Chinese flowering cabbage is susceptible to leaf yellowing, however, little is known about stem senescence after harvest. Herein, changes in the microstructures, lignin and cell wall polysaccharide ...contents, and expression of their corresponding genes during the stem senescence of Chinese flowering cabbage were investigated. Anatomical and chemical analyses revealed that an increase in cell wall thickness was accompanied by lignin deposition around the vascular cells in the stem. Concurrently, the collapse of parenchyma cells developed gradually, which was probably related to the degradation of cell wall polysaccharides including pectin, hemicellulose, and cellulose, among others. The outer stem tissues, including epidermal cells to vascular cells, could be directly peeled, and the middle of the stem was found to contain prominent parenchyma cells as pith tissues. Activity of lignin biosynthesis-related enzymes of phenylalanine ammonia lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD), and the expression of their corresponding genes BrPAL2/3/6, Br4CL1/4, BrCAD2/4/5/11, and BrPOD31/37 were higher in outer peeled tissues than in pith tissues. The enzyme activity of polygalacturonase and pectin methylesterase, and expression levels of the polysaccharide degradation-related genes BrXET2/3, BrCEL3, and BrMAN1/5 were higher in pith than in outer peeled tissues. These results suggest that lignin deposition around the vascular tissue, and cell wall degradation in pith tissues are involved in the stem senescence of Chinese flowering cabbage after harvest.
•Deposition of lignin around vascular bundles increase the stem firmness in CFC.•Destruction of parenchyma cells induces pith cavity as hollowed stem.•Pith cavity is due to disruption of cell wall polysaccharides of parenchyma cells.•Lignification and cell wall degradation occur simultaneously in stem senescence.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study investigates the efficacy of post-fire curing using carbonation with a 20% carbon dioxide concentration and a relative humidity cycle set between 40% and 90% for restoring the mechanical ...properties of thermally damaged high-performance concrete (HPC) specimens containing 0%–40% silica fume. The HPC specimens were exposed to temperatures of 600, 800, and 1000 °C for 1 h, and the compressive strength recovery was measured. The microstructure, porosity, pore size distribution, and chemical composition of the HPC specimens were analyzed to explore the strength recovery mechanism. After exposure to elevated temperatures, the average compressive strength of samples without silica fume decreased by 49.2 MPa. Subsequent carbonation recuring resulted in a significant recovery of 73.9 MPa in the average compressive strength. This recovery surpassed the original strength for the samples heated to 600 and 800 °C, attributable to the filling and coalescing effects of calcium carbonate polymorphs formed through the carbonation of residual cement particles and β-C2S. The samples containing 20% silica fume exhibited the second highest average strength recovery of 34.1 MPa. However, the strength recovery for the samples with 40% silica fume exposed to 800 and 1000 °C was negligible, as the microcracks exceeding 1 μm in width had barely been restored by the carbonation of the low-calcium calcium silicates with low reactivity. Overall, this study presents an exciting future prospect for the labor and cost-effective restoration of thermally damaged concrete structures through the use of carbonation curing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
•QT and TMCP HSS have different mechanical properties at elevated temperatures.•TMCP-S690 has similar elastic modulus but smaller yield strength than QT-S690 above 400 °C.•Stress-strain curves of QT ...and TMCP HSS at elevated temperatures can be fitted by EC 3 model.
