1,720,969 research outputs found
Ab Initio Insights into Zinc Dialkyldithiophosphate Linkage Isomers and Oxidative Degradation: Implications for Tribology
No full textZinc dialkyldithiophosphates (ZDDPs) are widely used as antiwear additives in lubricants, forming protective tribofilms that reduce wear and friction in metallic contacts. However, the atomic-scale mechanisms governing their performance remain poorly understood. A key factor is the role of linkage isomers─alternative molecular forms in which sulfur (S) and oxygen (O) atoms exchange positions within the ligand structure. These isomers arise through alkyl group transfers and may significantly influence tribofilm formation. Using density functional theory (DFT), we systematically characterize ZDDP linkage isomers by analyzing their stability, vibrational spectra, and dissociation pathways. Our results show that linkage isomers are more stable than standard ZDDP forms due to the greater strength of Zn–O bonds and primarily dissociate through Zn–S(O) bond cleavage under a 1 GPa load at ferrous interfaces. Additionally, we explore oxidative degradation pathways, where S atoms are replaced by O, altering the molecular stoichiometry. We find that oxidation is favorable in the gas phase, and it is exothermic when mediated by a ferrous substrate. To support experimental validation, we provide vibrational spectra for these isomers, enabling direct comparison with spectroscopic measurements. Bond strength analysis via static fragmentation and Integrated Crystal Orbital Overlap Population (ICOOP) further elucidates their structural stability
Zinc dialkyldithiophosphates adsorption and dissociation on ferrous substrates: An ab initio study
Full text linkZinc dialkyldithiophosphates (ZDDPs) have been commonly used as anti-wear additives in the automotive industry for the past 80 years. Despite their widespread use, a general agreement on their primary functioning mechanism is still lacking. The morphology and composition of the ZDDPs phosphate-based tribofilm, which is essential for its lubricant functioning, have been widely studied experimentally. However, the formation process and the relevant driving forces are still largely debated. In particular, it is unclear whether the stress-induced molecular dissociation occurs in the bulk oil or on the substrate. In this work, we employ ab initio density-functional theory simulations to compare ZDDP fragmentation in vacuum and over a reactive substrate, considering the effects of surface oxidation on the dissociation path. To do so, we developed a computational protocol to study the effects of shear stress on molecules. Our results show that the molecular dissociation is endothermic in the absence of a supporting substrate, while in the presence of an iron substrate, it becomes highly energetically favoured. Moreover, the presence of the substrate changes the reaction path, inducing the detachment of organophosphorus units from Zn-S ones. At the same time, surface oxidation reduces the molecule–substrate interaction. These findings provide valuable insights into the early stages of the formation of phosphate-based tribofilms
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
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
Tribology of 2D black phosphorus – Current state-of-the-art and future potential
No full textSince the first mechanical exfoliation of graphene in 2004, the interest in 2D materials has significantly risen due to their outstanding property combination. Multiple 2D materials have been synthesized until today, while black phosphorus (BP) resembles one of their latest additions. The unique properties of BP, especially for electronic and optical devices ( i.e. , high carrier mobility and electrical conduction, field-effect transistor, layer -dependent bandgap, anisotropic transport), have gained notable attention. However, its layered structure, similar to those of graphene and MoS 2 , is also advantageous to optimize the friction and wear performance. Moreover, the strong in -plane covalent bonds and weak interlayer van-der-Waals forces favour the formation of low -friction and wear -resistant films. Although BP holds a great tribological potential, the literature to date on this topic is rather scarce. Therefore, it is a timely moment to holistically summarize the synthesis approaches and properties of BP thus guiding interested researchers to use it in mechanical/tribological applications. The existing state-of-the-art regarding tribological research is critically discussed and compared to other 2D materials thus highlighting existing research gaps and paving the way for future research activities
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