•Hydrogen alloying with a proper concentration makes equiatomic FeCrNiMnCo alloy resistant to hydrogen embrittlement.•Hydrogen at the interface is the essential cause of the change in the mechanical ...properties of the material.•Hydrogen promoting the formation of nanotwins/stacking faults in high-entropy alloy.•The diffusion barrier of hydrogen in the high-entropy alloy and 316NG stainless steel were very close.
This study reports the effect of hydrogen behaviors on the tensile properties of an equiatomic FeCrNiMnCo high-entropy alloy. We reveal that the hydrogen at the interfaces (including grain boundaries and twin boundaries, etc.) is the main factor affecting the mechanical properties of the materials. We found that hydrogen alloying with a proper concentration makes the alloy resistant to hydrogen embrittlement and improves the strength and ductility of the material. This beneficial effect is positively correlated with the hydrogen concentration at the interface of the alloy, with hydrogen promoting the formation of stacking faults / nanotwins, which are excessively compensatory to the surface cracks introduced by the hydrogen. The influence of hydrogen at the interface of 316NG stainless steel on the tensile behavior has also been discussed. Although hydrogen embrittlement occurred at the same hydrogen-charged conditions, the deterioration of the ductility of the deformed 316NG with a high hydrogen concentration at the interface was significantly reduced. AIMD simulation has been used to study the diffusion of interstitial hydrogen in the HEA and FeCrNi model alloy. It was found that the diffusion barrier and diffusion coefficient of hydrogen in the two alloys were very close at different temperatures.
It is well-known that one key issue of solving the Helmholtz equation using finite element method (FEM) is the accuracy deterioration in the solution with increasing wave number due to the “numerical ...dispersion error”. Such a numerical dispersion error is essentially caused by the “overly-stiff” nature of the FEM model. To overcome this problem, this paper presents an edge-based smoothed finite element method (ES-FEM) for analyzing acoustic problems using linear triangular and tetrahedron elements that can be generated automatically, respectively, for complicated two-dimensional and three-dimensional domains. The discretized linear system equations for ES-FEM are established using the smoothed Galerkin weak form with smoothing domains associated with the edges of the triangles or surfaces of the tetrahedrons. The edge-based gradient smoothing operation provides proper softening effect, makes the ES-FEM model much softer than the “overly-stiff” FEM model and hence significantly reduces the numerical dispersion error. Numerical examples, including a 2D problem of acoustic pressure distribution in a vehicle passenger compartment and a 3D problem about the acoustic pressure distribution in an engine chamber, have been studied using the present ES-FEM. The results demonstrate that the ES-FEM possesses the following advantages compared with the standard FEM using the same meshes. First, ES-FEM achieves similar convergence rate but better accuracy especially at high frequency. Second, ES-FEM is less sensitive to the mesh distortion, meaning that the quality of mesh has less effect on the solution of ES-FEM. Third, it works well for triangular types of meshes, and thus for the problems with complicated geometry.
Expression of Interleukin‐17 in Ischemic Brain Tissue Li, G.‐Z.; Zhong, D.; Yang, L.‐M. ...
Scandinavian journal of immunology,
November 2005, 2005-Nov, 2005-11-00, 20051101, Letnik:
62, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Ischemic brain injury is acute local inflammation, leading to accumulation of pro‐inflammatory cytokines. Cytokines influence the recruitment of leucocytes and play a key role in the inflammatory ...injury processes. Recently, a number of studies have demonstrated a close relationship between brain ischemia and cytokines. Interleukin‐17 (IL‐17) is a newly identified T‐cell‐specific cytokine. In this study, we evaluated the source and the action of IL‐17 over the course of cerebral ischemia in rats (Sprague‐Dawley) and humans. The levels of IL‐17 in the ischemic hemisphere of the human brain, which was removed at necropsy, were assayed immunohistochemically. In rats, permanent middle cerebral artery occlusion (pMCAO) was obtained by inserting nylon monofilament into the right external carotid artery, occluding the right middle cerebral artery. The expression of IL‐17 mRNA in rat was assayed using oligoprobe in situ hybridization. IL‐17 production by neuroglial cells was assayed by double‐staining using antibody glial fibrillary acidic protein (GFAP) and antibody IL‐17. Levels of IL‐17 were elevated in the ischemic hemispheres of human brain compared with the opposite normal hemispheres and peaked at days 3–5 after brain ischemia. The IL‐17‐positive cells were found in the ischemic lesion region. IL‐17 mRNA was also elevated in ischemic hemispheres of pMCAO‐operated rats, which were slightly elevated after 1 h and peaked at 6 days. IL‐17 and GFAP double‐stained were extensive in rat ischemic hemisphere. The ischemia‐induced IL‐17 expression in human brain reported here for the first time was very similar to that in rat model except that the peak was slightly earlier. We found for the first time that IL‐17 was involved in an intense inflammatory reaction of brain ischemic injury in human. In pMCAO‐operated rats, our findings suggest that IL‐17 is produced by the neuroglial cells in the brain region undergoing ischemic insult. We suggest that in additional to T cells the neuroglial cell may be another cellular origin of IL‐17 in later progression of brain ischemia.
