1,720,958 research outputs found
Investigation on two Ti–B-reinforced Al alloys for Laser Powder Bed Fusion
No full textOnly few medium: and high-strength aluminium alloys can be processed by Laser Powder Bed Fusion without forming solidification cracks. This constraint limits the diffusion of this technology in many industrial fields, including aerospace and motorsport sectors. In this study, a novel high-strength aluminium alloy for Laser Powder Bed Fusion was designed and its solidification behavior, microstructure and mechanical performance were investigated. The results were compared with those achieved by processing the high-strength A20X alloy processed with the same technology. The alloy was designed based on the chemical composition of the widely used 2618 Al alloy, a conventional high strength Al–Cu–Mg alloy for high temperature applications. The chemical composition of the 2618 alloy was modified by adding Ti and B, which form TiB2 particles that act as nuclei for the solidification of primary α-Al grains. The resulting microstructure made of equiaxed grains revealed resistant to hot cracking. A20X and 2618-modified alloys produced with optimized parameters featured relative densities higher than 99,7% and crack-free microstructures. The A20X-T6 showed yield strength and ultimate tensile strength of 428 MPa and 485 MPa, respectively, while the modified 2618-T6 revealed upper yield strength and ultimate tensile strength of 370 MPa and 468 MPa, respectively. The two alloys also showed a remarkably high strength at 150 °C and 250 °C, exceeding the typical strength values of the 2618 alloy produced by forging
Microstructural Evolution of a High-Strength Zr-Ti-Modified 2139 Aluminum Alloy for Laser Powder Bed Fusion
Full text linkThe demand for high-performance aluminum components drives research into the design of novel alloys that can be processed by laser-based additive manufacturing. In recent years, the addition of grain refiners proved to be an effective strategy to reduce the hot-cracking of high-strength Al alloys. In this study, the solidification and aging behavior of an Al2139 alloy doped with additions of Zr and Ti for L-PBF was investigated. These elements favored the formation of a fine-grained structure free of cracks. The formation of Al-3(Zr,Ti) inoculants was predicted by Scheil simulations and observed as cuboidal particles in the center of ff-Al grains. The microstructure of the as-built material featured fine and fully equiaxed grains, which appeared comparatively finer at the edge (300-600 nm) and coarser (0.8-2.0 mu m) at the center of the molten pools. In both cases, there was evidence of Cu and Mg micro-segregations at the grain boundaries. The microhardness of 109.7 HV0.5 in the as-built state was increased to 186.1 HV0.5 after optimized T4 heat treatment, responsible for the precipitation of many rod-shaped Zr- and Ti-based second phases and quasi-spherical Cu-, Mn-, and Fe-rich particles. Prolonged exposure carried out to simulate high-temperature service caused a drop in microhardness and marked modification of the microstructure, evidenced by the rearrangement and subsequent spheroidization of Cu- and Mg-rich particles at the grain boundaries
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
IDENTIFICATION AND CHARACTERIZATION OF 3 CALMODULIN-BINDING SITES OF THE SKELETAL-MUSCLE RYANODINE RECEPTOR
No full textIn the present study, we have identified calmodulin binding sequences in the skeletal muscle
ryanodine receptor Ca2+ release channel. Ligand overlays on RYR fusion proteins indicate that the skeletal
muscle RYR contains three calmodulin binding regions defined by residues 2937-3225, 3546-3655, and
4425-4621. The RYR fusion protein PC28 (residues 2937-3225) bound calmodulin in the presence of
EGTA and Ca2+, while RYR fusion protein PC26 (residues 3546-3655) exhibited strong calmodulin binding
at 10 pM Ca2+. The RYR fusion protein PC15 (residues 4425-4621) did not bind calmodulin in the
presence of either EGTA or 10-50 HMC a2+. In the presence of 100-500 pM CaZ+t,h e RYR fusion protein
PC15 exhibited an affinity for calmodulin of approximately 50 nM. Peptides RYRl PM2 (residues 3610-
3629) and RYRl PM3 (4534-4552) encompassing putative RYR-calmodulin binding sites were synthesized.
