The effects of the initial microstructure of α′ martensite on the microstructural evolution during intercritical annealing and the tensile properties of annealed specimens were investigated for ...Fe–9Mn–0.05C (wt.%) steel. The hot-rolled specimen with fully α′ martensitic microstructure showed a mixed microstructure of lath-shaped ferrite (αL) and austenite (γL) after intercritical annealing. The αL grains had a high density of dislocations due to inactive recovery, and also had a low Mn concentration. The γL grains had a low density of dislocations and high Mn and C concentrations. The αL and γL grains were deformed simultaneously during the tensile test because the αL grains were as hard as the γL grains due to their high dislocation density, resulting in continuous yielding. The cold-rolled specimen with a deformed α′ martensite microstructure exhibited a mixed microstructure of globular-shaped ferrite (αG) and austenite (γG) after intercritical annealing. The αG grains had a low dislocation density due to active recovery, and also had a low Mn concentration. The γG grains had a low dislocation density and high Mn and C concentrations. The soft αG grains with a low dislocation density were easily deformed at the early stage of the tensile test, resulting in discontinuous yielding and a large yield point elongation.
Purpose
To compare choroidal vascular characteristics of age-related macular degeneration (AMD), polypoidal choroidal vasculopathy (PCV), and central serous chorioretinopathy (CSC) by qualitative and ...quantitative analyses using swept-source
en face
optical coherence tomographic (OCT) images.
Methods
Eyes with non-neovascular AMD (
n
= 32), neovascular AMD (
n
= 30), thick and thin choroid PCV (
n
= 33 and 27), and CSC (
n
= 34) were enrolled. Subfoveal choroidal thickness (SFCT) and the presence and patterns of pachyvessels were assessed.
En face
images of the large choroidal vessel layer were converted to binary images for the analysis of vascular density.
Results
Pachyvessels were identified in 8 (25%), 14 (46%), 28 (85%), 26 (96%), and 34 (100%) non-neovascular AMD, neovascular AMD, thin choroid PCV, thick choroid PCV, and CSC eyes, respectively (
P
< 0.001). The pattern of pachyvessels was focal in non-neovascular AMD (100%), neovascular AMD (79%), and thin choroid PCV (89%) while the pattern was mostly diffuse in CSC (88%) and thick choroid PCV (81%). The mean choroidal vascular density in a 6 × 6 mm
2
macular area of each group was 45.3%, 46.9%, 47.0%, 52.5%, and 54.8%, respectively (
P
< 0.001). Post hoc analysis revealed significantly higher vascular density in CSC compared with other types (all
P
< 0.001) except PCV with thick choroid (
P
= 0.066).
Conclusions
Similarities in vascular density of the large choroidal vessel layer and pachyvessel pattern were between CSC and thick choroid PCV and between AMD and thin choroid PCV, suggesting common pathophysiology involving choroidal changes in these eyes.
Employing two studies, this paper investigates incidental exposure to news online in terms of its influence on individual learning about public affairs as well as its predictors in the social media ...environment. Study 1, using an experimental design, shows that incidental exposure to news has significant effects on an individual's recognition and recall of information in news stories. The effects of incidental exposure on recall are mediated by actual exposure to information in the news (spending some time on reading), suggesting gateway effects of initial exposure by accident. Employing a national survey, Study 2 finds that social media network heterogeneity and proportion of weak ties are positively associated with likelihood of incidental exposure to news online, while most variables of individual characteristics are not. The significant effects of structural factors found suggest that incidental exposure can limit consequences of selective exposure. Further implications of the findings are discussed.
•We investigated whether and how incidental exposure affects information gain.•Incidental exposure has significant causal effects on recognition and recall.•Actual exposure mediates the link between initial incidental exposure and recall.•Network heterogeneity and weak ties have positive associations with incidental exposure.