A set of burning experiments were conducted to investigate the effect of vertical shaft height on natural ventilation in urban road tunnel fires. Two special phenomena, plug-holing and turbulent ...boundary-layer separation were observed, both of which will influence the effect of smoke exhaust. When shaft height is relatively small, the boundary layer separation is significant and vortexes form in the upstream region inside the shaft, causing the backflow of gas mixture and preventing the throughflow of smoke. With the increasing of shaft height, the boundary layer separation becomes inconspicuous and the plug-holing occurs, leading to the ambient fresh air beneath smoke layer being exhausted directly, which will strongly decrease the smoke exhaust efficiency. Therefore, it is not the case that the higher the vertical shaft, the better the smoke exhaust effect, there exist a critical shaft height in which the boundary layer separation can be diminished to a large extent and overmuch entrainment of fresh air such as plug-holing can be avoided. In addition, the critical shaft height related to better effect can be determined by the new criterion of Ri′(Ricritical′=1.4) proposed in this paper.
The usages of high-abundance rare-earth element Ce in the permanent magnet have drawn considerable interest from industrial and scientific societies. In this work, through PrCu addition combined with ...grain boundary diffusion process (GBDP), anisotropic hot deformed (HD) CeFeB magnets with Jr = 0.66 T, Hci = 514 kA/m, and (BH)max = 55 kJ/m3 can be acquired. The addition of intergranular phase PrCu in spark plasma sintering (SPS) is favorable to the improvement of the plastic deformation ability and the increase of the c-axis crystallographic texture of HDed magnet. Meanwhile, it can also act as a diffusion channel to increase the diffused efficiency during the subsequent GBDP. The observed three Curie temperatures on M-T curves, should be attributed to three various types of 2:14:1 phase, that is initial Ce2Fe14B phase and different (Pr, Ce)2Fe14B phases formed in the process of spark plasma sintering (SPS) and GBDP, respectively. Elemental metallurgical behavior revealed that, the intergranular phases are rich in Pr, Ce, and Cu but depleted in Fe. Intergranular phases analysis demonstrated that, Pr and Ce oxides including (Pr, Ce)O2, Pr12O22, and (Pr, Ce)2O3 can be identified, and amorphous phase is also observed. Through GBDP, magnetic properties, including the coercivity, remanence, and maximum energy product are all improved greatly, which is ascribed to the joint effects from the formation of (Pr, Ce)2Fe14B phase and intergranular phase.
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•Anisotropic hot deformed CeFeB magnets were prepared.•The addition of PrCu alloy is favorable to the increase of c-axis texture.•Three Curie temperatures were observed.•Intergranular phase containing multiple different phases was revealed.
The bulk of grass biomass potentially useful for cellulose-based biofuel production is the remains of secondary wall-containing sclerenchymatous fibers. Hence, it is important to uncover the ...molecular mechanisms underlying the regulation of secondary wall thickening in grass species. So far, little is known about the transcriptional regulatory switches responsible for the activation of the secondary wall biosynthetic program in grass species. Here, we report the roles of a group of rice and maize NAC and MYB transcription factors in the regulation of secondary wall biosynthesis. The rice and maize secondary wall-associated NACs (namely OsSWNs and ZmSWNs) were able to complement the Arabidopsis snd1 nst1 double mutant defective in secondary wall thickening. When overexpressed in Arabidopsis, OsSWNs and ZmSWNs were sufficient to activate a number of secondary wall-associated transcription factors and secondary wall biosynthetic genes, and concomitantly result in the ectopic deposition of cellulose, xylan and lignin. It was also found that the rice and maize MYB transcription factors, OsMYB46 and ZmMYB46, are functional orthologs of Arabidopsis MYB46/MYB83 and, when overexpressed in Arabidopsis, they were able to activate the entire secondary wall biosynthetic program. Furthermore, the promoters of OsMYB46 and ZmMYB46 contain secondary wall NAC-binding elements (SNBEs), which can be bound and activated by OsSWNs and ZmSWNs. Together, our results indicate that the rice and maize SWNs and MYB46 are master transcriptional activators of the secondary wall biosynthetic program and that OsSWNs and ZmSWNs activate their direct target genes through binding to the SNBE sites.
•An engineering scale experiment was conducted on a new three-layer porous laminate.•The flow and heat transfer of two- and three-layer porous laminate were compared.•Cylindrical, truncated cone, ...square and hexagonal pin-fins were compared.•The performance evaluation criteria of square pin–fin was superior to other forms.•An empirical correlations of four types of pin–fin heat transfer were fitted.
