting Polyurethane Therefrom
Full text linkThe thiol−ene click reaction to prepare biobased polyols is a strategy to promote the green and environmental protection of polyurethane. The excessive usage of thiol and low conversion of carbon−carbon double bonds (C=C) would severely limit the properties of polyurethane (PU). In this work, a set of eugenol-based polyols were prepared via the thiol−ene click reaction. Interestingly, the conversion of the C=C was nearly 100% at the eugenol and various thiol compounds (-SH) in a stoichiometric ratio without excess of -SH. Then, the prepared polyols were reacted with diphenylmethane-diisocyanate (MDI), followed by a series of structure adjustable thermosetting polyurethane networks with colorless transparency, high glass transition temperature (Tg), and good mechanical properties being obtained. In particular, the tensile strength was up to 54.88 MPa, and Tg can be adjusted from 36.45 to 77.21 °C. Moreover, it is revealed that the compounds with an allyl structure are conducive to the efficient click reaction, and its application in PU can be greatly extended
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
Effect of Diamine and Triamines Crosslinkers on the Adhesive Properties of Soybean Oil-Based Non-Isocyanate Polyurethane
No full textNowadays, polyurethanes (PUs) play a major role in the polymer industry and are more and more popular due to their advantages and unique mechanical and chemical properties in different applications like foams, paint, coatings, elastomers, and adhesives, Bio-based sources have recently gained attention as sustainable alternatives to conventional petroleum-based material. Due to growing environmental concerns and the excessive use of petroleum-based products, this study explores non-isocyanate polyurethanes (NIPUs) as sustainable, low-toxicity alternatives to traditional PUs. To achieve this, as a starting material, soybean oil (SBO) was used, and it was converted into epoxidized soybean oil (ESBO). ESBO was then converted into CSBO using a Parr autoclave reactor in the presence of tetrabutylammonium bromide (TBAB). Then synthesized CSBO was characterized using physicochemical experiments, e.g. FT-IR, Oxirane oxygen percentage (%EOC content), viscosity analysis, gel permeation chromatography (GPC), and also the 1H NMR spectra further verified the formation of CSBO, Following the successful synthesis of CSBO, we used solvent-free and catalyst-free methods to synthesize NIPU. For that, we used two different diamines, namely Isophorone diamine (IPDI) and Meta-xylylene diamine (m-XDA), or one triamine, e.g. Tris(2-aminoethyl)amine (TAA). The NIPU adhesive specimens containing IPDA and m-XDA as curing agents exhibit lap shear strength of 1.1 MPa and 4.97 MPa respectively on the wood coupon. However, TAA containing adhesive sample shows excellent shear strength of 7.62 MPa on stainless-steel metal coupon under the optimized condition. The thermal transition of all fabricated adhesive samples was investigated by DSC analysis which shows higher glass transition temperature (Tg) of 35.12 oC and 34.58 oC for CSBO_IPDA (1:4) and CSBO_TAA (1:2.5) respectively compared to CSBO_m-XDA (1:3.5) specimen (Tg 16.33C) indicating higher cross-linking in the polymer network
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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