High strength steel (HSS) has gained its popularity in high-rise and large-span structures in which fire is one of the extreme scenarios that needs to be considered in structural design. In view of different types of HSS manufactured from different heat-treatment processes, their mechanical behaviours under fire would be different. However, previous studies and modern design codes show inadequacy of information on their temperature-dependent mechanical properties, especially their mechanical differences due to the different heat-treatment methods. With the research gap being identified, high-temperature coupon tests were conducted on two types of S690 steel respectively manufactured from thermo-mechanically controlled process (TMCP) and quenching and tempering (QT) process. Both steady- and transient-state test methods were adopted. Microstructure changes were discussed and temperature-dependent mechanical properties were compared with each other and with those of mild steel produced through hot-rolling process. The test results revealed that TMCP-S690 steel exhibited similar elastic modulus at elevated temperatures as QT-S690 steel but smaller effective yield strengths when the thermal creep was more significant above 400 °C. Through this study, the heat-treatment dependent thermal elongations, elastic moduli and effective yield strengths at elevated temperatures were recommended for fire resistant design of HSS structural elements. The stress–strain constitutive model was also provided for numerical modelling.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Inducing thermo-mechanical loads during the machining of hard materials lead to the severe grain refinement and hardness variation into the machined surface. This variation significantly affects the ...performance and the service quality of the products. Inconel 718 superalloy is one of the difficult-to-machine materials employed widely in aerospace industries and its surface characteristics after final machining process is really important. The main objective of this study is to implement a reliable finite element (FE) model for orthogonal machining of Inconel 718 alloy and prediction of the microstructure changes during the process. At first, experimental results of cutting forces, chip geometry and maximum temperature were taken into account to identify the most suitable material model out of the seven models found in the literature. Then, the FE numerical model was properly calibrated using an iterative procedure based on the comparison between simulated and experimental results. Moreover, a user subroutine was implemented in FE code to simulate the dynamic recrystallization and, consequently, to predict grain refinement and hardness variation during the orthogonal cutting of Inconel 718 alloy. Zener–Hollomon and Hall–Petch equations were employed to respectively predict the grain size and microhardness. In addition, the depth of the affected layer was controlled using the critical strain equation. As overall, a very good agreement has been found between the experimental and simulated results in term of grain size, microhardness and depth of the affected layer.
•The most suitable Johnson–Cook material model was identified for machining simulation of Inconel 718.•FE numerical model is customized to predict grain refinement and affected layer during dry and cryogenic machining of Inconel 718 alloy.•Fe model can be used to predict parameters related to the surface integrity in turning processes of Inconel 718 alloy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Surface and subsurface gradient microstructures play a significant role in mechanical properties. To obtain gradient microstructures, a surface strengthening method, namely diamond rotary rolling ...treatment (DRRT), was proposed in this study. Varied gradient microstructures in 316 L stainless steel were obtained through different DRRT processing parameters. The micro-hardness distribution along the gradient microstructure was tested. The resulting gradient micro/nanostructures in terms of grain size, dislocation density and phase transformation were characterized and evaluated with electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses. The corresponding mechanical properties were investigated by slow strain rate test. The results showed that the DRRT could introduce a gradient hardening layer on the surface, accompanied by a gradient distribution of nano-grains, ultrafine grains, fine grains and coarse grains extending from the surface to the material interior. Besides, the gradient microstructure was associated with martensitic phase transformation, slip and dislocation. Compared to milled and untreated specimens, the DRRT-treated specimens exhibited a significant increase in yield strength and reduced ductility. Particularly, a well-designed DRRT process can enhance the yield limit while preserving higher ductility. Additionally, a quantitative relationship between the overall yield strength and the hardness distribution of the gradient microstructure was established.
•Diamond rotary rolling treatment (DRRT) is proposed to obtain gradient microstructures.•Gradient micro-nano structures are characterized.•Appropriate DRRT process can enhance the yield limit while preserving ductility.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The location of an acute ischemic stroke is associated with its prognosis. The widely used Gaussian model-based parameter, apparent diffusion coefficient (ADC), cannot reveal microstructural changes ...in different locations or the degree of infarction. This prospective observational study was reviewed and approved by the Institutional Review Board of Xiamen Second Hospital, China (approval No. 2014002).Diffusion kurtosis imaging (DKI) was used to detect 199 lesions in 156 patients with acute ischemic stroke (61 males and 95 females), mean age 63.15 ± 12.34 years. A total of 199 lesions were located in the periventricular white matter (n = 52), corpus callosum (n = 14), cerebellum (n = 29), basal ganglia and thalamus (n = 21), brainstem (n = 21) and gray-white matter junctions (n = 62). Percentage changes of apparent diffusion coefficient (ΔADC) and DKI-derived indices (fractional anisotropy ΔFA, mean diffusivity ΔMD, axial diffusivity ΔDa, radial diffusivity ΔDr, mean kurtosis ΔMK, axial kurtosis ΔKa, and radial kurtosis ΔKr) of each lesion were computed relative to the normal contralateral region. The results showed that (1) there was no significant difference in ΔADC, ΔMD, ΔDa or ΔDr among almost all locations. (2) There was significant difference in ΔMK among almost all locations (except basal ganglia and thalamus vs. brain stem; basal ganglia and thalamus vs. gray-white matter junctions; and brainstem vs. gray-white matter junctions. (3) The degree of change in diffusional kurtosis in descending order was as follows: corpus callosum > periventricular white matter > brainstem > gray-white matter junctions > basal ganglia and thalamus > cerebellum. In conclusion, DKI could reveal the differences in microstructure changes among various locations affected by acute ischemic stroke, and performed better than diffusivity among all groups.
