1,720,958 research outputs found
Effects of graphene oxide‐silicon oxide hybrid nanomaterials on rheological behavior of water at various time durations and temperatures: Synthesis, preparation and stability
No full textThe present empirical study investigates the synthesis of graphene oxide nanoparticles, preparation of water/graphene oxide‐silicon oxide hybrid nanofluid, and parameters affecting viscosity of the nanofluid. Graphene oxide nanoparticles are synthesized using the modified Hummer's method. Surface structure and atomic structure of the nanoparticles were studied using SEM and XRD tests. The nanofluid was then prepared using the two step method. DLS tests with various patterns were used, in addition to sedimentation photograph capturing method, to measure stability of the nanofluid. Results suggested that the nanofluid has a fairly suitable nanostructure. Viscosity of the nanofluid was measured and studied using Brookfield DV2EXTRA-Pro Viscometer, in the temperature range of 20–60 °C with volume concentrations of 0, 0.5, 0.1, 0.2, 0.4, 0.6, 0.8, and 1%. Furthermore, effects of parameters such as shear rate, and period of applying constant shear rate on viscosity of the nanofluid were investigated. The test results showed that viscosity behavior of the nanofluid is independent of the shear rate and time of shearing. Numerical viscosity measurement results show that viscosity of the nanofluid with volume concentration of φ = 1%, in temperature of 20 °C, increased considerably to μ = 2.42 mPa·s. Viscosity changes ratio increases intensively in higher concentrations. Comparing empirical results of water/graphene oxide nanofluid viscosity to results of the present study shows that, due to the modification of surface structure in nanoparticles, the viscosity values have improved considerably. An empirical equation is provided to measure the viscosity of the nanofluid using this data, which can be used to calculate viscosity of the base fluid under effect of temperature, and viscosity of the nanofluid under effect of temperature and volume concentration variables
Viable Recycling of Polystyrene via Hydrothermal Liquefaction and Pyrolysis
Get PDFChemical recycling is considered one of the most sustainable solutions to limit the environmental issues related to plastic waste pollution, whereby plastic is converted into more valuable compounds when mechanical recycling is not feasible. Among the most critical fast-growing components of municipal solid waste, polystyrene represents 1/3 of the filling materials in landfills. In this work, the chemical recycling of polystyrene via two main thermochemical processes is investigated: pyrolysis and hydrothermal liquefaction (HTL). The influence of temperature (HTL: 300-360 & DEG;C and pyrolysis: 400-600 & DEG;C) and reaction time (HTL: 1-4 h; pyrolysis: 30 min) on the products obtained was studied. The obtained liquid and solid products were analyzed by using gas chromatography-mass spectrometry (GC-MS), an elemental analysis (EA), Fourier-transform infrared spectroscopy (FT-IR) and a thermogravimetric analysis (TGA). During HTL, a temperature of 360 & DEG;C and reaction time of 4 h were needed to completely decompose the polystyrene into mainly oil (83%) and water-soluble compounds (10%). The former was mainly composed of aromatics while the water phase was mainly composed of aromatics and oxygenated compounds (benzaldehyde and acetophenone). The pyrolysis led to the formation of 45% gas and 55% oil at 500 & DEG;C, and the oil was 40% styrene. Pyrolysis was thus more selective towards the recovery of the styrene monomer while the HTL can be an effective process to produce renewable aromatics
Co-treatment of plastics with subcritical water for valuable chemical and clean solid fuel production
No full textPlastic nylon 66, ethylene-vinyl acetate (EVA) and polyvinyl chloride (PVC) were treated in subcritical water to produce value-added liquid chemicals and clean solid fuels. A synergistic effect was found in the co-treatment of PVC and the other two plastic polymers. Nylon 66 was totally decomposed to water-soluble oligomers with the reaction at 330 °C for 45 min. The same condition was required for the complete hydrolysis of EVA to produce acetic acid and deacetylated solid fuel. The activation energy for nylon 66 and EVA hydrolysis were 99.30 and 146.46 kJ/mol, respectively. However, a relatively low temperature (250 °C) was adequate for PVC dechlorination (efficiency >80%). The hydrochloric acid released from PVC worked as the acidic catalyst, which significantly accelerated the hydrolysis of nylon 66 and EVA, consequently more moderate reaction conditions (250 °C for 60 min) are required. Co-treatment of PVC with other polymers by subcritical water showed a great perspective
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
Hydrotreating of oak wood bio-crude using heterogeneous hydrogen producer over Y zeolite catalyst synthesized from rice husk
No full textHydrotreating is an effective method for bio-crude upgrading. However, the high cost of catalysts and gaseous hydrogen consumption limits its application. In this research, oak wood hydrothermal liquefaction bio-crude upgrading was conducted by using Zn as heterogeneous hydrogen producer and low-cost Ni supported Y zeolite synthesized from rice husk as catalyst. The Y zeolite was obtained by two-step synthetic route, using different Tetramethylammonium hydroxide (TMAOH)/silica mole ratios of 0, 0.03 and 0.08. Synthesized Y zeolite showed better performance than commercial one due to the higher total acid sites (24–28% higher). Compared with template-free Y zeolite, the introduction of TMAOH template brings more mesopore structure to the synthesized zeolite, improving its catalytic activity. The yield of upgraded oil increased from 65.5% of blank upgrading test to 80.0% of the synthesized 10%Ni/HY (0.08), and the coke amount reduced from 14.3% to 3.9%. The H/C ratio increased, and the O/C ratio decreased, consequently the higher heating value (HHV) raised from 30.04 to 33.13 MJ/kg. The area percentages of hydrogenation products: cyclopentanones and hydrogenated lignin-derived compounds increased in the catalytic upgraded oil samples consuming furan derivatives and lignin-derived compounds. Deactivation of the synthesized catalyst was observed due to the zeolite structure collapse, Ni active site oxidation, coke deposition and presence of ZnO impurity. The one-pot catalytic hydrothermal treatment of oak wood was also conducted with interesting result, bio-crude yield of 39.0% and HHV of 32.61 MJ/kg, which greatly simplified the process by combining the bio-crude production and upgrading steps together
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