The hydrogen embrittlement (HE) and H trapping sites of pearlitic steel specimens with various lamellar spacings (λ) were evaluated through slow strain rate tensile testing and thermal desorption ...analysis. When λ decreases, both tensile strength and resistance to HE were unusually improved. This is because tearing, which is the initiation of H cracking, was delayed in the specimen with fine λ and short cementite (θ) platelets. Undeformed H-charged specimens showed a peak (peak 1), which is separable into two sub-peaks (peak 1-1 and peak 1–2) in their H desorption rate curves, regardless of λ. Peak 1-1 and peak 1–2 were generated by H atoms detrapped from FP/θ interfaces and from dislocations inside FP, respectively. The Ea values of H desorption for peak 1-1 and peak 1–2 were 23.2 kJ/mol, and 26.1 kJ/mol, respectively. Meanwhile, deformed H-charged specimens exhibited the second peak (peak 2) with peak temperature (TP) of ∼600 K, as well as peak 1 with TP of ∼375 K. When tensile strain increased, peak 2 increased at the expense of peak 1. Primary H trapping sites for peak 2 are strained FP/θ interfaces with interfacial dislocations.
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The stacking-fault energy (SFE), dislocation slip, mechanical twinning, strain hardening, and yield and tensile strengths were systemically investigated in Fe–18Mn–0.6C–1.5Si twinning-induced ...plasticity (TWIP) steel. The results were also compared with those for Fe–18Mn–0.6C and Fe–18Mn–0.6C–1.5Al TWIP steels. The SFE decreased by 4mJm−2 per 1wt.% Si. The addition of Si increased both the yield strength, due mainly to solid solution hardening, and the tensile strength, owing to the high strain hardening that occurred while maintaining a large elongation of over 60%. To examine this high strain hardening, especially at low strains, the volume fractions of the primary and secondary mechanical twins were quantitatively evaluated by combining the merits of electron backscattered diffractometry and transmission electron microscopy. The volume fractions of both the primary and secondary twins were the highest in the Fe–18Mn–0.6C–1.5Si TWIP steel, which had the lowest SFE of the three TWIP steels. In particular, the volume fraction of the secondary mechanical twins increased rapidly with the addition of Si. The contributions of dislocation storage, mechanical twinning and dynamic strain aging (DSA) to the strain hardening were also quantitatively evaluated in the three TWIP steels. The Si-added TWIP steel had the highest strain hardening, due mainly to the active primary and secondary twinning, and experienced negligible DSA. In contrast, the Al-added TWIP steel exhibited the lowest strain hardening due to the reductions in both the mechanical twinning and DSA.
The objective of the present study is to clarify the mechanism of dynamic strain aging (DSA) causing serrations in tensile flow curves of Fe-5.15Mn-0.15C-0.37Si-0.0039N (wt%) medium-Mn steel ...specimens with triple phases of retained austenite (γR), ferrite (α) and tempered martensite (α'T). For the purpose, tensile tests were performed at various conditions of deformation temperature (Td = 273 - 333 K) and initial strain rate (έini = 5 × 10−4 - 1 × 10−2 s−1). The medium-Mn steel specimens revealed type A serrations after the propagation of the Lüders band in their tensile curves. The serrations were not related to both α and α'T; they were not caused by strain-induced martensitic transformation, but by DSA in γR. The DSA was not explained by the short-range diffusion model based on the interaction between partial dislocations and C-Mn complexes due to the absence of intersection between staying time and reorientation time. In a viewpoint of the dislocation arrest model involving long-range diffusion, critical strains of γR for serrations (ecγ) were measured. They showed the normal Portevine-Le Châtelier behavior that the ecγ value decreases with increasing Td and with decreasing έini. The activation energy measured using the ecγ values was similar to the activation energy for the dislocation pipe diffusion of C atoms. This result indicates that the DSA occurring in the present medium-Mn steel is explained by the dislocation arrest model involving the long-range pipe diffusion of C atoms, not by the short-range diffusion model involving the reorientation of C-Mn complexes.