The synthetic peptides interacted directly with dansylcalmodulin as demonstrated by their capacity to affect
the fluorescence emission of dansylcalmodulin. Missense mutation analysis indicates that the Lys and Arg
residues are essential for calmodulin binding to the synthetic peptide RYRl PM3. The RYR calmodulin
binding site defined by peptide PM3 lies in the myoplasmic loop 2, a few residues upstream of the putative
transmembrane segment M5; the other two calmodulin binding sites are next to the putative transmembrane
segments M’ and M”. Thus, the effect of calmodulin on Ca2+ release might involve the regulation of the
putative transmembrane segments M5, M’, and M”
A ryanodine receptor-like Ca2+ channel is expressed in nonexcitable cells
No full textIn this study we investigated the effects of 4-chloro-3-ethylphenol on Ca2+ homeostasis, and we report that this compound induces Ca2+ release from a ruthenium red-sensitive Ca2+ release channel present in skeletal muscle terminal cisternae. When tested with bovine cerebellar microsomes, the Ca(2+)-releasing activity of 4-chloro-3-ethylphenol was reduced by ruthenium red and unaffected by heparin. In PC-12 cells, HL-60 cells, human fibroblasts, the human hepatoma cell line PLC/PRF/5, and Jurkat cells, 4-chloro-3-ethylphenol released Ca2+ from intracellular thapsigargin-sensitive stores. Although decreased, its effect was retained after treatment of intact/permeabilized cells with inositol-1,4,5-trisphosphate (IP3)-mobilizing agonists/IP3, whereas pretreatment of permeabilized cells with ruthenium red reduced the Ca(2+)-releasing activity of 4-chloro-3-ethylphenol. These results provide functional evidence for the presence of a Ca2+ channel distinct from the IP3 receptor, having pharmacological similarities to the ryanodine receptor, in the intracellular Ca2+ stores of a variety of nonexcitable cells. We also demonstrate that a monoclonal anti-ryanodine receptor antibody recognizes a protein in human fibroblasts with similar apparent molecular mass the ryanodine receptor. Thus, the intracellular Ca2+ stores of mammalian cells appear to be endowed with two distinct intracellular Ca2+ channels
Effect of combined additions of Sc, Zr and Ti on hot-cracking resistance and precipitation behaviour in Al-Mg alloy by L-PBF
Full text linkThe request for high-performance aluminum components prompts research into innovative alloys compatible with laser-based additive manufacturing processes, leveraging grain refiners in their composition to mitigate hot- cracking and enhance strength. While the addition of Sc and Zr in Al-Mg alloys has been widely investigated, the high cost and supply risks associated with Sc necessitate reducing its amount and replacing, at least partially, with other inoculants. In this preliminary study, the amount of Sc replaceable with different concentrations of Zr or Ti is evaluated investigating the laser powder bed fusion processability of three powder feedstocks: a pre- alloyed Al-Mg-Zr-Sc powder, a blend of the previous alloy with addition of Zr particles, and a further blend of an alloy depleted of Zr with added Ti particles. The experimental analyses on the laser-processed alloys showed that the standard and the Zr-enriched alloys featured a bimodal microstructure free from cracks with fine equiaxed grains at the edge of the molten pools and coarser grains at their centers. In the alloy variant depleted in Zr with addition of Ti particles a columnar structure was observed and hot-cracks appeared. Thermodynamic simulations of phase formation allowed defining the precipitation kinetics during solidification and direct aging, showing increased precipitation in alloys with higher Zr content, while the presence of Ti resulted in sluggish precipitation. Experimental aging tests demonstrated significant increases in microhardness, with peak values of the modified alloys achieved after 12 h at 375 ◦ C
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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