The present work focuses on the friction stress and the Hall-Petch relationship in CoCrNi equi-atomic medium entropy alloy (MEA). The CoCrNi equi-atomic MEA and a Ni-40Co alloy were processed by ...high-pressure torsion and subsequent annealing. The specimens with fully-recrystallized microstructure with different grain sizes ranging from 199nm to 111μm were obtained. The Hall-Petch plot of the yield strength of the present specimens indicated that the friction stress of the CoCrNi MEA was much higher than Ni-40Co and pure metals, suggesting that the local lattice distortion in the equi-atomic alloy played an important role for the dislocation activity.
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The face-centered cubic medium-entropy alloy NiCoCr has received considerable attention for its good mechanical properties, uncertain stacking fault energy, etc, some of which have been attributed to ...chemical short-range order (SRO). Here, we examine the yield strength and misfit volumes of NiCoCr to determine whether SRO has measurably influenced mechanical properties. Polycrystalline strengths show no systematic trend with different processing conditions. Measured misfit volumes in NiCoCr are consistent with those in random binaries. Yield strength prediction of a random NiCoCr alloy matches well with experiments. Finally, we show that standard spin-polarized density functional theory (DFT) calculations of misfit volumes are not accurate for NiCoCr. This implies that DFT may be inaccurate for other subtle structural quantities such as atom-atom bond distance so that caution is required in drawing conclusions about NiCoCr based on DFT. These findings all lead to the conclusion that, under typical processing conditions, SRO in NiCoCr is either negligible or has no systematic measurable effect on strength.
In this study, we report the effect of elemental combinations on the friction stress and Hall-Petch relationship in medium entropy alloys (MEAs) and high entropy alloys (HEAs) which are defined as ...the alloys composed of four or less and five or more principal elements, respectively, with (near-) equi-atomic concentrations. The MEAs (CoCrFeNi, CoCrNi, etc.), which are subsystems of equi-atomic CoCrFeMnNi HEA, were highly deformed by high-pressure torsion (HPT) and subsequently annealed at different temperatures. The specimens with fully-recrystallized microstructures of FCC single-phase with various mean grain sizes down to sub-micrometer scale were obtained. Subsequently, tensile tests were performed at room temperature to obtain precise Hall-Petch relationships and friction stresses of the materials. Co20(CrNi)80 was successfully predicted as the alloy showing the highest strength among the MEAs by the modified Labusch model (so-called mean field Labusch model) for solution hardening. Experimental values of the friction stresses were found to fit with the model very well, indicating that the strength of the alloys was closely related to entirely distorted crystal lattice acting as high-density obstacles for dislocation motion in the alloys. At the same time, values of the average lattice distortion in the alloys were found comparable to those in some dilute alloys, although “severe” lattice distortion had been believed as a reason for the higher strength than dilute systems. Finally, a strengthening mechanism by element-element interaction was proposed as an additional mechanism to enhance the strength in FCC HEAs and MEAs.
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We consider the ground-state properties of an impurity particle (“polaron”) resonantly interacting with a Bose-Einstein condensate (BEC). Focusing on the equal-mass system, we use a variational wave ...function for the polaron that goes beyond previous work and includes up to three Bogoliubov excitations of the BEC, thus allowing us to capture both Efimov trimers and associated tetramers. We find that the length scale associated with Efimov trimers (i.e., the three-body parameter) can strongly affect the polaron’s behavior, even at densities where there are no well-defined Efimov states. However, by comparing our results with recent quantum Monte Carlo calculations, we argue that the polaron energy is a universal function of the Efimov three-body parameter for sufficiently low boson densities. We further support this conclusion by showing that the energies of the deepest bound Efimov trimers and tetramers at unitarity are universally related to one another, regardless of the microscopic model. On the other hand, we find that the quasiparticle residue and effective mass sensitively depend on the coherence lengthξof the BEC, with the residue tending to zero asξdiverges, in a manner akin to the orthogonality catastrophe.
Solid solution strengthening effect was investigated in AlxCoCrNi medium-entropy alloy (MEA) with different Al content (x = 0–7 at.%). The result of X-ray diffraction indicates that the fully ...recrystallized phase was a single face-centered cubic (FCC) structure for all compositions. The average grain size regarding a twin boundary as a grain boundary was approximately 16 μm. Tensile testing shows that the yield strength increases with the addition of Al. Here, Labusch's approach to random solid solution alloys is applied to confirm the strengthening mechanism in AlxCoCrNi MEA by using lattice constants and elastic moduli. The experimental results were found to be in good agreement with quantitative predictions of the solid solution contribution in AlxCoCrNi MEA.
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•The effect of dilute addition of Aluminum in equiatomic CoCrNi is investigated.•Single phase AlxCoCrNi have similar grain size but have different yield strength.•Strengthening mechanism in AlxCoCrNi is quantified by extended Labusch's approach.•Elastic constant and lattice constant highly involve in the strength prediction.