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Faint z ∼ 5 quasars with M1450 ∼ −23 mag are known to be potentially important contributors to the ultraviolet ionizing background in the postreionization era. However, their number density has not ...been well determined, making it difficult to assess their role in the early ionization of the intergalactic medium (IGM). In this work, we present the updated results of our z ∼ 5 quasar survey using the Infrared Medium-deep Survey (IMS), a near-infrared imaging survey covering an area of 85 deg2. From our spectroscopic observations with the Gemini Multi-Object Spectrograph on the Gemini-South 8 m telescope, we discovered eight new quasars at z ∼ 5 with −26.1 ≤ M1450 ≤ −23.3. Combining our IMS faint quasars (M1450 > −27 mag) with the brighter Sloan Digital Sky Survey quasars (M1450 < −27 mag), we derive the z ∼ 5 quasar luminosity function (QLF) without any fixed parameters down to the magnitude limit of M1450 = −23 mag. We find that the faint-end slope of the QLF is very flat ( ), with a characteristic luminosity of mag. The number density of z ∼ 5 quasars from the QLF gives an ionizing emissivity at 912 of 912 = (3.7-7.1) × 1023 erg s−1 Hz−1 Mpc−3 and an ionizing photon density of Mpc−3 s−1. These results imply that quasars are responsible for only 10%-20% (up to 50% even in the extreme case) of the photons required to completely ionize the IGM at z ∼ 5, disfavoring the idea that quasars alone could have ionized the IGM at z ∼ 5.
The objective of the present study was to investigate the influences of grain refinement on yielding, strain hardening, and mechanical twinning during tensile deformation in Fe-high Mn ...twinning-induced plasticity (TWIP) steel. For this purpose, Fe–18Mn–0.6C–1.5Al TWIP steels with average grain sizes of 2, 10, and 50μm were tensile tested at room temperature, and their stress–strain and strain hardening rate curves, dislocation densities, and microstructures were measured and analyzed by means of transmission electron microscopy and neutron diffractometry. The stress–strain curves showed a transition from continuous to discontinuous yielding with grain refinement, which was due to a lack of mobile dislocations, not due to mechanical twinning or martensitic transformation. The grain refinement increased the dislocation density, caused the planar to non-planar slip, and retarded primary and secondary mechanical twinning. The strain hardening rate–strain curves of TWIP steels used were able to be divided into five stages by the slope change. Until the stage III, dislocation hardening was predominant; at the stages IV and V mechanical twinning became more contributive to strain hardening. The suppression of both planar dislocation slip and mechanical twinning by grain refinement is most likely due to the increase in the back stress of dislocations on a slip plane, which was caused by the rapid accumulation of dislocations by plastic deformation in the fine-grained TWIP steel. A high level of back stress narrows the width of stacking faults, facilitates the cross slip of dislocations, and reduces the interactions between partial dislocations required for mechanical twinning.
This paper demonstrates that aging prior to extrusion (APE) can greatly enhance the mechanical properties of an extruded Mg–7.6Al–0.4Zn alloy. The fine Mg17Al12 precipitates formed by APE reduce the ...average size of dynamically recrystallized grains and increase the amount of small Mg17Al12 particles present after extrusion, thereby improving the strength of the alloy. This APE treatment also enhances the ductility of the extruded alloy by decreasing the amount of large banded Mg17Al12 particles, and suppressing the serrated flow during tensile deformation.
In the present study a Fe-8.8Mn-5.1Al-0.31C (wt pct) medium-Mn lightweight steel with martensitic matrix was newly designed, and the effect of tempering on its microstructure and tensile properties ...was investigated. When the medium-Mn lightweight steel specimen was quenched from annealing temperature of 1373 K (1100 °C), it revealed a triple-phase microstructure consisting of 64.6 pct fresh martensite, 20.2 pct ferrite, and 15.2 pct retained austenite. Tempering the as-quenched specimen at temperatures less than 573 K (300 °C) induced the precipitation of thin cementite or κ-carbide platelets in tempered martensite. With the increasing tempering temperature, the type of precipitate changed from cementite to κ-carbide, and thickening of platelets with the longer interspacing was observed by means of transmission electron microscopy and atom probe tomography. While the as-quenched specimen revealed high strain-hardening rate (SHR) and poor elongation (< 2 pct), tempered specimens exhibited moderate SHR and improved elongation (> 16.8 pct) mainly due to gradual transformation-induced plasticity in retained austenite stabilized by tempering. In particular, the 373 K (100 °C)-tempered specimen with tempered martensite embedded with thin cementite platelets revealed ultrahigh strengths (yield strength of 945 MPa and ultimate tensile strength of ~ 1.56 GPa) with moderate elongation of ~ 16.8 pct.
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