1,721,858 research outputs found
Manufacturing of aluminium metal matrix composites by high pressure torsion.
No full textAluminium (Al) and aluminium alloys (AA) are widely utilised in the industry because they are lightweight, inexpensive, ductile, thermally stable, and possess high electrical conductivity. However, poor stiffness, strength, and wear limit their use in aerospace, automobile, and transmission. Metal matrix composites (MMC) have shown the capability to make tailor-made materials to overcome the issues mentioned above. Moreover, nanomaterial-based MMC provides better mechanical properties and wear resistance. However, available methods of producing AA MMC have challenges such as porosity, brittle interfaces, and defects in nano-reinforcement. In the current study, a novel approach has been used to produce nanomaterial-based AA MMC to overcome these challenges. Graphene (Gr), Nanodiamond (ND), and Molybdenum disulfide (MoS2) have been added to CP Al and 7xxx alloys using severe plastic deformation (SPD). The current study provides deep insight into the nature of nanomaterials in metal nanomatrix and the resulting properties for industrial applications, particularly electrical transmission and self-lubrication in the automotive industry. The potential of graphene to improve the strength of aluminium alloy powder has been experimentally studied. Gr AA 7075 MMC is produced by high pressure torsion (HPT) at room temperature. Variations in the concentration of graphene nanosheets and HPT process parameters are applied to optimise the fabrication route. 0.5-1 wt.% Gr AA 7075 MMC were processed through 0.5 to 100 turns of HPT. Also, graphene-free AA 7075 samples were produced using the same process. The samples were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) line broadening analysis, which revealed the dislocation density and the crystallite size. XRD line broadening revealed a crystallite size of 28 nm for the 1 wt.% Gr AA 7075 MMC after 50 turns of HPT, which illustrates the capacity of HPT to produce a genuinely nanostructured material. Additionally, a comparison of the strength modelling of (1-5%) ND AA 7075 MMC and (1-10%) MoS2 AA 7075 MMC has been done using a similar methodology. The porosity evolution in the Al matrix during the early stages of HPT was analysed. The hardness of the material improved up to 300 % by HPT as compared to annealed bulk AA 7075 to reach a maximum hardness of 310 HV for the 0.5 wt.% Gr AA 7075 MMC processed by 20 turns of HPT. In contrast to cast and solution treated AA 7075, no consistent improvement in hardness is recorded in HPT processed AA 7075 due to artificial ageing. However, XRD results show that the microstructure changed after artificial ageing. In comparison, the addition of ND resulted in softening AA 7075. In contrast, MoS2 AA 7075 MMC have shown higher hardness than two predecessors AA 7075 MMC. A volume-averaged dislocation density model was applied for strength modelling of HPT processed samples. Considering future applications such as aerospace, and automobile parts, a focus on tribological applications of Gr AA 7075 MMC, ND AA 7075 MMC, and MoS2 AA 7075 MMC has been extensively studied. For comprehensive understanding, dry sliding ball on disc wear tests and post-wear analysis were done using tribometer, profilometry, and electron microscopy. Compared to currently available Al alloys, the HPT processed AA 7075 MMC demonstrated a 50% improvement in friction coefficient (0.2–0.3) and wear properties. Generally, Gr and MoS2 reduce the coefficient of friction (COF), whereas ND improves wear resistance in the coarse-grained AA MMC prepared by industrial methods. However, ND AA 7075 MMC shows better friction properties than Gr and MoS2-based AA 7075 MMC. Moreover, MoS2 AA 7075 MMC have a relatively poor wear rate. This study involves a descriptive analysis of the possible unusual role of nano-reinforcements in wear mechanisms. AA are used for electric transmission in many Asian countries, such as India, because of its low cost and good electrical conductivity. Earlier attempts to improve electrical conductivity included alloying and reinforcing with gold and silver. Moreover, considering the electrical properties of graphene, graphene nanosheets have been added to commercially pure Al to make 1% Gr AA 1050 MMC. However, the 4-point probe test shows a 40–60 % reduction in electrical conductivity (IACS). The current study involves the assessment of form factors for measuring the electrical conductivity of AA MMC. Overall, the current study shows the potential of HPT to create a new class of defect-free nanomaterials. Furthermore, experiments are conducted to examine the application-related roles of Gr, ND, and MoS2 in the AA MMC
First record of the heart urchin Metalia persica (Mortensen, 1940) (Spatangoida: Brissidae) from the Chennai coast, India
No full textKanagaraj, Chamundeeswari, Mooi, Rich, Kumar, Deepak Samuel Vijay, Premachandran, Hrishikesh, Rajendran, Abhilash Kottarathil, Rethinavelu, Sankar, Ramachandran, Purvaja, Ramachandran, Ramesh (2019): First record of the heart urchin Metalia persica (Mortensen, 1940) (Spatangoida: Brissidae) from the Chennai coast, India. Zootaxa 4624 (2): 296-300, DOI: 10.11646/zootaxa.4624.2.1
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
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
Hate Raids on Twitch: Echoes of the Past, New Modalities, and Implications for Platform Governance
No full textn the summer of 2021, users on the livestreaming platform Twitch were targeted by a wave of "hate raids," a form of attack that overwhelms a streamer's chatroom with hateful messages, often through the use of bots and automation. Using a mixed-methods approach, we combine a quantitative measurement of attacks across the platform with interviews of streamers and third-party bot developers. We present evidence that confirms that some hate raids were highly-targeted, hate-driven attacks, but we also observe another mode of hate raid similar to networked harassment and specific forms of subcultural trolling. We show that the streamers who self-identify as LGBTQ+ and/or Black were disproportionately targeted and that hate raid messages were most commonly rooted in anti-Black racism and antisemitism. We also document how these attacks elicited rapid community responses in both bolstering reactive moderation and developing proactive mitigations for future attacks. We conclude by discussing how platforms can better prepare for attacks and protect at-risk communities while considering the division of labor between community moderators, tool-builders, and platforms
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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