In this paper, we first elucidate the significant seasonality in long‐term trends in the Asian monsoon on a monthly mean basis. Advanced monsoon onsets over the Bay of Bengal and the western Pacific ...were evident in recent decades. Increasing rainfall in May along 10°N reflected the advanced monsoon onset. Decreasing rainfall trends in June along 10°N were also detected. Because the rainfall trends in July and August showed less significance, the monsoon transition phase should be discussed in the context of climate change rather than boreal summer mean field. The advanced monsoon onset and weakening of the monsoon during early summer are most likely to be attributed to the heat contrast between the Asian landmass and the tropical Indian Ocean. The heating trend over the Asian landmass primarily contributes to the heat contrast variability with the persistent SST increase in the Indian Ocean throughout the season.
Key Points
Seasonality in the long‐term monsoon trend
Advanced monsoon onset
New sight on the interpretation of the long‐term change in seasonal mean
Objective
Non-uniform attenuation correction using computed tomography (CT) improves the image quality and quantification of single-photon emission computed tomography (SPECT). However, it is not ...widely used because it requires a SPECT/CT scanner. This study constructs a convolutional neural network (CNN) to generate attenuation-corrected SPECT images directly from non-attenuation-corrected SPECT images.
Methods
We constructed an auto-encoder (AE) using a CNN to correct the attenuation in brain perfusion SPECT images. SPECT image datasets of 270 (44,528 slices including augmentation), 60 (5002 slices), and 30 (2558 slices) cases were used for training, validation, and testing, respectively. The acquired projection data were reconstructed in three patterns: uniform attenuation correction using Chang’s method (Chang-AC), non-uniform attenuation correction using CT (CT-AC), and no attenuation correction (No-AC). The AE learned an end-to-end mapping between the No-AC and CT-AC images. The No-AC images in the test dataset were loaded into the trained AE, which generated images simulating the CT-AC images as output. The generated SPECT images were employed as attenuation-corrected images using the AE (AE-AC). The accuracy of the AE-AC images was evaluated in terms of the peak signal-to-noise ratio (PSNR) and the structural similarity metric (SSIM). The intensities of the AE-AC and CT-AC images were compared by voxel-by-voxel and region-by-region analysis.
Results
The PSNRs of the AE-AC and Chang-AC images, compared using CT-AC images, were 62.2, and 57.9, and their SSIM values were 0.9995 and 0.9985, respectively. The AE-AC and CT-AC images were visually and statistically in good agreement.
Conclusions
The proposed AE-AC method yields highly accurate attenuation-corrected brain perfusion SPECT images.
Static recrystallization and texture development in a CoCrFeMnNi high entropy alloy cold-rolled to various strains and annealed were studied. Microstructural and crystallographic evolution was ...recorded by identical area observations using quasi in-situ electron backscatter diffraction (EBSD). The deformation texture was preserved after recrystallization, but the texture was weakened at this stage. Shear bands served as the preferential nucleation sites for recrystallization. Thin foils of the deformed alloy were in-situ observed during heating in a transmission electron microscope (TEM). It was observed that subgrains formed from deformed microstructures by dislocation rearrangement and annihilation. The subgrains coarsened by boundary migration and coalescence. These enlarged subgrains were the viable nuclei for the recrystallized grains.
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The July 2018 Japan Floods caused enormous damage to western Japan. Such disasters can especially impact elderly persons. Research has shown that natural disasters exacerbated a decline in cognitive ...function, but to date, there have been no studies examining the effects of this disaster on the elderly. The object of this study was to reveal the effect of this disaster in terms of cognitive decline among the elderly.
Study participants were certified users of the long-term care insurance (LTCI) system in Hiroshima, Okayama, and Ehime prefectures from May 2018 to June 2018. The observation period was from July 2018 to December 2018. Our primary outcome was cognitive decline after the disaster using a dementia symptomatology assessment. In addition to a crude model, a multivariate Cox proportional hazards model was used to assess the cognitive decline of victims, adjusting for age classification, gender, the level of dementia scale before the disaster occurred, residential environment, whether a participant used facilities shut down after the disaster, and population density. After we confirmed that the interaction term between victims and residential environment was statistically significant, we stratified them for the analysis.
The total number of participants was 264,614. Victims accounted for 1.10% of the total participants (n = 2,908). For the Cox proportional hazards model, the hazard ratio of the victims was 1.18 (95% confidential interval (CI): 1.05-1.32) in the crude model and 1.12 (95% CI: 1.00-1.26) in the adjusted model. After being stratified by residential environment, the hazard ratio of home victims was 1.20 (95% CI: 1.06-1.36) and the hazard ratio of facility victims was 0.89 (95% CI: 0.67-1.17).
This study showed that elderly living at home during the 2018 Japan Floods were at risk for cognitive decline. Medical providers, care providers, and local governments should establish a system to check on the cognitive function of elderly victims and provide necessary care support.
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