1,720,966 research outputs found
Grain-size effects on the deformation in nanocrystalline multi-principal element alloy
Full text linkMulti-principal element alloys (MPEAs) continue to garner great interest due to their potentially remarkable mechanical properties, especially at elevated temperatures for key structural and energy applications. Despite extensive literature examining material properties of MPEAs at various compositions, much less is reported about the role of grain size on the mechanical properties. Here, we examine a representative nanocrystalline BCC refractory MPEA and identify a crossover from a Hall-Petch to inverse-Hall-Petch relation. While the considered MPEA predominantly assumes a single-phase BCC lattice, the presence of grain boundaries imparts amorphous distributions that increase with decreasing grain size (i.e., increasing grain boundary volume fraction). Using molecular dynamics simulations, we find that the average flow stress of the MPEA increases with decreasing average grain size, but below a critical grain size of 23.2 nm the average flow stress decreases. This change in the deformation behavior is driven by the transition from dislocation slip to grain-boundary slip as the predominant mechanism. The crossover to inverse-Hall-Petch regime is correlated to dislocation stacking at the grain boundary when dislocation density reaches a maximum.This is a manuscript of an article published as Roy, Ankit, Ram Devanathan, Duane D. Johnson, and Ganesh Balasubramanian. "Grain-size effects on the deformation in nanocrystalline multi-principal element alloy." Materials Chemistry and Physics 277 (2022): 125546. DOI: 10.1016/j.matchemphys.2021.125546. Copyright 2021 Elsevier B.V. Posted with permission. DOE Contract Number(s): AC02-07CH11358; WBS 2.1.0.19
Vacancy formation energies and migration barriers in multi-principal element alloys
Full text linkMulti-principal element alloys (MPEAs) continue to garner interest as structural and plasma-facing materials due to their structural (phase) stability and increased resistance to radiation damage. Despite sensitivity of mechanical behavior to irradiation and point-defect formation, there has been scant attention on understanding vacancy stability and diffusion in refractory-based MPEAs. Using density-functional theory, we examine vacancy stability and diffusion barriers in body-centered cubic (Mo0.95W0.05)0.85Ta0.10(TiZr)0.05. The results in this MPEA show strong dependence on environment, originating from local lattice distortion associated with charge-transfer between neighboring atoms that vary with different chemical environments. We find a correlation between degree of lattice distortion and migration barrier: (Ti, Zr) with less distortion have lower barriers, while (Mo, W) with larger distortion have higher barriers, depending up local environments. Under irradiation, our findings suggest that (Ti, Zr) are significantly more likely to diffuse than (Mo, W) while Ta shows intermediate effect. As such, material degradation caused by vacancy diffusion can be controlled by tuning composition of alloying elements to enhance creep strength at extreme operating temperatures and harsh conditions.This is a manuscript of an article published as Roy, Ankit, Prashant Singh, Ganesh Balasubramanian, and Duane D. Johnson. "Vacancy formation energies and migration barriers in multi-principal element alloys." Acta Materialia 226 (2022): 117611. DOI: 10.1016/j.actamat.2021.117611. Copyright 2022 Acta Materialia Inc. Posted with permission. DOE Contract Number(s): AC02-07CH11358; CMMI-194404
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
Multi-Principal Element Alloys: Atomistic Features Governing The Structural Properties Of Refractory Multicomponent Alloys
No full textOver the past decade, select multi-principal element alloys (MPEAs) have exhibited excellent structural properties, especially at high temperatures, outperforming conventional alloys in some cases. Phase stabilization by entropy maximization has been attributed, albeit inconclusively, as one of the primary factors underlying such unique material properties. A conventional approach to discovering new MPEAs requires scavenging an enormous search space consisting of over half a trillion new material compositions. As MPEAs are comprised of three to six principal elements, discovering new compositions with promising properties at a wide range of temperatures is a major challenge. A more efficient screening technique is vital to explore the enormous search space. In this report we implement machine learning tools to predict the crystallographic phase and Young\u27s modulus of low, medium, and high-entropy alloys, as these MPEAs are composed of a family of 5 refractory elements. This tool lays the foundation to a potential technique for ultrafast screening of new compositions.Prior research has shown that certain low and medium-entropy alloys have exhibited superior structural properties, (hardness, Young\u27s modulus) relative to their higher-entropy counterparts composed of the same family of elements. Since incorporating higher number of constituent elements does not guarantee enhanced structural properties, it is evident that effects beyond entropy are driving the mechanisms that impart notable mechanical properties. Using a synergy of experimental measurements at room temperature, this report will highlight that the role of intrinsic lattice strain and cohesive energies, rather than configurational entropy, are found to be the predominant factors affecting the Young\u27s modulus and hardness of single-phase multicomponent alloys. An investigation into the high strength of MPEAs at elevated temperatures, found in chapter 4 is carried out via atomistic simulations. While at lower temperatures (<0.6 (melting temperature)), the primary resistance to deformation is caused by solid solution strengthening, the resistance to creep deformation at higher temperatures (>0.6 ) is primarily governed by the phenomenon of atomic diffusion. We employ molecular dynamics simulations in conjunction with first principles to examine the atomic diffusion of the different elemental species in a refractory MPEA containing Mo-Ta-Ti-W-Zr as the constituents. The initial results reveal that diffusion in MPEAs near melting temperature is one order of magnitude smaller than diffusion in reference metals in the pure state providing evidence of high creep resistance responsible for excellent mechanical properties at elevated temperatures. After understanding the strengthening mechanisms at room and high temperatures in MPEAs, a collated study of the data analytic approaches used by researchers, has been done in chapter 5 to gain an insight into the advances of fast machine learning methods being used to discover novel alloys. These algorithms use physics bases features, which incorporate the physics of strengthening mechanisms discussed in previous chapters, into algorithms that can then predict the mechanical properties of the MPEAs in a fraction of second. Further, Chapter 6 examines a representative nanocrystalline BCC refractory MPEA and identifies the crossover from a Hall-Petch to inverse-Hall-Petch relation. While the considered MPEA predominantly assumes a single-phase BCC lattice, the presence of grain boundaries imparts amorphous phase distributions that increase with decreasing grain size (i.e., increasing grain boundary volume fraction). Using molecular dynamics simulations, it was found that the yield strength of the MPEA increases with decreasing average grain size, but below a critical grain size < 23.2 nm the yield strength decreases. This change in the deformation behavior is driven by the transition from dislocation slip to grain-boundary slip as the predominant mechanism. The crossover to inverse-Hall-Petch regime is correlated to dislocation stacking at the grain boundary when dislocation density reaches a maximum
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