Pin-fin can promote heat transfer by increasing the effective heat transfer area and enhancing turbulence intensity. In this study, engineering scale comparative experiments between two- and three-layer porous laminates with the same pin-fins were examined to determine the differences in flow and cooling characteristics. Using the three-layer porous laminates, the effects of four types of pin–fin forms (cylindrical, truncated cone-shaped, square and hexagonal) on flow and cooling characteristics were comparatively researched, with Reynolds numbers ranging from 3,300 to 6,200. The results indicated that the heat transfer coefficient of the square pin–fin was 27.15%, 42.11%, and 19.84% higher than those of the cylindrical pin–fin, truncated cone-shaped pin–fin and hexagonal pin–fin, respectively. The cooling efficiency of the square pin–fin was 1.77%, 2.60%, and 1.18% higher than those of the cylindrical pin–fin, truncated cone-shaped pin–fin and hexagonal pin–fin, respectively. The performance evaluation criteria of the square pin–fin were superior to those of the other structures with the same consumption of pumping power. Empirical correlations of the Nusselt number and cooling efficiency of the four pin–fin forms of the three-layer porous laminate were obtained with prediction errors less than 15.00% and 0.3%, respectively.
A newly developed Ni–Fe-based alloy with high-creep strength and low cost has been developed and evaluated as the promising candidate boiler materials for 700 °C advanced ultra-supercritical ...coal-fired power plants applications. Three electron microscopy characterization methods–scanning electron microscopy and transmission electron microscopy and high-resolution transmission electron microscopy–were combined to obtain new insights into the microstructural and fracture surface characteristics after creep rupture tests at intermediate temperatures. The alloying elements distribution characteristics have been investigated at nanoscale through EDS mapping, especially Fe element. Fractographic analysis has been also conducted with the finding that the fracture mechanism of the crept specimens at 700 °C/300 MPa and 750 °C/150 MPa are intergranular fracture model. Dislocation configurations resulting from the creep deformation have been also performed on the crept specimens. At 700 °C/300 MPa, Orowan process combining climb of a/2 matrix dislocations was dominant mechanism. At 750 °C/150 MPa, the dominant mechanism is Orowan process combining slip of a/2 matrix dislocations and γ′ precipitates shearing. The formation α-Cr precipitation during the creep process could act as obstacle to impede the dislocation gliding and thus increase the creep strength.
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It is well known that the CoCrFeMnNi equiatomic high-entropy alloy (HEA) exhibits excellent irradiation resistance. It is very difficult to form vacancy clusters in this alloy. In the present study, ...vacancy cluster formation was investigated for three (CoCrNi) and four element medium-entropy alloys (MEAs) in a CoCrFeNi system with the same crystal structure as that of a CoCrFeMnNi HEA. Stacking fault tetrahedra (SFTs), which are a type of vacancy cluster, were observed clearly in both MEAs, which were deformed at high speed, after annealing at 373 K. For comparison, Ni and 316 L stainless steel (SS316L) were also subjected to high-speed deformation experiments. SFTs with high density were clearly observed in the Ni sample after annealing at 773 K, but these were not observed in the SS316L sample. The SFT density was significantly lower in MEAs than that in pure Ni. This result indicates that the CoCrNi and CoCrFeNi MEAs also exhibit good irradiation resistance similar to that of SS316L. Further, calculation results based on the first principles indicate that the binding energies of di-, tri-, and tetra-vacancy clusters in the CoCrNi and CoCrFeNi MEAs, are positive. However, the attractive energy of the tri-vacancy cluster in the CoCrFeMnNi HEA is negative.
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●High density SFTs were clearly observed in Ni after high-speed deformation, but these were not observed in the SS316L.●SFTs were also observed in the MEAs after high-speed deformation, but their density was significantly low.●Simulation results indicate that the binding energies of di-, tri-, and tetra-vacancy clusters in the MEAs are positive.●Vacancy clusters were formed by ion irradiation at 300 K, and some were stable even annealing at 773 K.●The attractive energy of the tri-vacancy cluster in the CoCrFeMnNi HEA is negative.
Secondary flux ropes are suggested to play important roles in energy dissipation and particle acceleration during magnetic reconnection. However, their generation mechanism is not fully understood. ...In this Letter, we present the first direct evidence that a secondary flux rope was generated due to the evolution of an electron vortex, which was driven by the electron Kelvin-Helmholtz instability in an ion diffusion region as observed by the Magnetospheric Multiscale mission. The subion scale (less than the ion inertial length) flux rope was embedded within the electron vortex, which contained a secondary electron diffusion region at the trailing edge of the flux rope. We propose that intense electron shear flow produced by reconnection generated the electron Kelvin-Helmholtz vortex, which induced a secondary reconnection in the exhaust of the primary X line and then led to the formation of the flux rope. This result strongly suggests that secondary electron Kelvin-Helmholtz instability is important for reconnection dynamics.
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