Abstract
After a thorough structural examination, a “Campo del Cielo” iron meteorite found in Argentina was forged at temperatures of about 1100 °C. This meteorite is classified as an IA group coarse ...octahedrite. Besides Fe, it also contains about 7 wt.% Ni and 1.5 wt.% Co, as well as small amounts of Mg, Si, Al, S, and P.
Heat treatments above the eutectoid temperature induce a α-γ transformation of the present (Fe,Ni) solid solution. Owing to the retransformation that takes place upon cooling, the typical microstructure of the meteorite vanishes and a mainly ferritic polycrystalline microstructure forms (kamacite α-(Fe,Ni)). Only minor changes could be observed for the initially present taenite γ-(Fe,Ni). Schreibersite, also referred to as rhabdite (Fe,Ni)
3
P, melts and dissolves into the surrounding matrix. At high temperatures, locally present graphite likewise dissolves and cementite or martensite are formed upon cooling.
Changes of other phases such as troilite (FeS) or lawrencite (Fe,Ni)Cl
2
could not be detected.
Given an initial weight of the meteorite fragment of approx. 1.5 kg, the intention was to manufacture a sword. However, since the meteorite broke apart during forging, only a knife could be manufactured.
The results of post‐fire brittle cracking susceptibility tests conducted on samples made of selected duplex type stainless steel grades exhibiting austenitic‐ferritic structure, in particular on ...standard duplex X2CrNiMoN22‐5‐3 steel and on lean duplex X2CrMnNiN21‐5‐1 steel, are presented and widely discussed. General conclusions are based on the force‐displacement graphs obtained by the instrumented Charpy impact test. Prior to the test all samples have been subjected to simulated fire action following the steady‐state heating regime and then cooled down to room temperature. Two heating levels have been considered, namely 600°C and 800°C. The first of these levels has been considered as to low, while the second as sufficiently high, to induce in the considered steel structural changes of permanent character. For comparison, two groups of samples have been tested. Samples belonging to the first group have been heated for one hour (simulation of a short fire), while the ones belonging to the second group have been heated for ten hours (simulation of a long fire). In addition, two alternative cooling modes have been considered, i.e. slow cooling in the muffle furnace and rapid cooling in water mist. The toughness tests on samples made of both steel grades have been conducted at two different temperature values, that is at +20°C to simulate the continued service in summer conditions and at ‐20°C to simulate this future service in winter conditions.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Flow softening of Ti-17 alloy with the lamellar structure during hot deformation is investigated in this work. For this purpose, hot compression tests are conducted with strain rate of ...0.001–10 s−1 at 780–860 °C. The experimental results are analyzed through theoretical calculation and microstructure observation (SEM, TEM and EBSD). Flow softening extent of Ti-17 alloy increases with the decreasing temperature and increasing strain rate. The softening behavior can be explained by the two aspects: deformation heating and microstructure changes. Deformation heating effect is caused by temperature rise, which is more serious at higher strain rate. Microstructure changes include the bending, kinking, rotation and separation of the lamellar alpha, which can be defined as the pan-globularization of alpha phase. In addition, the EBSD observations indicate that the continuous dynamic recrystallization occurs in beta phase. Microstructure changes of alpha and beta phases influence together flow softening behavior. Specifically, the pan-globularization of alpha phase and continuous dynamic recrystallization of beta phase result in flow softening of Ti-17 alloy.
•Flow softening and microstructure changes of Ti-17 alloy was investigated.•Flow softening is explained by deformation heating and microstructure changes.•The pan-globularization of alpha phase is first defined in this work.•The CDRX of beta phase is confirmed by the EBSD observations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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